Grazing Incidence X-ray Diffraction Research Articles

Impact of deposition pressure on the structural, nanomechanical, and tribological properties of δ-TaN coatings deposited via magnetron sputtering on Ti6Al7Nb alloy

In the present study, δ-TaN thin films were deposited by reactive magnetron sputtering (physical vapour deposition) on Ti6Al7Nb alloy by varying the deposition pressure (0.8–0.2 Pa). Their crystalline structure, chemical composition, surface roughness, and surface morphology were investigated by using grazing incidence X-ray diffraction, energy dispersive spectroscopy, scanning probe microscope, and field emission scanning electron microscopy (FESEM), respectively. Structural analysis results confirmed the deposition of cubic δ-TaN thin films along the (111) basal plane; moreover, spherical dome-like surface morphology was observed by FESEM. Further, to analyze the nanomechanical properties of the deposited δ-TaN coatings, such as hardness (H) and modulus (E), scratch tests were performed utilizing the nanomechanical system. Moreover, friction and wear properties of the coating and bare sample (substrate) were investigated on nano-tribometer equipment using a rotary ball-on-disk type configuration. The stainless steel (SS-316) and silicon nitride (Si3N4) balls were used as the counter materials for the tribological tests. The observations of nanomechanical tests revealed that H (GPa), E (GPa), and H/E ratio values increased from 11.83 to 28.30 GPa, 176.02 to 248.45 GPa, and 0.06 to 0.11, respectively, with the decrease of the deposition pressure. In the scratch test, the highest critical load (cohesion failure) was found for δ-TaN coating deposited at the lowest deposition pressure (0.2 Pa). Tribological results of δ-TaN coatings demonstrated average coefficient of friction (COF) value ranges between 0.066–0.092 and 0.072–0.029 against steel and Si3N4 balls, respectively. The wear rate values were observed to vary from 8.15 × 10−5 to 7.56 × 10−6 and from 1.77 × 10−3 to 8.99 × 10−6 against steel and Si3N4 balls, respectively. Generally, the average COF and wear rate decreased against 316 SS and Si3N4 balls as the deposition pressure of coatings decreased. However, the coating deposited at 0.8 and 0.6 Pa against Si3N4 ball showed early delamination of the coating, resulting in the sudden fluctuation in COF plots and higher wear rate in the range of 10−3 mm3/N.m.

Influence of deposition pressure on microstructure, mechanical and electrical properties of niobium thin films

Niobium (Nb) thin films were deposited on a Si substrate using magnetron sputtering system by varying the deposition pressure. The effect of deposition pressure on the microstructure, residual stresses, and electrical properties was investigated by systematically varying the deposition pressure from 0.15 to 0.60 Pa. The Nb thin films were characterized using hard x-ray reflectivity, grazing incidence x-ray diffraction, four point probe method, and atomic force microscopy. The films grown at lower deposition pressures had smooth surfaces and more compact structures, which are advantageous for lowering electrical resistance but had higher compressive stress. On the other hand, the films grown at higher deposition pressures had columnar type growth with less dense structures, which leads to increase in electrical resistance. However the nature of stresses transform from compressive to tensile. Hard X-ray reflectivity performed on Nb films provides direct insight into the growth and the microstructure which were correlated with the mechanical and electrical properties.

A novel water-in-deep eutectic solvent microemulsions for chemical polishing of single crystal KDP

Microemulsion (ME) has been investigated as a chemical polishing (CP) fluid for effective polishing of single crystal potassium dihydrogen phosphate (KDP), perfectly avoiding the generation of mechanical stress. In this work, a water-in-deep eutectic solvent ME was proposed as the polishing fluid for CP of single crystal KDP. Deep eutectic solvent (DES) is formulated using n-octanol as hydrogen bond donor and methyltrioctylammonium chloride (MTOAC) as hydrogen bond acceptor, with a mass ratio of 2:1. The ME was prepared by mixing DES as the oil phase (12.5 %, wt.), a hydrochloric acid solution as the water phase (12.5 %, wt.), and isopropanol as the cosolvent (75 %, wt.), without adding any other surfactants. The properties of the ME were characterized by conductivity measurements and ultraviolet (UV) spectroscopy. The reactivity of ME with KDP was measured by the conductivity method, and it was higher at low pH values. A hydrochloric acid solution with a pH of 3 was selected as aqueous phase, considering its effects on particle size, salt loading, and static etching rate. The water content affects the polarity of ME and the final water content was determined to be 12.5 % to ensure high polarity of ME. The surface quality of the KDP crystals before and after polishing was examined using grazing incidence X-ray diffraction (GIXRD) analysis. The average roughness of the KDP crystal surface was decreased from 1.96 nm to 1.43 nm, and the root-mean-square (RMS) roughness was reduced from 2.81 nm to 1.86 nm, demonstrating a significant polishing effect. Finally, the polishing mechanism was elucidated in terms of the irreversible chemical reaction between the active components in the microemulsion and the KDP crystals.

