Zn Diffusion Research Articles

Trap-limited diffusion of Zn in β−Ga2O3

Diffusion of Zn in (001)- and $(\overline{2}01)$-oriented $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ was studied using secondary-ion mass spectrometry and first-principles calculations based on hybrid and semilocal functionals. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ samples were sealed in quartz ampules together with a piece of metallic Zn and heated to temperatures of 900--1100 ${}^{\ensuremath{\circ}}\mathrm{C}$ for 1 h. The Zn concentration profiles as a function of depth were simulated by employing the trap-limited diffusion model. From this model the migration barrier for Zn diffusion was found to be ${E}_{m}=2.2\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{4.pt}{0ex}}$ and $2.1\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{4.pt}{0ex}}\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ in the (001) and ($\overline{2}01$) orientations of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$, respectively, with corresponding dissociation energies of ${E}_{d}$ = 3.5 $\ifmmode\pm\else\textpm\fi{}1.1$ and $3.2\ifmmode\pm\else\textpm\fi{}0.6\phantom{\rule{4.pt}{0ex}}\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. Results from the first-principles calculations predict an interstitialcy mechanism for the Zn diffusion when it is not in its trapped state. Using the nudged elastic band method, we obtain a barrier of 1.6 eV for migration of Zn split interstitials $({\mathrm{Zn}}_{i})$ in both the [001] and $[\overline{2}01]$ directions, in accordance with the results obtained from the trap-limited diffusion model. Interestingly, the Ga vacancy is found to be able to trap two Zn atoms forming a shallow donor complex labeled ${\mathrm{Zn}}_{i}{\mathrm{Zn}}_{\mathrm{Ga}}$. The energy needed for ${\mathrm{Zn}}_{i}$ to dissociate from this donor complex is estimated to be 2.99 eV, in reasonable agreement with the trap dissociation energies extracted from the diffusion model.

Does Zn mimic diffusion of Al in the HCP Al-Sc-Hf-Ti-Zr high entropy alloys?

The presence of Al in the hexagonal close-packed (HCP) Al-Sc-Hf-Ti-Zr high-entropy-alloy system was previously found to be a primary reason for partial D019 ordering. Since tracer measurements of Al self-diffusion are extremely challenging due to the absence of a suitable radioisotope, in this work, diffusion of Zn as a solute element is investigated for two HCP Al-Sc-Hf-Ti-Zr alloys. The experimental results on diffusion of the 65Zn radioisotope are benchmarked against Al diffusion rates predicted by kinetic Monte Carlo simulations using ab initio-informed calculations of the vacancy formation and migration energies. Furthermore, the partitioning of Zn and the mechanism of Zn diffusion are evaluated. Similarities between Zn and Al diffusion in the investigated HCP Al-Sc-Hf-Ti-Zr alloys are traced back to correlations between the corresponding chemically resolved site substitution energies and migration barriers.

Guard Ring Design to Prevent Edge Breakdown in Double-Diffused Planar InGaAs/InP Avalanche Photodiodes

We report on the design of an attached guard ring (AGR) and a floating guard ring (FGR) in a planar separate absorption, grading, charge, and multiplication In0.53Ga0.47As/InP avalanche photodiode to prevent premature edge breakdowns. The depths of the two Zn diffusions were utilized to manipulate the guard ring structures. Results from TCAD simulation indicate that the optimal AGR diffusion depth is right at the turning point where the breakdown current shifts from the edge of active region to the AGR region. The devices with optimal AGR depth contain significantly higher breakdown voltages than those of devices either with shallower-or without any- AGR. For the FGR design, a series of devices with different spacings between AGR and FGR and different FGR opening widths for diffusion were fabricated and characterized. We show that when the spacing is longer than the critical value, the breakdown voltage can increase ~1.5 V higher than those of the APD devices without FGR. In addition, the wider the FGR opening width, the higher the breakdown voltage. TCAD simulations were also performed to study the effect of FGR, but showed less pronounced improvements, which could be due the discrepancy between the calculated and experimental diffusion profile.

