Ultraviolet Photoelectron Spectroscopy Research Articles

Pd Nanoparticles Decorated CeZrOx for Enhanced Photocatalytic Hydrogenation of Biomass‐Derived Compounds

AbstractThe photocatalytic conversion of biomass‐derived compounds into value‐added chemicals presents a promising protocol for the sustainable production of renewable chemicals. Our study explores the hydrogenation of biomass model compounds under visible light illumination. Zr was incorporated into the CeO2 framework, forming a CeZrOx(1:0.5) solid solution, confirmed by powder X‐ray diffraction (PXRD) and X‐ray photoelectron spectroscopy (XPS) analyses. The light uptake capacity of the CeZrOx solid solution was characterized using UV–visible spectroscopy. Additionally, the band structure of the CeZrOx solid solution was assessed using valance band X‐ray photoelectron spectroscopy (VB‐XPS) and Ultraviolet photoelectron spectroscopy (UPS) analysis, revealing a Z‐Scheme, which was further confirmed by various control experiments. Upon decorating the CeZrOx(1:0.5) solid solution with 1 wt% palladium (Pd), the resulting 1Pd/CeZrOx(1:0.5) composite exhibited improved charge separation and enhanced visible light absorption capacity. This composite achieved ∼99% conversion of furfural to tetrahydrofurfuryl alcohol under a 15 W blue LED illumination and 0.2 MPa hydrogen. Similarly, it demonstrated ∼99% conversion of benzyl phenyl ether (BPE) to toluene and phenol under a 10 W blue LED illumination. Our findings elucidate the active sites and demonstrate the recyclability of mixed metal oxides for selective furfural hydrogenation and BPE hydrogenolysis under visible light.

Electronic structure of 2(5H)-thiophenone studied by UPS and soft X-ray spectroscopy

Abstract The electronic structure of 2(5H)-thiophenone in the gas phase was investigated by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the C 1s, O 1s, and S 2p edges. All assignments of the experimental results are supported by both ab-initio electron propagator OVGF calculations for the valence photoemission bands and density functional theory (DFT) and relativistic time dependent DFT calculations for the core levels XPS and NEXAFS spectra. Overall good agreement between experiment and theory is observed; this is especially true for core electron excitations which has permitted an unambiguous assignment of the observed spectral features in terms of single-particle excitations to virtual molecular orbitals. The assignment of the valence band spectra based on OVGF calculations, although satisfactory, points to the importance of electron correlations effects that partially break the single particle picture of ionization.

Exploring Pt-Impregnated CdS/TiO2 Heterostructures for CO2 Photoreduction

This work focuses on the production of methane through the photocatalytic reduction of carbon dioxide using Pt-doped CdS/TiO2 heterostructures. The photocatalysts were prepared using P25 commercial titania and CdS synthesized through a solvothermal methodology, followed by the impregnation of Pt onto the surface to enhance the physicochemical properties of the resulting photocatalysts. The pure and heterostructure-based materials were characterized using X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-Vis), ultraviolet photoelectron spectroscopy (UPS), and photoluminescence spectroscopy (PL). The obtained results show the successful synthesis of the heterostructure impregnated with Pt. Moreover, the observed key role of CdS and Pt nanoparticles in the final semiconductor is to reduce the electron-hole pair recombination rate by acting as an electron sink, which slows down the recombination process and increases the photocatalyst efficiency. Thus, Pt-doped CdS/TiO2 heterostructures with the best observed composition presents better catalytic activity than P25 titania with methane production values being 460 and 397 µmol CH4/g·h, respectively.

P-Type AgAuSe Quantum Dots.

Control over the carrier type of semiconductor quantum dots (QDs) is pivotal for their optoelectronic device applications, and it remains a nontrivial and challenging task. Herein, a facile doping strategy via K impurity exchange is proposed to convert the NIR n-type toxic heavy-metal-free AgAuSe (AAS) QDs to p-type. When the dopant reaches saturation at approximately 22.2%, the Femi level shifts down to near the valence band, with the p-type carrier characteristics confirmed through photoluminescence, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy analysis. First-principles calculations reveal that K impurities preferentially occupy interstitial positions and form complex defects when combined with the abundant cationic vacancy in AAS caused by the high mobility of Ag, thereby functioning as a shallow acceptor to enhance p-type conductivity. A p-n homojunction based on AAS QDs has been fabricated and served as the active layer in a photodiode device, which demonstrates an excellent room-temperature detectivity of up to 2.29 × 1013 Jones and an outstanding linear dynamic range of over 103 dB. This study provides guidance for future design of the p-n homojunction using the toxic-metal-free Ag-based QDs and further unleashes their potential in advanced optoelectronic device applications.

