Donor Concentration Research Articles

Transport and trap states in proton irradiated ultra-thick κ-Ga2O3

Changes induced by irradiation with 1.1 MeV protons in the transport properties and deep trap spectra of thick (>80 μm) undoped κ-Ga2O3 layers grown on sapphire are reported. Prior to irradiation, the films had a donor concentration of ∼1015 cm−3, with the two dominant donors having ionization energies of 0.25 and 0.15 eV, respectively. The main electron traps were located at Ec−0.7 eV. Deep acceptor spectra measured by capacitance-voltage profiling under illumination showed optical ionization thresholds near 2, 2.8, and 3.4 eV. The diffusion length of nonequilibrium charge carriers for ɛ-Ga2O3 was 70 ± 5 nm prior to irradiation. After irradiation with 1.1 MeV protons to a fluence of 1014 cm−2, there was total depletion of mobile charge carriers in the top 4.5 μm of the film, close to the estimated proton range. The carrier removal rate was 10–20 cm−1, a factor of 5–10 lower than in β-Ga2O3, while the concentration of deep acceptors in the lower half of the bandgap and the diffusion length showed no significant change.

CuO decorated graphene TiO2 derived MIL-125 nanocomposite with enhanced photo-response as a highly efficient indirect sunlight driven photocatalyst

Advanced Oxidation Processes (AOPs) are utilized to remove a large range of pollution in water by heterogeneous photocatalysis with production of electron-hole pairs by light. Herein, we showed the preparation of GO/MIL-125 by a simple solvothermal method and then the addition CuO by a simple wet impregnation method. MIL-125 and their derived have attracted considerable attraction due to high earth’s crust abundance, low toxicity, unique photo redox property and photocatalytic application. The photocatalyst, 5CuO/10GO/MIl-125 which was calcined at 600 ◦C (CuTG-600), with a bandgap of 2.82 eV, was utilized to degrade Rhodamine B (RhB) dye which is oxidized to CO2 and H2O. The characterization of different samples was investigated using FT-IR, XRD, XPS, SEM, EDX mapping, UV–vis spectroscopy, Linear sweep voltammetry, photocurrent response, electrochemical impedance spectroscopy (EIS) and Mott-Schottky plots. The combination of GO and CuO increases the degradation activity of RhB dye under irradiation of visible light (λ = 380–780), (blue LED lamp (λ = 450 nm) and red LED lamp (λ = 610 nm)) and the higher results were showed by 5CuTG-600. Photodegradation kinetics were explained by various parameters such as calcination, catalyst type, pH, dye concentration, catalyst dose, different lamps with different wavelengths, different scavengers and reusability. Furthermore, The Photoelectrochemical test results were noticed that the activity of 5CuTG-600 is higher than that of TG-600 and T-600 due to higher donor concentration (ND), and lower recombination process of the charge carrier. Finally, we obtain 5CuTG-600 which acts as an important photocatalyst and is used in environmental and electrochemical applications.

Electrical properties of highly nitrogen-doped 6H-SiC single crystals: Microwave cavity perturbation study

The silicon carbide (SiC) single crystals of 6H polytype with nitrogen donor concentration ND – NA) ≈ 1∙1017 ...4∙1019 cm –3 grown using the modified Lely method were studied applying the cavity perturbation method. From the temperature dependence of the resonant frequency shift and microwave loss of the cavity loaded with samples under study, the temperature dependence of the conductivity was estimated. From the temperature dependence of the natural logarithm of conductivity versus 1000/T, the activation energies for processes corresponding to electron transitions from impurity levels to the conduction band (ε1) and electron hopping over nitrogen donors in the D0 bands (ε3) were determined. It was found that in 6H-SiC ε1 = 50 meV for (ND – NA) ≈ 1∙10 17 cm –3 , ε1 = 32 meV and ε3 = 6 meV for (ND – NA) ≈ 1∙1019cm–3 , ε1 = 13.5 meV and ε3 = 3.5 meV for ((ND – NA) ≈ 4∙1019 cm–3.

