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Singlet fission (SF), as an effective way to break through the Shockley–Queisser limit, can dramatically improve energy conversion efficiency in solar cell areas. The formation, separation, and relaxation of triplet-pair excitons directly affect the triplet yield, especially triplet-pair separation; thus, how to enhance the triplet-pair separation rate becomes one of the key points to improve SF efficiency; the decay mechanism where the singlet state is converted into two triplet states is significant for the study of the SF mechanism. Herein, we employ ultrafast transient absorption spectroscopy to study the singlet-fission process of nano-amorphous 6, 13-bis(triisopropylsilylethynyl)-Pentacene (TIPS-pentacene) films in a diamond anvil cell (DAC). A kinetics model related to the structural geometric details, as well as an evaluation of the pressure manipulation impacts, is demonstrated based on the experimental results. The results indicate that pressure manipulation enhanced the triplet-pair separation rates of SF-based materials according to their structural micro-environmental improvement when compressed in DAC, while the triplet-exciton transportation lifetime is prolonged. This work shows that pressure may effectively optimize the structural disorder of SF materials, which were found to improve triplet-pair separation efficiency and potentially offer an effective way to further improve SF efficiency. [ABSTRACT FROM AUTHOR]

Singlet fission (SF), as an effective way to break through the Shockley–Queisser limit, can dramatically improve energy conversion efficiency in solar cell areas. The formation, separation, and relaxation of triplet-pair excitons directly affect the triplet yield, especially triplet-pair separation; thus, how to enhance the triplet-pair separation rate becomes one of the key points to improve SF efficiency; the decay mechanism where the singlet state is converted into two triplet states is significant for the study of the SF mechanism. Herein, we employ ultrafast transient absorption spectroscopy to study the singlet-fission process of nano-amorphous 6, 13-bis(triisopropylsilylethynyl)-Pentacene (TIPS-pentacene) films in a diamond anvil cell (DAC). A kinetics model related to the structural geometric details, as well as an evaluation of the pressure manipulation impacts, is demonstrated based on the experimental results. The results indicate that pressure manipulation enhanced the triplet-pair separation rates of SF-based materials according to their structural micro-environmental improvement when compressed in DAC, while the triplet-exciton transportation lifetime is prolonged. This work shows that pressure may effectively optimize the structural disorder of SF materials, which were found to improve triplet-pair separation efficiency and potentially offer an effective way to further improve SF efficiency.

Amorphous Cd-doped GeS2 films were prepared by thermal evaporation. In the Raman spectra of GeS2:Cd films with nominal Cd content above 8% at high laser power densities (above 200 kW/cm2), Raman peaks of the CdS LO and 2LO phonons are observed as evidence for the formation of CdS nanocrystals in the films under laser irradiation. The nanocrystals are formed due to the photoenhanced diffusion of atoms in the GeS2:Cd films, which is caused by non-thermal photofluidity (a drastic decrease of the film viscosity under illumination) that enables the aggregation of Cd and S atoms in nanocrystals. Factors responsible for the variation of the CdS LO phonon peak as a function of laser power density are discussed. [ABSTRACT FROM AUTHOR]

Zn-doped As2Se3 and As2S3 films were prepared by thermal evaporation. Their amorphous structure was confirmed by Raman spectroscopy. Zinc chalcogenide nanocrystals can be formed in the films under laser irradiation due to the photoenhanced diffusion of atoms in the arsenic chalcogenide films, which enables aggregation of Zn and S(Se) atoms in nanocrystals. For As2S3:Zn films, not only ZnS, but also ZnO crystallites can be formed under irradiation with UV laser light due to oxidation of the film surface with abundant zinc atoms. [ABSTRACT FROM AUTHOR]

The article summarizes the results of electron microscopic studies of 'in situ' crystallization of thin amorphous films. Data analysis is carried out based on the classification scheme of electron-beam crystallization of films, including structural-morphological and numerical characteristics. Layer polymorphous crystallization (as the analogue of Frank-van der Merwe growth mode), island polymorphous crystallization (as an analogue of the Volmer- Weber growth mode) and dendrite polymorphous crystallization (as an analogue of the Stransky-Krastanov growth mode) are identified. For each type of crystallization a dimensionless parameter of the relative length δ0 is determined. It is equal to the ratio of the characteristic length to the value, related to the size of the unit cell of the crystal. Based on the electron microscopic video registration of the process, kinetic crystallization curves are built for each type of the transformation. [ABSTRACT FROM AUTHOR]

