Energy Loss Spectra Research Articles

DNA Nucleobase Interaction Driven Selective Sensing Properties of Monolayer Delta Tellurene

In this study, we investigate the interaction between DNA nucleobases and semiconducting monolayer delta tellurene (δ(Te)) using a DFT framework with a vdW functional. Our results suggest that nucleobases adhere to the monolayer through physisorption, with Cytosine having the highest binding energy per atom and Thymine the lowest. The selectivity of signal detection produced by each nucleobase using δ(Te) is larger for Thymine (22.27%). Guanine exhibits a longer resident time due to its stronger binding energy with the tellurene surface, while Thymine displays the shortest residence time. The semiconducting behavior of the nucleobase+ δ(Te) system is captured in an STM-like setup, with tunneling current peaking at +1.2 V. These findings, coupled with modulations in quantum capacitance pre- and post-DNA binding, suggest promising sensing applications. Guanine exhibits a red shift of 0.60 eV in the imaginary part of the dielectric function, while adenine shows a 0.30 eV red shift in electron energy loss (EEL) spectra. Our results demonstrate the potential of δ(Te) monolayers in fabricating sensors for DNA sequencing devices.

Structural and optical evolution in CeO2 films induced by aluminum doping: A comprehensive study

This study investigates the impact of aluminum (Al) doping and oxygen vacancies on the structural, electronic, and optical properties of Cerium Oxide (CeO₂) films. The films were fabricated on glass substrates using the sol-gel spin coating method for both undoped and Al doped CeO₂. Theoretical insights from the DFT + U + V method further explore how Al doping and oxygen vacancies influence the electronic structure and optical behavior of ceria. Experimentally, Al doping was found to increase the lattice parameters and reduce the crystallite size without forming secondary phases. Raman spectroscopy revealed a shift to lower wavenumbers in Al-doped samples, while XPS analysis confirmed the presence of both Ce³⁺ and Ce⁴⁺ oxidation states, along with Al³⁺ and O2⁻ ions. Optical measurements showed a decrease in the optical band gap from 3.14 eV to 2.93 eV as the Al concentration increased to 5 %. Additionally, the optical dielectric constant slightly decreased, whereas optical conductivity improved with the incorporation of aluminum. Theoretical calculations show that oxygen vacancies were shown to reduce the band gap by introducing localized Ce³⁺ mid-gap states, while Al doping led to a gradual narrowing of the band gap without creating new states within it. The combination of Al doping and oxygen vacancies resulted in both further band gap narrowing and the appearance of mid-gap states. Optical property calculations revealed that both oxygen vacancies and Al doping reduced the intensity of the dielectric functions at 310 nm. Moreover, these two factors had opposing effects on the electron energy loss spectrum (EELS) at low energies: Al doping induced high-intensity peaks, while oxygen vacancies diminished these peaks.

Structural, electronic and optical properties of α -Si3N4, β-Si3N4 and γ-Si3N4 using density functional theory

Density Functional Theory (DFT) has in recent years gained a lot of popularity and has become an efficient and reliable tool in the study of material properties. This is specifically due to its computational convenience and excellent results in the prediction of material properties, which is aided by the development of highly efficient and accurate functionals. DFT has successfully been applied in a vast study of material at both ground and excited states. In this study based on DFT structural, optical, electronic properties and phonon frequency of silicon nitrides of different phases were studied using the GGA as exchange-correlation functional. For the electronic band gap calculation the results was obtained using the GGA and the hybrid HSE06 respectively for α -Si3N4 with space group (P31c), β-Si3N4 with space group (P63/m) and γ-Si3N4 phase polymorph with space group (14‾3d). Results obtained for the phases α -Si3N4 shows a narrow indirect band gap while β and γ -Si3N4 indicate a wide indirect band gap material for wide possible application in high temperature and high-power applications. Cohesive energy calculation and phonon frequencies were obtained to check the mechanical and dynamic stability of the three different phases. Results obtain for density of states, partial density of states and the optical properties, such as absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss spectra which all show good agreement with previous studies and relative experimental data.