Photoelectrochemical CO2 Reduction at a Direct CuInGaS2/Electrolyte Junction.

Photoelectrochemical (PEC) CO2 reduction has received considerable attention given the inherent sustainability and simplicity of directly converting solar energy into carbon-based chemical fuels. However, complex photocathode architectures with protecting layers and cocatalysts are typically needed for selective and stable operation. We report herein that bare CuIn0.3Ga0.7S2 photocathodes can drive the PEC CO2 reduction with a benchmarking 1 Sun photocurrent density of over 2 mA/cm2 (at -2 V vs Fc+/Fc) and a product selectivity of up to 87% for CO (CO/all products) production while also displaying long-term stability for syngas production (over 44 h). Importantly, spectroelectrochemical analysis using PEC impedance spectroscopy (PEIS) and intensity-modulated photocurrent spectroscopy (IMPS) complements PEC data to reveal that tailoring the proton donor ability of the electrolyte is crucial for enhancing the performance, selectivity, and durability of the photocathode. When a moderate amount of protons is present, the density of photogenerated charges accumulated at the interface drops significantly, suggesting a faster charge transfer process. However, with a high concentration of proton donors, the H2 evolution reaction is preferred.

Personalized medicine comes to a blood center near you

Personalized medicine comes to a blood center near you

Uniformity improvement of thickness and net donor concentration in halide vapor phase epitaxial β-Ga2O3 wafers prepared on miscut angle substrates

High uniformity of the thickness and net donor concentrations (N d-N a) in 100 mm diameter β-Ga2O3 (001) epitaxial wafer prepared by halide vapor phase epitaxy was demonstrated. An epitaxial wafer grown on a substrate with a miscut angle near 0° generated a specific epitaxial region with a lower growth rate and a higher N d-N a than the rest of the region, which deteriorated the wafer uniformity. In contrast, epitaxial wafers prepared on substrates with a miscut angle of –0.1° suppressed the occurrence of the specific epitaxial region, and an average thickness after chemical mechanical polishing of 10.6 μm with 5% tolerance and an average N d-N a without intentionally doping of 1.1 × 1016 cm−3 within 7% tolerance were successfully obtained.

Controlled Release of H2S from Biomimetic Silk Fibroin-PLGA Multilayer Electrospun Scaffolds.

The possibility of incorporating H2S slow-release donors inside biomimetic scaffolds can pave the way to new approaches in the field of tissue regeneration and anti-inflammatory treatment. In the present work, GYY4137, an easy-to-handle commercially available Lawesson's reagent derivative, has been successfully incorporated inside biomimetic silk fibroin-based electrospun scaffolds. Due to the instability of GYY4137 in the solvent needed to prepare silk fibroin solutions (formic acid), the electrospinning of the donor together with the silk fibroin turned out to be impossible. Therefore, a multilayer structure was realized, consisting of a PLGA mat containing GYY4137 sandwiched between two silk fibroin nanofibrous layers. Before their use in the multilayer scaffold, the silk fibroin mats were treated in ethanol to induce crystalline phase formation, which conferred water-resistance and biomimetic properties. The morphological, thermal, and chemical properties of the obtained scaffolds were thoroughly characterized by SEM, TGA, DSC, FTIR, and WAXD. Multilayer devices showing two different concentrations of the H2S donor, i.e., 2 and 5% w/w with respect to the weight of PLGA, were analyzed to study their H2S release and biological properties, and the results were compared with those of the sample not containing GYY4137. The H2S release analysis was carried out according to an "ad-hoc" designed procedure based on a validated high-performance liquid chromatography method. The proposed analytical approach demonstrated the slow-release kinetics of H2S from the multilayer scaffolds and its tunability by acting on the donor's concentration inside the PLGA nanofibers. Finally, the devices were tested in biological assays using bone marrow-derived mesenchymal stromal cells showing the capacity to support cell spreading throughout the scaffold and prevent cytotoxicity effects in serum starvation conditions. The resulting devices can be exploited for applications in the tissue engineering field since they combine the advantages of controlled H2S release kinetics and the biomimetic properties of silk fibroin nanofibers.

