N. Badi

Surface composition of BN, CN, and BCN thin films

Boron nitride (BN), carbon nitride (CN), and boron carbon nitride (BCN) thin films were deposited on sapphire and silicon using ion beam and electron cyclotron resonance plasma assisted physical vapor deposition. In situ Auger electron spectroscopy was used to investigate the effect of different growth parameters and postgrowth processing on the thin film surface composition. The bulk composition was determined by electron energy loss spectroscopy and electron microprobe analysis. Both BN and CN films show thermal stability up to 900 and 700 °C, respectively. Low growth temperatures favor nitrogen incorporation in CN films and the optimum temperature for quasistoichiometric BN is between 450 and 600 °C, depending on the nitrogen sources.

Low-cost carbon-silicon nanocomposite anodes for lithium ion batteries

The specific energy of the existing lithium ion battery cells is limited because intercalation electrodes made of activated carbon (AC) materials have limited lithium ion storage capacities. Carbon nanotubes, graphene, and carbon nanofibers are the most sought alternatives to replace AC materials but their synthesis cost makes them highly prohibitive. Silicon has recently emerged as a strong candidate to replace existing graphite anodes due to its inherently large specific capacity and low working potential. However, pure silicon electrodes have shown poor mechanical integrity due to the dramatic expansion of the material during battery operation. This results in high irreversible capacity and short cycle life. We report on the synthesis and use of carbon and hybrid carbon-silicon nanostructures made by a simplified thermo-mechanical milling process to produce low-cost high-energy lithium ion battery anodes. Our work is based on an abundant, cost-effective, and easy-to-launch source of carbon soot having amorphous nature in combination with scrap silicon with crystalline nature. The carbon soot is transformed in situ into graphene and graphitic carbon during mechanical milling leading to superior elastic properties. Micro-Raman mapping shows a well-dispersed microstructure for both carbon and silicon. The fabricated composites are used for battery anodes, and the results are compared with commercial anodes from MTI Corporation. The anodes are integrated in batteries and tested; the results are compared to those seen in commercial batteries. For quick laboratory assessment, all electrochemical cells were fabricated under available environment conditions and they were tested at room temperature. Initial electrochemical analysis results on specific capacity, efficiency, and cyclability in comparison to currently available AC counterpart are promising to advance cost-effective commercial lithium ion battery technology. The electrochemical performance observed for carbon soot material is very interesting given the fact that its production cost is away cheaper than activated carbon. The cost of activated carbon is about

Laser-induced modification of carbon nitride thin films

15/kg whereas the cost to manufacture carbon soot as a by-product from large-scale milling of abundant graphite is about

FIELD EMISSION FROM AS-GROWN AND SURFACE MODIFIED BN AND CN THIN FILMS

1/kg. Additionally, here, we propose a method that is environmentally friendly with strong potential for industrialization.

Metal–insulator–semiconductor Schottky barrier structures fabricated using interfacial BN layers grown on GaN and SiC for optoelectronic device applications

The results of experiments on local pulsed ultraviolet laser annealing of carbon nitride (CNx) thin films are reported. It is shown that laser radiation can be used for efficient graphitization of CNx thin films. The degree of local transformation of diamond-like sp3 bonded CNx compound films into graphite-like ones is dependent upon the radiation energy density. It is also shown that the electron field emission properties of the thin films can be modified by the laser treatment.

Photoenhanced reactive ion etching of III–V nitrides in BCl3/Cl2/Ar/N2 plasmas

We have investigated the electron field emission characteristics of BN and CN on highly conductive silicon thin films deposited by End-Hall ion source and electron cyclotron resonance plasma source-assisted physical vapor deposition. The thermal processing and surface laser modification effects on the field emission properties were investigated. Current density-field emission characteristics Iη(E) were tested in a high vacuum environment. Mg-doped BN thin films on silicon exhibited a turn-on field as low as 25 V/μm and a current density higher than 1 A/cm2. The deposition of a thin BN layer on copper lithium (CuLi) metallic substrate yields surfaces with a 75 V/μm onset field and a current density 1000 times higher than that obtained from uncoated surfaces. Under high vacuum laser annealing BN coated CuLi showed no enhancement but more stable emission characteristics. Our results show also that pulsed ultraviolet laser irradiation of CN films in vacuum results in an increase of the field emission current ...

