Study of radiation effects in Li-doped silicon solar cells
Radiation effects in lithium-doped silicon solar cells
Carter, J. R.↗
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Rapid Epitaxial Growth of GdBa{sub 2}Cu{sub 3}O{sub 7-σ} Films by Dilute Co Doping
The effect of dilute Co doping on the epitaxial growth of GdBCO films was investigated by self-developed fluorine-free polymer-assisted metal-organic deposition (PA-MOD) method. Under the same sintering heat treatment, dilute Co doping dramatically improved the crystallinity, microstructure, and critical current density (J{sub c}) of GdBCO films. High J{sub c} of 4.0 MA/cm{sup 2} at 77 K and self-field was obtained in Co-doped film after only sintering for 30 min, which is eight times of the J{sub c} for the undoped film. Also, Co-doped GdBCO film sintered for as short as 20 min still possesses a high J{sub c} of 1.5 MA/cm{sup 2}, whereas the J{sub c} is 0 for the similarly sintered pure film. These results suggest that dilute Co doping facilitates the epitaxial growth of the high-performance GdBCO film.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Characteristics of 0.8- and 0.2-microns gate length In(x)Ga(1-x) As/In(0.52)Al(0.48)As/InP (0.53 less than or equal to x less than or equal to 0.70) modulation-doped field-effect transistors at cryogenic temperatures
The performance characteristics of InP-based In(x)Ga(1-x)As/In(0.52)Al(0.48)As (0.53 is less than or equal to x is less than or equal to 0.70) pseudomorphic modulation-doped field-effect transistors (MODFET's) as a function of strain in the channel, gate, length, and temperature were investigated analytically and experimentally. The strain in the channel was varied by varying the In composition x. The temperature was varied in the range of 40-300 K and the devices have gate lengths L(sub g) of 0.8 and 0.2 microns. Analysis of the device was done using a one-dimensional self consistent solution of the Poisson and Schroedinger equations in the channel, a two-dimensional Poisson solver to obtain the channel electric field, and a Monte Carlo simulation to estimate the carrier transit times in the channel. An increase in the value of the cutoff frequency is predicted for an increase in In composition, a decrease in temperature, and a decrease in gate length. The improvements seen with decreasing temperature, decreasing gate length, and increased In composition were smaller than those predicted by analysis. The experimental results on pseudomorphic InGaAs/InAlAs MODFET's showed that there is a 15-30 percent improvement in cutoff frequency in both the 0.8- and 0.2-micron gate length devices when the temperature is lowered from 300 to 40 K.
Lai, Richard↗
Effects of rhodium doping on dislocation nucleation in a [001] SrNi 2 P 2 single crystal under spherical nanoindentation
Nanoindentation was performed on SrNi 2 P 2 single crystals and their dilute solid solutions, Sr(Ni 1–x Rh x ) 2 P 2 (x = 0 ~ 0.055), under [001] loading to investigate the effects of elemental doping on Young’s modulus and dislocation nucleation stress. The results show that Young’s modulus and the dislocation nucleation stress decrease as the Rh content increases, and their Rh content dependence also varies with the Rh content. Electron diffraction analysis and the anisotropic lattice distortion calculations revealed that a local structural transition from the orthorhombic superstructure to the tetragonal structure and local compressive residual stresses could be the main reasons for the decrease in Young’s modulus and dislocation nucleation stress, respectively. The overlap of stress–strain fields between Rh atoms and the associated local structural transition contribute to their Rh content dependence. Here, the results also indicate that elemental doping does not necessarily strengthen materials if the incipient plasticity is controlled by dislocation nucleation, unlike conventional solid solution strengthening.
