Grazing Incidence X-ray Diffraction Research Articles

Defect Tailoring in HfO2/Si Films upon Post-Deposition Annealing and Ultraviolet Irradiation

In the present work, a study of the structural defects in HfO2 thin films deposited by dip-coating on p-type silicon substrates treated under different conditions, such as air-annealing, ultraviolet irradiation, and simultaneous annealing–UV irradiation, is presented. HfO2 thin films were analyzed by grazing incidence X-ray diffraction, Raman spectroscopy, optical fluorescence, atomic force microscopy, and UV-Vis diffuse reflectance. Films treated at 200 °C and 350 °C present peaks corresponding to monoclinic HfO2. After UV treatment, the films became amorphous. The combination of annealing at 350 °C with UV treatment does not lead to crystalline peaks, suggesting that UV treatment causes extensive structural damage. Fluorescence spectroscopy and UV-Vis spectroscopy suggest that films present oxygen vacancies as their main structural defects. A reduction in oxygen vacancies after the second thermal treatment was observed, but in contrast, after UV irradiation, fluorescence spectroscopy indicated that more defects are created within the mobility gap, irrespective of the simultaneous annealing at 350 °C. An electronic band diagram was proposed assigning the observed fluorescence bands and optical transitions, which, in turn, explain the electrical properties of the films. The results suggest that the electronic structure of HfO2 films can be tailored with a careful choice of thermal annealing conditions along with the controlled creation of defects using UV irradiation, which could open the way to multiple applications of the materials either in microelectronics, optoelectronics, as well as in photocatalytic/electrocatalytic applications such as photodegradation and hydrogen generation.

Molecular Effects of Zwitterionic Peptide on Monolayer Lipid Membranes upon Enzyme-Catalyzed Degradation.

Secretory phospholipase A2 (sPLA2), an enzyme overexpressed in numerous diseases, has been used to trigger structural transformations in lipid-based drug delivery systems, enabling payload release at target sites. Zwitterionic peptides are known for their superior antifouling properties, often outperforming poly(ethylene glycol) (PEG) surface modification by resisting protein adsorption. In this study, we examined lipid monolayers at the water-vapor interface on a Langmuir trough, incorporating varying molar fractions of zwitterionic peptide-conjugated lipids or PEG-conjugated lipids. Synchrotron X-ray surface techniques, including X-ray reflectivity and grazing incidence X-ray diffraction, were employed to analyze molecular packing, enzyme adsorption, enzyme-catalyzed lipid degradation, and metabolite reorganization at the interface, and microscopy was used to observe domain morphologies. The results demonstrate that zwitterionic peptides exhibit a significantly greater efficiency than PEG in stabilizing the interfacial monolayer packing structure against enzyme-catalyzed lipid degradation. However, contrary to most studies reporting strong resistance of zwitterionic materials to nonspecific protein absorption, enzyme absorption to the interface, which is interfacial and phospholipids specific, was not impeded by the presence of zwitterionic peptides at low molar ratios (≤10 mol %).

Intensity corrections for grazing-incidence X-ray diffraction of thin films using static area detectors

Grazing-incidence X-ray diffraction (GIXD) is the technique of choice for obtaining crystallographic information from thin films. An essential step in the evaluation of GIXD data is the extraction of peak intensities, as they are directly linked to the positions of individual atoms within the crystal unit cell. In order to obtain reliable intensities independent of the experimental setup, a variety of correction factors need to be applied to measured GIXD raw data. These include the polarization of the incident beam, solid-angle variations, absorption effects, the transmission coefficient and the Lorentz correction. The aim of this work is to provide a systematic compilation of these intensity corrections required for state-of-the-art GIXD setups with static area detectors. In a first step, analytical formulae are derived on the basis of theoretical considerations. The obtained intensity corrections are then applied to measured GIXD raw data from samples with different textures, including a single crystal and thin films containing either randomly distributed or oriented crystallites. By taking advantage of the symmetries inherent in the different types of textures, integrated peak intensities are determined, and these are compared with intensities calculated from single-crystal diffraction data from the literature. Accurate intensity corrections promise an improved quality of crystal structure solution from thin films and contribute to achieving accurate phase and texture quantifications from GIXD measurements.

