2006 AVS

Prairie Chapter Meeting Naperville, IL June 12, 2006

Program and Schedule

Site map

The meeting is being held in the marked area, including three meeting rooms and the atrium. Badge pickup, registration, food service and the exhibitors are in the atrium. 101B contains the poster presentations, and the oral sessions will be in 101A+C. Lunches may be taken to the dining room if available, to 101C, the loft area, outside, or any other convenient location. You are also welcome to join the board for the chapter public business meeting in 101A during lunch. See schedule for details on sessions.

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Exhibitors:

Advent Associates

Pfeiffer Vacuum

Midwest Vacuum

D'arcy Micro Sciences

Meyer Tool

Control Plus

Varian Vacuum

Alan Burrill Technical Sales

Vacuum One

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SCHEDULE

Time 101A 101B 101C Atrium 7:30a Expo setup 8:00a

Poster setup

Badge pickup/late registration open (8:00am-12:00pm)

Surfaces and Nanointerfaces

Richard Rosenberg, Chair

Posters up 8:30-4:10

Expo open 8:30-3:30 8:40a Dave Sampson*, KLA-

Tencor Video Rate Atomic Force Microscopy

Microscopy and Nanostructures

Jerry Moore, Chair Breakfast/coffee 9:20a Nathan L. Yoder

Northwestern University Toward Stable Molecular Devices: Desorption of Cyclopentene from p-Si(100) with UHV-STM and Density Functional Theory

Amanda Petford-Long* Argonne National Lab Structure-property relationships in nanomagnetic materials

(through morning)

9:40a Sara DiBenedetto Northwestern University Organic Dielectric Materials for High Capacitance Applications: Modeling and Experiment

10:00a ------ Poster presentations (odd-numbered posters to be judged)

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10:40a John Weaver*, University of Illinois Urbana Champaign Synthesis and Characterization of Metal and Semiconductor Nanoparticles on Surfaces

Suzanne Raebel Stork Technimet Failure Analysis of Components Using Microscopic Techniques

11:00a Matthew T. Russell Northwestern University Master-less Fabrication of Poly(dimethylsiloxane) (PDMS) Stamps With Electron Beam Lithography

11:20a J.W. Elam, Argonne National Lab Atomic Layer Deposition of In2O3 Using Cyclopentadienyl Indium: A New Synthetic Route to Transparent Conducting Oxide Films

Eric Stach*, Purdue University Understanding the onset of plasticity in materials using quantitative in-situ nanoindentation

11:40a David J. Comstock, Northwestern University Fabrication of Integrated Scanning Electrochemical–Atomic Force Microscopy Probes by Atomic Layer Deposition of Aluminum Oxide

12:00p AVS Prairie Chapter Business Meeting (open to all)

Lunch served

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Nanoscience and

Technology Seth Darling, Chair

Lunch (continued)

1:00p John Randall* Zyvex, Inc. Atomically Precise Manufacturing Another Step in Analog to Digital Conversion

Atom Probe Tomography John Noonan, Chair

1:40p Joseph A. Letizia Northwestern University High Electron Mobility in Phenyl-Acyl-Thiophene Based Organic Field-Effect Transistors: From Vapor Deposition to Solution Processability

Dieter Isheim* Northwestern University Three-dimensional imaging and analysis of nano-scale structures in metals and alloys by atom-probe tomography

2:00p Igor Bolotin University of Illinois Chicago XPS and QCM Studies of PMMA and Teflon AF1600 Films Bombarded by 1-20 keV C60+ Ions

Afternoon refreshments

2:20p ----------- Poster presentations (even-numbered posters to be judged)

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3:00p David L. Frattarelli Northwestern University A Systematic Study of the Effects of Fluorination and Hydrogen Bonding Motif in a Series of Electro-Optically-Active Chromophores at both the Molecular and Thin-Film Level

Tom Kelly* Imago Scientific Instruments Three-Dimensional Atom Mapping with Atom Probe Tomography

3:20p Daniel J. Askunsis University of Illinois Chicago Valence-Band and Core-Level X-Ray Photoelectron Spectroscopy of Lead Sulfide Nanocrystal/Polymer Composites

3:40p Philippe Guyot-Sionnest* University of Chicago Semiconductor physics in solution: Colloidal quantum dots

Chantal Sudbrack Argonne National Lab Sub-nanometer compositional profile measurements with 3-D atom-probe tomography

4:20p closing/poster awardees

announced

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8:40am 101A Invited Speaker

Video Rate Atomic Force Microscopy

Andrew D.L. Humphris1 and David Sampson2

1 Infinitesima Ltd., Oxford Centre for Innovation, Mill Street, Oxford OX2 0JX, United Kingdom.

2 KLA-Tencor Corporation, 160 Rio Robles, San Jose, CA 9513. Scanning probe microscopy (SPM) offers unique imaging capabilities as it is able to provide nanometre resolution in air, liquid and vacuum environments, with no pre-treatment or coating of the sample. This has led to the very widespread use of SPM ranging from basic research in biology and material science through to industrial applications such as quality assessment and inspection. However, unlike far field imaging methods that collect data in a parallel fashion, due to the scanning nature of SPM, it is necessary for the image to be collected one pixel at a time, line by line in series, thus severely limiting the rate at which an image can be obtained. Typically, a conventional atomic force microscope (AFM) will take from 10 seconds to a few minutes to acquire an image. This severely limits the microscopes ability to follow processes at the molecular level, which often occur on the millisecond time scale due to the relaxation time of the molecules, and prevents large area inspection. Other applications that are limited by the low image acquisition rates include data storage and nanolithography. In this paper the limitations of conventional approaches to SPM will be considered and new methods that overcome these problems will be introduced. A video rate AFM will be presented that utilises a novel feedback system and micro resonant scanner [1]. The video rate AFM is capable of collecting images of a 3µm x 3µm area in less than 40 milliseconds, which is approximately 1000 time faster than conventional methods. To achieve this, the microscope operates with a tip velocity in excess of 20 cm per second compared to 20 μm per second in a conventional AFM. High speed dedicated hardware has been developed and enables the images to be collected and displayed to the operator in real time. The ability of the video rate AFM to follow processes at the molecular level with millisecond time resolution has been demonstrated by observing polymer processes such as crystallisation of a molten polymer surface and results will be presented. The high frame rate of the microscope also reduces the effect of the external environment and enables the user to explore the surface of the sample with nanometre resolution in real time. Large areas can be mapped with nanometre resolution by tiling individual high speed images. We believe that the presented video rate AFM demonstrates the step like improvement that SPM requires if these techniques are to deliver the capabilities sought by the advancing fields of biotechnology and nanotechnology. [1] A.D.L. Humphris, M.J. Miles and J.K. Hobbs, Appl. Phys. Lett., 034106 (2005).

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9:20am 101C Invited Speaker

Structure-property relationships in nanomagnetic materials

A K Petford-Long

Argonne National Laboratory, 9700 S Cass Ave, Argoone, IL 60439 One of the most spectacular examples of the application of nanomagnetic structures is the development of devices based on the giant magnetoresistance (GMR) phenomenon, such as the spin-valve and the spin-dependent tunnelling junction used for read heads or magnetoresistive random access memories. The materials from which these structures are fabricated are inhomogeneous at the nanoscale (polycrystalline, thin layers, nanoparticles). The novel magnetic and transport phenomena that these materials exhibit depend critically on their microstructure and composition, with variations on the atomic scale leading to variations in properties. We have applied high resolution electron microscopy (HREM), transmission electron microscopy (TEM) chemical mapping and three-dimensional atom probe (3DAP) analysis to a range of information storage materials including spin-dependent tunnel junctions, multilayers composed of materials suitable for spin-valves and magnetic nanoparticles. This paper will present some of these results. For example, changes in the TMR ratio and RA product for unpinned tunnel junction structures have been shown by a combination of 3DAP and HREM to be the result of a change in the morphology and composition of the tunnel barrier, with underoxidised and unannealed fully-oxidised barriers being highly non-uniform [1, 2]. The behaviour of these materials relies on the local magnetic domain structure and magnetization reversal mechanism, and one of the techniques enabling micromagnetic studies at the sub-micron scale is Lorentz transmission electron microscopy (LTEM) which allows the magnetic domain structure and magnetization reversal mechanism of a FM material to be investigated dynamically in real-time with a resolution of a few nanometres [3]. We have used LTEM and in-situ magnetizing experiments to make qualitative and quantitative studies of magnetization reversal in a range of materials including spin-tunnel junctions, patterned thin film elements and magnetic antidot arrays. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach, which enables access to the phase change experienced by the electrons as a function of magnetic induction in the sample [4]. The result is the ability to produce quantitative maps of the in-plane magnetic induction of the sample in a plane perpendicular to the electron beam. A second technique that can be used to image the magnetic domain structure is off-axis electron holography, which again relies on reconstructing quantitative maps of the magnetic induction from the phase change experienced by the electrons [3]. In addition to the local variations in the magnetic properties induced by the microstructure of the films, further variations arise when the films are patterned to form small elements and results will be presented for a range of structures patterned both from single layers and from device structures. [1] A K Petford-Long, D J Larson, Y Q Ma, A Cerezo, E W Singleton and B W Karr, J. Appl. Phys. 98, 124904 (2005). [2] A Cerezo, A K Petford-Long, D J Larson, S Pinitsoontorn and E W Singleton, J. Mat. Sci. (in Press). [3] Chs in Magnetic microscopy of nanostructures, eds. H. Hopster and H.P. Oepen (Springer, Berlin, 2005). [4] A. Kohn, A.K. Petford-Long and T.C. Anthony, Phys. Rev B 72 014444 (2005)