Morphology-Dependent Photocatalytic Activity of Nanostructured Titanium Dioxide Coatings with Silver Nanoparticles.

This study aims to improve the photocatalytic properties of titanium dioxide nanorods (TNRs) and other related nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) by modifying them with silver nanoparticles (AgNPs). This preparation is carried out using a two-step method: sol-gel dip-coating deposition combined with hydrothermal crystal growth. Further modification with AgNPs was achieved through the photoreduction of Ag+ ions under UV illumination. The investigation explores the impact of different growth factors on the morphological development of TiO2 nanostructures by modulating (i) the chemical composition, the water:acid ratio, (ii) the precursor concentration involved in the hydrothermal process, and (iii) the duration of the hydrothermal reaction. Morphological characteristics, including the length, diameter, and nanorod density of the nanostructures, were analyzed using scanning electron microscope (SEM). The chemical states were determined through use of the X-ray photoelectron spectroscopy (XPS) technique, while phase composition and crystalline structure analysis was performed using the Grazing Incidence X-ray Diffraction (GIXRD) method. The results indicate that various nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) can be obtained by modifying these parameters. The photocatalytic efficiency of these nanostructures and Ag-coated nanostructures was assessed by measuring the degradation of the organic dye rhodamine B (RhB) under both ultraviolet (UV) irradiation and visible light. The results clearly show that UV light causes the RhB solution to lose its color, whereas under visible light RhB changes into rhodamine 110, indicating a successful photocatalytic transformation. The nanoball-like structures' modification with the active metal silver (TNRs 4 Ag) exhibited high photocatalytic efficiency under both ultraviolet (UV) and visible light for different chemical composition parameters. The nanorod structure (TNRs 2 Ag) is more efficient under UV, but under visible-light photocatalyst, the TNRs 6 Ag (dense nanorods) sample is more effective.

Atomic Layer Deposition of Cu Catalysts on Gas Diffusion Electrodes for Electrochemical CO2 Reduction

Electrochemical CO2 conversion is gaining attention as an important process for carbon fixation through the use of renewable electricity to address the climate change crisis. Copper is a unique single-element catalyst that can induce C-C coupling reactions to generate high-value-added compounds. The triple phase boundary has been successfully controlled at the catalyst interface using gas diffusion electrodes (GDEs) over the past few years, resulting in high C-C coupling performance. Therefore, methods to engineer the catalyst interface on the 3D structure of GDE are of significant importance. Generally, the catalyst on the GDE is introduced through physical vaper deposition (PVD) using sputtering or E-beam evaporation, or through solution methods such as spray coating and drop-casting of nano-particles. However, the porous and tortuous 3D structure of the GDE often result in limited conformality and difficulty in obtaining a uniform and controlled infiltration of the catalyst into the support structure.In this study, we synthesized Cu catalysts directly onto GDE surfaces using plasma-enhanced atomic layer deposition (PE-ALD), which allowed for precise tuning of the catalyst size and loading at the nanoscale [1]. The synthesized catalysts were confirmed to be polycrystalline Cu nanoparticles using grazing incidence X-ray diffraction. To demonstrate the advantages of the conformal and tunable control of PE-ALD deposition, we deposited the same areal mass loading of Cu catalyst onto the GDE substrates using PVD, and compared the CO2 reduction activity in an H-cell environment. The PE-ALD Cu catalyst showed more than 3 times higher current density than the PVD catalyst at the same electrode potential, a low (~10%) Faradaic efficiency (FE) for the hydrogen evolution reaction (HER), and greater than 75% FE for C-C coupling to form C2+ products including ethylene and ethanol, which is comparable to the highest performances reported to date for metallic Cu catalysts in a H-cell environment. Furthermore, stable operation was observed for a duration of 15 hours, with minimal changes in activity and selectivity. In conclusion, the introduction of catalysts using PE-ALD on GDE electrodes represents a powerful new synthesis method that can increase both C-C coupling performance and selectivity compared to PVD deposition, due to its adjustable Cu nanoparticle size and high conformality. Reference 1) J. D. Lenef, S.Y. Lee, K. M. Fuelling, K. E. Rivera Cruz, A. Prajapati, D. O. D. Cornejo, T. H. Cho, K. Sun, E. Alvarado, T. S. Arthur, C. A. Roberts, C. Hahn, C. C. L. McCrory, N. P. Dasgupta, Nano Lett. 23, 10779-10787 (2023)

Enhanced Glucose Sensing Performance through Controlled Pulsed Laser Deposition of Au Clusters on Anodized Glassy Carbon Electrodes