Structure Modulation and Self-Lubricating Properties of Porous TiN–MoS2 Composite Coating Under Humidity–Fluctuating Conditions

To improve the friction performance and service life of protective coatings in humidity-fluctuating environments, porous hard titanium nitride (TiN)–molybdenum disulfide (MoS2) composite coatings were prepared by using direct current magnetron sputtering (DCMS) with the mode of oblique angle deposition (OAD) and chemical vapor deposition (CVD) technologies. The structure and chemical component were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The tribological properties of these TiN–MoS2 composite coatings were investigated. The results indicate that the porous TiN–MoS2 composite coating exhibited outstanding friction performance and long service life under humidity-fluctuating environments. At the initial 20% relative humidity (RH) stage, the MoS2 on the porous TiN–MoS2 composite coating surface worked as an effective lubricant; thus, the coating demonstrated excellent lubrication performance, and the friction coefficient (COF) was about 0.05. As the humidity was alternated to 70% RH, the lubrication effect diminished due to the production of molybdenum oxide (MoO3), and the COF was about 0.2, which was attributed to the degradation of MoS2 on the wear track and the release of fresh MoS2 from the porous TiN matrix. After the environmental conditions shifted from 70% to 20% RH, the MoO3 was removed, and the lubrication effect was restored. In summary, TiN–MoS2 porous composite coating offers a promising approach for lubrication in humidity-fluctuating environments.

Optimizing the growth conditions of superconducting MoSi thin films for single photon detection

We investigate the growth of amorphous MoSi thin films using magnetron co-sputtering and optimize the growth conditions with respect to crystal structure and superconducting properties (e.g., critical temperature ). The deposition pressure, Mo:Si stoichiometry and substrate temperature are systematically varied to achieve a transition temperature of 8.4(3) K for films with a thickness of 17.7(8) nm and 6.2(9) K for a 4.3(4) nm thick film. For Mo concentrations above 81% the crystalline phase Mo3Si is observed in grazing incidence X-ray diffraction measurements. The same phase appears when the working pressure during deposition is reduced below 3.1×10-3mbar and when the substrate temperature during deposition is increased above C. By choosing a sufficient Si concentration and optimum deposition pressure we identify deposition conditions that ensure a homogeneous amorphous growth of the superconducting thin film. We then fabricate superconducting nanowire single-photon detectors which exhibit an unitary internal efficiency to single photons at an operational temperature of 1.2 K while simultaneously having a dark count rate below 1 Hz. Our results establish the link between MoSi film deposition, morphology and the performance of SSPD.

A Novel (AlCrNbTaTi)N Multilayer Hard High-Entropy Alloy Nitride Coating with Variable Aluminum Content Deposited by Cathodic Arc Ion Plating

Traditional binary coatings like TiN and CrN display limited thermal stability and wear resistance under extreme conditions. High-entropy alloy nitride (HEAN) coatings offer a promising solution due to their customizable composition and unique properties, including high hardness, corrosion resistance, and thermal stability. This study focused on (AlCrNbTaTi)N HEAN coatings to address a critical need for materials capable of enduring extreme mechanical and tribological demands by examining the impact of aluminum content on their structural and mechanical properties, providing insights for optimizing coatings in harsh conditions through a self-assembled nanolayer structure with enhanced resilience and performance. The coatings were deposited via a cathodic arc by employing an AlCrNbTaTi alloy target composed of aluminum (20, 50, 60, 70%) and equal molar ratios of Cr, Nb, Ta, and Ti. The coatings were characterized through grazing incidence X-ray diffraction, SEM, HR-TEM, a nano-indentation test, and a friction and wear test. The results indicated that with increasing Al content, the structure of (AlCrNbTaTi)N coatings shifted from FCC to an amorphous state, leading to a reduction in the hardness and elastic modulus, accompanied by an increase in the wear rate and friction coefficient. The (AlCrNbTaTi)N coating, with an equal atomic ratio of metallic elements, showed potential as a hard tool coating. It demonstrated outstanding mechanical and tribological properties, with a 34.5 GPa hardness, 369 GPa modulus, 0.35 friction coefficient, and 8.2 × 10−19 m2·N−1 wear rate. The findings highlight the potential of (AlCrNbTaTi)N coatings to extend tool life and improve operational efficiency, helping advance materials engineering for industrial applications.