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10:40am 101A Invited Speaker

Synthesis and Characterization of Metal and Semiconductor Nanoparticles on Surfaces

John H. Weaver

Department of Materials Science and Engineering

1University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

In the area of nanostructures, the goal is to produce structures of arbitrary material on a substrate of arbitrary material, with size selection and patterning so that new science can be learned and new devices can be fabricated. There are many ways to approach this synthesis, and all have their limitations. In our laboratory, we have developed a way to produce clusters or nanostructures of a wide range of materials and to deliver them to atomically clean surfaces (of any type) where their interactions can be investigated. The process involves physical vapor deposition onto an inert buffer layer where nucleation and growth occurs at low temperature. Subsequent desorption of the buffer delivers the clusters in the ultimate of "soft landing"; the thickness of the buffer layer gives control over the cluster size distribution. This talk will emphasize clusters delivered to surfaces derived from Si(111)-7x7, Ag(111), GaAs(110), and amorphous graphite. Scanning tunneling microscopy makes it possible to explore issues related to wetting, atomic rearrangement, interface bonding and adhesion, and manipulation. STM results show that these nanocrystals range in size from 100 to 600,000 atoms, depending on growth parameters, and we will emphasize their novel properties. For example, silver nanocrystals on Si(111) can be pushed by mechanical contact with the tip, and they leave behind a Ag track due to site-selective Ag atom transfer to the Si surface. Ag clusters delivered to ideal Ag(111) wet the surface and produce hexagonal multilayer islands that decay while Cu clusters produce islands that are mobile because of the highly incommensurate interface. Transmission electron microscopy results provide insights into cluster diffusion and coalescence on the buffer as it desorbs. Diffusion is activated by the elementary excitations of the particle and the support (phonons). For small particles (~ 5 nm mean radius, ~ 3x104 atoms), the diffusivity is also enhanced by the energy of coalescence. For large ramified nanostructures (>2x105 atoms), the diffusivity scales as the inverse of the contact area, indicating fast slip diffusion. Coalescence can be modeled via diffusion limited aggregation. Applications of this technique to Cd-based II-VI semiconductor particles shows dependencies of the photoluminescence signal on particle shape. Extensions of this growth procedure will be discussed, along with possible ways to achieve patterning.

11:20am 101C Invited Speaker Understanding the onset of plasticity in materials using quantitative

in-situ nanoindentation

E. A. Stach1, A. M. Minor2, O. Warren3 A.S. Asif3, D. Ge2, Z. Shan2, M. Jin,4 J.W. Morris, Jr4. and T. Wyrobek3

1 School of Materials Engineering, Purdue University, West Lafayette, IN 47906, USA

2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 2 Hysitron Corporation, 10025 Valley View Road Minneapolis, MN 55344

4 Department of Materials Science and Engineering, University of California, Berkeley, CA 947290 *Correspondence: eastach@purdue.edu

Nanoindentation is widely accepted as the preferred technique to study localized mechanical deformation

phenomena in materials. However, the mechanisms of deformation can only be inferred from the load-displacement data obtained during a typical instrumented nanoindentation test. In order to elucidate the underlying physics of these process, we have developed and exploited a new technique, that of in-situ nanoindentation in a transmission electron microscope (TEM). In this technique, a voltage-actuated piezoceramic tube is used to position a sharp diamond in-plane with the edge of an electron transparent sample. The tip is then driven into the material using a three-plate capacitive transducer which allows direct measurement of load and displacement data to be recorded concomitant with real time images of the indentation response of the material. In this paper we will briefly review the details of our experimental technique, as well as summarize our results from two model systems, aluminum thin metal films, and nanofabricated silicon.

In aluminum, we have found that the onset of plasticity in these materials does not occur via sub-surface nucleation of dislocations at the point of ultimate strength, but is rather induced by surface forces.[1] Detailed studies of grain boundary motion and grain size effects have shown that indentation loading conditions result in stress-induced coalescence, and thus grain growth [2,3].

In silicon, detailed studies of size effects have indicated that the sample thickness and geometry have a controlling effect on the deformation pathway. As sample size decreased to the micron-scale a prevalence for dislocation-based plasticity is favored over the phase transformation pathways observed in bulk materials. Additional changes are found as a function of loading and loading rate, and indicate that the indentation geometry and lack of material constraint strongly affect the deformation response.[4] [1] A.M. Minor, A.M. Minor, S.A. Syed Asif, Z.W. Shan, E.A. Stach, E. Cyrankowski, T. Wyrobek and O. Warren, in review. [2] A.M. Minor, E.T. Lilleodden, E.A. Stach and J.W. Morris, Jr., J. Elect. Mat., 31 (10), 2002, 958-964 [3] M. Jin, A.M. Minor, E.A. Stach and J.W. Morris, Jr., Acta Mat. 52(18), 2004, 5381-87. [4] D. Ge, A. M. Minor, E.A. Stach and J.W. Morris Jr.,, in press, Phil Mag A. [5] This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and DOE

Phase I SBIR grant (DE-FG02-04ER83979) awarded to Hysitron, Inc.

Figure 1 (above): Load and displacement data plotted as a function of time of the test (b) Load as a function of displacement Figure 2 (right): (A) Initial bright field (g = 220) TEM image taken prior to the indentation experiment. Note that the indented grain is initially free of dislocations. (B-C) Extracted video frames corresponding to the transient arrowed as “1” in Figure 1. (D-E) Extracted video frames corresponding to the transient arrowed as “2” in Figure 1. (F-G) Extracted video frames corresponding to the transient arrowed as “3” in Figure 1.

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1:00pm 101A Invited Speaker

Atomically Precise Manufacturing Another Step in Analog to Digital Conversion

John N. Randall

Chief Technical Officer Zyvex Corporation

Manufacturing is based on modularity and precision. Improvements in manufacturing processes are generally improvements in the precision on the parts and processes. Revolutions in manufacturing generally involve the modularity of the process are parts, such as assembly line manufacturing or planar processing of integrated circuits. In the information industries there has been a clear trend of modularization or digitization the storage, processing, and communication of information. While analog representation and processing still find niche applications, the digital revolution is almost complete. The tolerance and error correction made available by digital processing allows for highly complex yet highly reliable systems. We have digital: computers, music, videos, telephones, cameras, and communications. As the resolution of our advanced manufacturing techniques is now in the tens of nanometers laterally (lithography) and in the single nanometers vertically (deposition), there is an opportunity to take advantage of the modularity of matter. This talk will describe Zyvex’s efforts to develop Atomically Precise Manufacturing that will create products with top down control and bottom up efficiency.

