Amorphous-crystalline Phase Transition Research Articles

Strong and Fatigue-Resistant Carbon Nanotube Composites Enabled by Amorphous/Crystalline Heterophase Shell.

Lightweight materials with high strength and long cyclic lifespan are greatly demanded in practical applications, yet these properties are usually mutually exclusive. Here, we present a strong, lightweight, highly deformation-tolerant, and fatigue-resistant carbon nanotube (CNT) composite enabled by an amorphous/crystalline heterophase carbon shell. In particular, we obtain nanocrystallites with CNT-induced crystalline orientation uniformly embedded within an amorphous matrix by controlled thermal annealing. The heterophase carbon shell effectively alleviates the stress concentration and inhibits crack propagation, which renders our composite superior mechanical properties and high fatigue resistance (106 compression cycles at 20% strain with high stress of 144 kPa, or 5 × 105 cycles at 50% strain with stress up to 260 kPa). This study provides a deep understanding of amorphous-crystalline phase transition and insight into utilizing phase engineering to design and develop other high-performance functional materials such as structural materials and catalysis.

Amorphous-crystalline phase transition and intrinsic magnetic property of nickel organic framework for easy immobilization and recycling of β-Galactosidase

This work describes the synthesis of fibrous nickel-based metal organic framework (Ni-ZIF) via simple solvothermal method. The material formed was calcinated at 400, 600, 800 °C to improve its surface area, porosity and enzyme binding capacity. Changes in X-ray diffraction pattern after calcination revealed the Ni-ZIF transitioned from amorphous to crystalline structure. The surface area, pore volume and pore size for Ni-ZIF@600 were found to be 312.15 m2/g, 0.88 cm3/g and 10.28 nm, with an enzyme loading capacity of 593.85 mg/g after 30 h The free (β-Gal-LEH) and immobilized β-Galactosidase were stable at pH 7.5, temperature 50 °C, and yielded 70.70 and 63.95 mM glucose after milk lactose hydrolysis, respectively. The Ni-ZIF@600@β-Gal-LEH exhibited high enzyme retention capacity, maintaining 59.44 % of its original activity after 6-cycles. The enhanced magnetic property, enzyme binding capacity and easy recoverability of the calcinated Ni-ZIF could guarantee its industrial significance as immobilization module for enzyme-mediated catalysis.

Effect of Amorphous-Crystalline Phase Transition on Superlubric Sliding

Structural superlubricity describes the state of greatly reduced friction between incommensurate atomically flat surfaces. Theory predicts that, in the superlubric state, the remaining friction sensitively depends on the exact structural configuration. In particular the friction of amorphous and crystalline structures for, otherwise, identical interfaces should be markedly different. Here, we measure friction of antimony nanoparticles on graphite as a function of temperature between 300 and 750K. We observe a characteristic change of friction when passing the amorphous-crystalline phase transition above 420K, which shows irreversibility upon cooling. The friction data is modeled with a combination of an area scaling law and a Prandtl-Tomlinson type temperature activation. We find that the characteristic scaling factor γ, which is a fingerprint of the structural state of the interface, is reduced by 20% when passing the phase transition. This validates the concept that structural superlubricity is determined by the effectiveness of atomic force canceling processes.

Bound states in the continuum versus material losses: Ge2Sb2Te5 as an example

Photonic bound states in the continuum (BI\cyrchar\CYRS{}s) were investigated depending on material and radiation losses on the example of the phase-change chalcogenide ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ and two types of resonators in the form of a cylinder and a ring which support quasi-BIC according to the Friedrich-Wintgen mechanism. The complex refractive index for the amorphous and crystalline phases of ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ was measured experimentally. It was found that as the material losses increase, the quasi-BIC becomes practically a dark mode, while the usual resonator eigenmodes continue to remain intense. At the same time the strength of the mode coupling has been not affected, that is, the Rabi splitting remains unchanged in the studied range of losses. Photonic mode switching during the amorphous-crystalline phase transition was also investigated and two mechanisms were identified, including an efficient Fano resonance mechanism that can be used in real devices.