The role of RF sputtering parameters on the uniformity and stability of Tb4O7 thin films on silicon substrates for passivation applications

Abstract In this study, the effects of different radio frequency (RF) parameters, were studied from the physical perspective of terbium oxide (Tb4O7) thin films deposited on silicon (Si) substrates, emphasizing their uniformity and stability for passivation applications. The findings for sample B, indicate that an optimal sputtering power of 110 W for 40 min enhances film uniformity while minimizing surface roughness, which is critical for achieving a stable passivation film. Notably, all the studied samples revealed a crystalline nature and maintained a stable phase, with no impurities detected from the grazing incident X-ray diffraction (GIXRD) patterns. Sample B revealed the highest value of crystallite size measured at 38 nm. Additionally, band gap energy (Eg) values between 2.19 and 2.78 eV were measured using the Kubelka-Munk (K-M) method. Photoluminescence (PL) analysis showed sample B achieved the highest peak intensity at 548 nm, corresponding to the 5D4 → 7F5 transition. Studies have been conducted on the formation of Tb4O7thin films deposited by RF sputtering on Si substrates, annealed in an argon (Ar) atmosphere. This study introduces a new approach to enhance film quality by adjusting the RF power during the sputtering process and subsequently annealing the sputtered samples. The aim was to investigate the benefits of nitrogen (N) annealing on the formation of a uniform passivation film of Tb4O7 material.

Grazing-incidence X-ray diffraction elucidates structural correlations in fluid monolayers of lipids and surfactants.

Biological membranes predominantly consist of fluid lipid phases featuring lateral mobility and a considerable disorder of their hydrocarbon chains. Langmuir monolayers of lipids at the air/water interface are versatile model systems for fundamental physicochemical and biophysical membrane investigations. Grazing-incidence X-ray diffraction (GIXD) is a powerful tool for the structural characterization of such monolayers but has so far been used almost exclusively for lipid phases of crystalline ordering giving rise to sharp diffraction peaks. Here, we use GIXD for the characterization of fluid monolayers of phospholipids and of water-soluble surfactants. We find that these layers feature spatiotemporally localized, structurally correlated hydrocarbon chain regions that involve only a few molecules and have only a small extension vertically. The abundance of these regions increases with increasing lateral packing density due to compression until the transition into an ordered phase occurs.

Optimization of CZTSe Thin Films Using Sequential Annealing in Selenium and Tin-Selenium Environments.

Cu2ZnSnSe4 (CZTSe) is a promising material for thin-film solar cells due to its suitable band gap, high absorption coefficient, and composition of earth-abundant and nontoxic elements. In this study, we prepared CZTSe thin films from Cu/SnSe2 and ZnSe stacks using a two-step annealing process. Initially, Cu-Sn-Se (CTSe) films were synthesized by sequential deposition and annealing of Cu and SnSe2 precursors in either a selenium (Se) or tin-selenium (Sn+Se) atmosphere. After the deposition of a ZnSe layer on top of CTSe films, the stack underwent a second annealing process, again in either a Se or Sn+Se atmosphere, resulting in four distinct annealing combinations: Se→Se, Sn+Se→Se, Se→Sn+Se, and Sn+Se→Sn+Se. The first annealing step enabled the formation of CTSe, while the second annealing step, performed after ZnSe deposition, led to the formation of the CZTSe phase. Comprehensive characterization including grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrical measurements was conducted. GIXRD and Raman analysis revealed kesterite CZTSe phase peaks, with some samples showing a split in the main peak at ∼27° (2θ), indicating the presence of CuxSe and ZnSe secondary phases. SEM analysis showed the impact of Sn and Se annealing on grain size, with larger grains observed in films annealed in Sn+Se atmospheres, particularly in the second heat treatment process. EDS results displayed consistent elemental composition across samples, with varying Cu/(Zn+Sn), Zn/Sn and Se/metal ratios influencing the band gap values from 1.09 to 1.63 eV. Hall measurements indicated p-type conductivity with carrier concentrations between 1016 and 1023 cm-3. These results highlight the effectiveness of our two-step annealing process, particularly the Sn+Se atmosphere, in optimizing CZTSe thin films for potential use in high-efficiency thin-film solar cells.

Fabrication and Coating of Porous Ti6Al4V Structures for Application in PEM Fuel Cell and Electrolyzer Technologies.

