X-ray Reflectivity Research Articles

A Deep Dive into Black Hole Spin Measurement Using Continuum Fitting

This paper explores the continuum fitting method for estimating the spin of stellar-mass black holes in X-ray binaries. By fitting the thermal emission created by the accretion disk to theoretical models, this method provides a precise and accessible way to estimate the spin of black holes. Key developments, including the use of KERRBB and SIMPL models, improve accuracy by accounting for disk structure and Compton scattering effects. This paper reviews recent applications of this technique and compare it to the X-ray reflection method, noting that continuum fitting is highly accurate for black holes with strong thermal emission. This paper also gives the new spin measurement of some black hole, especially the Cygnus X-1, that has the spin a_*>0.976, but also use it to prove that the continuum fitting method which relies heavily on knowing the black holes three parameters. Finally, this paper discusses both the advantages and challenges of this method, with an expectation of future improvements in modeling and observations that can expand its use.

Magnetic-proximity-induced anomalous Hall effect at the EuO/Sb2Te3 interface

Time-reversal symmetry breaking of a topological insulator phase generates zero-field edge modes which are the hallmark of the quantum anomalous Hall effect (QAHE) and of possible value for dissipation-free switching or non-reciprocal microwave devices. But present material systems exhibiting the QAHE, such as magnetically doped bismuth telluride and twisted bilayer graphene, are intrinsically unstable, limiting their scalability. A pristine magnetic oxide at the surface of a TI would leave the TI structure intact and stabilize the TI surface, but epitaxy of an oxide on the lower-melting-point chalcogenide presents a particular challenge. Here we utilize pulsed laser deposition to grow (111)-oriented EuO on vacuum cleaved and annealed Sb2Te3(0001) surfaces. Under suitable growth conditions, we obtain a pristine interface and surface, as evidenced by x-ray reflectivity and scanning tunneling microscopy, respectively. Despite bulk transport in the thick (2 mm) Sb2Te3layers, devices prepared for transport studies show a strong AHE, the necessary precursor to the QAHE. Our demonstration of EuO-Sb2Te3epitaxy presents a scalable thin film approach to realize QAHE devices with radically improved chemical stability as compared to competing approaches.

Hydrodynamic slip in nanoconfined flows: a review of experimental, computational, and theoretical progress.

Nanofluidics has made significant impacts and advancements in various fields, including ultrafiltration, water desalination, biomedical applications, and energy conversion. These advancements are driven by the distinct behavior of fluids at the nanoscale, where the solid-fluid interaction characteristic lengthscale is in the same order of magnitude as the flow conduits. A key challenge in nanofluidics is understanding hydrodynamic slip, a phenomenon in which fluids flow past solid boundaries with a non-zero surface velocity, deviating from the classical no-slip boundary condition. This review consolidates experimental, computational, and theoretical efforts to elucidate the mechanisms behind hydrodynamic slip in nanoconfined flows. Key experimental methods, such as the surface force apparatus, atomic force microscopy, and micro-particle image velocimetry are evaluated alongside emerging techniques like suspended microchannel resonators, dynamic quartz crystal microbalance, and hybrid graphene/silica nanochannels, which have advanced hydrodynamic slip characterization at the nanoscale. In addition to direct slip measurement techniques, methods like sum frequency generation spectroscopy, X-ray reflectometry, and ellipsometry are discussed for their roles in probing solid-liquid interfacial interactions, shedding light on the origins of hydrodynamic slip. The review also highlights the contributions of molecular dynamics simulations, including both non-equilibrium (NEMD) and equilibrium (EMD) approaches, in modeling interfacial phenomena and slip behavior. Additionally, it explores the influence of factors such as surface wettability, shear rate, and confinement on slip, emphasizing the interaction between liquid structuring and solid-liquid interactions. Advancements made so far have uncovered more complexities in nanoconfined flows which have not been considered in the past, inviting more investigation to fully understand and control fluid behavior at the molecular level.

Lanthanide binding peptide surfactants at air–aqueous interfaces for interfacial separation of rare earth elements