Impact of Temperature and Substrate Type on the Optical and Structural Properties of AlN Epilayers: A Cross-Sectional Analysis Using Advanced Characterization Techniques

AlN, with its ultra-wide bandgap, is highly attractive for modern applications in deep ultraviolet light-emitting diodes and electronic devices. In this study, the surface and cross-sectional properties of AlN films grown on flat and nano-patterned sapphire substrates are characterized by a variety of techniques, including photoluminescence spectroscopy, high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and Raman spectroscopy. The results indicate that different sapphire substrates have minimal impact on the photoluminescence spectrum of the epitaxial films. As the temperature increased, the radius of curvature of the AlN films increased, while the warpage decreased. The AlN films grown on nano-patterned substrates exhibited superior quality with less surface oxidation. During the growth of AlN thin films on different types of substrates, slight shifts in the energy bands occurred due to differences in the introduction of carbon-related impurities and intrinsic defects. The Raman shift and full width at half maximum (FWHM) of the E2(low), A1(TO), E2(high), E1(TO), and E1(LO) phonon modes for the cross-sectional AlN films varied with the depth and temperature. The stress state within the film was precisely determined with specific depths and temperatures. The FWHM of the E2(high) phonon mode suggests that the films grown on nano-patterned substrates exhibited better crystalline quality.

Changes in electronic structure within NiSx (0.60 < x < 1.53) compound series

In this article, changes in electronic properties of NiSx series of films with different sulfur content (x = S/Ni) are studied using X-ray (XPS) and ultra-violet (UPS) photoelectron spectroscopy techniques. NiSx (0.60 < x < 1.53) films are synthesized on native oxide of Si(111) substrates via reactive deposition of Ni and S in an ultra-high vacuum chamber by varying the sulfur pressures and substrate temperatures. The binding energy (BE) of Ni2p3/2 core level, the separation between the Ni2p3/2 main peaks and satellite peaks, and the Ni3d valence band binding energies are all found to vary nearly linearly with the sulfur content in NiSx series of compounds, suggesting a direct dependence of Ni electronic charge on the sulfur content. The shift of the Ni3d and S3p states (to higher and lower BE, respectively) with an increase in the S content provides experimental confirmation of the theoretical prediction previously reported (Wen et al., 2020) [1]. All NiSx films showed density of states (DOS) at the Fermi level, indicating their metallic nature. The Ni2p3/2 binding energy shift of NiSx films are much smaller than that of oxide-based compounds, confirming the significantly more covalent nature of the sulfides. NiSx film grown on Si (111) substrate showed nickel silicide interface formation. This study provides information on the growth and trends in the electronic properties of NiSx relevant for their applications in catalysis, energy storage, and electronic devices.

Physical, optical properties and antibacterial activity of silver nanoparticles: Nanoclusters to nanoparticles formation on glass substrate by in-situ annealing

Silver nanoparticles (AgNPs) formed on in-situ annealed microscopic glass substrates from silver nanoclusters (AgNCs) generated by DC magnetron sputtering with inert gas condensation (IGC) technique. The substrate’s annealing temperature was below and above the glass transition temperature of 500 ºC and 600 ºC. The influence of annealing temperature on the surface morphology was studied using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the surface composition, chemical states, and electronic states of the AgNPs on the glass substrates. On the in-situ annealed glass substrate at 500 ºC, the produced AgNPs revealed accumulation and aggregation. For in-situ annealed at 600 ºC, a homogeneous distribution of AgNPs on the glass substrate was witnessed. The refractive index test revealed that AgNPs deposition at 600 ºC achieved higher sensitivity with 27 nm/RIU (Refractive index unit). The antibacterial activity of AgNPs was also investigated using Escherichia coli and Bacillus cereus. In contrast, better antibacterial activity was obtained with in-situ annealing at 500 ºC, where 4-fold reductions compared with the control sample. Pre-determined properties can be precisely executed to achieve the desired performance as the so-called application-oriented engineered surface in the UHV system is established. This research highlighted the differences between two different annealing temperatures' effect on the base substrate material, which subsequently impacts the structure of AgNPs and their applications. Furthermore, the outcome of this work could contribute to the multifunctional surface for detecting heavy metals, various organic pollutants, and disinfection of water and food-borne pathogenic diseases.