Improvement of Magnetic Properties of Zn-bonded Sm-Fe-N Magnets and Investigation of Microstructural Changes at Sm<sub>2</sub>Fe<sub>17</sub>–Zn Interface

This paper reviewed development of Zn-bonded Sm-Fe-N magnets in our group, and reported interfacial diffusion and phase changes at the Sm2Fe17–Zn interface during annealing. For increasing magnetic properties of Zn-bonded Sm-Fe-N magnets, decreasing oxygen content, improving dispersibility of Zn, and increasing relative density are necessary, therefore we prepared low oxygen content Sm-Fe-N and fine Zn powders. The powders were sintered by spark plasma sintering process for increasing density under low oxygen atmosphere resulting in obtaining high (BH)max of 200 kJm-3 with relatively high coercivity of 1.28 MAm-1 and β(HcJ) of –0.34%C-1. In order to further improve the (BH)max, it is necessary to control interfacial diffusion and reaction between Sm2Fe17N3 and Zn phases. Thus, as a first step, microstructural changes and interdiffusion coefficient at the Sm2Fe17–Zn interface were investigated using Sm2Fe17–Zn diffusion couples, in this study. It was clear that interdiffusion of Zn, Fe and Sm occurred during annealing below melting temperature of Zn, and the diffusion rate of Zn was faster than those of Fe and Sm. Furthermore, with Zn diffusing into Sm2Fe17 phase, the Sm2Fe17 decompose to ThMn12-Sm(Zn,Fe)12 and α-FeZn phases with specific crystal orientation relationship.

Microstructural evaluation in dissimilar liquid phase bonding of cast Al–Si alloy and stainless steel using pure zinc filler metal

The metallurgical joining between cast A359 aluminium alloy and AISI321 stainless steel using pure Zn as the interlayer was performed slightly above Al–Zn eutectic temperature. The liquid phase was formed by a eutectic reaction between Al and Zn and subsequently isothermally solidified by diffusion of Zn into the A359 base metal (i.e. reactive transient liquid phase bonding). The formation of a Zn-rich diffusion affected zone in A359, incorporation of Si particles into the bond zone, formation of a thin Al–Fe–Si intermetallic at the steel interface, and isothermal solidification of the liquid phase and subsequent Al–Zn eutectoid transformation govern the microstructure of the joint. The resultant bond microstructure does not deleteriously affect the heat sink function of Al base metal.

Zn–Al pack co-cementation on AISI 1020 steel: structural, mechanical and tribological appraisal

ABSTRACT This study examined the effect of different Al concentrations on the structural transformation of pack cementation Zn–Al coatings on AISI 1020 steel. The resultant Zn–Al coatings were investigated using scanning electron microscopy, energy dispersive spectroscopy and X–ray diffraction to observe the coating morphology, thickness, structure, and compositional migration. A laminated coating assembly was prepared, in which an initial intermediate Zn–rich layer was followed by an Fe–Zn inner layer and Fe–Al top layer. Elemental analysis revealed a correlation between the formation of voids and the diffusion of Al, Fe, and Zn. The coated specimen demonstrated desirable mechanical strength and improved abrasive resistance, whereas the tribological capability of the Zn–Al coating could be tailored by varying the Al concentration.

Mechanism of room-temperature superplasticity in ultrafine-grained Al–Zn alloys

Superplastic deformation of polycrystalline materials is usually accommodated by diffusion-assisted grain boundary (GB) sliding at high temperatures. Lowering the temperature requirement for commercial superplastic forming enables green and cost-effective manufacturing. Recently, room-temperature (RT) superplasticity was realized in ultrafine-grained Al–Zn based alloys, but the underlying mechanism remains unclear. Here, we conducted in-situ tensile straining and post-mortem electron microscopy characterization, and atomistic density functional theory simulation to understand the RT superplasticity of an Al–15 Zn (at%) alloy. Results showed that the superplasticity is achieved by GB sliding and grain rotation, assisted by the continuous diffusion of Zn. In-situ observations showed Zn atoms diffusing from within grains to GBs, resulting in a Zn nanolayer at the GBs that acts as a solid lubricant to decrease the energy barrier of GB sliding. This research advances our understanding of diffusion-assisted deformation mechanism that is a prerequisite for the rational design of new materials with RT superplasticity.