Rare earth elements (REEs) are critical materials to modern technologies. They are obtained by selective separation from mining feedstocks consisting of mixtures of their trivalent cation. We are developing an all-aqueous, bioinspired, interfacial separation using peptides as amphiphilic molecular extractants. Lanthanide binding tags (LBTs) are amphiphilic peptide sequences based on the EF-hand metal binding loops of calcium-binding proteins which complex selectively REEs. We study LBTs optimized for coordination to Tb3+ using luminescence spectroscopy, surface tensiometry, X-ray reflectivity, and X-ray fluorescence near total reflection, and find that these LBTs capture Tb3+ in bulk and adsorb the complex to the interface. Molecular dynamics show that the binding pocket remains intact upon adsorption. We find that, if the net negative charge on the peptide results in a negatively charged complex, excess cations are recruited to the interface by nonselective Coulombic interactions that compromise selective REE capture. If, however, the net negative charge on the peptide is -3, resulting in a neutral complex, a 1:1 surface ratio of cation to peptide is achieved. Surface adsorption of the neutral peptide complexes from an equimolar mixture of Tb3+ and La3+ demonstrates a switchable platform dictated by bulk and interfacial effects. The adsorption layer becomes enriched in the favored Tb3+ when the bulk peptide is saturated, but selective to La3+ for undersaturation due to a higher surface activity of the La3+ complex.

Annealing Process-Induced Microstructural Variation in NiV/B4C Multilayers

The annealing process is one of the most common methods used to study the thermal stability of multilayers. To study the effect of the annealing process on the microstructural variation in NiV/B4C multilayers, different annealing experiments were performed on NiV/B4C multilayers with a d-spacing of 8 nm. This work provides a foundation for the fabrication of non-periodic NiV/B4C multilayers. The NiV/B4C multilayers were investigated by grazing-incidence X-ray reflectometry (GIXR), X-ray diffuse scattering (XRS), atomic force microscopy (AFM), X-ray diffraction (XRD), grazing-incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). The temperature-dependent experiments showed that annealing at 70–290 °C slightly increased the period thickness and interface width. Annealing at higher temperatures resulted in significant structural changes and thickness ratio (Г = dNiV/d) changes from 0.4 to 1/3 at 340 °C. The time-dependent results showed that the microstructural variations primarily occurred after 60 min. The XRD, XRS, GISAXS and TEM were further used to study microstructural changes. It was found that the NiV/B4C multilayers exhibited a microcrystal structure after annealing, and that enhanced crystallinity and an increase in interface roughness were the main reasons for the microstructural changes.

Low temperature growth of single-phase and preferentially oriented ɛ-Ga2O3 films on sapphire substrates via atomic layer deposition

As an ultrawide-bandgap semiconductor, Ga2O3 has promising applications in electronics and optoelectronics. ɛ-Ga2O3 has attracted much attention as it performs the polarization effect, whereas single-phase and preferentially oriented ɛ-Ga2O3 films have not been prepared by the atomic layer deposition (ALD) method at low temperatures. In this paper, Ga2O3 films are prepared on sapphire substrates through the ALD method at different substrate temperatures and using different O sources. The x-ray reflectivity measured thicknesses and x-ray photoelectron spectroscopy spectra both demonstrate that the Ga source of triethylgallium cannot reacts continuously with the O source of H2O layer-by-layer. The growth rates of Ga2O3 films using O3 or PE-O2 as the O source range from 0.342 to 0.448 Å/cycle. X-ray diffraction (XRD) results indicate that the as-grown Ga2O3 films at 250 °C are amorphous, no matter using O3 or PE-O2 as the O source. They both crystallize into the single-phase and (−201) preferentially oriented β-Ga2O3 films after a high-temperature annealing of 900 °C. When the growth temperature rises to 350 °C, single-phase and (0002) preferentially oriented ɛ-Ga2O3 films occur if using PE-O2 as the O source. The full width at half maximum for the (0004) plane of ɛ-Ga2O3 from the XRD rocking curve is 0.937° while the atomic force microscopy measured surface roughness RMS is 1.24 nm. The crystal structure of the as-grown ɛ-Ga2O3 films can be maintained at an annealing temperature of 700 °C and they transform into polycrystalline β-Ga2O3 films at 900 °C. The results are beneficial for the applications of Ga2O3-based microelectronic devices.

AN APPROACH FOR THICKNESS ESTIMATION OF ANODIZED TITANIUM OXIDE USING DIGITAL CAMERA

This paper presents a novel approach for estimating the thickness of anodized titanium oxide layers using digital imaging and thin film interference principles. Traditional methods for thin film thickness measurement, such as ellipsometry and X-ray reflectivity, offer high precision but can be costly and complex. In contrast, the proposed technique leverages the correlation between oxide layer thickness and the interference colors observed in anodized titanium surfaces. Using a digital camera, images of the anodized samples are captured under controlled lighting conditions, followed by color calibration and analysis. Specialized software then interprets the interference patterns to estimate oxide thickness. This method provides a non-destructive, cost-effective, and accessible alternative for thickness measurement, with potential applications in quality control and material characterization across industries such as aerospace and biomedical devices.

