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Nanosized graphene sheets enhanced photoelectric behavior of carbon film on p-silicon substrate
We found that nanosized graphene sheets enhanced the photoelectric behavior of graphene sheets embedded carbon (GSEC) film on p-silicon substrate, which was deposited under low energy electron irradiation in electron cyclotron resonance plasma. The GSEC/p-Si photodiode exhibited good photoelectric performance with photoresponsivity of 206 mA/W, rise and fall time of 2.2, and 4.3 μs for near-infrared (850 nm) light. The origin of the strong photoelectric behavior of GSEC film was ascribed to the appearance of graphene nanosheets, which led to higher barrier height and photoexcited electron-collection efficiency. This finding indicates that GSEC film has the potential for photoelectric applications.
On the main photoelectric characteristics of three-junction InGaP/InGaAs/Ge solar cells in a broad temperature range (–197°C ≤ T ≤ +85°C)
This study is aimed at investigating the main photoelectric characteristics of three-cascade InGaP/InGaAs/Ge photoelectric converters in a broad temperature range (–197°C ≤ T ≤ +85°C). On account of analysis of photosensitivity spectra and optical current–voltage characteristics, such temperature dependences as the open-circuit voltage (V{sub oc}), filling factor of the current–voltage characteristic (FF), and the photoelectric conversion efficiency of solar radiation are determined. Investigations are performed at illumination intensities corresponding to operation under concentrated radiation. Decreased temperatures facilitate the selection of samples with the minimal “parasitic” potential barriers. The influence of excitationtransfer processes from a cascade into a cascade is estimated by means of secondary luminescent radiation. The highest photoelectric conversion efficiency of 52% is measured at a concentration multiplicity of 100 “suns” and a temperature of–160°C.
Photoelectric Properties of GaN Layers Grown by Plasma-Assisted Molecular-Beam Epitaxy on Si(111) Substrates and SiC/Si(111) Epitaxial Layers
The photoelectric properties of GaN/SiC/Si(111) and GaN/Si(111) heterostructures grown by plasma-assisted molecular-beam epitaxy under the same growth conditions on identical silicon substrates, but with different buffer layers, are experimentally investigated. The GaN/SiC/Si(111) structure is formed on a Si substrate with the SiC buffer layer grown by a new atom-substitution technique and the GaN/Si(111) structure, on a Si substrate subjected to pre-epitaxial plasma nitridation. The significant effect of carbon-vacancy clusters contained in the SiC layer on the growth of the GaN layer and its optical and photoelectric properties is found. It is experimentally established that the GaN/SiC/Si(111) heterostructure has a higher photosensitivity than the GaN/Si(111) heterostructure. In the GaN/SiC/Si(111) heterostructure, the coexistence of two oppositely directed p–n junctions is observed. One p–n junction forms at the SiC/Si interface and the other, at the GaN/SiC interface. It is shown that the occurrence of an electric barrier in the GaN/Si(111) heterostructure at the GaN/Si(111) heterointerface is caused by the formation of a thin silicon-nitride transition layer during pre-epitaxial plasma nitridation of the Si(111) substrate.
Photoelectrical, photophysical and photocatalytic properties of Al based MOFs: MIL-53(Al) and MIL-53-NH{sub 2}(Al)
Two Al based MOFs (MIL-53(Al) and MIL-53-NH{sub 2} (Al)) were synthesized, and their photoelectrical, photophysical and photocatalytic properties towards oxygen evolution from water were investigated. Different from the ligand to metal charge transfer process previously reported, we proposes a new photocatalytic mechanism based on electron tunneling according to the results of theoretical calculation, steady state and time resolved fluorescence spectra. The organic linkers absorb photons, giving rise to electrons and holes. Then, the photogenerated electrons tunnel through the AlO{sub 6}-octahedra, which not only inhibit the recombination of photogenerated charge carriers, but also is a key factor to the photocatalytic activity of Al based MOFs. - Graphical abstract: The photoelectrical, photophysical and photocatalytic properties towards oxygen evolution from water of two Al based MOFs were investigated. A new photocatalytic mechanism was proposed based on electron tunneling according to the results of both theoretical calculation and steady state, time resolved fluorescence spectra. The electron tunneling process not only inhibit the recombination of photogenerated charge carriers, but also is a key factor to the photocatalytic activity of Al based MOFs.
