Properties Of Polycrystalline Thin Films Research Articles

Correlative Imaging of Individual CsPbBr3 Nanocrystals: Role of Isolated Grains in Photoluminescence of Perovskite Polycrystalline Thin Films.

We report on the optical properties of a CsPbBr3 polycrystalline thin film on a single grain level. A sample composed of isolated nanocrystals (NCs) mimicking the properties of the polycrystalline thin film grains that can be individually probed by photoluminescence spectroscopy was prepared. These NCs were analyzed using correlative microscopy allowing the examination of structural, chemical, and optical properties from identical sites. Our results show that the stoichiometry of the CsPbBr3 NCs is uniform and independent of the NCs' morphology. The photoluminescence (PL) peak emission wavelength is slightly dependent on the dimensions of NCs, with a blue shift up to 9 nm for the smallest analyzed NCs. The magnitude of the blueshift is smaller than the emission line width, thus detectable only by high-resolution PL mapping. By comparing the emission energies obtained from the experiment and a rigorous effective mass model, we can fully attribute the observed variations to the size-dependent quantum confinement effect.

Optical properties of polycrystalline films of lead telluride with distributed stichiometry

In this article, the optical properties of polycrystalline thin films based on PbTe with disturbed stoichiometry are considered. It is shown that in PbTe films with a lead excess of 1.2 wt %, the intrinsic absorption edge is shifted to shorter wavelengths of the spectrum, and this is due to the presence of shallow levels in the forbidden band. It was found that in the band of p-type PbTe spectra with an excess of tellurium of 2.8 and 3.8 wt %, there are additional bands with the cutoff energy hw=0.132 eV, which are associated with the presence of free tellurium.

Effects of Relatively low pH on Chemically Deposited PbS Thin Films

This study probed, through an experimental process, the structural and morphological properties of polycrystalline thin films of lead (II) sulfide (PbS) produced by using the chemical bath deposition technique. The effects of pH were examined within the scale of 7–11 in detail. The atomic absorption data showed that the reaction rate decreased when the pH of the solutions was reduced. A structural analysis was carried out by using the X-ray diffraction (XRD) pattern. The preferred orientation of the films shifted from the (111) plane to the (002) plane, according to the XRD pattern, when the pH of the solutions was reduced. A significant changing was formed in crystallite sizes. When pH of the solution was not changed, the crystallite size was calculated as to be 84 nm. On the other hand, when pH was decreased, the crystallite size was decreased up to 30 nm. Surface morphologies were analyzed through scanning electron microscopy. The lowered pH showed that lead (II) sulfide can be produced in cubic forms.

Constructing the Electronic Structure of CH3NH3PbI3 and CH3NH3PbBr3 Perovskite Thin Films from Single-Crystal Band Structure Measurements.

Photovoltaic cells based on halide perovskites, possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single-crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3), we reveal the band dispersion in two high-symmetry directions and identify the global valence band maxima. With these benchmark data, we construct "standard" photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature for determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.

Kinetic Phenomena and Thermoelectric Properties of Polycrystalline Thin Films Based on PbSnAgTe Compounds

Kinetic Phenomena and Thermoelectric Properties of Polycrystalline Thin Films Based on PbSnAgTe Compounds

Surface effects on electrical and magnetic properties of Ni75.2Mn23.6Pt1.2 alloy films

We report on the magnetic, electrical resistivity and ferromagnetic resonance (FMR) properties of polycrystalline thin films of Ni75.2Mn23.6Pt1.2 prepared by electron beam evaporation with thicknesses from 10 to 800nm. We measured field cooled magnetization as a function of temperature as well as hysteresis loops in parallel and perpendicular geometries (field parallel/perpendicular to film surface) at selected temperatures. We observe asymmetric double–shifted hysteresis loops below the freezing temperature, Tf, which can be attributed to the competition of unidirectional and uni-axial anisotropy fields.At low temperatures below Tf, the main contribution to the temperature dependence of the resistivity is the scattering of conduction electrons by spin-waves, while in the intermediate temperature range between Tf and the Curie temperature, Tc, the resistivity has a logarithmic temperature dependence due to electron-spin fluctuation scattering. At high temperatures, the most important contribution arises from the electron-phonon scattering mechanism.Finally, FMR measurements were used to probe the magnetic state. We considered the simplest form of the Hamiltonian and used a model based on the Landau-Lifshitz equation. By a rigorous analysis of the angle dependence of the FMR measured at several temperatures, we determined the values of the bulk and surface anisotropy constants, and the exchange stiffness constant. The fitting parameters show that the magnetic ordering is modified significantly by film thicknesses due to the surface anisotropy fields.

Photoinduced Emissive Trap States in Lead Halide Perovskite Semiconductors

The recent success of lead halide perovskites is given by their optimal primary optoelectronic properties relevant for photovoltaic and, more in general, for optoelectronic applications. However, a lack of knowledge about the nature of instabilities currently represents a major challenge for the development of such materials. Here we investigate the luminescence properties of polycrystalline thin films of lead halide perovskites as a function of the excitation density and the environment. First we demonstrate that in an inert environment photoinduced formation of emissive sub-band gap defect states happens, independently of the chemical composition of the lead halide semiconductor, which quenches the band-to-band radiative emission. Carrier trapping occurs in the subnanosecond time regime, while trapped carriers recombine in a few microseconds. Then, we show that the presence of oxygen, even in a very small amount, is able to compensate such an effect.