Atomic layer deposition of tin monosulfide thin film using Sn(acac)2 and H2S

In this study, we deposited tin monosulfide (SnS) thin film using Tin(II) 2,4-pentanedionate [Sn(acac)2] precursor and hydrogen sulfide (H2S) reactant. And we performed post annealing to improve the crystallinity of SnS thin films. The process window was 130 °C–150 °C, and the growth rate was 0.34 Å/cycle. To investigate crystallinity and the phase of SnS thin films, grazing incidence x-ray diffraction (GI-XRD) and Raman spectroscopy were performed. SnS thin films showed a single orthorhombic phase after annealing. In addition, transmission electron microscopy (TEM) was utilized to confirm the two-dimensional (2D) layered structure of SnS thin films. Post-annealed SnS thin film clearly showed a 2D layered structure. X-ray photoelectron spectroscopy (XPS) was performed to confirm the bonding state of the thin film. The results indicated that the SnS thin film only shows binding energies corresponding to the oxidation states of Sn2+ in the Sn 3d spectra and S2- in the S 2p spectra. Ultraviolet–visible (UV–vis) spectroscopy and ultraviolet photoelectron spectroscopy (UPS) were performed to confirm the optical properties and to calculate the band structure of the thin film. All of SnS thin film showed a p-type characteristic. The post-annealed SnS thin films exhibited better electric properties, confirmed by Hall measurement.

Mimicking somatic behavior of neurons using the integrate and fire model of 2D SnS memristive switching characteristics

This Letter presents the fabrication and characterization of a 2D SnS memristor, proposing its integrate and fire (I&amp;F) model as a potential hardware implementation of neuronal somatic behavior. The memristor comprises a thin layer of tin (II) sulfide (SnS) sandwiched between copper (Cu) electrodes on a silicon (Si) substrate. This structure exhibits an impressive Roff:Ron ratio of 103 at a read voltage Vrd of 0.25 V with exceptionally low switching Vsw and set Vset voltages of 0.3 and 0.35 V, respectively, with ∼3 order variation between the maximum Rmax and Rmin resistances offered during single voltage sweep cycle. We have explained the memristive behavior using the dual ionic conduction mechanism in the SnS active layer. We extracted the real-time band diagram of SnS using ultraviolet photoelectron spectroscopy, explaining the low Vsw observed. We propose that the emulation of the I&amp;F artificial neuron model exhibited by the fabricated device could serve as a promising application in the field of artificial neuron spiking.

Novel Carbon@BaMoZrFe12O19 photocatalytic peroxymonosulfate activation for ibuprofen removal

This study reports a successful synthesis of a novel Carbon@BaMoZrFe12O19 Mhexaferrite photocatalyst (NPs) using the coprecipitation method. Afterthat, the NPs were used as an activator for peroxymonosulfate (PMS) to remove ibuprofen (IBU) from water. NPs were subjected for a thorough characterization process utilizing various analytical techniques including XRD, FTIR, UV, PL TEM, SEM/EDS, and X-ray photoelectron spectroscopy (XPS). Significantly, the utilization of NPs for PMS activation demonstrated a notable improvement in the elimination of IBU under visible light. The research conducted a thorough investigation into the effects of various parameters, such as activating systems, initial pH, inorganic salts, IBU contents, and water matrix on the efficiency of IBU degradation. The significance of reactive oxygen species, such as sulfate and hydroxyl radicals, as well as singlet oxygen, in the removal of IBU, was clarified by chemical quenching tests. In addition, NPs exhibited competent magnetic separation and reprocessing capacities. The magnetic NPs revealed excellent constancy and recyclability, by sustaining degrading productivity after five consecutive cycles. Therefore, the present study offers a significant contributions to the understanding of photocatalytic degradation for organic pollutants through the utilization of magnetic photocatalysts.

Incorporating ReS2 Nanosheet into ZnIn2S4 Nanoflower as Synergistic Z-Scheme Photocatalyst for Highly Effective and Stable Visible-Light-Driven Photocatalytic Hydrogen Evolution and Degradation.