Mechano-induced photoluminescence colour change in tetraphenylethylene -based aza-N,O-chelated boron difluoride complexes

Two new asymmetric aza-N,O-chelated organoboron complexes DMFPT ((E)-5-(4-(dimethylamino)phenyl)-2,2-difluoro-3-(4-(1,2,2-triphenylvinyl)benzylidene)-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide) and DFPT ((E)-2,2-difluoro-5-phenyl-3-(4-(1,2,2-triphenylvinyl)benzylidene)-2,3-dihydro-1,3,4,2-oxadiazaborol-3-ium-2-uide) have been designed and synthesized. The incorporation of a dimethylamino donor unit into organoboron complexes resulted in a more pronounced AIE and mechanofluorochromic response. PXRD (powder X-ray diffraction), DSC (differential scanning calorimetry) and spectral data indicated that the reversible mechanofluorochromic behavior of the two asymmetric organoboron compounds was attributed to the crystalline-amorphous phase transition. The planarization of the molecular conformation and subsequent PICT (planar intramolecular charge transfer) resulted in the red-shift of fluorescence spectra upon grinding. The newly emerged organoborons may be the candidates for potential applications in sensing, and optical data storage fields, and so on. We expect the obtained results would be helpful to promote the future design and applications of more advanced aza-N,O-chelated organoboron based dyes.

Supporting plasma processes for fabrication of n-doped nano-crystalline silicon thin film on low-cost glass substrates

Nano-crystalline silicon is an excellent material for applications in the optoelectronics industry. This intermediate material combines both the advantages of amorphous and crystalline silicon. However, the typical fabrication process of nano-crystalline silicon previously required high-quality substrates such as quartz or silicon wafers, which limited its potential applications. Recently, plasma treatments have been recognized as the most efficient and customizable methods for transforming materials. In this study, corona plasma was used to treat the low-cost glass substrates to improve their adhesion to silicon thin films. It allowed the film to become more uniform with a surface roughness of less than 10% at the thickness of about 1 μm. The conventional thermal annealing process was replaced by a high-power hydrogen plasma process, which does not cause harmful effects on the glass substrates and stimulates the amorphous-crystalline phase transition. The increasing of the crystalline fraction, which is known as the order of arrangement of silicon atoms network, affects the doped concentration as well as the electrical properties of the nc-Si:H thin films. The resulting n-doped nano-crystalline silicon thin film has a crystalline fraction of 32.8%, corresponding to a sheet resistance of 104 Ω/square.

Pre-Crystallization Criteria and Triple Crystallization Kinetic Parameters of Amorphous–Crystalline Phase Transition of As40S45Se15 Alloy

This framework focuses mainly on a detailed study of the pre-crystallization criteria that characterize the As40S45Se15 glassy alloy in various heating rates ranging from 5 to 40 (K/min) by Differential Scanning Calorimetry (DSC). These criteria aim to clarify the relationship of the tendency of glass-forming by the heating rate for the investigated glassy alloy. The crystallization parameters were calculated using different methods.The activation energy of crystallization Ec(χ) as a function of conversion (χ) was obtained using the iso-conversional models of Flynn–Wall–Ozawa (FWO), Starink and Kissinger–Akahira–Sunose (KAS). The results show a slight increase of Ec(χ) with conversion (χ) which accounts for a single-step mechanism controlling the crystallization process. Moreever, the conversion dependence of the Avrami exponent n(χ) show an increase with conversion (χ), average values of n(χ) can be accounted for two and three-dimensional crystal growth with heterogeneous nucleation. On the other hand, the fitting of the experimental DSC data to the calculated DSC curves indicated that the crystallization process of the studied glasses cannot be satisfactorily described by the Johnson–Mehl–Avrami (JMA) model. On the contrary (SB) model is more suitable to describe the crystallization process for the studied of As40S45Se15 Alloy. Finally, the crystalline structure of the study sample was recognized by X-ray diffraction (XRD) and electron scanning microscope (SEM).