The production of green hydrogen through proton exchange membrane water electrolysis (PEMWE) is a promising technology for industry decarbonization, outperforming alkaline water electrolysis (AWE). However, PEMWE requires significant investment, which can be mitigated through material and design advancements. Components like bipolar porous plates (BPPs) and porous transport films (PTFs) contribute substantially to costs and performance. BPPs necessitate properties like corrosion resistance, electrical conductivity, and mechanical integrity. Titanium, commonly used for BPPs, forms a passivating oxide layer, reducing efficiency. Effective coatings are crucial to address this issue, requiring conductivity and improved corrosion resistance. In this study, porous Ti64 structures were fabricated via powder technology, treating them with thermochemical nitriding. The resulting structures with controlled porosity exhibited enhanced corrosion resistance and electrical conductivity. Analysis through scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), grazing incidence XRD and X-ray photoelectron spectroscopy (XPS) confirmed the effectiveness of the coating, meeting performance requirements for BPPs.

A metastable temperature-strain phase diagram of HfxZr1−xO2 thin films based on synchrotron-based in situ 2D GIXRD investigation

The in-plane strain in the ferroelectric HfxZr1−xO2 (HZO) thin films has been considered to be the global factor behind many process parameters affecting the concentration of metastable polar-orthorhombic phase (O-phase Pca21) formed in the transformation pathway from tetragonal to monoclinic phase. However, the strain is generally effective in crystal phase nucleation and transition with the thermal budget and itself also changes with the thermal budget. The issue of how the O-phase is formed and changed in real time with effect of both thermal budget and in-plane strain has not been clarified, which is critical for engineering the O-phase concentration. Focusing on this issue, this work demonstrates the co-effect of strain and temperature on phase formation and transition in HZO by employing the synchrotron-based in situ two-dimensional (2D) grazing incidence x-ray diffraction (GIXRD) investigation. HZO thin films with different process parameters exhibit four types of phase transition processes during heating and cooling. Meanwhile, the in-plane strain magnitude and each phase concentration in the films during annealing are extracted. Based on both, the study established a universal temperature-strain phase diagram of HZO films and proposed a kinetic model for optimizing the ferroelectric O-phase formation. The study provides deep insights into O-phase engineering and ferroelectricity optimization in HZO thin films.

Room-Temperature Deposition of δ-Ni5Ga3 Thin Films and Nanoparticles via Magnetron Sputtering.

Magnetron sputtering is a versatile method for investigating model system catalysts thanks to its simplicity, reproducibility, and chemical-free synthesis process. It has recently emerged as a promising technique for synthesizing δ-Ni5Ga3 thin films. Physically deposited thin films have significant potential to clarify certain aspects of catalysts by eliminating parameters such as particle size dependence, metal-support interactions, and the presence of surface ligands. In this work, we demonstrate the potential of magnetron sputtering for the synthesis and analysis of thin film catalysts, using Ni5Ga3 as a model system. Initially, deposition conditions were optimized by varying the deposition pressure, followed by an investigation of the temperature effects, aiming to map a structure zone dependence on temperature and pressure as in the Thornton model. The evolution of film crystallinity was monitored using a combination of grazing incidence X-ray diffraction (GI-XRD) and high-resolution scanning electron microscopy (HR-SEM). Additionally, ultrathin films were synthesized and annealed in H2 at high temperatures to demonstrate the possibility of producing size-controlled nanoparticles by adjusting the annealing conditions. This work demonstrates the full potential of magnetron sputtering as a technique for synthesizing model system catalysts in various forms, opening new avenues for the research and development of additional catalytic systems.

Influence of Molybdenum Addition on the Structure, Mechanical Properties, and Cutting Performance of AlTiN Coatings

