Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

Wet‐Etching Induced Abnormal Phase Transition in Highly Strained VO2/TiO2 (001) Epitaxial Film

The metal–insulator transition (MIT) behavior in vanadium dioxide (VO₂) epitaxial film is known to be dramatically affected by interfacial stress due to lattice mismatching. For the VO₂/TiO₂ (001) system, there exists a considerable strain in ultra‐thin VO₂ thin film, which shows a lower T_c value close to room temperature. As the VO₂ epitaxial film grows thicker layer‐by‐layer along the “bottom‐up” route, the strain will be gradually relaxed and T_c will increase as well, until the MIT behavior becomes the same as that of bulk material with a T_c of about 68 °C. Whereas, in this study, we find that the VO₂/TiO₂ (001) film thinned by “top‐down” wet‐etching shows an abnormal variation in MIT, which accompanies the potential relaxation of film strain with thinning. It is observed that even when the strained VO₂ film is etched up to several nanometers, the MIT persists, and T_c will increase up to that of bulk material, showing the trend to a stress‐free ultra‐thin VO₂ film. The current findings demonstrate a facial chemical‐etching way to change interfacial strain and modulate the phase transition behavior of ultrathinVO₂ films, which can also be applied to other strained oxide films.     

Luminescence induced by elastic deformation of ZnS:Mn nanoparticles

When the thin film of ZnS:Mn nanoparticles deposited on a glass substrate is elastically deformed by applying a load, then initially the mechanoluminescence (ML) intensity increases with time, attains a peak value I_m at a particular time t_m, and later on it decreases with time. The rise and decay characteristics of the ML produced during release of the load are also similar to those produced during the application of load. Similar rise, occurrence of peak and then decrease in ML intensity are also found, when the film is deformed impulsively by dropping a steel ball of small mass from a low height; however, in this case, the time durations for the occurrence of ML and decay time of ML are very short. In the cases of loading and impulsive deformation ,after t_m, initially the ML intensity decreases at a fast rate and then at a slow rate, in which the decay time of fast decrease is equal to the time-constant for rise of pressure and the decay time for slow decrease is equal to the relaxation time of the surface charges. In the case of loading, the peak intensity I_m and the total intensity I_T of ML increase quadratically with the magnitude of applied pressure; however, in the case of impulsive deformation, both the I_m and I_T increase linearly with the height through which the ball is dropped on to the sample. In the case of deformation of the samples at a fixed strain rate, I_m should increase linearly with the applied pressure. The elastico ML in ZnS:Mn nanoparticles can be understood on the basis of the piezoelectrically-induced electron detrapping model, in which the local piezoelectric field near the Mn²⁺ centres reduces the trap-depth, and therefore, the detrapping of filled electron traps takes place, and subsequently the energy released non-radiatively during the electron-hole recombination excites the Mn²⁺ centres and de-excitation gives rise to the ML. The equal number of photons emitted during the application of pressure, release of pressure, and during the successive applications of pressure, indicates that the detrapped electron-traps get filled during the relaxation of the surface charges induced by the application and release of pressure because the charge carriers move to reduce the surface charges. On the basis of the piezoelectrically-induced electron detrapping model, expressions are derived for different characteristics of the ML of ZnS:Mn nanoparticles and a good agreement is found between the theoretical and experimental results. The expressions explored for the dependence of ML intensity on several parameters may be useful in tailoring the suitable nanomaterials capable of exhibiting ML during their elastic deformation. The values of the relaxation time of surface charges, time-constant for the rise of pressure, and the threshold pressure can be determined from the measurement of the time-dependence of ML. It seems that the trapping and detrapping of charge carriers in materials can be studied using ML.     

Sensing behaviour of tin doped chromium oxide gas sensor toward ethanol

In this paper, the enhancement of gas sensing response due to addition of tin into Cr₂O₃ has been reported. Sn-doped Cr₂O₃ nanoparticles have been prepared by a co-precipitation method and characterised by X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis. X-ray diffraction studies revealed the substitution of Cr³⁺ ions by Sn⁴⁺ ions. Field emission scanning electron microscopy images exhibited presence of clusters and agglomerates on the surface. The concentration of tin, used as dopant, was varied from 1 to 5?wt.% and its effect on gas sensing response has been studied. Synthesised powders were applied as thick film onto alumina substrate and tested for ethanol sensing at different operating temperatures and all the sensors gave an optimum response at 250?^°C. The activation energy of conduction for all the samples was estimated using Arrhenius plots and it was observed that the sample doped with 4?wt.% Sn possesses minimum activation energy, and interestingly this sample gave the best sensing response in the lot.     

