Polycrystal Films Research Articles

Distributed Feedback Laser Based on Single Crystal Perovskite

We demonstrate a single crystal perovskite based, with grating-structured photoresist on top, highly polarized distributed feedback laser. A lower laser threshold than the Fabry–Perot mode lasers from the same single crystal CH3NH3PbBr3 microplate was obtained. Single crystal CH3NH3PbBr3 microplates was synthesized with one-step solution processed precipitation method. Once the photoresist on top of the microplate was patterned with electron beam, the device was realized. This one-step fabrication process utilized the advantage of single crystal to the greatest extend. The ultra-low defect density in single crystalline microplate offer an opportunity for lower threshold lasing action compare with poly-crystal perovskite films. In the experiment, the lasing action based on the distributed feedback grating design was found with lower threshold and higher intensity than the Fabry-Perot mode lasers supported by the flat facets of the same microplate.

Identifying Key Factors towards Highly Reflective Silver Coatings

This paper attempts to identify key factor(s) for highly reflective silver (Ag) coatings. Investigation was made over the crystal orientation and surface roughness, using several types of surfaces, including electroplated Ag polycrystal films, physical vapour deposited polycrystal Ag films, and single crystal Ag foils with different crystal orientations. In each type of the surfaces, surface roughness was varied so that, for different combinations of crystal orientation, roughness would elucidate the key factors towards highly reflective Ag coatings. It is found that surface roughness plays a critical role in determining the reflectance, while the crystal orientation has negligible effect. The mean reflectance and one-way ANOVA analysis indicate that the single crystal Ag foils with three orientations performed statistically the same in the same roughness group at significance levelα= 0.05. Moreover, correlation between the surface reflectance and surface roughness has been proposed for the benefit of coating design. Refection data obtained from the polycrystalline silver samples are used to verify the accuracy of the proposed correlations. It was observed that the development surface area ratio,Sdr, is a better roughness indicator in predicting the reflectance of polycrystalline silver films than the arithmetic average roughness,Ra.

Temperature and Flow Rate Control of Diffusing Chamber

The temperature and flow rate control of diffusing chamber is one of the key technologies in the production of poly-crystal silicon thin film. As there exist some modeling uncertainties and errors in the actual system, it is difficult to guarantee the chamber variable temperature conditions and the flow rate of diffusion gas being controlled within its targeted range in the rapid thermal processing (RTP). In this paper, the control applies the programmable logic controller (PLC) to configure control hardware system, proposes expert proportional integral derivative (PID) control method to regulate the gas flow rate and H∞ control strategy to attenuate chamber modeling uncertainties and disturbances, respectively, to steer the chamber rapid variable temperature very close to the expected product temperatures. Furthermore, it designs human-machine integrated user control interface (HMI) and achieves rapid and accurately control performances for user operating production. The designed control system are simulated and tested in the application, which demonstrates that the control method has strong robustness when the modeling uncertainties, errors, parameters perturbation and disturbances, the temperature and flow rate meet the requirements of precisely trajectory following.

The investigation of band gap and N chemical bond structure of N–TiO2 film prepared by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by the direct current pulse magnetron sputtering technique. Then the surface of TiO2 film was implanted by the N ion beam at room temperature. Through this way, N-doped TiO2 (N–TiO2) film was obtained and the band gap of N–TiO2 film was decreased to 2.97 eV. XPS result revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. N ion was substitutionally/interstitially doped into TiO2 crystal lattice and Ti–N bond was formed. N ion was doped into amorphous TiO2 and Ti–ON bond was formed. The polycrystal TiO2 film could result in that more N ion was substitutionally/interstitially doped into TiO2 crystal lattice, which could effectively narrow the band gap of N–TiO2 film. This work provides a potential N doping method which could be applied commercially.

Preparation and magnetoresistance of submicron CrO2 thin film on poly-crystal SnO2 film

Abtract The submicron chromium dioxide (CrO 2 ) thin films have been fabricated on poly-crystal stannic oxide (SnO 2 ) films by atmospheric pressure chemical vapor deposition method. At low temperature, the CrO 2 thin film has sharp increase in the MR at low fields. This should be mainly attributed to spin-dependent tunneling through grain boundaries between adjacent CrO 2 grains. At high temperature, the magnetoresistance (MR) of CrO 2 thin film has small value and shows linear dependence on applied magnetic field. The resistivity of CrO 2 thin film decreases significantly as temperature increases, which can be best described by the fluctuation-induced tunneling model below 220 K. The MR for the CrO 2 thin film on SnO 2 film also decreases rapidly with increasing temperature.

