Energy Distribution Of States Research Articles

Single crystal growth and the electronic structure of Rb2Na(NO3)3: Experiment and theory

Rb2Na(NO3)3 crystals demonstrate nonlinear optical properties and can be used as a converter of laser radiation in the shortwave region. The crystals were grown in the present work by the Bridgman–Stockbarger method in a ratio of 75 ​wt%(RbNO3) and 25 ​wt%(NaNO3). After the growth, a transparent centimeter size single crystal (6 ​cm long) was obtained for the first time that is very important for its practical application. The unit cell volume of double Rb2Na(NO3)3 nitrate is intermediate between the cell volumes of simple rubidium and sodium nitrates, RbNO3 and NaNO3. Electronic structure of Rb2Na(NO3)3 was studied in the present work from both experimental and theoretical viewpoints. In particular, employing X-ray photoelectron spectroscopy, we have measured binding energies of core electrons and energy distribution of the electronic states within the valence band region of the Rb2Na(NO3)3 crystal and established rather big binding energies for N 1s and O 1s core-level electrons. The bombardment of middle-energy Ar+ ions induces transformation of some nitrogen atoms of the analyzing topmost layers of the Rb2Na(NO3)3 crystal surface from the NO3– group to the NO2– group. To explore in detail the filling of the valence band of Rb2Na(NO3)3 by electronic states associated with constituting atoms, we use first-principles calculations within a density functional theory (DFT) framework. The DFT calculations reveal that O 2p states are the principal contributors to the valence band bringing the main input in its upper portion. The theoretical finding is supported experimentally by fitting the X-ray photoelectron valence band spectrum and the X-ray emission O Kα band on the total energy scale. The conduction band bottom of Rb2Na(NO3)3 is composed by unoccupied O 2p and N 2p states in almost equal proportion.

Localized photonic states and dynamic process in nonreciprocal coupled Su-Schrieffer-Heeger chain.

We investigate the localized photonic states and dynamic process in one-dimensional nonreciprocal coupled Su-Schrieffer-Heeger chain. Through numerical calculation of energy eigenvalue spectrum and state distributions of the system, we find that different localized photonic states with special energy eigenvalues can be induced by the nonreciprocal coupling, such as zero-energy edge states, interface states and bound states with pure imaginary energy eigenvalues. Moreover, we analyze the dynamic process of photonic states in such non-Hermitian system. Interestingly, it is shown that the nonreciprocal coupling has an evident gathering effect on the photons, which also break the trapping effect of topologically protected edge states. In addition, we consider the impacts of on-site defect potentials on the dynamic process of photonic states for the system. It is indicated that the photons go around the defect lattice site and still present the gathering effect, and different forms of laser pulses can be induced with the on-site defect potentials in different lattice sites. Furthermore, we present the method for the quantum simulation of current model based on the circuit quantum electrodynamic lattice.

Structure, refractive and electronic properties of K2SO4:Cu2+ (3%) crystals

K2SO4:Cu2+ (3%) crystal has been synthesized and its crystal structure is characterized by means of the X-ray diffraction method and discussed within the second coordination environment description. Experimental dispersions of the refractive indices and birefringence have been studied. The introduction of impurity leads to a decrease in refractive indices values for all principal directions and significantly change the absolute birefringence values, without altering the character of the dispersions. Electronic structure and optical spectra of K2SO4:Cu2+ (3%) crystal are calculated using the density functional theory. To verify data of the present band-structure calculations, X-ray photoelectron spectroscopy and X-ray emission spectroscopy were used. These allowed to measure binding energy values of the core-level electrons of the constituting atoms, energy distribution of electronic states within the valence-band region and partial distribution of O 2p states. The experimental data is found to be in good agreement with theoretical band-structure calculations.

Temperature dependence of interface state density distribution determined from conductance–frequency measurements in Ni/n-GaP/Al diode

The conductance measurements of the non-annealed (D1) and 400 °C annealed (D2) Ni/n-GaP/Al diodes were made over a wide frequency range of (10 kHz to 5 MHz) and temperature of (100–320 K with steps of 20 K) with bias voltage as a parameter. The capacitance and conductance measurement method is one of the most popular non-destructive methods to obtain information about metal–semiconductor (MS) diode interfaces. The interface state density distribution curves were determined over the band-gap energy near the semiconductor energy midgap. The interface state density (Dit) has been seen to be of the order of ∼1012 eV−1 cm−2. The Dit∼T curves have been plotted for different values of bias voltage. The value of Dit increased with increasing measurement temperature, and with increasing voltage from negative bias to positive bias voltage for both diodes. It was seen that the Dit value for D2 diode was greater than that for the D1 diode at each measurement temperature and bias voltage. It was seen in the interface state energy distribution or density distribution curves that the value of Dit has increased from the valence band maximum (Ev) towards conduction band minimum (Ec) at each measurement temperature.