Gradient multi-layered aluminum sheet with excellent corrosion resistance

Diffusion is a very important phenomenon in the thermal processing, including Cu diffusion, Si diffusion and Zn diffusion in the sheet during brazing. Specifically, the migration of Si affects the amount of liquid metal that can be used to form joint, and further affects the solubility of solid substrate at the liquid–solid interface between the clad alloy and core alloy. In addition, Cu accumulates on Al(Fe,Mn)Si precipitates and in Al–Si eutectic at the grain boundaries. Compared with Al matrix, the formation of Al(Fe,Mn,Cu)Si enhances the potential difference between these materials. These events greatly damaged the corrosion resistance of the sheets. Due to the existence of the interlayer, Zn in the interlayer diffuses to the core layer, and the concentration of dissolved zinc decreases with the increase of depth, resulting in an increasing potential of the Al matrix towards the core layer. With depth from the surface to the core layer, the Al matrix is more cathodic, which promoting lateral corrosion within the interlayer region, prevents through failure and which protects the core alloy. Diffusion during brazing leads to microstructure evolution and local electrochemical characteristics of different layers. The optimized potential gradient of the clad layer-interlayer-core layer can greatly improve the corrosion resistance of the alloy.

Slow-Release Humic Acid-Based Zinc Fertilizers Improve Growth and Nutrition of Maize and Brachiaria Grass Successively Grown in Oxisols

Zinc (Zn) fertilization efficiency is often low in Oxisols due to the interaction of Zn with soil constituents and phosphorus (P). When Zn is supplied in soil fertilization as a complex via slow-release organomineral fertilizers (OMFs), it is less prone to react with soil constituents and P, thus increasing the efficiency of Zn supply to crops. However, obtaining effective synthesis routes for the production of enhanced-efficiency Zn-OMFs for Oxisols is still a challenge. In this study, we synthesized Zn-OMFs based on humic acid (HA) components in order to assess features concerning Zn complexation and release kinetics, as well as the agronomic performance of such products on biomass production, and Zn and P nutrition of maize and Brachiaria grass successively grown in two Oxisols with contrasting texture and soil organic matter (OM) content. Infrared analyses indicated that Zn was complexed in OMFs by sulfur and carbon groups, with kinetics studies showing that Zn is gradually released to soil from Zn-OMFs. Consequently, Zn diffusion and initial content in soil solution were reduced in Oxisols. At least one of the OMFs overperformed ZnSO4 in terms of maize biomass production and Zn shoot accumulation. Moreover, residual effects of OMFs were greater than those of ZnSO4 in Oxisols for Brachiaria grass cultivated after maize, with increases in biomass production and shoot Zn content varying depending on OMFs and Oxisol properties. A secondary effect of OMFs increasing P availability in the soil and P uptake by maize and Brachiaria grass plants was also noteworthy. Our findings showed that the overall agronomic performance was greater for OMFs when compared with ZnSO4, which is likely related to the slow release of nutrients by the synthetized OMFs due to Zn complexation by HA.

