X‐ray photoelectron spectroscopy analysis of Ge–Sb–Se pulsed laser deposited thin films

Pulsed laser deposition was used to prepare amorphous thin films from (GeSe₂)_100?x(Sb₂Se₃)_x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe₄] and [SbSe₃] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)₃ and (Ge,Sb)–Sb–(Se)₂ entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.     

Compositional dependence of crystallization in Ge–Sb–Se glasses relevant to optical fiber making

For fiber‐optic mid‐infrared bio‐ and chemical‐sensing, Ge–Sb–Se glass optical fibers are more attractive than Ge–As–Se because of: (i) lowered toxicity and (ii) lower phonon energy and hence transmission to longer wavelengths, with potential to reach the spectral “fingerprint region” for molecular sensing. There is little previous work on Ge–Sb–Se fibers. Here, fibers are fabricated from two glass compositions in the Ge_xSb₁₀Se_90?x atomic (at.) % series. Both glass compositions are of similar mean‐coordination‐number, lying in the overconstrained region, yet of different chemical composition: stoichiometric Ge₂₅Sb₁₀Se₆₅ at. % and non‐stoichiometric Ge₂₀Sb₁₀Se₇₀ at. %. Thermal analysis on bulk glasses has previously shown that the former exhibited the maximum glass stability of the series. However, during fiber‐drawing of Ge₂₅Sb₁₀Se₆₅ at. %, the preform tip is found to undergo surface‐devitrification to monoclinic GeSe₂ alone, the primary phase, no matter if the preform is an annealed, as‐melted rod or annealed, extruded rod. The heating rate of the preform‐tip to the fiber‐drawing temperature is estimated to be up to ~100°C/min to ~490°C. Lower heating rates of 10°C/min using thermal analysis, in contrast, encourage crystallization of both Sb₂Se₃ and GeSe₂. The non‐stoichiometric: Ge₂₀Sb₁₀Se₇₀ at. % composition drew successfully to low optical loss fiber, no matter whether the preform was an annealed, as‐melted rod or annealed, extruded rod.     

Correlating Structure with Threshold Behavior of Chalcogenide Glasses Within Ge–Sn–Se Ternary System

A systematic investigation of the optical and structural properties of chalcogenide glasses in Ge–Sn–Se ternary system is presented. We have found a threshold behavior of optical property, namely, existence of transitional composition of the Ge–Sn–Se glasses, with progressive replacement of Se by Sn. Calculation of mean coordination number indicates that the transition‐like feature of optical property is associated with the evolution of chemical ordering of the Ge–Sn–Se network. Analysis of Raman spectra of the glasses explains that the interaction between Se–Se bonds, Sn(Se_1/2)₄ tetrahedra, and Sn–Sn homopolar bonds is the origination of such optical phenomenon.     

Germanium-antimony-selenium-tellurium thin films: Clusters formation by laser ablation and comparison with clusters from mixtures of elements

Quaternary germanium-antimony-selenium-tellurium (Ge-Sb-Se-Te) thin films deposited from Ge_19.4Sb_16.7Se_63.9−xTe_x (x = 5, 10, 15, and 20) glass-ceramics targets by radio frequency magnetron sputtering were studied using laser ablation quadrupole ion trap time of flight mass spectrometry. Binary, ternary, and quaternary Ge_aSb_bSe_cTe_d clusters were formed and their stoichiometry was determined. By comparison of the clusters obtained from quaternary Ge-Sb-Se-Te thin films and those from ternary Ge-Sb-Te materials, we found that Ge-Te species are not detected from the quaternary system. Furthermore, Ge-Se and Se-Te species are missing in mass spectra generated from Ge-Sb-Se-Te thin films. From the Ge-Sb-Se-Te thin films, 16 clusters were detected while ternary Ge-Sb-Se glasses yielded 26 species. This might be considered as a signal of higher stability of Ge-Sb-Se-Te thin films which is increasing with a higher content of Te. The missing (Se₂⁺, Ge_aSb⁺ (a = 1–4), and GeSe_c⁺ (c = 1, 2)) and new (Ge⁺ and Sb_bTe⁺ (b = 1–3)) clusters may indicate that some of the structural features of the films (Ge₂Se_6/2 and Se₂Sb-SbSe₂) were replaced by (GeSe_4−xTe_x and SbSe_3−xTe_x) ones. In addition, when comparing the stoichiometry of clusters formed from Ge-Sb-Se-Te thin films with those from the mixtures of the elements, only Sb₃⁺ and SbSe⁺ were observed in both cases. The knowledge gained concerning clusters stoichiometry contributes to the elucidation of the processes proceeding during plasma formation used for the chalcogenide thin films deposition.     