Energy distribution of interface states generated by oxygen plasma treatment for control of threshold voltage in pentacene thin-film transistors

Pentacene metal-oxide-semiconductor (MOS) capacitors with a SiO2 dielectric treated by oxygen plasma have been studied by capacitance-voltage (C-V) measurements to investigate the energy distribution of the interface states. Oxygen plasma treatment, which is used for control of the threshold voltage in pentacene thin-film transistors, shifted the C-V curves of pentacene MOS capacitors to a positive gate voltage as well as the transfer curves of pentacene thin-film transistors (TFTs). The shift is explained by electrons captured at interface states generated by oxygen plasma treatment. The interface states capturing the electrons are expected to locate at low energy levels. The energy distribution of the interface states locating at middle or high energy levels was extracted by a method equivalent to the Terman method. By use of the method in two steps, the interface state densities distributed at middle and high energy levels (D M and D H) were separately obtained. D M and D H were of the order of 1010–1012 cm−2 eV−1, and increased with an increase in plasma treatment time.

The Two Emission States of PSR B1534+12

Abstract We have observed PSR B1534+12 (J1537+1155), a pulsar with a neutron star companion, using the Five-hundred-meter Aperture Spherical radio Telescope. We found that this pulsar shows two distinct emission states: a weak state with a wide pulse profile and a burst state with a narrow pulse profile. The weak state is always present. We cannot, with our current data, determine whether the pulse energy of the weak state follows a normal or a log-normal distribution. The burst state energy distribution follows a power law. The amplitude of the single-pulse emission in the burst state varies significantly; the peak flux intensity of the brightest pulse is 334 times stronger than that of the average pulse. We also examined the timing precision achievable using only bright pulses, which showed no demonstrable improvement because of pulse jitter and therefore quantified the jitter noise level for this pulsar.

Open-circuit voltage of organic solar cells: Effect of energetically and spatially nonuniform distribution of molecular energy levels in the photoactive layer

Abstract Here, the open-circuit voltage (VOC) of organic solar cells (OSCs) in which the energy levels of the frontier molecular orbitals of the photoactive materials vary depending on the position within the active layer is investigated. The VOC in these devices is critically affected by the energy level of the frontier molecular orbitals that are spatially located near the electrodes (i.e., the highest occupied molecular orbital of the donor near the anode and the lowest unoccupied molecular orbital of the acceptor near the cathode). Other parameters such as the charge generation/recombination and the energy distribution of charge-transfer states appear to exert less influence on the VOC. This work demonstrates that, to maximize the VOC, the spatial distribution of molecular energy levels should be controlled, especially in OSCs that exhibit spatial variation of the energy levels of organic materials within their active layer.

Spray-deposited PbS colloidal quantum dot solid for near-infrared photodetectors

Colloidal PbS quantum dots (QDs) are promising candidates for various optoelectronic applications based on solution-processed thin-film techniques. In this work, a versatile layer-by-layer (LBL) spray deposition of the QDs is introduced aiming for a future large-scale fabrication process of optoelectronic devices. As compared to spin-coated QD solids, a smaller inter-dot distance and a better-ordered superlattice stacking behavior of the QDs are found in the spray-deposited QD solids as confirmed by grazing-incidence small-angle X-ray scattering (GISAXS). The spectral mapping combined time-resolved photoluminescence analysis indicates a longer charge carrier lifetime and better order of the energy state distribution of the spray-deposited QD solid comparing with the spin-coated one. Thus, photodetectors based on spray deposition of QD solids demonstrate an excellent device performance, with the responsivity achieving 365.1 A/W and the detectivity reaching up to 1.4 × 1012 Jones under an illumination power of 63.5 μW/cm2 at a wavelength of 1250 nm. The spray-deposited device performances indicate a great potential of spray deposition of large sized QDs in large-scale fabrications for optoelectronics using longer wavelengths.

Photophysics of TADF Guest-Host Systems: Introducing the Idea of Hosting Potential.

