George Peterson

Semiconducting boron carbides with better charge extraction through the addition of pyridine moieties

The plasma-enhanced chemical vapor (PECVD) co-deposition of pyridine and 1,2 dicarbadodecaborane, 1,2-B10C2H12 (orthocarborane) results in semiconducting boron carbide composite films with a significantly better charge extraction than plasma-enhanced chemical vapor deposited semiconducting boron carbide synthesized from orthocarborane alone. The PECVD pyridine/orthocarborane based semiconducting boron carbide composites, with pyridine/orthocarborane ratios ~3:1 or 9:1 exhibit indirect band gaps of 1.8 eV or 1.6 eV, respectively. These energies are less than the corresponding exciton energies of 2.0 eV–2.1 eV. The capacitance/voltage and current/voltage measurements indicate the hole carrier lifetimes for PECVD pyridine/orthocarborane based semiconducting boron carbide composites (3:1) films of ~350 µs compared to values of ≤35 µs for the PECVD semiconducting boron carbide films fabricated without pyridine. The hole carrier lifetime values are significantly longer than the initial exciton decay times in the region of ~0.05 ns and 0.27 ns for PECVD semiconducting boron carbide films with and without pyridine, respectively, as suggested by the time-resolved photoluminescence. These data indicate enhanced electron–hole separation and charge carrier lifetimes in PECVD pyridine/orthocarborane based semiconducting boron carbide and are consistent with the results of zero bias neutron voltaic measurements indicating significantly enhanced charge collection efficiency.

Increased drift carrier lifetime in semiconducting boron carbides deposited by plasma enhanced chemical vapor deposition from carboranes and benzene

Plasma-enhanced chemical vapor (PECVD) codeposition of benzene and 1,2-dicarbadodecaborane, 1,2-B10C2H12 (orthocarborane) and benzene, 1,7 dicarbadodecaborane, and 1,7-B10C2H12 (metacarborane) results in semiconducting boron carbide composite films with significantly longer drift carrier lifetimes than plasma-enhanced chemical vapor deposited semiconducting boron carbide synthesized from orthocarborane or metacarborane alone. Capacitance versus voltage C ( V ) and current versus voltage I ( V ) measurements indicate the hole carrier lifetimes for PECVD benzene/orthocarborane based semiconducting boron carbide composites increase to 2.5 ms from values of ≤35 μs for the PECVD semiconducting boron carbide films fabricated without benzene. For PECVD benzene/metacarborane based semiconducting boron carbide composites, there is an increase in the hole carrier lifetime to roughly 300 ns from values of 50 ns for those films fabricated without benzene.

Morphology Dependent Photocatalytic Properties of ZnO Nanostructures Prepared by a Carbon-Sphere Template Method

Organic contaminants are a typical byproduct of industrial wastewater, and nanostructured ZnO photocatalysts have been investigated as an environmentally benign process to remove the contaminants through a degradation process. The degradation efficiency under UV irradiation can be markedly enhanced when using a catalyst with a nanostructure. The larger specific area of a nanostructure has been found to significantly enhance degradation efficiency. The complex synthesis process, expensive material costs, and generation of environmental contaminants during the synthesis process currently hinder practical application of photocatalysts. This research provides a template for a photocatalyst that is non-toxic, producing mesoporous ZnO hollow spheres and nanorods through an environmentally friendly carbon-sphere template utilizing a hydrothermal process. This research demonstrates that controlling the precursor concentration (zinc acetate) allows for the manipulation of the morphology and specific area of the ZnO nanostructures. A zinc acetate concentration of 0.171 mol/L produced uniform ZnO mesoporous hollow spheres with diameters of approximately 180 nm. Increasing the zinc acetate concentration resulted in an increase in the number of nanorods present. In contrast to nanorods, mesoporous ZnO hollow spheres have a higher specific area and higher concentration of pores in the 2-50 nm range, which result in better photocatalytic activity. This research reports the complete degradation of rhodium boride (RhB) within 50 min by means of mesoporous ZnO hollow spheres and nanorods with a degradation rate of 0.0978 min-1.

