Change In Preferred Orientation Research Articles

High-sensitive and fast-responsive In2O3 thin film sensors for dual detection of NO2 and H2S gases at room temperature

In this work, the room-temperature dual gas sensing characteristics of indium oxide (In2O3) thin films towards NO2 and H2S have been studied. In2O3 thin films were synthesized by the thermal oxidation of indium metal films of various thicknesses in the range of 50–250 nm deposited by thermal evaporation method. Grazing incidence X-ray diffraction (GI-XRD) revealed the change in preferred orientation of In2O3 thin films corresponding to varying thickness, while field-emission electron microscopy studies showcased evolving surface morphologies from individual grains to granular network with respect to the increase in film thickness. Investigations were made on the ability of In2O3 thin films to detect various low concentrations of nitrogen dioxide (NO2) and hydrogen sulfide (H2S) gases at ambient temperature. In2O3 thin films synthesized using 100 nm thick In films exhibited good sensing response of around 58 and 68 % towards NO2 and H2S gases of 5 ppm respectively, at room temperature (27 °C) with the response time of 36 and 18 s. Remarkably, the lower experimental detection limit of these toxic gases could be extended up to 100 ppb. Using X-ray photoelectron spectroscopy, a large presence of surface oxygen is observed on the In2O3 thin film. The sensor has demonstrated remarkable sensing abilities, including strong selectivity, quick sensing response, and good repeatability.

Effects of self-avoidance on the packing of stiff rods on ellipsoids.

Using a statistical-mechanics approach, we study the effects of geometry and self-avoidance on the ordering of slender filaments inside nonisotropic containers, considering cortical microtubules in plant cells, and packing of genetic material inside viral capsids as concrete examples. Within a mean-field approximation, we show analytically how the shape of the container, together with self-avoidance, affects the ordering of the stiff rods. We find that the strength of the self-avoiding interaction plays a significant role in the preferred packing orientation, leading to a first-order transition for oblate cells, where the preferred orientation changes from azimuthal, along the equator, to a polar one, when self-avoidance is strong enough. While for prolate spheroids the ground state is always a polar-like order, strong self-avoidance results with a deep metastable state along the equator. We compute the critical surface describing the transition between azimuthal and polar ordering in the three-dimensional parameter space (persistence length, eccentricity, and self-avoidance) and show that the critical behavior of this system is in fact related to the butterfly catastrophe model. We calculate the pressure and shear stress applied by the filament on the surface, and the injection force needed to be applied on the filament in order to insert it into the volume. We compare these results to the pure mechanical study where self-avoidance is ignored, and discuss similarities and differences.

Study on Microstructure and Tribological Mechanism of Mo Incorporated (AlCrTiZr)N High-Entropy Ceramics Coatings Prepared by Magnetron Sputtering.

(AlCrTiZrMox)N coatings with varying Mo content were successfully prepared using a multi-target co-deposition magnetron sputtering system. The results reveal that the Mo content significantly affects the microstructure, hardness, fracture toughness, and tribological behavior of the coatings. As the Mo content in the coatings increases gradually, the preferred orientation changes from (200) to (111). The coatings consistently exhibit a distinct columnar structure. Additionally, the hardness of the coatings increases from 24.39 to 30.24 GPa, along with an increase in fracture toughness. The friction coefficient is reduced from 0.72 to 0.26, and the wear rate is reduced by 10 times. During the friction process, the inter-column regions of the coatings are initially damaged, causing the wear track to exhibit a wavy pattern. Greater frictional heat is generated at the crest of the wave, resulting in the formation of a MoO2 lubricating layer. The friction reaction helps to reduce the shear force during friction, demonstrating the lower friction coefficient of the (AlCrTiZrMox)N coatings. Both the hardness and fracture toughness work together to reduce the wear rate, and the (AlCrTiZrMox)N coatings show excellent wear resistance. Most notably, although the columnar structure plays a negative role in the hardness, it contributes greatly to the wear resistance.