Improved GaInP/GaAs/GaInAs inverted metamorphic triple-junction solar cells by reduction of Zn diffusion in the top subcell

The growth of heavily doped tunnel junctions in inverted metamorphic multijunction solar cells induces a strong diffusion of Zn via a point-defects-assisted mechanism. The redistribution of Zn can compensate the n-type doping in the emitter of the GaInP top junction, degrading severely the conductivity of the whole solar cell and its conversion efficiency. This work evaluates different epitaxial growth strategies to achieve control on the Zn profile of an inverted metamorphic triple-junction structure, including: the reduction of the doping concentration in the tunnel junction to minimize the injection of point defects that trigger the diffusion mechanism; the use of different barrier layers to keep the injected point defects away from active layers and, finally, the minimization of Zn concentration in the AlGaInP back-surface-field layer of the GaInP subcell. This last approach enables a high-conductivity multijunction solar cell device without redesigning the tunnel junction as well as a high electronic quality in the GaInP subcell, which shows a collection efficiency higher than 93% and an open-circuit-voltage offset of 410 mV at 1 sun irradiance. The characterization of final triple-junction devices, including quantum efficiency, electroluminescence, and light current-density-voltage curves at different irradiances, demonstrates a successful integration of all the subcell and tunnel junction components. This way, final solar cells with peak efficiencies exceeding 40% at 500 suns are demonstrated, despite using doping levels in the AlGaInP:Zn back-surface-field of the GaInP subcell and using non-optimized antireflective coatings.

Study on Bi3+-Al3+ co-doped YIG for co-firing YIG-Al0.2/NZF ferrite composite substrates

Y2.5-xBi0.5AlxFe5O12 (YIG-Alx) ceramics have been synthesized at 1175 ℃ by the solid-state reaction method. The effects of the co-doped Bi3+, Al3+ ions on the phases, micromorphology, and dielectric and magnetic properties of the yttrium iron garnets (YIG) were investigated. Excessive introduction of Al3+ ions led to the collapse of the YIG lattice and precipitation of the Bi3+ and Fe3+ ions; while moderate Al3+ doping improved the dielectric properties, but not the saturation magnetization. The YIG-Al0.2 ceramics proved to have particularly good electromagnetic properties (εr = 18.34 ± 0.05@11.19 GHz, tanδ = 3.09 ± 0.55 × 10−4, Ms = 19.82 ± 0.55 emu/g). Additionally, tightly bonded Y2.3Bi0.5Al0.2Fe5O12/Ni0.8Zn0.2Fe2O4 (YIG-Al0.2/NZF) composite substrates were prepared by co-firing at 1175 ℃. The composite substrates exhibited superior electromagnetic properties (YIG-Al0.2: εr = 18.37 ± 0.05@11.15 GHz, tanδ = 3.08 ± 0.55 × 10−4, Ms = 21.09 ± 0.55 emu/g; NZF: Ms = 67.5 ± 0.55 emu/g), which were slightly affected by the diffusion of Ni and Zn from the NZF. Our findings show that YIG-Al0.2/NZF substrates have great potential for use as RF band circulators.

Zinc isotope fractionation in mantle rocks and minerals, and a revised δ66Zn value for the Bulk Silicate Earth

