CAREER: Nanoelectronic and NanophotonicCharacterization of Hybrid Hard and Soft Materials

Mark C. Hersam, Northwestern University, DMR-0134706

Figure Caption: (a) Cross-section of the metal-oxide-semiconductor (MOS) capacitor that will be used as test structure to verify the performance of Bridge Enhanced NIM. (b) Atomic force microscopy topography image (top view) of the electron beam lithography patterned MOS test structures. The calculated capacitance values of these structures have been overlaid on the image. As expected, the capacitance scales with the area of the top gold electrode. The box drawn on the image corresponds to the region that is imaged on the next slide.

For geometrical reasons, most nanostructures possess small capacitances on the order of 1 fF.

While nanoscale impedance microscopy (NIM) can probe capacitive charge transport with nanometer scale spatial resolution, spurious fringe capacitance on the order of 1 pF corrupts accurate measurements at this length scale.

Consequently, the effects of the fringe capacitance must be eliminated in order to probe capacitive charge transport in most nanomaterials.

A novel technique – Bridge Enhanced NIM – has been invented to overcome this problem. The metal-oxide-semiconductor test capacitors shown in the figure serve as a proof-of-principle of this technique.

n-type Si

SiO2

AuMOS Capacitor(Cross-section):

C ~ εA/dd ~ 500 nm

Top view:

SiO2 Au

(a)

(b)

CAREER: Nanoelectronic and NanophotonicCharacterization of Hybrid Hard and Soft Materials

Mark C. Hersam, Northwestern University, DMR-0134706

BridgeEnhanced

NIM:

StandardNIM:

1 μm

Topography Current Map Phase Map

1 μm

Figure Caption: (a-c) 6 μm x 6 μm BE-NIM topography (a), current magnitude (b), and current phase (c) images of the MOS test structure sample that was introduced on the previous slide. These images were gathered at 2 kHz and 150 mVRMS oscillation amplitude with a -3 V DC offset applied to the silicon substrate. (d-f) 6 μm x 6 μm topography (d), magnitude (e), and phase (f) images of the same electrode set gathered by Standard NIM under the identical driving conditions. Note that the noise resulting from the fringe capacitance completely corrupts the Standard NIM images.

Major Result: Bridge Enhanced NIM improves the sensitivity of nanoscale capacitive charge transport measurements by 5 orders of magnitude as illustrated in the side-by-side comparison below of Bridge Enhanced NIM and Standard NIM.Significance: Bridge Enhanced NIM will allow frequency dependent and spatially dependent electrical characterization of nanoscale devices and materials including nanoscale organic light emitting diodes and carbon nanotube / polymer nanocomposites.

CAREER: Nanoelectronic and NanophotonicCharacterization of Hybrid Hard and Soft Materials

Mark C. Hersam, Northwestern University, DMR-0134706

Broader Impacts: In collaboration with the NSF funded Nanoscale Science and Engineering Center, Mark Hersam serves as the director of the Research Experience for Undergraduates (REU) program at Northwestern University. During the summer of 2005, this program brought 20 undergraduate students from around the country to Evanston, IL for a 9 week summer research experience. The program achieved excellent diversity with 10 female students and 10 underrepresented minorities.

The final undergraduate research papers will be considered for publication in Nanoscape: The Journal of Undergraduate Research in Nanoscience, which was founded by Mark Hersam in 2004. This journal exposes undergraduate students to the publication process and enables broad dissemination of their research results. Cover of the first issue of Nanoscape