Young Gyu Rho

Dictation of the shape of mesoscale semiconductor nanoparticle assemblies by plasmid DNA

We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455‐basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self‐assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates.

Formation of rare‐earth oxide doped silicon by spark processing

In this work, we report a method for the incorporation of rare‐earth oxides onto silicon surfaces. This process uses a high‐energy dc spark to convert salts of rare‐earth ions such as europium and erbium to the corresponding oxide phase(s) with concomitant formation of a porous layer. Scanning electron micrographs of the silicon substrate show an irregular, pitted surface morphology for those areas exposed to spark processing. Photoluminescence, infrared spectroscopy, and electron microscopy of the spark‐processed regions of the Si substrate are clearly consistent with the formation of the desired luminescent oxide phase.

Fabrication of a Porous Silicon Diode Possessing Distinct Red and Orange Electroluminescent Regions

Porous silicon light emitting diodes with distinct red and orange electroluminescent (EL) regions have been fabricated. Red luminescence is obtained by sonication of the as-formed orange-emitting porous silicon layers. While the red luminescence in the as-formed substrate is unstable in air or under irradiation, deposition of a thin layer of poly(9-vinyl cabazole) (PVK) by spin-coating effectively circumvents the oxidation process. The overall EL efficiency of the red and orange regions can be improved by depositing a thin film of a 1 :1 (w/w) mixture of PVK and PBD [2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1, 3, 4-oxadiazole] on the porous Si surface.

Effect of a Ge Barrier on the Microstructure of BaTiO3 Deposited on Silicon by Pulsed Laser Ablation

BaTiO 3 (BT) thin films deposited using pulsed laser ablation on substrates of (100) Si and (100) Si with 0.3 μm Ge were examined. For one set of samples, approximately 2000 A of BT was deposited at 70°C at O 2 pressures of 0, 1.0 and 10.0 mT. In a second set, O 2 pressures of 0 and 1.0 mT were used during deposition of 200 A of BT at 450°C followed by a 5 minute anneal and deposition of an additional 2000 A at 750°C. This gave a total sample matrix of 10 samples. Cross-sectional TEM revealed that an interfacial layer formed in the BT on Si samples but not in the BT on Ge samples. HREM analysis of the interfaces showed that the interfacial layer was amorphous. On Ge, the BT films were found to have large areas of epitactic growth along the interface. This was confirmed by diffraction tilt angle experiments which showed a strong preferred orientation of BT on Ge. No preferred orientation was found for BT on Si. Statistical grain size analysis of the films using multiple regression showed that the film microstructures were affected most strongly by the substrate type (Ge or Si) followed by the deposition temperature of the substrate. Only a weak effect of O 2 pressure was observed.

Nanostructured DNA templates.

We have developed methods for nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assemblage of individual semiconductor nanoparticles. Use of the circular plasmids pUCLeu4 and phi chi 174 when anchored to a suitably derivatized substrate yields arrays of semiconductor nanoparticles matching the shapes of the biopolymer stabilizer. The viability of the methodology was confirmed using high-resolution transmission electron microscopy and selected-area electron diffraction.

Gas‐Phase Desorption of Diphenylamine from Porous Silicon

In this work, the desorption of diphenylamine from different five types of porous Si substrates under low vacuum is examined. These substrates include (i) freshly prepared porous Si; (ii) ambient‐oxidized porous Si, and rapidly oxidized porous Si samples processed at the maximum temperatures of (iii) 400°C, (iv) 600°C, and (v) 1180°C. A typical experiment involves the measurement of the rate of desorption as a function of surface morphology, composition, and temperature. These results suggest that desorption from the porous matrix is limited by strong capillary forces and can be overcome by external factors such as temperature. The chemical composition of the porous Si surface also plays a role in desorption and can increase or lower desorption rates. The clearest difference in diphenylamine desorption behavior is detected between the freshly prepared porous Si surface and porous Si samples rapid thermally oxidized at 600 and 1180°C.