Shyankay Jou

Electron emission characterization of diamond thin films grown from a solid carbon source

Diamond films of various morphologies and compositions have been deposited on silicon substrates by a plasma-enhanced chemical transport (PECT) process from a solid carbon source. Electron emission efficiency of these diamond films is related to their morphology and composition. The electric field required to excite emission in a boron-doped polycrystalline diamond film ranged between 20 to 50 MV m−1. In an undoped conducting nanocrystalline diamond composite film, the field was as low as 5–11 MV m−1. The cold field electron emission of these films is confirmed from the Fowler-Nordhelm plots of the data. Enhancement of electron emission by band-bending and by the nanocrystalline microstructure are discussed. New diamond emitters made of nanocrystalline boron-doped diamond composite are proposed.

Scratch properties of nickel thin films using atomic force microscopy

Experiments using atomic force microscopy (AFM) as a machining tool for scratching patterns on nickel thin films have been conducted with an emphasis on establishing the material scratchability or more general, the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and scratch direction, on the size of the scratched geometry were investigated. The primary factors that measure the scratchability were then assessed. The scratchability of Ni as compared to that of Si was specifically evaluated and discussed. A stress-hardness analysis was also performed to further validate the experimental and correlation results. All results indicate that the Ni thin film possesses excellent scratchability and one order of magnitude higher than that of Si. Based on the correlation formula developed, Ni should be able to be precisely scratched by AFM tip with the required dimension and nanoscale accuracy and precision.

Development of latent fingerprint by ZnO deposition

Vacuum metal deposition (VMD) utilizing sequential Au and Zn depositions has been an effective technique to develop latent fingerprint on plastic surfaces. A simplified vacuum deposition process was conducted to develop fingerprint in this study. While pure ZnO was thermally evaporated in a vacuum system, ZnO could condense on polyethylene terephthalate (PET) surface. Direct deposition of ZnO, without applying Au seeding, yielded normal development of latent fingerprint. The development of aged fingerprint by ZnO deposition was more effective than that by Au/Zn VMD.

Diamond coatings from a solid carbon source

Abstract A plasma-enhanced chemical transport process was developed to deposit diamond films from a solid carbon source in a subatmospheric pressure hydrogen environment (106–400 mbar (80–300 Torr)). The process uses inexpensive simple equipment. The diamond films were examined by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. High quality diamond films were grown at 1 ωm h−1 deposition rate in static and dynamic flow systems. The effect of various surface coatings on diamond nucleation on a silicon substrate was investigated. The nucleation density on bare silicon was 4×106 cm−2. A high nucleation density up to 109 cm−2 was found on a fullerence-enriched carbon-coated silicon substrate. Diamond film morphology variations with deposition conditions were studied.

Origin of the anomalous temperature evolution of photoluminescence peak energy in degenerate InN nanocolumns

Photoluminescence (PL) behaviour in InN nanocolumns reveal decreasing, increasing and near invariant peak energies (E(PL)) as a function of temperature. Samples, having E(PL)~0.730 eV at 20 K, showed temperature invariance of E(PL). Samples possessing E(PL) on the lower and higher energy side of 0.730 eV demonstrate a normal redshift and anomalous blueshift, respectively, with increasing temperature. This temperature evolution can be effectively explained on the basis of a competition between a conventional red shift from lattice dilation, dominant for low carrier density sample, on one hand, and a blue shift of the electron and hole quasi Fermi-level separation, dominant for high carrier density samples, on the other.

Photoemission from diamond and fullerene films for advanced accelerator applications

The photoemission properties of thin diamond and fullerene films were investigated for advanced accelerator applications, using subpicosecond laser pulses at three different wavelengths (650, 325, and 217 nm). The quantum efficiency (QE) obtained at 217 nm with a boron-doped, p-type, (111) polycrystalline diamond film (2.6/spl middot/10/sup -4/) was only five times smaller than the QE obtained with a mirror polished copper sample (1.3/spl middot/10/sup -3/) but more than nine times larger than the QE obtained with a pure diamond film or with natural diamond monocrystals. Similar results were obtained for the two-photon electron yields at 325 mm. The electron yields obtained with pure fullerene films were small and comparable to the ones observed with the pure diamond samples. With 650 mn pulses, the damage threshold of the [110] Type IIa natural diamond monocrystal (9.38/spl middot/10/sup 4/ /spl mu/J cm/sup -2/), defined here as the fluence leading to an onset of ion emission, was 25 times larger than the damage threshold for a copper sample (3.75/spl middot/10/sup 3/ /spl mu/J cm/sup -2/). The damage threshold of the boron-doped sample at the same wavelength was two times larger than that of copper. Damage thresholds with 325 nm pulses were lower, and with 217 mn pulses ion emission was observed at all fluences probably attributed to ablation of surface hydrocarbon contaminants. Results show that high-quality high-boron concentration diamond films could be a good candidate for high-RF electron guns.

Complementary resistive switching of annealed Ti/Cu2O/Ti stacks

Ti/Cu2O/Ti stacks with 25-nm-thick Cu2O layers were produced by sputter deposition and lift-off processes utilizing three photolithographic masks. Subsequent annealing of the Ti/Cu2O/Ti stacks at 250 °C in a vacuum induced interfacial reactions between the Ti and Cu2O layers and converted the Ti/Cu2O/Ti stacks to a Ti/TiO x /Cu/TiO x /Ti structure. This pentalayered stack resembled a pair of antiserial Ti/TiO x /Cu and Cu/TiO x /Ti resistive switching devices and, therefore, demonstrated complementary resistive switching behaviors.

Indium Nitride Thin Film Growth Using Chemical Beam Epitaxy

We report on the successful growth of high-quality indium nitride (InN) thin films on the GaN(001)/SA(001) substrate, via the technique of chemical beam epitaxy (CBE) using the highly volatile source reagent HN3. A detailed characterization of the as-grown films have also been carried out using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), selected-area electron diffractometry (SAED), X-ray diffractometry (XRD) and rocking curve (XRC). HR-TEM micro graphs and SAED patterns show the high crystallinity and nearly epitaxial growth of InN. In addition, using the GaN(001)/SA(001) substrate without any buffer layer, the deposited InN films exhibit nearly single (001) out-plane orientation. The effects of deposition temperature and rate on the surface morphology and out-plane orientation have been observed and discussed.

Formation of Novel Silicon Nitride with Face-Centered Cubic Crystal Structure in a TaN/Ta/Si(100) Thin Film System

We discovered a new silicon nitride with cubic symmetry formed in the silicon at the Ta/Si interface of the TaN/Ta/Si(100) thin film system when the silicon wafer was annealed at 500 or 600°C. The cubic silicon nitride grew into the silicon crystal in the shape of an inverse pyramid after the annealing process. The boundary planes of the inverse pyramid were the {111} planes of the silicon crystal. The orientation relationship between the silicon nitride and silicon crystal is cubic to cubic. The lattice constant of the new silicon nitride is a=0.5548 nm and is about 2.2% larger than that of the silicon crystal.