Metal-Halide Perovskite Submicrometer-Thick Films for Ultra-Stable Self-Powered Direct X-Ray Detectors

Metal-halide perovskites are revolutionizing the world of X-ray detectors,due to the development of sensitive,fast,and cost-effective devices.Self-powered operation,ensuring portability and low power consumption,has also been recently demonstrated in both bulk materials and thin films.However,the signal stability and repeatability under continuous X-ray exposure has only been tested up to a few hours,often reporting degradation of the detection performance.Here it is shown that self-powered direct X-ray detectors,fabricated starting from a FAPbBr_(3)submicrometer-thick film deposition onto a mesoporous TiO_(2)scaffold,can withstand a 26-day uninterrupted X-ray exposure with negligible signal loss,demonstrating ultra-high operational stability and excellent repeatability.No structural modification is observed after irradiation with a total ionizing dose of almost 200 Gy,revealing an unexpectedly high radiation hardness for a metal-halide perovskite thin film.In addition,trap-assisted photoconductive gain enabled the device to achieve a record bulk sensitivity of 7.28 C Gy^(−1)cm^(−3)at 0 V,an unprecedented value in the field of thin-film-based photoconductors and photodiodes for“hard”X-rays.Finally,prototypal validation under the X-ray beam produced by a medical linear accelerator for cancer treatment is also introduced.

Evaluation on residual stresses of silicon-doped CVD diamond films using X-ray diffraction and Raman spectroscopy

The effect of silicon doping on the residual stress of CVD diamond films is examined using both X-ray diffraction (XRD) analysis and Raman spectroscopy measurements. The examined Si-doped diamond films are deposited on WC-Co substrates in a home-made bias-enhanced HFCVD apparatus. Ethyl silicate (Si(OC2H5)4) is dissolved in acetone to obtain various Si/C mole ratio ranging from 0.1% to 1.4% in the reaction gas. Characterizations with SEM and XRD indicate increasing silicon concentration may result in grain size decreasing and diamond [110] texture becoming dominant. The residual stress values of as-deposited Si-doped diamond films are evaluated by both sin2ψ method, which measures the (220) diamond Bragg diffraction peaks using XRD, with ψ-values ranging from 0° to 45°, and Raman spectroscopy, which detects the diamond Raman peak shift from the natural diamond line at 1332 cm-1. The residual stress evolution on the silicon doping level estimated from the above two methods presents rather good agreements, exhibiting that all deposited Si-doped diamond films present compressive stress and the sample with Si/C mole ratio of 0.1% possesses the largest residual stress of ~1.75 GPa (Raman) or ~2.3 GPa (XRD). As the silicon doping level is up further, the residual stress reduces to a relative stable value around 1.3 GPa.

Dual-phase coexistence enables to alleviate resistance drift in phase-change films

The amorphous phase-change materials with spontaneous structural relaxation leads to the resistance drift with the time for phase-change neuron synaptic devices. Here, we modify the phase change properties of the conventional Ge_2Sb_2Te_5(GST) material by introducing an SnS phase. It is found that the resistance drift coefficient of SnS-doped GST was decreased from 0.06 to 0.01. It can be proposed that the origin originates from the precipitation of GST nanocrystals accompanied by the precipitation of SnS crystals compared to single-phase GST compound systems. We also found that the decrease in resistance drift can be attributed to the narrowed bandgap from 0.65 to 0.43 eV after SnS-doping. Thus, this study reveals the quantitative relationship between the resistance drift and the band gap and proposes a new idea for alleviating the resistance drift by composition optimization, which is of great significance for finding a promising phase change material.

X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by X-ray absorption near edge structure spectra and X-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t2g and eg levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

X-ray Photoelectron Spectroscopy Studies of Ti_(x)Al_(1-x)N Thin Films Prepared by RF Reactive Magnetron Sputtering

TixAl1-xN films have been prepared by RF reactive magnetron sputtering. X-ray diffraction results showed that TixAl1-xN thin films in this study were hexagonal wurtzite structure with the Ti content up to 0.18. X-ray photoelectron spectrocopy studies provided that the Nls core-electron spectrum of TixAl1-xN thin film brodend with increasing Ti content, and the difference of the chemical shifts for Ti2p3/2 line between TiN and TixAl1-xN th77pj in film was 0.7 eV.