Diabetes, a global health problem, necessitates precise blood glucose measurement for effective management. Despite their prevalence, enzymatic glucose sensors suffer from sensitivity to temperature and pH and limited lifetime of the enzyme, thus requiring replacement every two weeks (Teymourian et al., 2020). In contrast, non-enzymatic sensors offer enhanced durability, superior sensitivity, and ease of miniaturization, making them promising for the so-called "fourth generation" glucose sensors (Aun et al., 2021). Noble metals like Pt (Kim et al., 2012), Au (Shen et al., 2022), Pd (Elkholy et al., 2019), and Ir (Dong et al., 2018) have emerged as prospective candidates for glucose sensing due to their ability to oxidize glucose at a physiological pH of 7.4. Among these, Au has gained attention due to its remarkable electroactivity for glucose electro-oxidation (Vassilyev et al., 1985), despite its weak chemisorptive properties arising from filled d-orbitals (Hammer & Nørskov, 1995). Various methods have been employed to fabricate nanostructured gold electrodes, encompassing direct electrostatic assembly, covalent linking, polymer entrapment or co-mixing, sol-gel processes, electrochemical etching, and electrodeposition (Dahan et al., 2023). Nevertheless, many of these fabrication approaches entail the use of hazardous chemicals or involve cumbersome procedures, de facto limiting their practical application. As a result, scalable solutions to catalyst fabrication and deposition are needed to seamlessly integrate with the cleanroom process flows to build non-enzymatic glucose sensors.In this study, 7x7mm glassy carbon electrodes (GCs) served as working electrodes in a three-electrode system, with a reversible hydrogen electrode employed as a reference and a Pt mesh as a counter electrode. The GCs underwent meticulous polishing using alumina slurry of varying sizes (1μm, 0.3 μm, and 0.01 μm). Subsequently, they were anodized in 1M KOH at 1.8V for 2 hours in ambient air conditions. The electroactive area of the GCs was determined by measuring the capacitance with EIS before and after anodization, and by later dividing by the specific capacitance (13 μF/cm2). A remarkable tenfold increase in surface area was observed after anodization. With a custom-built cluster deposition apparatus (Figure 1a), four monolayers of gold clusters were deposited on three bare GCs (BareGC) and three anodized ones (AnGC). Field Emission Scanning Electron Microscopy (FE-SEM) images captured the morphology of BareGC and AnGC, both with and without clusters (Figure 1b). Atomic force microscopy was also utilized to complement the morphology study of the electrodes' surface. Grazing Incidence X-ray Diffraction (XRD) at 0.5 degrees revealed a peak corresponding to the Au(111) plane in Au+BareGC (Figure 1c). Rutherford backscattering was employed to quantify the gold loading on the samples. To facilitate the generation of active Au-OH species on the nanoclusters, the electrodes underwent cycling between 0.43V and 1.53V in 0.1M PBS, devoid of chlorides. Subsequently, the sensing performance towards glucose was evaluated via chronoamperometric methods, maintaining the potential at 0.884V under stirring conditions (250 rpm). Gradual increases in glucose concentration were applied in steps of 0.25 mM and later in 1 mM increments up to 7 mM (Figure 1d).Both Au+BareGC and Au+AnGC electrodes exhibited an extremely linear response (R²=0.99) within the 0.25 mM to 7 mM linear range. After calibration, the electrodes underwent cycling in 0.5 M H2SO4 between 0.015V and 1.715V (vs RHE). The gold oxide reduction peak was integrated (Figure 1e), allowing estimation of the electroactive surface area (ESA) using the formula ESA=(Integrated charge)/(scan rate*0.386 mC/cm-2). A comparative analysis with similar nanostructured Au samples (Table 1) revealed that Au+AnGC displayed a four times higher sensitivity and substantially lower detection limits.The impact of chlorides was explored by repeating the chronoamperometric calibration in a PBS+0.1M KCl buffer. Chloride adsorption led to complete catalyst deactivation and eventually to gold loss from both samples. Notably, Au+BareGC displayed higher sensitivity to Cl etching, experiencing a 50% reduction in gold ESA compared to a 30% drop in Au+AnGC.This work has proved that the deposited nanoclusters possess an extremely high density of active sites towards glucose electro-oxidation. In addition, the deposition on highly porous electrodes decreases the poisoning effect of chlorides. These findings show significant promise as a scalable fabrication strategy to glucose sensor development.References in Table 1:[1] https://www.sciencedirect.com/science/article/pii/S001346861400766X#bib0060[2] https://pubs.acs.org/doi/10.1021/jp810235v[3] https://www.sciencedirect.com/science/article/pii/S0925400515007133?via%3Dihub[4] https://www.sciencedirect.com/science/article/pii/S0039914012008971[5] https://pubs.acs.org/doi/10.1021/ac035143t Figure 1

Maximizing Quantum Hole Collection on Anatase TiO2 Thin Films with (001) Facets for Photoelectrochemical Oxigen Evolution Reaction Efficiency

