Alloy Thin Films Research Articles

Metal–Semiconductor–Metal Photodetectors Based on β-MgGaO Thin Films

Ultrawide-bandgap (UWBG) deep-ultraviolet photodetectors have received great attention due to their versatile applications in the fields of scientific research, civilian infrastructure, military defense, etc. In this perspective, we fabricated deep-ultraviolet β-MgGaO metal–semiconductor–metal photodetectors with interdigital Pt/Au metal contacts. β-Phase MgGaO ternary alloy thin films of different Mg atomic percentages were grown using oxygen plasma-assisted molecular beam epitaxy. Ultrawide bandgaps of 5.03, 5.09, 5.15, and 5.22 eV were achieved for thin films with and without Mg2+ incorporation, and light transmittances of all samples were around 90% in the visible region. Raman spectra indicate that Mg2+ atoms have replaced the position of Ga3+ ions in both octahedral and tetrahedral chains. The responsivity of the detectors was investigated. The irradiation wavelength-, temperature-, and power-dependent I–V curves, photocurrent spectra, and dynamics of the photocurrents were measured. This work suggests that UWBG β-MgGaO semiconductors have a potential for deep-ultraviolet photodetectors and other photonic device applications.

Effect of Different Concentration of Boron on Properties of Electroplated Nickel-ferrous-boron Alloy Thin Films

Effect of Different Concentration of Boron on Properties of Electroplated Nickel-ferrous-boron Alloy Thin Films

Optoelectronic artificial synapse based on Si1-xSnx alloyed film

The emergence of big data has increased the requirements for computing and processing systems. Memristors–electrical components that simulate the synapses and neurons of the human brain—have been proposed to help meet these requirements. Optoelectronic synapses are excited by optical signals and have the advantages of low crosstalk, high bandwidth, and low power consumption. Herein, a MOS structure optoelectronic synapse device based on an amorphous silicon (a-Si1-xSnx; x = 0.0457) alloy thin film and an AlOy thin film was fabricated via oxygen vacancy energy band and heterostructure design. Significantly, the device exhibited ultralong decay time of 3576.07 s and a broadband response from the visible to the near-infrared-I region. A series of important synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation, short-term memory to long-term memory transition, and learning experience behaviour, was successfully simulated on the device. We simulated a 3 × 3 optoelectronic synapse array, which can simulate the visual memory of images observed by the human eye. The effect of ‘pupil’ scaling on image memory was simulated by adjusting the read voltage. Based on these advantages, the optoelectronic synaptic device developed in this study has significant potential for application in the new generation of artificial synaptic systems.

Understanding non-stochiometric deposition of multi-principal elemental NiCoCr thin films

Multi-principal elemental NiCoCr thin films with compositional flexibility have potential applications as a thermal barrier, corrosion-resistant coatings, and functional energy materials. In this study, the non-stochiometric multi-principal element alloy thin film formation behavior from an equiatomic ablation target of NiCoCr using pulsed laser deposition has been reported. Here, the effect of varying laser fluence on compositions of constituent elements in the NiCoCr thin films is systematically investigated. The increase in laser fluence typically increases the likelihood of acquiring undesirable particulates in thin films. Therefore, to maintain the film quality the laser fluences are adjusted within the range of 1.3–3.3 J·cm−2, while the film thicknesses are kept constant at ∼30 nm. Results show that the constituent elements are well-distributed in the formed NiCoCr thin films, however, having average atomic percentages of Ni and Cr twice as high as Co irrespective of the equiatomic composition of individual elements in the ablation target. This stochiometric alteration in the as-deposited thin films is governed by the rate of ablation and subsequent evaporation of each element, which is facilitated by the optical properties and vapor pressure of individual constituent elements. Additionally, electron energy-loss spectroscopy and x-ray absorption spectroscopy analysis reveal that the thin films have partially oxidized, with the Cr oxidation contributing the most to the O-K edge in comparison to Ni and Co. This study presents a laser-assisted pathway for fabricating compositionally flexible NiCoCr thin films and develops an understanding of the non-equilibrium laser-material interactions and how the intrinsic properties of constituent elements affect the stoichiometric flow of materials from the target to the final film deposition.

