Study of the effects of radiation on lithium doped solar cells Semiannual report
Test facilities for studying electron irradiation effects on lithium-doped silicon solar cells
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The Preparation Conditions of Chromium Doped ZnSe and Their Effect on The Infrared Luminescence Properties
We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the Physical Vapor Transport method. Room temperature lifetime values between 6 and 8 microseconds were measured for samples with Cr (2+) concentrations from low 10 (exp 17) to high 10 (exp 18) per cubic centimeter range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10 (exp 19) per cubic centimeter.
Burger, A.↗
The Preparation Conditions of Chromium Doped ZnSe and Their Effect on the Infrared Luminescence Properties
We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8 micro seconds were measured for samples with Cr2+ from low 10(exp 17) to high 10(exp 18) / cubic cm range. Lifetime data taken down to 78 K was found to be rather temperature independent, reconfirming previous reports indicating a quantum yield of the corresponding emission of close to 100% at room temperature. A strong decrease in the room temperature lifetime was found for chromium concentrations higher than 10(exp 19) / cubic CM.
Burger, A.↗
Proton and Gamma Radiation Effects in Undoped, Single-doped and co-doped YLiF4 and LuLiF4
Proton and gamma radiation effects in various YLiF4 and LuLiF4 crystals have been investigated. The radiation induced color centers compared with six different kinds of crystal samples in ranges up to 200 krads and 200 MeV. The radiation induced absorption coefficients are strongly dependent on polarization and concentration of rare-earth ions.
Lee, Hyung↗
Ferroelectricity‐Enhanced Piezo‐Phototronic Effect in 2D V‐Doped ZnO Nanosheets
Emerging 2D electronic materials have shown great potential for regulating and controlling optoelectronic processes. A 2D ferroelectric semiconductor coupled with the piezo-phototronic effect may bring unprecedented functional characteristics. Here, a heterojunction photodetector made of p-Si/V-doped-ferroelectric-ZnO 2D nanosheets (FESZ-PD) is fabricated, and the ferroelectricity-enhanced piezo-phototronic effect on the photoresponse behavior of the FESZ-PD is carefully investigated. By introducing the ferroelectricity and the piezo-phototronic effect, improved current rectification performance is achieved and the photoresponse performance of the heterojunction is enhanced in a broad spectral range. The applied voltage bias during measurement naturally causes ferroelectric spontaneous polarizations to align, resulting in a change in band structure near the interface and the local piezo-phototronic effect. The modulated energy band promotes the generation, separation, and transportation efficiency of photogenerated carriers greatly. Compared with the Si/ZnO 2D nanosheets photodetector without ferroelectricity under strain-free conditions, the photoresponsivity R of the FESZ-PD increases by 2.4 times when applying a -0.20‰ compressive strain at +1 V forward bias. These results confirm the feasibility of coupling the ferroelectricity with the piezo-phototronic effect in 2D ferroelectric materials to enhance the photoresponse behavior, which provides a good way to enable the development of high-performance electronic and optoelectronic devices.
36 MATERIALS SCIENCE↗
Neutron irradiation-enhanced grain growth in tungsten and tungsten alloys
Herein, to understand the microstructural stability of candidate plasma-facing materials under fusion-relevant environments, neutron irradiation of W and W-3%Re alloys with and without K and La dopants was performed in the mixed-spectrum High Flux Isotope Reactor at nominal temperatures of ~850 °C and ~1100 °C to calculated doses between 0.42 and 0.47 dpa. To the best of our knowledge, this study presents the first experimental evidence of radiation-enhanced recrystallization in W and undoped W–Re alloys at ~850 °C, conditions where thermal annealing does not cause any grain growth in a similar timescale. Potassium- or lanthanum-doped tungsten alloys showed more resistance to radiation-enhanced grain growth. We explain the acceleration of grain growth by analyzing the self-diffusion constant under atomic displacement environments. The microstructural observations of the studied W variants suggest that La doping is more effective than K doping for mitigating recrystallization. This study also found that radiation-enhanced recrystallization is an important consideration when designing and applying W to plasma-facing components in future nuclear fusion reactors.