Compositions, structures, and mid-infrared transparency of Sb–Te–Se thin films synthesized using a combinatorial method

The dielectric function of phase-change materials (PCMs) presents a tremendous difference for the amorphous and crystalline states. Therefore, the measurement of the mid-infrared transparency of thin films of PCMs will provide a cost-efficient method to reveal the dependence of amorphous-crystalline phase transition on their compositions. Although Sb–Te–Se system has shown the advantages of the high speed, low power consumption and long retention life, the information on the mid-infrared transparency of Sb–Te–Se thin films is still insufficient. In our investigation, combinatorial materials libraries of Sb–Te–Se thin films were synthesized. The composition and mid-infrared spectral transmittance of each pixel of Sb–Te–Se thin film in the library were characterized using the energy dispersive X-ray analysis (EDX) and Fourier-transform infrared (FTIR) spectrometer, respectively. The in-depth chemical composition for randomly selected pixels was identified using secondary ions mass spectroscopy (SIMS). The crystallographic structure of some pixels was also identified using micro-area X-ray diffraction (μ-XRD). It can be found that, with the change of composition in Sb–Te–Se thin films, their mid-infrared spectral transmittance can be organized into three distinctive groups, corresponding to amorphous Sb–Se, Sb2Se3 orthorhombic structure and Sb2Te3 rhombohedral structure, respectively. Therefore, the amorphous-crystalline phase transition and the phase-change from the orthorhombic structure of Sb2Se3 to the rhombohedral structure of Sb2Te3 can be completely reflected in the mid-infrared spectral transmittance of Sb–Te–Se thin films.

Proposal for a universal nonvolatile logic device based on the phase change magnetic material

Memory devices that are capable of logic functions have shown great potential in constructing non-von Neumann parallel computing architecture. Here, we proposed a universal nonvolatile logic device, utilizing the amorphous–crystalline phase transition behavior and phase change control of ferromagnetism property of Mn-doped GeTe phase change magnetic material (PCMM). The materials implication (IMP) logic in one step and sequential NAND logic were presented theoretically, based on which the functional completeness of Boolean logic could be realized. The logic operating results can be stored directly in the residual magnetization of the PCMM. This proposal may promote the design and future experimental implementation of next generation electromagnetic devices for data storage and computing.

Structural properties, linear, and non-linear optical parameters of ternary Se80Te(20−x)Inx chalcogenide glass systems

Ternary chalcogenide glass systems of Se80Te(20−x)Inx, where x=0, 5, 10wt.%, were synthesized via fast quenching of their melts. Bulk samples were ground into fine powder and thermally evaporated onto silica glass substrate, under vacuum, in order to obtain homogeneous thin films. DSC analysis of bulk samples revealed the presence of small endothermic peak, that identifies the glass transition temperature Tg, followed by an exothermic peak that defines the amorphous-crystalline phase transition Tp. These results confirmed the amorphous nature of the bulk samples. XRD analysis confirmed the amorphous nature of the studied thin films. Inclusion of indium in the glass matrix contributed to elevating refractive index and showed wide transmission window in the visible and near IR regions. Linear and nonlinear optical parameters are calculated and discussed in terms of the glass composition. Results of refractive index, first and third order susceptibilities nominate the studied thin films for applications in IR waveguides and sensors.

X-Ray Diffraction Analysis of the Amorphous–Crystalline Phase Transition in Ni

Systematic data on the amorphous–crystalline transition in Ni have been obtained by high-temperature X-ray diffraction analysis. It is established that the amorphous structure of Ni nanoparticles is stable up to 200°C. Ni nanocrystals, which have coherent-scattering regions (CSRs) 5–15 nm in size (depending on the isothermal annealing temperature) are formed in the temperature range of 300–600°C. The activation energy of nanocrystal growth has been estimated to be 67.3 kJ/mol. The dependence of the unit-cell parameter of nanocrystalline Ni on the CSR size is determined. An increase in the lattice constant is observed with an increase in CSR in nanocrystalline Ni particles.

A fluorescent sensor for detection of grinding force and fluoride ion based on acylhydrazone derivative

A new AIE-active pyrene-substituted acylhydrazone derivative (PSD) with multi-stimuli-responsive fluorescence switching behaviors has been designed and synthesized. The PSD exhibits the unusual AIE property and mechanofluorochromism (MFC) behavior with emission colors reversibly changing from blue-green to yellowish-green upon grinding and annealing. The MFC properties might be attributed to the synergetic effect of the different pyrene excimers formation and the crystalline-amorphous phase transition. Simultaneously, the PSD exhibited high-contrast fluorescent switching properties with high selectivity to F−. In the presence of F−, the PSD in DMSO dilute solution fluorescence quenched, and visible color changed from transparent to orange by the naked eye. The binding constant of PSD-F−complex calculated from the Benesi-Hildebrand plot was 5.08 × 103 M−1 and the detection limit for sensing F− in DMSO solution was 0.159 μM.