Improved humidity sensing performances of boron doped ZnO nanostructured thin films depending on boron concentration

Abstract This study details the production and analysis of undoped zinc oxide (uZnO) and boron (B) doped zinc oxide nanostructured thin films, with a specific focus on assessing the influence of varying B doping concentrations on humidity sensing performance. The synthesis of undoped ZnO and B doped ZnO nanoparticles was carried out using sol–gel method. B doping concentrations within the ZnO lattice were adjusted to 1, 3, 4, 5, and 10 mol%. Subsequently, nanostructured thin films were obtained through the spin coating technique on glass substrates. X-ray diffraction analysis revealed a hexagonal wurtzite structure for all nanostructured thin films. Notably, a change in preferential orientation from the (002) plane to the (100) plane occurred when B doping concentration exceeded 5 mol%. Scanning electron microscopy showcased nano-sized grains and capillary nanopores on the surface of each thin film. Energy dispersive X-ray spectra confirmed the presence of zinc, oxygen, and boron elements in the nanostructured thin films. Humidity sensing performance was assessed through electrical resistance measurements in the range of 45%–90% relative humidity at room temperature. All fabricated sensors exhibited sensitivity to humidity. Remarkably, the sensor with a 5 mol% B doping concentration demonstrated the highest humidity sensitivity (438.44 times) and the fastest response (2.0 s) and recovery times (14.2 s). The study concluded that the optimal B doping concentration for designing a highly efficient humidity sensor was determined to be 5 mol%. Overall, the study underscores the potential of B doped ZnO nanostructures for humidity sensor applications, given their exceptional sensor performance.

Achieving ultrastrong-tough CrAlN coatings with low friction coefficient by Y incorporating

Despite having otherwise outstanding hardness and oxidation resistance, CrAlN-based hard coatings are limited by poor fracture toughness and high friction. Although incorporating alloying elements such as C and Magnéli phase-forming elements like V, W, Nb, etc, offer one opportunity for additional toughness and low friction, it requires significant and undesirable compromises to high-temperature performance. Therefore, this work explores an alternative, facile route to achieve ultrastrong-tough CrAlN-based coatings with low friction by incorporating Y. The results indicated that the doped Y elements primarily dissolved in the CrAlN crystalline lattice. Increasing the Y content from 0 to 2 at.% resulted in a change in preferred orientation from (111) to (200), accompanied by a crystal transition from typical columnar grains to unusual equiaxed grains. Notably, when the Y content was about 1.2 at.%, the coating exhibited the maximum toughness of 9.65 MPa·m1/2, almost 2 times larger than that of pure CrAlN coating. Additionally, this coating demonstrated a high hardness of 36.7 GPa and a reduced coefficient of friction (COF) of 0.32. These improvements were attributed to the synergistic contribution of the ultrastrong-tough capability and the formation of Cr2O3 lubricating phases, facilitated by the small amount of Y doping.

Hydrogen‐Bond‐Based Polymer‐Ammonium Intermediates Induced Buried Interface Engineering for High‐Performance Inverted Perovskite Solar Cells

AbstractPerovskite interfaces where defects enrich are pivotal for both device efficiency and stability. Herein, a high‐molecular‐weight polyvinyl pyrrolidone (PVP) is proposed as a robust multi‐functional interlayer to engineer the buried interface. Besides the well‐known defect passivation, perovskite crystallization is intriguingly modulated via the formation of hydrogen‐bond‐based polymer‐ammonium intermediates (e.g., PVP‐FA+ or PVP‐MA+, where MA and FA are methylamine and formamidine, respectively). The interaction energies derived from density functional theory calculations (−34.5, −26.8, and −9.9 kcal mol−1 for PVP‐FA+, PVP‐MA+, and PVP‐Pb2+) suggest that PVP predominately interacts with ammonium cations to form the intermediates, thus largely excluding other chemical interactions and retarding the perovskite crystallization. As such, the hydrophilic PVP interlayer leads to spontaneous perovskite spreading yet a counterintuitively similar nucleation density with respect to the hydrophobic poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA), a change of preferred crystal orientation, improved crystallinity, and remarkably suppressed non‐radiative recombination. These conducive effects jointly minimize the open‐circuit voltage loss and give rise to superior power conversion efficiency for small‐area and large‐area devices.

