Donor States Research Articles

Effect of Al doping on optical properties of ZnO thin films: theory and experiment

The structural, electronic, and optical properties of zinc oxide thin films with Al-doping have been investigated experimentally and with density functional theory (DFT) calculations. Changes in properties of doped thin films, which are deposited on a glass substrate by a high-frequency magnetron sputtering method, are monitored using X-ray diffraction data and UV measurements. Our theoretical calculations show that the electronic structure of ZnO: Al can be well described by the DFT+U method. The XRD measurements demonstrated the formation of a pure single ZnO phase and Al atoms is well incorporated in the ZnO lattice. Also, we determine the optical constants such as optical dielectric function, refractive index, optical band gap values, extinction coefficient, and optical conductivity of the doping films through transmittance spectra. The calculated results show the change of lattice parameters Al-doped ZnO. The optical band gap of ZnO: Al is increased compared with pure ZnO. Besides, around the Fermi level of Al-doped ZnO was emerged the shallow donor states from mainly 3s-Al states. Our DFT calculations of optical properties Al-doped ZnO agree satisfactorily with the experimentally measured transmittance values.

Investigation of Intramolecular Through-Space Charge-Transfer States in Donor-Acceptor Charge-Transfer Systems.

Commonly, thermally activated delayed fluorescence (TADF) emitters present a twisted donor–acceptor structure. Here, electronic communication is mediated through-bond via π-conjugation between donor and acceptor groups. A second class of TADF emitters are those where electronic communication between donor and acceptor moieties is mediated through-space. In these through-space charge-transfer (TSCT) architectures, the donor and acceptor groups are disposed in a pseudocofacial orientation and linked via a bridging group that is typically an arene (or heteroarene). In most of these systems, there is no direct evidence that the TSCT is the dominant contributor to the communication between the donor and acceptor. Herein we investigate the interplay between through-bond localized excited (LE) and charge-transfer (CT) states and the TSCT in a rationally designed emitter, TPA-ace-TRZ, and a family of model compounds. From our photophysical studies, TSCT TADF in TPA-ace-TRZ is unambiguously confirmed and supported by theoretical modeling.

The role of affect, satisfaction and internal drive on personal moral norms during COVID-19.

Background and ObjectiveSocieties require prosocial activities during crises. The COVID‐19 pandemic presents individuals with unique challenges that may affect their emotional state leading to reformed personal moral norms. Crucially, personal moral norms are important predictors of moral behaviour. Given the longevity of the pandemic, studying its impact on affect, satisfaction and internal drive of (non‐)donors during COVID‐19 and if personal moral norms are affected is paramount.Material and MethodsThis study relies on longitudinal data, consisting of six waves carried out biweekly. Our panel is representative for the German population, capturing changes in affect, satisfaction, internal drive and personal moral norms. We compare the emotional state and personal moral norms of (non‐)donors in the pandemic to pre‐pandemic phase. Moreover, we analyse changes in emotional state and personal moral norms during the pandemic and investigate the role of emotional state on personal moral norms.ResultsFirstly, our results show that personal moral norms of (non‐)donors drop compared to pre‐pandemic. Within pandemic, personal moral norms of active donors are not further altered. Secondly, we find significant changes of emotional state in the pandemic compared to pre‐pandemic phase, for example individuals feel more optimistic, but less satisfied and less energetic. Thirdly, we find that feeling more grateful increases personal moral norms of non‐donors.ConclusionThis study provides insights into how crises shape (non‐)donors’ emotional state and its impact on relevant donor motivations, that is, personal moral norms. Blood banks can use this knowledge to enhance recruiting and retention efforts during crises.

High n-type conductivity and carrier concentration in Si-implanted homoepitaxial AlN

We demonstrate Si-implanted AlN with high conductivity (>1 Ω−1 cm−1) and high carrier concentration (5 × 1018 cm−3). This was enabled by Si implantation into AlN with a low threading dislocation density (TDD) (<103 cm−2), a non-equilibrium damage recovery and dopant activation annealing process, and in situ suppression of self-compensation during the annealing. Low TDD and active suppression of VAl-nSiAl complexes via defect quasi Fermi level control enabled low compensation, while low-temperature, non-equilibrium annealing maintained the desired shallow donor state with an ionization energy of ∼70 meV. The realized n-type conductivity and carrier concentration are over one order of magnitude higher than that reported thus far and present a major technological breakthrough in doping of AlN.