The phenomenon of spontaneous spin reorientation in Gd–Сo amorphous films, which results from the competition between the perpendicular magnetic anisotropy and shape anisotropy, is studied. It is shown that the reorientation occurs via the formation of a fine-grained nonuniform magnetic structure called hypercritical state in a wide temperature range. Magnetic domains in the spin-reorientation region are characterized using magnetic and magneto-optical measurements. Based on the experimental magnetometric data and results of simulating the temperature dependences of spontaneous magnetization, the phase diagram of the films containing 16–26 at % Gd is constructed, which, being plotted on coordinates elemental composition—temperature, exhibits the ranges of existence of the perpendicular anisotropy, transition magnetic anisotropy (hypercritical state), and planar magnetization state. [ABSTRACT FROM AUTHOR]

The effects of mold cavity geometry and imprinting temperature on imprinted amorphous ZrCu films are studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effects are investigated in terms of shear strain, flow field, loading force, relationship between pattern filling height and mold displacement, and pattern elastic recovery. The simulation results show that imprinting should be conducted at high temperatures (slightly above the glass transition temperature), followed by unloading at 300 K. Imprinting at higher temperatures shortens the pattern filling time, decreases the required loading force, and lowers the shear strain concentration inside the films. Unloading at 300 K leads to a low pattern elastic recovery, which increases with increasing temperature. Imprinting using a groove pattern on the mold requires a larger loading force and less filling time compared to those required when using a tip-like pattern on the mold. For imprinting using a tip-like pattern on the mold at temperatures of 300–475 K, shear transformation zones form inside the films in the form of a ring surrounding the mold. [ABSTRACT FROM AUTHOR]

Initial stages of vacuum condensation of As-S amorphous films on carbon substrates at the stages of nucleation and formation of condensed phase islands are studied using the electron microscopy technique. Two stages of the processes of critical nuclei formation were found: intense primary nucleation and slow secondary nucleation that occurs in parallel with the growth of the formed nuclei. The sizes of the critical nuclei of the amorphous As-S films, the primary nuclei density, the size distribution of the condensed phase islands at the moment of the nucleation processes termination and the mean diffusion length for different atomic particles of the As-S vapor phase on the substrate surface were determined. The results obtained show that at room condensation temperatures most of various multi atomic particles of the AsnSm vapor have rather high diffusion mobility over the carbon substrate surface. Therefore, when simulating the condensation processes, the As-S materials could be considered as a non-equilibrium two-dimensional gas with an extremely complicated chemical composition. [ABSTRACT FROM AUTHOR]

We report a systematic investigation on room temperature and temperature dependent magnetic properties of [Fe \- Ta \- \C ( y )/Ta( 1~\nm ) ]n = {0-{4}}/FeTaC( y )/substrate] films prepared on thermally oxidized Si substrates at ambient temperature and postannealed at different temperatures (T_A) for 30 minutes. All the as-made films exhibit amorphous structure. The stripe domain structure with a large coercivity (H_C) observed in FeTaC (200 nm) single layer film due to stress induced during film deposition transforms to in-plane orientation of magnetization with multilayer structure. Postannealing at 200 ^\circ \C reduces H_C largely and annihilates the strip domains. On further increasing T_A, H_C increases initially at 300 ^\circ \C and reduces slightly for 400 ^\circ \C annealed films. Also, the values of H_C strongly depend on the number of multilayers. The magnetization reversal process of multilayer films annealed above 250 ^\circ \C depicts multistep reversal behavior due to an individual switching of ferromagnetic layer. High temperature thermomagnetization studies display a strong dependence of Curie temperature on T_A and multilayer structure. The observed results are discussed on the basis of stress-induced perpendicular anisotropy developed during film deposition, topological coupling at the interface, and magnetostatic interaction between the ferromagnetic layers. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Elaboration of Si-rich and C-rich thin films of amorphous silicon carbide. [•] Using a co-sputtering d.c magnetron of Si target and different 32–86 of 6H–SiC sprigs. [•] Structural and optical properties has been performed with applications in environmental field. [•] Different devices structures based on thin films have been investigated as gas sensor. [ABSTRACT FROM AUTHOR]

Abstract: IR laser- and UV laser-induced ablation of titanium monoxide (TM) in hydrogen (50Torr) is compared to the same process induced in vacuum and shown to result in deposition of hydrated surface modified nanostructured titanium suboxide films. Complementary analyses of the films deposited in vacuum and in hydrogen by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, X-ray diffraction and electron microscopy allowed to determine different features of both films and propose a mechanism of surface modification of ejected particles, which involves hydrothermal reduction of TM and subsequent reactions of evolved water. The films exert good adhesion to metal and quartz surfaces and are hydrophobic in spite of having their surface coated with adsorbed water. [Copyright &y& Elsevier]