Modeling Changes in Measured Conductance of Thin Boron Carbide Semiconducting Films Under Irradiation

Semiconducting, p-type, amorphous partially dehydrogenated boron carbide films (a-B10C2+x:Hy) were deposited utilizing plasma enhanced chemical vapor deposition (PECVD) onto n-type silicon thus creating a heterojunction diode. A model was developed for the conductance of the device as a function of perturbation frequency (f) that incorporates changes of the electrical properties for both the a-B10C2+x:Hy film and the silicon substrate when irradiated. The virgin model has 3 independent variables (R1, C1, R3), and 1 dependent variable (f). Samples were then irradiated with 200 keV He+ ions, and the conductance model was matched to the measured data. It was found that initial irradiation (0.1 displacements per atom (dpa) equivalent) resulted in a decrease in the parallel junction resistance parameter from 6032 Ω to 2705 Ω. Further irradiation drastically increased the parallel junction resistance parameter to 39000 Ω (0.2 dpa equivalent), 77440 Ω (0.3 dpa equivalent), and 190000 Ω (0.5 dpa equivalent). It is believed that the initial irradiation causes type inversion of the silicon substrate changing the original junction from a p-n to a p-p+ with a much lower barrier height leading to a lower junction resistance component between the a-B10C2+x:Hy and irradiated silicon. Additionally, it was found that after irradiation, a second parallel resistor and capacitor component is required for the model, introducing 2 additional independent variables (R2, C2). This is interpreted as the junction between the irradiated and virgin silicon near ion end of range.

Band Bending at the Gold (Au)/Boron Carbide-Based Semiconductor Interface

Abstract We have used X-ray photoemission spectroscopy to study the interaction of gold (Au) with novel boron carbide-based semiconductors grown by plasma-enhanced chemical vapor deposition (PECVD). Both n- and p-type films have been investigated and the PECVD boron carbides are compared to those containing aromatic compounds. In the case of the p-type semiconducting PECVD hydrogenated boron carbide samples, the binding energy of the B(1s) core level shows a shift to higher binding energies as the Au is deposited, an indication of band bending and possibly Schottky barrier formation. In the case of the n-type boron carbide semiconductors the interaction at the interface is more typical of an ohmic contact. Addition of the aromatic compounds increases the change in binding energies on both n-type and p-type PECVD boron carbide semiconductors, and the gold appears to diffuse into the PECVD boron carbides alloyed with aromatic moieties.

Improved a-B10C2+xHy/Si p-n heterojunction performance after neutron irradiation

The impact of neutron irradiation, in the energy range of ∼0.025 eV, on amorphous semiconducting partially dehydrogenated boron carbide (a-B10C2+xHy) on silicon p-n heterojunction diodes was investigated. The heterojunction devices were created by synthesizing a-B10C2+xHy via plasma enhanced chemical vapor deposition on n-type silicon. Unlike many electronic devices, the performance of the a-B10C2+xHy heterojunction diode improved with neutron irradiation, in spite of the large neutron cross section of 10B. There is also increased charge carrier lifetime of more than 200% with modest neutron irradiation of approximately 2.7 × 108 to 1.08 × 109 neutrons/cm2.The impact of neutron irradiation, in the energy range of ∼0.025 eV, on amorphous semiconducting partially dehydrogenated boron carbide (a-B10C2+xHy) on silicon p-n heterojunction diodes was investigated. The heterojunction devices were created by synthesizing a-B10C2+xHy via plasma enhanced chemical vapor deposition on n-type silicon. Unlike many electronic devices, the performance of the a-B10C2+xHy heterojunction diode improved with neutron irradiation, in spite of the large neutron cross section of 10B. There is also increased charge carrier lifetime of more than 200% with modest neutron irradiation of approximately 2.7 × 108 to 1.08 × 109 neutrons/cm2.