Though AlTiN coating has been intensively studied, there is still a need to develop AlTiN coating to meet the growing demand of industrial machining. One effective way to improve the performance of AlTiN coating is by adding alloying elements. In this study, AlTiN and AlTiMo coatings were deposited using multi-arc ion plating to investigate the influence of molybdenum addition on the structure, mechanical properties, and cutting performance of AlTiN coatings. Spherical droplets formed on the surfaces of both coatings, with the AlTiMoN coating exhibiting more surface defects than the AlTiN coating. The grazing incidence X-ray diffraction results revealed the formation of an (Al,Ti)N phase formed in the AlTiN and AlTiMoN coatings. Molybdenum doping in the AlTiMoN coating slightly reduced the grain size. Both coatings exhibited excellent adhesion to the substrate. The hardness (H), elastic moduli (E), H/E, and H3/E2 ratios of the AlTiMoN coating were higher than those of the AlTiN coating. The improvement in the mechanical properties was attributed to grain refinement and solution strengthening. Molybdenum doping improved the tribological properties and cutting performance of the AlTiN coatings, which was ascribed to the formation of MoO3 as a solid lubricant. These results show a path to increase the performance of AlTiN coating through molybdenum addition and provide ideas for the application of AlTiMoN coatings for cutting tools.

Amphiphilicity of Tetraazaporphyrins Containing Four Terminal Carboxylic Acid and Four Alkyl Groups Promotes Face-On Orientation in Langmuir Films.

Control over the orientation of polycyclic aromatic dyes in thin films is paramount to tailoring their optical, electronic, and mechanical properties. Their supramolecular assembly in films is tuned here by converting the macrocyclic dyes to large amphiphiles. Two octaalkythio-substituted tetraazaporphyrins (TAPs) with one 5-carboxypentyl and one pentyl or dodecyl chain per pyrrole ring were synthesized as statistical mixtures of four regioisomers. The unsymmetrically substituted maleodinitrile precursors were prepared in good yield with a flow reactor. Neither the tetraester precursor TAPs nor the tetraacid TAPs show mesomorphism, and both belong to the small class of porphyrin derivatives that display isotropic liquid phases at or close to room temperature. Interfacial properties of the two amphiphilic tetraacids were probed using Langmuir films on aqueous subphases at different pH values, and Langmuir-Blodgett films were transferred onto mica substrates. The tetraacid with the longer dodecyl chains forms inhomogeneous films comprising a combination of monolayer, stacked macrocycles with interdigitated chains, and 3D structures, with the latter favored at higher subphase pH and higher surface pressures. In contrast, films of the tetraacid with the shorter pentyl chains yielded relatively homogeneous monolayers. The combination of atomic force microscopy imaging and packing correlations elucidated by grazing incidence X-ray diffraction suggests that these form spider-like conformations, with the macrocycles close packed and oriented parallel to the substrate (face-on). This difference in molecular packing is attributed to a possible intramolecular mixing of 5-carboxypentyl and pentyl chains that gives a better match between the footprints of the macrocycle, acid groups, and alkyl groups. The longer dodecyl chains are too large for filling the space between 5-carboxypentyl chains (mixing) and too small for filling the footprint of a TAP macrocycle. We demonstrate that by judicious tailoring of the chain length and subphase conditions, a desirable homogeneous film of face-on oriented macrocycles can be formed.

Antimicrobial Carboxymethyl Cellulose-Bacterial Cellulose Composites Loaded with Green Synthesized ZnO and Ag Nanoparticles for Food Packaging.

Bacterial cellulose (BC) has earned a well-defined place among biopolymers due to its unique physicochemical properties. Unfortunately, native BC lacks antimicrobial and antioxidant properties. To address this limitation, many BC-based nanocomposites with antimicrobial properties have been developed, primarily for applications in the biomedical field, but also for use in food packaging. Many nanoparticles can be incorporated into BC membranes, often in combination with other bioactive molecules. Among the available methods for nanoparticle synthesis, green synthesis has emerged as promising, as it avoids the use of hazardous chemicals. The aim of this paper is to develop and characterize antimicrobial composite materials fabricated using carboxymethyl cellulose (CMC) and bacterial cellulose fibrils loaded with zinc oxide and silver nanoparticles (NPs) obtained using turmeric extract by green synthesis. NP-loaded CMC-BC composites were characterized using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, Grazing incidence X-ray diffraction (GI-XRD), and thermal analysis (TA). The antibacterial potential of such composites was tested against Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), and Candida albicans (C. albicans).

Intermediate-Controlled Synthesis of Quasi-2D (PEA)2MA4Pb5I16 in the 20-30% Relative Humidity Glovebox Environment for Fabricating Perovskite Solar Cells with 1 Month Durability in the Air.