Comparative study of electrical properties of semi-insulating GaN substrates grown by hydride vapor phase epitaxy and doped with Fe, C, or Mn

The electrical properties of semi-insulating GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn) grown by hydride vapor phase epitaxy are presented. Hall effect measurements were performed at temperatures ranging from 300 to 800 K. At all of the investigated temperatures, the Mn-doped samples exhibited the highest resistivity. The Fe-doped samples showed n-type conduction, whereas the C-doped samples and the Mn-doped sample with a Mn concentration of 1 × 1019 cm−3 showed p-type conduction. A detailed analysis of the temperature dependence of the carrier concentration showed that all of the impurities formed acceptor levels at EC −(0.59–0.61) eV for Fe, at EV +(0.90–1.07) eV for C, and at EV +1.55 eV for Mn. The Mn-doped sample with a Mn concentration of 8 × 1017 cm−3 showed a negative Hall coefficient (suggesting n-type conduction) at high temperatures, contradicting the formation of acceptor levels by Mn. We successfully explained the negative value by considering the conduction of both holes and electrons with different mobilities. On the basis of the results, we calculated the relationship between the resistivity and doping concentration for each dopant. The calculations indicated that the highest resistivity can be realized in Mn-doped GaN with an optimized doping concentration (depending on the residual donor concentration). All of the dopants can effectively realize high resistivity at room temperature. Mn is an effective dopant for attaining high resistivity, especially at high temperatures (e.g., 800 K).

Nanowire single-crystal grain and single grain boundary silicon field effect transistors for direct electrical characterization of grain boundaries

Single crystal grain (s-G) and single grain boundary (s-GB) Si field effect transistors (FETs) were investigated for direct measurement of the electrical activity of GBs. Ultrahigh-performance nanowire s-G FET with 1360 cm2V−1s−1 electron field-effect mobility (μ ef) was achieved on a transparent substrate. The significant difference of μ ef values between nanowire and microwire FETs proved that uniaxial tensile strain typically contributed to μ ef enhancement in nanowire FETs. Longitudinal GBs typically increased the leakage current and S factor due to a large donor concentration. The donor concentration generated by Σ3 and other CSL-type s-GBs was estimated.

Organic Photodiodes with Thermally Reliable Dark Current and Excellent Detectivity Enabled by Low Donor Concentration.

Reducing the dark current (Jd) under reverse bias while maintaining a high external quantum efficiency (EQE) is essential for the practical application of organic photodiodes (OPDs). However, the high Jd of OPDs is generally difficult to reduce because its origin in organic photodiodes is still not well understood and is strongly temperature dependent. To address the issues related to high Jd in typical OPDs, we investigate fullerene-based OPDs with various donor concentrations. It is surprising that OPDs with a low donor concentration in the active layer can achieve a very low Jd of 1.68 × 10-7 mA cm-2 at a reverse bias of -2 V, which is almost temperature-independent owing to the low polymer content. More importantly, the fullerene-based OPDs with a low donor concentration of 5 wt % can still achieve an external quantum efficiency (EQE) as high as 40%, resulting in a promisingly high detectivity of above 1013 Jones at 300-800 nm compared to the OPDs with a standard donor/acceptor ratio. The presented optimized OPD device can also be used for real-time heart rate detection, indicating its potential for practical photon-sensing applications.