The thermally activated delayed fluorescence (TADF) donor–acceptor (D–A) molecule, DMAC–TRZ, is used as a TADF emitter “probe” to distinguish the environmental effects of a range of solid-state host materials in guest–host systems. Using the guest’s photophysical behavior in solution as a benchmark, a comprehensive study using a variety of typical TADF organic light-emitting diode hosts with different characteristics provides a clearer understanding of guest–host interactions and what affects emitter performance in solid state. We investigate which are the key host characteristics that directly affect charge-transfer (CT) state energy and singlet triplet energy gaps. Using time-resolved photoluminescence measurements, we use the CT state energy distribution obtained from the full width at half-maximum (fwhm) of the emission band and correlate this with other photophysical properties such as the apparent dynamic red shift of CT emission on-set to estimate the disorder-induced heterogeneity of D–A dihedral angles and singlet triplet gaps. Further, the delayed emission stabilization energy value and time-dependent CT band fwhm are shown to be related to a combination of host’s rigidity, emitter molecule packing, and the energy difference between guest and host lowest energy triplet states. Concentration dependence studies show that emitter dimerization/aggregation can improve as well as reduce emission efficiency depending on the characteristics of the host. Two similar host materials, mCPCN and mCBPCN, with optimum host characteristics show completely different behaviors, and their hosting potential is extensively explored. We demonstrate that type I and type III TADF emitters behave differently in the same host and that the materials with intrinsic small ΔEST have the smallest disorder-induced CT energy and reverse intersystem crossing rate dispersion. We also present an optimized method to define the actual triplet energy of a guest–host system, a crucial parameter in understanding the overall mechanism of the TADF efficiency of the system.

Minimal unlinking pathways as geodesics in knot polynomial space

Physical knots observed in various contexts – from DNA biology to vortex dynamics and condensed matter physics – are found to undergo topological simplification through iterated recombination of knot strands following a common, qualitative pattern that bears remarkable similarities across fields. Here, by interpreting evolutionary processes as geodesic flows in a suitably defined knot polynomial space, we show that a new measure of topological complexity allows accurate quantification of the probability of decay pathways by selecting the optimal unlinking pathways. We also show that these optimal pathways are captured by a logarithmic best-fit curve related to the distribution of minimum energy states of tight knots. This preliminary approach shows great potential for establishing new relations between topological simplification pathways and energy cascade processes in nature.

First-principles DFT computation and X-ray spectroscopy study of the electronic band structure and optical constants of Cu2HgGeS4

We present results of a complex study of the electronic structure and optical constants from experimental and theoretical points of view of quaternary copper mercury germanium sulfide, Cu2HgGeS4. Partly, based on measurements employing X-ray photoelectron (XP) spectroscopy, we evaluate binding energy of core-level electrons for atoms constituting the sulfide under study using a high-quality Cu2HgGeS4 crystal. Furthermore, the energy distribution of the electronic valence states in Cu2HgGeS4 is evaluated on measurements of the valence band XP spectrum of the crystal under study. To find the best correspondence of the shape of the valence band XP spectrum to theoretical total density of states (DOS) curve, different approaches for exchange-correlation (XC) potential are explored in the present work. We find that the best correlation of the shapes of the theoretical total DOS curve and the experimental valence band XP spectrum is obtained when the first-principles calculation within a framework of density functional theory (DFT) are made using modified Becke-Johnson (mBJ) functional and treating also the correction parameter U (Hubbard parameter) and effect of spin-orbit (SO) coupling (mBJ + U + SO technique). Based on the present mBJ + U + SO calculation, we explore in detail projected DOS curves, bands dispersion, and the main optical constants. The projected DOS data are found to be in excellent agreement with X-ray emission bands measured for the main contributors to the valence-band region of the compound under study. The present experimental and theoretical results allow for statement that Cu2HgGeS4 is a promising photovoltaic absorber material.

The Blue Light Defects Activation in A-Si:H Pin Photodiode as a Biosensor

The microfluidic Lab-On-Chip (LOC) systems, based on the CMOS technology, today grow rapidly based on requirement of the Point-of-care-testing (POCT). It is a need for a high sensitive biotransducers, as a part of biosensors to be integrated on LOC system. To detect low-level of light emitted by an analyte, promising material and devices are a p-i-n a-Si:H photodiodes. The observed absorbance of blue light in human cells HeLa (cervical carcinoma) induct H2O2 in same cells and consequently, chemical reaction with NO, detected as chemiluminescence signal by the photodiode, as well as formation of cytotoxic singlet oxygen. On the other side a-Si:H p-i-n photodiode has a high sensitivity on blue light at low-light intensity, good spectral responsivity and small reflectance for blue light, low dark current, low-noise in the range of low reverse bias voltages. The photoconductivity of a-Si:H p-i-n photodiode is influenced by the native and light induced localized state density and their energy distribution in the energy gap of intrinsic a-Si:H. It is observed that the defect states of i-layer at various bias voltages contribute to the detection of HeLa cells chemiluminescence. The optical bias dependence of modulated photocurrent method (OBMPC) using the blue LED light is applied to clarify the energy gap density of state nature and energy distribution, respectively in a-Si:H p-i-n photodiode i-layer.