Inspired by natural photosynthesis, the visible-light-driven Z-scheme system is very effective and promising for boosting photocatalytic hydrogen production and pollutant degradation. Here, a synergistic Z-scheme photocatalyst is constructed by coupling ReS2 nanosheet and ZnIn2S4 nanoflower and the experimental evidence for this direct Z-scheme heterostructure is provided by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. Consequently, such a unique nanostructure makes this Z-scheme heterostructure exhibit 23.7 times higher photocatalytic hydrogen production than that of ZnIn2S4 nanoflower. Moreover, the ZnIn2S4/ReS2 photocatalyst is also very stable for photocatalytic hydrogen evolution, almost without activity decay even storing for two weeks. Besides, this Z-scheme heterostructure also exhibits superior photocatalytic degradation rates of methylene blue (1.7 × 10-2 min-1) and mitoxantrone (4.2 × 10-3 min-1) than that of ZnIn2S4 photocatalyst. The ultraviolet-visible absorption spectra, transient photocurrent spectra, open-circuit potential measurement, and electrochemical impedance spectroscopy reveal that the superior photocatalytic performance of ZnIn2S4/ReS2 heterostructure is mostly attributed to its broad and strong visible-light absorption, effective separation of charge carrier, and improved redox ability. This work provides a promising nanostructure design of a visible-light-driven Z-scheme heterostructure to simultaneously promote photocatalytic reduction and oxidation activity.

Phthalocyanine interfaces with MoS2(0001): The effect of the metal centre on the charge transfer

Semiconductor interfaces are of great importance nowadays because of their tuneable properties. In this study, the interfaces of metal phthalocyanines (H2Pc, MnPc, and CuPc) and a single crystal of 2H-MoS2 are studied by X-ray and Ultraviolet photoelectron spectroscopies to understand their physiochemical properties. For this purpose, the molecules were in situ deposited onto a clean substrate stepwise and after each deposition step, the interface was characterised. The obtained results show that all three molecules exhibit a flat-lying orientation on the substrate. Additionally, it is evident that the metal centre acts as a channel for electron transfer from the molecules to the substrate. Finally, the electron and hole barriers were calculated and the CuPc demonstrated the highest ones with values of 1.8 eV and 0.8 eV respectively.

Investigation on the Surface Properties of Annealed Copper Selenide Thin Films with Various Compositional Ratios

Copper‐based metal chalcogenides are versatile materials used for a variety of electronic devices, yet realizing the full scope of copper‐based composite materials is hindered by limited understanding of their chemical properties. In this work, copper selenide thin films (TFs) are fabricated using radio frequency (RF) magnetron co‐sputtering to investigate the effects of composition and annealing temperature on the films. The surface composition of the TFs is examined using energy dispersive X‐Ray spectroscopy (EDS) and X‐Ray photoelectron spectroscopy (XPS). In the unannealed films, an increase in Se composition leads to smaller grain sizes and smoother surfaces. The influence of higher Se content on the dispersive surface free energy (SFE) is shown through contact angle measurements. Work functions (WFs), determined by Kelvin probe (KP) and ultraviolet photoelectron spectroscopy (UPS), rose with increasing Se content. After annealing, the TFs exhibited opposite trends. As the films transitioned from an amorphous to a crystalline phase due to annealing, their roughness significantly increased.

Spectroscopic Analysis of Electrical Phenomena and Oxygen Vacancy Generation for Self-Aligned Fully Solution-Processed Oxide Thin-Film Transistors.

This work unveils critical insights through spectroscopic analysis highlighting electrical phenomena and oxygen vacancy generation in self-aligned fully solution-processed oxide thin-film transistors (TFTs). Ar inductively coupled plasma treatment was conducted to fabricate an amorphous indium zinc oxide (a-InZnO) TFT in a self-aligned process. Results showed that the Ar plasma-activated a-InZnO regions became conductive, which means that a homogeneous layer can act as both channel and electrode in the device. Several techniques were employed to probe specific aspects of the source-drain-channel interface in the fully solution-processed TFTs. X-ray absorption near-edge structure and Extended X-ray absorption fine structure were conducted to investigate the existence of oxygen vacancies, which is the main driving factor in inducing a conductive region. X-ray photoelectron spectroscopy was also used to explain the oxygen refilling mechanism. Ultraviolet Photoelectron Spectroscopy was conducted to analyze the valence band maximum and work function. Integration of these results facilitated the construction of the energy band diagram at the interface, wherein a Schottky barrier height of ∼0.37 eV was observed. By leveraging these techniques, insights into the electronic properties and performance of next-generation transistors are gained, enabling their future widespread adoption.