36 MATERIALS SCIENCE↗
Effect of Carbon Doping on CO 2 –Reduction Activity of Single Cobalt Sites in Graphitic Carbon Nitride
Single atom catalysts have demonstrated interesting activity in a variety of applications. In this study, we prepared single C o2+ sites on graphitic carbon nitride (C 3 N 4 ), which was doped with carbon for enhanced activity in visible-light CO 2 reduction. The synthesized materials were characterized with a variety of techniques, including microscopy, X-ray powder diffraction, UV-vis spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, and X-ray absorption spectroscopy. Here, doping C 3 N 4 with carbon was found to have profound effect on the photocatalytic activity of the single Co 2+ sites. At relatively low levels, carbon doping enhanced the photoresponse of C 3 N 4 in the visible region and improved charge separation upon photoactivation, thereby enhancing the photocatalytic activity. Furthermore, high levels of carbon doping were found to be detrimental to the photocatalytic activity of the single Co 2+ sites by altering the structure of C 3 N 4 and generating defect sites responsible for charge recombination.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unusual effects of Be doping in the iron-based superconductor FeSe
Recent superconducting transition temperatures (T c ) over 100 K for monolayer FeSe on SrTiO 3 have renewed interest in the bulk parent compound. In KCl:AlCl 3 flux-transport-grown crystals of FeSe 0.94 Be 0.06 , FeSe 0.97 Be 0.03 and, for comparison, FeSe, this work reports doping of FeSe using Be—among the smallest of possible dopants, corresponding to an effective 'chemical pressure'. According to lattice parameter measurements, 6% Be doping shrank the tetragonal FeSe lattice equivalent to a physical pressure of 0.75 GPa. Using this flux-transport method of sample preparation, 6% of Be was the maximum amount of dopant achievable. At this maximal composition of FeSe 0.94 Be 0.06 , the lattice unit cell shrinks by 2.4%, T c —measured in the bulk via specific heat—increases by almost 10%, the T c versus pressure behavior shifts its peak T$onset\atop{c}$downwards by ~1 GPa, the high temperature structural transition around T S = 89 K increases by 1.9 K (in contrast to other dopants in FeSe which uniformly depress T S), and the low temperature specific heat γ increases by 10% compared to pure FeSe. Also, upon doping by 6% Be the residual resistivity ratio, ρ(300 K)/ρ(T → 0), increases by almost a factor of four, while ρ(300 K)/ρ(T=$+\atop{c}$) increases by 50%.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effect of Pt Doping on Nucleation and Crystallization in Li2O.2SiO2 Glass: Experimental Measurements and Computer Modeling
Heterogeneous nucleation and its effects on the crystallization of lithium disilicate glass containing small amounts of Pt are investigated. Measurements of the nucleation frequencies and induction times with and without Pt are shown to be consistent with predictions based on the classical nucleation theory. A realistic computer model for the transformation is presented. Computed differential thermal analysis data (such as crystallization rates as a function of time and temperature) are shown to be in good agreement with experimental results. This modeling provides a new, more quantitative method for analyzing calorimetric data.
Narayan, K. Lakshmi↗
Ab initio prediction of FeCr sigma (001)/FCC Fe(111) interfacial energy: Effect of interfacial doping of C, B, and N
Interfacial energy plays a crucial role for high-temperature material systems in determining their microstructure evolution and mechanical properties. Optimizing the interfacial energy through doping can improve the stability, performance, and overall functionality of these materials. Here, the present study delivers theoretical investigation on the sigma FeCr (001)//FCC Fe (111) interfacial energy using ab initio methods, focusing on the implications of interfacial doping with important interstitial elements carbon (C), boron (B), and nitrogen (N). The calculated interfacial energy without doping is 0.183J/m 2 . Upon doping, notable reductions in interfacial energy were observed. Doping with B decreased the interfacial energy to 0.046J/m 2 , with single C doping to 0.126J/m 2 , with two C doping to 0.098J/m 2 , and with a single N doping to 0.071J/m 2 . These findings not only shed light on the atomistic origin for the effect of stabilizing the microstructure of stainless steel at elevated temperatures by interstitial doping, but also present a systematic, thorough ab initio approach to predict interfacial doping properties and guide alloy design to enhance the performance and stability.