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry of Glasses and Amorphous Films from Ge–As–Se System

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry was exploited for the characterization of Ge–As–Se chalcogenide glasses and corresponding thin films fabricated using pulsed laser deposition. Main achievement of the paper is the determination of laser generated clusters’ stoichiometry. The clusters observed were As_b⁺ (b = 1–3), Se₂^?, binary As_bSe⁺ (b = 1–3), As_bSe_c^? (b = 1–3, c = 1–4), Ge₂Se_c^? (c = 2–3), As₃Se₂⁺, Ge₂As_b^? (b = 2–3), Ge₃As_b^? (b = 1–2), Ge₃Se₄^?, As₅Se_c^? (c = 4–5), GeAsSe₄^?, Ge_aAsSe₅^? (a = 1–4), GeAs₂Se₃^?, GeAs₃Se₂^?, Ge₂As₂Se₂^?, Ge₂AsSe_c^? (c = 6–7), and GeAs₃Se_c^? (c = 5–6) (in positive as well as in negative ion mode). The stoichiometries of identified species are compared with the structural units of the glasses/thin films revealed via Raman scattering spectra analysis. Some species are suggested to be fragments of bulk glass as well as thin films. Described method is useful also for the evaluation of the contamination of chalcogenide glasses or their thin films.     

Synthesis and properties of KTN films by sol-gel deposition and RF-magnetron sputtering

Homogeneous KTN (Potassium Tantalate Niobate) solutions were prepared using potassium acetate and metal alkoxides in 2-methoxyethanol by controlled hydrolysis with 1:2 (KTN/H₂O) molar ratio. We report on the synthesis of sol-gel KTN for both the fabrication of homogeneous, dense and stoichiometrically correct ceramic discs by hot isostatic pressing and the deposition of spin-on as well as sputtered thin films. The spin-on KTN films on Pt/Si or r-sapphire were polycrystalline and stoichiometric, however, sputtered films on sapphire were fully (100) oriented and polycrystalline on Pt/SiO₂/Si substrates with some potassium deficiency. The refractive indices of sputtered, dense KTN films on sapphire were between 2.00 and 2.05.     

Microwave dielectric and nonlinear optical studies on radio‐frequency sputtered Dy2O3‐doped KNN thin films

We report the effect of oxygen mixing percentage (OMP) on structural, microstructural, dielectric, linear, and nonlinear optical properties of Dy₂O₃‐doped (K_0.5Na_0.5)NbO₃ thin films. The (K_0.5Na_0.5)NbO₃ + 0.5 wt%Dy₂O₃ (KNN05D) ferroelectric thin films were deposited on to quartz and Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering. An increase in the refractive index from 2.08 to 2.21 and a decrease in the optical bandgap from 4.30 to 4.28 eV indicate the improvement in crystallinity, which is also confirmed from Raman studies. A high relative permittivity (ε_r=281‐332) and low loss tangent (tanδ=1.2%‐1.9%) were obtained for the films deposited in 100% OMP, measured at microwave frequencies (5‐15 GHz). The leakage current of the films found to be as low as 9.90×10^?9 A/cm² at 150 kV/cm and Poole‐Frenkel emission is the dominant conduction mechanism in the films. The third order nonlinear optical properties of the KNN05D films were investigated using modified single beam z‐scan method. The third order nonlinear susceptibility (?χ⁽³⁾?) values of KNN05D films increased from 0.69×10^?3 esu to 1.40×10^?3 esu with an increase in OMP. The larger and positive nonlinear refractive index n₂=7.04×10^?6 cm²/W, and nonlinear absorption coefficient β=1.70 cm/W were obtained for the 100% OMP film, indicating that KNN05D films are good candidates for the applications in nonlinear photonics and high‐frequency devices.     