Hydrogen production from water, a key element in the renewable energy portfolio, offers a solution to reduce reliance on fossil fuels. Photoelectrochemical (PEC) hydrogen production, using light-absorbing semiconductors and catalysts, offers a clean and cost-effective method for harnessing solar energy. To enhance the efficiency of PEC, this study explores the use of anatase TiO2 thin film photoelectrodes as an alternative to expensive and rare catalysts, aiming to generate hydrogen as a clean fuel with oxygen as a byproduct.Anatase titanium dioxide is a well-established functional material widely applied in the fields of environment and energy. Recognized as one of the premier materials for photocatalysis and a promising photoanode material for water splitting, titanium dioxide (TiO2) finds use in diverse applications such as dye-sensitized solar cells, perovskite-based solar cells, and cleaning devices. Its band gap of 3.2 eV, stability, strong absorption in the UV region, and energetics of the valence and conduction band edges make anatase particularly suitable for PEC water splitting, especially for the oxygen evolution reaction (OER).Our research focuses on the development of anatase thin films with strong [001] texture and (001) facets at the surface of the film. The (001) facets are known to accumulate photogenerated hole states while the [001] orientation imparts a negative flat band potential. We hypothesize that these two properties, (001) facets and [001] texture, are ideal for OER. This study combines these two structural characteristics within the semiconductor TiO2 layer to enhance PEC performance and maximize the efficiency of hole collection during water oxidation.Anatase TiO2 thin films with (001) facets and [001] orientation were hydrothermally synthesized on a fluorine-doped tin oxide (FTO) substrate and annealed at 500°C. The films exhibited [001] orientation and (001) faceting as shown by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Photoelectrochemical measurements via cyclic voltammetry in a 0.1 M KOH and Na2SO3 solution demonstrated the films' hole collection efficiency under a 365 nm UV light source. The photoelectrochemical (PEC) and oxygen evolution reaction (OER) characteristics of anatase thin films were observed both under dark and light conditions. Prior to illumination, only the Ti3+/Ti4+ redox couple was observed with an onset potential of 0.01 V (RHE) and negligible OER at anodic potentials. When UV irradiated, the TiO2 thin films exhibited a photocurrent that increased through the anodic scan. The onset potential of photocurrent, measured in the presence of the hole scavenger, exhibited a negative shift ranging from -100 to -200 mV compared to the KOH onset potential. This shift is attributed to the film surface's limited efficiency in collecting holes for water oxidation at low potentials, as rapid recombination kinetics compete with water oxidation. Interestingly, the photocurrent observed with Na2SO3 electrolyte was 0.15 to 0.3 times more than what we saw with KOH electrolyte. Our preliminary results indicate a current density of ~2.0-2.5 mA cm-2 at 1.8 V and a hole collection efficiency of ~84 % at 1.23 V vs RHE, the thermodynamic water oxidation potential. In summary, we have made significant progress toward enhancing the PEC activity of anatase TiO2 thin films by optimizing the film structure for both reactivity and charge transport.

Material Changes of Bimetallic Ag–Cr, Fe, Co, Ni, Cu, Sn Electrocatalysts during Alkaline Oxygen Reduction in Fundamental Versus Alkaline Membrane Exchange Fuel Cell Conditions

The more apparent challenges of climate change drastically increase the global demand for sustainable fuel production and usage.1 In this context, hydrogen fuel cells (FCs) powered by renewable electricity are among the promising technologies.2 Addressing the sluggish cathode reaction in FCs, the oxygen reduction reaction (ORR), these devices hold immense potential for sustainable energy conversion and storage. An alkaline environment allows for the utilization of more abundant and cost-effective metals in contrast to current platinum-based catalysts. Silver (Ag), for instance, exhibits high selectivity for the ORR, i.e., forming hydroxide instead of peroxide.3 When combined with secondary metals, bimetallic Ag catalysts show enhanced activity, making them viable alternatives to platinum-group materials for ORR.In our highly collaborative research, we investigated the material transformations of bimetallic Ag thin films with chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and tin (Sn) as secondary metals for ORR electrocatalysis in fundamental rotating disk electrode (RDE) setups and the application device, anion-exchange membrane FC (AEMFC). Grazing-incidence X-ray diffraction (GI-XRD) conducted prior to electrochemical testing reveals no evidence of alloying except for the Ag-Sn bimetallic thin film. However, X-ray photoelectron spectroscopy (XPS) indicates a shift of the Ag 3d peaks to higher binding energies for all catalysts, suggesting a hybridization of Ag and the secondary metals. The composition of the metal surface, native oxide formation, ORR performance, and material changes post-RDE testing vary distinctly among the Ag bimetallic catalysts depending on the secondary metal. Intriguingly, performance is either enhanced (Ag-Co, Ag-Sn), maintained with reduced Ag content (Ag-Fe, Ag-Cr), or falls in between the two monometallic materials (Ag-Ni) compared to monometallic Ag thin films. Density functional theory (DFT) calculations offer insights into the catalyst performances and changes in metal oxidation states and surface composition prior and post electrocatalysis. AEMFC tests reveal promising performances under device conditions contradicting our fundamental RDE measurements. The integration of fundamental and application device tests, along with material characterization and DFT calculations, enables a comprehensive exploration of material changes under varying electrochemical conditions. This underscores the complexity of bimetallic catalysts and the importance of testing under device conditions, positioning Ag-bimetallic catalysts as highly promising alternatives to platinum-group metal catalysts for alkaline ORR.