Photoactivity under visible light of defective ZnO investigated by EPR spectroscopy and photoluminescence

The photochemical and photophysical properties of a defective zinc oxide prepared by precipitation have been investigated using mainly electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. As already reported in the literature the band gap of the oxide contains intra band gap states related to the presence of point defects (mainly cation vacancies) in the structure. The concentration and the energy levels of such defects, a fraction of them being paramagnetic, are the basis of a mechanisms of double and multiple excitations allowing visible photons with energy lower than the band gap value (hν <Eg) to promote electrons from the valence band (VB) to the conduction band (CB) similarly, though less efficiently, to what done by UV light with hν >Eg. Remarkably, some of the paramagnetic defects present in the bulk of the as prepared materials derive from excitation of VB electrons induced by ambient light illumination.The electron excitation from VB to CB has been observed upon irradiation under vacuum at 77 K with polychromatic light and applying four different filters to the emitted radiation with cut-off in the range between 400 nm and 495 nm. The process has been monitored by EPR as the photoexcitation ends up in the formation of trapped electron centers (signal at g = 1.96) and trapped hole centers (signal in the range 2.021 >g > 2.003) both clearly detected by this technique. A scheme of the energy state distribution in the band gap of the defective oxide, obtained coupling EPR and photoluminescence results, is proposed. Finally, a non-negligible fraction of the visible light generated carriers reach the surface of the nanocrystals, entailing the typical redox reactions of photocatalysis as indicated by the detection of hydroxyl radicals in solution performed by spin-trapping. For this reason, the wet chemistry prepared zinc oxide can be considered a visible light active (VLA) system.

Using the Energy Distribution as a Benchmarking Among Models for Adiabatic Quantum Processing in the Protein Folding Problem

Determining the tertiary complexity of proteins using ab-initio algorithms is a hard problem. Adiabatic Quantum Computing allows to construct simple Ising-like Hamiltonians in order to elucidate the aminoacid interactions minimizing the conformation energy of the protein. Exploring the energy distribution of the Hamiltonian allows to compare the efficiency of different models there proposed. This article compare the efficiency of two algorithms through the conformation energy of a protein stating a benchmark through the energy distributions of the conformation states.

Optimization of laser-target parameters for the production of stable lithium beam.

A laser ion source coupled with a radio frequency quadrupole linac accelerator is being proposed as a suitable system for the production of a low energy, high-current stable lithium beam. In order to maximize the lithium yield, plasmas generated by laser ablation of different materials based on lithium (Li, LiOH, and LiNbO3) have been characterized by using a Faraday cup and an electrostatic ion analyzer in the time of flight configuration. A wide range of laser power density has been investigated (109-1012 W/cm2) using two Nd:YAG lasers operating at different wavelengths (1064 nm and 532 nm), pulse durations (6 ns and 17 ns), and maximum energies (1400 mJ and 210 mJ). This paper outlines the pros and cons of the investigated materials by studying how the ion energy, yields, and charge state distributions are modified when the laser power density is changed. Considerable attention has been paid to the higher charge states of oxygen, which may occur with the same mass-to-charge ratio of Li3+. The analysis has evidenced that LiNbO3 represents a valid target since it allows minimizing the O6+/7Li3+ ratio down to 2.5% by using a laser power density of 1.8 × 1010 W/cm2. For such a condition, a Li3+ current of 1.4 mA/cm2 has been measured.

Atom-by-atom construction of attractors in a tunable finite size spin array

We demonstrate that a two-dimensional finite and periodic array of Ising spins coupled via RKKY-like exchange can exhibit tunable magnetic states ranging across three distinct magnetic regimes: (1) a conventional ferromagnetic regime, (2) a glass-like regime, and (3) a new multi-well regime. These magnetic regimes can be tuned by one gate-like parameter, namely the ratio between the lattice constant and the oscillating interaction wavelength. We characterize the various magnetic regimes, quantifying the distribution of low energy states, aging relaxation dynamics, and scaling behavior. The glassy and multi-well behavior results from the competing character of the oscillating long-range exchange interactions with respect to the lattice. The multi-well structure features multiple attractors, each with a sizable basin of attraction. This may open the possible application of such atomic arrays as associative memories.