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1:40pm 101C Invited Speaker

Three-dimensional imaging and analysis of nano-scale structures in

metals and alloys by atom-probe tomography

Dieter Isheim

Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208-3108, USA

Atom-probe tomography (APT) allows for three-dimensional (3-D) materials analysis with subnanometer spatial resolution, based on position-sensitive time-of-flight mass spectrometry of individual atoms. APT generates a 3-D atom-by-atom reconstruction of a specimen volume with up to 100 x 100 nm2 cross section and several micrometer length. Once the 3-D atom-by-atom image is reconstructed with the aid of a computer, local compositions and the morphology of the material’s nanostructure can be determined quantitatively with subnanometer resolution, utilizing appropriate software. This type of information is invaluable for understanding microstructure-properties relationships which are the basis for modern materials design. This presentation focuses on the application of APT to the development of nano-scale copper precipitation-strengthened ferritic steels with a combination of high strength and good fracture toughness at comparatively low carbon levels. Since high tensile strength is achieved by copper precipitation, martensite formation is not needed and alloying additions such as Cr and Mo can be omitted. From a manufacturing point of view, the absence of martensite also simplifies greatly welding processes. Potential applications include bridges, railcars, truck beds, pipelines, and ship hulls. At maximum strength of the steel, the Cu-rich precipitates are about 3 nm in diameter and have a metastable bcc structure. APT reveals that the precipitates are not pure Cu but contain a significant amount of Fe, which has important implications for understanding the strenghening mechanism. The copper precipitation in these steels is affected by Ni and Al alloying additions, which are varied to increase strength. APT demonstrates that Ni and Mn segregate to the interface of the bcc Cu-rich precipitates. Aluminum, however, enriches in the interior of these precipitates, thereby stabilizing their metastable bcc structure. At increased Al and Ni concentrations of the alloy, regions enriched in equal proportions of Ni and Al are found adjacent to the Cu-rich precipitates. At the same time, the precipitation of a phase with stoichiometry near NiAl, with a putative B2 structure, is observed at grain boundaries, substantiating that this phase is thermodynamically stable at this steel’s composition. The possibility of co-precipitation of Cu-rich and NiAl-based precipitates offers the potential to further improve the technologically interesting properties of this family of steels. The Northwestern University Center for Atom-Probe Tomography (NUCAPT) operates a LEAP tomograph with laser-assisted anaylsis capability, manufactured by Imago Scientific Instruments Corp. Applications of modern atom probe tomography and field-ion microscopy techniques to materials problems are briefly discussed.

3:00pm 101C Invited Speaker

Three-Dimensional Atom Mapping with Atom Probe Tomography

Thomas F. Kelly, Keith Thompson, David J. Larson, Robert M. Ulfig, Joseph H. Bunton, and Jesse D. Olson

Imago Scientific Instruments Corporation, 5500 Nobel Drive, Madison, WI 53711,

tkelly@imago.com, www.imago.com Atom probe tomography is the highest spatial resolution analytical technique known. It provides three-dimensional structural and compositional analysis of materials at the atomic scale. With recent developments in LEAP® technology by Imago Scientific Instruments, the atom probe’s compositional imaging capabilities are now accessible to non-experts for analysis of a wide variety of materials including metals, magnetic media, semiconductors, ceramics, geological materials, and even synthetic organics and polymers. Imago’s atom probe technology has many advantages in analysis speed, large field of view, and ease of operation. The LEAP 3000X™ accomplishes these objectives while incorporating the ability to field evaporate the specimen atom by atom with either a laser pulse or a voltage pulse. Imago’s reflectron-based atom probe technology (from Oxford nanoScience) offers the highest attainable mass resolution for voltage-pulsed instruments. Important examples of analyses of metals, semiconducting, and organic nanostructures will be shown. Arsenic atoms (purple) implanted into the source/drain of a transistor. Blue feature is an isoconcentration surface for oxygen which delineates the gate dielectric on the left and the silicon and polysilicon surfaces.

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3:40pm 101A Invited Speaker

Semiconductor physics in solution: Colloidal quantum dots

Philippe Guyot-Sionnest

University of Chicago Small ~ 10 nm, semiconductor nanocrystals exhibit many of the features of their bulk counterparts. There are however major differences: i) the spatial confinement leads to strong tuning of the electronic energies available, and they are called quantum dots or artificial atoms, ii) they have a large number of surface atoms, hence surfaces may control much of the carrier dynamics, iii) they are available as solutions which opens up many other possiblities of processing. I will present some examples that illustrate these various characteristics and which were pioneered in my group.

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9:20am 101A Speaker

Toward Stable Molecular Devices: Desorption of Cyclopentene from p-Si(100) with UHV-STM and Density Functional Theory

Nathan L. Yoder, N.P. Guisinger, M.C. Hersam

Department of Materials Science, Northwestern University

In recent years, substantial progress has been made in the emerging field of molecular electronics. Of particular interest is the integration of molecular electronic devices with conventional silicon microelectronic technology. The presence of the energy band gap in silicon provides opportunities for resonant tunneling through individual molecules, leading to interesting effects such as room temperature negative differential resistance [1,2]. Additionally, studies of organic molecule-silicon junctions can yield important insights into the feasibility of future hybrid molecule-silicon devices. In particular, the reliability of these molecular junctions is of critical importance to potential devices, and consequently warrants further investigation. Single cyclopentene molecules on silicon provide a useful test case, since the binding geometry has been studied both experimentally and theoretically. In this study, a combination of experimental and theoretical tools were employed to investigate the stability of cyclopentene molecules on a degenerately doped p-type Si(100) surface. Experiments were performed using a cryogenic ultra-high vacuum scanning tunneling microscope [3]. At 80 K, cyclopentene desorbs from the surface at both positive and negative sample bias polarities over a range of tunneling currents. The desorption rate is roughly linear with tunneling current, indicating a single-electron/hole process. The desorption yield is a strong function of bias, and has turn-on voltage of –2.5 V at negative bias and 3.5 V at positive sample bias. The magnitude of the yield ranges from 2x10-12 to 1x10-8 events/electron at both polarities, which is 500-1000 times smaller than the reported yields of Benzene on Si(100)-(2x1) and Chlorobenzene on Si(111)-(7x7). Density functional theory and reaction path calculations were performed in order to determine the details of the desorption process following resonant excitation. [1] N. P. Guisinger, M. E. Greene, R. Basu, A. S. Baluch, and M. C. Hersam, Nano Letters, 4, 55 (2004). [2] N. P. Guisinger, N. L. Yoder, and M. C. Hersam, Proc. Nat. Acad. Sci., 102, 8838 (2005). [3] E. T. Foley, N. L. Yoder, N. P. Guisinger, and M. C. Hersam, Rev. Sci. Instrum., 75, 5280 (2004).

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9:40am 101A Speaker

Organic Dielectric Materials for High Capacitance Applications: Modeling and Experiment

Sara DiBenedetto1, Antonio Facchetti1, Tobin J. Marks1, 2, and Mark A. Ratner1

1Department of Chemistry, Northwestern University, Evanston, IL

2Department of Materials Science and Engineering, Northwestern University, Evanston, IL One of the major challenges facing the Si-based microelectronics industry is an increase in SiO2 gate-insulator leakage current from 10-12 to 10 A/cm2 at 1V when the insulator thickness is reduced from 3.5 to 1.5 nm. Since then, considerable effort has been focused on measuring the electrical properties of organic molecules arranged in self-assembled monolayers (SAMs). Organic-based dielectrics could be superior gate insulators in thin film transistors (TFTs), compared to traditional high-dielectric constant (εr) inorganic oxides, because of their amenability to forming low-leakage, nanometer-thick insulating films by solution-based processes at low temperatures, and furthermore, because of their tailorable dielectric constants, which can potentially exceed that of SiO2. Different types of organic dielectrics, such as self-assembled superlattices (SASs), crosslinked polymer blends (CPBs), and nanocomposites, have been fabricated and shown experimentally to afford high capacitances and low TFT operating voltages. In an effort to better understand charge storage and energy densities of these dielectric structures, approaches for computing the effective dielectric constants of each nanodielectric motif is discussed. The dielectric constant of the SAS material can be calculated from two capacitors in series model and also from the Clausius-Mossotti relation. Whereas effective medium approximations (EMAs), such as Maxwell-Garnett and Bruggeman formulas, are used to calculate the effective dielectric constant of the CPBs and nanocomposites. The desired organic dielectrics not only have large dielectric constants but also have low leakage current densities at moderate field strengths. Preliminary results from leakage current densities in SAS MIS capacitors at different temperatures show that it will be possible to deduce the conduction mechanism based on standard conduction equations. Characterization of the conduction mechanism is important for the improvement of leakage current and dielectric breakdown in high capacitance devices.

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10:40am 101C Speaker

Failure Analysis of Components Using Microscopic Techniques

Suzanne Raebel

Stork Technimet, Inc.