Properties of ultrathin BSA films interacted by monovalent ions

Abstract The current study explores the properties of pure alongside monovalent Na+ ions interacted ultrathin films of bovine serum albumin (BSA) immobilized on hydrophilic and hydrophobic solid silicon (Si) surfaces. Such ultrathin BSA films were prepared by dip coating method, and then their structural, morphological, and hydrophobic properties were obtained using X-ray reflectivity (XRR), atomic force microscopy (AFM), and water contact angle (WCA) analysis, respectively. Pure BSA solution helps to deposit pure BSA ultrathin monolayer films of BSA molecules in their native globular shape in tilted alignment on hydrophilic Si and an almost identical tilted monomolecular layer of molecules of BSA is deposited on hydrophobic Si also but tilting is higher implying the deposition of thicker and denser BSA ultrathin layer. Monovalent ions-interacted BSA solution helps to deposit an ultrathin bilayer film on hydrophilic Si, which consists of a side-on oriented bottom layer and a less tilted top layer of BSA molecules, while on hydrophobic Si, an ultrathin bilayer of BSA molecules consisting of tilted bottom and a top layer of BSA molecules was immobilized. Thus, higher immobilization of molecules of BSA has occurred on hydrophilic Si and also on hydrophobic Si due to the incorporation of monovalent ions in the BSA solution. The globular form of the BSA molecules is displayed by pure as well as ions interacted films of BSA on both surfaces. A sessile drop WCA study is employed to explore its hydrophobic properties. All ultrathin BSA films showed WCAs ≥ 60° and higher WCA implying higher hydrophobicity is recorded for monovalent ions-interacted ultrathin BSA films compared to pure BSA films. The incorporation of monovalent ions in the BSA solution facilitates higher immobilization of BSA molecules to help to deposit thicker ultrathin film and, at the same time, helps to expose their inner hydrophobic region towards the outer free surface, contributing to the increment in hydrophobicity.

Modeling Multiple X-Ray Reflection in Super-Eddington Winds

It has been recently discovered that a few super-Eddington sources undergoing black hole super-Eddington accretion exhibit X-ray reflection signatures. In such new systems, one expects the coronal X-ray emissions to be mainly reflected by optically thick super-Eddington winds instead of thin disks. In this paper, we conduct a series of general-relativistic ray-tracing and Monte Carlo radiative transfer simulations to model the X-ray reflection signatures, especially the characteristic Fe Kα line, produced from super-Eddington accretion flows around nonspinning black holes. In particular, we allow the photons emitted by a lamppost corona to be reflected multiple times in a cone-like funnel surrounded by fast winds. We find that the Fe Kα line profile most sensitively depends on the wind kinematics, while its exact shape also depends on the funnel open angle and corona height. Furthermore, very interestingly, we find that the Fe Kα line can have a prominent double-peak profile in certain parameter spaces, even with a face-on orientation. Moreover, we compare the Fe Kα line profiles produced from super-Eddington and thin disks and show that such lines can provide important insights into the understanding of black hole systems undergoing super-Eddington accretion.

HfO2/Al2O3 Multilayer on Parabolic Cylinder Substrate to Monochromatize and Collimate Divergent X-Ray Beam

A monochromatic parallel X-ray beam is essential for some X-ray applications and a multilayer on a parabolic cylinder substrate is a good choice to obtain it. In this work, an HfO2/Al2O3 multilayer with a period of 3.80 nm and a bilayer number of 60 is grown on a smooth, flat Si substrate via atomic layer deposition for a monochromatizing Cu kα 0.154 nm X-ray and the first-order peak of the X-ray reflectivity is about 45%. The multilayer-coated Si substrate is then glued on a pre-made stainless steel body with a designed parabolic cylinder profile to convert divergent X-rays from a laboratory X-ray source into a parallel beam. The surface profiles before and after gluing Si on the stainless steel body are almost the same and basically consistent with the designed one. The results show that a monochromatic parallel X-ray (0.154 nm) beam can be acquired by an HfO2/Al2O3 multilayer on a parabolic cylinder substrate and the divergence angle of the reflected beam is 0.67 mrad.

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.

