Thermal annealing of arsenic tri-sulphide thin film and its influence on device performance

Arsenic tri-sulphide (As₂S₃)thin filmwaveguides have been used successfully as nonlinear optical devices for all-optical signal processors. For such devices, low propagation loss is vital if high performance is to be obtained. In this study, thermal annealing was employed not only to stabilize the physical properties of the films, but also to reduce the sources of light attenuation in the as-deposited material. Here we investigated heat-induced changes to the microstructure and optical properties of As₂S₃thin films and, based on this information, determined the best annealing conditions. The refractive index of the films rises with annealing due to thermal densification and increased heteropolar bond density. The growth of surface roughness and thermal stress in the film, however, limits the annealing temperature to ∼130 °C. We fabricated and analyzed waveguides produced from as-deposited and annealedfilms and found that the propagation loss of the guides dropped by ∼0.2 dB/cm as a result of appropriate annealing.Rayleigh scattering and absorption from defects associated with phase separation, homopolar bonds, voids, and dangling bonds in the as-deposited film are shown to contribute to the higher light attenuation in unannealed films.This research was supported by the Australian Research Council through its Centre of Excellence program

Transition threshold in Ge x Sb 10 Se 90-x glasses

GexSb10Se90-x glasses with Ge content from 7.5 to 32.5at.% have been prepared by melt-quench technique, and the physical parameters including glass transition temperature (Tg), density (ρ), compactness (C), shear elastic moduli (Cs), compression elasti

Conversion of p–n conduction type by spinodal decomposition in Zn-Sb-Bi phase-change alloys

Phase-change films with multiple resistance levels are promising for increasing the storage density in phase-change memory technology. Diffusion-dominated Zn2Sb3 films undergo transitions across three states, from high through intermediate to low resistance, upon annealing. The properties of the Zn2Sb3 material can be further optimized by doping with Bi. Based on scanning transmission electron microscopy combined with electrical transport measurements, at a particular Bi concentration, the conduction of Zn-Sb-Bi compounds changes from p- to n-type, originating from spinodal decomposition. Simultaneously, the change in the temperature coefficient of resistivity shows a metal-to-insulator transition. Further analysis of microstructure characteristics reveals that the distribution of the Bi-Sb phase may be the origin of the driving force for the p–n conduction and metal-to-insulator transitions and therefore may provide us with another way to improve multilevel data storage. Moreover, the Bi doping promotes the thermoelectric properties of the studied alloys, leading to higher values of the power factor compared to known reported structures. The present study sheds valuable light on the spinodal decomposition process caused by Bi doping, which can also occur in a wide variety of chalcogenide-based phase-change materials. In addition, the study provides a new strategy for realizing novel p–n heterostructures for multilevel data storage and thermoelectric applications

Partial masquerading and background matching in two Asian box turtle species (<i>Cuora</i> spp.)

Animals living in heterogeneous natural environments adopt different camouflage strategies against different backgrounds, and behavioral adaptation is crucial for their survival. However, studies of camouflage strategies have not always quantified the effect of multiple strategies used together. In the present study, we used a human visual model to quantify similarities in color and shape between the carapace patterns of two Cuora species and their preferred habitats. Our results showed that the color of the middle stripe on the carapace of Cuora galbinifrons (Indochinese box turtle) was significantly similar to the color of their preferred substrates. Meanwhile, the middle stripe on the carapace of C. mouhotii (keeled box turtle) contrasted more with their preferred substrates, and the side stripe matched most closely with the environment. Furthermore, the carapace side stripe of C. galbinifrons and the carapace middle stripe of C. mouhotii highly contrasted with their preferred substrates. We quantified the similarity in shape between the high-contrast stripes of both Cuora species and leaves from their habitats. The carapace middle stripe of C. mouhotii was most similar in shape to leaves from the broad-leaves substrate, and the carapace side stripe of C. galbinifrons was the most similar in shape to leaves from the bamboo-leaves substrate. We determined that these species adopt partial masquerading when their entire carapace is exposed and partially match their background when they semi-cover themselves in leaf litter. To the best of our knowledge, this is the first study to demonstrate that partial masquerading and background matching improve the camouflage effect of Asian box turtles in their preferred habitats. This is a novel study focusing on the influence of the shape and color of individual carapace segments on reducing detectability and recognition.</p

The Impact of Thermal- and Photo-annealing of Chalcogenide Films for Optical Waveguides