(Invited) Role of Oxidant Gas for Atomic Layer Deposition of HfxZr1−XO2 Thin Films on Ferroelectricity of Metal-Ferroelectric-Metal Capacitors

Since the first report of ferroelectricity in HfxZr1−xO2 (HZO) in 2011 [1], a lot of attention has been devoted for future non-volatile memory device applications due to its scalability (< 10 nm), low thermal budget (< 400°C) and matured atomic layer deposition (ALD) technique [2]. The thermal ALD process using H2O or O3 is generally employed for the fabrication of ferroelectric HZO thin films. On the other hand, the effect of the plasma-enhanced ALD process using O2 plasma gas on the crystallinity and ferroelectricity has not been systematically clarified. In this paper, we report the importance of ALD oxidant gases for HZO films using H2O or O2 plasma on the ferroelectricity of metal–ferroelectric–metal (MFM) capacitors.MFM capacitors with the H2O- and O2 plasma-based HZO films were fabricated as follows. A 10-nm-thick HZO films were deposited on a TiN bottom-electrode (BE-TiN) by ALD at 300°C using H2O or O2 plasma as oxidant gases and (Hf/Zr)[N(C2H5)CH3]4 (Hf:Zr = 1:1) cocktail precursor. The Hf/Zr ratios in both types of HZO films were estimated to be 0.4/0.6 using X-ray photoelectron spectroscopy (XPS). Next, a post-deposition annealing (PDA) process was carried out at 400 °C for 1 min under a N2 atmosphere. Finally, a TiN top-electrode was deposited by DC sputtering.First, the crystallinity and remanent polarization (2P r = P r + − P r −) of the H2O- and O2 plasma-based HZO films were investigated. Nanocrystals with ferroelectric orthorhombic (O), tetragonal (T), cubic (C) phases partially existed in the O2 plasma-based film after the ALD process, while an amorphous structure dominantly existed in the H2O-based film, analyzed by the grazing-incidence X-ray diffraction analysis and cross-sectional transmission electron microscopy images [3]. This could be because of a strong oxidation power and high energy ion/electron bombardment of O2 plasma. After the PDA process, the O phase was formed more in the O2 plasma-based HZO film than the H2O-based film. Therefore, the nanocrystal grains in the as-grown O2 plasma-based HZO film could play an important role as nuclei for the crystallization and formation of O phase [3,4]. From the polarization–electric field hysteresis curves, the PDA-treated O2 plasma-based capacitor exhibited 2P r of 20 µC/cm2, which was 1.5 times higher than that (13 µC/cm2) of the H2O-based capacitor. Thus, these results indicate that the crystallization and O phase formation of HZO films were promoted by using O2 plasma gas as an ALD oxidant, resulted in a higher 2P r.Next, endurance properties of these MFM capacitors were evaluated. In the wake-up state, both capacitors showed almost the same increase rate (~8%) of switching polarization (P sw). In the fatigued state, on the other hand, the O2 plasma-based capacitor exhibited less P sw degradation (~33%) after 106 cycles, whereas the P sw of H2O-based capacitor decreased by ~47%. To clarify these different fatigue properties, the TiOxNy interface reaction layer (IRL) formation at the HZO/BE-TiN interface was analyzed using synchrotron hard X-ray photoelectron spectroscopy (HAXPES). For the HAXPES Ti 2p spectra, the Ti-O peak intensity for the O2 plasma-based capacitor was larger than that of the H2O-based capacitor [5]. Therefore, an oxygen-rich TiON-IRL could be formed at the HZO/BE-TiN interface during ALD process due to the stronger oxidizing power of O2 plasma. Additional oxygen vacancies (VO) were reported to formed in HfO2-based films during field cycling due to the interface reaction between the HfO2-based film and TiN electrode. Moreover, one of the origins of the P sw degradation was thought to be domain pinning caused by VO [6]. Therefore, an oxygen-rich TiON-IRL for the MFM capacitor with the O2 plasma-based HZO film could prevent the interface reaction and formation of additional VO in HZO films, led to superior fatigue properties.In summary, the MFM capacitor with the O2 plasma-based HZO film showed superior 2Pr and fatigue resistance compared to those of the H2O-based one. Based on these experimental results, it is important to consider the selection of an ALD oxidant for fabrication of HZO-based MFM capacitors.This work was partly supported by JSPS KAKENHI (Nos. JP21J01667, JP20H02189, and JP18J22998) and MEXT Leading Initiative for Excellent Young Researchers (No. JPMXS0320220213). The HAXPES measurements were performed under approval of the NIMS Synchrotron X-ray Station (2020A4602 and 2020A4651).[1] J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011).[2] J.-H. Kim et al., ACS Appl. Electron. Mater. 5, 4726 (2023).[3] T. Onaya et al., APL Mater. 10, 051110 (2022).[4] T. Onaya et al., Microelectron. Eng. 215, 111013 (2019).[5] T. Onaya et al., Solid State Electron. 210, 108801 (2023).[6] M. Pešić et al., Adv. Funct. Mater. 26, 4601 (2016).