A turn-on mechanochromic luminescent material serving as pressure sensor and rewritable optical data storage

Mechanochromic luminescent (ML) materials can be roughly classified into two categories: turn-off type and turn-on type. Clearly the latter is more reliable because it has higher sensitivity and lower false-positive signals or background noises. Herein, a turn-on type ML material, (E)-4-((2-hydroxy-5-methylbenzylidene)amino)-3-methylbenzoic acid (MMA), is presented, which is designed by integrating appropriate electron donor-acceptor (D-A) moieties into a twisted conjugation core. MMA displays both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) properties. In addition, it glows weakly but exhibits notable emission enhancement under mechanical stimuli, and the two emission states can be repeatedly switched by grinding-fumigation treatment. Unlike the ML materials based on crystalline-amorphous phase transition, the ML of MMA is ascribed to the coupling and decoupling of the D-A units, regardless of the phase state. And this new working mechanism is confirmed by crystallographic data and DFT calculations. A pressure sensor based on MMA was fabricated, affording a low detection limit down to 21.6 Mpa. MMA further facilitates the fabrication of a ML recording medium, which allows for piezo-writing and fumigation-erasing of data, demonstrating a reliable prototype of optical data storage.

Investigation of Structural and Optical Properties of Amorphous-Crystalline Phase Transition of As40S45Se15 Thin Films

Investigation of Structural and Optical Properties of Amorphous-Crystalline Phase Transition of As₄₀S₄₅Se₁₅ Thin Films

Fundamentals and Applications of Chalcogenide Phase‐Change Material Photonics

AbstractRecently, chalcogenide phase‐change materials (PCMs) photonics have become an emerging research field because the optical properties of the PCMs undergo a dramatic change during the amorphous–crystalline phase transition. The chalcogenide PCMs can be efficiently switched by electrical or short optical pulses, offering versatility in photonic applications and extraordinary capability to engineer light. The authors introduce the fundamentals of chalcogenide PCM‐tuned photonics. The progress in the field is reviewed. Particularly, recent developments of metal–chalcogenide–metal (MCM) trilayered plasmonic nanostructures are presented. The authors then discuss the methodology of designing reconfigurable MCM‐based photonic devices, their advantages, and their existing challenges. Finally, requirements and prospects to successfully implement chalcogenide PCMs in growing areas of photonics are discussed.

Effects of biaxial strain on interfacial intermixing and local structures in strain engineered GeTe-Sb2Te3 superlattices

Van der Waals (vdW) layered GeTe-Sb2Te3 superlattices (GST-SL) have attracted enormous attentions due to the ultralow power consumption for nonvolatile phase change memory. In this paper, effects of biaxial strain on interfacial intermixing and local structures in strain engineered GST-SL were studied. Highly (0 0 l) textured GST-SL with thickness-varied Sb2Te3 sublayers were fabricated by magnetron sputtering and investigated with multiple analyses on surfaces and interfaces. The appearance of Ge-Sb-Te alloys indicated the interfacial Ge/Sb intermixing in strain engineered GST-SL, which actually were composed of Sb2Te3 quintuple layers, Ge-Sb-Te vdW layers and isolated GeTe bilayers. Grazing incidence x-ray diffraction (GID) and x-ray photoelectron spectroscopy (XPS) results revealed that biaxial strain not only facilitated the interfacial intermixing, but also caused the reconfiguration of Ge-Sb-Te vdW layers. Raman spectra indicated that vertical and in-plane vibrations of GeTe layers were not affected by the interfacial intermixing and the newly-formed Ge-Sb-Te layers had similar vibration characteristics as that of GeTe layers. A modified switching mechanism of GST-SL, relating to both the amorphous-crystalline phase transition of GeTe and Ge-Sb-Te layers incorporated into the Sb2Te3 matrix, was then presented. The present studies shed new light on strain engineering for GST-SL and indicate their potential optoelectronic applications.