Knowledge of the root cause of any failure is essential to properly implementing solutions in order to prevent recurrence. In order to determine the root cause of a component failure, one must perform a failure analysis, which is a methodical and sequential study including preliminary information gathering, component testing, and interpretation of results. The appropriate testing and evaluation techniques for a given failure analysis are governed by parameters such as sample condition, sample size, failure mode, time restraints, and cost limitations. Microscopic techniques, such as stereomicroscopy, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), are particularly useful for analyzing electrical component failures, thin films (whether intentionally placed or a result of wear, contamination, or corrosion), and small particles (e.g. debris). This presentation details the failure analysis process, and includes selected case histories of component failures that were characterized using microscopic techniques.

11:00am 101C Speaker

Master-less Fabrication of Poly(dimethylsiloxane) (PDMS) Stamps With Electron Beam Lithography

Matthew T. Russell,1 Liam S.C. Pingree,2 Mark C. Hersam,2 and Tobin J. Marks1,2

1Department of Chemistry, Northwestern University

2Department of Materials Science and Engineering, Northwestern University Patterning the chemical functionality of surfaces is necessary for further progress in the fields of: sensors, catalysis, microelectronics, and microfluidics. In the later case, the chemical and thermal stability of the traditional microfluidic material, PDMS, has limited the degree to which the chemical functionality can be tailored. Here, electron beam lithography has been employed in an attempt to pattern the chemical functionality of the PDMS surface on the nano- to sub-micron scales. Using moderate dosages (100-10,000 μC/cm2) and accelerating voltages (15-30 kV), the surface chemical functionalization and topography of PDMS is patterned, as verified by secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM). The ability to pattern both the topography and the chemical functionality in a single process has several advantages compared to traditional PDMS patterning techniques. Modification of cured pre-patterned PDMS stamps with electron beam lithography can extend the utility of existing stamps. The rapid and master-less nature of this patterning technique allows for rapid prototyping and testing of stamp designs. Finally, direct-write patterning of surface chemistry with this technique could allow for novel devices to be realized. Here, a demonstration of the topographic and chemical patterning abilities will be given, a patterning mechanism will be proposed, and patterned stamps will be utilized in several soft lithographic applications.

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11:20am 101A Speaker

Atomic Layer Deposition of In2O3 Using Cyclopentadienyl Indium: A New Synthetic Route to Transparent Conducting Oxide Films

J. W. Elam1, A. B. F. Martinson1,2, M. J. Pellin1, and J. T. Hupp2

1Argonne National Laboratory, 2Northwestern University

Indium Oxide (In2O3) forms the basis for an important class of transparent conducting oxides (TCOs) that see wide use in optoelectronic devices, flat-panel displays and photovoltaics. Here we present a new method for depositing In2O3 thin films by atomic layer deposition (ALD) using alternating exposures to cyclopendadienyl indium and ozone. Using a precursor vaporization temperature of 40°C and deposition temperatures of 200-450°C, we measure growth rates of 1.3-2.0 Å/cycle. A significant advantage of this synthesis route over previous techniques is the ability to conformally coat porous materials such as anodic aluminum oxide (AAO) membranes. The deposited films are nanocrystalline, cubic phase In2O3 and are highly transparent and conducting. In situ quadrupole mass spectrometry and quartz crystal microbalance measurements reveal a mechanism in which approximately 1 in 6 of the initial Cp ligands remain on the surface following each InCp exposure, and the remaining Cp ligand is burned off during the subsequent O3 exposure to form CO2. Using this method, we demonstrate for the first time the conformal coating of very high aspect ratio, nanoporous AAO membranes with ALD In2O3. The figure shows a backscattered electron scanning electron micrograph of a cross section of an AAO membrane with 13 nm ALD In2O3 coating. The white lines visible along the pore walls are the In2O3 coating. This technique will enable the functionalization of porous materials with In-based TCO films for the fabrication of novel photovoltaic devices.

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11:40am 101A Speaker Fabrication of Integrated Scanning Electrochemical–Atomic Force Microscopy Probes by Atomic Layer Deposition of Aluminum Oxide

David J. Comstock1, J. W. Elam2, M. J. Pellin2, M. C. Hersam1

1Northwestern University, Evanston, IL 60208, 2Argonne National Laboratory, Argonne, IL 60439

Integrated scanning electrochemical–atomic force microscopy (SECM-AFM) is a powerful tool for characterizing electrochemical and biological processes ranging from corrosion to membrane transport. SECM-AFM utilizes probes consisting of a tip electrode integrated onto a conventional atomic force microscopy cantilever, allowing for simultaneous but independent topographic and electrochemical imaging. In this study, we describe a novel process for fabricating integrated SECM-AFM probes using atomic layer deposition (ALD) techniques. ALD allows for the deposition of highly conformal, continuous insulating films with precise thickness control and is thus well suited for this project. Fabrication starts with commercially available conductive AFM probes, onto which a 50 nm thick aluminum oxide film is deposited by ALD. This insulating film serves to encapsulate the probe body, cantilever, and tip and eliminate electrical leakage currents when operating in an electrochemical environment. The tip nanoelectrode is fabricated using focused ion beam milling to selectively remove aluminum oxide from the tip apex and expose the underlying conductive film. The integrated probes are characterized by scanning electron microscopy (SEM) throughout fabrication to determine both the quality and morphology of the insulating film and the dimensions of the electrode. The films and fabricated probes are electrochemically characterized by cyclic voltammetry, in which the diffusion-limited redox current is used to determine the area of the exposed nanoelectrode. In addition, silver electrodeposition is used to visually confirm that the electrochemical activity of the probe is limited solely to the nanoelectrode at the tip apex. Both SEM imaging and electrochemical characterization have revealed tip electrodes with diameters as small as 50 nm.

1:40pm 101A Speaker

High Electron Mobility in Phenyl-Acyl-Thiophene Based Organic Field-Effect Transistors: From Vapor Deposition to Solution Processability

Joseph A. Letizia, Antonio Facchetti, Mark A. Ratner*, and Tobin J. Marks*

Department of Chemistry and the Materials Research Center,

Northwestern University, Evanston, IL

The most common technique for depositing organic semiconductors is physical vapor deposition, which yields highly crystalline films exhibiting excellent charge transport characteristics and low trap densities. However, solution processability is desirable due to its adaptability, large area coverage, low cost, and scalability. In addition to the challenges of achieving soluble semiconductors, electron transporting (n-type) materials are rare and highly sensitive to device fabrication method, environmental doping, and charge trapping. The combination of these challenges has resulted in very few solution processable n-type organic semiconductors and even fewer of these are polymers. A family of molecules and polymers is designed and synthesized having a phenyl-acyl-thiophene structure. Several materials are found to have favorable volatility and solubility, allowing for vapor deposition and solution casting of semiconductor films. Thin film field effect transistors are fabricated with a fluorinated molecule having a n-type mobility up to ~0.6 cm2 V-1 s-1 and drop cast films having a mobility, remarkably, of ~0.3 cm2 V-1 s-1. Studies with one polymer demonstrate electron mobilities of 10-6 cm2 V-1 s-1. Drop-casting polymer/molecule blends has resulted in films having electron mobilities up to 0.01 cm^2 V^-1 s^-1. The crystal structure is obtained for two molecules and shows nearly planar thiophene cores having herringbone packing motifs. Quantum chemical calculations are performed to assess the charge carrier hoping rates and other important parameters for these novel materials.

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21

2:00pm 101A Speaker

XPS and QCM Studies of PMMA and Teflon AF1600 Films Bombarded by 1-20 keV C60

+ Ions

Igor Bolotin, Stephanie H. Tetzler, and Luke Hanley

Department of Chemistry, University of Illinois at Chicago, m/c 111, 845 West Taylor Street, 4500 SES, Chicago, Illinois 60607-7061

keV C60 ions are widely used as projectiles in secondary ion mass spectrometry of polymeric materials. Evidence exists that the mechanism of sputtering by C60 ions allows their use for damage-free depth profiling. Surface analysis studies are presented to probe absolute sputtering yields and surface modification of two polymer films by C60 ions. Polymethylmethacrylate (PMMA) and Teflon AF1600 spin-casting films studied during different bombardment doses of C60 ions with energies of 1-20 keV by quartz-crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). Measurements for the total sputter yield of films are acquired using a QCM. Mass-lost rate data show that each 20 keV C60 cluster leads to emission ~106 amu of polymer, indicating that the non-overlapping crater regime exists for doses of <1012 ion/cm2. Sputtering yields of these polymer films are ~5 higher than those of polycrystalline gold films at >10 keV. Chemical modification is also probed by XPS of the target surface before and after ion bombardment. Both polymers display little to no damage to their film structure at ion fluences below ~1013 ion/cm2. Changes in C 1s XPS spectra during higher fluence bombardment can be explained predominantly by differential charging effects. However, ion fluences >1015 ion/cm2 modify the film composition to a carbon-rich material with various degradation products.