The initial stages of nucleation of amorphous chalcogenide semiconductor films were investigated theoretically and experimentally. The important role of the complex mass spectrometry of the vapor phase in the process of nucleation and growth of amorphous chalcogenides island on uniform substrate surface was found. [ABSTRACT FROM AUTHOR]

This work describes the laser annealing of a-SiC and a-SiCN films deposited on (100) Si and quartz substrates by RF magnetron sputtering. Two samples of a-SiCN thin films were produced under different N/Ar flow ratios. Rutherford backscattering spectroscopy (RBS), Raman analysis and Fourier transform infrared spectrometry (FTIR) techniques were used to investigate the composition and bonding structure of as-deposited and laser annealed SiC and SiCN films. [ABSTRACT FROM AUTHOR]

Chalcostibite CuSbS2 thin films have been deposited on no heated glass substrates by single source vacuum evaporation method. The pressure during evaporation was maintained at 10-5 Torr. All the as-deposited films were amorphous. The structural, optical and electrical properties have been investigated relating the thickness variation. The optical properties revealed the presence of direct band gaps with energies in the 1.36 to 2.21eV range. Absorption coefficients higher than 105 cm-1 were found. The X-ray diffraction analysis show an improvement in the crystallinity of the films as thickness values increases. Secondary phases are observed corresponding to the Sb2S3. The electrical conductivity of the CuSbS2 thin film is in order 10-5 Ω-1 cm-1. Hot probe testing indicated that this is p-type. So, the absorbor material is a good candidate for photovoltaic applications. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report the fabrication and characterization of a SiC/SiO2/Si piezoresistive pressure sensor. The sensor structure consists of six PECVD SiC thin-film piezoresistors configured in Wheatstone bridge on a thermally oxidized micromachined silicon diaphragm. In order to fabricate this sensor, three lithographic masks were designed: one to define the square diaphragm (1800 μm×1800 μm), another for the piezoresistors and the third for the Ti/Au metal lines. The diaphragm was formed by anisotropic etching of Si in KOH solution and the piezoresistors by reactive ion etching (RIE) of SiC. The sensor chip size is 4.5 mm×4.5 mm. It was bonded on an alumina substrate using silicone and an aluminum cup was used for protection. The output voltage of the sensor was measured for applied pressure ranging from 0 to 12 psi and voltage suply of 12V. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous metals are interesting candidates for use as H2 purification membranes and also occur in some applications of H2 storage. We have recently introduced methods that combine first principles density functional theory calculations and statistical mechanics to make predictions of the properties of interstitial H in amorphous metals. In this paper, we apply these methods to investigate H solubility, diffusivity and permeability in amorphous Zr36Ni64 and Zr30(Ni0.6Nb0.4)70, two materials for which experimental data is available. Our calculations, which require no experimental input, agree well with the available experimental data, indicating that our methods can make reliable predictions about performance of amorphous metal membranes for hydrogen purification. [Copyright &y& Elsevier]

Abstract: Silicon coordination compounds of the general formula Si(O2CCH3)2(RCOCH2COR)2 (R=methyl, tert-butyl), were studied as precursors for the photochemical deposition of amorphous thin films of SiO2. Solutions of the inorganic complexes were spin coated on p-type silicon (100) substrates and photolyzed at room temperature using a 254nm UV light. The acetylacetonate derivatives underwent a photochemical reaction [quantum yield (Φ)∼0.01], resulting in the formation of amorphous SiO2 thin films. Auger electron spectroscopy indicated that the final film is carbon-free SiO2 while FTIR spectroscopy indicated the film has characteristics of silica glass rather than silica gel. Thin films prepared with the precursor complexes were photolyzed through a lithography mask, followed by rinsing with a chloroform/petroleum ether mixture, to yielding 2μm feature patterned lines of SiO2 without need for a photoresist/etching process. [Copyright &y& Elsevier]