Magneto‐optical effects of Ge‐Ga‐Sb(In)‐S chalcogenide glasses with diamagnetic responses

The Faraday effects of Ge‐Ga‐Sb(In)‐S serial chalcogenide glasses were investigated at the wavelengths of 635, 808, 980, and 1319 nm, respectively. The compositional dependences were analyzed and associated influencing factors including the absorption edge, the concentration of Sb³⁺/In³⁺ ions, and the wavelength dispersion of refraction index were discussed. 80GeS₂·20Sb₂S₃ composition glass was found to have the largest Verdet constant (V=0.253, 0.219, 0.149, and 0.065 min·G^?1·cm^?1 for wavelengths 635, 808, 980, and 1319 nm, respectively) in these glasses, which is larger than that of commercial diamagnetic glasses (Schott, SF 6, V=0.069 min·G^?1·cm^?1@633 nm, for example). Sb³⁺ ions with high polarizability possessing s²‐sp electron jumps involving ¹S₀→¹P₁, ³P_0,1,2 transitions are responsible for large Verdet constant, and Becquerel rule is proved to be an effective guidance for estimating the Verdet constant and further optimizing the compositions in chalcogenide glasses.     

Thickness‐dependent domain wall reorientation in 70/30 lead magnesium niobate‐ lead titanate thin films

Continued reduction in length scales associated with many ferroelectric film‐based technologies is contingent on retaining the functional properties as the film thickness is reduced. Epitaxial and polycrystalline lead magnesium niobate‐lead titanate (70PMN‐30PT) thin films were studied over the thickness range of 100‐350 nm for the relative contributions to property thickness dependence from interfacial and grain‐boundary low permittivity layers. Epitaxial PMN‐PT films were grown on SrRuO₃/(001)SrTiO₃, while polycrystalline films with {001}‐Lotgering factors >0.96 were grown on Pt/TiO₂/SiO₂/Si substrates via chemical solution deposition. Both film types exhibited similar relative permittivities of ~300 at high fields at all measured thicknesses with highly crystalline electrode/dielectric interfaces. These results, with the DC‐biased and temperature‐dependent dielectric characterization, suggest irreversible domain wall mobility is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films, the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The temperature at which a peak in the relative permittivity is observed was the only measured small signal quantity which was more thickness‐dependent in polycrystalline than epitaxial films. This is attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. Finally, the effective interfacial layers are found to contribute to the measured thickness dependence in the longitudinal piezoelectric coefficient.     

Composition control of lead-free piezoelectric BNT thin ceramic films deposited by ex situ sputtering

(Bi_0.5Na_0.5)TiO₃ thin film growth by ex situ sputtering has been investigated and reported in this paper. An original approach, based on the growth process, was used in order to precisely control the film composition, which has never been reported in BNT growth. The bismuth content in the films and so the composition of amorphous sputtered films was controlled by a slight heating of the substrate during the growth (150–240°C). Then, films were crystallized, obviously without any change in composition, by a post-annealing treatment. More precisely, without substrate heating and using a stoichiometric target, the film presents an excess of Bi but when it is deposited at 200°C the film becomes stoichiometric. It was shown that the sticking coefficient of Bi is particularly sensitive even at low substrate temperatures, whereas Na and Ti sticking coefficients are not impacted. Followed by a post-annealing in air at 650°C, the composition of the amorphous BNT films deposited at 200°C remains stoichiometric and the film exhibits a high (100) preferred orientation in a pure perovskite phase and a dense microstructure. The evaluation of the electrical properties as a function of the Bi content in the film, adjusted by the deposition temperature, shows a strong impact on the ferroelectric properties where the best performances were obtained with the stoichiometric BNT film deposited at 200°C.     