3:00pm 101A Speaker

A Systematic Study of the Effects of Fluorination and Hydrogen Bonding Motif in a Series of Electro-Optically-Active Chromophores at

both the Molecular and Thin-Film Level

David L. Frattarelli,1 Michele Schiavo,1 Antonio Facchetti,1 Mark Ratner,1 and Tobin J. Marks1

1Department of Chemistry, Northwestern University

The organization of nonlinear optical chromophores into a noncentrosymmetric architecture has been a daunting challenge in the electro-optics (EO) community for many years. The most recent approach to fabricating accentric, EO-active films, know as physical vapor deposition (PVD), is employed for thin-film growth of a variety of innovative chromophores. Here, a series of new chromophores suitable for PVD deposition are designed, investigated theoretically, and synthesized. These systems are characterized by the presence of H-bonding donor and acceptor groups and fluorinated molecular fragments to enhance volatility, thermal stability, and film forming properties. Molecular modeling studies include: DFT, INDO/S, and SOS perturbation theory for the determination of the first hyperpolarizability (β). These methods allow the screening of diverse chromophore families so to fully understand the effects of fluorination and changes of the hydrogen bonding motifs on the molecular hyperpolarizability and optical transparency. Modeling reveals that for some chromophores, fluorination increases β by a factor of two while conjugative decoupling between the chromophore π-donor and the hydrogen bonding donor sites gives rise to small increases of β. SHG spectroscopy demonstrates similar EO trends with χ2 increasing by ~ 40 pm/V upon fluorination of various derivatives. Both theoretical modeling and second harmonic generation (SHG) analysis play a critical role in helping better understand the structure-function relationship at both the nanoscopic (molecules) and microscopic (films) levels and help to identify new chromophores affording higher χ and stronger χ2 response, further advancing the knowledge base in eletro-optical materials.

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23

3:20pm 101A Speaker Valence-Band and Core-Level X-Ray Photoelectron Spectroscopy of

Lead Sulfide Nanocrystal/Polymer Composites

Daniel J. Asunskis1, Luke Hanley1

1University of Illinois at Chicago

Lead salt nanocrystals have been the subject of intense recent interest due to their potential applications in photovoltaics, near infrared sensors, and other optoelectronic devices. However, relatively few studies have used photoemission to probe the electronic structure of these novel nanomaterials. Valence-band and core-level X-ray photoelectron spectroscopy (XPS) are therefore used to probe different lead sulfide (PbS) nanocrystal-polymer nanocomposites. Composite materials are prepared by trapping monodisperse 3 and 10 nm lead sulfide nanocrystals in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly (2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene or MEH-PPV. Additional composites with polydisperse lead sulfide nanocrystals were synthesized by growing the particles in the presence of MEH-PPV and poly (vinyl alcohol). These materials are initially characterized by UV/Vis optical absorption and transmission electron microscopy to monitor the particle size in the composites. Monochromatic XPS with charge neutralization is then used to collect both core-level and valence-band spectra. The composites with monodisperse particle sizes exhibit a shift to lower energy of the highest occupied molecular orbital as the lead sulfide particle size increases from 3 to 10 nm. Oxidation of the sulfur content in the particles by air during fabrication and transport was minimal as evident by the small contribution of oxidized sulfur in the XPS spectra. The core level XPS results also show additional states in the lead core XPS regions that change as the particle size changes. The monodisperse composites are compared to the other composites synthesized having varied particle size, showing the effects of size variance and polymer/particle bonding in the core level and valence band XPS spectra.1

1This work is supported by the U.S. Department of Defense.

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3:40pm 101C Speaker

Sub-nanometer compositional profile

measurements with 3-D atom-probe tomography

Chantal K. Sudbrack1,*, K. E. Yoon1, R. D. Noebe2 and D. N. Seidman1

1Northwestern University, 2NASA Glenn Research Center

The advantage of 3-D atom-probe tomography (3-D-APT) over other microanalytical techniques is its ability to visualize and reconstruct on a subnanoscale 3-D microstructures and to characterize their compositions quantitatively on an atom-by-atom basis. Particularly strong in the study of buried interfaces, 3-D-APT is one of the few techniques that can observe directly the initial genesis of new phase in condensed matter. To address the earliest stages of phase separation with 3-D-APT, sophisticated computer-based analytical methods are needed. One such method, the proximity histogram compositional profile [1], developed at Northwestern University, generates a 1-D radial compositional profile, from 3-D data, which originates from buried interfaces and is effective in addressing quantitatively interfacial segregation associated with nanometer-sized microstructural features. Employing this method, we examine in great detail at the temporal evolution of the compositional profiles during the earliest stages of γ(f.c.c.)/γ'(L12)-phase separation in model Ni-based superalloy when aged isothermally at 873 K. In the initial stages the γ'-precipitates have an average radius of 0.75 nm. After the longest aging time (1024 h), precipitates are ca. 10 nm in radius. Sub-nanometer scale compositional profiles across the interfaces demonstrate that the compositions of both the γ-matrix and γ'-precipitates evolve temporally. Observed chemical gradients of Al-depletion and Cr-enrichment adjacent to the γ'-precipitates are initially transient, consistent with well-established model predictions for time dependent diffusion-limited growth, and mark the first detailed observation of this phenomenon. Furthermore, it is shown that Cr atoms are kinetically trapped in the growing γ'-precipitates. This research is supported by the National Science Foundation, Division of Materials Research under DMR-0241928. [1] O. C. Hellman, J. A. Vandenbroucke, J. Rüsing, D. Isheim, and D. N. Seidman, “Analysis of Three-Dimensional Atom-Probe Data by the Proximity Histogram,” Microsc. Microanal., 6 (2000), 437-444. * Currently at Argonne National Laboratory, Materials Science Division

25

Poster Presentations (note the presentation number and page number are identical) P26 Eldad Herceg “Spectroscopic characterization of intermediates on Pt(111) related to the catalytic synthesis of HCN from CH4 and NH3 “ P27 Alexander A. Green “Tunable Separation of Single-Walled Carbon Nanotubes by Structure in Density Gradients” P28 Marie A. Mayer “Photoluminescence investigation of defect levels in CuGaSe2“ P29 Damon Hebert “Luminescence of CuInSe2 Bicrystals” P30 Norma E. S. Cortes “Controlling the Electronic Properties of Transparent Conducting Oxide Surfaces with Conductive AFM” P31 H. T. Johnson-Steigelman “Production of a hafnium silicate dielectric layer for use as a gate oxide by solid-state reaction” P32 B. Cho “P incorporation during Si(001):P gas-source molecular beam epitaxy: effects on growth kinetics and surface morphology” P33 S.S. Parihar “Atomic-Scale Visualization of Surface Alloys: Sb/Au(110)”

P34 Abhishek Agrawal “Cl-Induced Etching of Si(100)-(2x1) under Conditions of Super-Saturation: An Unexplored Regime of Surface Coverage” P35 Lian Wang “High-Performance Transparent, Flexible Inorganic-Organic Hybrid Thin-Film Transistors” P36 Christina Freyman “Synthesis of Titanium Oxide/Aluminum Oxide Multilayer Coatings by Reactive Pulsed D.C. Magnetron Sputtering with Enhanced Hardness” P37 S. T. Christensen “Structural characterization of Pt nanocrystals supported on SrTiO3 (001)”

P38 Matt Virgo “Investigation of NEA Photocathodes for High Average Power Radiation Sources” P39 Allen J. Hall “Kelvin Prove Force Microscopy Of Large Multigrain Epitaxial CuInSe2”

P40 Chantal K. Sudbrack “3D Atom Probe Studies of a Ni-50 Ti-20 Pt Shape Memory Alloy” P41 Mihaela Tanase “Domain Behavior in Thin Film Nanostructures”

P26

Spectroscopic characterization of intermediates on Pt(111) related to the catalytic synthesis of HCN from CH4 and NH3