Complementary Analysis on the SEI of Thin Film Siox Using X-Ray Photoemission Spectroscopy and X-Ray Reflectivity Methods

Silicon materials are expected as a high-capacity anode material for lithium-ion batteries. However, the life of the cell with such silicon materials tends to be short due to the pulverization of silicon associated with its large volume change, and electrolyte consumptions associated with the continuous growth of solid electrolyte interphase (SEI). Compared to pure silicon anodes, silicon oxide (SiOx) has been reported to mitigate such issues and extend the life of the battery1,2. In this study, we combined ex situ XPS (X-ray photoemission spectroscopy) and operando XRR (X-ray reflectivity) methods to investigate the phase transformations in the thin-film SiOx and the nature of SEI during the first lithiation/delithiation cycle to obtain the insights to improve the cycle performances.Using ex situ XPS, we examined the depth profile of the thin-film SiOx sample (Figure 1) at some representative potentials during the first cycle. This elucidated the evolution of chemical nature and thickness of the SEI, and simultaneously the irreversible phase changes in the SiOx. In recent years, the operando XRR method has been successfully applied to the pure silicon thin films3,4, revealing the nature (like thickness and electron density) of top and bottom SEI layers in early cycles. In this study, XRR was applied to thin-film SiOx for the first time. The insight from XPS and that from XRR were integrated for a comprehensive understanding on the evolution of the SEI layer and the SiOx electrode. A systematic comparison was made using the electrolytes with FEC and without FEC to better understand the importance of FEC. It was found out that the SEIs in both systems commonly show breathing behaviors, but the thickness of the SEI is almost always smaller in the FEC containing system. These findings can be a foundation for the high-performance batteries.1. Chen, T.; Wu, J.; Zhang, Q.; Su, X. Recent Advancement of SiOx Based Anodes for Lithium-Ion Batteries. J Power Sources 2017, 363, 126–144.2. Hsu, C.-H.; Chen, H.-Y.; Tsai, C.-J. Stoichiometry Dependence of Electrochemical Behavior of Silicon Oxide Thin Film for Lithium Ion Batteries. J Power Sources 2019, 438, 226943.3. Cao, C.; Steinrück, H.-G.; Shyam, B.; Stone, K. H.; Toney, M. F. In Situ Study of Silicon Electrode Lithiation with X-Ray Reflectivity. Nano Lett 2016, 16 (12), 7394–7401.4. Cao, C.; Steinrück, H.; Shyam, B.; Toney, M. F. The Atomic Scale Electrochemical Lithiation and Delithiation Process of Silicon. Adv Mater Interfaces 2017, 4 (22), 1700771. Figure 1

Niobium Interlayer Coating: Is it a Practical Approach to Tune the Protective Pt Loading in PEM Water Electrolyzers?

The surge in energy demand, along with global warming emissions from natural energy sources, has accelerated the transition towards renewable energies at an unprecedented rate. Among the array of potential candidates, green hydrogen stands out as a particularly promising alternative. In this regard, proton exchange membrane water electrolyzers (PEMWE) have gained widespread acceptance for green hydrogen generation due to their high efficiency and low operating temperatures. However, the relatively high cost of PEMWE components like catalysts, porous transport layer (PTL) and bipolar plates remains a challenge. For instance, commercial PTLs, comprising over 20% of the total PEM stack, often incorporate precious metal coatings to prevent passivation. In this study, we aimed to address the cost issue by replacing precious metal with non-precious metals. Niobium is known for its corrosion resistivity within acidic electrolytes [1]. Here, niobium thin films were deposited onto commercial titanium felt PTLs using pulsed laser deposition (PLD), a technique that allows precise control over film thickness and composition. Corrosion tests were conducted using an electrochemical potentiostat, with end-of-life tests employed for comparison. Results showed improvements in the performance of niobium-supported titanium felts compared to uncoated felts, indicating promise for cost optimization in PEM stacks.To deposit niobium thin films, a pulsed KrF laser with a wavelength of 248 nm was employed. Prior to each deposition, the chamber was evacuated to 5 × 10−5 mbar, followed by the introduction of specific gases such as N2 or He into the chamber during deposition. The choice of background gas is presumed to impact the composition of the niobium based thin films on PTL [2]. The corrosion resistivity of the produced niobium-coated titanium PTLs using two different gases were evaluated using a three electrodes cell. An ex-situ electrochemical setup was designed and 0.5 M H2SO4 electrolyte was used to simulate the electrolyzer media. The temperature was set at 70 °C. Chronopotentiometry was employed to assess the end-of-life characteristics of the samples over a period of at least 10 hours.The thickness of each sample was controlled by X-ray reflectivity (XRR) accompanied by the cross-section scanning electron microscopy (SEM). Corrosion tests were performed on Nb-based thin films with a thickness of 120 nm. Figure 1(a) demonstrate the chronopotentiometry results of niobium-coated samples using nitrogen and helium in compared to bare PTL. In these tests, a constant current density of 400 mA/cm² was applied for an extended duration, allowing the potential to change within the 0-10 V range. These graphs show that with the same current density, the electrochemical potential was found to be lower in niobium-coated Ti PTLs compared to the uncoated counterpart, indicative of enhanced surface conductivity post-coating. It is observed that the potential of uncoated titanium PTL rises after 3 hours of this test. In contrast, both niobium-coated films demonstrated prolonged test duration, with no cessation even after 10 hours, underscoring the advantage of niobium-coated films over bare titanium PTLs. Intriguingly, niobium films subjected to nitrogen gas exhibited a lower potential than counterparts grown in helium, suggesting the potential presence of nitride compounds replacing oxides within the thin film structure of niobium. Given that the electrical conductivity of NbN is higher than that of the NbO structure [3], it can be inferred that the presence of nitrogen may enhance both the electrical conductivity and corrosion resistance of the PTL. Figure 1 (b)-(d) reveals the SEM images of these samples after three hours of the corrosion tests. These results confirm that the surface of the niobium thin film grown in nitrogen exhibited less peeling compared to other niobium-coated and uncoated titanium PTLs. Hence, it is inferred that niobium thin films grown in a nitrogen-rich environment exhibit noteworthy potential for prolonged stability when contrasted with both the uncoated PTL and the niobium-coated PTL developed under nitrogen-deficient conditions.Fig. 1 (a) Chronopotentiometry curve obtained for different coated and uncoated titanium PTLs. The SEM images of the (b) Nb:He, (c) Nb: N2, and (d) uncoated titanium PTLs after three hours of corrosionWe would like to acknowledge the support of the Natural Sciences and Engineering Research Council of Canada, Canada Research Chair and PRIMA Québec and Niobay team for their constant support.