Absorber texture and the efficiency of polycrystalline thin film CdTe solar cells

A range of microstructural changes occur during the deposition and activation of CdTe based thin film solar cells. In particular, the cadmium chloride (CdCl2) activation treatment results in wholesale recrystallisation which transforms the conversion efficiency of the solar cell. One of the noticeable effects is the change of preferred orientation of the CdTe absorber. Highly orientated [111] texture is observed in as deposited or under-treated CdTe based devices. Optimized activation results in a more randomized texture and the [111] preferred texture component is significantly weakened. In this paper we use Electron Backscatter Diffraction to characterise absorber cross-sections. The focus is on how randomization of the absorber texture reflects device performance. We have had access to a range of CdTe devices using a variety of deposition techniques. We have observed a clear pattern that shows that devices with a highly orientated [111] texture have poor efficiency. Devices with a randomized texture have much higher efficiency. Here we illustrate this empirical correlation using devices deposited by Metal Organic Chemical Vapour Deposition with a range of efficiencies from 13.1 % to 17 %. We have also included the analysis of an absorber from a 18.7 % high efficiency CdSeTe/CdTe device to show that texture is similarly important in these advanced devices. We have been able to quantify the effect of texture by using multiples of uniform density or (MUD) values from the inverse pole figures. MUD figures close to 1 correlate with highest efficiency. Although the random texture of the absorber microstructure is only one of several important process factors, it appears to be a necessary feature for highest efficiency CdTe-based polycrystalline solar cells.

Evaluation of Ni–B alloy electroplated with different anionic groups

In order to study the effects of the main nickel salt on the electroplated nanocrystalline Ni–B alloy coating, the deposition rates, surface morphology, crystallinity, grain sizes, hardness, and corrosion resistance of the Ni–B films electrodeposited with plating baths containing separately nickel sulfate (NS) and nickel sulfamate (NSA) under various temperatures and current densities were compared. Under all conditions, the NSA bath system offered higher deposition rates and lower B contents than the NS counterpart because of the formation of Ni-ammonium complex, which can be adsorbed faster than nickel ions. These two groups of coatings had similar surface morphology and crystallinity under all plating conditions except for those plated with the NS bath system at 60 °C, wherein significant changes in surface texture and preferred crystal orientation as well as an abrupt increase in grain size occurred. The coating hardness was optimized by reducing the grain size and increasing the boron content because of the combined effects of grain refinement strengthening and solid solution strengthening. The differences between the two main salt systems can be explained by the presence of ammonium ions in the NSA bath, which not only increased the deposition rate but also maintained the preferred orientation in Ni (111) at high temperature. Our results indicate that, under high current density and high temperature operation conditions, the NSA main salt plating system is a more favorable option for obtaining higher quality Ni–B alloy coatings.

ZnO and La-doped ZnO films by USP method and their characterizations for ultraviolet photodetectors and photocatalysis applications

In this study, ZnO, Zn1-xLaxO [2, 5, 10, 15 at.%] thin films were grown on glass substrates using the spray-pyrolysis technique, to investigate the effect of doping on the structural, morphological, thermoelectric and optical properties of the layers, Also the samples were tested as UV photodetectors and photocatalyst for MB degradation. Firstly, diffraction patterns showed a hexagonal structure, with preferential grain orientation along the (002) direction, for pure ZnO and 2%La_ZnO layers, and at 5 at.% the preferential orientation changes, and crystallite sizes range from 10 nm to 19 nm. However, SEM images reveal that the ZnO and 2%La_ZnO layers are nanorods distributed over their surfaces, and the other 5%LZO, 10%LZO and 15%LZO layers characterized by nanocrystals were hexagonal prisms. The UV–visible analysis of the prepared layers shows high transparency (80–90%) in the visible range, with a constant optical gap of 3.26 eV. Thermoelectric measurements show that the ZnO and LZO layers are non-degenerate, with a maximum charge concentration of 9.18 × 1017 cm−3 for the 15% LZO films. The thin films show an ability for UV detection, while the 5%La_ZnO layers remain the best for UV photodetection with a good sensitivity (5.07) compared with the other layers. In terms of methyl blue degradation, the 5%La_ZnO thin films had a better degradation of 95%.