Saturation Mobility of 100 cm2 V-1 s-1 in ZnO Thin-Film Transistors through Quantum Confinement by a Nanoscale In2O3 Interlayer Using Spray Pyrolysis.

In this study, we present a comprehensive study on the fabrication and characterization of heterojunction In2O3/ZnO thin-film transistors (TFTs) aimed at exploiting the quantum confinement effect to enhance device performance. By systematically optimizing the thickness of the crystalline In2O3 (c-In2O3) layer to create a narrow quantum well, we observed a significant increase in saturation mobility (μSAT) from 12.76 to 97.37 cm2 V-1 s-1. This enhancement, attributed to quantum confinement, was achieved through the deposition of a 3 nm c-In2O3 semiconductor via spray pyrolysis. Various In2O3 layer thicknesses (2-5 nm) were obtained by adjusting precursor solution concentration, flow rate, and number of spray cycles. Post annealing treatments were employed to reduce the defects at the interface and within the oxide film, enhancing device stability and performance. Transmission electron microscopy (TEM) confirmed the uniformity of the c-In2O3 film thickness, while variations in thickness significantly influenced TFT performance, particularly the turn-on voltage (VGS) due to changes in the carrier concentration. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) supported the formation of a potential well with a two-dimensional electron gas (2DEG). The study of single and multiple superlattice structures of consecutive c-In2O3 and c-ZnO layers provided insights into the effects of multiple quantum wells on the TFT performance. This research presents an advanced approach to TFT optimization, highlighting high reliability, and environmental and bias stabilities. These lead to enhanced mobility and performance uniformity through the precise control of c-In2O3 layer thickness for the quantum confinement effect.

Dual efficacy of potassium-doping in perovskite solar cells: Reducing hysteresis and boosting open-circuit voltage

The incorporation of potassium into perovskite solar cells (PSCs) has been empirically validated to mitigate hysteresis phenomena and boost the power conversion efficiency (PCE). However, the doping mechanism of potassium ions in the perovskite film and their effect on photocarrier recombination remains a topic of debate. Here, we grew doped MAPbI3: K single crystals by inverse temperature crystallization using KI as a dopant, and then perovskite thin films were spin-coated with dissolved MAPbI3: K crystals as a precursor. The doped MAPbI3: K perovskite films exhibit better crystal quality with large columnar grains and lower defect density. Employing Hall effect, ultraviolet photoelectron spectroscopy, and Kelvin probe force microscopy measurements, we definitively demonstrate that K-doping transforms the conductivity type of the perovskite film from a marginally N-type to a distinct P-type semiconductor. Furthermore, this doping strategy induces a concurrent downward shift in both the conduction band minimum and valence band maximum. As a result, the PCE of the PSCs increases from 15.15% to an impressive 20.66%, and the J–V curve hysteresis almost disappears. Additionally, theoretical simulations using SCAPS-1D software reveal a profound modification in the device's energy band diagram after K+-doping. Specifically, the energy level offset between the perovskite layer and the electron transport layer diminishes from 0.24 to 0.14 eV, with a result of bigger quasi-Fermi energy level splitting. This, in turn, elevates the open-circuit voltage (Voc) of the doped perovskite solar cell, underscoring the profound impact of potassium doping on enhancing PSC performance.

Ultrafast Charge Transfer-Induced Unusual Nonlinear Optical Response in ReSe2/ReS2 Heterostructure.

Ultrafast charge transfer in van der Waals heterostructures can effectively engineer the optical and electrical properties of two-dimensional semiconductors for designing photonic and optoelectronic devices. However, the nonlinear absorption conversion dynamics with the pump intensity and the underlying physical mechanisms in a type-II heterostructure remain largely unexplored, yet hold considerable potential for all-optical logic gates. Herein, two-dimensional ReSe2/ReS2 heterostructure is designed to realize an unusual transition from reverse saturable absorption to saturable absorption (SA) with a conversion pump intensity threshold of approximately 170 GW/cm2. Such an intriguing phenomenon is attributed to the decrease of two-photon absorption (TPA) of ReS2 and the increase of SA of ReSe2 with the pump intensity. Based on the characterization results of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, femtosecond transient absorption spectrum, Kelvin probe force microscopy, and density functional theory calculation, a type-II charge-transfer-energy level model is proposed combined with the TPA of ReS2 and SA of ReSe2 processes. The results reveal the critical role of ultrafast interfacial charge transfer in tuning the unusual nonlinear absorption and improving the SA of ReSe2/ReS2 under different excitation wavelengths. Our finding deepens the understanding of nonlinear absorption physical mechanisms in two-dimensional heterostructure materials, which may further diversify the nonlinear optical materials and photonic devices.