The isotope composition of zinc (Zn) can be an important tracer of planetary formation and differentiation, but estimates of the Bulk Silicate Earth (BSE) and the extent and origin of Zn isotope variations in the mantle continue to be debated. We report 153 high-precision Zn isotope analyses of whole-rock samples and minerals of well-characterized, mantle-derived spinel and garnet peridotites from five sites in Siberia, Mongolia and China: 38 xenoliths in basaltic rocks (fertile to strongly melt-depleted as well as variably metasomatized or veined peridotites) and 3 orogenic peridotites. Data quality was rigorously tested by twenty-two duplicated analyses using several dissolution techniques. Spinel (Sp) contains 760–1460 μg/g Zn and hosts up to 58 % of whole-rock Zn budget in the peridotites followed by olivine (Ol, 30–66 % of whole-rock Zn budget), orthopyroxene (Opx), clinopyroxene (Cpx) and garnet, with abundance ratios of [Zn]Sp/[Zn]Ol = 15–47, [Zn]Ol/[Zn]Opx = ∼1.5, [Zn]Ol/[Zn]Cpx = ∼6. Spinel has higher δ66Zn values than coexisting silicates (∼0.12 ‰ higher than in Ol). Minerals in orogenic peridotites show disequilibrium Zn element and isotope partitioning due to slow inter-grain Zn diffusion at retrograde metamorphism.Fertile peridotites (≥3 wt% Al2O3) contain 52–60 μg/g Zn, usually higher than melt-depleted (<3 wt% Al2O3) rocks (40–53 μg/g). The δ66Zn values in the majority of spinel and garnet peridotites range from 0.11 to 0.26 ‰ and show no systematic co-variations with melt extraction indices (e.g., Al2O3, Mg#), suggesting, unlike some previous studies, that partial melting does not appreciably affect Zn isotope composition of residual mantle. Garnet lherzolites yield an average δ66Zn of 0.22 ± 0.09 ‰ (2SD), similar to that (0.18 ± 0.07 ‰, 2SD) for shallower spinel peridotites, indicating uniform Zn isotope composition with depth. Four fertile lherzolites from earlier work, duplicated in this study to assess inter-laboratory bias, fall in the same δ66Zn range, suggesting that previously reported higher δ66Zn for these samples could be due to analytical problems. We thus estimate the δ66Zn of the BSE at 0.19 ± 0.08 ‰ (2SD) based on suitable fertile peridotites from several localities in this study and the literature.The δ66Zn values (−0.10 to 0.04 ‰) are much lower in Fe-rich (9.3–13.1 wt% FeOT) and veined spinel peridotites as well as in spinel pyroxenite veins from Mongolia (−0.20 to 0.11 ‰). The Fe-rich peridotites and pyroxenites are rich in Zn (up to 113 μg/g) and were previously found to have anomalously low δ56Fe (−0.33 to − 0.27 ‰) and δ53Cr (−1.36 to − 0.05 ‰). We attribute these features to kinetic isotope fractionation during reaction with mafic melts migrating in conduits in the lithospheric mantle or intrusion of Fe-Zn-rich melts with light Fe-Zn isotope compositions. Kinetic Zn isotope fractionation, rather than equilibrium partial melting, may be a major cause of Zn isotope heterogeneity in the mantle.

(Invited) Achieving High-Power Single-Mode Operation in Vertical-Cavity Surface-Emitting Lasers Via Scalable, Higher-Order Mode Suppression Techniques

Achieving high-power single-mode operation in Vertical-Cavity Surface-Emitting Lasers (VCSELs) has received renewed interest because of applications that span facial recognition and 3D imaging in mobile telephones, Light Detection and Ranging (LiDAR) for autonomous vehicles, and Pulse Amplitude Modulation (PAM-4) for high-speed (>100 Gbps) data transmission within data centers. A key challenge with oxide-confined VCSELs is that the strong refractive index contrast between the oxidized ~AlAs aperture and surrounding AlGaAs layers combined with the oxide aperture size create a photonic cavity that fundamentally supports multiple transverse modes. When the size of the aperture is reduced to create a single-mode cavity, the output power is limited by the electrically pumped gain region within the aperture. There is thus a fundamental trade-off between size and power which manifests itself in a limited capability to simultaneously achieve high power and single mode operation. Various methods have been employed by groups working on VCSELs to overcome this limitation. Neglecting external cavity methods which are fundamentally not scalable, the most promising results have been achieved by groups using etched surface relief where a pattern is etched in the top layer or layers to change the standing wave pattern in the cavity and reduce modal gain by lowering the magnitude of the electric field in regions overlapping with the quantum wells, which provide laser gain. A downside of this approach is that material is removed, impacting the uniformity of current injection across the area of the device. A key question of interest is therefore how to achieve mode suppression in large area devices in a way that does not impact current injection. In this presentation, novel methods for mode control that rely on spatial variation of modal gain across the area of the VCSEL aperture will be discussed, and results on high-power single-mode operations of VCSELs will be presented. Two distinct mode control methods will be reviewed. The first method of mode control uses deposited optical coatings on the top surface of the VCSEL to spatially modify the electric field standing wave in the quantum well heterostructure region. Through patterning the coating in either a pillar or anulus, specific modes can be suppressed by selectively changing the gain available for those modes. These filters have been made using both SiO2/TiO2 stacks and alternatively a single layer of silicon. The capability to pattern these layers in a wafer-scale process makes this method attractive for volume manufacturing. The second method of mode control utilizes impurity-induced layer disordering via patterned diffusion of Zn to selectively intermix Distributed Bragg Reflector (DBR) layers, thereby creating a top laser mirror whose reflectivity varies spatially across the aperture. Designing the diffused region to maximize overlap with high-order modes while minimizing overlap with the fundamental mode provides mode suppression and enhanced single-mode power. An added benefit of this approach is a reduction in resistance through the device top DBR layers brought about by the higher p-doping level in the Zn-diffused regions, minimizing Ohmic losses and heat generation. Through the use of strain control in the diffusion mask, diffusion front shape is also shown to be controllable in a way that can be used to minimize the impact of the diffused region on fundamental mode reflectivity. Tensile and compressive strain of diffusion masks are shown to have differing effects on vertical (into the device) versus lateral (across the area of the device under the mask) diffusion, allowing more precise spatial control of reflectivity. Using these methods, single-mode output powers in excess of 10 mW have been demonstrated, with side-mode suppression ratios in excess of 30 dB. These results will be discussed, as well as further work to enhance VCSEL performance. Figure 1