A novel Yb3+/Tm3+ co-doped semiconductor sensitized up-conversion strategy for β-In2S3 photoanode with enhanced photoelectrochemical properties

N-type β-Indium sulfide (β-In2S3) has emerged as one of the most promising semiconductor photoanode for use in photoelectrochemical water-splitting in recent years, its defective spinel structure facilitates the incorporation of foreign ions to adjust the photoelectrochemical (PEC) performance. Lanthanide ions with excellent optical properties and abundant energy level structure have attracted much attention. In this study, the semiconductor sensitized up-conversion strategy was first applied to improve the PEC performance of β-In2S3 by inhibiting electron-hole pairs recombination. Yb3+/Tm3+ co-doped β-In2S3 (YTS) were successfully prepared on FTO substrate in-situ as PEC water splitting photoanode by a simple hydrothermal method, the effects of Yb3+/Tm3+ co-doping on PEC properties, charge-transport properties and energy band structure are discussed. When Yb3+ ions in the total cations of precursor accounted for 3%, and Tm3+ ions accounted for 0.5%, the photocurrent density of Yb3+/Tm3+ co-doped β-In2S3 (YTS-3) is 0.42 mA/cm2 (0.5 V vs. Ag/AgCl), which is about 1.68 times higher than pure β-In2S3 (0.25 mA/cm2). No photocurrent response was detected under 980 nm single-wavelength LED, proving that host material sensitization is more effective than direct excitation. The improved PEC properties for Yb3+/Tm3+ co-doped β-In2S3 might be attributed to the semiconductor sensitized up-conversion strategy, which realize a cycle of energy released by electron-hole pairs recombination. Moreover, the donor states formed after doping inhibits the recombination of electron-hole pairs by capturing electrons. The ways that the Yb3+/Tm3+ dopants modified the energy band structure and PEC properties of β-In2S3 demonstrated in this study have guiding significance for the design of lanthanide ions doped semiconductor photoanode.

Impurity band conduction in Si-doped β -Ga2O3 films

By combining temperature-dependent resistivity and Hall effect measurements, we investigate donor state energy in Si-doped β-Ga2O3 films grown using metal-organic vapor phase epitaxy. High-magnetic field (H) Hall effect measurements (–90 kOe ≤ H ≤ +90 kOe) showed non-linear Hall resistance for T < 150 K, revealing two-band conduction. Further analyses revealed carrier freeze out characteristics in both bands yielding donor state energies of ∼33.7 and ∼45.6 meV. The former is consistent with the donor energy of Si in β-Ga2O3, whereas the latter suggests a residual donor state. This study provides critical insight into the impurity band conduction and the defect energy states in β-Ga2O3 using high-field magnetotransport measurements.

UN Human Rights Shaming and Foreign Aid Allocation

Does public condemnation or shaming of human rights abuses by the United Nations influence foreign aid delivery calculus across Western donor states? I argue that countries shamed in the United Nations Human Rights Council (formerly known as the United Nations Commission on Human Rights) encourage donor states to channel more aid via international and local non-governmental organizations. Furthermore, I find this effect to be more pronounced with increased media coverage. The findings of this paper suggest that international organizations do influence advanced democracies’ foreign policy. Moreover, the paper also finds that donor governments do not punish recipient leaders by scaling back on government-to-government aid, which is more fungible, despite public condemnations of their human rights practices owing largely to strategic concerns. These results are robust to a number of alternative data and estimation techniques.

The Montreal Criteria and uterine transplants in transgender women.