Beyond the random phase approximation (RPA): First principles calculation of the valence EELS spectrum for KBr including local field, quasiparticle, excitonic and spin orbit coupling effects

The low energy region (< 50 eV) of the electron energy loss spectrum (EELS) can contain a great deal of spectral detail associated with excitations of the valence electrons. Calculation of the spectra from first principles can assist with interpretation and the most widely used method is the random phase approximation (RPA), usually neglecting local field effects (LFE). For KBr this approach is insufficient due to the importance of quasiparticle and excitonic effects. Calculations including these multi-electron effects are shown to give much improved agreement with the experimental spectra, and the inclusion of spin-orbit coupling (SOC) reproduces the excitonic doublet just above band-edge onset. A review of the complex theory behind these methods is given along with practical guidance on performing these calculations.

A study of optical properties and electron energy loss spectra of ZnS by linear response theory

The linear response theory has been applied to study the optical properties and electron energy loss spectra of ZnS. The ground state is built using the Full-Potential Linearized Augmented Plane Wave method. Thereafter, the electronic properties such as band structure and density of states are calculated. Calculations of electron energy loss spectra and optical properties are performed on the top of these ground state electronic properties. The calculations are performed using three exchange–correlation kernels namely, adiabatic local density approximation, long range contribution, and the bootstrap. The random phase approximation is also considered. An approach proposed by us to find the material dependent parameter α is used in long range contribution kernel to capture more accurate optical properties. Three values of α viz 0.78, 1.09, and 1.22 are considered. It is observed that the α = 0.78 gives very good results. This proposed scheme is found to work very well for ZnS also. The effect of local field and electron–hole interaction on the spectra is examined. For example after incorporating local field effect the high frequency dielectric constant ε∞ [i.e. ε1E→0eV ], reduces by 9.19, 12.26, 13.51 and 11.02% for random phase approximation, adiabatic local density approximation, long range contribution and bootstrap kernel respectively. In EELS plasmon peak positions are found using the three kernels and random phase approximation. A good accord with experimental results is noted after incorporating local field effects. It is observed that local field effect causes redshift of prominent peak (i.e. plasmon peak) in electron energy loss spectra by 0.61 eV.

Atomic-Scale Mechanism of Enhanced Electron-Phonon Coupling at the Interface of MgB2 Thin Films.

In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, electron-phonon coupling is the fundamental mechanism of superconductivity. For instance, the superconductivity of magnesium diboride (MgB2) comes from the coupling between E2g modes (in-plane boron-boron bond vibrations) and self-doped charge carriers. In thin films and ceramics of BCS superconductors, interfaces with discontinuous chemical bonds may alter the local electron-phonon coupling. However, such effects remain largely unexplored. Here, we investigate the heterointerface of the MgB2 film on the SiC substrate at the atomic scale using electron microscopy and spectroscopy. We detect the presence of a thin MgO layer with a thickness of ∼1 nm between MgB2 and SiC. Atomic-level electron energy loss spectra (EELS) show MgB2-E2g mode splitting and softening near the MgB2/MgO interface, which enhances electron-phonon coupling at the interface. Our findings highlight the potential of interface engineering to enhance superconductivity via modulating local phonon states and/or electron states.

On-demand performance optimization of AlGaN/GaN high electron mobility transistors using stoichiometric variation of dielectric alloy AlxTayO

The current research investigates the potential advantages of optimally combining wide bandgap Al2O3 with high dielectric constant (high-κ) Ta2O5 for gate dielectric applications. Various compositions of 10 nm AlxTayO oxide films are grown on the Al0.3Ga0.7N/GaN heterostructure by co-sputtering Al and Ta metals, followed by thermal oxidation at 500 °C. The average root-mean-square roughness of the grown oxide films is ∼1.2–1.4 nm compared to 0.4 nm for as-deposited metal. X-ray photoelectron spectroscopy and transmission electron microscopyconfirm the formation and thickness of the grown oxide films. The bandgap (Eg) of the oxide films calculated from O1s electron energy loss spectra show a linear increase from 4.85 eV for pure Ta2O5 to 6.4 eV for pure Al2O3. The dielectric constant (εox) calculated from capacitance–voltage (CG−VG) measurements decreases linearly from 25.7 for Ta2O5 to 7.9 for Al2O3. The interface trap density (Dit) is estimated from the frequency dispersion of capacitance–voltage (CG−VG) characteristics. The DC and radio frequency (RF) characteristics of AlxTayO/Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) devices are measured and compared with the Schottky HEMT devices (without any gate oxide). Compared to Schottky HEMT devices, AlxTayO/Al0.3Ga0.7N/GaN HEMT devices show superior DC characteristics, which helps us achieve maximum RF output power. Furthermore, the OFF-state measurements show that the AlxTayO/Al0.3Ga0.7N/GaN HEMT devices can sustain higher source-to-drain voltages, from a minimum of 88 V on pure Ta2O5 metal-oxide-semiconductor (MOS)-HEMTs to a maximum of 138 V on pure Al2O3 MOS-HEMTs before the dielectric breakdown happens, compared to a 57 V breakdown voltage on Schottky HEMT devices. An oxide variation of AlxTayO, with Al composition ratio of 0.34, shows an exceptional ION/IOFF ratio of 4 × 1011, a gate leakage current of 8 × 10−12 A/mm, a near-ideal subthreshold slope of 63.8 mV/dec, and the unity current gain frequency (fT) of 25.6 GHz.