Liquid metal embrittlement cracking behavior in iron-zinc (Fe/Zn) couple: Comparison of ferritic and austenitic microstructures

• The liquid–metal-embrittlement (LME) was studied in ferritic and austenitic samples. • The ferritic sample showed higher sensitivity to LME crack initiation. • The austenitic specimen displayed higher LME crack propagation rate. • Crack propagation was accelerated by phase transformation and segregation. Liquid metal embrittlement (LME) has emerged as a major concern when developing high-strength automotive steels. However, information regarding the impact of initial microstructure on LME severity is limited in the Fe/Zn couple. Specifically, there is no consensus as to which ferritic and austenitic microstructures are more susceptible to LME cracking. The present study aims to examine the LME cracking behavior of fully ferritic and austenitic microstructures under the same thermomechanical conditions. It was shown that the ferritic microstructure has a higher sensitivity to LME crack initiation, whereas the austenitic specimen displayed a much longer average crack length, which indicates higher crack propagation rate than the ferritic specimen. It has been determined that in-situ austenite to ferrite transformations during Zn diffusion, as well as grain boundary segregation of alloying elements such as Cr and Ti, contribute to the LME propagation rate.

Wood-based electrodes enabling stable, anti-freezing, and flexible aqueous zinc-ion batteries

• 3D hierarchical Zn electrode is prepared by using wood veneer as the raw material. • The wood-based electrode owns large electrical conductivity and tensile strength. • The desolvation, Zn deposition kinetics, and deposition uniformity can be promoted. • The wood-based electrode can inhibit Zn dendrites and harmful side reactions. • The wood-based battery shows high tolerance to deformations and low temperatures. As the treasure on the earth, forest resources should be utilized in a high value-added and efficient way. Herein, a wood-based quasi-solid-state aqueous zinc ion battery (AZIB) is developed to address the issues of AZIBs, i.e. , low Zn stripping/plating reversibility and poor tolerance to low-temperature environments. Particularly, the anode is fabricated by ultraviolet light irradiation-assisted delignification of wood veneer and subsequent decoration of metallic Ni and Zn. This wood-based electrode exhibits large electrical conductivity, good affinity to aqueous electrolyte, high tensile strength, and can combine the advantages of unique structure and cellulose framework from wood. It is found that this electrode can considerably restrict two-dimensional diffusion of Zn 2+ ions, facilitate desolvation process, improve Zn deposition kinetics, and inhibit Zn metal corrosion, thereby significantly stabilizing Zn deposition behavior. Thanks to that, the Zn//Zn cell with wood-based electrodes can deliver a long lifespan of 900 h at 2 mA cm −2 and 2 mAh cm −2 . Besides, wood-derived current collector and nanocellulose are used to construct cathode and hydrogel electrolyte, respectively. The assembled wood-based AZIB delivers superior performances even at −20 °C and under bending. The strategy in this work could be extended in other flexible energy storage systems.