Eldad Herceg and Michael Trenary

Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607

A variety of fundamental issues in surface chemistry are associated with the industrially important synthesis of HCN from CH4 and NH3 over Pt gauze catalysts. Foremost among these are the identification of the nitrogen and carbon-containing species involved in the C-N bond formation step. Because the overall reaction is endothermic, indirect methods are needed to mimic the key steps of the reaction on a well-characterized surface under ultrahigh vacuum conditions. We have investigated this system with numerous experimental surface science techniques (RAIRS, TPD, LEED, AES, and XPS). In addition, theoretical calculations (DFT) have been used to aid in the identification of the surface intermediates formed in the course of the overall reaction. The relevant surface intermediates were generated through the thermal decomposition of CH3I or C2H4 and the electron induced dissociation or oxydehydrogenation of NH3. Methyl iodide decomposes stepwise through the CH3 and CH intermediates to give surface carbon atoms at ~460 K. Oxydehydrogenation of ammonia leads to formation of a well-ordered p(2×2)-N structure at 400 K. The p(2×2)-N atoms are readily hydrogenated at 300 K to a NH species characterized by an intense and narrow peak at 3321 cm-1. The NH species has been also formed upon electron bombardment of ammonia. This species remains on the surface up to ~400 K when it dissociates yielding surface N and H atoms. Comparison of experimental spectra with the ones obtained from DFT calculations has shown that the NH species is adsorbed at three-fold hollow sites with the molecular axis aligned close to the surface normal. The formation of surface CN is detected through HCN desorption at 500 K in the TPD experiments. The appearance of the vibrational features characteristic of the aminocarbyne (CNH2) species upon hydrogenation of surface CN at 300 K in the RAIR spectra has been used to establish the CN bond formation temperature (see Figure below). The structure and vibrational properties of CNH2 were investigated in detail with DFT calculations. The RAIRS results indicate that HCN desorption at 500 K is kinetically limited by the formation of the CN bond at this temperature from surface C and N atoms but that the HCN desorption order is determined by dissociation of the CNH2. The formation of CN is suppressed in the presence of high coverages of surface carbon, in agreement with previous model reactor kinetic studies. In contrast, the coverage and overlayer structure of surface nitrogen has a negligible influence on the coupling reaction. Our results indicate that the high temperatures used in the industrial synthesis of HCN are needed primarily to activate methane and ammonia dissociative adsorption on the Pt catalyst surface.

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P27

Tunable Separation of Single-Walled Carbon Nanotubes by Structure in Density Gradients

Alexander A. Green, Michael S. Arnold, Samuel I. Stupp, Mark C. Hersam

Northwestern University

One of the main impediments to the utilization of single-walled carbon nanotubes (SWNTs) in molecular electronics, opto-electronics, and sensing is the polydispersity in both diameter and electronic type of SWNTs produced by existing synthesis methods. Here, we demonstrate the bulk separation and enrichment of SWNTs by structure via density gradient ultracentrifugation.(1) The separation is driven by subtle variations in the buoyant density of these nanomaterials, which arises from small changes in their physical structure and electronic properties. After centrifugation in a density gradient, these variations in buoyant density produce colored bands of individual SWNTs grouped according to structure (Fig. 1). By fractionating the contents of the centrifuge tube and characterizing the absorbance and photoluminescence spectra of the sorted SWNTs, the relationship between nanotube structure and buoyant density can be determined. This structure-density relationship is sensitive to the species solubilizing the SWNTs and can be tuned to significantly improve the quality of the separation and to target specific chiralities. Our scalable and non-destructive separation strategy employs centrifugation equipment already used in the solution-based processing of carbon nanotubes, and simultaneously separates isolated and aggregated SWNTs. In addition, our technique has been successfully applied to SWNTs spanning a diameter range of 0.7-1.9 nm, indicating that density gradient ultracentrifugation may provide a general route to the bulk purification of SWNTs by structure. (1) M. S. Arnold et al., Enrichment of Single-Walled Carbon Nanotubes by Diameter in Density

Gradients, Nano Lett., 2005, 5, 713.

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28

P28

Photoluminescence investigation of defect levels in CuGaSe2

Marie A. Mayer1, Angus Rockett1, Susanne Siebentritt2

1University of Illinois, Urbana, Illinois, 2Hahn-Meitner-Institut, Berlin, Germany CuGaSe2 is currently used as the absorber layer in high efficiency thin-film solar cells. However, this wide bandgap material (Eg = 1.58 eV) does not perform as well as desired, most likely due to local defects and composition fluctuations. These lead to the formation of band tails and defects in the energy gap, as well as band edge fluctuations. Recombination effects can be analyzed as a first step to improve solar cell efficiency. Low temperature photoluminescence measurements were taken on epitaxial CuGaSe2 grown on GaAs in order to analyze subgap defect levels in the material. Although investigations are currently in progress, initial results show defects in CuGaSe2 at 0.80 eV and 0.74 eV. Both of these photoluminescence peaks show excessive broadening and are fit using Gaussian analysis.

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P29

Luminescence of CuInSe2 Bicrystals

Damon Hebert1, Julio Soares1, James Mabon1, Angus Rockett1

1University of Illinois, Urbana, Illinois, 61801

CuInSe2 and its alloys are the leading choice for absorber layers in high-efficiency thin film solar cells due to their direct gap, high absorption coefficient and excellent thermal stability. Although the reason is yet unknown, photovoltaic devices made of polycrystalline CuInSe2 absorber layers consistently outperform their single crystal counterparts. This may be due to advanced deposition techniques for the polycrystalline films, but little is known about the effect of grain boundaries on spatial defect distribution in CuInSe2. Epitaxial CuInSe2 thin films were deposited on GaAs bicrystal substrates using a hybrid sputtering and evaporation technique. The substrate consists of two grains separated by a single, easily visible boundary. Electron microscopy and x-ray diffraction have verified the registry of the CuInSe2 epilayers to the GaAs bicrystal substrate. This allows us to isolate and optically characterize individual grains and their boundary. Photoluminescence measurements were taken using a Ge detector for visible and near-IR emission. A Fourier transform infrared detector was used to capture mid-IR emission. In addition, cathodoluminescence was carried out in order to generate carriers from micron-wide excitation areas and to directly correlate excitation position with morphology and proximity to the grain boundary. This allows for greater control of micron-scaled spatial variation. Results indicate variation of luminescence spectra as a function of grain orientation and excitation position relative to the grain boundary.

P30

Controlling the Electronic Properties of Transparent Conducting Oxide Surfaces with Conductive AFM

Norma E. S. Cortes1, T. J. Marks2, and M. C. Hersam1

1Materials Science and Engineering Department, Northwestern University, 2Chemistry Department,

Northwestern University

Transparent conducting oxides (TCOs) are a vital component in optoelectronics, their surfaces in particular play a crucial role in device performance. Tin-doped indium oxide (ITO) is the most widely used TCO in optoelectronics. Yet, its surface properties are not fully understood due to its chemical and electronic complexity arising from its non-stoichiometric nature and defect chemistry. ITO’s performance as an electrode in devices is also highly dependent on its preparation method and surface processing.

Here we investigate the tip-sample interactions of a conductive atomic force microscopy (AFM) probe with ultra smooth commercial ITO that lead to a localized electrochemical change, namely patterning of its electronic, and perhaps chemical, properties. The electrochemical change, induced by the conductive tip scanning while applying a bias, manifests itself in controlled changes in the surface conductance. SIMS data suggest electrochemical reactions of the residual carbon contamination—with itself or with the oxide—within the water meniscus at the tip-sample junction. An electrochemical reaction is further evidenced by the lack of any detectable topographic changes with clear evident changes in lateral forces. These results suggest that the surface electronic changes result from new chemical species or a changed chemical state at the surface rather than physical growth of a modified oxide. These patterns are robust namely they persist after solvent-based cleaning, exposure to UV ozone treatments, and 5-minute exposure to elevated temperatures (~100 °C). Lastly, the pattern contrast ratios (ratios of currents through patterned vs. un-patterned regions) of up to 100 have been achieved with the pattern contrast being dependent on the extent of surface cleanliness. Unveiling the details of the patterning mechanism will likely require invoking ITO’s complexities such as surface dipoles, depletion layer, and the residual organic contamination layer reported even after extensive cleaning treatments. In closing, conductive AFM nanolithography has yielded a novel type of patterning on ITO surfaces that provide controlled, localized changes in the electronic properties of this important transparent conducting oxide.