Structural and electrochemical aspects of vanadium oxide films recently reported from ICMCB/ ENSCPB have been examined using appropriate structural models. It is shown that amorphous films are nonstoichiometric as a result of pre-deposition decomposition of V2O5. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V2O5 and V2O4 regions. Lithium intercalation into these regions is considered to occur sequentially and determined by differences in group electronegativities. Open circuit voltages (OCV) have been calculated for various stoichiometric levels of lithiation using available thermodynamic data with approximate corrections. Sequestration of lithium observed in experiments is shown to be an interfacial phenomenon. X-ray photoelectron spectroscopic observation of the formation of V3+ even when V5+ has not been completely reduced to V4+ is shown to be entirely consistent with the proposed structural model and a consequence of initial oxygen nonstoichiometry. Based on the structural data available on V2O5 and its lithiated products, it is argued that the geometry of VOn polyhedron changes from square pyramid to trigonal bipyramid to octahedron with increase of lithiation. A molecular orbital based energy band diagram is presented which suggests that lithiated vanadium oxides, LixV2O5, become metallic for high values of x. [ABSTRACT FROM AUTHOR]

Abstract: Ternary Boron–Nitrogen–Carbon (B–N–C) thin films were deposited, onto silicon substrates, by reactive radio frequency (RF) sputtering from a boron carbide (B4C) target in a gas mixture of nitrogen and argon. The influence of the RF power (P RF) on the structure and the chemical composition of these films are studied by Fourier transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements. The two techniques reveal the presence of B, C and N atoms in the deposited films. The presence of nitrogen in the atmosphere of the deposition chamber produces ternary B–N–C films composed mainly with a mixture of B–N and Cs revealed by these techniques. The boron content increases while carbon and nitrogen contents decrease with P RF. The higher proportion of boron atoms produced a strong contribution of the boron nitride in the final compound B–N–C films. [Copyright &y& Elsevier]

The amorphization of Co–Mo multilayered films was investigated by ion beam assisted deposition (IBAD). The amorphous phase was obtained within the composition range of 35–60 at.% Co fraction. When Co content in the films was less than 35 at.%, a Mo-based bcc solid solution was observed, and the maximal solubility of Mo in Co was about 40 at.%. The Gibbs free-energy diagram of the Co–Mo system was calculated according to Miedema’s model and the mechanism of phase evolution was interpreted in terms of thermodynamics. The kinetics of IBAD was also considered. [Copyright &y& Elsevier]

The microstructure of annealed Cr–Si–Ni–Al films was investigated by transmission electron microscopy (TEM). Sputtered amorphous Cr–Si–Ni–Al films crystallized into two phases: the intermetallic phase Cr(Al,Si)2 and the pure silicon phase. The formation of the crystallization phases resulted in a significant increase in both the electrical resistivity and the temperature coefficient of resistance (TCR) for the annealed Cr–Si–Ni–Al films. Particularly, the intermetallic Cr(Al,Si)2 particles, which were embedded in the amorphous matrix, were responsible for achieving a zero TCR. In addition, the growth rate of the crystallized phases at the initial stage of reaction was faster than that at the final stage, resulting from the combined redistribution of Cr, Si, Al and Ni elements between the initial crystallization phases and the parent amorphous phase. [Copyright &y& Elsevier]

• A model delineating competing fracture modes in film/substrate systems is developed. • The mechanism responsible for film thickness dependent fracture behavior is unveiled. • Effect of crack growth in the film on plastic deformation of substrate is identified. The architecture consisting of a thin film resting on a substrate is a common feature in a wide variety of applications. Understanding of the failure mechanisms is essential for design of reliable film/substrate systems. Recent experiments showed that shear banding induced fracture and brittle cracking of films are two major fracture modes in the structure composed of an amorphous metallic glass film bonded to a metal substrate. In this study, we carry out numerical analyses of fracture in amorphous films resting on ductile substrates, with the aim to unveil the mechanisms governing the competition between the two fracture modes observed in the experiments. In the calculations, the brittle cracking of amorphous films is modeled using the cohesive zone framework and the shear banding induced fracture in films is characterized by a simple local fracture criterion. The results show that brittle cracking of amorphous films occurs in the case of thin films, while the shear banding induced fracture dominates in the case of thick films. For the films with intermediate thickness, the mixed fracture modes are observed. Such a film thickness effect predicted by numerical simulations is consistent with the experimental observations. We further reveal that the film thickness effect is related to substrate constraint. In addition, it is identified that the cohesive strength and toughness of amorphous films also play an important role in controlling the fracture modes of the film/substrate systems. [ABSTRACT FROM AUTHOR]

Electrical and structural properties of Schottky-barrier diodes formed with TiBx and ZrBx amorphous layers on n-6H-, 15R- and 4H-SiC (with epi-layer) were studied. High thermal stability of ideality factors and barrier heights in the formed contacts was explained by the thermal stability of an interface TiBx(ZrBx)-SiC after rapid thermal annealing at 800°C for 60 s. [ABSTRACT FROM AUTHOR]