Comprehensive Analysis for PDA Effect on SiO2/SiNx/Si Stacked Structure Using Multiple Technique

Silicon nitride (SiNx) thin film in multi-stacked structure plays an important role as a charge trapping layer in flash memory device such as Silicon-Oxide-Nitride-Oxide-Silicon (SOMOS) and Metal-Oxide-Nitride-Oxide-Semiconductor (MONOS) memory [1, 2]. Thus, the performances of these memory devices strongly depend on the qualities of dielectric films which are controlled by deposition and annealing condition. Hence, the systematic evaluation of the quality of dielectric film in multi-stacked layers has been required to understand the chemical composition within each layer.In this study, comprehensive analysis for the annealing effect on SiO2/SiNx/Si stacked structure can be performed by multiple technique.The chemical components of SiNx films in SiO2/SiNx /Si-sub. stacked structures were evaluated by photoelectron spectroscopy (PES), X-ray reflectivity (XRR), Fourier transform–infrared (FT-IR) and secondary ion mass spectrometer (SIMS) analyses. SiNx (5 nm) and SiO2 (5 nm) were sequentially deposited on Si substrate by plasma enhanced atomic layer deposition (PEALD). Then, SiO2/SiNx /Si-sub. stacked structures were fabricated. The post deposition annealing (PDA) was conducted at 1000 ºC under N2 for 90 seconds. The chemical compositions of stacked layers were analyzed by PES using monochromated Cr-Kα (5.4 keV) and Al-Kα (1.5 keV) as the excitation source.To understand the chemical compositions of the stacked layers, PES with Cr-Kα was performed. In Si 1s core-level spectra, four components assigned to Si0, SiNx (Si-rich), SiNx and SiO2 were observed. SiNx (Si-rich) represents excess silicon in SiNx matrix [3]. The components of SiNx (Si-rich) and SiNx decreased after annealing. Furthermore, the component assigned to SiON increased after 1000 ºC annealing. These results indicate that the SiNx layer was oxidized by PDA treatment. It plausibly originates from the SiO2/ SiNx interface reaction and oxygen diffusion into SiNx layer.Next, silanol group (Si-OH) within SiO2 layer that is key factor of the electric property was analyzed by using chemical modification-PES with Al-Kα. In conventional PES, the peak derived from Si-OH can not be separated from the main peak of O-Si derived from SiO2 in O1s spectra. In chemical modification PES, Si-OH is labeled by the reagent contained in fluorine as the sample treatment.Thus, quantitative analysis of Si-OH is available by analyzing the concentration of fluorine. In this result, the amount of Si-OH within SiO2 layer was reduced by PDA treatment. This result is in good agreement with FT-IR and SIMS results.In summary, complementary analysis to help elucidate the properties of dielectric film is indispensable for the optimization of fabrication process and the realization of high-performance memory devices.[1]M. L. French et al., IEEE Trans. Compon. Packag. Technol., 17 390-397 (1994).[2]S. Fujii et al., Jpn. J. Appl. Phys., 51 124302 (2012).[3]S. V. Nguyen et al., J. Electrochem. Soc., 134, 2324-2329 (1987).