Enhancement of oxygen evolution reaction performance of FeCoNiCrMn high entropy alloy thin film electrodes through in-situ reconstruction

Due to the large number of defects and high entropy properties, high entropy alloy thin film electrodes prepared by magnetron sputtering are beneficial for electrocatalytic oxygen evolution reaction (OER). However, the electrocatalytic OER performance of high entropy alloy thin film electrodes without activation is limited. In this work, in-situ reconstruction (chloride corrosion) is applied to activate FeCoNiCrMn high entropy alloy thin film electrodes for promoting the electrocatalytic OER performance. The research reveals that high entropy hydroxides and high entropy (oxy)hydroxides, which are real active centers of OER electrocatalysts, are generated on the surface of FeCoNiCrMn high entropy film electrodes during in-situ reconstruction. Moreover, it is also proved that there is an obvious quantitative relationship among elements in the surface of the high entropy alloy thin film electrodes after complex chloride corrosion reaction: Ni>Mn>Fe>Co>Cr. In addition, the OER performance of FeCoNiCrMn high entropy film electrodes with in-situ reconstruction can achieve an overpotential of 263 mV and a Tafel slope of 50.9 mVdec−1. Moreover, sponge-like structures created by in situ reconstitution can help to increase surface active areas and the increased contents of high-valence elements after in situ reconstruction contribute to enhance electrocatalytic OER activity.

Preparation of FeNi-based nanoporous amorphous alloy films and their electrocatalytic oxygen evolution properties

The progress of this research is the preparation of FeNi alloy thin films by magnetron sputtering. Each step of the experimental process is based on the electrocatalytic performance of the sample, and characterized by many characterizations means such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray energy spectrometry (EDS) and step gauge thickness test for morphology, structure and elemental composition, etc. The analysis of the characterization results is used as a support for the experimental process. Adjustment of various preparation process parameters for material growth and subsequent processing include doping of non-metallic elements and construction of nanostructures. Doping of C elements can make FeNi based alloy films further amorphous. Zn element is used as a pore-forming agent. The two processes of doping and high-temperature vacuum dealloying can make the film obtain a nanoporous structure, which greatly increases the specific surface area. These two strategies reduce the overpotential (η10) of oxygen evolution reaction (OER) of FeNi alloy thin films to 393 mV and 314 mV, which are reduced by 47 mV and 79 mV step by step. The electrochemical properties of the finally obtained alloy film are: overpotential of 314 mV, Tafel slope of 61.8 mV/dec and the stability of only 10% decay at a current density of 10 mA/cm2 for 12 h. In this study, low-cost transition metals were used as the main materials to design OER catalysts, and the catalytic efficiency was comparable to that of commercial noble metal catalysts. The physical preparation methods made each sample have good reproducibility. It provides the experimental basis and theoretical basis for the design and synthesis of new catalytic materials at a higher level.

Evaluation of magnetocaloric behavior and refrigeration performance of Gd3Co10Al87 nanostructured thin film alloy with multiple Curie temperatures

Evaluation of magnetocaloric behavior and refrigeration performance of Gd3Co10Al87 nanostructured thin film alloy with multiple Curie temperatures

Soft magnetism in single phase Fe3Si thin films deposited on SrTiO3(001) by pulsed laser deposition

The development of devices relying on spin phenomena requires of an ideal spin polarized electron source. This can be achieved by taking advantage of half-metallic full Heusler alloy thin films. However, their implementation requires a controlled growth of stoichiometric films with large activation volumes. In this work, we report on the growth of epitaxial Fe3Si ultra-thin films by pulsed laser deposition on SrTiO3(001) substrates, analyzing the effect of deposition temperature in the structural, morphological and magnetic properties of the deposited films. We conclude that optimal compromise between phase purity and interface quality is obtained at 200 ºC, obtaining the best magnetic response under this condition.