Characterization of Thin Films by Low Incidence X-Ray Diffraction

Glancing Angle X-ray Diffraction (GAXRD) is introduced as a direct, non-destructive, surface-sensitive technique for analysis of thin films. The method was applied to polycrystalline thin films (namely, titanium oxide, zinc selenide, cadmium selenide and combinations thereof) obtained by electrochemical growth, in order to determine the composition of ultra-thin surface layers, to estimate film thickness, and perform depth profiling of multilayered heterostructures. The experimental data are treated on the basis of a simple absorption-diffraction model involving the glancing angle of X-ray incidence.

Centimeter-sized Cs_(3)Cu_(2)I_(5)single crystals grown by oleic acid assisted inverse temperature crystallization strategy and their films for high-quality X-ray imaging

Low-dimensional halide perovskites have become the most promising candidates for X-ray imaging,yet the issues of the poor chemical stability of hybrid halide perovskite,the high poisonousness of lead halides and the relatively low detectivity of the lead-free halide perovskites which seriously restrain its commercialization.Here,we developed a solution inverse temperature crystal growth(ITCG)method to bring-up high quality Cs_(3)Cu_(2)I_(5)crystals with large size of centimeter order,in which the oleic acid(OA)is introduced as an antioxidative ligand to inhibit the oxidation of cuprous ions effieiently,as well as to decelerate the crystallization rate remarkalby.Based on these fine crystals,the vapor deposition technique is empolyed to prepare high quality Cs_(3)Cu_(2)I_(5)films for efficient X-ray imaging.Smooth surface morphology,high light yields and short decay time endow the Cs_(3)Cu_(2)I_(5)films with strong radioluminescence,high resolution(12 lp/mm),low detection limits(53 nGyair/s)and desirable stability.Subsequently,the Cs_(3)Cu_(2)I_(5)films have been applied to the practical radiography which exhibit superior X-ray imaging performance.Our work provides a paradigm to fabricate nonpoisonous and chemically stable inorganic halide perovskite for X-ray imaging.

Evaluation of multiaxial stress in textured cubic films by x-ray diffraction

X-ray diffraction is used extensively to determine the residual stress in bulk or thin film materials on the as- sumptions that the material is composed of fine crystals with random orientation and the stress state is biaxial and homogeneous through the x-ray penetrating region. The stress is calculated from the gradient of ε ～ sin^2 φ linear relation. But the method cannot be used in textured films due to nonlinear relation. In this paper, a novel method is proposed for measuring the multiaxial stresses in cubic films with any [hkl] fibre texture. As an example, a detailed analysis is given for measuring three-dimensional stresses in FCC films with [111] fibre texture.

X-RAY STUDY ON TITANIUM NITRIDE FILMS DEPOSITED BY VCAD METHOD

TiN films deposited by the VCAD method at the substrate of stainless steel and superhigh speed tool steels are uniform and dense.Their colour,orientation and lattice parameter depend on deposited condition The lattice structure of deposited film,the change of the lattice parameter and its preferred orientation were studied by the XRD method,different behaviours of TiNx film were analysed.The lattice parameter of TiNx films is increased with the nitrogen content and The colour of TiNx film is strongly related to the content of Nitrogen also.The change of preferred orientation depends mainly on the Bias.

Flavor Amidst Plainness:An Examination of the Subjectivity of the“People’s Films”From the Perspective of Classical Aesthetics

The“People’s Films,”when examined from the perspective of classical aesthetics,present a unique visual style that creates artistic conceptions through sparse filming and deliver a scenery-based ideology through background shots,contributing to the overall aesthetic taste dominated by plainness.Chinese national aesthetic tastes,distinguished by implicitness,symbolism,and ethereality,have the magical power to present charming conceptions via plain and simple scenes,thus endowing the“People’s Films”with natural,plain,and harmonious frames that are unique to China.Behind the silent and plain scenes are representations of personal cultivation and essential values cherished by the Chinese people,which are achieved via the momentary presence and entirety of scenes photographed in the films,delivering an internal transcendence of people’s consciousness.