Raman study of ion beam irradiation damage on nanostructured TiO2 thin film

90 MeV Xe and 25.78 MeV Cu ion irradiation effect on nanostructured anatase TiO2 thin film, prepared by sol-gel method, was investigated by Raman spectroscopy. The nonirradiated films show five Raman modes corresponding to the anatase phase. Raman spectra of irradiated films reveal crystalline-amorphous phase transition, fact evidenced by a progressive vanishing of Raman peaks correlated by emergence of a novel broad band at higher fluence, attributed to the amorphous structure. The broadening and blue shift of Raman peaks after irradiation indicate the generation of non-stoichiometric oxygen deficiency caused eventually by a preferential sputtering upon irradiation. A compressive stress was thus developed in the lattice which leads to the shortening of Ti–O bonds and the reduction of the crystallinity. The strain calculations reveal a correlation between the amorphization process and lattice strain enhancement. At higher fluence, the relaxation of the compressive stress may occur and results in volume expansion and hillocks formation. The strain and disorder calculations indicate that Xe irradiated films are completely amorphous, whereas, the anatase phase may still be present in Cu irradiated films. This behavior is explained by the difference in the electronic stopping power, which is manifested also in the disorder damage cross section. This latter is similar to that obtained by strain calculations and previously by XRD analysis.

Reconfigurable Ultraviolet and High-Energy Visible Dielectric Metamaterials.

Photonic materials with tunable and switchable ultraviolet (UV) to high-energy visible (HEV) optical properties may benefit applications such as sensing, high-density optical memory, beam-steering, adaptive optics, and light modulation. Here, for the first time we demonstrate a nonvolatile switchable dielectric metamaterial operating in the UV-HEV spectral range. Nanograting metamaterials in a layered composite of low-loss ZnS/SiO2 and the chalcogenide phase-change medium germanium-antimony-telluride (Ge2Sb2Te5 or GST) exhibit reflection resonances at UV-HEV wavelengths that are substantially modified by light-induced (amorphous-crystalline) phase transitions in the chalcogenide layer. Despite the presence of the lossy GST, resonance quality factors up to Q ∼ 15 are ensured by the transparency (low losses) of ZnS/SiO2 in the UV-HEV spectral range and values of Q increase as the refractive index of Ge2Sb2Te5 decreases, upon crystallization. Notably, however, this switching leaves resonance spectral positions unchanged.

Combining Ultrafast Calorimetry and Electron Microscopy: Reversible Phase Transformations in SeTeAs Alloys.

Reversible amorphous–crystalline phase transitions are studied using complementary ultrafast differential scanning calorimetry and transmission electron microscopy techniques, which together allow a wealth of thermal and structural properties to be determined. The SeTe(As) system is investigated because these chalcogenide based materials have favorable properties as a phase-change memory material and in optical systems. Using calorimetry, we find that the addition of 10 at. % As to SeTe alloys strongly increases their glass forming ability, increasing both glass transition and crystallization temperatures while reducing critical quench rate. Ex situ investigation of SexTe90–xAs10 using electron microscopy and elemental mapping reveals a two-phase lamellar segregation mechanism, where a trigonal SeTe-phase and an amorphous As-rich phase are formed. These findings demonstrate the power of combining thermal and structural analysis techniques.

Atomic-scale study of the amorphous-to-crystalline phase transition mechanism in GeTe thin films

The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of 57Fe emission Mössbauer spectroscopy, following dilute implantation of 57Mn (T½ = 1.5 min) at ISOLDE/CERN, to study the electronic charge distribution in the immediate vicinity of the 57Fe probe substituting Ge (FeGe), and to interrogate the local environment of FeGe over the amorphous-crystalline phase transition in GeTe thin films. Our results show that the local structure of as-sputtered amorphous GeTe is a combination of tetrahedral and defect-octahedral sites. The main effect of the crystallization is the conversion from tetrahedral to defect-free octahedral sites. We discover that only the tetrahedral fraction in amorphous GeTe participates to the change of the FeGe-Te chemical bonds, with a net electronic charge density transfer of ~ 1.6 e/a0 between FeGe and neighboring Te atoms. This charge transfer accounts for a lowering of the covalent character during crystallization. The results are corroborated by theoretical calculations within the framework of density functional theory. The observed atomic-scale chemical-structural changes are directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.