We applied thermal- and band-edge light annealing on an as-deposited As2S3 film to mitigate its phase separation and, thus to improve the propagation losses of fabricated optical waveguides. Studies of the film micro structure revealed a difference between atomic bonds and linked phases among the as-deposited, thermally-annealed, and optically-annealed films. We fabricated rib-type waveguides with 4 micron width from 0.85 μm thick films, and measured the insertion losses. Around 0.4 and 0.2 dB/cm propagation losses were obtained in the waveguides produced from as-deposited and annealed films, respectively. The waveguides produced from photo-annealed film showed almost the same propagation losses to those from thermally-annealed material. Our results, however, indicate optical-annealing provides some advantages over thermal annealing for waveguide fabrication, such as the absence of film cracking which observed at high temperature processing

The feasibility of Sn, In, or Al doped ZnSb thin film as candidates for phase change material

The potentials of Sn, In, or Al doped ZnSb thin film as candidates for phase change materials have been studied in this paper. It was found that the Zn-Sb bonds were broken by the addition of the dopants and homopolar Zn-Zn bonds and other heteropolar bonds, such as Sn-Sb, In-Sb, and Al-Sb, were subsequently formed. The existence of homopolar Sn-Sn and In-In bonds in Zn₅₀Sb₃₆Sn₁₄ and Zn₄₁Sb₃₆In₂₃ films, but no any Al-Al bonds in Zn₃₅Sb₃₀Al₃₅ film, was confirmed. All these three amorphous films crystallize with the appearance of crystalline rhombohedral Sb phase, and Zn₃₅Sb₃₅Al₃₅ film even exhibits a second crystallization process where the crystalline AlSb phase is separated out. The Zn₃₅Sb₃₀Al₃₅ film exhibits a reversible phase change behavior with a larger Ea ( 4.7 eV), higher Tc (~ 245ᴼ C), better 10-yr data retention (~ 182ᴼ C), less incubation time (20 ns at 70 mW), and faster complete crystallization speed (45 ns at 70 mW). Moreover, Zn₃₅Sb₃₀Al₃₅ film shows the smaller root-mean-square (1.654 nm) and less change of the thickness between amorphous and crystalline state (7.5%), which are in favor of improving the reliability of phase change memory.This work was financially supported by the Natural Science Foundation of China (Grant Nos. 61306147, 61377061), the Public Project of Zhejiang Province (Grant No.2014C31146), the Young Leaders of academic climbing project of the Education Department of Zhejiang Province (pd2013092), the Natural Science Foundation of Zhejiang Province (Grant No. LQ15F040002), the Scientific Research Foundation of Graduate School of Ningbo University, and sponsored by K. C. Wong Magna Fund in Ningbo University

Nanoscale phase separation in ultrafast pulsed laser deposited arsenic trisulfide (As₂S₃) films and its effect on plasma etching

We have observed nanoscale phase separation in amorphous arsenic trisulfide (As₂S₃)films produced by ultrafast pulsed laser deposition and its effect on the surface morphology of the film after plasma etching. When the film was etched in CF₄–O₂plasma, a grainy structure was observed on the surface. From Raman and x-ray photoelectron spectroscopies, we concluded that the grainy structure of the etchedsurfaces comes from the differential chemical attack between different phases in the film.This research was supported by the Australian Research Council through its Centres of Excellence and Federation Fellow Programs

The evolution of bond structure in Ge33As12Se55 films upon thermal annealing

The evolution of bond structure of laser deposited Ge33As12Se55 films under various processing conditions has been investigated by X-ray photoelectron spectroscopy. It was found that a large number of Se-rich structures in the as-grown film may coalesce with As and Ge after annealing at high temperatures. In addition, both Ge and As 3d spectra show the presence of oxides. The oxygen distribution exponentially decays along the normal direction of the films regardless of different processing conditions. The critical thickness of the oxidized layer was extracted for the film annealed at various pressures and temperatures

Annealing induced phase transformations in amorphous As2S3 films

Amorphous arsenic sulphide (As2S3) films prepared by ultrafast pulsed laser deposition have been vacuum annealed at a range of different temperatures. Measurements of the glass transition temperature indicate that a crystallization process initiates at annealing temperatures around 170 °C. In combination with Raman scattering analysis, we conclude that phase separation is intrinsic for our as-deposited films. During annealing two sorts of phase transformation are identified: one between different amorphous polymorphs, and another from the amorphous to a crystalline state. We point out a correlation between these two types of transformation and two characteristic time scales identified from measurements of the relaxation of the refractive index, and explain the Arrhenius and non-Arrhenius behaviors leading to the observed temporal characteristic