Structural, magnetic and Magnetic-Microstructural properties of sputtered FeCoNi thin films

This paper reports the effect of growth rate and substrate temperature on the composition, structure, microstructure, magnetic and magnetic microstructural properties of Fe-Co-Ni alloy thin films. 200 nm thick Fe-Co-Ni thin films were grown by high power impulse magnetron sputtering on Si 〈100〉 at different growth rates (viz., 1 – 2.4 Å/s). Films were also thermally processed by modifying the substrate temperatures. Room temperature deposited films showed the presence of FCC structure for all the films. However, films grown at higher substrate temperatures displayed presence of BCC phase co-existing with FCC phase. High saturation magnetization combined with low coercivity has been obtained for the Fe-Co-Ni films grown at higher growth rate and enhanced substrate temperature. Magnetization and magnetic microstructural studies using Kerr microscopy showed anisotropic magnetic properties along the plane of the film with the magnetization reversal dominated by domain wall motion and domain wall rotation.

Optical Properties and Electronic Characteristics of Polycrystalline and Amorphous Thin Films of the Al4Sm Alloy

Optical Properties and Electronic Characteristics of Polycrystalline and Amorphous Thin Films of the Al4Sm Alloy

Optical properties of AgxCu1–xI alloy thin films

We report on the excitonic transition energy E0 and spin–orbit split-off energy Δ0 of γ-AgxCu1–xI alloy thin films studied by using reflectivity measurements at temperatures between 20 K and 290 K. The observed bowing behavior of the E0 transition as a function of the alloy composition is explained based on first-principles band structure calculations in terms of different physical and chemical contributions within the description of ordered alloys. The spin–orbit coupling is found to increase from a value of 640 meV for CuI to approximately 790 meV for AgI. Furthermore, we show that the temperature-dependent bandgap shift between 20 K and 290 K decreases with increasing Ag-content from 25 meV for CuI to 6 meV for AgI. We attribute this behavior mostly to changes in the contribution of thermal lattice expansion to the bandgap shift.

Smooth Thin Film of a CoNiCu Medium-Entropy Alloy Consisting of Single Nanometer-Sized Grains Formed by Electrodeposition in a Water-in-Oil Emulsion

High-entropy and medium-entropy alloys are new classes of alloys that exhibit excellent strength and toughness. These alloys are expected to be used as multifunctional catalysts given that methods for producing nanoparticles of such alloys have been established. By contrast, the production methods to form thin films of such alloys are still very limited. Here, we show that electrodeposition in a chemically stabilized water-in-oil emulsion functions as a general method to form thin films of such alloys. The key to forming thin films of these alloys by electrodeposition is to conduct reduction under diffusion-limited conditions and to confine the distribution of concentration in a droplet. This situation is not achieved in conventional bulk aqueous or nonaqueous single-phase solution but is achieved in a water-in-oil emulsion. Here, we found aerosol OT as a suitable surfactant for the present water-in-oil emulsion to stabilize the emulsion during electrodeposition. It is also clarified that the increase in viscosity of the aqueous solution within water droplets by the addition of glycerol decreases the roughness greatly. The strategy demonstrated here is expected to spur further applied research into thin films of high- and medium-entropy alloys.

Stabilizing far-from-equilibrium (Mo,Ti)S2 thin films by metal sulfurization at reduced temperature

We report the synthesis of large-area, high-Ti-content, Mo1−xTixS2 alloy thin films in the 2H phase at temperature as low as 500 °C using a scalable two-step method of metal film deposition, followed by sulfurization in H2S. Film processing at higher temperature accelerates Ti segregation, film coarsening, and the formation of TiS2 in the 1T phase. Crystal growth at higher temperature results in the formation of multiple binary sulfide phases, in agreement with the equilibrium phase diagram. Making highly metastable, smooth, and uniform single-phase alloy films, therefore, hinges on developing low-temperature processing. Our results are relevant to the development of technologies based on designer transition metal dichalcogenide alloys, including in photonic integrated circuits and gas sensing.

Chemical reaction of Al-Sm sputtered amorphous electrode for stable encapsulation-free organic electronics

An Al-based amorphous metal alloy (i.e., metallic glass) is fabricated in the form of a thin film electrode for an organic solar cell. The chemical stability of the amorphous alloy thin film is analysed via electrochemical analyses, which reveals that the random atomic arrangement within the electrode suppresses the oxidation reaction upon contact with harsh conditions. Incorporation of an amorphous metal thin film as a top electrode for organic solar cell devices results in considerable enhancement in device stability, as the metallic surface with the amorphous phase hinders the ambient moisture and oxygen from permeating into the underlying organic layers. The electrical parameters of the amorphous electrodes are analysed before and after aging and compared with those of a conventional crystalline metal electrode, which presents the advantage of amorphous electrodes in maintaining high charge transport properties for an extended time.