Current map of cAFM-induced patterns on ultra smooth commercial ITO (left) and corresponding SIMS map (right; m/z = +88, 10 micron bar) show region-specific

changes in surface conductance and chemical properties.

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P31

Production of a hafnium silicate dielectric layer for use as a gate oxide by solid-state reaction

H. T. Johnson-Steigelman, A.V. Brinck, and P.F. Lyman

Laboratory for Surface Studies and Department of Physics

University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211 The formation of hafnium silicate films (HfSixOy) for use as gate oxides with large dielectric constant by solid state reaction of Hf metal and high quality thermal oxide and native oxide SiO2/Si(001) substrates was investigated using low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Thin, fully reacted silicate films could be formed, and were thermally stable in vacuum to temperatures in excess of 800˚C. Spectroscopic evidence indicates that the interface between a hafnium silicate layer and the silicon substrate was stable against SiO2 formation. The observed binding energy (BE) shift provides evidence that the hafnium silicate/Si interface will be stable against interfacial SiO2 formation (as predicted by Hubbard and Schlom1). The thermodynamic driving force for interfacial SiO2 formation when most oxides are placed in contact with Si is the large heat of formation of the SiO2 phase. While Si is rather electro-positive, Hf is even more electropositive, and HfO2 has a higher heat of formation than does SiO2. The shift of the Si oxide XPS feature to shallower BE indicates2,3 that Hf donates charge to the SiO2 complexes in the newly formed silicate compound. This shift, therefore, corroborates that Hf is able to reduce SiO2; conversely, Si will be unable to reduce HfO2, and interfacial SiO2 formation will be thermodynamically unfavorable. The morphology of the surface was determined by AFM to be smooth and featureless on the length scale of hundreds of nanometers. LEED results show the surface to be amorphous and free of pinholes. 1. K.J. Hubbard, D.G. Schlom: J. Mater. Res. 11, 2757 (1996). 2. T.L. Barr: Crit. Rev. Anal. Chem. 22, 115 (1991). 3. T.L. Barr: J. Vac. Sci. Technol. A 9, 1793 (1991).

98100102104106

Thermal Oxide

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

a

c

b

d

e

a: 800 Cb: 640 Cc: 460 Cd: RTe: RT - No Hf

Si 2p

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P32

P incorporation during Si(001):P gas-source molecular beam epitaxy: effects on growth kinetics and surface morphology

B. Cho1, J. Bareno1, Y.L. Foo2, S. Hong3, T. Spila1, I. Petrov1, and J.E. Greene1

1 Department of Materials Science and the Frederick Seitz Materials Research Laboratory, University of

Illinois, 104 South Goodwin Avenue, Urbana, Illinois 61801 2 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602

3 School of Materials Science and Engineering Seoul National University, San 56-1, Shilim-dong, Gwanak-ku, Seoul 151-744, Korea

The effects of P doping on growth kinetics and surface morphological evolution during Si(001):P gas-source molecular-beam epitaxy from Si2H6 and PH3 at temperatures Ts = 500-900 °C have been investigated. With increasing PH3/Si2H6 flux ratio JP/Si at constant Ts, we observe a decrease in the film growth rate R, accompanied by increased surface roughening and pit formation. At constant JP/Si, R increases with increasing Ts, while the incorporated P concentration CP initially increases, reaches a maximum at Ts = 700 °C, and then decreases at higher growth temperatures. We use in-situ isotopically tagged D2 temperature programmed desorption (TPD) to follow changes in film surface composition and dangling bond density θdb as a function of JP/Si and Ts. Measurements are carried out on both as-deposited Si(001):P layers and P-adsorbed Si(001) revealing β1 and β2 peaks due to D2 desorption from Si monohydride and dihydride species, respectively, as well as the formation of a third peak β3 corresponding to D2 desorption from mixed Si-P dimers. Dissociative PH3 adsorption on Si(001) results in a decrease in θdb and an initial increase in P surface coverage θP with increasing Ts. θP reaches a maximum value of 0.95 ML at Ts = 550 °C, and decreases with Ts > 600 °C due to the onset of P2 desorption. Comparison of θP(Ts) with CP(Ts) results obtained during film growth reveals the presence of strong P surface segregation. From measurements of θP vs. CP in Si(001):P layers, we obtain a P segregation enthalpy ΔHs= -0.86 eV. Using the combined set of results, we develop a predictive model for CP vs. Ts and JP/Si, incorporating the dependence of the PH3 sticking probability SPH3

on θP, which provides an excellent fit to the experimental data.

P33

Atomic-Scale Visualization of Surface Alloys: Sb/Au(110)

S.S. Parihar, V.L. Shneerson, R. Fung, H.T. Johnson-Steigelman, E. D. Lu, D.K. Saldin and P.F. Lyman

Department of Physics, Laboratory for Surface Studies, University of Wisconsin- Milwaukee

Surface x-ray diffraction (SXRD) allows quantitative, high-resolution determinations of surface structure via χ2 refinement of a model structure to the observed data. However, the most difficult step in this process is often generating model structures to refine. While this is often possible based, e.g., on chemical intuition, a model-independent method of generating accurate starting structures is sorely needed. We have developed an iterative algorithm to supply the phases, normally not accessible to experiment, from data that are oversampled (relative to the Nyquist frequency of the normal dimensions of the selvedge) along the crystal truncation rods. The algorithm alternately satisfies known constraints of these oversampled data in real and reciprocal space, and incorporates knowledge of the bulk structure, to progressively determine the surface structure factor phases. An inverse Fourier transform then constructs an "image" of the atomic contents of a unit cell of the selvedge.1 We have discovered a rich sequence of Sb-induced reconstructions on Au(110). A c(2x2) appears at 0.5 ML, changing continuously to a 07.5433 R× structure at higher Sb coverages; finally, a p(5x6) structure emerges for several ML Sb deposition. We have applied our novel SXRD algorithm to these surfaces to directly visualize the Sb and Au atomic locations, and thereby solve these structures. This breakthrough affords an automated, model-independent method of determining unknown structures of the outermost few atomic layers of a crystal surface. 1 P.F. Lyman, V.L. Shneerson, R. Fung, R.J. Harder, E. D. Lu, S.S. Parihar, and D.K. Saldin, Phys. Rev. B 71, 081402(R) (2005).

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P34

Cl-Induced Etching of Si(100)-(2x1) under Conditions of Super-Saturation:

An Unexplored Regime of Surface Coverage

Abhishek Agrawal, R.E. Butera, and J.H. Weaver

1Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A.

We investigated the consequences of Cl uptake beyond "saturation" on Si(100)-(2x1), and we discovered a new etching pathway. Si(100)-(2x1) surfaces that were saturated with Cl and had one adatom per dangling bond were exposed to a constant flux of Cl2 in the temperature range of 750-850 K. They were then imaged at room temperature with atomic resolution scanning tunneling microscopy. We found that additional Cl can be accommodated via insertion in the Si-Si dimer bond or backbond to produce a super-saturated surface. This allowed the surface to evolve along a novel and previously unobserved etching pathway. Isolated dangling bonds created on the surface by phonon-assisted electron-stimulated desorption (PAESD) of Cl act as mediators for the insertion process. An abstraction reaction to re-saturate the dangling bond with Cl dissociates the incoming Cl2 to produce atomic Cl on the surface, which then inserts. SiCl2 desorption from the super-saturated surface leads to etching that produces pits elongated along the dimer row direction. The rate limiting step in the etching process is the Cl insertion via the PAESD controlled dangling bond creation. The energetics of the etching process and the sequence of events leading to it will be presented.

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P35

High-Performance Transparent, Flexible Inorganic-Organic Hybrid

Thin-Film Transistors

Lian Wang and Tobin J. Marks

Department of Chemistry and Materials Research Center, Northwestern University, Evanston, IL 60208

Inorganic-organic hybrid thin-film transistors (TFTs) are fabricated at room temperature on both rigid and polymeric substrates using transparent semiconducting In2O3 thin films (60-120 nm) grown by ion-assisted deposition with spin-coated or self-assembled thin film organic dielectrics. The In2O3 thin films exhibit high visible-region optical transparency (> 90%), smooth morphologies, and substantial crystallinity, even when grown at room temperature. These environmentally robust TFTs combine the advantageous characteristics of a high-mobility inorganic semiconductor with a nanoscopic high-capacitance/low-leakage organic gate dielectric. Thus, the resulting inorganic-organic hybrid TFTs are able to exhibit near-1.0V operating characteristics with large field-effect mobilities of > 140 cm2/V·s, Ion/Ioff ~ 105, and near-zero threshold voltage. This performance level provides significant improvements over previously reported organic and metal-oxide-based TFTs, and even rivals poly-Si TFTs. In addition, the present novel hybrid TFTs open a new window to realize transparent, flexible optoelectronics.