Continuous, crystalline Sb2S3 ultrathin light absorber coatings in solar cells based on photonic concentric p-i-n heterojunctions

Many modern types of solar cells that rely exclusively on earth-abundant non-toxic materials include interfaces between a heavier metal chalcogenide and another type of semiconductor. Often, the chemical (adhesion) and physical (charge transfer) characteristics of those interfaces are the defining factors for the final device performance. Here, we describe that a ZnS adhesion layer is not sufficient to prevent the dewetting of Sb2S3 upon annealing a thin layer of it on an oxidic surface if the substrate is not planar and features highly curved surfaces. An ALD-coated sacrificial capping layer of ZnO prevents the morphological rearrangements of Sb2S3 during thermal crystallization and can be removed subsequently. When implemented towards a photovoltaic p-i-n heterojunction, this strategy furnishes perfect conformality of the layer stack but unsatisfactory performance. The correlation of interface chemistry with the electrical properties and the device performance identifies a reducing effect of ZnO atomic layer deposition chemistry on the Sb2S3 surface as the cause of Zn diffusion into the light absorbing semiconductor. This deleterious doping can be prevented by a preliminary oxidative treatment of the Sb2S3 surface with ozone. When applied to a structured substrate consisting of ordered arrays of nanospheres, this approach yields the first ever concentric p-i-n heterojunction solar cells with photonic light trapping effect—a geometry which in comparison with standard scattering layers’on top’ inherently generates a very large refractive index contrast. In the red part of the visible spectrum, light absorption amounts to the value expected with four passes through a planar layer of the thickness used here (35 nm Sb2S3). This effect allows us to demonstrate >5% overall solar energy conversion efficiency with only 35 nm of a simple light absorber phase that uses no toxic, rare materials.

Cobalt-doped molybdenum disulfide with rich defects and extended layered structure for rechargeable zinc-ion batteries

Zinc-ion batteries (ZIBs) have become potential energy storage devices due to its low cost, environmentally friendly and high safety. The development of ZIBs is facing huge challenges especially in cathode materials. Here, we report a strategy of doping Co into MoS 2 to get Co x Mo 1−x S 2 nanosheets with rich dislocation-defects and expanded layer spacing. MoS 2 itself has poor Zn 2+ diffusivity and low specific capacity due to small layer spacing. The diffusion of Zn 2+ is greatly improved by doping of Co. When Co x Mo 1−x S 2 nanosheets are used as positive electrode in ZIBs, the capacity increased from 31.3 mA h g −1 to 164.1 mA h g −1 , which is increased by more than five times. What’s more, even if the current is increased ten times, it still has high capacity (about 40% capacity retention). In addition, the peaks of the Zn 2+ intercalation/deintercalation in the Co x Mo 1−x S 2 electrode have been effectively improved, which indicates a much more efficiency Zn 2+ intercalation kinetic. Therefore, its capacity has been greatly improved. This research provides a general and effective strategy to reduce the embedding energy barrier of Zn 2+ to increase the diffusion rate of Zn 2+ and the capacity of ZIBs. • The addition of Co leads to dislocations defects and extending the layer spacing. • The transition metal doping method is convenient and efficient. • The rapid diffusion of Zn 2+ is achieved and the capacity is increased.