Surface morphology and photoelectric properties of FTO ceramic thin films under a simple transparent cover-assisted laser annealing
Highlights: • A simple transparent cover-assisted laser annealing method was employed on FTO films. • The presence of coverslip or PET significantly affected the film surface morphology. • Coverslip- or PET-assisted laser annealing greatly increased grain size of the film. • The PET-assisted laser annealed FTO film exhibited the best photoelectric property. - Abstract: A simple transparent cover-assisted laser annealing strategy, which used a coverglass or a PET sheet as the transparent cover, was proposed to improve photoelectric properties of fluorine-doped tin oxide (FTO) thin films. Pure laser annealing was also performed for comparison. Transparent cover-assisted laser annealing was found to be more effective for producing densely distributed particles, decreasing surface roughness and increasing grain size, thus enhancing transmittance and conductivity of the film. More importantly, compared with coverglass-assisted laser annealing, PET-assisted laser annealing enabled the film surface to be covered with more uniform and denser particles and exhibit a remarkable increase in grain size. Therefore the film had the highest total transmittance of 84.32%, the highest specular transmittance of 75.88%, a slightly decreased haze of 10.01% and the lowest sheet resistance of 7.36 Ω/sq. The simple PET-assisted laser annealing method may be a promising substitution for the conventional laser annealing treatment.
CsPbBr 3 Perovskite Nanocrystal Grown on MXene Nanosheets for Enhanced Photoelectric Detection and Photocatalytic CO 2 Reduction
All-inorganic CsPbX 3 (X = Cl, Br or I) perovskite nanocrystals have attracted extensive interest recently due to their exceptional optoelectronic properties. In an effort to improve the charge separation and transfer following efficient exciton generation in such nanocrystals, novel functional nanocomposites were synthesized by the in situ growth of CsPbBr 3 perovskite nanocrystals on two-dimensional MXene nanosheets. Efficient excited state charge transfer occurs between CsPbBr 3 NCs and MXene nanosheets, as indicated by significant photoluminescence (PL) quenching and much shorter PL decay lifetimes compared with pure CsPbBr 3 NCs. The as-obtained CsPbBr 3 /MXene nanocomposites demonstrated increased photocurrent generation in response to visible light and X-ray illumination, attesting to the potential application of these heterostructure nanocomposites for photoelectric detection. The efficient charge transfer also renders the CsPbBr 3 /MXene nanocomposite an active photocatalyst for the reduction of CO 2 to CO and CH 4 . This work provides a guide for exploration of perovskite materials in next-generation optoelectronics, such as photoelectric detectors or photocatalyst.
Photoelectric absorption cross section of silicon near the bandgap from room temperature to sub-Kelvin temperature
The use of cryogenic silicon as a detector medium for dark matter searches is gaining popularity. Many of these searches are highly dependent on the value of the photoelectric absorption cross section of silicon at low temperatures, particularly near the silicon bandgap energy, where the searches are most sensitive to low mass dark matter candidates. While such cross section data have been lacking from the literature, previous dark matter search experiments have attempted to estimate this parameter by extrapolating it from higher temperature data. However, discrepancies in the high temperature data have led to order-of-magnitude differences in the extrapolations. In this paper, we resolve these discrepancies by using a novel technique to make a direct, low temperature measurement of the photoelectric absorption cross section of silicon at energies near the bandgap (1.2 eV–2.8 eV).
Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings
Sunlight drives photosynthesis and associated biological processes, and also influences inorganic processes that shape Earth’s climate and geochemistry. Bacterial solar-to-chemical energy conversion on this planet evolved to use an intricate intracellular process of phototrophy. However, a natural nonbiological counterpart to phototrophy has yet to be recognized. In this work, we reveal the inherent “phototrophic-like” behavior of vast expanses of natural rock/soil surfaces from deserts, red soils and karst environments, all of which can drive photon-to-electron conversions. Using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy and X-ray absorption spectroscopy, Fe and Mn (oxyhydr)oxide-rich coatings were found in rock varnishes, as were Fe (oxyhydr)oxides on red soil surfaces and minute amounts of Mn oxides on karst rock surfaces. By directly fabricating a photoelectric detection device on the thin section of a rock varnish sample, we have recorded the first in situ photocurrent micromapping of the coatings, which behave as highly sensitive and stable photoelectric systems. Additional measurements of red soil and powder separated from the outermost surface of karst rocks yielded photocurrents that are also sensitive to irradiation. The prominent solar-responsive capability of the phototrophic-like rocks/soils is ascribed to the semiconducting Fe and Mn (oxyhydr)oxide mineral coatings. The native semiconducting Fe/Mn-rich coatings may play a role similar in part to photosynthetic systems and thus provide a distinctive driving force for redox (bio)geochemistry on Earth’s surfaces.
Fourier Spectroscopy as a Method of Investigation of Photoelectric Properties of Organic Systems
A new method of investigation of photoelectric properties of layered thin-film structures based on broadband Fourier spectroscopy exhibiting a harmonically modulated optical delay is proposed. In contrast to traditional approaches to study photoelectric properties, which are based on application of dispersive spectral devices, the proposed method allows not only simultaneously covering the ultraviolet, visible, and infrared spectral ranges, while demonstrating a wide dynamic range and high spectral resolution, but also easily varying low-frequency modulation of the action of light. The capabilities of the method are demonstrated using a polycrystalline organic heterostructure as an example. Its spectral sensitivity, speed, and specific detectivity are measured. A model and an equivalent electric circuit are proposed for explanation of the results of the measurements.
X-Ray Spectro-polarimetry with Photoelectric Polarimeters
We derive a generalization of forward fitting for X-ray spectroscopy to include linear polarization of X-ray sources, appropriate for the anticipated next generation of space-based photoelectric polarimeters. We show that the inclusion of polarization sensitivity requires joint fitting to three observed spectra, one for each of the Stokes parameters, I(E), U(E), and Q(E). The equations for Stokes’ I(E) (the total intensity spectrum) are identical to the familiar case with no polarization sensitivity, and for which the model-predicted spectrum is obtained by a convolution of the source spectrum, F(E′), with the familiar energy response function, ϵ(E′) R(E′, E), where ϵ(E′) and R(E′, E) are the effective area and energy redistribution matrix, respectively. In addition to the energy spectrum, the two new relations for U(E) and Q(E) include the source polarization fraction and position angle versus energy, a(E′), and ψ{sub 0}{sup ′}(E{sup ′}), respectively, and the model-predicted spectra for these relations are obtained by a convolution with the “modulated” energy response function, μ(E′) ϵ (E′)R(E, E′), where μ(E′) is the energy-dependent modulation fraction that quantifies a polarimeter’s angular response to 100% polarized radiation. We present results of simulations with response parameters appropriate for the proposed PRAXyS Small Explorer observatory to illustrate the procedures and methods, and we discuss some aspects of photoelectric polarimeters with relevance to understanding their calibration and operation.