Structural, magnetic, dielectric and spectroscopic impedance analysis of magnesium iron oxide thin films synthesized by electrodeposition: Effect of preferred orientation

Magnesium iron oxide is the most valuable and versatile spinel system with reduced eddy current and dielectric losses. Spinel ferrites are electrically non-conductive. The electrodeposition is used to synthesize thin films on Cu substrate. A set of five thin films is prepared by varying the in-situ oxidation time (10 min, 15 min, 20 min, 25 min and 30 min) and a fixed deposition time of 25 min. The x-ray diffractometer XRD (phase confirmation), Scanning Electron Microscope SEM (morphological analysis), Fourier transforms infra-red spectroscope FT-IR (bond-formation), impedance analyzer (dielectric-measurements) and vibratory sample magnetometer VSM (magnetic properties) has been utilized to examine the prepared samples. All the studied samples have been found, single-phase spinel structures. XRD shows the pure phase formation of spinel MgFe2O4 at 20 min, 25 min, and 30 min. The exchange of the preferred orientation (PO) from (731) mixed phase to (533) spinel is observed. This change in preferred orientation has been caused the changes in the properties of prepared thin films. The average lattice constant, cell volume, x-ray density and crystallite size of magnesium-iron oxide were found at 8.3814 Å, 588.58 (Å)3, 3.2098 g/cm3 and 24.0392 nm respectively. In FTIR analysis of magnesium-iron oxide, two characteristic spinel bands are observed below 700 cm−1. The SEM result showed a smooth granular structure at 30 min. The normal behavior of the dielectric constant and single semicircle is observed in cole-cole plot. All the prepared thin films are ferromagnetic in nature. At 30 min, a higher dielectric constant, 20.2 (log f = 5) and 162.3 emu/cm3 saturation magnetization. The remarkable dielectric and magnetic findings are promising for using electrodeposited thin films in electronic and spintronic devices.

Optimization of Growth Parameters of the RF-Sputtered CuInGaSe2 Thin Films for Photovoltaic Applications

CuInGaSe2 (CIGS) thin films were deposited by RF sputtering using a single quaternary target. The effects of various sputtering parameters, such as substrate temperature, sputtering power, and gas flow rate, were studied systematically. The structural, morphological, compositional, and optical properties of the films were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and UV–vis-NIR spectroscopy. The samples exhibited the chalcopyrite type tetragonal structure of CIGS, as confirmed by the XRD analysis. Raman spectroscopy represents the presence of Cu poor ordered vacancy compound (OVC) phase in all the present samples. The growth of the sample at a higher substrate temperature resulted in a higher crystalline nature with a suppressed OVC phase and energy bandgap of 1.18 eV. The deposition of CIGS at 160 W sputtering power favors growth towards (112) Bragg crystal plane, suppressing the (220)/(204) plane of CIGS, shows change in preferred orientation with a lower sputtering power at 80 and 120 W. The sample grown at a gas flow rate of 60 standard cubic centimeters per minute (SCCM) exhibited compact grain growth with marginally improved crystallinity. The sample grown at 160 W, 300 °C, and 60 SCCM showed better crystalline and morphological properties, and it can be used as an absorber layer for highly efficient CIGS thin-film solar cells.