Defect-Free SiGe/Si Multistacks for Next-Generation CFET Architectures

The complementary FET (CFET) is the leading architecture choice for upcoming logic applications. Leveraging a stacked pMOS and nMOS design, this architecture is expected to enhance device performance with a reduced footprint [1,2]. The fabrication of the channels in these devices requires the deposition of SiGe/Si multistacks. The difference in etching rate of Si and SiGe is exploited, allowing for the selective removal of the SiGe layers and the resulting formation of free-standing Si channels.In this contribution, we present fully strained pseudomorphic SiGe/Si epitaxial multistacks for the use as channel regions in CFET devices. All layers were grown in a 300 mm ASM reduced-pressure chemical vapor deposition (RPCVD) reactor on Si(001) substrates.A targeted multistack structure for 1x1 nanosheet channel is displayed in Fig. 1(a). Two types of SiGe layers are present in the stack, having Ge concentration of 22% and 38%, respectively. Fig. 1(b) shows the X-ray diffraction (XRD) Omega-2Theta scan acquired for the deposited stack at the Si(004) Bragg reflection. The experimental spectrum is accurately simulated using a model closely resembling the nominal structure, thereby confirming that the thicknesses and germanium concentrations of the stack’s constituent layers are well within the targeted specifications. The X-ray reflectivity (XRR) spectrum acquired on the same sample and shown in Fig. 1(c) exhibits a high signal-to-noise ratio even at high incidence angles, suggesting a low surface roughness of the sample. Fig. 1(d) displays the asymmetric reciprocal space map (RSM) acquired around the Si(113) reflection. The stack's diffraction peaks are very narrow and horizontally aligned, indicating the absence of strain-relaxation in the sample. The within-wafer non-uniformity (WWNU) of thickness and Ge concentration was first minimized for single SiGe/Si bilayers. The optimized growth parameters were then successfully applied to the growth of multi-layered structures. Fig.2 depicts the haze map measured via deep-UV (DUV) laser scattering for the same multistack considering a 3 mm wafer edge-exclusion. The measured intensity ranges between 0.59 and 0.69 ppm, indicating a highly smooth surface morphology.AFM inspections, as shown in Fig. 3(a), confirm that the stack is fully strained, as evidenced by the absence of cross-hatch pattern in the examined areas with dimension 20x20 μm2. The RMS roughness (Rq) of the sample surface is found to be as low as 0.1 nm, which reduces to 0.07 nm on a 2x2 μm2 inspection area (Fig. 3(b)).The cross-sectional TEM analysis of a 3x3 nanosheet channel stack, as shown in Fig. 4(a), indicates that the layer thicknesses are highly consistent and in good agreement with the targeted nominal values. The energy-dispersive X-ray spectroscopy (EDS) elemental mapping of the same cross-section also reveals a close match between the measured Ge concentration and the expected value. Furthermore, the high-resolution HAADF-TEM image presented in Fig. 4(b) demonstrates the excellent crystalline quality of the epitaxial stack and indicates the presence of sharp compositional transitions between the layers.Finally, Fig. 5 displays the Omega-2Theta spectra measured for the first and last 1x1 nano-sheet channel stacks fabricated in a batch processing of 25 wafers. Notably, the two spectra exhibit perfect overlapping, with identical peak positions and intensities, showcasing ideal run-to-run repeatability of the process.In this work, we have demonstrated the fabrication of complex SiGe/Si multistacks that exhibit excellent agreement with the targeted specifications, are free of relaxation-defects and have extremely low surface haze values. These results highlight the effectiveness of our growth process in overcoming typical challenges associated with the development of advanced CFET devices.[1] P. Schuddinck et al., 2022 IEEE Symposium on VLSI, pp. 365-366.[2] E. Park et al., IEEE Transactions on VLSI Systems, 31(2), , 2022, pp.177-187. Figure 1