FeCr sigma phase↗
Effects of heteroatom doping on hydrogen uptake in tungsten oxide
Redox-active transition metal oxides (TMOs) that can undergo proton-insertion coupled electron transfer (PICET) are promising candidates for catalyzing molecular conversion reactions which require the transfer of hydrogen atoms (or the thermochemical equivalent, H + , e − ). Herein, we studied the effects of isovalent (Mo 6+ ) and aliovalent (V 5+ and Nb 5+ ) heteroatom doping on the electrochemical PICET behavior of monoclinic tungsten oxide (WO 3 ). Cyclic voltammetry in aqueous acidic electrolytes shows that the addition of redox-active heteroatoms (Mo 6+ and V 5+ ) leads to systematic shifts in redox couple half-wave potentials (E 1/2 ), broadening, and an overall decrease in the current response. Conversely, the non-redox active heteroatom (Nb 5+ ) only reduces the current response with no observable peak-current broadening. This broadening is attributed to changes in the proton binding affinities of oxygen in different chemical environments, i.e., bridging different pairs of redox-active transition metal cations. We determined the hydrogen bond dissociation free energy (H BDFE) values to elucidate the thermodynamic effect of heteroatom substitution. Density functional theory calculations reveal a differentiation in the hydrogen binding and oxygen vacancy formation energies between heteroatom doped structures. The PICET-induced structural phase transitions of the pristine and doped samples were further probed with operando electrochemical X-ray diffraction (EC-XRD) and with ex situ chemical reduction. The broadening of the potential-dependent current response with increased heteroatom doping manifests in the operando EC-XRD results as prolonged structural regions where multiple hydrogen bronze phases exist and the appearance of cubic bronze phases at lower degrees of reduction compared to pristine WO 3 .
Holzapfel, Noah P. [North Carolina State Universit↗
Effect of chromia doping of thermal stability of silica fibers
Commercial silica fibers of the type being evaluated for reusable surface insulation for reentry vehicles were found to be porous and composed of subfibers. The effect on shrinkage and devitrification of soaking such silica fibers in water, acetic acid, chromium acetate, and chromium nitrate solutions was studied. Felted specimens made of chromia-doped fibers shrunk only about one-half as much as those made of untreated fibers after exposure in air for 4 hours at 1300 C. The devitrification rate of fibers given prolonged soaks in chromium nitrate was as low as that of as-received fibers.
Zaplatynsky, I.↗
Magnetocaloric Effect in Lightly‐Doped Fe 5 Si 3 Single Crystals
Abstract Development of promising new materials for above room temperature magnetic cooling applications relies on careful balancing of structure and composition to maximize accessible metastable phases that can drive a strong magnetocaloric effect (MCE). However, the working temperatures of these materials may fall outside of desired application windows. In this work, it is shown that it is possible to control metastable phase stability temperatures of Fe 5 Si 3 through selection of appropriate spin and charge doping. Here, the parent material's desired structure appears only within a narrow temperature range from 1098 to 1303 K. Doping with Mn and P is shown to allow stabilization of the parent's high temperature phase and resulting MCE to room temperature. The structural and magnetic properties, and the magnetocaloric effect of single crystal Fe 4.83 Mn 0.16 Si 2.91 P 0.09 (FMSP) are investigated experimentally and theoretically. A first‐order magneto‐elastic transition is observed at 348 K, where magnetic onset is accompanied by a change in lattice volume without an apparent change in crystal symmetry. Although the trace Mn and P doping are found to decrease the T C , the maximum magnetic entropy change Δ S Max ( T ) and the relative cooling power (RCP) of FMSP are enhanced compared to polycrystalline Fe 5 Si 3 . As a result, an intrinsically broader entropy change over a larger temperature span is generated in the lightly doped single crystal of Fe 5 Si 3 . The magnetic moment of the system is also enhanced. Density functional theory (DFT) calculations are performed to gain microscopic insights into the experimental findings. The results suggest that the hexagonal Fe 5 Si 3 is a new giant room temperature MCE material that is on par with La–Fe–Si and Fe‐Mn‐P‐Si systems.