Ever since its first documented live birth in 2014, the use of uterine transplantation (UTx) for the treatment of absolute uterine factor infertility (UFI) has seen major clinical advances, which include the use of alternative surgical approaches, different donor states, and diverse patient populations. In addition to the thorough research programs that developed the technique, this accomplishment has occurred in large part following a number of ethical frameworks, such as the Montreal Criteria and the Indianapolis Consensus, which paved the way to transition from experimental animal trials to human ones. To date, over 60 uterine transplants have been performed in the world, and at least 18 births have been thus far confirmed. While the procedure remains experimental, the vast knowledge and procedural experience amassed over the last 20 years of rigorous research have hinted at the next step of discovery. In particular, advancing social circumstances have prompted the question regarding the use of this technology in transgender individuals. Though the potential use of uterine transplants in the transgender population has been hypothesized, no in-depth ethical framework has been developed towards this purpose. Herein, we explore the ethical issues revolving around the use of this technology in this patient population and provide key insights that may advance this cause.

A quantum optics approach to photoinduced electron transfer in cavities.

We study a simple model for photoinduced electron transfer reactions for the case of many donor-acceptor pairs that are collectively and homogeneously coupled to a photon mode of a cavity. We describe both coherent and dissipative collective effects resulting from this coupling within the framework of a quantum optics Lindblad master equation. We introduce a method to derive an effective rate equation for electron transfer by adiabatically eliminating donor and acceptor states and the cavity mode. The resulting rate equation is valid for both weak and strong coupling to the cavity mode and describes electronic transfer through both the cavity-coupled bright states and the uncoupled dark states. We derive an analytic expression for the instantaneous electron transfer rate that depends non-trivially on the time-varying number of pairs in the ground state. We find that under proper resonance conditions, and in the presence of an incoherent drive, reaction rates can be enhanced by the cavity. This enhancement persists, and can even be largest, in the weak light-matter coupling regime. We discuss how the cavity effect is relevant for realistic experiments.

Opening the black box of international aid: understanding delivery actors and democratization

Donor states may delegate to other actors to deliver aid through partnerships. We ask whether some partnerships are more effective than others with democratization aid. We identify five actors, arguing that they can affect the recipient’s democracy outcomes via the fungibility of the funds. We hypothesize that organizations that have relationships of accountability and dependency to the donor are most likely to use aid for its intended purposes (least fungible), making them the most likely to see positive effects on democratization. Those that do not have these relationships may use the money for other purposes, making them the least likely to see positive effects on democratization. We test these with data from 32 OECD countries and 126 recipients from 2004 to 2018. Using the electoral indicator from the Varieties of Democracy project, we find that NGO- and IGO-delivered aid is associated with significantly larger increases in a democracy than aid delivered by corporations.

Sensitized Luminescence Kinetics as a Tool for Identification of Nonradiative Energy Transfer

A simple equation is proposed for calculating the sensitized luminescence kinetics of acceptors caused by nonradiative excitation energy transfer (Forster Resonance Energy Transfer (FRET)) from donors. As parameters, the equation includes the lifetimes of the donor and acceptor excited states and the experimental luminescence decay kinetics of donors in the presence of FRET. The equation does not specify a certain FRET mechanism. It is proposed to use this equation to fit the experimental sensitized luminescence kinetics in order to quantitatively confirm the existence of FRET between donor and acceptors.

First principles study of small hole polaron formation in doped olivine LiFe1−xCoxPO4: Effects of Li deficiency

Small hole polarons, charge carriers for electronic conductivity, play crucial roles in the performance of olivine LiMPO4 (M = Fe, Co, Mn, Ni) batteries, yet their formation mechanism and effects have not been completely explored. This work is aimed to apply density functional theory with additional on-site Hubbard corrections (DFT+U) to investigate the formation mechanism and the effects of small hole polarons in olivine LiFe1−xCoxPO4. It is found that small hole polarons always localize first at the Fe sites and then at the Co sites only when the Fe sites are fully occupied. The results show that much less bond-length distortion of CoO6 than that of FeO6 is required to form a small hole polaron; hence, Co doping helps to create small hole polarons and to stabilize the structures, as indicated by lower formation energy. Moreover, Co doping enhances the electronic conductivity of LiFePO4 because of Co donor states and also increases the intercalation voltage due to the difference of 3d electron configurations between the Fe2+/Fe3+ states and the Co2+/Co3+ states.

Spiral Donor Design Strategy for Blue Thermally Activated Delayed Fluorescence Emitters.