Structural and optical characteristics of NiO films deposited using the PLD technique

NiO films were deposited on glass and Si(100) substrates by reactive pulsed laser deposition from the Ni target. Nd: YAG laser (1064 nm) was used. The oxygen pressure was between 0.05 and 0.3 Torr. The optimum conditions for a good-quality NiO film are an oxygen pressure of 0.1 Torr and a laser power of 410 mW. Preferred orientation changes from (200) to (220) and D decreases from 27 to ∼9 nm as the temperature increases from 200 to 300°C. The preferred orientation changes into (111), nanoparticles size reduces from 46 to 26 nm and D drops from 27 to 10 nm as laser power increases from 410 to 820 mW. The oxygen pressure is significantly affecting the composition and morphologies of the NiO films. The optical band gap was 3.35 eV.

Microstructure Formation and Mechanical Properties of Metastable Titanium-Based Gradient Coating Fabricated via Intense Pulse Ion Beam Melt Mixing.

The unique flash heating characteristics of intense pulsed ion beams (IPIB) offer potential advantages to fabricate high-performance coatings with non-equilibrium structures. In this study, titanium-chromium (Ti-Cr) alloy coatings are prepared through magnetron sputtering and successive IPIB irradiation, and the feasibility of IPIB melt mixing (IPIBMM) for a film-substrate system is verified via finite elements analysis. The experimental results reveal that the melting depth is 1.15 μm under IPIB irradiation, which is in close agreement with the calculation value (1.18 μm). The film and substrate form a Ti-Cr alloy coating by IPIBMM. The coating has a continuous gradient composition distribution, metallurgically bonding on the Ti substrate via IPIBMM. Increasing the IPIB pulse number leads to more complete element mixing and the elimination of surface cracks and craters. Additionally, the IPIB irradiation induces the formation of supersaturated solid solutions, lattice transition, and preferred orientation change, contributing to an increase in hardness and a decrease in elastic modulus with continuous irradiation. Notably, the coating treated with 20 pulses demonstrates a remarkable hardness (4.8 GPa), more than twice that of pure Ti, and a lower elastic modulus (100.3 GPa), 20% less than that of pure Ti. The analysis of the load-displacement curves and H-E ratios indicates that the Ti-Cr alloy coated samples exhibit better plasticity and wear resistance compared to pure Ti. Specifically, the coating formed after 20 pulses exhibits exceptional wear resistance, as demonstrated by its H3/E2 value being 14 times higher than that of pure Ti. This development provides an efficient and eco-friendly method for designing robust-adhesion coatings with specific structures, which can be extended to various bi- or multi-element material systems.

Investigation on structural, optical and electrical properties of Zn doped indium oxide thin film for gamma dosimetry

Zinc-doped indium oxide thin film was deposited on the glass substrate using the spray pyrolysis method at a substrate temperature of 723K for various Zn concentrations in the range of 2–10 at%. The obtained film confirmed a polycrystalline cubic structure with a shift in preferred growth orientation from (400) to (222) on higher doping levels. The morphological study also exhibited a microstructure change which corroborates with the XRD spectra. Moreover, surface morphology has a great influence on the physical properties of the film. Cubic crystallization of doped In2O3 with no impurity phase and the presence of oxygen vacancies is confirmed by Raman spectra. It also confirms the In substitution by Zn. Optical transmittance decreased with doping which is supported by a decrease in bandgap energy from 3.68 to 3.5. The Refractive index is estimated using three different models with the Herve-Vandamme model showing the least deviation. Urbach energy shows an inverse relation with energy band gaps. Violet-blue emission was observed in the photoluminescence spectra. Zn doping also had an influence on the electrical properties of the material. Thermoluminescence spectroscopy validates Zn-doped In2O3 films' suitability for gamma dosimetry. XPS peak intensity corresponds to oxygen vacancies observed to be higher for Zn doped sample relative to undoped, indicates the formation of defects after doping. The resistivity increased up to 6 at% and then decreased, which can be due to the preferred orientation change to (222) at higher dopant concentrations. From the investigation, it is concluded that 4% Zn doped In2O3 can be used for sensor applications due to its good structural, optical and electrical properties and also lesser defects.