36 MATERIALS SCIENCE↗
Effective Selective Area Doping for GaN Vertical Power Transistors Enabled by Innovative Materials Engineering
GaN vertical power transistors have emerged as promising candidates for future high efficiency high power electronic applications, with the potential to outperform conventional GaN lateral power devices in terms of power, breakdown, and avalanche characteristics. However, the development of current GaN vertical power transistors is seriously hindered by the poor materials performance of selective area doped p-n junctions. A mechanistic understanding of these fundamental materials issues is essential in order to achieve high performance selective area doped p-n junctions and consequently to advance the GaN vertical power transistor technology. To address this challenge, we carried out a comprehensive research program that advance fundamental knowledge in the selective area doping for GaN materials, and which will lead to the development of high performance GaN vertical power transistors. First, we developed innovative fabrication processes, including novel surface etching, surface passivation, and metalorganic chemical vapor deposition (MOCVD) growth, which provided enhanced opportunities for solving the unique challenges of selective area doping in GaN materials. Second, we performed a fundamental materials study using powerful characterization methods including transmission electron microscopy (TEM), ultraviolet (UV-), x-ray and angle-resolved photoelectron spectroscopy (UPS/XPS/ARPES), electron holography, and cathodoluminescence (CL); Third, we investigated several related issues, including Mg incorporation, polarization effects in carrier transport, and non-ideal material effects, which have rarely been explored so far. At the end of this project, we successfully demonstrated (1) fundamental understanding of selective area etching, regrowth, and doping of GaN, and associated knowledge on defects, interface, and breakdown properties. (2) Effective etch and regrowth processing recipes to achieve etch/regrowth GaN p-n diodes with very low leakage of 3.5 nA at 600 V, which meets the ARPA-E target. (2) High performance vertical GaN p-n didoes and vertical junction termination extension (JTE) devices with breakdown voltage of ~ 2 kV, and breakdown electric field of ~ 3.5 MV/cm, which are close to the performance limit of GaN. The successful outcome has resulted in new fundamental understandings in the selective area doping and regrowth process for GaN, which will lead to groundbreaking GaN vertical transistors for high performance next generation power electronics.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Inkjet-printed SnO x as an effective electron transport layer for planar perovskite solar cells and the effect of Cu doping
Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO 2 has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO 2 ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnO x ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnO x ETL. The low-temperature SnO x exhibited an amorphous structure and outperformed high-temperature crystalline SnO 2 . The improved performance was attributed to enhanced charge extraction and transport and suppressed charge recombination at ETL/perovskite interfaces, which originated from enhanced electrical and optical properties of SnO x , improved perovskite film quality, and well-matched energy level alignment between the SnO x ETL and the perovskite layer. Furthermore, SnO x was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnO x , leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnO x ETLs, decreasing at first and turning into inverted hysteresis afterwards with increasing Cu doping level. This tunable hysteresis was related to the interplay between charge/ion accumulation and recombination at ETL/perovskite interfaces in the case of electron extraction barriers.