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals

The present paper reports the luminescence induced by plastic deformation of coloured alkali halide crystals using pressure steps. When pressure is applied onto a γ-irradiated alkali halide crystal, then initially the mechanoluminescence (ML) intensity increases with time, attains a peak value and later on it decreases with time. The ML of diminished intensity also appears during the release of applied pressure. The intensity I_m corresponding to the peak of ML intensity versus time curve and the total ML intensity I_T increase with increase in value of the applied pressure. The time t_m corresponding to the ML peak slightly decreases with the applied pressure. After t_m, initially the ML intensity decreases at a fast rate and later on it decreases at a slow rate. The decay time of the fast decrease in the ML intensity is equal to the pinning time of dislocations and the decay time for the slow decrease of ML intensity is equal to the diffusion time of holes towards the F-centres. The ML intensity increases with the density of F-centres and it is optimum for a particular temperature of the crystals. The ML spectra of coloured alkali halide crystals are similar to the thermoluminescence and afterglow spectra. The peak ML intensity and the total ML intensity increase drastically with the applied pressure following power law, whereby the pressure dependence of the ML intensity is related to the work-hardening exponent of the crystals. The ML also appears during the release of the applied pressure because of the movement of dislocation segments and movements of dislocation lines blocked under pressed condition. On the basis of the model based on the mechanical interaction between dislocation and F-centres, expressions are derived for the ML intensity, which are able to explain different characteristics of the ML. From the measurements of the plastico ML induced by the application of loads on γ-irradiated alkali halide crystals, the pinning time of dislocations, diffusion time of holes towards F-centres, the energy gap E_a between the bottom of acceptor dislocation band and the energy level of interacting F-centres, and work-hardening exponent of the crystals can be determined. As in the elastic region the strain increases linearly with stress, the ML intensity also increases linearly with stress, however, as in the plastic region, the strain increases drastically with stress and follows power law, the ML intensity also increases drastically with stress and follows power law. Thus, the ML is intimately related to the plastic flow of alkali halide crystals.     

Formation of hydroxyl and water layers on MgO films studied with ambient pressure XPS

To understand the interaction of water with MgO(100), a detailed quantitative assessment of the interfacial chemistry is necessary. We have used ambient pressure X-ray photoelectron spectroscopy (XPS) to measure molecular (H₂O) and dissociative (OH) water adsorption on a 4 monolayer (ML) thick MgO(100)/Ag(100) film under ambient conditions. Since the entire 4 ML metal oxide (Ox) film is probed by XPS, the reaction of the MgO film with water can be quantitatively studied. Using a multilayer model (Model 1) that measures changes in Ox thickness from O 1s (film) and Ag 3d (substrate) spectra, it is shown that the oxide portion of the MgO film becomes thinner upon hydroxylation. A reaction mechanism is postulated in which the top-most layer of MgO converts to Mg(OH)₂ upon dissociation of water. Based on this mechanism a second model (Model 2) is developed to calculate Ox and OH thickness changes based on OH/Ox intensity ratios from O 1s spectra measured in situ, with the known initial Ox thickness prior to hydroxylation. Models 1 and 2 are applied to a 0.15 Torr isobar experiment, yielding similar results for H₂O, OH and Ox thickness changes as a function of relative humidity.     

Development of mechanoluminescence technique for impact studies

A new technique called, mechanoluminescence technique, is developed for measuring the parameters of impact. This technique is based on the phenomenon of mechanoluminescence (ML), in which light emission takes place during any mechanical action on solids. When a small solid ball makes an impact on the mechanoluminescent thin film coated on a solid, then initially the elastico ML (EML) intensity increases with time, attains a maximum value I_m at a particular time t_m, and later on it decreases with time. The contact time T_c of ball, can be determined from the relation T_c=2t_c, where t_c is the time at which the EML emission due to compression of the sample becomes negligible. The area from where the EML emission occurs can be taken as the contact area A_c. The maximum compression h is given by h=A_c/(πr), where r is the radius of the impacting ball, and thus, h can be determined from the known values of A_c and r. The maximum force at contact is given by F_m=(2mU₀)/T_c, where m is the mass of the impacting ball and U₀ is the velocity of the ball at impact. The maximum impact stress σ_m can be obtained from the relation, σ_m=F_m/A_c=(2mU₀)/(T_cA_c). Thus, ML provides a real-time technique for determining the impact parameters such as T_c, A_c, h, F_m and σ_m. Using the ML technique, the impact parameters of the SrAl₂O₄:Eu film and ZnS:Mn coating are determined. The ML technique can be used to determine the impact parameters in the elastic region and plastic region as well as fracture. ML can also be used to determine the impact parameters for the collision between solid and liquid, if the mechanoluminescent material is coated on the surface of the solid. The measurement of fracto ML in microsecond and nanosecond range may provide a tool for studying the fragmentations in solids by the impact. Using the fast camera the contact area and the depth of compression can be determined for different intervals of time.     