Herein, quasi-two-dimensional (Q-2D) (PEA)2MA4Pb5I16 (prepared by a two-step process) and hole transport layer of a solar cell were fabricated in a high relative humidity (25 ± 5%) environment. The PSC behavior of most Q-2D perovskites is worse than that of three-dimensional perovskites owing to the horizontal alignment of the innate characteristic organic plates on the substrate. Using hybrid immersion solvents (HISs), we have improved vertical alignment in an appropriate ratio to enhance the efficiency of charge transfer and the high coverage of the first priming layer (first step). The grazing incidence X-ray diffraction pattern of the optimized structures revealed a preferential orientation for the vertical alignment of (111), which improved the charge transfer in PSCs and micrometer-level grain size growth. The second step was processed in a high-humidity environment (50 ± 5%) (methylammonium iodide solution embedded), and Q-2D (PEA)2MA4Pb5I16 demonstrated distinct grain boundaries. The power conversion efficiency (PCE, 13.09%) of the champion device of the first priming layer prepared using the HIS system increased by >55% compared to the single-immersion solvent (8.3%). The PCE of the ion-modified ETL PSCs was 16.02% (CsF-3) and 14.58% (CsCl-3) and demonstrated 22 and 11% improvement, respectively. The ion-modified electron transport layer (ETL) was deposited in the air, which reduced the power consumption of preparing perovskite solar cells (PSCs). Finally, all Q-2D PSCs were stored in the air, and three PSCs (DMF/DMSO, CsF-3, and CsCl-3) using HIS exhibited long-term stability for 1 month maintaining 80-88% of PCE, demonstrating the importance of the HIS system to improve the first step of growth orientation, which enhances the stability and photovoltaic properties of PSCs.

Probing the Electrode-Electrolyte Dynamics of Metal Electrocatalysts for Oxygen Reduction with Multimodal X-Ray Scattering and Mass Spectrometry Techniques

The electric double layer is a highly dynamic and complex region with a consequential effect on electrocatalyst performance. The plethora of processes in this near-electrode microenvironment are a function of the catalyst material, electrolyte composition, potential range, and temperature among others. For the electrochemical oxygen reduction reaction (ORR) in acidic media, perchloric acid is commonly used as the electrolyte in fundamental studies due to the perchlorate anion’s minimal interaction with most metal catalysts compared to other anions. However, such anions classically thought to be spectator species influence several electrode processes including, but not limited to, roughening, competitive adsorption, interfacial electric field attenuation, and water structure modulation. Some of these phenomena have been shown to occur over millisecond timescales while others occur over tens of minutes, and with dependence on the ionic species in solution. Moreover, industrial devices operate with ionomer materials on the catalyst such as Nafion that contain sulfonate groups which are chemically dissimilar to perchlorate anions. Given this discrepancy between how catalysts are evaluated in fundamental studies and how they are practically applied, there is motivation to understand the effect of anions in acidic environments during catalyst operation. This line of investigation will help bridge the fundamental-to-device gap and uncover details about catalyst dynamics as a function of microenvironment.In this work, we resolve key electrolyte-dependent and potential-dependent electrode processes contributing to changes in the catalyst surface structure by utilizing x-ray scattering techniques and on-line mass spectrometry. Taking palladium (Pd) and silver (Ag) thin films as a model ORR system based on their high material stability in acid, we have previously shown the effects of anions on ORR onset potential and selectivity in a variety of pH 1 acids. For the ORR onset potential, the elucidated trend for Ag was HClO4 > HNO3 > H2SO4 > HCl ≫ HBr, whereas for Pd, it was HClO4 ∼ H2SO4 > HNO3 > HCl > HBr. Since the previous study, we have constructed an electrochemical flow cell coupled to an on-line inductively coupled plasma-mass spectrometry (ICP-MS) that can quantify metal dissolution with part-per-billion sensitivity in each of these five electrolytes. In these five oxygen-saturated electrolytes, Pd is tested in the range of 0 to 0.9 V vs Reversible Hydrogen Electrode (RHE) and elevated rates of dissolution are measured at potentials above 0.55 V vs RHE for all electrolytes. Notably, Pd in HNO3 and H2SO4 is more stable than in HClO4 around the onset potential region which breaks the trend of onset potential. For Ag in the same electrolytes in potentials between 0.5 V and -0.5 V vs RHE, the evolution of nanoparticles from the surface is detected along with ionic dissolution near the ORR onset potential. Ag also experiences unexpectedly high dissolution in HNO3 possibly due to competition from electrochemical nitrate reduction that may destabilize the surface. These findings from ICP-MS contribute to greater understanding of electrode instability but do not reveal surface and double layer structure changes.To investigate the surface structure specifically, a combination of synchrotron grazing incidence x-ray diffraction (GI-XRD) and x-ray reflectivity (XRR) are employed on Ag and Pd thin films with the same electrolytes. GI-XRD reveals the near-surface crystal structure and demonstrated slight electrolyte-dependent and potential-dependent shifts in diffraction peaks, indicating that surface strain can be affected by anions in the double layer. On a two-dimensional detector, non-specular diffraction patterns also enable the determination of preferential grain orientation during catalysis as a function of electrolyte. Furthermore, XRR data clearly indicates the transient roughening of the metal surface during catalysis as evidenced by changes in the amplitude and spacing of Kiessig fringes. Fitting these XRR datasets has previously been shown to successfully elucidate anion distributions in the first few nanometers away from the electrode surface, key information for understanding how anions behave as a function of potential. With this information about dynamic surfaces in various acidic environments under operating conditions, we develop hypotheses on the relation of the near-surface anion distribution, anion physisorption, and anion chemisorption to interfacial processes. Alongside other insights from ICP-MS, XRR, and GI-XRD datasets, an even clearer picture of dynamic electrode processes emerges with regard to the effect of anions and potential. This experimental framework enhances present understanding of the double layer region and its crucial role in processes that lead to both electrode dissolution and reorganization. Understanding the double layer could enable higher efficiency for key electrochemical devices and speed up the adoption of these technologies towards a more sustainable energy future.