14 SOLAR ENERGY↗
Effect of Ce doping on the resistance of Na over V2O5-WO3/TiO2 SCR catalysts
Highlights: • Different forms of Na poisoning CeO{sub 2}-V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts were prepared by impregnation method. • The comparison of the poisoning effect between Na{sub 2}O and NaCl over Ce{sub 10}VWTi catalyst was studied. • The poisoning effect of Na{sub 2}O is lighter than that of NaCl because the 4Na{sub 2}O-Ce{sub 10}VWTi catalyst exists more acid sites. • The reasons contributing to the catalytic activity and Na poisoning resistance of CeVWTi catalyst were proposed. - Abstract: Enhanced performance of Ce doping on the catalytic activity of V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts and its resistance properties to Na poisoning have been investigated in the research. Different Na species (NaCl and Na{sub 2}O) were deposited on CeO{sub 2}-V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts by impregnation method. The results presented that CeO{sub 2}-V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts exhibited a higher NH{sub 3}-SCR activity and better Na resistance than the V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalyst, and its poisoning resistance to Na{sub 2}O is more superior than to NaCl, caused by more acid sites over the 10%CeO{sub 2}-V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} (Ce{sub 10}VWTi) catalyst, which indicated that the poisoning resistance of Na{sub 2}O on Ce{sub 10}VWTi catalysts is higher than that of NaCl. Combined with the characterization results, the dopant of Ce could enhance the surface chemisorbed oxygen on the Na poisoning V{sub 2}O{sub 5}-WO{sub 3}/TiO{sub 2} catalysts, facilitate the redox cycle, and increase the intensity of acid sites due to the newly formed Brønsted acid sites stemmed from Ce{sup 3+}−NH{sub 4}{sup +}, thereby promoting catalytic activity and Na poisoning resistance.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effect of Lithium Doping on MgO Hydroxylation and Carbonation
Recovery of magnesium from brines can potentially be used to source MgO (periclase) as a CO 2 sorbent or for Mg-based cements. However, it is not clear how common impurities in brines, such as lithium, affect the resulting MgO reactivity. Here, to test the effect of lithium incorporation on MgO reactivity for hydration and carbonation, we combined computational simulations with experiments. Experimentally altered (Mg,Li)O with a low dopant concentration (0.012 ± 0.002% w/w Li) was characterized using synchrotron-based X-ray scattering and high-resolution electron microscopy to measure reaction layer formation on (Mg,Li)O. Single-crystal X-ray diffraction analysis of (Mg,Li)O demonstrates that the incorporation of lithium leads to the formation of oxygen vacancies. The presence of vacancies is likely causing faster hydroxylation rates as predicted by ab initio molecular dynamics simulations. However, the faster hydroxylation rates likely lead to faster passivation of the surface because we observe thinner reaction layers on (Mg,Li)O samples both over short time periods (30 days) and over long time periods (28 years). After 28 years, the reaction layer on the (Mg,Li)O sample was less than one-third of the thickness of that of the pure MgO sample. In addition, over 30 days, reaction layers on (Mg,Li)O samples primarily formed at steps rather than on terraces, in contrast to our previous observations on MgO. Based on our results, naturally occurring impurities in MgO modify its reactivity even at very low concentrations and need to be considered for accurate reaction rate prediction for application of MgO as a CO 2 sorbent or in cements.
MgO↗
Tailoring Bandgap of Perovskite BaTiO 3 by Transition Metals Co-Doping for Visible-Light Photoelectrical Applications: A First-Principles Study
The physical and chemical properties of V-M" and Nb-M" (M" is 3d or 4d transition metal) co-doped BaTiO 3 were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M" co-doping is more favorable than Nb-M" co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO 3 , the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO 3 . The optimal co-doping effect comes from the V-Cr co-doping system, which not only has smaller impurity formation energy, but also significantly reduces the bandgap. Detailed analysis of the density of states, band structure, and charge-density distribution in the doping systems demonstrates the synergistic effect induced by the V and Cr co-doping. The results can provide not only useful insights into the understanding of the bandgap engineering by element doping, but also beneficial guidance to the experimental study of BaTiO 3 for visible-light photoelectrical applications.
36 MATERIALS SCIENCE↗
Study of radiation effects in Li-doped silicon solar cells Quarterly report, Aug. - Oct. 1968
Radiation effects in lithium doped silicon solar cells
Carter, J. R.↗