Local structure and magnetic properties of a nanocrystalline Mn-rich Cantor alloy thin film down to the atomic scale

The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multi-functionality. Herein, we apply multi-edge X-ray absorption spectroscopy (extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), and X-ray magnetic circular dichroism (XMCD)) to probe the structural, electronic, and magnetic properties of all individual constituents in the single-phase face-centered cubic (fcc)-structured nanocrystalline thin film of Cr20Mn26Fe18Co19Ni17 (at.%) high-entropy alloy on the local scale. The local crystallographic ordering and component-dependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature. A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances (2.54–2.55 Å) to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed. XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states, the changes in the electronic structure, and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film. The spin and orbital magnetic moments of Fe, Co, and Ni components were quantitatively evaluated. The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.

Probing the composition dependence of residual stress distribution in tungsten-titanium nanocrystalline thin films

Nanocrystalline alloy thin films offer a variety of attractive properties, such as high hardness, strength and wear resistance. A disadvantage is the large residual stresses that result from their fabrication by deposition, and subsequent susceptibility to defects. Here, we use experimental and modelling methods to understand the impact of minority element concentration on residual stresses that emerge after deposition in a tungsten-titanium film with different titanium concentrations. We perform local residual stress measurements using micro-cantilever samples and employ machine learning for data extraction and stress prediction. The results are correlated with accompanying microstructure and elemental analysis as well as atomistic modelling. We discuss how titanium enrichment significantly affects the stress stored in the nanocrystalline thin film. These findings may be useful for designing stable nanocrystalline thin films.

Biocompatible Ti3Au–Ag/Cu thin film coatings with enhanced mechanical and antimicrobial functionality

BackgroundBiofilm formation on medical device surfaces is a persistent problem that shelters bacteria and encourages infections and implant rejection. One promising approach to tackle this problem is to coat the medical device with an antimicrobial material. In this work, for the first time, we impart antimicrobial functionality to Ti3Au intermetallic alloy thin film coatings, while maintaining their superior mechanical hardness and biocompatibility.MethodsA mosaic Ti sputtering target is developed to dope controlled amounts of antimicrobial elements of Ag and Cu into a Ti3Au coating matrix by precise control of individual target power levels. The resulting Ti3Au-Ag/Cu thin film coatings are then systematically characterised for their structural, chemical, morphological, mechanical, corrosion, biocompatibility-cytotoxicity and antimicrobial properties.ResultsX-ray diffraction patterns reveal the formation of a super hard β-Ti3Au phase, but the thin films undergo a transition in crystal orientation from (200) to (211) with increasing Ag concentration, whereas introduction of Cu brings no observable changes in crystal orientation. Scanning and transmission electron microscopy analysis show the polyhedral shape of the Ti3Au crystal but agglomeration of Ag particles between crystal grains begins at 1.2 at% Ag and develops into large granules with increasing Ag concentration up to 4.1 at%. The smallest doping concentration of 0.2 at% Ag raises the hardness of the thin film to 14.7 GPa, a 360% improvement compared to the ∼4 GPa hardness of the standard Ti6Al4V base alloy. On the other hand, addition of Cu brings a 315—330% improvement in mechanical hardness of films throughout the entire concentration range of 0.5—7.1 at%. The thin films also show good electrochemical corrosion resistance and a > tenfold reduction in wear rate compared to Ti6Al4V alloy. All thin film samples exhibit very safe cytotoxic profiles towards L929 mouse fibroblast cells when analysed with Alamar blue assay, with ion leaching concentrations lower than 0.2 ppm for Ag and 0.08 ppm for Cu and conductivity tests reveal the positive effect of increased conductivity on myogenic differentiation. Antimicrobial tests show a drastic reduction in microbial survival over a short test period of < 20 min for Ti3Au films doped with Ag or Cu concentrations as low as 0.2—0.5 at%.ConclusionTherefore, according to these results, this work presents a new antimicrobial Ti3Au-Ag/Cu coating material with excellent mechanical performance with the potential to develop wear resistant medical implant devices with resistance to biofilm formation and bacterial infection.Graphical