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P36

Synthesis of Titanium Oxide/Aluminum Oxide Multilayer Coatings by Reactive Pulsed D.C. Magnetron Sputtering with Enhanced Hardness

Christina Freyman and Yip-Wah Chung

Northwestern University, Evanston, IL

There are two important requirements for wear-protective coatings used at high temperatures under oxidizing conditions. One is their oxidation resistance. Another is their hardness properties at high temperatures. Maximal valence oxides, by definition, satisfy the first requirement. However, most oxides are relatively soft. Our approach is to use oxide nanolayers to improve the hardness. Specifically, titanium dioxide/aluminum oxide multilayers have been deposited by reactive pulsed d.c. magnetron sputtering with no deliberate substrate heating. Apart from the formation of Al2TiO5, titanium oxide and aluminum oxide are immiscible at temperatures up to 1600oC. This helps to stabilize the multilayer architecture. Our studies indicate that such multilayer coatings can be synthesized, with rutile TiO2 and amorphous Al2O3 as the primary constituents. Structure and hardness properties were explored as a function of substrate bias and oxygen partial pressure. With amorphous Al2O3 as primary constituent of the layer, the multilayer retains the high hardness of the rutile TiO2 layer while retaining the fracture toughness of the Al2O3. The hardness of these oxide multilayer coatings is at least twice the rule-of-mixtures values. These results suggest that such oxide multilayers may have promise in high-temperature wear applications.

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P37

Structural characterization of Pt nanocrystals supported on SrTiO3 (001)

S. T. Christensen1, A. Kazimiriov1,2, T.-L. Lee1, D.L. Marasco1, M. J. Bedzyk1,3 ,

M. C. Hersam1

1 Department of Materials Science & Engineering, Northwestern University, Evanston, IL U.S.A;2 CHESS, Cornell University, Ithaca, NY U.S.A.; 3 Materials Science Division, Argonne National Laboratory, Argonne, IL U.S.A.; Fundamental research on the platinum/strontium titanate interface impacts many fields including microelectronics, thin film deposition, and catalysis. For example, Pt/SrTiO3 serves as a model catalyst system for producing hydrogen from water [1]. At submonolayer Pt coverage, we employ a variety of experimental techniques – including atomic force microscopy (AFM) [2], grazing incidence X-ray scattering (GISAXS) [3] and X-ray standing waves (XSW) [4] – to compare the Pt nanoscale morphology on the SrTiO3(001) surface with the internal atomic structure of the Pt relative to the SrTiO3 substrate. GISAXS and AFM measurements indicate the presence of Pt nanoclusters on the order of one nanometer in size. Summation of the Pt Fourier components from XSW measurements reveals face centered cubic crystal packing and (001) epitaxy for Pt on the SrTiO3 substrate. The evolution of the Pt nanocrystal structure as a function of annealing will also be presented. [1] R. G. Carr and G. A. Somorjai, Nature 290, 576 (1981). [2] M. E. Greene, A. N. Chiaramonti, S. T. Christensen, L. X. Cao, M. J. Bedzyk, and M. C. Hersam, Adv.

Mater., 17, 1765 (2005). [3] J. R. Levine, L. B. Cohen, Y.-W. Chung, P. Georgopoulos, J Appl Crystallogr 22,

528 (1989). [4] M. J. Bedzyk, in The Encyclopedic Dictionary of Condensed Matter Physics edited by G. F. Bassani, G. L. Liedl, and P. Wyder, Academic Press (Elsevier), 2005.

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P38

Investigation of NEA Photocathodes for High Average Power Radiation Sources

Matt Virgo1, J.F Moore2, J.W. Lewellen1, S.G. Biedron1

1Argonne National Laboratory, 2MassThink

Free electron based light sources, such as synchrotron rings and free electron lasers, require high quality electron beams to produce high quality photon beams. For short wavelength or high average power radiation sources, photocathode-based electron sources have been successfully used to produce the required beam characteristics. It is necessary that the photocathodes used in these systems be both rugged and efficient. Finding this combination of properties in a material has proven an elusive goal. The aim of this work is to evaluate the cesium-activated gallium nitride photocathode for use in an accelerator. When GaN is coated with a thin layer of cesium, the vacuum level at the surface bends below the conduction band minimum, so that electrons excited to the surface have a high probability of escape. This condition is called negative electron affinity (NEA). In this poster, issues specific to using NEA GaN in an accelerator are addressed. These include approaches for maintaining the correct surface conditions in an imperfect vacuum environment, and the ways in which an NEA cathode behaves under high current loads.

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P39 Kelvin Prove Force Microscopy Of Large Multigrain Epitaxial CuInSe2

Allen J. Hall, A. Rockett

University of Illinois at Urbana-Champaign

In an attempt to better study grain-boundary behavior in copper indium diselenide (CuInSe2), a bicrystal of CuInSe2 was grown on gallium arsenide (GaAs) multigrain wafers using a hybrid sputtering/effusion growth process. Preferred {112} tetragonal facet orientation on these non-standard growth orientations was confirmed. Preliminary results of Kelvin Probe Force Microscopy show no serious electrical barrier at the high-angle boundary between the two major grain orientations. Morphological changes at the boundary may indicate different growth rates as well as possible atom transport during growth across the boundary between the two major grains.

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P40

3D Atom Probe Studies of a

Ni-50 Ti-20 Pt Shape Memory Alloy

Chantal K. Sudbrack1,(2), A. Garg3, J. Hiller2, R. D. Noebe3 and D. N. Seidman2

1Northwestern University, 2Argonne National Laboratory, 3NASA Glenn Research Center

The ability of conventional Ni-Ti shape memory alloys to recover deformation when heated through the martensite-to-austenite transformation and exhibit super-elastic behavior has made them widely used for solid state actuation and sensors. Their low transformation temperature, however, limits them to application below 100 °C and no commercial alloys are available for elevated temperature use. Pt additions substituted for Ni in NiTi alloys are known to increase the transformation temperature but only at fairly high Pt levels with little knowledge of the microstructural stability. Three-dimensional atom-probe allows for precise knowledge of compositional evolution of the fine-scale microstructure, which is key in designing alloys with the highest temperature capability possible. Using three-dimensional atom probe analysis, we correlate changes in transformation temperature (~200-300°C) with the Ti(Ni,Pt) martensite-phase composition as a Ni-50 Ti-20 Pt alloy is annealed at 500°C. Composition measurements suggests that an unknown Pt-rich phase is Ti2(Ni,Pt)3. Further analysis shows that this phase consists of 10 nm thick alternating laths with slight composition deviations. Non-standard specimen preparation methods were developed for atom-probe studies and these methods are presented in further detail.

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P41

Domain Behavior in Thin Film Nanostructures

M Tanasea, A K Petford-Longa, B Kabiusa, K. Buchanana, J Sortb , W-K Kwoka

a Materials Science Division, Argonne National Laboratory

bUniversitat Autonoma de Barcelona Lithographically - patterned magnetic heterostructures have recently become the object of intense research due to their potential application in ultrahigh density magnetic recording media, magnetic random access memories (MRAM), miniature magnetic field sensors and spintronic logic devices. The nanoscale confinement of the magnetization leads to the existence of new magnetization states (flux closure states or vortices) which give rise to new magnetization reversal mechanisms. These together with interlayer exchange-coupling effects have been investigated by magnetic force microscopy, magneto-opticall Kerr effect, micro-Hall effect, scanning electron microscopy and more recently by Lorentz microscopy. We are using Lorentz microscopy to look at the magnetization states and reversal mechanism of 1 μm lithographically-defined exchange-biased dots of composition Cu5nm/Py12nm /IrMn5 nm /Cu2 nm , spaced 4 μm apart, subject to the variable magnetic field of the objective lens. Observations of the chirality of the vortex upon annihilation and subsequent nucleation allow the assessment of the quality of the exchange bias. The exchange field can be determined quantitatively from the vortex motion with the help of micromagnetic simulations.

Thank you for participating!

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