Epitaxial Fe3Si/Ge/Fe3Si thin film multilayers grown on GaAs(001)

We demonstrate Fe3Si/Ge/Fe3Si/GaAs(001) structures grown by molecular-beam epitaxy and characterized by transmission electron microscopy, electron backscattered diffraction, and X-ray diffraction. The bottom Fe3Si epitaxial film on GaAs is always single crystalline. The structural properties of the Ge film and the top Fe3Si layer depend on the substrate temperature during Ge deposition. Different orientation distributions of the grains in the Ge and the upper Fe3Si film were found. The low substrate temperature Ts of 150°C during Ge deposition ensures sharp interfaces, however, results in predominantly amorphous films. We find that the intermediate Ts (225°C) leads to a largely [111] oriented upper Fe3Si layer and polycrystal films. The high Ts of 325°C stabilizes the [001] oriented epitaxial layer structure, i.e., delivers smooth interfaces and single crystal films over as much as 80% of the surface area.

Preparation and characterization of In2O3 films with (111) preferred orientation

In this study, In2O3 films were prepared by three methods and resulted in three different film structures. We firstly produced In2O3 polycrystal films by the evaporation of In source under oxygen ambient. In the second attempt, In2O3(111) films were fabricated by oxidation of In films. The surface scattering contributed to the resistivity of the oxidized In film and resulted a poor conductivity. As the third approach, a combination of the first and the second way, we prepared an ultrathin In film, oxidized it, and made it served as a seeding layer in the evaporation of In source under oxygen ambient. Due to the specific fabrication, we obtained the In2O3(111) films, in which a better conductivity and a smooth surface were observed in the In2O3(111) film through the third approach.

Surface topography and the spectral and photoelectric properties of intercalated molybdenum disulfide films

The structural and photoelectric properties of nanodispersed molybdenum disulfide films intercalated with cationic organic compounds (rhodamine 6G, oxazine, triethylbenzylammonium, hexadecyltrimethylammonium, and polyvinylpyrrolidone) and hydroxocomplexes of Zn, Co, Ni, and Cd are studied. It is found that the greatest differences between the absorption spectra of MoS2 films intercalated with compounds of various natures are observed in the range of 500–850 nm, and the conductivities (dark and photo-) of MoS2 films intercalated with Ni or Co hydroxocomplexes rise by one or more orders of magnitude, respectively, compared to films of intercalated molybdenum disulfide. The correlation between photoconductivity and the corresponding values of dark conductivity is determined, proving that charge transport (and not generation processes) in films is the limiting step for photocurrent. It is concluded that highly conductive polycrystal films of intercalated MoS2 with conductivities close to those in MoS2 monocrystals are of interest for practical use in optoelectronics.

Multiple Healing Fatigue Damage by Laser Shock Peening for Copper Thin Film

Multiple healing fatigue damage for polycrystal copper film was investigated by laser shock peening (LSP). The damaged specimens were healed several times under the optimal laser parameters. The relationship among the fatigue life, healing times and the damage degree were investigated. The experimental results showed that the multiple heal based on LSP can maximize fatigue life of the damaged specimens under the definite optimal condition with the obtained at damage degree of 0.4 and healing times of 3, in which nearly 4.6 times increase in residual fatigue life for the damaged specimens, and 7.8 times increase in the accumulated fatigue life.

Tailoring the ground state of the ferrimagnet La2Ni(Ni1/3Sb2/3)O6

We report on the magnetic and structural properties of La2Ni(Ni1/3Sb2/3)O6 in polycrystal, single crystal and thin film samples. We found that this material is a ferrimagnet (Tc≈100K) which possesses a very distinctive and uncommon feature in its virgin curve of the hysteresis loops. We observe that bellow 20K it lies outside the hysteresis cycle, and this feature was found to be an indication of a microscopically irreversible process possibly involving the interplay of competing antiferromagnetic interactions that hinder the initial movement of domain walls. This initial magnetic state is overcome by applying a temperature dependent characteristic field. Above this field, an isothermal magnetic demagnetization of the samples yield a ground state different from the initial thermally demagnetized one.