The structural, mechanical, electronic, and optical properties of monolayer and bilayer ABC3(A [dbnd] Ga, In; B [dbnd] Si, Ge; C [dbnd] S, Se, Te)

This paper studies the structural, mechanical, optical, and electronic characteristics of monolayer and bilayer ABC3 (AGa, In; BSi, Ge; CS, Se, Te). Their characteristics are obtained using the density functional theory with van der Waals (vdW) correction. The stability is confirmed by examining Born’s criterion, cohesive energy, phonon dispersions, and COHP analysis. In addition, the stability of these monolayers against tensile strain is explored. The electronic properties are extensively studied through band structure, PDOS, and effective masses. The optical properties are investigated for possible applications in optoelectronic devices. In the following, bilayer ABC3 with three different stacking orders is investigated. Most of the monolayers and bilayers ABC3 show an indirect bandgap. The contributions of each element at the valence and conduction bands are explored through the projected density of the state. The effective mass is derived for the valence and conduction band valleys, whereas the Γ-valley shows the lowest effective mass. Additionally, both real and imaginary parts of the dielectric constant, electron energy loss spectra, and optical absorption are studied, which might lead to intriguing usages in photovoltaic and electroluminescent systems. The analysis of the optical properties reveals that the studied monolayers and bilayers have acceptable visible-range absorption characteristics. Furthermore, the monolayer and bilayer ABC3 dielectric function and absorption coefficient spectra display prominent optical peaks in the UV light range. Due to their distinct band gaps and optical characteristics, monolayer and bilayer ABC3 materials are good prospects for upcoming electrical and optoelectronic applications.

DFT study of electron energy loss spectra of sulfur in Janus MoSSe, MoSTe, WSSe and WSTe monolayers

In this paper, electronic properties of Janus MSX monolayers (M = Mo, W; X = Se or Te), including electron energy loss near edge structures (ELNES), as K and [Formula: see text] edge spectra of sulfur atoms, have been calculated using a full potential scheme and the augmented plane wave plus local orbitals (APW+lo) method in the framework of density functional theory (DFT). Due to the lack of experimental results, the obtained spectra are compared with the corresponding spectra of MoS2 monolayer. The band structure analysis shows that the Janus MoSSe and WSSe monolayers are direct bandgap semiconductors, while the Janus MoSTe and WSTe monolayers are indirect bandgap semiconductors. In comparison to MoS2, the main structures of the K edge ELNES spectra of sulfur atoms in Janus monolayers occur at lower energies, due to the structural change and increased bond length. The relative reduction of intensities in the main structures predicts the possibility of reducing the number of partial densities of states (PDOS), that is, the reduced p PDOS for the K edge in the corresponding energy range. In the K ([Formula: see text] edge ELNES spectra of the sulfur atom in Janus monolayers and MoS2 monolayers, the main structures are due to the electron transfer to the unoccupied [Formula: see text] and [Formula: see text] states (3s of sulfur and 4d states of the transition metal).

SF6 Negative Ion Formation in Charge Transfer Experiments.

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. Chem. Phys.1975, 10, 235-259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the negative ions formed in K + SF6 collisions, in a wide energy range from 10.7 up to 213.1 eV in the centre-of-mass frame, show that the main anion is assigned to SF5- and contributing to more than 70% of the total ion yield, followed by the non-dissociated parent anion SF6- and F-. Other less intense anions amounting to <20% are assigned to SF3- and F2-, while a trace contribution at 32u is tentatively assigned to S- formation, although the rather complex intramolecular energy redistribution within the temporary negative ion is formed during the collision. An energy loss spectrum of potassium cation post-collision is recorded showing features that have been assigned with the help of theoretical calculations. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom are performed to support the experimental findings. Apart from the role of the different resonances participating in the formation of different anions, the role of higher-lying electronic-excited states of Rydberg character are noted.