Nonradiative Energy Transfer through Distributed Bands in Piezochemically Synthesized Cesium and Formamidinium Lead Halide Perovskites.

Repeated absorption of emitted photons, also called photon recycling, in large crystals and thick films of perovskites leads to delayed photoluminescence (PL) and decrease of PL intensity. The role of distinct band gaps, which act as donors and acceptors of energy, and nonradiative energy transfer on such delayed, low intensity emission is yet to be rationalized. Here we report delayed emission by nonradiative energy transfer across a distribution of energy states in close-packed crystallites of cesium lead bromide CsPbBr3 , formamidinium lead bromide FAPbBr3 , or the mixed halide FAPb(BrI)3 perovskite synthesized in the form of thick pellets by the piezochemical method. The PL lifetime of the bromide-rich domain in the mixed halide pellet is considerably decreased when compared with a pure FAPbBr3 pellet. Here the domains with higher bromide composition act as the energy donor, whereas the iodide-rich domains are the acceptors. Time-resolved PL measurements of CsPbBr3 , FAPbBr3 , and the mixed halide FAPb(BrI)3 perovskite pellets help us to clarify the role of nonradiative energy transfer on photon recycling.

Impact of charge carrier recombination and energy disorder on the open-circuit voltage of polymer solar cells

Charge carrier recombination and energy disorder in organic solar cells both have a profound impact on the open-circuit voltage of the device. In this paper, both traditional fullerene-(PC&lt;sub&gt;71&lt;/sub&gt;BM) and nonfullerene-(O-IDTBR) based solar cells were fabricated using the same electron donor material (PTB7-Th). The room-temperature current density–voltage characteristics showed that despite the values of their power conversion efficiencies were very close, there was a huge open circuit voltage (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt;) difference between the PC&lt;sub&gt;71&lt;/sub&gt;BM and O-IDTBR devices. To understand the sources of the &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt; variation, characterization techniques such as impedance spectra, low temperature electrical characterization method, transient photovoltage, and electroluminescent spectra were carried out. Temperature-dependent &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt; of the devices were measured in a large temperature range between 120 K and 300 K. The charge transfer state energy (&lt;i&gt;E&lt;/i&gt;&lt;sub&gt;CT&lt;/sub&gt;&lt;italic/&gt;) of the fullerene and the nonfullerene cells were determined to be 1.13 V and 1.34 V, respectively. Furthermore, the Mott-Schottky equation was applied to analyze the capacitance- voltage curves of the fabricated devices. Results showed that the built-in voltage (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;bi&lt;/sub&gt;) of the O-IDTBR based cell (1.38 V) was much higher than that of the PC&lt;sub&gt;71&lt;/sub&gt;BM cell (1.15 V). By analyzing the above data, it was easy to speculate that charge carrier recombination loss in the PC&lt;sub&gt;71&lt;/sub&gt;BM device was more serious since the net electric field was relatively weak. Impedance spectra were used to measure the charge carrier recombination process in both devices. Fitting results through the equivalent circuit stated clearly that values of the recombination resistance in the O-IDTBR device were much higher in the test range, indicating that the charge carrier was less easy to recombine in the nonfullerene device. This speculation could be verified by the transient photovoltage (TPV) measurements since the carrier lifetime in the O-IDTBR device was much longer. The excited states in the devices were investigated by the electroluminescence spectra. Since the full width at half maximum (FWHM) of the O-IDTBR emission spectrum was narrower, the excited state energy distribution in the O-IDTBR device was more uniform. Based on the above analyses, the higher &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt; in the O-IDTBR device was attributed to the mild charge carrier recombination and low energy disorder.