Photophysics and photovoltaic properties of Zn-alloyed Ag-In-S quantum dots sensitized solar cells

Quantum dots (QDs) have attracted attention for use in photovoltaic applications. However, till now, QDs sensitized liquid junction solar cells (QDSCs) are primary concentrated on binary QDs that contain toxic elements which limit their practical applications in regarding of environmental issues. Hence, the study of less-toxic ternary such as AgInS2 (AIS) and CuInS2 (CIS) or core/shell AIS/ZnS and CIS/ZnS QDs with high power conversion efficiency (PCE) is the most common way for commercial applications. Although significant improvement has been realized for AIS (CIS) QDSCs by overgrowth of wide bandgap ZnS to form quasi type-I core/shell structure for eliminating surface trapping defects where the PCE is comparable or even better than toxic QDs, simultaneously the shell could also cause impeding electron injection from QDs to metal oxide matrix (TiO2) and hole scavenge. For resolving this problem, diffusion of Zn2+ into QDs forming alloyed QDs is a better strategy to improve the conductivity and thus the PCE owing to alloyed QDs could not only reduce the density of trap defects but also regulate the bandgap and contribute to electron injection. Herein, the highly luminescent heavy-metal free and hydrophilic Ag-In-S-Zn alloyed QDs with broad light harvesting range to near infrared (NIR) were synthesized as effective sensitizer for constructing QDSCs, where the optimal PCE of 3.12% was achieved. Moreover, surface passivation by deposition of ZnS layer over the sensitized electrode was also primarily studied to decrease the QDs/electrolyte/TiO2 interface recombination and a champion PCE of 3.78% was obtained.

Electronic transport mechanism and defect states for p-InP/i-InGaAs/n-InP photodiodes

We have studied the defect states and electronic transport mechanisms in the mismatched p-InP/i-InGaAs/n-InP photodiode grown by molecular beam epitaxy (MBE) using deep-level transient spectroscopy (DLTS) and current–voltage (I–V) measurements. Two defect states were observed in the p-InP layer, which could have originated from Zn diffusion, and another one detected in i-InGaAs acted as a dislocation defect. The total defect density of the device estimated by DLTS and space-charge limited current (SCLC) was about 4 × 1013, which was much lower than the device grown by other methods. I–V measurements pointed out that the leakage current in this photodiode was caused by the existence of defect states and the small conduction band offset. Therefore, to suppress the leakage current in the devices, it is urgent to reduce the trap density and optimize the thickness of the p-InP layer. The study of defect state and electronic transport mechanism in p-InP/i-InGaAs/n-InP PIN diodes could help to develop a strategy to improve the SWIR sensing technology in the future.

Control over the Surface Properties of Zinc Oxide Powders via Combining Mechanical, Electron Beam, and Thermal Processing.

The surface properties of zinc oxide powders prepared using mechanical activation, electron beam irradiation, and vacuum annealing, as well using combinations of these types of treatments, were studied using X-ray photoelectron spectroscopy. The structure of the obtained materials was studied by an X-ray diffraction technique and by scanning electron microscopy. We found that over five hours of grinding in an attritor, the size of nanocrystals decreases from 37 to 21 nm, and microdeformations increase from 0.3% to 0.6%. It was also found that a five-hour grinding treatment promoted formation of vacancies in the zinc sublattice at the surface and diffusion of Zn2+ cations into the bulk of the material. Irradiation of commercial zinc oxide powders with an electron beam with an energy of 0.9 MeV and a dose of 1 MGy induced breaking of Zn–O bonds, diffusion of interstitial zinc ions into the bulk, and oxygen atom escape from regular positions into the gas phase. A combined treatment of five hours of grinding and electron beam irradiation promoted accumulation of interstitial zinc ions at the surface of the material. Annealing of both initial and mechanically activated ZnO powders at temperatures up to 400 °C did not lead to a significant change in the properties of the samples. Upon exceeding the 400 °C annealing temperature the X-ray photoelectron spectra show almost identical atomic composition of the two types of materials, which is related to diffusion of interstitial zinc ions from the bulk of the material to the surface.