Microstructure and properties of graphene oxide reinforced copper-matrix composite foils fabricated by ultrasonic assisted electrodeposition

In this paper, graphene oxide (GO)/Cu composite (GO/Cu) foils with high thermal and mechanical properties were prepared by ultrasonic-assisted direct current electrodeposition. The effect of ultrasonic power and graphene concentration on the microstructure and properties of the composite foils was systematically investigated. It was found that the average grain size can be refined by both the addition of GO reinforcement and ultrasonic treatment. Under the optimized preparation condition with 120 W ultrasonic power and GO concentration of 0.8 g/L GO in plating solution, the average grain size was about 0.26 μm and illustrated strong crystallographic orientation of (220). In addition, the GO content in the composites was increased from 0.67 wt% without ultrasonic treatment to 1.72 wt%, and it was uniformly dispersed in the composite foil with ultrasonic effect. Compared with pure copper foil, the hardness value of the GO/Cu composite foil nearly doubled to 74.6 HV0.1, the average friction coefficient was decreased from 0.87 to 0.72 and the tensile strength of the composite foil was improved to 239 MPa with an elongation of 17%. Meanwhile, the thermal conductivity with optimized condition increased 39.8% to 556.57 W m−1 K−1. The improved mechanical and thermal properties of the GO/Cu composite foil were mainly ascribed to the grain refinement, change of preferred orientation and the presence of reduced GO reinforcement as a network in the composite foil.

Sr2TiSi2O8 (STS) Polar Glass-Ceramics: Effect of Na2O and CaO Additions in the Parent Glass on the Crystallization Mechanism and on the Piezoelectric Properties

Glass-ceramics containing pyroelectric Sr2TiSi2O8 (STS) crystals are produced from parent glasses of compositions STS + 0.8 SiO2 + (0.2 − x) Na2O + x CaO, with x = 0; 0.05; 0.10; and 0.15. The aim of this work is to investigate the effect of the additions to the stoichiometric STS composition on the crystallization mechanisms and on the piezoelectric properties of the glass-ceramic. The DSC analyses evidence that the glass transition temperatures Tg, the onset temperature of the crystallization peak To and the temperature Tc of the maximum of this peak increase with the CaO/Na2O ratio. On the basis of the DSC data, the crystallization of the parent glass samples was operated by thermal treatment. The observation of the cross-sections of the heat-treated samples highlights that the competition between the surface and volume crystallization mechanisms is influenced by the CaO/Na2O ratio and the temperature. For all the samples, the XRD analyses performed on the surfaces as obtained after the crystallization treatment evidenced a preferential orientation of the STS crystals with the plans (00l) parallel to the surface. The XRD analyses performed after grinding the surface show that only the surface crystallized layers are preferentially oriented. Moreover, changes in preferential orientation to plans (202) or (201) are observed over the depth, depending on the composition and the temperature of the thermal treatment. These changes influence the polarization of the surface crystallized layer and, consequently, its piezoelectric charge coefficient d33. The highest values of d33 were measured on the glass-ceramic samples exhibiting mainly a (202) preferential orientation over their thickness.

A facile one-step gel process for precipitation of multifractal NaCl crystals and morphology evolution from sodium silicate gel

• Crystallization of NaCl in colloidal-salt system by a one-step gelation process. • Varying the pretreatment and gel conditions synthesizes DLA and dendrite patterns. • XRD analysis explains the dendrite pattern with distinct preferred orientation. • <110> and <111> directions determine the three- and four-fold symmetry dendrites. • Higher gelation degree contributes to precipitate regular fractal dendrite. In the colloidal-salt system of sodium silicate and sodium chloride, three-fold and four-fold symmetric dendrites and diffusion-limited aggregation (DLA) of sodium chloride crystals have been synthesized by a simple one-step gelation process without changing the solution composition. The morphology variation is realized by changing the sol pretreatment and gelation process’s heating mode. And the gelation degree of sodium silicate and the anisotropy of crystal growth is the morphology formation mechanism. Four-fold symmetric dendrites are related to preferential growth in the <110> direction, while three-fold symmetric dendrites are due to preferential orientation changes from <111> to <100> and then to <111>. EDS composition analysis showed that the high gelling degree is more accessible to precipitate regular fractal dendrites with preferred orientation.