A New Search for Low-mass Dark Matter and an Examination and Reduction of the Uncertainty due to the Photoelectric Absorption Cross Section using a Cryogenic Silicon Detector with Single-charge Sensitivity
Many astrophysical observations point to the abundant existence of dark matter (DM) in the universe composed of particles beyond the Standard Model. However despite numerous experiments using different techniques, DM particles have yet to be directly observed. The Super Cryogenic Dark Matter Search (SuperCDMS) SNOLAB experiment will employ silicon and germanium crystal detectors operated at temperatures as low as 15~mK to probe DM interactions using phonon and ionization signals. Recently, R\&D; facilities have developed gram-sized high-voltage eV-scale (HVeV) silicon detectors that achieve single-electron-hole-pair resolution. By probing effective DM-electron interactions, these devices can be used for searches of low-mass DM candidates.This dissertation presents a DM search experiment known as HVeV Run~2 that employs a second-generation HVeV detector operated in an above-ground laboratory at Northwestern University (IL, USA). Energy spectra are obtained from a blind analysis with 0.39 and 1.2\,g-days of exposure with the detector biased at 60 and 100\,V, respectively. The 0.93~gram detector achieves a 3\,eV phonon energy resolution, corresponding to a world-leading charge resolution of 3\,\% of a single electron-hole pair for a detector bias of 100\,V. With charge carrier trapping and impact ionization effects incorporated into the DM signal models, the resulting exclusion limits are reported for inelastic DM-electron scattering for DM masses from 0.5--$10^{4}$\,MeV$/c^{2}$; in the mass range from 1.2--50\,eV$/c^{2}$ the limits for dark photon and axion-like particle absorption are reported.Several DM search experiments, including HVeV Run~2, are sensitive to low-mass DM candidates that rely on the temperature-dependent photoelectric absorption cross section of silicon. However discrepancies in the underlying literature data result in dominating systematic uncertainties on the DM exclusion limits. In order to reduce these systematic uncertainties, this dissertation presents a novel method of making a direct, low-temperature measurement of the photoelectric absorption cross section of silicon at energies near the band gap (1.2--2.8\,eV).
The Influence of EL2 Centers on the Photoelectric Response of an Array of Radial GaAs/AlGaAs Nanowires
We have studied the role of EL2 centers in formation of the photoelectric response of an array of radial n-type GaAs/Al{sub x}Ga{sub 1 –x}As (x = 0.3) nanowires (NWs) grown by molecular beam epitaxy on a p-type silicon substrate. Results revealed a significant decrease in the time of NW photoresponse recovery as compared to that in a bulk crystal upon the transition of EL2 centers from a metastable nonactive state to the normal ground state.
CALiPER Report 22.1: Photoelectric Performance of LED MR16 Lamps
This report is a follow-up to CALiPER Application Summary Report 22, which investigated the photometric performance of LED MR16 lamps. The initial report found that many of the LED MR16 lamps did not perform as required by ENERGY STAR based on their equivalency claims, although they generally did provide substantial efficacy advantages compared to halogen MR16 lamps. All testing was completed using laboratory power supplies, with all but one product tested at 12 V AC. In contrast, this report examined the photoelectric performance of the same set of lamps, using commercially available transformers and dimmers as well as laboratory power supplies providing both AC and DC power.
CALiPER Report 22.1: Photoelectric Performance of LED MR16 Lamps
This report looks at the photoelectric performance of the same set of lamps assessed in Report 22, using commercially available transformers and dimmers as well as laboratory power supplies providing either AC or DC. The investigation explores several issues related to the testing and use of MR16 lamps in lighting systems and examines the range of performance that is possible for a given lamp model, based on the system to which it is connected.
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.
Stoichiometric Effects on the Photoelectric Properties of LiInSe 2 Crystals for Neutron Detection
6 LiInSe 2 is a promising semiconductor candidate for thermal neutron detection due to its large capture cross-section. However, the charge collection efficiency is still insufficient for high resolution for the grown-in defects induced by the stoichiometric deviation. In this work, we report photoelectric properties of stoichiometric LiInSe 2 crystal boules up to 70 mm in length and 20 mm in diameter grown by the vertical Bridgman method. Inductively coupled plasma measurements demonstrate that the ratio of Li, In, and Se of the as-grown crystal is very close to 1:1:2, which is optimized by low temperature synthesis processing. The obtained single crystals display high bulk resistivity in the range of 10 11 –10 12 Ω·cm and a direct band gap of 2.01–2.83 eV with a changeable color from red to yellow. The electronic structure of LiInSe 2 was studied using first-principles density functional theory calculations, which predicts that the antisite defects of In Li and Li In are the dominant factor for the different crystal colors observed. The stoichiometric LiInSe 2 crystal gives an improved energy resolution, for a semiconductor detector when illuminated with a 241 Am@5.48 MeV α source, of 23.3%. In conclusion, the electron mobility-lifetime product (μτ) is ~2.5 × 10 –5 cm 2 V –1 .