Raj Solanki

Chemical vapor deposition of graphene films

Graphene films were grown on nickel films and foils using chemical vapor deposition. To date, similar growth has been reported at around 1000 degrees C using methane or ethylene as source gases. However, by using acetylene, we have achieved growth of graphene films between 650 and 700 degrees C. The electrical and optical properties, including high resolution transmission electron microscopy of these films, suggest that this technique is both viable and scalable for potential large area optoelectronic applications.

Photodeposition of aluminum oxide and aluminum thin films

Uniform films of Al2O3 have been photodeposited using an excimer laser operating at 248 nm (KrF) or at 193 nm (ArF) and trimethylaluminum and N2O as the reactants. Deposition rates were typically 2000 A/min and the physical, chemical, and electrical properties of the photodeposited Al2O3 films are comparable to films deposited using conventional techniques. Properties of photodeposited aluminum films are also presented.

Low‐temperature refractory metal film deposition

We have deposited uniform films of Mo, W, and Cr over large areas (>5 cm2) using UV laser photodissociation of their respective hexacarbonyls. The depositions were made at room temperature over pyrex and quartz plates, as well as silicon wafers. We have examined the resistivity, reflectivity, stress, and step coverage of these films.

Hollow cathode metal ion lasers

A new class of metal ion lasers with significant CW output power in the UV (220-320 nm) and near IR (800-2000 nm) spectral regions is described. In a hollow cathode discharge the upper laser levels are excited via charge transfer collisions between ground state buffer gas ions and ground state metal atoms. At the present stage of development, hollow cathode metal ion lasers are shown to be comparable in UV output power to rare-gas ion lasers but with lower threshold currents by a factor of more than twenty. Visible output powers are lower than rare-gas ion lasers. In the text we present device progress to date, measurements of important plasma parameters, and an outline of potential applications of hollow cathode metal ion lasers.

Remote plasma assisted growth of graphene films

Single and multiple layers of graphene films were grown on (111) oriented single crystals of nickel and polycrystalline nickel films using remote plasma assisted chemical vapor deposition. Remote plasma was employed to eliminate the effect of the plasma electrical field on the orientation of the grown graphene films, as well as to reduce the growth temperature compared to conventional chemical vapor deposition. The electrical and optical properties, including high resolution transmission electron microscopy of these films, suggest that this approach is both versatile and scalable for potential large area optoelectronic applications.

Laser induced deposition of zinc oxide

We have used an excimer laser to photodeposit uniform (±5%) films of zinc oxide from dimethylzinc and nitrogen dioxide. Deposition rates of 3000 A/min over 2 cm×5 cm areas were obtained. We have measured the stress, refractive index, etch rate, adhesion, pinhole density, and the stoichiometry of these photodeposited films.

A simple and scalable route to wafer-size patterned graphene

Producing large-scale graphene films with controllable patterns is an essential component of graphene-based nanodevice fabrication. Current methods of graphene pattern preparation involve either high cost, low throughput patterning processes or sophisticated instruments, hindering their large-scale fabrication and practical applications. We report a simple, effective, and reproducible approach for patterning graphene films with controllable feature sizes and shapes. The patterns were generated using a versatile photocoupling chemistry. Features from micrometres to centimetres were fabricated using a conventional photolithography process. This method is simple, general, and applicable to a wide range of substrates including silicon wafers, glass slides, and metal films.

Laser Photolytic Deposition of Thin Films

An excimer laser is used to photochemically deposit thin films of silicon dioxide, silicon nitride, aluminum oxide, and zinc oxide at low temperatures (100–350deg;C). Deposition rates in excess of 3000 A/min and conformal coverage over vertical walled steps were demonstrated. The films exhibit low defect density and high breakdown voltage and have been characterized using IR spectrophotometry, AES, and C-V analysis. Device compatibility has been studied by using photodeposited films as interlayer dielectrics, diffusion masks, and passivation layers in production CMOS devices. Additionally, we have deposited metallic films of Al, Mo, W, and Cr over large (>5 cm 2 ) areas using UV photodissociation of trimethylaluminum and the refractory metal hexacarbonyls. Both shiny metallic films as well as black particulate films were obtained depending on the deposition geometry. The black films are shown to grow in columnar grains. The depositions were made at room temperature over pyrex and quartz plates as well as silicon wafers. We have examined the resistivity, adhesion, stress and step coverage of these films. The films exhibited resistivities at most ∼20 times that of the bulk materials and tensile stress no higher than 7 × 10 9 dynes/cm 2

Nanoparticle-Enhanced Sensitivity of a Nanogap-Interdigitated Electrode Array Impedimetric Biosensor

Interdigitated electrode (IDE) arrays with nanometer-scale gaps have been utilized to enhance the sensitivity of affinity-based detection. The geometry of nanogap IDEs was first optimized on the basis of simulations of the electric field and current density. It was determined that the gap (G) between the electrodes was the most important geometric parameter in determining the distribution and strength of the electric field and the current density compared to the width (W) and height (H) of the IDEs. Several devices were materialized and analyzed for their sensitivity to the electrochemical environment using faradic electrochemical impedance spectroscopy (EIS) as the detection technique. Nanogap optimized IDEs were then employed as biosensors for the label-free, affinity-based detection of antitissue transglutaminase antibodies (αtTG-Abs), a biomarker for the detection of autoimmune disorder celiac sprue, triggered by ingesting gluten. The label-free biosensor assay was found to be less sensitive compared to on-chip ELISA. Gold nanoparticles (GNPs) were then employed to improve the sensitivity of the nanogap IDE-based biosensor. With GNPs, the transducer sensitivity increased by 350% over that of label-free detection. The suitability of nanogap IDEs as biosensor transducers for EIS in label-free and GNP-labeled formats was established. The immunobiosensor assay detection sensitivity with the GNPs was found comparable to ELISA.

Multiwatt operation of Cu II and Ag II hollow cathode lasers

We report multiwatt pulsed (120 μs pulsewidth, 40Hz) laser operation of silver and copper hollow cathode lasers. Peak output powers of 65 mW at 224 nm, 500 mW at 248 nm, 1.3 W at 318.1 nm, and 2.3 W at 478.8 nm have been achieved. Measurements of small-signal gains of selected laser transitions and new laser lines in Cu, Ag, Kr, and Ar are presented.