Joseph E. Van Nostrand

Surface damage produced by 20 keV Ga bombardment of Ge(001)

Abstract Surface damage on Ge(100) due to single 20 keV Ga + ion impacts was investigated by in situ scanning tunneling microscopy (STM). Two types of damage structures were observed: the first appears as small disruptions of the surface on the scale of 1 × 1 nm 2 , while the second consists of large craters on the scale of 85 nm 2 . The small damage features are produced by a large fraction of the ions, but only ∼ 10 −3 ions produce craters.

Surface morphology of GaAs(001) grown by solid- and gas-source molecular beam epitaxy

Abstract Scanning tunneling microscopy is used to characterize the surface of homoepitaxial GaAs(001) films deposited on GaAs(001) substrates miscut 0.2° towards [110]. Films are grown using solid-source (A 4 ) and gas-source (AsH 3 ) arsenic at temperatures ranging from 500 to 650°C. The surface morphology of GaAs(001) is found to be extremely sensitive to growth temperature - for both solid- and gas-source molecular beam epitaxially grown films. Further, the presence of arsenic hydrides (hydrogen) reduces the surface roughness in the multilayer growth mode.

Improved Si3N4/Si/GaAs metal-insulator-semiconductor interfaces by in situ anneal of the as-deposited Si

Si interlayers in GaAs metal‐insulator‐semiconductor structures are essential for interfaces with device quality. The incompatible growth temperature of Si on GaAs, however, presents a dilemma between the crystallinity of Si and the stoichiometry of GaAs. We circumvented this dilemma by a new approach: a high‐temperature in situ anneal following the low‐temperature Si deposition. The idea is that the GaAs surface covered with a few monolayers of Si can stand a much higher temperature, and the crystal quality of the Si is resumed during the high‐temperature anneal. The surface morphology of the as‐deposited and the in situ annealed Si was examined with a scanning tunneling microscope, the results of which confirmed high crystal quality of the Si layer and full coverage of the GaAs surface. With in situ anneal, interface trap densities of high 1010 eV−1 cm−2 were routinely obtained in Si3N4/Si/GaAs metal‐insulator‐semiconductor capacitors, as determined with conductance measurements.

Surface roughness and pattern formation during homoepitaxial growth of Ge(001) at low temperatures

The evolution of surface roughness during growth of Ge(001) by molecular beam epitaxy at 155°C is characterized using in situ scanning tunneling microscopy. The range of film thickness studied spans more than three orders of magnitude, 0.1–200 nm. Beginning at a film thickness near 100 nm, a periodic pattern of growth mounds is observed. The average in‐plane separation of growth features d evolves continuously with film thickness t, following a power law d=t0.42. The vertical roughness of the film does not follow a single power‐law behavior over this range of film thickness.

Electrical conductivity of cationized ferritin decorated gold nanoshells

We report on a novel method of controlling the resistance of nanodimensional, gold-coated SiO2 nanoparticles by utilizing biomolecules chemisorbed to the nanoshell surface. Local electronic transport properties of gold-coated nanoshells were measured using scanning conductance microscopy. These results were compared to transport properties of identical gold nanoshells biofunctionalized with cationized ferritin protein both with and without an iron oxide core (apoferritin). Measured resistances were on the order of mega-ohms. White light irradiation effects on transport properties were also explored. The results suggest that the light energy influences the nanoshells’ conductivity. A mechanism for assembly of gold nanoshells with cationized ferritin or cationized apoferritin is proposed to explain the resistivity dependence on irradiation.