Analysis of the Ag M4,5 EELS edge to study silver nanoparticle corrosion.

Electron energy loss spectra collected from fresh and corroded silver nanoparticles are compared with those from a number of reference materials, focusing on the M4,5 edge. Chemical shifts and changes in the energy loss near edge structure (ELNES) are described and found to be sufficient to distinguish metallic silver from chemically oxidised silver. The measurements, in conjunction with electron energy loss spectrum imaging, are used to assess the mechanisms for atmospheric corrosion of silver nanoparticles. We unambiguously assign the corrosion product under atmospheric conditions to be silver sulphide, but show the reaction process to be distinctly inhomogeneous, producing a variety of types of corroded particles. LAY DESCRIPTION: >Here, we use analytical electron microscopy to track the corrosion of silver nanoparticles and present chemical maps of the corrosion products. We show clear spectroscopic differences between metallic and corroded silver using the M4,5 electron energy loss spectral feature, which is not commonly studied. Our study shows that corrosion is due to interactions with sulphur in the atmosphere; and the corrosion is not uniform, but appears to develop from specific points on the surface of the nanoparticles.

Optical properties of hafnium-dioxide derived from reflection electron energy loss spectroscopy spectra

The optical properties of HfO2 have practical applications. As an important gate dielectric material with high-k dielectric, HfO2 is beneficial to reduce the leakage current of the complementary metal-oxide-semiconductor (CMOS) gate and improves the gate structure. HfO2 also plays a key role in optical coating materials field for its high transmittance in the ultraviolet to near-infrared band, and high laser damage threshold. Therefore, it is of practical significance for the accurate knowledge of optical properties of HfO2. Here we present the optical constants and dielectric function of HfO2 based on the energy loss function (ELF) in the energy loss range of 0–200 eV for nanocrystalline film. Our new data are derived from the analysis of the reflected electron energy loss spectra by using the latest version of our reverse Monte Carlo modelling. Sum rules are used to check the reliability of the new data. We have found that up to 30 eV there are three main peaks, and the first-principles calculation also confirms the three peak structures. A comparison with previous results indicates that the ELF peak positions of HfO2 with different crystal structures are similar, but the peak intensity and shape are different. The heterogenicity of the crystal structure of HfO2 leads to different measurement results for different samples.

Correlating the electronic structures of β-Ga2O3 to its crystal tilts induced defects at nanoscale

Crosslinking structural transformation mechanism at nanoscale to the corresponding anisotropically electronic properties is essential to both the atomic-level controlled synthesis and extreme-conditional applications of the ultrawide bandgap semiconductors. Here, we report the first direct observation of bandgap variation at certain microstructural flaws in monoclinic crystal β-Ga2O3 via scanning transmission electron microscopy-electron energy loss spectrum (STEM-EELS) technology with both high energy and spatial resolution. Atomic-scale tilt of the Mosaic blocks relative to [010] zone axis is demonstrated to cause specific point defects accumulation at block boundaries, resulting in the formation of vacancy lines (or clusters) and then the crystal deformation induced flaws. These as-formed tiny Mosaic tilts observed from both in-plane and out-of-plane geometry are correlated to the corresponding electronic structure obtained by density functional calculations, indicating the carrier mobility limits transferred from intrinsic polar optical phonon scattering to the ionized oxygen atoms scattering in the defective monoclinic crystal. These findings provide a new insight on these anisotropic defect formation induced electronic structural variation, paving the way for precise synthesis and development of high-performance ultra-wide bandgap materials.

Improved Dielectric Response of Solids: Combining the Bethe-Salpeter Equation with the Random Phase Approximation.

The Bethe-Salpeter equation (BSE) can provide an accurate description of low-energy optical spectra of insulating crystals-even when excitonic effects are important. However, due to high computational costs it is only possible to include a few bands in the BSE Hamiltonian. As a consequence, the dielectric screening given by the real part of the dielectric function can be significantly underestimated by the BSE. Here, we show that universally accurate optical response functions can be obtained by combining a four-point BSE-like equation for the irreducible polarizability with a two-point Dyson equation that includes the higher-lying transitions within the random phase approximation. The new method is referred to as BSE+. It has a computational cost comparable to the BSE but a much faster convergence with respect to the size of the electron-hole basis. We use the method to calculate refractive indices and electron energy loss spectra for a test set of semiconductors and insulators. In all cases the BSE+ yields excellent agreement with experimental data across a wide frequency range and outperforms both the BSE and the random phase approximation.

