George Peterson

In₂O₃ nanostructures were successfully synthesized via physical vapor deposition (PVD). It was found that the morphology of nanostuctures could be controlled by manipulation of the synthesis temperature, growth time, use of a Au-catalyst, selection of substrate material, and vapor pressure. A higher synthesis temperature is more favorable for the formation of 1D nanostructures. An increased growth time increased the width and length of the 1D nanostructures. Through the use of a Au-catalyst coated Si (1 0 0) substrate, we were able to preferentially synthesize (1 0 0) In₂O₃ nanostructures, even at lower growth temperatures. This research shows that a Au-catalyst is necessary for the formation of one-dimensional (1D) In₂O₃ nanostructures. Three dimensional (3D) octahedral nanoparticles are resultant from a Au-free Si (1 0 0) substrate. Al₂O₃ (1 0 0) substrates were found to be energetically favorable for the synthesis of nanofilms, not 1D nanostructures, regardless of the presence of Au-catalyst. The photoluminescence curves indicate that the defect related luminescence is not a function of morphology, but rather the ratio of the partial vapor pressures of the constituent elements (In and O), which were controlled by the growth pressure.

1D Zn _0.9 Cd _0.1 S nanostructures were successfully synthesized via one-step physical vapor deposition. The separation of ultraviolet (UV) emission peaks in the cathodoluminescence (CL) curves, taken in combination with x-ray diffraction (XRD) patterns, proves the coexistence of wurtzite and zincblende phases. The diversity of morphology in nanostuctures originates from Au catalyst splitting during the growth process. The similar photoluminescence spectrums at different positions prove that the composition and defect types were homogeneous, and that defect distribution and density have very small fluctuation at the micron scale. In contrast, the CL curves taken from different locations showed that the defect types and distribution were not uniform on the nanoscale level.

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.

The plasma-enhanced chemical vapor (PECVD) co-deposition of pyridine and 1,2 dicarbadodecaborane, 1,2-B ₁₀ C ₂ H ₁₂ (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 µ s compared to values of ⩽35 µ s 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.