Growth and electronic structure of the nodal line semimetal in monolayer Cu2Si on Cu(111)

Cu2Si, a single-layer two-dimensional material with a honeycomb structure, has been proposed to have Dirac nodal line fermions. In this study, the synchrotron radiation X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and angle-resolved photoemission spectroscopy (SR-XPS, SR-UPS, and SR-ARPES) techniques were used to investigate the dynamic process of in situ deposition of single-layer Cu2Si on a Cu(111) crystal surface via molecular beam epitaxy (MBE). Cu2Si existed as a monolayer (ML) alloy, and there were competing mechanisms of distinct chemical states of silicon in different growth periods, according to a detailed examination of the experimental SR-XPS and SR-UPS spectra. Additionally, a weak interaction between the Cu2Si ML and Cu(111) was demonstrated via SR-ARPES and first-principles computations. The unique electronic structure of the Cu2Si ML was not destroyed by either this weak interaction or the disordered silicon produced on the surface during the growth process. The study of the Cu2Si growth kinetics provides a guarantee and a basis for the future exploration of the exotic properties of Cu2Si.

Engineering of Interface Barrier in Hybrid MXene/GaN Heterostructures for Schottky Diode Applications.

The Fermi level position at the interface of a heterostructure is a critical factor for device functionality, strongly influenced by surface-related phenomena. In this study, contactless electroreflectance (CER) was utilized for the first time to investigate the built-in electric field in MXene/GaN structures with the goal of understanding the carrier transfer across the MXene/GaN interface. Five MXenes with high work functions were examined: Cr2C, Mo2C, V2C, V4C3, and Ti3C2. The physicochemical properties of the MXene/GaN structures were analyzed by using X-ray and UV photoelectron spectroscopies. It was shown that upon the coverage of the GaN surface by all investigated MXenes, a shift in the position of the surface Fermi level occurs, consequently raising the interface barrier. Additionally, the physicochemical stability of MXenes on the GaN surface was studied after annealing the structures at 750 °C. Our findings indicate that the annealing process increases the barrier height and the ionization energies of all studied structures. Furthermore, it has been shown that removing excess MXene material from the surface did not significantly impact the built-in electric field, emphasizing the robust physicochemical stability of the MXenes on the GaN surface. To validate the potential of engineering of MXene/GaN interface barrier, Schottky diodes with MXenes exhibiting the highest barrier height (Mo2C and V2C) were demonstrated.

Comprehensive surface and crystallographic structure investigation of MnGaGe nanoislands grown on GaAs

The growth of islands with nanometer height and diameter sizes of the ternary compound MnGaGe with tetragonal structure on the GaAs (001) substrate surface was investigated. Topographic analyses performed by atomic and magnetic force microscopy are consistent with the formation of ferromagnetic MnGaGe nanoislands, constituted by the preferential stacking of (001) and (110) planes whose are the most favorable to the epitaxial relationship on the (001) surface of GaAs wafer, not tested yet. As the spontaneous magnetization tends to align preferentially perpendicular to the Mn basal planes of the tetragonal crystallographic structure, one part of the nanoislands has magnetic dipole or even single- domains whose magnetization is in-plane and another part out-of-plane directions, in the remanent state. Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy analysis obtained the work function, not measured in the literature, and indicates the intermetallic character of the MnGaGe nanoislands, whose near-stoichiometry and good crystalline structure are confirmed by energy dispersive X-ray spectroscopy, X-ray diffraction together with nanodiffraction probe and X-ray fluorescence mapping carried out at a synchrotron installation. The high chemical stability of the MnGaGe nanoislands exhibiting ferromagnetism at room temperature with magnetization perpendicular to the substrate is very promising for spintronic applications at nanoscale.