A Comprehensive Study of Ferroelectric Properties of Fluorite-Structured Hf1-XZrxO2 Thin Films Grown on Mo Electrode with Various Thicknesses and Compositions

Since ferroelectricity in Si-doped HfO2 was first reported in 2011,[1] HfO2-based thin films have attracted significant attention as an emerging material for ferroelectric devices due to their advantages such as scalability and compatibility with Complementary Metal-Oxide-Semiconductor (CMOS) processes. Generally, TiN has been used as electrode material in semiconductor processes. However, other electrode materials such as W and Mo have attracted increasing interest for HfO2-based ferroelectric thin films due to their higher remanent polarization (Pr) than the TiN electrode.[2 ,3 ] Recently, it has been reported that Mo electrodes can be easily oxidized even at low temperatures such as atomic layer deposition (ALD) processes, and the formed MoOx layer can sufficiently act as the oxygen supplier, resulting in the larger orthorhombic phase fraction and higher remanent polarization compared with TiN electrodes.[3] Nevertheless, the effect of the film thickness and composition on the ferroelectric properties of HZO thin films grown on Mo electrodes is yet to be elucidated. Therefore, in this study, the electrical, physical, and chemical properties of HZO films with various thicknesses (6 – 11 nm) and Zr/(Hf+Zr) ratios (0.5 – 0.7) are examined.In the case of the HZO films grown on the TiN electrode, when the film thickness decreases or the Zr/(Hf+Zr) ratio increases, the switchable polarization (2Pr) decreases with a distortion of polarization-electric field (P-E) curves owing to the increased fraction of the antiferroelectric tetragonal phase. However, 2Pr as high as 57.5 µC/cm2 on the Mo electrode could be achieved even in the 7.6 nm-thick Hf0.4Zr0. 6O2 thin film with a little distortion of the P-E curve. The highest 2Pr of 68.3 µC/cm2 was observed in the 10.9 nm thick Hf0.4Zr0. 6O2 film, which is 31.3 % higher than the highest 2Pr (52.0 µC/cm2) of the HZO thin film on TiN reported so far.[ 4] Additionally, in the (Grazing Incidence X-ray Diffraction) results of all samples, it can be observed that the m-phase which deteriorates the Pr values is sufficiently suppressed. These results are consistent with the tendency of previously reported results.[3] Therefore, It is believed that the Mo electrode would induce a higher orthorhombic phase fraction in HZO thin films compared to the TiN electrode resulting in higher 2Pr values. This enables ferroelectricity to be achievable within a wider range of film thicknesses and Zr/(Hf+Zr) ratios.