YBCO半导体薄膜及Bolometer特性

就Si为衬底的钇钡铜氧(分子式：Y₁Ba₂Cu₃O_7-δ ,δ≥05,简称YBCO)薄膜的半导体性质,及用于红外测辐射热计(Bolometer)的探 测性能进行了研究.通过测定温度电阻系数(TCR)和霍尔(Hall)系数,并采用XRD、拉曼散射 光谱等手段分析了YBCO半导体薄膜的微观结构和光谱响应特性,认为该薄膜是非制冷红外焦 平面的新型探测元材料. 关键词： YBCO半导体薄膜 测辐射热计 温度电阻系数     

Laser-induced desorption of overlayer films off a heated metal substrate

The temperature-induced desorption of adsorbed overlayer films with thicknesses between 4 and 200 ML off a suddenly heated metal substrate is studied using molecular-dynamics simulation. We observe that the rapid heating vaporizes the surface-near part of the overlayer film. The initial heating-induced thermoelastic pressure and the vapor pressure in the vapor film drive the remaining film as a large relatively cold cluster away from the surface. In our simulations, the material present in the developing vapor film amounts to roughly 2 ML and is quite independent of the overlayer film thickness. For cluster thicknesses beyond 40 ML, the desorption time increases only little with film thickness, while the resulting cluster velocity decreases only slightly.     

Nanostructured ZnO thin film for hydrogen peroxide sensing

A thin film of zinc oxide (ZnO) was deposited over the surface of a glass substrate by spray pyrolysis technique. To obtain ZnO thin film with nano-grains in this process, the substrate temperature was optimized and fixed at 503 K. Zinc acetate dihydrate was used as a precursor at an optimal concentration of 0.05 M. The structural and morphological properties of the film were investigated using X-ray Diffraction (XRD) and Field Emission–Scanning Electron Microscopy (FE–SEM), respectively. The peaks in the XRD pattern, confirmed the polycrystalline nature of the film with hexagonal wurtzite structure. Purity of the film has been confirmed through Energy Dispersive X-ray analysis (EDAX). Further the sensing behavior of the film was studied for various concentrations of hydrogen peroxide (H₂O₂) at optimized operating temperatures of 323 and 373 K. The nanostructured ZnO film exhibited good sensitivity in the range of 500 and rapid response–recovery time of 30–60 s, respectively, towards lower concentrations of H₂O₂.     

Magnetic ordering in a [Fe/Co]<Subscript>35</Subscript> BCC film studied by nuclear resonant reflectometry

An analysis of the angular dependences of nuclear resonant reflectivity time spectra for different models of magnetic ordering in films reveals an ambiguity in the magnetization direction determined from spectra measured at one orientation of the sample. This analysis explains features in the spectra of the nuclear resonant reflectivity from a MgO/[Fe(6 ML)/Co(3 ML)]₃₅/V (1 nm) film measured before and after sample rotation by 90° about the normal to the surface. It is shown that the spectrum measured only at one orientation of the sample determines only the effective azimuth angle of magnetization γ^eff. This does not exclude the occurrence of a domain structure, while the angle γ^eff does not correspond to the true direction of the preferred orientation of magnetization. The results of measurements at two orientations of the sample can be satisfactorily matched using a model that considers a coherent mixture of states with magnetization directed along the 〈110〉 axis (77%) and with a chaotic orientation of the magnetic hyperfine field B _hf in the film plane for the other nuclei.     

