250 research outputs found
ab initio Electronic Transport Model with Explicit Solution to the Linearized Boltzmann Transport Equation
Accurate models of carrier transport are essential for describing the
electronic properties of semiconductor materials. To the best of our knowledge,
the current models following the framework of the Boltzmann transport equation
(BTE) either rely heavily on experimental data (i.e., semi-empirical), or
utilize simplifying assumptions, such as the constant relaxation time
approximation (BTE-cRTA). While these models offer valuable physical insights
and accurate calculations of transport properties in some cases, they often
lack sufficient accuracy -- particularly in capturing the correct trends with
temperature and carrier concentration. We present here a general transport
model for calculating low-field electrical drift mobility and Seebeck
coefficient of n-type semiconductors, by explicitly considering all relevant
physical phenomena (i.e. elastic and inelastic scattering mechanisms). We first
rewrite expressions for the rates of elastic scattering mechanisms, in terms of
ab initio properties, such as the band structure, density of states, and polar
optical phonon frequency. We then solve the linear BTE to obtain the
perturbation to the electron distribution -- resulting from the dominant
scattering mechanisms -- and use this to calculate the overall mobility and
Seebeck coefficient. Using our model, we accurately calculate electrical
transport properties of the compound n-type semiconductors, GaAs and InN, over
various ranges of temperature and carrier concentration. Our fully predictive
model provides high accuracy when compared to experimental measurements on both
GaAs and InN, and vastly outperforms both semi-empirical models and the
BTE-cRTA. Therefore, we assert that this approach represents a first step
towards a fully ab initio carrier transport model that is valid in all compound
semiconductors
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Research advances towards large-scale solar hydrogen production from water
CRADA Final Report: Process development for hybrid solar cells
TCF funding of a CRADA between LBNL and RSLE leveraged RSLE's original $1M investment in LBNL research and led to development of a solar cell fabrication process that will bring the high efficiency, high voltage hybrid tandem solar cell closer to commercialization. RSLE has already built a pilot line at its Phoenix, Arizona site
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Aging and Fracture of Human Cortical Bone and Tooth Dentin
Mineralized tissues, such as bone and tooth dentin, serve as structural materials in the human body and, as such, have evolved to resist fracture. In assessing their quantitative fracture resistance or toughness, it is important to distinguish between intrinsic toughening mechanisms which function ahead of the crack tip, such as plasticity in metals, and extrinsic mechanisms which function primarily behind the tip, such as crack bridging in ceramics. Bone and dentin derive their resistance to fracture principally from extrinsic toughening mechanisms which have their origins in the hierarchical microstructure of these mineralized tissues. Experimentally, quantification of these toughening mechanisms requires a crack-growth resistance approach, which can be achieved by measuring the crack-driving force, e.g., the stress intensity, as a function of crack extension ("R-curve approach"). Here this methodology is used to study of the effect of aging on the fracture properties of human cortical bone and human dentin in order to discern the microstructural origins of toughness in these materials
Carbon neutral manufacturing via on-site CO2 recycling.
The chemical industry needs to significantly decrease carbon dioxide (CO2) emissions in order to meet the 2050 carbon neutrality goal. Utilization of CO2 as a chemical feedstock for bulk products is a promising way to mitigate industrial emissions; however, CO2-based manufacturing is currently not competitive with the established petrochemical methods and its deployment requires creation of a new value chain. Here, we show that an alternative approach, using CO2 conversion as an add-on to existing manufactures, can disrupt the global carbon cycle while minimally perturbing the operation of chemical plants. Proposed closed-loop on-site CO2 recycling processes are economically viable in the current market and have the potential for rapid introduction in the industries. Retrofit-based CO2 recycling can reduce annually between 4 and 10 Gt CO2 by 2050 and contribute to achieving up to 50% of the industrial carbon neutrality goal
Few electron double quantum dot in an isotopically purified Si quantum well
We present a few electron double quantum dot (QD) device defined in an
isotopically purified Si quantum well (QW). An electron mobility of is observed in the QW which is the highest mobility
ever reported for a 2D electron system in Si. The residual concentration
of Si nuclei in the Si QW is lower than , at the
verge where the hyperfine interaction is theoretically no longer expected to
dominantly limit the spin dephasing time. We also demonstrate a
complete suppression of hysteretic gate behavior and charge noise using a
negatively biased global top gate.Comment: 4 pages, 3 figure
Electrochemical CO reduction builds solvent water into oxygenate products
Numerous studies have examined the electrochemical reduction of CO (COR) to oxygenates (e.g., ethanol). None have considered the possibility that oxygen in the product might arise from water rather than from CO. To test this assumption, C^(16)O reduction was performed in H_2^(18)O electrolyte. Surprisingly, we found that 60–70% of the ethanol contained 18O, which must have originated from the solvent. We extended our previous all-solvent density functional theory metadynamics calculations to consider the possibility of incorporating water, and indeed, we found a new mechanism involving a Grotthuss chain of six water molecules in a concerted reaction with the *C–CH intermediate to form *CH–CH(^(18)OH), subsequently leading to (^(18)O)ethanol. This competes with the formation of ethylene that also arises from *C–CH. These unforeseen results suggest that all previous studies of COR under aqueous conditions must be reexamined
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Electron-phonon scattering in Si doped GaN
Phonon-plasmon scattering in non-resonant Raman spectroscopy is used to determine the free electron concentration in Si doped GaN films. For various doping concentration and variable temperature the correlation with magneto-transport data is established. The freeze-out of the carrier concentration at low temperature is thus observed in a purely optical detection scheme. We observe a very long transient time of several hours for the carrier concentration as a reaction to temperature variation. This indicates an indirect capture and emission process with a very small cross section. The value of the Faust-Henry coefficient is determined
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