Structure and physical properties of Ge15Sb20Se65‐xSx glasses

We explored the structure and physical properties of Ge₁₅Sb₂₀Se_65‐xS_x (with x = 0, 16.25, 32.5, 48.75, and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se‐based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature T_g, optical bandgap E_g and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high‐resolution X‐ray photoelectron spectra to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge–Se/S, Sb–Se/S) were dominated in these glasses. With the increase in chalcogen Se/S ratio, the number of the Se‐related chemical bonds (Ge–Se, Sb–Se and Se–Se) increased and that of S‐related chemical bond (Ge–S, Sb–S and S–S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S–Ge(Sb) and Se–Ge(Sb).     

Compositional dependence of the optical properties of novel Ga–Sb–S–XI (XI = PbI2, CsI,AgI) infrared chalcogenide glasses

A novel family of Ga₂S₃–Sb₂S₃–XI (XI = PbI₂, CsI, AgI) was investigated to understand the role of metal halides and exploit new chalco‐halide glasses for infrared optics. The dependence of the thermal properties, infrared optical properties, and structural information of the novel family on different metal–iodines was investigated. Results showed that metal halides increase the glass stability but decrease the glass network connectivity. The compositional dependence of the short‐wave cut‐off edge is associated with the electronegativity difference between the cations and anions of the metal halides. Raman study showed that the metal–iodine modified the glass structure mainly through the iodide content, and the cations dissolved in the glass network mostly as charge compensators for the aperiodic network. For the glasses in the series Ga₂S₃–Sb₂S₃–XI–Dy³⁺, Dy³⁺ emission increased in the PbI₂‐ and CsI‐doped glasses but decreased in the AgI‐doped glass due to the combined effect of dysprosium and oxygen. For all that, these novel glasses are highly promised for use in infrared optics.     

高介电HfO_xN_y薄膜的制备及其光学性能研究

采用直流反应磁控溅射方法,在硅衬底制备了高介电HfOxNy薄膜。用椭偏仪研究了后期退火处理对薄膜光学性质的影响,结果表明,薄膜的折射率随退火温度的升高而增加,这主要是由于高温退火导致薄膜内部缺陷减少,使得薄膜松散的内部结构变得更加致密;薄膜的消光系数随退火温度的升高而降低,这是由于因为退火后薄膜内的缺陷减少。光学禁带宽度随退火温度的升高而增加,这是由于退火过程中薄膜中N含量的减少而导致。     

衬底温度对HfO_xN_y薄膜相关物性的影响

采用射频反应磁控溅射法制备了HfOxNy栅介质薄膜,并研究了HfOxNy栅介质薄膜的化学特性和界面结构随淀积温度的变化而发生的变化规律。光电子能谱测试表明,随着衬底温度的升高,薄膜中的氮含量也随之增加。傅立叶红外吸收光谱研究表明,随着淀积温度的增加,界面层SiO2的厚度也逐渐增高。     

High‐performance varistors prepared by hot‐dipping tin oxide thin films in Sb2O3 powder: Influence of temperature

A series of SnO_x–Sb₂O₃ thin film varistors were fabricated through hot‐dipping tin oxide films deposited by radio‐frequency magnetron sputtering in Sb₂O₃ powder at varied temperatures in air. With the increase in hot‐dipping temperature (HDT) from 200°C to 600°C, the nonlinear coefficient (α) of the samples increased first and then decreased, reaching the maximum at 500°C, which was mainly determined by the completeness of high‐resistant Sb₂O₃ layer at tin oxide grain boundary and the chemical composition of tin oxide films. Correspondingly, the leakage current (I_L) decreased first and increased later. The breakdown electric field (E_100 mA) decreased constantly with increasing HDT. The SnO_x–Sb₂O₃ film varistors prepared at 500°C exhibited the optimum nonlinear properties with the maximum α of 10.88, the minimum I_L of 36.3 mA/cm², and an E_100mA of 0.0188 V/nm. The obtained nanoscaled film varistors would be promising in electrical/electronic devices working in low voltage.     