36 MATERIALS SCIENCE↗
Mechanistic insight into the effects of A-site doping in perovskite nanorods on interfacial Li-ion and Na-ion transport in polymer–perovskite composite electrolytes
Composite polymer electrolytes (CPEs) offer a promising pathway to safer and higher energy density electrochemical energy storage yet optimizing interfacial ion transport remains a critical challenge due to high resistances and a lack of understanding of the complex interfacial electrostatic interactions. This work investigates the mechanistic origins of the interfacial ion transport enhancement in single-ion conducting (SIC) polymer electrolytes filled with A-site disordered perovskite LaxMyTiOz (LMTO) (M = Li, Na, K) nanorods. By integrating Density Functional Theory (DFT) with broadband dielectric spectroscopy (BDS) and pulsed-field-gradient NMR (PFG-NMR), we analyze the ion transport behavior in Li-based and Na-based SIC systems containing compositionally distinct LMTO fillers (LMTO800 and LMTO900). Specifically, we introduce the site-to-site energy difference (ΔE) descriptor, which extends beyond single-site descriptors such as adsorption energy and ion binding energies. We demonstrate that ΔE together with ion binding energies provide a more comprehensive picture of the energy landscape at the polymer–ceramic interface. The combined DFT and experimental results show that A-site doping in the ceramic filler can effectively modulate ΔE and ion binding energies, creating a favorable potential energy landscape that promotes enhanced ion transport along the interface. This comprehensive study illustrates the impact of ceramic compositional tuning on interfacial ion transport and provides materials design rules towards real-world applications.
B shepard, Lauren [Pennsylvania State University]↗
Effective masses in Zr-doped superconducting ceramic SrTiO sub 3.
Zr doped superconducting ceramic strontium titanate, noting effective electron mass variations and transition temperature
Eagles, D. M.↗
An Acoustic Charge Transport Imager for High Definition Television Applications: Reliability Modeling and Parametric Yield Prediction of GaAs Multiple Quantum Well Avalanche Photodiodes
Reliability modeling and parametric yield prediction of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiodes (APDs), which are of interest as an ultra-low noise image capture mechanism for high definition systems, have been investigated. First, the effect of various doping methods on the reliability of GaAs/AlGaAs multiple quantum well (MQW) avalanche photodiode (APD) structures fabricated by molecular beam epitaxy is investigated. Reliability is examined by accelerated life tests by monitoring dark current and breakdown voltage. Median device lifetime and the activation energy of the degradation mechanism are computed for undoped, doped-barrier, and doped-well APD structures. Lifetimes for each device structure are examined via a statistically designed experiment. Analysis of variance shows that dark-current is affected primarily by device diameter, temperature and stressing time, and breakdown voltage depends on the diameter, stressing time and APD type. It is concluded that the undoped APD has the highest reliability, followed by the doped well and doped barrier devices, respectively. To determine the source of the degradation mechanism for each device structure, failure analysis using the electron-beam induced current method is performed. This analysis reveals some degree of device degradation caused by ionic impurities in the passivation layer, and energy-dispersive spectrometry subsequently verified the presence of ionic sodium as the primary contaminant. However, since all device structures are similarly passivated, sodium contamination alone does not account for the observed variation between the differently doped APDs. This effect is explained by the dopant migration during stressing, which is verified by free carrier concentration measurements using the capacitance-voltage technique.
Hunt, W. D.↗
Giant and reversible room-temperature magnetocaloric effect in Ti-doped Ni-Co-Mn-Sn magnetic shape memory alloys
The practical applications of magnetocaloric materials for magnetic refrigeration require not only large magnitude but also reversibility, as well as room-temperature operating temperature, of the magneto caloric effect. However, it is a complex problem to simultaneously meet these demands in the Heusler-type Ni-(Co)-Mn-X (X = In, Sn, Sb, Ga) magnetic shape memory alloys which are a promising candidate for magnetocaloric materials, owing to the interdependence of magnetostructural transformation parameters. In this work, through synergic tuning of magnetostructural transformation parameters via alloying with Ti in Ni 42-x Ti x Co 9 Mn 39 Sn 10 alloys, we achieved a large reversible room-temperature magnetocaloric effect. By alloying with a proper amount of Ti, the martensitic transformation temperature was brought down to room temperature and the sensitivity of transformation temperature to magnetic field change was greatly enhanced with the transformation entropy change still remaining a large value, while the thermal hysteresis and the transformation interval only slightly increased. Thus, the field required to induce the complete and reversible transformation was significantly reduced. As a result, a large reversible room-temperature magnetic entropy change ΔS m of 18.7 J kg -1 K -1 under 5 T was achieved in the Ni 41 Ti 1 Co 9 Mn 39 Sn 10 alloy. This is the first report on reversibleΔS m in Ni-Mn-Sn-based Heusler alloys and the ΔS m we achieved represents the highest reversible ΔS m under 5 T reported heretofore in Ni-Mn-based Heusler alloys. Furthermore, the Ni 41 Ti 1 Co 9 Mn 39 Sn 10 alloy shows good compressive properties and stable martensitic transformation during thermal cycling, beneficial for potential magnetocaloric applications. This study is instructive for the development of high-performance magnetocaloric materials for room-temperature magnetic refrigeration.
