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Silicide phase formation by Mg deposition on amorphous Si. Ab initio calculations, growth process and thermal stability
摘要： Formation of magnesium silicides on amorphous silicon by deposition of Mg at room temperature is studied by electron energy loss spectroscopy, differential reflectance spectroscopy and high resolution transmission electron microscopy. Optimal crystal structures of Mg silicides under high pressure are found by ab initio DFT calculations. These structures are related to the particular minima of enthalpy. Dielectric functions are calculated for these structures. The transitions from the cubic phase c-Mg2Si to orthorhombic o-Mg2Si at 5.6 GPa and then from o-Mg2Si to hexagonal h-Mg2Si at 22.3 GPa are predicted using the USPEX code. The experimental spectra and the data obtained from the calculated dielectric functions are mutually consistent. Optical reflectance is suitable for monitoring the growth and transformations of the phases during experiments. During Mg deposition onto amorphous Si, the o-Mg2Si phase forms first, then the c-Mg2Si phase grows upon it. The observed sequence of phase formation is related with the compression stress arising in the depth of the Mg-Si mixture.
关键词： optical reflection spectroscopy,electron energy loss spectroscopy,solid state reactions,thin films,high resolution transmission electron spectroscopy,ab initio calculations
更新于2025-09-09 09:28:46
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Surface plasmon resonance, photoluminescence and surface enhanced Raman scattering behaviour of Ag/ZnO, ZnO/Ag and ZnO/Ag/ZnO thin films
摘要： The surface plasmon resonance (SPR) of Ag thin films in ZnO/Ag, Ag/ZnO bilayers and ZnO/Ag/ZnO multilayers produced by vacuum thermal evaporation has been studied. The role of thickness of the individual layers in the range of 5-50 nm was investigated. Detailed studies were carried out by fixing the thickness of the plasmon active layer and varying the dielectric layer thickness and vice versa. These studies reveal that the SPR of Ag is very sensitive to the geometry of the structures and as a consequence it has a strong effect on the photoluminescence (PL) as well as Surface enhanced Raman Scattering (SERS) behaviour. The PL peak of 5 nm thickness pure ZnO films which was centred at around 370 nm, was red shifted at higher thickness of 50 nm. Further, this peak was blue shifted to 324 nm when a 5 nm thickness Ag layer is introduced underneath the ZnO layer. The SERS behaviour of these structures was tested using R6G as the analyte. The enhancement factor for a 5 nm thickness pure Ag film was found to be 5x103. The highest enhancement factor for ZnO/Ag, Ag/ZnO and ZnO/Ag/ZnO trilayer films was found to be 7.4x106, 4.4x105 and 8.9x104, respectively.
关键词： surface plasmon resonance,surface enhanced Raman scattering,photoluminescence,Ag-ZnO multilayer films
更新于2025-09-09 09:28:46
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An Inverted Magnetron Operating in HiPIMS Mode
摘要： An ionized physical vapor deposition technique for thin ferromagnetic films is proposed. The technique is based on high power impulse magnetron sputtering (HiPIMS) with positive discharge polarity. A gapped-target was employed as the cathode of the magnetron. By applying positive HiPIMS pulses to the anode, sputtered particles inside the magnetron source were ionized and extracted through the gap. Using a discharge current with a peak of about 13 A, an ion flux in the order of 1021 m?2s?1 was obtained at a distance of 45 mm from the magnetron. In addition, deposition rates of up to 1.1 ?/s for nickel films were achieved using a 30 Hz repetition rate and 300 μs pulse width.
关键词： ferromagnetic,ionized physical vapor deposition,HiPIMS,magnetron sputtering,thin films
更新于2025-09-09 09:28:46
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Stochastic Resonance in Bioinspired Electronic Device Using Polymer Field Effect Transistors
摘要： Stochastic resonance (SR) phenomenon is emerged in organic field effect transistors (OFETs) using π-conjugated polymer, where application of external noise to the OFET system enhances signal/information processing performance which is often found in biological systems. The channel conductivity of the OFET is slightly increased by spin-coating using heated semiconductor polymer solution with heated glass substrate. In order to improve frequency responses of OFET, optimal width of the gate electrode is explored. Furthermore, it turns out that scratching and removing semiconductor film outside the source-drain electrodes and the channel enhances the On-Off current ratio of the device. These fabrication processes lead to steeper nonlinearity on the IDS vs. VGS curve, resulting in emergence of SR, which is fingerprinted in increase of correlation value between input and output signals with increase of intensity of external noise.
关键词： Stochastic resonance,Polymer thin films,Organic semiconductors,Bioinspiration,Field effect transistors
更新于2025-09-09 09:28:46
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A New Route to Synthesize MnSe Thin Films by Chemical Bath Deposition Method
摘要： Manganese selenide (MnSe) crystalline thin film was produced with chemical bath deposition on substrates (commercial glass). Transmittance, absorption, optical band gap and refractive index were investigated by UV/VIS spectrum. The hexagonal form was observed in the structural properties in XRD. The structural and optical properties of the MnSe thin films were analyzed at different pHs. SEM and EDX analysis were used for the surface analysis in the films. The films had the best crystalline at pH: 9. At pHs of 11 and 10 the MnSeO4 structure was observed. The films with the lowest film thickness were found in baths prepared with pH: 11. The highest refractive index was observed in films produced with a pH of 10 at a film density of 1.96. The grain size of MnSe thin films has a higher value at pH: 9.