Transition in the preferred orientation of RF sputtered ZnO/Si thin films by thermal annealing: Structural, morphological, and optical characteristics

Polycrystalline ZnO thin films having preferential growth along the polar (002) plane are prepared on Si (111) substrate using RF sputtering technique. A gradual build-up of the semipolar (103) plane with the dominant (002) polar plane of 400–700 °C annealed films is revealed by the Glancing incidence angle X-Ray diffraction (GXRD) pattern. However, a change in preferred orientation from polar (002) to semi-polar (103) and non-polar (100) planes is observed with further annealing in the temperature range 800–1200 °C. This occurs due to an increase in the mobility of adatoms due to annealing which encourages diffusion across grain boundaries and competitive growth among planes leading to the growth of (103) plane. This structural deviation of film from (002) plane to (103) plane leads to the change in surface morphology of annealed films around 800 °C as depicted in Field Emission Scanning Electron Microscopy (FESEM) images. The observed changes in surface morphology of films are further correlated with the variation in optical band gap values and diffuse reflectance spectra. The low reflectance values of the samples represent their anti-reflection property which makes ZnO/Si thin film a conceivable applicant in optoelectronics.

Preparation and high temperature performance of NbC layer in TRISO particles

TRISO particles with new coating layers was designed to adapt higher temperature. In this work, NbC coating layers were prepared by a novel two-step method: The original NbC coating layer was prepared from NbCl5 and C3H6 by chemical vapor deposition method. The flow rate of the C3H6 should be relatively low to avoid the C impurity. The NbC layer was then heated with carbon powders at high temperature. Since the C atoms can diffuse into the NbC coating layer and react with Nb2C at high temperature. The Nb2C impurity comes from the deposition was removed after the thermal treatment. The crystal of NbC layer grow up and has a change of preferred orientation at high temperature. The heat treatment has slight effect on the hardness of the pure NbC layer. Our result shows the NbC coating layer has good adaptability to the high temperature environment in VHTR.

Confined crystallization and polymorphism in iPP thin films

The morphological and structural evolution of isotactic polypropylene (iPP) in thin and ultrathin films casted by hot-solution spin coating is investigated by means of atomic force microscopy (AFM) and grazing incidence wide angle X-ray scattering (GIWAXS). When reducing the film thickness from 300 nm to 15 nm, changes from a 3D to a quasi-2D morphology are observed. The quasi-2D confined morphology is found in the 220-40 nm thickness range and is characterized by a predominant edge-on orientation (EO) of the lamellae. A transition to the flat-on (FO) orientation paired to a drastic decrease of the sample roughness is observed for thicknesses below 30 nm. Surprisingly, a mixed morphology where orthorhombic γ-phase branches develop from FO α-phase lamellae is observed at the lowest prepared thickness of 15 nm. The unexpected appearance of the γ-phase for the iPP grade used here is due to the favourable flat-on lamellar orientation at the lowest film thickness. Thanks to a quantitative analysis of the GIWAXS patterns, the relative amount between edge-on and flat-on oriented lamellae (χ EO /χ FO ) is calculated, providing useful insights on the real morphological composition of the iPP thin films, a task that is very challenging to achieve with microscopy techniques. • Isotactic polypropylene thin film prepared by hot-solution spin coating present confined crystallization behaviour. • Morphology evolution is investigated via AFM, nanostructural composition and lamellar orientation is studied by means of GIWAXS. • Lamellae maintain a mixed morphological structure, preferential orientation changes from edge-on to flat-on on the substrate. • Formation of the orthorhombic γ-phase is induced by increasing the degree of confinement ( i.e. : decreasing film thickness).