36 MATERIALS SCIENCE↗
Effect of Gd-doped ceria infiltration into Ni-YSZ on reversible solid oxide cell operation
Gadolinium doped ceria (GDC) infiltration into Ni-(Y 2 O 3 ) 0•08 (ZrO 2 ) 0.92 (Ni-YSZ) fuel electrodes has been shown to significantly improve solid oxide electrolysis cell performance and stability. However, the effects of GDC infiltration on cells operated reversibly between fuel cell and electrolysis modes have not been reported previously. Here we present reversible solid oxide cell life test results for different GDC infiltration loadings into Ni-YSZ electrodes in two types of fuel-electrode-supported solid oxide cells. Electrochemical impedance spectroscopy reveals that GDC infiltrant lowers the initial cell area specific resistance (ASR) and limits the degradation – for example, the GDC-infiltrated electrode ASR increased by 0.1 Ω cm 2 over 1000 h of reversible operation at ±0.5 A cm –2 and 800 °C, compared to 0.19 Ω cm 2 for non-infiltrated cells. Cell voltage degradation rates were reduced by infiltration during operation at a current density of ±0.5 A cm –2 at 800 °C, and during at 700 °C at ±0.75 A cm –2 . Furthermore, scanning electron microscopy observations show that the infiltrated GDC nanoparticles mitigate Ni particle coarsening in the Ni-YSZ electrode, possibly explaining the enhanced cell stability.
25 ENERGY STORAGE↗
Nickel doped graphitic carbon nitride nanosheets and its application for dye degradation by chemical catalysis
Highlights: • Nickel doped Graphitic carbon nitride (GCN) was synthesized chemically. • Mott-Schottky was done to calculate the flat band potentials and donor densities of pure and doped samples. • Toxic Methyl Orange dye was degraded efficiently by doped samples in the presence of NaBH{sub 4} accompanied by hydrogen evolution. • Enhancement of catalytic activity with increasing doping concentration was studied in presence of varying amount of NaBH{sub 4}. • A plausible mechanism for catalytic degradation was discussed in details. - Abstract: A facile synthesis of transition metal-nickel doped graphitic carbon nitride (NiGCN) nanosheets with varying doping concentrations has been reported. X-Ray diffraction and Fourier transformed infrared spectroscopic study were performed to analyse the structural phase formation and different bonds present in the samples, whereas, field emission and transmission electron microscopic study provided the morphological information. The thermal stability of the samples was measured from the TG-DTA analysis. Photoluminescence spectroscopy was performed to elucidate the emissive property of the samples. The flat band potential of the samples was measured by Mott-Schottky analysis. First principle study was carried out to delineate the probable doping site of the Ni atom along with the effect of doping on the pure material. The samples were effectively utilized to degrade toxic methyl orange (MO) dye from water in the presence of sodium borohydride (NaBH{sub 4}) without exploiting any visible light source. The plausible catalysis mechanism following a series of several chemical reactions has been discussed in details.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Implications of doping on microstructure, processing, and thermoelectric performance: The case of PbSe
Abstract In this work, we highlight the often-overlooked effects of doping on the microstructure and performance of bulk thermoelectric materials to offer a broader perspective on how dopants interact with their parent material. Using PbSe doped with Na, Ag, and K as a model material system, we combine original computational, experimental, and microscopy data with established trends in material behavior, to provide an in-depth discussion of the relationship between dopants, processing, and microstructure, and their effects on thermoelectric efficiency and thermal stability. Notable observations include differences in the microstructure and mass loss of thermally treated samples of Na- and Ag-doped PbSe, as well as findings that Na and K cations exist predominantly as substitutional point defects while Ag also occupies interstitial sites and exhibits lower solubility. We discuss how these differences in point defect populations are known to affect a dopants’ ability to alter carrier concentration and how they may affect the mechanical properties of PbSe during processing. Graphic Abstract
Grovogui, Jann A. (ORCID:0000000200481049)↗
Superconductivity in alkaline earth metal doped boron hydrides
Effects of alkaline earth metal atoms doping in boron hydrides at high pressure are investigated by first-principles calculations. The calculated results showed that doping with Mg, Ca, Ba, and Sr in B8H16 at 50 GPa is thermodynamically favorable and dynamically stable. The doping changes the B 8 H 16 from a semiconductor to a metal with substantial electronic density-of-state around the Fermi level. The superconductivity of the alkaline earth metal doped B 8 H 16 is studied based on electron-phonon coupling mechanism. The calculated critical superconducting transition temperatures (T c ) range from 10 to 25 K at 50 GPa upon doping. These results suggest that doping metal atoms in boron hydrides is an efficient way in designing superconducting materials.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
High Mobility SiGe/Si n-Type Structures and Field Effect Transistors on Sapphire Substrates
SiGe/Si n-type modulation doped field effect transistors (MODFETs) fabricated on sapphire substrates have been characterized at microwave frequencies for the first time. The highest measured room temperature electron mobility is 1380 sq cm/V-sec at a carrier density of 1.8 x 10(exp 12)/sq cm for a MODFET structure, and 900 sq cm/V-sec at a carrier density of 1.3 x 10/sq cm for a phosphorus ion implanted sample. A two finger, 2 x 200 micron gate n-MODFET has a peak transconductance of 37 mS/mm at a drain to source voltage of 2.5 V and a transducer gain of 6.4 dB at 1 GHz.