Surface modification of PDMS using atmospheric glow discharge polymerization of tetrafluoroethane for immobilization of biomolecules

In this study an atmospheric glow discharge with a fluorocarbon gas as precursor was used to modify the surface of polydimethyl siloxane (PDMS -[(CH₃)₂SiO]_n-). The variation in protein immobilizing capability of PDMS was studied for different times of exposure. It was observed that the concentration of proteins adsorbed on the surface varied in an irregular manner with treatment time. The fluorination results in the formation of a thin film of fluorocarbon on the PDMS surface. The AFM and XPS data suggest that the film cracks due to stress and regains its uniformity thereafter. This Stranski-Krastanov growth model of the film was due to the high growth rate offered by atmospheric glow discharge.     

Patterning of porous silicon by metal-assisted chemical etching under open circuit potential conditions

Porous silicon is the most studied Si-based light-emitting material. The potential for the application of porous silicon in optoelectronics and also for chemical or biochemical sensing is high. Therefore, the successful patterning of porous silicon on Si wafers is of great interest. HF-based aqueous solutions containing H₂O₂ as oxidizing agent, in combination with appropriate metal deposition, can supply the necessary current in order to sustain the electrochemical etching of single crystalline Si under no external anodic bias. The H₂O₂ concentration can tune the etching rate of the Si wafers as well as the observed photoluminescence intensity and photon energy. We demonstrate that porous silicon growth can be preferentially initiated at sites where metal (Pt) has been deposited and effectively be confined there, in order to form a well-defined pattern of desired geometry. Conventional DC sputtering using stainless-steel masks was applied in order to test various patterning geometries and lengthscales. Photoluminescence spectroscopy, atomic force and optical microscopy were used in order to characterize the produced porous silicon patterns. This method could be a simple, cost-effective way for the production of porous silicon patterns on Si wafers, which could be used in various fields of application.     

Study on the changes of ultrasonic parameters over supercritical Ni-Co electroplating process

This work discusses the influence of changes to ultrasound (US) parameters over the nickel cobalt (Ni-Co) metal thin film properties produced by supercritical CO₂ (SC-CO₂) electroplating. Additionally, Ni-Co films were produced by conventional electroplating and silent SC-CO₂ and compared against each other.The discussion on metal thin film properties revolves around variations to the bath type ultrasonic power (15 W and 20 W) and frequency (42 k Hz and 72 kHz) during experiments. The properties provided by the three electroplating processes and analyzed include: grain sizes, film elemental content analyses, surface microstructures, film hardness, corrosion resistance, surface roughness, crystalline structure and preferential growth, etc. From the results it was clear that quality of films produced by US-SC-CO₂ was improved compared to that of films produced by silent SC-CO₂, which itself was better than those produced by conventional electroplating. However, when US power was varied we observed a decline in the mechanical properties of the produced films.The combination of ultrasonic agitation with SC-CO₂ allows for improved mechanical properties such as: lower surface roughness, finer grain size and surface morphologies, increased corrosion resistance and film hardness. The ultrasound agitation applied to SC-CO₂ electroplating enhanced the formation of alloyed metal as ultrasonic agitation increased the electrolyte flowability during electroplating process resulting in increased mass transfer while at the same time achieving a surface cleaning effect which removed metal ions with poor adhesion and other unwanted particles. Moreover, application of ultrasonic agitation avoids the use of surfactants so only changes to the physical phenomena and no changes to the chemical composition of the deposited thin films were observed, meaning less pollution to the electrolyte and higher purity of the deposited films.The US-SC-CO₂ electroplating method described in this work effectively enhanced the mechanical properties of the deposited thin films compared to those produced by both silent SC-CO₂ and conventional electroplating processes.     

Properties of the interaction of europium with Si(111) surface

Formation of the Eu/Si(111) system as the metal layer thickness gradually increases from 0.5 to 60 monolayers (ML) deposited on the silicon surface at room temperature, and after heating at up to 900 °C, has been studied by Auger electron spectroscopy, electron-energy-loss spectroscopy, and low-energy-electron diffraction. It is shown that room-temperature film growth passes through three stages, depending on the Eu layer thickness: metal chemisorption, interdiffusion of the metal and substrate atoms, and buildup of the metal on the surface of the system. Heating of ultrathin (about one ML) Eu films deposited at room temperature results in ordering of metal atoms on the silicon surface with only weak interaction. Heating thick (above 15 ML) Eu layers on the silicon surface produces silicides whose structure depends on the heating temperature. Fiz. Tverd. Tela (St. Petersburg) 40, 562–567 (March 1998)     

Change in the C<Subscript>60</Subscript> fullerite film growth mechanism on a sulfur-doped Nb(100) surface observed under changes in the chemical state of the surface