A preliminary study of the effects of plastic film-mulched raised beds on soil temperature and crop performance of early-sown short-season spring maize(Zea mays L.) in the North China Plain

To identify a strategy for earlier sowing and harvesting of spring maize(Zea mays L.) in an alternative maize–maize double cropping system, a 2-year field experiment was performed at Quzhou experimental station of China Agricultural University in 2014 and 2015. A short-season cultivar, Demeiya number 1(KX7349), was used in the experiment. Soil temperature to 5 cm depth in the early crop growth stage, crop growth, crop yield, and water use of different treatments(plastic film-mulched raised bed(RF) and flat field without plastic film mulching(CK) in 2014; RF, plastic film-mulched flat field(FF), and CK in 2015)were measured or calculated and compared. Soil temperature in the film-mulched treatments was consistently higher than that in CK(1.6–3.5 °C in average) during the early growth stage. Crops in plastic film-mulched treatments used 214 fewer growing-degree days(GDDs) in 2014 and 262 fewer GDDs in 2015. In 2014, the RF treatment yielded 32.7%higher biomass than CK, although its 9.4% higher grain yield was not statistically significant. Also, RF used 17.9% less water and showed 33.1% higher water use efficiency(WUE) than CK. In 2015, RF and FF showed 56.2% and 49.5% higher yield, 15.0% and 4.5%lower water use(ET), and 63.4% and 75.7% higher WUE, respectively, than CK. RF markedly increased soil temperature in the early crop season, accelerated crop growth, reduced ET,and greatly increased crop yield and WUE. Compared with FF, RF had no obvious effect on crop growth rate, although soil temperature during the period between sowing and stem elongation was slightly increased. However, RF resulted in lower ET and higher WUE than FF. Effects of RF on soil water dynamics as well as its cost-effectiveness remain topics for further study.

Metal Precursor Influence on Performance of CuIn1-xGaxSe2 Films

CUIn1-xGaxSe2 （CIGS） films were prepared by a two-stage method, in which Cu-In-Ga metallic precursors were firstly deposited on unheated Mo-coated soda lime glass substrates by direct current sputtering CuGa （20%Ga） and radio frequency sputtering In targets in an Ar atmosphere, followed by selenization at 520 ℃ for 40 min in Se vapor. By adjusting the sputtering thickness ratio of surface CuGa （20%Ga） and bottom CuGa （20%Ga） alloy layers in metal precursor, different CIGS thin films were fabricated. Through X-ray diffraction spectra, Raman spectra, local energy dispersive spectrometer, planar- and cross- sectional views of scanning electron microscopy measurements, it revealed that the CIGS thin films from selenization of metal precursor with CuGa：In：CuGa thickness ratio of 7：20：3 （sample-2-se） was of chalcopyrite structure with the preferred （112） orientation, and the grains sizes ranged from 0.5 μm to 2 μm, and sample-2-se had no binary compound phase of In-Se and order defect compound phase. Consequently, the results of illuminated current- voltage curve and quantum efficiency measurements showed that the CIGS film device made from sample-2-se had relative higher photo-electric conversion efficiency （3.59%） and good spectrum response.

Characterization and Structural Property of Indium Tin Oxide Thin Films

In this study, Indium Tin Oxide (ITO) thin films were deposited by electron beam evaporation on white glass substrates with thicknesses of about 50, 100 and 170 nm. We investigated structural properties by X-ray Diffraction (XRD) and X-ray reflectivity (XRR). The results showed that ITO thin films have a crystalline structure with a domain that increases in size with increasing thickness. For uniform electron density, as the thin film roughness increases, reflectivity curve slope also increases. Also thinner film has more fringes than thicker film. The roughness determines how quickly the reflected signal decays. XRR technique is more suitable for very thin films, approximately 20 nm and less.

MISCIBILITY AND MORPHOLOGY OF THIN FILMS OF BLENDS OF POLYSTYRENE WITH BROMINATED POLYSTYRENES: EFFECTS OF VARYING THE MOLECULAR WEIGHT, BROMINATION DEGREE AND ANNEALING

Thin films of incompatible polymer blends can form a variety of structures during preparation and subsequent annealing process. For the polymer blend system consisting of polystyrene and poly（styrene-co-p-bromo-styrene）, i.e., PS/PBrxS, its compatibility could be adjusted by varying the degree of bromination and the molecular weight of both components comprised. In this paper, surface chemical compositions of the cast and the annealing films were investigated by X-ray photoelectron spectroscopy （XPS） and contact angle measurement; meanwhile, surface topographical changes are followed by atomic force microscopy （AFM）. In addition, substantial attention was paid to the effect of annealing on the morphologic variations induced by phase separation and/or dewetting of the thin film. Moreover, the influences of the molecular weight, Mw, as well as the brominated degree, x%, on the sample surface are explored systematically, and the corresponding observations are explained in virtue of the Flory-Huggins theory, along with the dewetting of the polymer thin film.

