2013 01 Electronics Ground

Building electronics from the ground up14 January 2013, by Steven Powell

Nanodots of iron oxide were laid out in a highly orderedpattern without the use of templates. The averagediameter of the particles was 25 nanometers, withregular spacing of 45 nm.

(Phys.org)There's hardly a moment in modern lifethat doesn't involve electronic devices, whetherthey're guiding you to a destination by GPS ordeciding which incoming messages merit a beep,ring or vibration. But our expectation that the nextshopping season will inevitably offer an upgrade tomore-powerful gadgets largely depends on size namely, the ability of the industry to shrinktransistors so that more can fit on ever-tinier chipsurfaces.

Engineers have been up to the task of electronicsminiaturization for decades now, and the principlethat the computer industry will be able to do it on aregular schedule as codified in Moore's Law won't come into doubt any time soon, thanks toresearchers like the University of South Carolina'sChuanbing Tang.

Tang is a leader in constructing minisculestructures from the bottom up, rather than the topdown. Currently, modern electronics are primarilyfabricated by the latter method: the smooth surfaceof a starting material say, a wafer of silicon isetched through micro- or nanolithography to

establish a pattern on it.

The top-down method might involve a prefabricatedtemplate, such as a photomask, to establish thepattern. But the approach is becoming more andmore challenging, because reducing the size of thefeatures on the requisite templates is gettingextremely expensive as engineers work their wayfurther down the nanoscale. "Going from 500 tosub-30 nanometers is cost prohibitive for large-scale production," said Tang, an assistant professorin the department of chemistry and biochemistry inUSC's College of Arts and Sciences.

Chuanbing Tang (right) and Christopher Hardy usedatomic force microscopy to characterize the nanoscalepatterns they built from the bottom up.

As a chemist, Tang uses a bottom-up approach: heworks with the individual molecules that go onto asurface, coaxing them to self-arrange into thepatterns needed. One established method of doingthis involves block copolymers, in which a polymerchain is made up of two or more sections ofdifferent polymerized monomers.

If the different block sections are properly designed,the blocks will self-aggregate when placed on asurface, and the aggregation can be harnessed tocreate desirable patterns on the nanoscale withoutthe need for any templates. Di-block copolymers ofpoly(ethylene oxide) and polystyrene, for example,

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have been used to construct highly ordered arraysof perpendicular cylinders of nanoscale materials.Solvent evaporation, or annealing, of thesepolymers on surfaces exerts an external directionalfield that can enhance the patterning process andcreate nearly defect-free arrays.

Tang's laboratory just published a paper for thespecial "Emerging Investigators 2013" issue of thejournal Chemical Communications that takes thismethod to a new level. Working together withgraduate student Christopher Hardy, Tang led ateam that fabricated nanoparticles of pure,crystalline iron oxide with controlled size andspacing on silicon wafers by covalentlyincorporating a ferrocene moiety into a tri-blockcopolymer.

Incorporating metals into nanoscale designs iscrucial for fabricating electronic devices, and Tang'smethod is a step forward for the field. Becauseferrocene is covalently bonded to the blockcopolymer, there is no need for a complexationstep to add a metal-containing compound to thesurface a burdensome requirement of mostprevious methods. Moreover, their technique is astep beyond related polymer systems that containcovalent ferrocenylsilane linkages, in whichremoval of the organic components leaves behindsilicon oxide as an impurity in the metal oxide.

The technique is a promising addition to theavailable tools for addressing the chronic need todecrease the size of electronic components. "Theindustry won't replace top-down methods," Tangsaid, "but they plan to use bottom-up together withthe existing top-down methods soon."

There's versatility in the technique as well. "Herewe use a ferrocene-containing polymer, which weconvert into the inorganic iron oxide. But if wereplace the ferrocene in the polymer with carbonprecursor, we could make a perpendicular carbonnanorod, which would have a lot of potential uses,"Tang said. "Or we can incorporate a semi-conducting polymer, like polythiophene, whichwould be very useful in solar cell applications."

More information:dx.doi.org/10.1039/C2CC36756D

Provided by University of South Carolina

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APA citation: Building electronics from the ground up (2013, January 14) retrieved 1 May 2015 from http://phys.org/news/2013-01-electronics-ground.html

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