Preparation and magnetic properties of submicron CrO2 thin film on poly-crystal TiO2 film

The submicron chromium dioxide(CrO2) thin film was fabricated on a poly-crystal titania(TiO2) film using Si wafers as substrates by atmospheric pressure chemical vapor deposition(CVD) method. X-Ray diffraction patterns show that the CrO2 films were pure rutile structure. Scanning electron microscopy(SEM) images indicate that the CrO2 films consisted of submicron grains with a grain size of 250–750 nm. The magnetic researches reveal that the magnetic easy axis is parallel to the films, and at room temperature, the CrO2 films show linear magnetoresistance.

Performance Limits of Microactuation with Vanadium Dioxide as a Solid Engine

Miniaturization of the steam engine to the microscale is hampered by severe technical challenges. Microscale mechanical motion is typically actuated with other mechanisms ranging from electrostatic interaction, thermal expansion, and piezoelectricity to more exotic types including shape memory, electrochemical reaction, and thermal responsivity of polymers. These mechanisms typically offer either large-amplitude or high-speed actuation, but not both. In this work we demonstrate the working principle of a microscale solid engine (μSE) based on the phase transition of VO2 at 68 °C with large transformation strain (up to 2%), analogous to the steam engine invoking large volume change in a liquid-vapor phase transition. Compared to polycrystal thin films, single-crystal VO2 nanobeam-based bimorphs deliver higher performance of actuation both with high amplitude (greater than bimorph length) and at high speed (greater than 4 kHz in air and greater than 60 Hz in water). The energy efficiency of the devices is calculated to be equivalent to thermoelectrics with figure of merit ZT = 2 at the working temperatures, and much higher than other bimorph actuators. The bimorph μSE can be easily scaled down to the nanoscale, and operates with high stability in near-room-temperature, ambient, or aqueous conditions. On the basis of the μSE, we demonstrate a macroscopic smart composite of VO2 bimorphs embedded in a polymer, producing high-amplitude actuation at the millimeter scale.

Controllable Growth Orientation of Ag2O and Cu2O Films by Electrocrystallization from Aqueous Solutions

We demonstrate that Ag2O and Cu2O polycrystal films with a cubic cuprite structure can be grown on F:SnO2 substrates with controllable crystal orientation between ⟨111⟩ and ⟨100⟩ directions by galvanostatic electrocrystallization from aqueous electrolytes. The Ag2O and Cu2O films have been electrodeposited at different applied current densities determined by linear-sweep voltammetry (LSV) measurements, and their crystal structure and morphology were characterized with X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The XRD results show the preferred growth orientation changed from ⟨111⟩ to ⟨100⟩ with increasing and decreasing current density for Ag2O and Cu2O, respectively. The surface morphology, especially for the Cu2O films, was also changed from a three-sided pyramidal shape to a four-sided pyramidal shape corresponding to the orientation. We also give a reasonable explanation for the observed trend in the growth orientation by considering the formation rate of AgOH an...

P‐93: Structure and Properties of Azo Dye Films for Photoalignment and Photochromic Applications

AbstractProperties of both amorphous and polycrystal films of azodye AD‐1 have been investigated. The films' structure depends on conditions of thermal treatment, light polarization and intensity. High dichroic ratio (>20) has been obtained. Film structure control allows fabrication of good photoaligning coatings.

A Critical Appraisal of the Nanoindentation Creep 'Nose' Effect in Ni Thin Films

The creep behaviour of polycrystal Ni thin films under the same maximum load (Pmax = 8000 microN) and different unloading periods (ranging from 1 to 250 s) has been investigated at room temperature using nanoindentation tests. A 'nose' has been observed in the unloading segment of the load-penetration depth curve when the holding time at peak load is short and/or the unloading rate is small, and when the peak load is sufficient high. When a 'nose' presents, the apparent unloading stiffness Su, defined as dP/dh, is negative, and the reduced modulus can no longer be calculated from the Oliver-Pharr method. Taking such uncertainties into account, a critical appraisal is proposed for ranking creep propensities exhibited during nanoindentation under specified conditions.