Enhanced free carrier generation in boron nitride films by pulsed laser radiation

Metal–insulator–semiconductor Schottky barrier structures on GaN and 6H-SiC using highly stable interfacial BN layers have been investigated. As reported earlier, such structures fabricated with Ti contacts are capable of withstanding up to 350 and 600 °C when based on 6H-SiC and GaN, respectively. In this work we fabricated diode structures using interfacial BN layers and optically transparent Au contacts. Visible–blind photosensitive structures on GaN and 6H-SiC and prebreakdown light-emitting diode (LED) structures on 6H-SiC have been characterized. The radiant and spectral sensitivities of the photosensitive structures were measured in the range of 200–400 nm. The potential barrier heights determined from photoresponse measurements were 2.7 and 2.88 eV for GaN- and SiC-based samples, respectively. The spectrum of 6H-SiC and p-GaN-based prebreakdown LED structures measured through transparent Au electrodes extended to the ultraviolet region. The optical emission power of the 6H-SiC-based LED structures...

Positron annihilation studies in GaxIn1−xAs

Gallium nitride (GaN) and boron nitride (BN) are known as superior semiconductor materials for UV optoelectronic and high power, high temperature applications. As a result of their high molecular bond strength these materials are extremely difficult to etch. In this article, reactive ion etching (RIE) tests were performed on GaN and BN thin films using respectively BCl3/Cl2/Ar and Cl2/Ar chemistries. In order to improve the etch rates at lower rf powers and thus reduce ion bombardment-induced damage, a photoassisted RIE process was investigated. The same plasma chemistries in combination with a xenon arc lamp were utilized. In an attempt to minimize surface nitrogen depletion, N2 was used instead of Ar as dilution gas. Photoenhancement was observed for both GaN and BN etching. As expected, the etch rate increased with rf power for both unassisted and photoassisted etching conditions. The combination of illumination and N2 led to a nitrogen-rich surface for GaN. In the case of BN, photoassisted etching in ...

Reactive Ion Etching of Boron Nitride and Gallium Nitride Materials in C1 2 /Ar and BCl 3 /Cl 2 /Ar Chemistries

A transient laser photoconductivity (PC) technique is applied to the investigation of non-linear multi-photon excitation of mixed cBN/hBN films. A selection of sub-micron thickness films on sapphire substrates with different stoichiometries were synthesized using ion-assisted and ECR-plasma CVD techniques. Efficient free carrier generation in these thin films is demonstrated under nanosecond pulses excitation from VIS/UV harmonics of a Nd:YAG laser. The effect is shown to be influenced largely by the nitrogen deficiency and the carbon impurities present in the BN thin films. Both parameters are responsible for the existence of donor and acceptor levels in the material. A laser generated 400 mV electrical signal was realized when using 200 nm boron-rich hBN films. A method for further enhancing the carrier generation efficiency via post-growth X-ray irradiation of the films is demonstrated.

Pressure dependence of band gaps in GaAs, GaP, InP, and InAs

Abstract The effect of alloying on the electron-positron momentum densities, ϱ(p), in GaxIn1−xAs is reported. Our computations of ϱ(p) are based on the independent particle approximation (IPM) coupled with the empirical pseudopotential method (EPM). To make allowance for the chemical disorder, the virtual crystal approximation is used, including a correction to the alloy potential. An illustrative result of the electron-positron momentum densities show a deviation from linearity at low momentum which indicates the alloying effect (bowing effect).