Alterovitz, Samuel A.↗
Effects of Nd, Er Doping on the Structure and Magnetic Properties of YFeO{sub 3}
Nd, Er co-doped YFeO{sub 3} compounds were synthesized by sol-gel method. The prepared compounds were characterized by powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX), and vibrating sample magnetometer (VSM) integrated in a physical property measurement system (PPMS-9), respectively. The results show that the compounds possess orthorhombic perovskite structure. The Y{sub 0.5}Er{sub 0.1}Nd{sub 0.4}FeO{sub 3} compound mainly consists of five elements (Er, Nd, Y, Fe, and O) and atom ratio matched well with the formula. With the increase of Nd{sup 3+} doping content in Y{sub 0.5}Er{sub 0.5−x}Nd{sub x}FeO{sub 3} (x = 0, 0.1, 0.2, 0.3, and 0.4), the coercivity increases gradually while the saturation magnetization and remanent magnetization decrease at the same time. Introducing Nd{sup 3+} and Er{sup 3+} ions into YFeO{sub 3} will make a change on a structure distortion, resulting in the decrease of the Fe–O–Fe angle and the consequent reduction of superexchange effect. From our research results, the relationship between the r (R{sup 3+}) and the superexchange bond angle is different from pure-phase orthoferrites R FeO{sub 3}.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Tuning the extent of porosity and composition of N-doped carbon materials by NaNO3 and its effect on electrochemical activity
Highlights: • One-pot method using cheap NaNO{sub 3} as etching agent was developed to tune the porous structure. • NaNO{sub 3} was added into NaCl/ZnCl{sub 2} (NaCl 80 mol%) to form ionothermal salts. • The resultant carbon possesses a 3D hierarchical structure, with more mesopores ratio than micropores. • When NaNO{sub 3} amount is 5% in the salt mixture, the optimal ORR activity was obtained. - Abstract: A facile one-pot method using NaNO{sub 3} as etching agent in a molten salt medium is developed to tune the porous structure and composition of N-doped carbon materials derived from biomass at high temperatures. SEM and TEM analyses reveal that by increasing the amount of NaNO{sub 3}, the structures of the obtained carbons become more open and graphene-like layers are formed. N{sub 2} adsorption/desorption isotherms show that the hierarchical porous structure could be efficiently tuned by adjusting the amount of NaNO{sub 3} in the salt mixture. It is observed that the specific surface area of the as-prepared N-doped carbon using NaNO{sub 3} can reach 1430.1 m{sup 2} g{sup −1}, a much higher value than that of the sample prepared in the absence of NaNO{sub 3}. The micropore ratio decreases with increased amount of NaNO{sub 3}, from 49.42% to 9.98%. Whilst the surface composition of the obtained carbon materials is affected by NaNO{sub 3}. The N content increases and O decreases respectively, by increasing the amount of NaNO{sub 3}. Analysis on the N 1s high resolution reveals that the sum of pyridinic-N and graphitic-N increased, whereas the sum of pyridinic-N oxide and NO{sub x} decreases from NC-0 to NC-0.75. It is also found that the changes of the porous structure and the oxygen-containing groups from NC-0 to NC-0.75 led to changes in hydrophilicity. When the as-prepared carbon materials are used as catalysts for the oxygen reduction reaction, high catalytic activity values are obtained, sample NC-0.5 shows the best performance due to the porous structure and doping effect of N atoms. More importantly, it is concluded that producing N-doped carbon materials from soybean dregs in molten salt medium using NaNO{sub 3} as etching agent could provide a promising approach for the synthesis of opened N-doped carbons of controlled porous structures and large specific surface areas based on biomass precursors.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