Unveiling the secrets of non-evaporable getter films: Activation temperature, activation time, and achievable activation degree

Non-evaporable getter films play an important role in the creating and maintaining of high or ultra-high vacuum environments in advanced scientific disciplines. Prior to application, thermal activation in a vacuum environment is essential. Despite numerous attempts to reduce the film activation temperature, uncertainty remains as to whether extending the activation time at a relatively lower activation temperature will ensure a fully-activated state of the film. To address this issue, the microstructure and activation performance of the film has been investigated. Techniques, such as scanning electron microscopy, grazing incidence X-ray diffraction, energy dispersive spectroscopy, and in-situ X-ray photoelectron spectroscopy were employed. Experimental investigations show that a fully-activated state of the film cannot be achieved at around 150°C, regardless of the activation time. Further analysis shows that, at activation temperatures below about 200°C, the migration trend of oxygen atoms within TiZrV/TiZrHfV films exhibits asynchronous features. This process was accompanied by boundary effects of foreign atom migration channels. In addition, the achievable activation degree of the film shows a step characteristic. These results improve the understanding of the relationship between activation temperature, activation time, and the achievable activation degree of the film.

Electrosynthesis-Induced Pt Skin Effect in Mesoporous Ni-Rich Ni-Pt Thin Films for Hydrogen Evolution Reaction.

A Pt skin effect, i.e., an enrichment of Pt within the first 1-2 nm from the surface, is observed in as-prepared electrodeposited Ni-rich Ni-Pt thin films. This effect, revealed by Rutherford backscattering (RBS), is present for both dense thin films and mesoporous thin films synthesized by micelle-assisted electrodeposition from a chloride-based electrolyte. Due to the Pt skin effect, the Ni-rich thin films show excellent stability at the hydrogen evolution reaction (HER) in acidic media, during which a gradient in the Pt/Ni ratio is established along the thickness of the thin films, while the activity at the HER remains unaffected by this structural change. Further characterization by elastic recoil detection with He ions analysis shows that hydrogen profiles are similar to those of Pt: a surface hydrogen peak coincides with the Pt skin, and a gradient in hydrogen concentration is established during HER in acidic media, together with a considerable uptake in hydrogen. A comparative study shows that in alkaline media, hydrogen evolution has little to no effect on the structural properties of the thin films, even for much longer times of exposure. The mesoporous thin films, in addition to their higher efficiency at HER compared to dense thin films, also show lower internal stress, as determined by Rietveld refinement of grazing incidence X-ray diffraction patterns. The latter also reveal a fully single-phase and nanocrystalline structure for all thin films with varying Ni contents.

Spin-transport across semi-crystalline polyvinylidene fluoride thin films in Ta/Co/PVDF/NiFe pseudo spin-valve devices

Room temperature magnetoresistance (MR) across semi-crystalline polyvinylidene fluoride (PVDF) thin films in Ta(2 nm)/Co(15 nm)/PVDF/NiFe(28 nm) pseudo-spin-valve devices (PSVs) are systematically investigated by varying PVDF thicknesses from 80 − 230 nm and applied bias voltages up to 100 mV. NiFe, Ta/Co magnetic bottom and top electrodes, and PVDF thin films are deposited by DC magnetron sputtering and spin-coating methods. The structural, microstructural, and magnetic natures have been evaluated using grazing incidence X-ray diffraction, atomic force microscopy, and magneto optic kerr effect systems. Electrical characteristics reveal a maximum MR of ∼0.25 % at 60 mV bias voltage across PVDF-80 nm and ∼0.08 % across PVDF-230 nm & PVDF- 120 nm devices. A constant MR is found across all the devices up to 100 mV applied bias voltages. In addition to the electrical spin injection evaluation, coplanar waveguide ferromagnetic resonance measurements are utilized to validate the spin injection into PVDF layers by estimating the Gilbert damping parameters of NiFe and PVDF/NiFe bilayers. Furthermore, low MR in PSVs is discussed with the parallel spin-dependent conducting channels corresponding to PVDF’s amorphous, alpha, and beta crystalline phases.