Advanced SiGe:B Raised Sources and Drains for p-type FD-SOI MOSFETs

We have evaluated the feasability of selectively growing (at 600°C-700°C, 20 Torr and with a SiH2Cl2 + GeH4 + B2H6 + HCl chemistry) SiGe:B Raised Sources and Drains on each side of PMOS FD-SOI devices with a vertical Ge concentration gradient. The reason was twofold : (i) inject meaningful amounts of uniaxial compressive strain and boost hole mobility thanks to really high Ge concentrations (50%) in layers on each side of the channel and (ii) benefit from SiGe:B 20% to 30% layers on top, that are easier to germano-salicide, for instance with Ni or NiPt. As the diborane flow increased, we had, whatever the Ge concentration (20%, 30% or 50%), (i) sub-linear SiGe:B growth rate increases (from +14% up to + 23%) and (ii) linear decreases of the “apparent” Ge concentration from X-Ray Diffraction (XRD), as shown in Figures 1a and 1b. They were due to (i) a catalysis of H/Cl desorption by B adatoms and (ii) compressive strain compensation by small size B atoms, respectively. The resulting substitutional B concentrations increased almost linearly with the B2H6 mass-flow. The slopes of those increases were steeper and B concentrations systematically higher for higher Ge contents, however (at most 2.2x1020 cm-3 for 50% of Ge), as illustrated in Figure 1c. We otherwise showed, for Si0.7Ge0.3:B layers, that the Ge atomic concentration was steady as the B2H6 mass-flow increased. Atomic, substitutional and ionized B concentrations (from Secondary Ions Mass Spectrometry, XRD and Hall effect measurements) were the same for the lowest diborane flow probed (e.g. 7x1019 cm-3). For a medium flow, atomic and substitutional B concentrations were equal (e.g. 1.4x1020 cm-3), while the ionized B concentration was ~80% of it. Discrepancies were the highest for the highest diborane flow probed, with substitutional and ionized B concentrations ~80% and ~60% the atomic B concentration of 2.3x1020 cm-3, then (Figure 1d). The specifics of SiGe:B Selective Epitaxial Growth (SEG) in sources and drains regions on each side of FD-SOI devices (Figure 2) were then described, such as (i) loading effects, because of the presence of dielectrics, resulting in significant growth rate increases (x1.5 - x1.7), together with slight Ge and B concentrations increases that might impact the layer quality on patterned wafers, (ii) facet formation, (iii) the importance of proper surface preparation prior to epitaxy and of tight SiN hard masks on top of poly-Si gates, (iv) the strain loss happening upon germano-salicidation and so on. Growing a thin Si(:B) cap on SiGe:B is another way of obtaining uniform and stable metallic contacts. This is why we have studied the capping, with pure Si, of SiGe 20% or 30% layers. As growth had to be conducted, for the SEG of Si with a chlorinated chemistry, at temperatures significantly higher than that of SiGe (750°C, typically, to be compared with 700°C for SiGe 20% and 650°C only for SiGe 30%), we have quantified the impact of using temperature ramping-ups with SiH2Cl2 + HCl flowing into the growing chamber. The purpose of such active ramps was to avoid elastic strain relaxation, e.g. the formation of SiGe surface undulations that would happen with temperature ramping-ups under H2 only. Superior quality 2D SiGe / Si stacks were then obtained, as shown by X-Ray Reflectivity and XRD. Energy Dispersive X-ray maps of such stacks enabled us to quantify loading effects on patterned wafers. SiGe growth rates in small, recessed windows were 1.5 times (SiGe 30%) – 1.8 times higher (SiGe 20%) than on bulk, blanket Si. Meanwhile, Ge concentrations were 2% to 3% higher. Finally, Si growth rates were lower than bulk, most probably because of the presence of thick buried oxide layers on those patterned wafers that impacted the effective surface temperature during growth. Figure 1

Structural Reorganizations and Nanodomain Emergence in Lipid Membranes Driven by Ionic Liquids.

Ionic liquids (ILs) have promising applications in pharmaceuticals and green chemistry, but their use is limited by toxicity concerns, mainly due to their interactions with cell membranes. This study examines the effects of imidazolium-based ILs on the microscopic structure and phase behavior of a model cell membrane composed of zwitterionic dipalmitoylphosphatidylcholine (DPPC) lipids. Small-angle neutron scattering and dynamic light scattering reveal that the shorter-chain IL, 1-hexyl-3-methylimidazolium bromide (HMIM[Br]), induces the aggregation of DPPC unilamellar vesicles. In contrast, this aggregation is absent with the longer alkyl chain IL, 1-decyl-3-methylimidazolium bromide (DMIM[Br]). Instead, DMIM[Br] incorporation leads to the formation of distinct IL-poor and IL-rich nanodomains within the DPPC membrane, as evidenced by X-ray reflectivity, differential scanning calorimetry, and molecular dynamics simulations. The less evident nanodomain formation with HMIM[Br] underscores the role of hydrophobic interactions between lipid alkyl tails and ILs. Our findings demonstrate that longer alkyl chains in ILs significantly enhance their propensity to form membrane nanodomains, which is closely linked to enhanced membrane permeability, as shown by dye leakage measurements. This heightened permeability likely underlies the greater cytotoxicity of longer-chain ILs. This crucial link between nanodomains and toxicity provides valuable insights for designing safer, more environmentally friendly ILs, and promoting their use in biomedical applications and sustainable industrial processes.