High Throughput Solution Combustion Generated Nickel Oxide Films As a Hole Transport Layer for Perovskite Photovoltaics

Nickel oxide remains a prominent hole transport layer (HTL) for use in inverted perovskite photovoltaic devices owing to its high optical transmission as a thin film, hole mobility, and chemical tunability. Numerous approaches have been posited for forming high quality nickel oxide thin films with solution combustion synthesis (SCS) as one of the most promising to yield high quality oxide thin films at high throughputs. However, the resulting characterization of the nickel oxide generated can be challenging owing to nickel oxide’s surface reactivity under ambient conditions and its instability against common laboratory techniques such as X-ray photoelectron spectroscopy (XPS) with argon depth sputtering.Here, we present a multi-modal synchrotron radiation characterizations of nickel oxide thin films generated via solution combustion synthesis with a curing duration of 1 min at 300 ºC for perovskite solar cells. We explore the role of varying the ligand structure and fuel/oxidant ratio of the nickel oxide precursor and assess the resulting properties of the nickel atoms using extended X-ray absorption fine structure, ex situ X-ray absorption near edge spectroscopy, and grazing-incidence X-ray diffraction along with lab-scale XPS. We have also performed some of the first in situ analysis of the combustion process using synchrotron radiation with 5 second time resolution. As a result, we can provide unprecedented sensitivity to correlate between the chemical state of Ni in the film bulk and surface to device performance and stability.

(Invited) Low-Temperature Processing of Mixed Conducting Oxides: Control of Defects, Transport, and Reactions Away from Equilibrium

Low-to-intermediate temperature processing and use of mixed conducting oxides targets the following potential benefits: ultra-fine nanostructuring with avoidance of coarsening, control of surface chemistry, lower energy consumption, integration with thermally sensitive components, and slower degradation vs. conventional high temperature synthesis and use. In this lower temperature regime, we have pursued two routes for non-equilibrium control of defect chemistry and therefore properties of mixed ionic/electronic conductors (MIECs) in the ferrite perovskite family: crystallization and illumination.Room-temperature growth followed by mild anneals to induce crystallization has proven to yield superior oxygen surface exchange kinetics, attributed to development of facile charge transfer and pristine surface chemistry in our prior work. The close link between crystallinity and oxygen stoichiometry appears to play an important role in the structural evolution and electrical response. However the effect of evolving crystallinity on the ionic conductivity has not been studied in-depth. Therefore we recently pursued an approach combining in-situ synchrotron grazing-incidence X-ray diffraction with ac and dc electrical methods on thin-film blocking electrode cells to evaluate evolution of transference numbers during crystallization. In certain ferrite films we observe a ~2 orders-of-magnitude increase in ionic conductivity during crystallization, while the electronic conductivity increases much more. Through the process, we demonstrate that it is possible to turn a predominantly ionic conductor into a predominantly electronic conductor - and to access almost any ionic transference number in between - simply by controlling the degree of crystallinity. [1]Oxygen stoichiometry can alternatively be controlled at low-to-intermediate temperatures through application of low fluence above-gap illumination. We have shown in certain non-dilute ferrite films that UV light causes oxygen to enter the films from the gas phase with kinetics limited by the oxygen surface-exchange reaction, which is largely unchanged by the presence of excited carriers. We explain the response through simulations of excited state defect equilibria and transient absorption spectroscopy measurements. [2]Together these processing strategies indicate that low-temperature control of oxygen stoichiometry is feasible in mixed conductors, enabling wide tailoring of properties and potential for use in low-to-intermediate temperature solid-state ionic devices.[1] H.B. Buckner, J. Simpson-Gomez, A. Bonkowski, K. Rubartsch, H. Zhou, R.A. De Souza, N.H. Perry (in review)[2] E. Skiba, H.B. Buckner, G. McKnight, C. Lee, R. Wallick, R. van der Veen, E. Ertekin, N.H. Perry (in review)We gratefully acknowledge funding from the US Department of Energy, Basic Energy Sciences, under DOE Early Career grant DE-SC-0018963 and from the US National Science Foundation, through the University of Illinois at Urbana-Champaign Materials Research Science and Engineering Center DMR-2309037.