It is shown that the growth of a nanosized fullerite film in the C₆₀ molecules-Nb(100) surface adsorption system depends essentially on the chemical state of adsorbed sulfur. In particular, sulfur as the surface sulfide NbS with a concentration of (9±0.2) × 10¹⁴ cm^?2 has almost no effect on the adsorption: as on the pure metal, fullerene molecules from the first and, partially, second layers undergo considerable degradation and do not desorb at any temperatures upon the subsequent heating. On the contrary, C₆₀ molecules retain their structure on a valence-saturated NbS₂ monolayer with almost the same surface concentration of S atoms, build a fullerite film as crystallites without the formation of an intermediate monolayer (Volmer-Weber mechanism), and completely leave the surface at 800 K, which remains unchanged and uncontaminated.     

Immobilization of bovine serum albumin on TiO2 film via chemisorption of H3PO4 interface and effects on platelets adhesion

In the present study, bovine serum albumin (BSA) was successfully covalently immobilized on the surface of anatase TiO₂ film by a three-step method, i.e. application of H₃PO₄ chemisorption to increase surface -OH, which increases the amount of coupling 3-aminopropyl-triethoxylsilane (APTES), thus linking with BSA by imide bond using EDC/NHS/MES. There is no significant -OH group increase on rutile film when using the same method of phosphoric acid treatment, which suggest it is difficult for further chemical modification of the rutile film. After covalent immobilization of BSA on anatase film, an improved hemocompatibility of anti-platelet adhesion and aggregation in vitro could be recognized by LDH and SEM analysis. This study suggests BSA-immobilized anatase surface can serve as hemocompatibility material in vivo.     

Optical properties of rare earth doped strontium aluminate (SAO) phosphors: A review

After the first news on rare earth (RE) doped strontium aluminate (SAO) phosphors in late 1990s, researchers all over the world geared up to develop stable and efficient persistent phosphors. Scientists studied various features of long lasting phosphors (LLP) and tried to earmark appropriate mechanism. However, about two decades after the discovery of SrAl₂O₄: Eu²⁺, Dy³⁺, the number of persistent luminescent materials is not significant. In this review, we present an overview of the optical characteristics of RE doped SAO phosphors in terms of photoluminescence (PL), thermoluminescence (TL) and afterglow spectra. Also, we refresh the work undertaken to study diverse factors like dopant concentration, temperature, surface energy, role of activator, etc. Simultaneously, some of our important findings on SAO are reported and discussed in the end.     

异质界面对Ca(Mg1/3Nb2/3)O3/CaTiO3叠层薄膜结构和介电性能的影响

采用异质叠层方式制备出一定厚度的Ca(Mg_1/3Nb_2/3)O₃/CaTiO₃(CMN/CT)叠层薄膜,研究了异质界面对薄膜结构、微观形貌及介电性能的影响及其规律.根据实验测试结果,提出CMN/CT叠层薄膜的模拟等效电路,建立介电常数和介电损耗的理论计算公式.结果表明:CMN/CT异质叠层薄膜具有完全正交钙钛矿结构,结构致密,厚度均匀,薄膜中存在独立的CMN和CT相.异质界面处存在过渡层,随着薄膜中异质界面个数增加,介电常数增大,介电损耗减小.减小界面过渡层的厚度,有利于提高CMN/CT叠层薄膜的介电性能.     

Direct conversion of a metal organic compound to epitaxial Sb-doped SnO2 film on a (0 0 1) TiO2 substrate using a KrF laser, and its resulting electrical properties

Epitaxial Sb-doped SnO₂ (0 0 1) thin film on a TiO₂ (0 0 1) substrate was successfully prepared by laser-assisted metal organic deposition at room temperature. The effects of the precursor thin film and laser fluence on the resistivity, carrier concentration, and mobility of the Sb-doped SnO₂ film were investigated. The resistivity of the Sb-doped SnO₂ film prepared by direct irradiation to metal organic film is one order of magnitude lower than that of film prepared by irradiation to amorphous Sb-doped SnO₂ film. From an analysis of Hall measurements, the difference between the resistivity of the Sb-doped SnO₂ film prepared using the metal organic precursor film and that of amorphous precursor film appears to be caused by the mobility. Direct conversion of the metal organic compound by excimer laser irradiation was found to be effective for preparing epitaxial Sb-doped SnO₂ film with low resistivity.