Study on the charge transport behaviour of mxene- polymer nanocomposite-based self-assembled floating films at the air-liquid interface

This study explores the fabrication and charge transport behavior of MXene-polymer nanocomposite-based self-assembled floating films at the air-liquid interface. Utilizing ultrasonic dispersion of MXene nanosheets was integrated into a DPP-TTT polymer matrix, significantly enhancing the alignment and crystallization of the polymer chains. The films were fabricated using a unidirectional floating film transfer method (UFTM), which proved to be both simple and cost-effective. UV–visible and grazing incidence X-ray diffraction (GIXD) analyses confirmed increased π–π stacking and improved structural arrangement within the nanocomposites. Organic field-effect transistors (OFETs) fabricated from these films demonstrated that a 3% MXene inclusion resulted in the highest mobility, measuring 3.1 cm2V-1s-1 with an on-off ratio in the order of 104, compared to 1.3 cm2V-1s-1 in pristine DPP-TTT films. However, further increases in MXene content reduced mobility, emphasizing the importance of precise compositional tuning.

Direct Laser Writing Crystal Polymorphs of Organic Semiconductors for Phase Change Electronics.

The many diverse polymorphic behaviors observed in organic electronic materials offer opportunities to modulate electronic properties through reversibly switching crystal structures. Here, we access the prolific polymorphism observed in two-dimensional quinoidal terthiophene via laser writing to locally heat and direct the phase transitions. We access a metastable polymorph IV through rapid cooling and observe distinct symmetry as well as packing through grazing incidence X-ray diffraction (GIXD). Using our open-source PolyChemPrint patterning platform, we direct laser heating to initiate the IV-I transition, switching the conductance by >2 orders of magnitude. This is confirmed via a combination of GIXD and Raman spectroscopy. Finally, we demonstrate switching of transistor devices as well as discrete tuning of conductance via laser writing.

Influence of topography on nano-mechanical properties of cylindrical magnetron sputtered TiN films

Numerous studies on Nano-mechanical behavior of the thin films explained primarily in terms of their film morphology and particle size rather than film topography. Therefore, the current study investigates the effect of film topography on the nano-mechanical characteristics of the film. Ti/TiN multilayer thin films were deposited at varying deposition pressures by using an indigenously developed Cylindrical Magnetron Sputtering (CMS) unit. Surface crystallographic information is characterized by synchrotron-based Grazing Incidence XRD analysis. Film growth follows self-assembled nano hill architecture as revealed by AFM and in situ Scanning Probe Microscopy images. The tribo-mechanical properties of the film is dependent on the height and spacing of its self-assembled structure, which experiences either crushing or buckling under the indenter load, thereby affecting film characteristics. Film deposited at moderate pressure exhibits superior wear behavior, attributed to the interplay between Plasticity Index (PI) and Depth Recovery Ratio (DRR). The study primarily focused on film growth phenomena by using cylindrical targets and their influence on nanomechanical properties of the film.

Fabricating Cu2Zn(SnxGe1-x)Se4 thin-film solar cells with back surface Ge grading by magnetron sputtering

In this paper, an approach of forming a band gap gradient by depositing a layer of Ge between the Mo layers by magnetron sputtering is proposed. The diffusion depth of the Ge into Cu2ZnSnSe4 (CZTSe) thin film can be effectively controlled by the Mo transition layer, resulting in the formation of Cu2Zn(SnxGe1-x)Se4 (CZTGSe) thin film with a band gap grading along the back surface. To validate the formation of the Ge gradient in the absorber, energy dispersive spectrometer line scanning and grazing incidence X-ray diffraction were performed. Furthermore, the impact of Ge layer on the morphologies of CZTSe was assessed using scanning electron microscopy. As a result, the introduced Ge layer formed a Ge grading along the back surface and improved the crystal quality of the absorber. Compared to CZTSe solar cells, the power conversion efficiency (PCE) of CZTGSe solar cells with a Ge gradient improved from 5.79 % to 9.28 %.

Deposition pressure-controlled phase tailoring and stability of β-W for spintronic applications

Understanding the nucleation and growth of tungsten (W) is technologically important in spin-to-charge interconversion for realizing energy-efficient spintronic devices. Here, we have systematically investigated the effect of Ar deposition pressure (PAr) on the nucleation and growth of W. The observed surface topography as a function of PAr reveals a microstructural transition from zone T to zone 1 in the structure zone model. The physical origin for the increasing roughness as a function of PAr correlates with the surface diffusion of adatoms and growth kinetics in the Volmer–Weber growth mechanism. Grazing incidence x-ray diffraction (GIXRD) results show that W exhibits a structural phase transition from a mixed phase of (α+β)-W to a single phase of β-W as a function of PAr. The analysis of the electron diffraction patterns obtained from the films grown on amorphous-SiNx windows also supports these observations. The observed transition is fundamentally correlated with the growth kinetics in zone T and zone I. Thickness-dependent GIXRD results qualitatively prove that the film grown in zone T exhibits compressive strain, whereas that grown in zone I exhibits only tensile strain. The critical thickness for the phase transition is strongly attributed to the strain during nucleation and growth. The increasing resistivity as a function of PAr corroborates the change in structural phases. Thickness-dependent resistivity measurements correlate with the degree of crystallinity via relative intensity observed from the GIXRD results. Our results strongly suggest that W structural phases can be deterministically controlled via PAr for developing low-power spintronic devices.