关键词： Bath pH,MnSe thin films,Chemical Bath Deposition
更新于2025-09-09 09:28:46
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Plasma Preparation of the Top-Quality Phase Change Materials Based on As-Se-Te Chalcogenide System
摘要： The excellence of the Plasma-Enhanced Chemical Vapor Deposition (PECVD) approach in terms of preparation of the top-quality phase change materials based on As-Se-Te chalcogenide ternary system has been demonstrated. The samples were synthesized via direct interaction of arsenic, selenium and tellurium vapors into low-temperature non-equilibrium RF (40 MHz) plasma discharge at low pressure. The amorphous films with high degree of structural and chemical uniformity have been prepared in the broad range of contents, in particular, the chemical compositions going beyond the region of glass formation.
关键词： PECVD,chalcogenide films,phase change materials
更新于2025-09-09 09:28:46
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Surface Chemistry and Long-Term Stability of Amorphous Zn-Sn-O Thin Films
摘要： Amorphous (a-) oxides form an important category of transparent conducting/semiconducting thin films used as electrodes and channel layers in thin film transistors. The compositional flexibility of amorphous states, through doping, makes it possible to fine tune the electrical properties of films from conducting to semiconducting. However, surface chemistry and stability of these films are rarely addressed. Surface studies of amorphous materials, in general, are scarce due to disorder. Here, long-term surface stability of a-Zn-Sn-O films is investigated using grazing incidence X-ray absorption spectroscopy techniques. We present a detailed description of film surface structures and their evolution over time. It is found that the surface structure is, locally, a close analogue of the crystalline counterpart and that surface chemistry is governed by vacancies, strain, composition, and film density. It will be shown that the long-term stability of a film is questionable when the film has a high Zn content and a low density.
关键词： Zn-Sn-O thin films,Long-term stability,Grazing incidence X-ray absorption spectroscopy,Surface chemistry,Amorphous oxides
更新于2025-09-09 09:28:46
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Entanglement Reduction Induced by Geometrical Confinement in Polymer Thin Films
摘要： We report simulation results on melts of entangled linear polymers confined in a free-standing thin film. We study how the geometric constraints imposed by the confinement alter the entanglement state of the system compared to the equivalent bulk system using various observables. We find that the confinement compresses the chain conformation uniaxially, decreasing the volume pervaded by the chain, which in turn reduces the number of the accessible interchain contact that could lead to entanglements. This local and nonuniform effect depends on the position of the chain within the film. We also test a recently presented theory that predicts how the number of entanglements decreases with geometrical confinement.
关键词： simulation,polymer thin films,primitive path,geometrical confinement,entanglement
更新于2025-09-09 09:28:46
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Achieving Amorphous Ultralong Room Temperature Phosphorescence by Coassembling Planar Small Organic Molecules with Polyvinyl Alcohol
摘要： Development of novel strategies for achieving amorphous ultralong organic phosphorescence (UOP) at room temperature is highly desired. Herein, a simple approach is reported by coassembling small organic molecules with polyvinyl alcohol (PVA) to afford amorphous UOP. These small organic molecules with planar conformation present quenched triplet state emission in an excessive stacking solid state. When coassembling these molecules with PVA, their planar structures are well confined in coassembly films. Such a confined environment leads to restricted molecular rotation and vibration, permitting these molecules to show stable triplet state and generate UOP. In control studies, corresponding structurally distorted molecules are also coassembled with PVA. However, they exhibit very weak or quenched UOP, since distorted structures with molecular rotation and vibration could easily dissipate the excitation energy in dilute film state. By employing this polymer confinement strategy, multicomponent luminescence dyes are further coassembled with PVA for multicolor luminescence displays, providing multicolor, uniform, and flexible luminescence films. This work demonstrates a general strategy of employing small organic molecules to coassemble with PVA to obtain amorphous UOP, which greatly expands the scope of organic molecules for developing simple but useful UOP films.
关键词： ultralong organic phosphorescence,distorted molecules,coassembly,planar molecules,flexible luminescence films
更新于2025-09-09 09:28:46
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Manipulating the Ferroelectric Domain States and Structural Distortion in Epitaxial BiFeO3 Ultrathin Films via Bi Nonstoichiometry
摘要： Exploring and manipulating the domain configurations in ferroelectric thin films are of critical importance for the design and fabrication of ferroelectric heterostructures with novel functional performance. In this study, BiFeO3 (BFO) ultrathin films with various Bi/Fe ratios from Bi-excess to Bi-deficient have been grown on (La0.7Sr0.3)MnO3 (LSMO) covered SrTiO3 substrates by laser molecular beam epitaxy system. Atomic force microscopy and piezoresponse force microscopy measurements show that both the surface morphology and ferroelectric polarization of the films are relevant to the Bi nonstoichiometry. More significantly, the Bi-excess thin films show upward (from substrate to film surface) uniform ferroelectric polarization, while a Bi-deficient thin film exhibits downward uniform polarization, which means the as-grown polarization of the BFO thin films can be controlled by changing Bi contents. Atomic-scale structural and chemical characterizations and second harmonic generation measurements reveal that two different kinds of structural distortion and interface atomic configuration in the BFO/LSMO heterostructures can be induced by the change of Bi nonstoichiometry, leading to the two opposite as-grown ferroelectric polarizations. It has also been revealed that the band gap of the BFO thin films can be modulated via Bi nonstoichiometry. These results demonstrate that Bi nonstoichiometry plays a key role on the ferroelectric domain states and physical properties of BFO thin films, and also open a new avenue to manipulate the structure and ferroelectric domain states in BFO thin films.
关键词： BiFeO3 ultrathin films,interface atomic configuration,ferroelectric domain states,Bi nonstoichiometry,structural distortion
更新于2025-09-09 09:28:46