Ultraclean Suspended Graphene by Radiolysis of Adsorbed Water.

Access to intrinsic properties of a 2D material is challenging due to the absence of a bulk that would dominate over surface contamination, and this lack of bulk also precludes effective conventional cleaning methods that are almost always sacrificial. Suspended graphene and carbon contaminants represent the most salient challenge. This work has achieved ultraclean graphene, attested by electron energy loss (EEL) spectra unprecedentedly exhibiting fine-structure features expected from bonding and band structure. In the cleaning process in a transmission electron microscope, radicals generated by radiolysis of intentionally adsorbed water remove organic contaminants, which would otherwise be feedstock of the notorious electron irradiation induced carbon deposition. This method can be readily adapted to other experimental settings and other materials to enable previously inhibited undertakings that rely on the intrinsic properties or ultimate thinness of 2D materials. Importantly, the method is surprisingly simple and robust, easily implementable with common lab equipment.

Cherenkov radiation in a bianisotropic medium with magnetoelectric effect

Cherenkov radiation (CR) has been extensively explored in a large variety of media; however, its characteristics in a medium showing both magnetoelectric (ME) and anisotropy effects have not been addressed so far. The aim of this study is to address this gap by analytically investigating CR in a dispersive bianisotropic medium with ME effect. In this research, founded upon a vector-potential approach, we demonstrate that notable features such as double cones of CR with different angles can be formed due to ME coupling in bianisotropic media. We also calculate the emitted electromagnetic fields to obtain radiated power and momentum-resolved electron energy-loss spectra for a medium with varying ME coefficients, as well as for a medium without ME effects in order to illustrate the impact of this coupling on the characteristics of the CR and propose methods for the characterization of ME materials.

First principle investigations of opto-electronic and thermoelectric response of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds

We have investigated the structural, electronic, optical, and thermoelectric behavior of halide-based double perovskites A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds to reveal their potential in various opto-electronic and thermoelectric applications using first-principle calculations. For the computation of the various properties of A2TlAsX6 (A = K, Rb; X = Cl, Br) compounds, we have used approximations available within density functional theory (DFT). The energy bands and density of states have been used to elucidate the electronic response of the studied compounds, while the interpretation of optical properties is presented in terms of dielectric tensor, absorption coefficient, reflectivity, refraction and energy loss spectra. The investigated compounds exhibit a direct band gap within the energy range of 1.36 to 2.24 eV, indicating the promising nature of these compounds for diverse optoelectronic applications. Moreover, thermoelectric properties such as the figure of merit, power factor, Seebeck coefficient, specific heat, electric and thermal conductivity have also been computed for the studied compounds. Our investigation unveils the remarkable optoelectronic characteristics of the studied perovskites, which can be attributed to their advantageous bandgap and highly effective light absorption capabilities. Furthermore, these perovskites showcase exceptional thermodynamic stability, elevated electrical conductivity, favorable figure of merit (ZT) values, and reduced thermal conductivities. These findings suggest their suitability for applications in optoelectronic devices and thermoelectric applications. In this study, it is found that A2TlAsBr6 compounds exhibit significant absorption in the visible spectrum, rendering them more favorable for optoelectronic applications compared to A2TlAsCl6 compounds. Conversely, for thermoelectric applications, the Cl-based perovskites studied show greater promise than their Br-based counterparts. The modified Becke–Johnson (mBJ) potential emerges as the most precise approach for analyzing the electronic, optical, and thermoelectric characteristics of A2TlAsX6 (where A = K, Rb; X = Cl, Br) perovskites, surpassing other approximations utilized in present study.

Low-lying Negative Ion States Probed in Potassium - Ethanol Collisions.