Exploring the performance of Co/Al2O3–ZrO2 nanocatalysts developed through the thermal evaporation method in dry reforming of methane

Abstract This study aimed to investigate the performance of the thin layer nanostructures of Co/Al2O3–ZrO2 in the dry reforming of methane (DRM) in a microchannel reactor. The nanostructures were prepared via utilizing the thermal evaporation method. Reactor tests were carried out at various coating times of 2, 3, and 4 min and temperatures of 700, 750, and 800 °C with a feed flow rate of 10 ml/min and a 1:1:8 ratio of helium, carbon dioxide, and methane. Also, grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) were used to identify catalyst features. According to the obtained results, the highest percentage of conversion in all samples was observed at 800 °C. The results of the reactor tests also revealed that the activity of catalyst layers highly depends on coating time. The findings demonstrated that raising deposition time improves the distribution of particle size and catalyst loading. Considering the nanostructure of Co/Al2O3–ZrO2, the sample undergoing 4 min coating time yielded the highest amount of primary methane conversion (89.3 %), primary carbon dioxide conversion (92.4 %), and H2/CO molar ratio (0.91). The stability test of the catalyst layers for 28 h at the optimum condition (P = 1 atm, T = 800 °C, t = 4 min deposition time, CH4/CO2 = 1, and GHSV = 48,000 mL g−1 h−1) showed that the catalysts prepared by this method had a good stability.

The effect of RF sputtering power on structural, nanomechanical and tribological properties of single layered TaN coatings

Single-layered TaN thin coatings were deposited on Ti6Al7Nb alloy substrates using reactive radiofrequency magnetron sputtering, with variations in target power. To assess the crystalline structure, chemical composition, and surface topography of these coatings, Grazing Incidence x-ray Diffraction (GIXRD), Energy Dispersive Spectroscopy (EDS), and Scanning Probe Microscopy (SPM) were employed, respectively. The study revealed that deposition power impacts the structure and composition of TaN coatings. Further analysis using x-ray Photoelectron Spectroscopy (XPS) indicated that the TaN coatings predominantly consisted of Ta and N, with trace amounts of oxygen (O 1s). Additionally, nanomechanical testing was conducted to evaluate hardness (H), modulus (E), and scratch properties. Results suggested that multiphase hex-TaN coatings exhibited superior H, E, and scratch properties compared to other cubic-structured TaN coatings. Friction and wear properties against steel balls under dry sliding conditions were determined using a ball-on-disk nanotribometer. The findings showed that mix-phase TaN coating exhibited a minimum coefficient of friction of 0.054 and a wear rate of 2.14 × 10−6 mm3/N.m. Abrasion, ploughing and oxidation were identified as the primary wear mechanism responsible for the wear of the TaN coatings.

Effect of Temperature on the Structure and Tribological Properties of Ti, TiN and Ti/TiN Coatings Deposited by Cathodic Arc PVD

Monolayers of Ti and TiN coatings, as well as a Ti/TiN bilayer coating, were deposited on AISI M2 steel substrates using the PVD cathodic arc technique. The coatings had a thickness close to 5 μm and an average roughness between 98.6 and 110.1 μm due to the presence of microdroplets on the surface. The crystalline structure of the materials was analyzed using Grazing Incidence X-ray Diffraction (GIXRD) with an increase in temperature to study the dynamics of oxide formation. A phase composition study was conducted using the Rietveld refinement method. At the temperatures where critical growth of titanium oxides, both anatase and rutile, was observed, pin-on-disk tests were performed to study the tribological properties of the materials at high temperatures. It was determined that the oxidation temperature of Ti is around 450 °C, promoting the formation of a combination of anatase and rutile. However, the formation of rutile inhibits the formation of anatase, which is stable above 600 °C. In contrast, TiN showed an oxidation temperature of 550 °C, with an exclusive growth of the rutile phase. The Ti/TiN bilayer exhibited mixed behavior, with the initial growth of anatase promoted by Ti, followed by the formation of rutile. Oxidation and tribo-oxidation dominated the wear behavior of the surfaces, showing a transition from mechanisms related to abrasion at low and medium temperatures to a combination of abrasion and adhesion mechanisms at high temperatures (800 °C).