(Invited) Photoemission-Based Characterization of Gate Dielectrics and Stack Interfaces

In the development of Metal-Insulator-Semiconductor (MIS) devices, gate dielectric technologies are of great importance and include major scientific and technological issues to be solved for required device performance and reliability. To gain a better understanding of physics of gate dielectric stacks and insights into interface control, characterization of electronic structures of gate dielectrics and quantification of electronic defects in dielectric stacks are imperative. In this work, we have demonstrated how energy dependent dielectric responses of gate dielectrics are evaluated by photoelectron energy loss spectroscopy (PEELS) [1, 2] and how energy distributions of defect states in wide gap materials and their interfaces are quantified by total photoelectron electron yield spectroscopy (PYS) [3-5]. Determination of Complex Dielectric Function The analyses of core-line photoemission spectra have been extensively conducted to characterize chemical bonding features in materials and heterointerfaces of interest. On the other hand, electron energy loss spectroscopy is an effectively used method for study the excitation spectra of atoms, molecules, and solids. Thus, we have measured and analyzed energy loss signals (ELS) incidental to core-line spectra not only to determine energy bandgap values of dielectrics but also to characterize dielectric functions of dielectrics since, inherently, photoexcited electrons passing through dielectrics can suffer inelastic losses due to electronic excitations such as plasmons and band-to-band transitions. As the first step, we examined a complex dielectric function of 50nm-thick SiO2 grown at 1000 ºC in dry O2 from the ELS analyses of both Si2p3/2 and O1s lines. In each analysis, based on photoelectron take-off angle dependence of ELS, the pure bulk component being proportional to the negative imaginary part of inverse dielectric function was extracted carefully, and then the real part of inverse dielectric function can be calculated by Kramers-Kronig transformation of the extracted bulk component. Almost the same results were obtained from the ELS analyses of both Si2p3/2 and O1s photoelectrons, and are very consistent with the dielectric function calculated from reported optical constants of SiO2 glass [6]. Notice that obtained dielectric function enables us to confirm the validity of the energy band gap value determined simply from the onset energy of ELS. We have extended this PEELS to characterization of dielectric functions of CVD SiO2 formed by reaction between SiH4 and remote O2 plasma, Hf- and Al-silicates prepared by plasma-assisted ALD, and confirmed that spectral broadening and tailing become significant with an increase in structural fluctuation and incorporation of Hf and Al atoms. Quantification of Energy Distribution of Defect States Since photoelectron yield is obtained by counting the total number of photoelectrons emitting from the sample as a function of incident photon energy and normalized by the incident photon flux, the spectrum is related to an integral over the occupied density of states involving photoemission near the sample surface. Changes in photoelectron yield spectrum with wet-chemical thinning of 5.2nm SiO2 formed 500ºC by remote plasma enhanced CVD on n-type GaN(0001) show presence of occupied defects in SiO2, near the interface and in GaN but a relatively large number of defects are located within ~1.5nm from the SiO2/GaN interface. From the 1st derivative of the measured yield spectrum with respect to incident photon energy which leads us to the energy distribution of occupied defect state densities in consideration of density of states of the GaN valence band (VB), we found that occupied states are reduced down to ~1x1011cm-2eV-1 at the energy corresponding to the midgap of GaN near the SiO2/GaN interface with N2 anneal at 800ºC. The defect state density near the conduction band edge, which was crudely estimated in consideration of electron occupation probability based on the Fermi-Dirac distribution, are in good agreements with the result obtained from the capacitance-voltage (C-V) analysis using the Terman method. We also found that, for Hf-silicate with a compositional ratio of Hf/(Si+Hf) = ~75% and a relative dielectric constant of ~16 formed on GaN by plasma-assisted ALD and followed by 800ºC anneal in N2 ambience, a similar energy distribution of defect state density to the 800ºC-annealed SiO2/GaN was obtained in the energy range from ~1eV above the GaN valence band edge toward the conduction band edge.

Photoresponses of Supported Au Single Atoms on TiO2(110) through the Metal-Induced Gap States.

When a metal single-atom (SA) catalyst is supported on a semiconducting photocatalyst, the charge transfer of the photoexcited carriers to metal SAs can provide a synergetic activity for the co-catalysts. Here, we report the interfacial electronic coupling of the Au SAs on the TiO2(110) surface using scanning tunneling microscopy/spectroscopy, in combination with first-principles calculations. Distinct energy and spatial distributions of the metal-induced gap states (MIGSs) are experimentally revealed for the Au SAs adsorbed at the terminal Ti sites and the oxygen vacancies. The localized MIGS below the Fermi level provides a dedicated channel for the transfer of a photoexcited hole from the TiO2 substrate to the adsorbed Au SAs. The hole can weaken the Ti-Au bonding and activate the diffusion of Au SAs. Our results shed light on combining the advantages of photocatalysis and metal SA catalysis using a co-catalyst, which is promising to promote chemical reactions at low temperatures.