(Invited) sald: Versatility of the Deposition Process Combined with in-Situ Characterization Methods

We have proposed and demonstrated a novel thin film deposition technique by transferring the principles of atomic layer deposition (ALD), known with gaseous precursors, towards precursors dissolved in a liquid. 'Solution ALD'(sALD) shares the fundamental properties of standard ‘gas ALD’ (gALD), specially the self-limiting growth and the ability to coat conformally deep pores. It has been already shown that it is possible to transfer standard reactions from gALD to sALD such as oxides and sulfides deposition. However, sALD also offers novel opportunities such as overcoming the need for volatile and thermally robust precursors, offering the possibility to grow materials that cannot be obtained by gALD and using mild conditions which allow the growth on sensitive substrates. Recently we extended the understanding of the nucleation of selected materials grown by sALD such as Cu-BDC, MAPI, CuSCN, TiO2 and SnSx. The study of the nucleation process relies on, first the identification of the absorbed chemical species at the surface by in-situ infra-red spectroscopy, second the ability to determine the type of interaction of the precursor with the surface by ex-situ solid state nuclear magnetic resonance (NMR) and third the evolution of nuclei formation with in-situ x-ray reflectometry (XRR) and atomic force microscopy. We developed the necessary instrumentation to obtain measurement compatible in liquid environment for each in-situ method. Form IR we can identify the phase preferential phase that is obtained as well as the defects formation for extremely thin films and NMR shows the chemical bonding of precursors at an early stage. Additionally, the AFM and XRR investigations are needed to follow the evolution of the nuclei size and their distribution of a surface as well as the nuclei density of each half cycle.The extension of the knowledge on the reaction mechanism in sALD process appears to be crucial to design next reactions and to understand later on the properties of the layers obtained with sALD. Wu, D. Döhler, M. Barr, E Oks,M. Wolf, L. Santinacci and J. Bachmann, Nano Lett. 2015, 15, 6379 Fichtner, Y. Wu, J. Hitzenberger, T. Drewello and J. Bachmann, ECS J. Solid State Sci. Technol. 2017,6, N171 M. K. S. Barr, S. Nadiri, D.-H. Chen, P. G. Weidler, S. Bochmann, H. Baumgart, et al, .Chemistry of Materials 2022, 34, 9836-9843

Dynamically patterning x-ray beam by a femtosecond optical laser.

Modern science and technology have greatly benefitted from our ability to precisely manipulate light waves, in both their spatial and temporal degrees of freedom. In the x-ray region, however, spatial control has been virtually static mainly due to stringent requirements for realizing high-performance optical elements. The lack of dynamic spatial control of x-ray beam has prevented researchers from realizing more sophisticated use of the wave field, which has rapidly advanced in the optical region in the past decades. In this study, we propose a practical scheme to dynamically control local x-ray reflectivity of a perfect silicon crystal by a femtosecond optical laser and demonstrate a programmable spatial x-ray modulator. Our modulator aims for spatial manipulation of the x-ray amplitude and is shown to produce arbitrary grayscale patterns with spatial frequencies up to 25 per millimeter. The proposed modulation scheme opens up a platform to enable advanced x-ray sensing and imaging techniques that can fully harness the wave nature of x-rays.

An in Silico Investigation into Polyester Adsorption onto Alumina toward an Improved Understanding of Hydrogenolysis Catalysts.

Chemical recycling of end-of-life plastic wastes through hydrogenolysis is a promising pathway for achieving a circular plastics economy and reducing overall energy costs. Understanding molecular interactions at the inorganic-organic depolymerization interface is crucial for enhancing catalyst performance and overcoming challenges posed by mixed plastic waste streams. We investigated a fundamental step in the depolymerization process: physisorption of polymers onto the metal oxide support preceding diffusion to and reaction at the catalyst-support junction. Molecular dynamics simulations, augmented with well-tempered metadynamics, were conducted to explore the adsorption of polylactic acid (PLA) and polyethylene terephthalate (PET) oligomers onto a hydroxylated alumina support surface. Our findings revealed multiple layers of highly oriented solvent molecules (1,4-dioxane) above the surface, creating significant barriers to polyester adsorption. Disrupting and displacing these solvent layers led PET oligomers to adsorb closer to and interact stronger with the surface than PLA oligomers, possibly contributing to the higher reaction temperatures needed to achieve full conversion in PET versus PLA hydrogenolysis. We further suggest an experimental approach to validate our results of solvent layering behavior through predictions of X-ray reflectivity that are consistent with our initial experiments. The insights gained in this study can be leveraged to refine our understanding of catalytic mechanisms to predict depolymerization reactivity and selectivity and improve future hydrogenolysis catalyst designs.