Fabrication and characterization of Ag-BaF2/GaSb Schottky diode

The Ag-BaF2/GaSb Schottky diode measurement has been investigated by using voltage versus current (I-V) at different temperatures, voltage versus capacitance (C-V) and hotoelectric measurements on n-type GaSb carrier per cm-3, Current – voltage measurement were used to study the interface layer. Near ideal characteristics were observed for Ag-BaF2/GaSb contact with ideality factor values (1.21-1.451). The Schottky barrier height and donor concentration (Nd) have been obtained from C-V characteristics. Barrier height results from these methods were the same approximately with the results obtained from current – voltage measurement and were in the same range which suggests that the Fermi level is pinned in the lower half of the band gap. Photoelectric measurements were used for barrier height measurements by applying the fowler method. The surfaces of sample was analyses using scanning electron microscopy (SEM) and also the x-ray is used to investigate the reasons for the non-ideal behavior of Ga contacts and to study the surface of Ag-BaF2 layer on the air-cleaved n-GaSb surface.

Injectable polysaccharide hydrogels as localized nitric oxide delivery formulations.

A series of injectable polysaccharide hydrogels were prepared with oxidized dextran and diethylenetriamine-modified carboxymethylcellulose or hyaluronic acid. Rheological evaluation revealed that carboxymethylcellulose-based hydrogels achieved the largest storage moduli (>1 kPa) when prepared from 5 wt. % solutions. However, carboxymethylcellulose-based hydrogels with storage moduli >100 Pa were prepared from solutions with concentrations as low as 2 wt. %. Hyaluronic acid-based hydrogels demonstrated smaller storage moduli but had swelling ratios more than four times that of the carboxymethylcellulose systems at the same polymer concentrations. The incorporation of N-diazeniumdiolate NO donors into the hydrogels resulted in reduced hydrogel storage moduli as a function of NO donor concentration. The impact of the hydrogel architecture on NO-release kinetics proved dependent on the identity of the NO donor. Hydrogel degradation over 14 d was measured at pH 5.4 and 7.4 and indicated that hyaluronic acid-based hydrogels degraded more rapidly than carboxymethylcellulose hydrogels and that the addition of NO to the hydrogels increased the rate at which they degraded. In vitro cytotoxicity of hydrogel extracts was evaluated against five cell lines, with no observed toxicity except for that of hyaluronic acid-based hydrogel extracts against human gingival fibroblasts. The diverse properties, versatility, and non-toxic characteristics of these injectable hydrogels should facilitate local delivery of nitric oxide for a range of biomedical applications.

Repurposing nitric oxide donating drugs in cancer therapy through immune modulation

BackgroundNitric oxide-releasing drugs are used for cardiovascular diseases; however, their effects on the tumor immune microenvironment are less clear. Therefore, this study explored the impact of nitric oxide donors on tumor progression in immune-competent mice.MethodsThe effects of three different nitric oxide-releasing compounds (SNAP, SNP, and ISMN) on tumor growth were studied in tumor-bearing mouse models. Three mouse tumor models were used: B16F1 melanoma and LL2 lung carcinoma in C57BL/6 mice, CT26 colon cancer in BALB/c mice, and LL2 lung carcinoma in NOD/SCID mice. After nitric oxide treatment, splenic cytokines and lymphocytes were analyzed by cytokine array and flow cytometry, and tumor-infiltrating lymphocytes in the TME were analyzed using flow cytometry and single-cell RNA sequencing.ResultsLow doses of three exogenous nitric oxide donors inhibited tumor growth in two immunocompetent mouse models but not in NOD/SCID immunodeficient mice. Low-dose nitric oxide donors increase the levels of splenic cytokines IFN-γ and TNF-α but decrease the levels of cytokines IL-6 and IL-10, suggesting an alteration in Th2 cells. Nitric oxide donors increased the number of CD8+ T cells with activation gene signatures, as indicated by single-cell RNA sequencing. Flow cytometry analysis confirmed an increase in infiltrating CD8+ T cells and dendritic cells. The antitumor effect of nitric oxide donors was abolished by depletion of CD8+ T cells, indicating the requirement for CD8+ T cells. Tumor inhibition correlated with a decrease in a subtype of protumor macrophages and an increase in a subset of Arg1-positive macrophages expressing antitumor gene signatures. The increase in this subset of macrophages was confirmed by flow cytometry analysis. Finally, the combination of low-dose nitric oxide donor and cisplatin induced an additive cancer therapeutic effect in two immunocompetent animal models. The enhanced therapeutic effect was accompanied by an increase in the cells expressing the gene signature of NK cell.ConclusionsLow concentrations of exogenous nitric oxide donors inhibit tumor growth in vivo by regulating T cells and macrophages. CD8+ T cells are essential for antitumor effects. In addition, low-dose nitric oxide donors may be combined with chemotherapeutic drugs in cancer therapy in the future.