Study the Structural/Microstructural and Electrical Properties of CdTe:Sb Thin Films Deposited by Flash Evaporation

in this research studied the structure and electrical properties of the Pure CdTe and metal Sb-doped CdTe thin films with 0.5, 1, and 1.5 wt.%, respectively. Theydeposited on glass substrates using flash evaporation technique. It was found that theprepared films had a cubic structure and a strong preferred &lt;111&gt; crystal orientation.Atomic force microscopy (AFM) results showed that the film surface doped Sb wasmore compact and uniform and also the root mean squared (RMS) roughnessincreased with Sb contents. The electrical properties were investigated as function ofSb wt.% doping. The results showed that the electrical conductivity (6) increasingtrend with increasing the wt.% of dopant , while the activation energies (E,i, E,2)showed an opposite trend, where the activation energies decreased with dopant.1. Introduction Thin films of II-VI semiconductors are widely used in many semiconductordevices such as photo electrochemical cells, field effect transistors, IR detectors,photodiodes, photo conductors and photovoltaic solar cells[1, 2]. CdTe has long beenidentified as a candidate for the absorber layer in low cost thin film photovoltaic solarcells because of its direct bandgap, high absorption coefficient and the possibility of avariety of preparation techniques such as close spaced sublimation (CSS)[3], vacuumdeposition [4], electrodeposition [5], and RF sputtering[6], close spaced vaportransport [7]. In this present work we focused attention on the prominent techniquesfor the deposition of thin films of multicomponent alloys whose constituents havedifferent vapor pressures. Thin films of CdTe have been prepared under suitablegrowth conditions by a simple flash evaporation (FE) technique. This techniquerequires only one boat maintained at sufficiently high temperature to evaporate theleast volatile component of the alloy. The main advantage of (FE) is that it does notrequire maintaining the critical vapor pressures of the components and temperatures ofthe boats unlike multisource thermal evaporation[8] . CdTe thin film still has many defects, such as it has extremely high resistivity. Tosolve this issue, the implying of the technique Sb-doped CdTe film to change electricalproperties [9]. In this work deposited Sb-doped CdTe films using the mixed powder of TO -AA suet Talal = - VN - Kya lal ayy cll 212 alae

Cathodic arc deposition of high entropy alloy thin films with controllable microstructure

High entropy alloys (HEAs) are a novel class of materials exhibiting properties of high strength, high corrosion and oxidation resistance, and superb thermal stability. Cathodic arc deposition is an established physical vapor deposition (PVD) technology offering high deposition rate and high degrees of plasma ionization with controllable ion kinetic energy. Here we employed cathodic arc deposition to fabricate AlCrFeCoNiCu0.5 HEA thin films. To elucidate the growth mechanisms and microstructures of the HEA thin film microstructures, we varied arc and duct currents. The crystallography of the films was investigated using X-ray diffraction (XRD). The film chemistry and microstructure of the film-substrate interphase were comprehensively studied using transmission electron microscopy (TEM). Atomic force microscopy (AFM) was applied to study the surface morphology, and mechanical properties were evaluated using nanoindentation. It is demonstrated that the grain size in HEA thin films can be effectively controlled by the deposition rate, while the HEA film hardness and surface roughness are modulated by the grain size. The results presented here have important implications for the fabrication of HEA thin films using cathodic arc deposition as an industrially scalable technique.

Low magnetic damping constant in half-metallic Co2FeAl Heusler alloy thin films grown by molecular beam epitaxy

Half-metallic Co2FeAl Heusler alloy thin films with various thickness were prepared by MBE method and its magnetic and crystalline properties were investigated. At the thickness of 20 nm and above, good magnetic properties and high B2-order parameter was obtained. In addition, magnetic damping constant was evaluated from peak-to-peak linewidth measured by FMR and ultra-low magnetic damping constant below 0.001 was obtained at the film thickness of 30 nm. These results are thanks to the excellent half-metallicity in the Co2FeAl films prepared by MBE.