Temperature dependence of the Hall effect in pentacene field-effect transistors: Possibility of charge decoherence induced by molecular fluctuations

Temperature dependence of the Hall effect is measured for both single-crystal and thin-film field-effect transistors of pentacene. At room temperature, the inverse Hall coefficient $1/{R}_{H}$ exceeds field-induced charge density $Q$ by a factor of 2 at each gate-electric field for all the samples, regardless of their charge-carrier mobility and detailed subthreshold properties. Violating the band-transport model that $1/{R}_{H}$ equals to $Q$, the excess $1/{R}_{H}$ does not measure the charge amount anymore so that the result possibly indicates insufficient electromagnetic coupling due to somewhat reduced charge coherence. At lower temperatures, the deviation of $1/{R}_{H}$ from $Q$ gradually diminishes to approach the band-transport behavior. Interestingly, the degree of the deviation has been universal for the measured five samples, including both polycrystal and single-crystal pentacene films. The result suggests that significant molecular fluctuation near room temperature can affect the fundamental electronic state.

Morphology-tuned synthesis of arrayed one-dimensional ZnO nanostructures from Zn(NO3)2 and dimethylamine borane solutions and their photoluminescence and photocatalytic properties

This paper reports morphology-tuned synthesis of arrayed one-dimensional ZnO nanostructures on Ag-coated glass substrates from Zn(NO3)2 and dimethylamine borane (DMAB) aqueous solutions and their photoluminescence and photocatalytic properties. By adjusting the Zn(NO3)2 concentration in the solutions, the ZnO nanoneedle arrays, nanorod arrays, and polycrystal films can be obtained. Low Zn(NO3)2 concentrations result in ZnO nanoneedle arrays. The ZnO nanoneedles grow along the 〈0001〉 directions. The growth process of the ZnO nanoneedles at low Zn(NO3)2 concentrations goes through the formation of the equiaxial ZnO granules, the growth of the equiaxial granules into small nanorods, the growth of the small nanorods into nanoneedles, the growth of the nanoneedles in diameter and length, the growth of the nanoneedles into nano-obelisks, and the growth of the nano-obelisks into thick hexangular rods. So the morphologies of the arrayed 1D ZnO nanostructures can be tuned from arrayed nanoneedles through arrayed nanorods and nano-obelisks to arrayed thick hexagonal rods by controlling the Zn(NO3)2 concentration in the DMAB and Zn(NO3)2 solutions and/or the deposition time in our process. The ZnO nanoneedle arrays have the largest ratio of the visible to ultraviolet emission and the highest photocatalytic activity.

Bandgap modifications by lattice deformations in β-FeSi 2 epitaxial films

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi 2 epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature ( T a ) were observed in β-FeSi 2 epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi 2/Si.

Characterization of rubrene polycrystalline thin film transistors fabricated using various heat-treatment conditions

We observed the crystal structure changes of rubrene (5,6,11,12-tetraphenylnaphthacene) polycrystal thin films on SiO2/Si(100) substrates at various heat-treatment temperatures by X-ray diffraction, and a near-field microwave microprobe technique. An amorphous rubrene thin film was initially observed at heat-treatment temperature of 35°C. After the treatment with in-situ vacuum post-annealing at 80°C for 22h, the rubrene thin film was transformed from the amorphous phase into a crystalline phase of orthorhombic structure. We could obtain a higher field effect mobility of 0.047cm2/V·s and lower threshold voltage of −4V for the following heat-treatment process: pre-annealing at 80°C, cooling at 40°C, and post-annealing at 80°C for 22h.

Optical and structural characterization of cerium doped LYSO sol–gel polycrystal films: potential application as scintillator panel for X-ray imaging

The optical and structural properties of sol–gel prepared polycrystalline films of Cerium doped Lutetium and Yttrium oxyorthosilicates (Ce:LYSO) are investigated by means of optical spectroscopy, XRD diffraction and Raman spectroscopy. The sol–gel samples are compared to commercially available Ce-doped LYSO single crystals, and a detailed study of the emission properties from the different cerium sites is performed. The main result is that the polycrystalline films do show very good radioluminescence properties for possible applications as X-ray scintillating panels. The structural characterization indicates that the sol–gel polycrystals have similar phase composition to commercial monocrystals; concerning the excitation and emission properties, the same radiative recombination channels are observed in the polycrystals and commercial monocrystals with a slightly faster decay time in the first case. In addition, low temperature measurements (8 K) indicate the presence of a non-radiative cross-relaxation mechanism among cerium ions in the sol–gel grown samples in the two possible crystallographic sites. The results indicate the possibility to develop sol–gel synthesized polycrystalline thin films as scintillating materials in the X-ray energy range.