All-quantum dot based Förster resonant energy transfer: key parameters for high-efficiency biosensing.

While colloidal quantum dots (QDs) are commonly used as fluorescent donors within biosensors based on Förster resonant energy transfer (FRET), they are hesitantly employed as acceptors. On the sole basis of Förster theory and the well-known behaviour of organic dyes, it is often argued that the QD absorption band over the UV-visible range is too wide. Discarding these preconceptions inherited from classical fluorophores, we experimentally examine the FRET process occurring between donor and acceptor CdTe QDs and provide a mathematical description of it. We evidence that the specific features of QDs unexpectedly lead to the enhancement of acceptors' emission (up to +400%), and are thus suitable for the design of highly efficient all-QD based FRET sensors. Our model enables us to identify the critical parameters maximizing the contrast between positive and negative biosensing readouts: the concentrations of donors and acceptors, their spectral overlap, the densities of their excitonic states, their dissipative coupling with the medium and the statistics of QD-QD chemical pairing emerge as subtle and determinant parameters. We relate them quantitatively to the measured QD-QD FRET efficiency and discuss how they must be optimized for biosensing applications.

Effect of Sn4+–Isovalent doping concentration on giant dielectric properties of Sn Ta0.025Ti0.975-O2 ceramics

The Sn x Ta 0.025 Ti 0.975- x O 2 ( x %Sn(TTO)) ceramics with x = 2.5–10% were prepared using a standard mixed-oxide method and sintered at 1450 °C for 3 h to achieve a dense microstructure. The effects of the isovalent–Sn 4+ doping concentration on the crystal structure, microstructure, giant dielectric behavior, and electrical properties were systematically investigated. Continuously enlarged lattice parameters and bond lengths with a single rutile–TiO 2 phase were observed as x % increased. The mean grain size was slightly reduced (∼17.3–14.6 μm) due to an increased oxygen vacancy and the solute drag effect. The dielectric permittivity (ε′) decreased with increasing x %, whereas the loss tangent (tanδ) was remarkably reduced. The semiconducting grain resistance of the x %Sn(TTO) ceramics remained unchanged owing to the same Ta 5+ donor concentration. The insulating grain boundary (GB) resistance was extremely increased by more than two orders of magnitude when x % increased from 2.5 to 5.0%, leading to the significantly improved giant dielectric properties. The optimized low tanδ∼0.02 and high ε′∼10 4 with temperature coefficient less than ±15% in the range of -60–210 °C were reasonably described by the internal barrier layer capacitor model. Improved dielectric properties can be obtained by engineering GB by varying the Sn 4+ –isovalent doping concentration. This study provides an important approach for improving the dielectric properties of co–doped TiO 2 without the creation of complex defect clusters inside the grains.