采用磁控溅射法在细菌纤维素膜上制备高性能的铟锡氧化物薄膜

Microbial cellulose (MC) membranes produced by Acetobacter xylinum NUST4.1,were used as flexible substrates for the fabrication of transparent indium tin oxide (ITO) electrodes.Transparent and conductive ITO thin films were deposited on MC membrane at room temperature using radio frequency (RF) magnetron sputtering.The optimum ITO deposition conditions were achieved by examining crystalline structure,surface morphology and op-toelectrical characteristics with X-ray diffraction (XRD),scanning electron microscopy (SEM),atomic force mi-croscopy (AFM),and UV spectroscopy.The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated.The results reveal that the preferred orientation of the deposited ITO crystals is strongly dependent upon with oxygen content (O2/Ar,volume ratio) in the sputtering chamber.And the ITO crystalline structure directly determines the conductivity of ITO-deposited films.High conductive [sheet resis-tance ～120 Ω·square-1 (Ω·sq-1)] and transparent (above 76%) ITO thin films (240 nm thick) were obtained with a moderate sputtering power (about 60 W) and with an oxygen flow rate of 0.25 ml·min-1 (sccm) during the deposi-tion.These results show that the ITO-MC electrodes can find their potential application in optoelectrical devices.     

Direct visualization of magnetic‐field‐induced magnetoelectric switching in multiferroic aurivillius phase thin films

Multiferroic materials displaying coupled ferroelectric and ferromagnetic order parameters could provide a means for data storage whereby bits could be written electrically and read magnetically, or vice versa. Thin films of Aurivillius phase Bi₆Ti_2.8Fe_1.52Mn_0.68O₁₈, previously prepared by a chemical solution deposition (CSD) technique, are multiferroics demonstrating magnetoelectric coupling at room temperature. Here, we demonstrate the growth of a similar composition, Bi₆Ti_2.99Fe_1.46Mn_0.55O₁₈, via the liquid injection chemical vapor deposition technique. High‐resolution magnetic measurements reveal a considerably higher in‐plane ferromagnetic signature than CSD grown films (M_S=24.25 emu/g (215 emu/cm³), M_R=9.916 emu/g (81.5 emu/cm³), H_C=170 Oe). A statistical analysis of the results from a thorough microstructural examination of the samples, allows us to conclude that the ferromagnetic signature can be attributed to the Aurivillius phase, with a confidence level of 99.95%. In addition, we report the direct piezoresponse force microscopy visualization of ferroelectric switching while going through a full in‐plane magnetic field cycle, where increased volumes (8.6% to 14% compared with 4% to 7% for the CSD‐grown films) of the film engage in magnetoelectric coupling and demonstrate both irreversible and reversible magnetoelectric domain switching.     

(001)-oriented BiFeO3 films integrated on Si with enhanced electrical performances

Highly (001)-oriented pure-phase BFO films were prepared on traditional Si substrates via radio frequency magnetron sputtering (RFMS). The crystallinity of the films is found to be increased, that is, higher degree of (001) texture, larger grain size, less grain boundary, denser surface morphology, and better thickness uniformity, with increased film thickness. These factors have significant influences on the electrical properties of BFO films, that is, dielectric response, as well as ferroelectric polarization and leakage current characteristics. The 240-nm-thick film exhibits relatively poor electrical properties compared with other three thicker films, which is mainly due to its small grain, the enhancement of the clamping effect of neighboring grains, and the absence of domain walls. The essential roles of the evolution and distribution of grains/domains and defect charges in leakage mechanism and ferroelectric switching polarization were also investigated systematically. It was found that 600-nm-thick BFO film has the lowest leakage current density (as low as 1.8 × 10⁻⁶ A / cm² @ 90 kV/cm) and followed a mixed SE or SCLC conduction behavior, while the leakage behavior in other films is dominated by SE and P-F currents. All (001)-BFO films have a giant electrical polarization which is solely originated from the contribution of ferroelectric domain switching, and it has lower switching voltage and faster switching rate in thicker films.