The nanopatterning of Si/SiGe layers by PFOTS (perfluorooctyl trichlorosilane) -aided AFM (atomic force microscopy) lithography is demonstrated. We use self-assembled PFOTS monolayers as a resist for AFM exposure and then transfer patterns in to underlying SiGe layers by a two-step selective wet etching. Linewidths well under 100nm can be achieved with improved uniformity and repeatability compared to AFM lithography without PFOTS. This lithography technique was used to pattern the carrier supply layer in Si/SiGe 2-D hole gases to localize holes for epitaxially passivated quantum dot applications.

Research in synthetic materials with controlled transport properties has been inspired by the exquisite selectivity exhibited by natural transmembrane proteins such as ion channels (for selectively transporting ions like sodium and potassium, etc) and aquaporins (for conducting high fluxes of water and excluding ions). In this poster we focus on the transport behavior of highly ordered mesoporous silica thin films synthesized by evaporation induced silica/surfactant self-assembly (EISA). This process allows us to integrate the nanostructures into electronic and fluidic systems by simple coating or spraying procedures, facilitating the characterization of their transport behaviors. Also, the nanocomposite architecture made by this process gives precisely defined pore size, orientation and surface chemistry, allowing tailoring of the motion of molecules and ions transported across the nanochannels. To approach our final goal of understanding and characterizing the transport behavior of our materials, we designed our experiments into three steps: first, we employed focused ion beam (FIB) lithography to drill a single sub-100-nm pore on a substrate support, providing a platform enabling the characterization of trans-membrane behavior of ions/molecules. Second, we developed two EISA approaches to form cubic thin film silica mesophases spanning the FIB-drilled pore. In one approach, we adapted our aerosol-assisted EISA where fusion of liquid crystalline aerosol droplets creates a thin membrane spanning the substrate pore. In the other approach, we modified our synthetic protocol to form ultra thin (20-nm) spanning films by spin-coating. Films with pore sizes ranging from 2nm to 7nm and surface chemistries including –OH, -COOH and –NH2 terminated pore surfaces were prepared in this fashion and integrated to the FIB-drilled single pore substrate support with uniformity to allow tailoring of the motion of ions and molecules. Third, we designed an electrochemical cell in which the FIB-drilled substrates are integrated to enable the measurements of ion fluxes using standard “patch-clamp” instruments. Experiments are conducted to demonstrate the transport characteristics of our materials by measuring transmembrane ion fluxes when specific molecules such as DNA are applied, a method relevant to low cost DNA sequencing. Also, by chemically or physically blocking all but one or several membrane pores, we are attempting to measure ion and water transport in individual synthetic nanopores and compare results with natural ion and water channels.

The use of DNA to template the assembly of gold nanowires from gold nanoparticles is reported. Double-stranded calf thymus DNA, was deposited on a polystyrene-coated silicon wafer substrate. The substrate was then exposed to an aqueous dispersion of positively charged gold nanoparticles (~ 4 nm diameter), which adsorbed at the negatively charged DNA template. The adsorbed nanoparticles were then enlarged and enjoined by electroless deposition leading to formation of continuous nanowires of 85 nm average diameter. Gold electrodes were then overlaid on individual nanowires using conventional lithographic techniques. Two-terminal current-voltage measurements were employed to characterize the electrical characteristics of single nanowires. The nanowires exhibit resistivity values < 6 × 10-7 Ωm. These and related findings have implications for the design and assembly of next generation electronic devices.

Thin film contraction under external mechanical stress can be used to miniaturize size and increase density of patterned features on top. Nonlinear Finite Element Analysis is used to provide guidance on this contraction process. It was found that the substrate contraction causes stress accumulation along interfaces between protruded features and substrate. These stress accumulation complexes the control of profile changes on patterned features and suggest a design of patterned features arranged beyond a critical distance to avoid cross-interference.

Germanium nanoparticle nucleation was studied in organized arrays on HfO2 using a SiO2 thin film mask with ~20-24 nm pores and a 6×1010 cm-2 pore density. Poly(styrene-b-methyl methacrylate) diblock copolymer was employed to pattern the SiO2 film. Hot wire chemical vapor deposition produced Ge nanoparticles using 4-19 monolayer Ge exposures. By seeding adatoms on HfO2 at room temperature before growth and varying growth temperatures between 725-800 K, nanoparticle size was demonstrated to be limited by Ge etching of SiO2 pore walls.