HVPE Growth and Characterization of Thick κ-Ga2O3 layers on GaN/Sapphire Templates

Ga2O3 layers with thickness from 10 to 86 μm were grown by halide vapor phase epitaxy (HVPE) on GaN(0001)/sapphire templates in a hot wall reactor at 570 °C, with the growth rate of about 3–4 μm h−1. The grown layers consisted of pure (001)-oriented κ-Ga2O3 polymorph with no admixture of β-Ga2O3 or α-Ga2O3 phases. The narrowest (004) X-ray rocking curves were observed for 13–20 μm thick κ-Ga2O3 layers. A further increase in thickness results in deterioration of the crystal quality which is indicated by the broadening of rocking curves. Electrical measurements of the thick layers revealed that they were n-type, with the concentration of shallow donors gradually decreasing from ∼1016 cm−3 to ∼1015 cm−3. Deep level transient spectroscopy (DLTS) measurements revealed the presence of deep traps with levels near Ec−0.3 eV, Ec−0.6 eV, Ec−0.7 eV, Ec−0.8 eV, Ec−1 eV, with the Ec−0.8 eV being predominant.

Water --- a source electrically active centres in CdHgTe

Influence of water solutions with various pH and electrochemical treatment in cathode position on concentration of charge carriers in samples CdxHg1-xTe with x=0.2-0.3 is investigated. Cathodic treatment cadmium-mercury-tellurium at small density current increases concentration of donors, and at high density acceptors are formed. It is supposed that hydroxyl groups create acceptors centers, introduce in interstitial cadmium-mercury-tellurium. At treatment for a long time (it is more than 20 h) or acceptors are formed with concentration at level of 1016 cm-3 (at high activity of hydrogen), or donors with concentration of 1014 cm-3 (at low activity of hydrogen) are uniform distribution on all thickness of cadmium-mercurytellurium film and does not vary with the subsequent increase in time of treatment. Keywords: CdHgTe, electrochemical treatment, acceptors, activity of hydrogen.

Вода --- источник электрически активных центров в CdHgTe

Influence of water solutions with various pH and electrochemical treatment in cathode position on concentration of charge carriers in samples CdxHg1−xTe with x = 0.2−0.3 is investigated. Cathodic treatment cadmium-mercury-tellurium at small density current increases concentration of donors, and at high density acceptors are formed. It is supposed that hydroxyl groups create acceptors centers, introduce in interstitial cadmium-mercury-tellurium. At treatment for a long time (it is more than 20 h) or acceptors are formed with concentration at level of 1016 cm−3 (at high activity of hydrogen), or donors with concentration of 1014 cm−3 (at low activity of hydrogen) are uniform distribution on all thickness of cadmium-mercurytellurium film and does not vary with the subsequent increase in time of treatment.

Influence of the content of impurities and structural defects on the properties of the Cd0.9Mn0.1Te:V-based detector

The paper highlights the results of quantitative studies of the influence of the content of impurities and structural defects on the electrophysical and detector properties of Cd0.9Mn0.1Te:V — resistivity and concentrations of free charge carriers, life time of nonequilibrium charge carriers τ, charge collection efficiency η. The optimal ranges of energy change and deep donor concentration, which ensure a high-resistive state and acceptable values of τ and η, are established. The authors study the compensation of cadmium vacancies with vanadium admixture.

Enantioselective transesterification of a propargyl tertiary alcohol by Candida antarctica lipase A: A reaction medium engineering approach

Lipase A from Candida antarctica (CAL-A) is widely known to accept bulky substrates, such as tertiary alcohols. These compounds are important building blocks in organic synthesis processes, and they are found in many natural products. Under an organic medium and in the presence of an acyl donor, CAL-A can act as a chiral catalyst in the kinetic resolution (KR) of these substrates via an enantioselective transesterification reaction. Herein, we report a new protocol developed for the KR of the propargyl tertiary alcohol 2-phenyl-3-butyn-2-ol ((rac)-1) catalyzed by CAL-A. A reaction medium engineering study was performed by varying the following conditions involved in the system: temperature, solvent, acyl donor, acyl donor concentration, and enzyme loading. After optimization, we developed a more efficient system with a lower enzyme/substrate ratio using a commercially available and immobilized wild-type CAL-A.