Thermally activated delayed fluorescence (TADF) emitters with a spiral donor show tremendous potential toward high-level efficient blue organic light-emitting diodes (OLEDs). However, the underlying design strategy of the spiral donor used for blue TADF emitters remains unclear. As a consequence, researchers often do "try and error" work in the development of new functional spiral donor fragments, making it slow and inefficient. Herein, we demonstrate that the energy level relationships between the spiral donor and the luminophore lead to a significant effect on the photoluminescent quantum yields (PLQYs) of the target materials. In addition, a method involving quantum chemistry simulations that can accurately predict the aforementioned energy level relationships by simulating the spin density distributions of the triplet excited states of the spiral donor and corresponding TADF emitters and the triplet excited natural transition orbitals of the TADF emitters is established. Moreover, it also revealed that the steric hindrance in this series of molecules can form a nearly unchanged singlet (S1) state geometry, leading to a reduced nonradiative decay and high PLQY, while a moderated donor-acceptor (D-A) torsion in the triplet (T1) state can induce a strong vibronic coupling between the charge-transfer triplet (3CT) state and the local triplet (3LE) state, achieving an effective reverse intersystem crossing (RISC) process. Furthermore, an electric-magnetic coupling is formed between the high-lying 3LE state and the charge-transfer singlet (1CT) state, which may open another RISC channel. Remarkably, in company with the optimized molecular structure and energy alignment, the pivotal TADF emitter DspiroS-TRZ achieved 99.9% PLQY, an external quantum efficiency (EQE) of 38.4%, which is the highest among all blue TADF emitters reported to date.

Comparing US and Chinese Foreign Aid in the Era of Rising Powers

ABSTRACT China is emerging as a key state actor in international development – a sector that has been dominated by the United States for decades. US and Chinese foreign aid programs can be compared on the basis of several benchmarks: 1) official state definition and accounting of foreign aid programs; 2) historical foundations and origins; 3) sectoral distribution, particularly in terms of the professed goals and objectives of the aid program; 4) nature of targeted recipient actors; 5) institutional mechanisms for delivery in recipient countries. Notwithstanding particular differences, Chinese and US foreign aid portfolios demonstrate their respective strategic political and economic interests in two ways: they shape the domestic politics of recipient countries in ways that accommodate the donor government’s policy preferences, and they enhance the social reputation and legitimacy of the donor state in the international system.

N-type doping feasibility of Cu2O with In and Al for cost-effective photovoltaics: An ab initio investigation

The present work deals with the first principle calculations under the framework of density functional theory to realize n-type conductivity in Cu2O by doping it with practically feasible dopants: In and Al. From the electronic density of states and band structure calculations, it was found that both In and Al create deep level donor states at 0.84 eV and 1.32 eV respectively above the valence band maximum. The optical band gap was found to be widened from 2.04 eV for pure Cu2O to 2.66 eV and 3.05 eV for In and Al doping respectively. The optical absorption coefficient was found to be ∼106 m−1 for pure Cu2O and ∼107 m−1 for the doped systems. The charged defect formation energy calculation shows that both these cationic substitutional defects are thermodynamically more favourable under Cu rich conditions.

Causes of color in purple- and yellow- quartz

Quartz is a variety of gemstone consisting of SiO2. The various colors of quartz are caused by Fe as a trace element. This study focused on the investigation of Fe oxidation states affecting colorations of purple- and yellow- quartz by X-ray absorption spectroscopy (XAS) and UV-Vis-NIR spectroscopy. The amethyst (purple- quartz) and citrine (yellow- quartz) were collected as the samples. As the XAS results, there was only Fe3+ oxidation state on both purple-and yellow- quartz considering with the absorption energy position at the Fe K-edge compared to the Fe-oxide chemical standards i.e., FeO and Fe2O3. However, the UV-Vis-NIR absorption spectra of the purple- and yellow- quartz were different. Therefore, we propose that the coloration of purple- and yellow- quartz was caused by Fe3+ oxidation states as the donor states at 3.59 eV and 2.28 eV with the different energy band gaps of the purple- and yellow- quartz that were 4.13 eV and 4.88 eV respectively derived from Tauc Plot method.