Dissociative electron transfer in collisions between neutral potassium atoms and neutral ethanol molecules yields mainly OH-, followed by C2H5O-, O-, CH3 - and CH2 -. The dynamics of negative ions have been investigated by recording time-of-flight mass spectra in a wide range of collision energies from 17.5 to 350 eV in the lab frame, where the branching ratios show a relevant energy dependence for low/intermediate collision energies. The dominant fragmentation channel in the whole energy range investigated has been assigned to the hydroxyl anion in contrast to oxygen anion from dissociative electron attachment (DEA) experiments. This result shows the relevant role of the electron donor in the vicinity of the temporary negative ion formed allowing access to reactions which are not thermodynamically attained in DEA experiments. The electronic state spectroscopy of such negative ions, was obtained from potassium cation energy loss spectra in the forward scattering direction at 205 eV impact energy, showing a prevalent Feshbach resonance at 9.36±0.10 eV with character, while a less pronounced contribution assigned to a shape resonance has been obtained at 3.16±0.10 eV. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom have been performed to support the experimental findings.

Pressure effects on the structural, electronic, elastic, optical, and vibrational properties of YMg intermetallic compounds: a first-principles study

The properties of YMg in B2 structure have been comprehensively analysed using the first-principles plane-wave pseudopotential method. Specifically, the structural, electronic, elastic, vibrational, and optical properties were investigated using the generalized gradient approximation (GGA) method in the context of density functional theory. The Vienna ab initio simulation package (VASP) was utilized for these calculations. The computed lattice parameter (3.803 Å) and bulk modulus (41.33 GPa) are consistent with the earlier data on ambient pressure. The electronic band structure and energy-dependent density of states reveal the metallic nature of the titled compounds. The Born stability requirements confirmed the mechanical stability. The analysis of Pugh’s and Poisson’s ratios and Cauchy’s pressure reveals that YMg is ductile under the pressures in consideration. According to several anisotropy indices, the compound is noticeably anisotropic both in ambient and under pressure. Our investigation includes an analysis of several fundamental mechanical parameters of the material, including the bulk modulus, the pressure derivative of the Zener anisotropy factor, Poisson’s ratio, isotropic shear modulus and Young’s modulus with a particular focus on their dependence on pressure. We have determined that the elastic constants obtained remain mechanically stable, satisfying the Born Stability conditions even at high pressures of up to 60 GPa. To explore the dynamic stability of YMg, we analysed the material’s phonon dispersion curves. The examined compound displays stability under dynamic conditions from 0 GPa to 30 GPa, as evidenced by its positive vibration frequencies. However, this stability is not sustained under higher pressure, as the compound becomes unstable after 30 GPa to 70 GPa. The electronic band structure and density of states diagrams demonstrate YMg’s metallic properties. At atmospheric pressure (0 GPa), the total density of states (TDOS) near the Fermi level is approximately 1.63 states/eV, with pressure application reducing DOS. The dielectric function, refractive index, and energy loss spectra are examined within the 0–20 eV energy range. YMg exhibits its highest absorption between 4 and 11 eV. The peak optical conductivity is observed around 0.78 eV (equivalent to 1589.5409 nm), while the most significant energy loss occurs at 11.90 eV, roughly corresponding to 2.8 Hz in the ultraviolet spectrum. Moreover, we extensively analyzed the material’s phonon thermodynamic and optical properties, providing insights into its behavior under various conditions. The outcomes acquired at zero pressure are generally coherent with the current theoretical values.

The heterointerface characterization of BaF2 or MgF2 on the hydrogenated diamond by X-ray photoelectron spectroscopy

Group-II fluorides (BaF2 and MgF2) insulators are deposited on hydrogenated (C–H) diamonds by E-beam evaporator at room temperature. The bandgaps, chemical bonds and band offsets of fluorides are investigated by the high-resolution X-ray photoelectron spectroscopy (XPS) measurements. The XPS results show bandgap energies of 9.4 ± 0.2 eV for BaF2 and 9.7 ± 0.2 eV for MgF2 by F 1s energy loss spectra. The valence band offsets (ΔEV's) of BaF2/MgF2 on the C–H diamond are determined as 5.2 ± 0.2 and 4.8 ± 0.2 eV, respectively. There are both type II energy band configuration for BaF2 and MgF2 on the C–H diamond with conduction band offsets of 1.3 ± 0.2 eV and 0.6 ± 0.2 eV, respectively. The relatively oxygen-weak or oxygen-free fluoride/C–H diamond interface and large ΔEV suggest that fluorides are an excellent gate dielectric for the C–H diamond field-effect transistors with high hole mobility and low gate leakage.