Microstructure and optical absorption properties of Au/NiO thin films

Au nanoparticles dispersed NiO composite films were prepared by a chemical solution method.The phase structure,microstructure,surface chemical state,and optical absorption properties of the films were characterized by X-ray diffraction,transmission electron microscopy,X-ray photoelectron spectroscopy,and Uv-vis spectrometer.The results indicate that Au particles with the average diameters of 35-42 nm are approximately spherical and disperse in the NiO matrix.The optical absorption peaks due to the surface plasmon resonance of Au particles shift to the shorter wavelength and intensify with the increase of Au content.The bandwidth narrows when the Au content increases from 8.4wt% to 45.2wt%,but widens by further increasing the Au content from 45.2wt% to 60.5wt%.The band gap Eg increases with the increase of Au contents from 8.4wt% to 45.2wt%,but decreases by further increasing the Au content.

Density changes with substrate negative bias for ta-C films deposited by filter cathode vacuum arc

Specular X-ray reflectivity (XRR) measurements were used to study the density and cross-section information of tetrahedral amorphous carbon (ta-C) films deposited by filter cathode vacuum arc(FCVA) system at different substrate bias. According to the correlation between density and substrate negative bias, it is found that the value of density reaches a maximum at -80 V bias. As the substrate bias increases or decreases, the density tends to lower gradually. Based on the density of diamond and graphite, sp3 bonding ratio of ta-C films was obtained from their corresponding density according to a simple equation between the two. And a similar parabolic variation was observed for ta-C films with the sp3 content changes with substrate negative bias. The mechanical properties such as hardness and elastic modulus were also measured and compared with the corresponding density for ta-C films. From the distribution of data points, a linear proportional correlation between them was found, which shows that the density is a critical parameter to characterize the structure variation for ta-C films.

Growth of Fluorocarbon Films by Low-Pressure Dielectric Barrier Discharge

Plasma polymerized fluorocarbon （FC） films have been deposited on silicon substrates from dielectric barrier discharge （DBD） plasma of C4Fs at room temperature under a pressure of 25～125 Pa. The effects of the discharge pressure and frequency of power supply on the films have been systematically investigated. FC films with a less cross linked structure may be formed at a relatively high pressure. Increase in the frequency of power supply leads to a significant increase in the deposition rate. Static contact angle measurements show that deposited FC films have a stable, hydrophobic surface property. All deposited films show smooth surfaces with an atomic surface roughness. The relationship between plasma parameters and the properties of the deposited FC films are discussed.

A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6×6×0.5 mm^3 is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than 10^12 W· cm. Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 n A under an electric field of 30 k V cm^-1. The time response is 220 ps. The sensitivity is about 125 m A W^-1 under a biasing voltage of 100 V.A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.

Effect of Reaction Temperature and Time on the Structural Properties of Cu(In,Ga)Se_2 Thin Films Deposited by Sequential Elemental Layer Technique

Thin films of copper indium gallium selenide Cu（In,Ga）Se2 （CIGS） were prepared by sequential elemental layer deposition in vacuum at room temperature. The as-deposited films were heated in vacuum for compound formation, and were studied at temperature as high as 1250℃ for the first time. These films were concurrently studied for their structural properties by X-ray diffraction （XRD） technique. The XRD analyses include phase transition studies, grain size variation and microstrain measurements with the reaction temperature and time.It has been observed that there are three distinct regions of variation in all these parameters. These regions belong to three temperature regimes： 〈450℃, 450-950℃, and 〉950℃. It is also seen that the compound formation starts at 250℃, with ternary phases appearing at 350℃ or above. Whereas, there is another phase shift at 950℃ without any preference to the quaternary compound.

Effect of Substrates on the Properties of ZnO Thin Films Grown by Pulsed Laser Deposition

Polycrystalline zinc oxide (ZnO) thin films have been deposited at 450°C onto glass and silicon substrates by pulsed laser deposition technique (PLD). The used source was a KrF excimer laser (248 nm, 25 ns, 5 Hz, 2 J/cm2). The effects of glass and silicon substrates on structural and optical properties of ZnO films have been investigated. X-ray diffraction patterns showed that ZnO films are polycrystalline with a hexagonal wurtzite—type structure with a strong (103) orientation and have a good crystallinity on monocrystalline Si(100) substrate. The thickness and compositional depth profile were studied by Rutherford Backscattering spectrometry (RBS). The average transmittance of ZnO films deposited on glass substrate in the visible range is 70%.