Activated InN nanocolumns as sensitive halogen sensor

We herein present the development of sensitive halogen sensors based on InN nanocolumns (NCs) directly grown onto p-Si(111). Their activation with InN QDs then followed this growth by using plasma-assisted molecular beam epitaxy (PA-MBE). The activated NCs were then probed for their morphological, structural, optical, and electrical properties. Atomic force microscopy divulges the presence of the InN QDs on top of the NCs, which further confirm by deconvoluted two peaks in PL measurements. The XPS valance band measurements confirm the pinning to the conduction band with ∼ 0.15 eV, which manifests the presence of positively charged surface donor states. We further have utilized these surface donor states and investigated these activated NCs toward halogen ions. The results demonstrated the sensitivity of 0.724 µF/cm2/M, 2.32 mF/m2/M, and 0.95 mF/cm2/M, for fluoride, chloride, and bromide ions, respectively. Moreover, we have not observed any effect due to hydroxide ions on the areal capacitance of the InN NCs.

Study of the structural, electrokinetic and magnetic characteristics of the Er1-xZrxNiSb semiconductor

Peculiarities of the structural, electrokinetic, energetic, and magnetic characteristics of Er1-xZrxNiSb semiconductive solid solution, х=0–0.10, were studied. It was suggested that when Zr (4d25s2) atoms were introduced into the structure of the ErNiSb half-Heusler phase by substitution of Er (5d06s2) atoms in 4a position, Zr atoms can also simultaneously occupy the 4c position of Ni (3d84s2) atoms. As a result, in Er1-xZrxNiSb semiconductor, the structural defects of donor nature in position 4a and ones of acceptor nature in position 4c were generated simultaneously. In this case, in the band gap of Er1-xZrxNiSb, the energy states of impurity donor and acceptor bands (donor-acceptor pairs) appear and determine the electrical conductivity mechanism of the semiconductor.

CNT facilitated interfacial charge transfer of TiO2 nanocomposite for controlling the electron-hole recombination

We studied the nucleation and growth of TiO2 nanoflowers and carbon nanotubes-TiO2 nanocomposite (n-CNT-TiO2) by the hydrothermal method in a single step at 150 °C and tested them for the photocatalytic degradation of MB. The microstructural analysis confirmed the transformation of TiO2 nanoflowers to CNT-TiO2 spheres due to the role of surface energy of CNT. The XRD peak profile analysis of TiO2 and n-CNT-TiO2 confirmed the formation of pure rutile phase of Titania sintered at 400 °C. A red-shift in the bandgap of n-CNT-TiO2 nanocomposite (2.7eV) was observed due to the donor states towards the conduction band edge. The core-level of XPS showed the strong interaction between carbon and titanium atoms. The CNT facilitate the interfacial charge transfer or avoid the formation of charge recombination due to the variation of Ti4+ to Ti3+ sites. The highest photocatalytic degradation was achieved by using the photocatalyst of n-CNT-TiO2 nanocomposite. The incorporation of CNT provides the interfacial charge transfer facility that creates new interbands energy states for the delay of electron-hole recombination, which cater the environmental remediation.

Sn doping of (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy

Sn doping of (010) β-Ga2O3 grown by conventional plasma-assisted molecular beam epitaxy (PAMBE) and via metal oxide catalyzed epitaxy (MOCATAXY) using a supplied indium flux during molecular beam epitaxy (MBE) growth was investigated. While high Sn concentrations were achievable over a range of growth conditions in conventional PAMBE, Sn doping less than 1019 cm−3 resulted in non-uniform doping profiles for constant Sn cell temperatures, as well as run-to-run variation in doping. Sn doping in MOCATAXY grown β-Ga2O3 allowed for sharp doping profiles and a wide range of donor concentrations from 3.9 × 1016 cm−3 to 2 × 1019 cm−3 and a maximum room temperature Hall mobility of 136 cm2/V s at 3.9 × 1016 cm−3. From temperature-dependent Hall measurements, Sn was found to have a relatively deep donor state at 77 meV below the conduction band edge. The samples showed low electron mobility at cryogenic temperatures, suggesting the existence of high background impurity levels in the MBE grown films and the need for impurity control in the oxide MBE growth environment.