The electrical transport properties of simultaneously deposited, B-doped homoepitaxial and polycrystalline diamond thin films have been evaluated by Hall-effect and resistivity measurements over a temperature range of 80–600 K. The same films were later characterized by scanning electron microscopy, secondary-ion-mass spectroscopy, and an oxidation defect etch. The study involved four sets of chemical-vapor-deposited diamond films with individual B concentrations ranging from 1.5×1017 to 1.5×1020 cm−3. In each of the four cases the mobility of the polycrystalline film was lower than that of the homoepitaxial film by 1–2 orders of magnitude over the entire temperature range. Polycrystalline films also incorporated 2–4 times more B, had 3–5 times higher compensation ratios, and displayed activation energies that were 0.05–0.09 eV lower than in the homoepitaxial films. Hopping conduction was observed in both types of films at low temperatures, but was enhanced in polycrystalline films as evident by higher transition temperatures. Preliminary efforts have been made to evaluate these results by considering the possible effects of crystal structure, compensation, impurity segregation, grain-boundary trapping, and impurity conduction.
In an ongoing effort to address the clear clinical unmet needs surrounding breast conserving surgery (BCS), our group has developed a next-generation multiplexed optical-fiber-based tool to assess breast tumor margin status during initial surgeries. Specifically detailed in this work is the performance and clinical validation of a research-grade intra-operative tool for margin assessment based on diffuse optical spectroscopy. Previous work published by our group has illustrated the proof-of-concept generations of this device; here we incorporate a highly optimized quantitative diffuse reflectance imaging (QDRI) system utilizing a wide-field (imaging area = 17cm2) 49-channel multiplexed fiber optic probe, a custom raster-scanning imaging platform, a custom dual-channel white LED source, and an astronomy grade imaging CCD and spectrograph. The system signal to noise ratio (SNR) was found to be greater than 40dB for all channels. Optical property estimation error was found to be less than 10%, on average, over a wide range of absorption (μa = 0–8.9cm-1) and scattering (μs’ = 7.0–9.7cm-1) coefficients. Very low inter-channel and CCD crosstalk was observed (2% max) when used on turbid media (including breast tissue). A raster-scanning mechanism was developed to achieve sub-pixel resolution and was found to be optimally performed at an upsample factor of 8, affording 0.75mm spatially resolved diffuse reflectance images (λ = 450–600nm) of an entire margin (area = 17cm2) in 13.8 minutes (1.23cm2/min). Moreover, controlled pressure application at the probe-tissue interface afforded by the imaging platform reduces repeated scan variability, providing <1% variation across repeated scans of clinical specimens. We demonstrate the clinical utility of this device through a pilot 20-patient study of high-resolution optical parameter maps of the ratio of the β-carotene concentration to the reduced scattering coefficient. An empirical cumulative distribution function (eCDF) analysis is used to reduce optical property maps to quantitative distributions representing the morphological landscape of breast tumor margins. The optimizations presented in this work provide an avenue to rapidly survey large tissue areas on intra-operative time scales with improved sensitivity to regions of focal disease that may otherwise be overlooked.
The preparation of electrodeposited semiconductors for Hall effect measurements is complicated by the fact that these materials are, by necessity, attached to highly conducting substrates. As a result, methods were developed to reproducibly remove large area samples from their conducting substrates, and suitably prepared samples were used for temperature‐dependent Hall measurements and resistivity measurements. Apparatus was designed and built to routinely measure Hall voltages as low as 250 μV for source impedances up to 1012 Ω using films about 1 μm in thickness. Measurements were performed on numerous electrodeposited materials: normalCdTe , normalCdS , normalCdSe , and HgxCdfalse(1−xfalse)normalTe . Argon annealed electrodeposited normalCdTe was found to be consistently p‐type, with resistivity values typically 106–107 · Ω · cm p → n conversion of normalCdTe was achieved by diffusion of Cd at high temperature. HgxCdfalse(1−xfalse)normalTe was also p‐type, but had much lower resistivity and higher carrier concentration than normalCdTe . normalCdS and normalCdSe were both n‐type with carrier concentrations typically 1016 cm−3 and 1014–1016 cm−3, respectively.
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