Highly conductive grain boundaries in copper oxide thin films

High conductivity in the off-state and low field-effect mobility compared to bulk properties is widely observed in the p-type thin-film transistors of Cu2O, especially when processed at moderate temperature. This work presents results from in situ conductance measurements at thicknesses from sub-nm to around 250 nm with parallel X-ray photoelectron spectroscopy. An enhanced conductivity at low thickness is explained by the occurrence of Cu(II), which is segregated in the grain boundary and locally causes a conductivity similar to CuO, although the surface of the thick film has Cu2O stoichiometry. Since grains grow with an increasing film thickness, the effect of an apparent oxygen excess is most pronounced in vicinity to the substrate interface. Electrical properties of Cu2O grains are at least partially short-circuited by this effect. The study focuses on properties inherent to copper oxide, although interface effects cannot be ruled out. This non-destructive, bottom-up analysis reveals phenomena which are commonly not observable after device fabrication, but clearly dominate electrical properties of polycrystalline thin films.

Temperature dependent optical properties of CH3NH3PbI3 perovskite by spectroscopic ellipsometry

Mixed organic-inorganic halide perovskites have emerged as a promising new class of semiconductors for photovoltaics with excellent light harvesting properties. Thorough understanding of the optical properties of these materials is important for photovoltaic device optimization and the insight this provides for the knowledge of energy band structures. Here we present an investigation of the sub-room temperature dependent optical properties of polycrystalline thin films of CH3NH3PbI3 perovskites that are of increasing interest for photovoltaics. The complex dielectric function of CH3NH3PbI3 in the energy range of 0.5–4.1 eV is determined between 77 K and 297 K using spectroscopic ellipsometry. An increase in optical permittivity as the temperature decreases is illustrated for CH3NH3PbI3. Optical transitions and critical points were analyzed using the energy dependent second derivative of these dielectric functions as a function of temperature.

Excellent optical quality versus strong grain boundary effect in a double-layer ZnO structure

ZnO samples with a double-layer structure and top nanorod arrays on the bottom film layer were grown by metal-organic chemical vapor deposition at a temperature range from 340 to 400 °C. The ZnO nanorods show excellent optical quality and no obvious defect related emission can be detected below 40 K except for I6 line and the surface bound exciton emission. The free exciton emission and its phonon replicas dominate the near band edge emission between 40 and 295 K. For the film layer, the temperature-dependent Hall measurements showed that the conduction region is degenerate. In the conduction region, the carrier mobility is mainly limited by the grain boundary effect, which can be weakened by thermal annealing. The conduction mechanism in this region before and after annealing can be fitted by a uniform and a non-uniform conduction model, respectively. The results indicate that grain boundary effects strongly limit the mobility and consume large amounts of carriers by the trap states. Furthermore, we propose a qualitative model to explain the expansion of the conduction regions by annealing. It reveals a mechanism for the improvement of electrical properties of polycrystalline thin films by annealing treatments.

Investigation of structural and optical properties of 100 MeV F7+ ion irradiated Ga10Se90-xAlx thin films

Present work focuses on the effect of swift heavy ion (SHI) irradiation of 100 MeV F7+ ions by varying the fluencies in the range of 1 × 1012 to 1 × 1013 ions/cm2 on the morphological, structural and optical properties of polycrystalline thin films of Ga10Se90-xAlx (x = 0, 5). Thin films of ~300 nm thickness were deposited on cleaned Al2O3 substrates by thermal evaporation technique. X-ray diffraction pattern of investigated thin films shows the crystallite growth occurs in hexagonal phase structure for Ga10Se90 and tetragonal phase structure for Ga10Se85Al5. The further structural analysis carried out by Raman spectroscopy and scanning electron microscopy verifies the defects or disorder of the investigated material increases after SHI irradiation. The optical parameters absorption coefficient (α), extinction coefficient (K), optical band gap (Eg) and Urbach’s energy (EU) are determined from optical absorption spectra data measured from spectrophotometry in the wavelength range 200–1100 nm. It was found that the values of absorption coefficient and extinction coefficient increase while the value of optical band gap decreases with the increase in ion fluence. This post irradiation change in the optical parameters was interpreted in terms of bond distribution model.

Thermoelectric Properties of Polycrystalline Thin Films Under an External Magnetic Field

A theoretical model is proposed to predict the Seebeck coefficient and the electrical conductivity for a polycrystalline thermoelectric (TE) thin film under an external magnetic field. The model considers the distribution of electrons in the microstructure of TE thin-film materials, taking the scattering effect of electrons at the grain boundary as the boundary condition for electron transport in the grain. The transmission coefficient is introduced to describe the probability of electrons passing through the grain boundary potential barrier, while the relationships between the Seebeck coefficient, the electrical conductivity, and the transmission coefficient are studied. Furthermore, the results from the calculations of the Seebeck coefficient, the electric conductivity, and the power factor of TE materials under various applied magnetic fields, transmission coefficients, and grain sizes indicate that the applied external magnetic field has a very significant influence on the TE properties of polycrystalline thin films.

Grain-boundary-limited charge transport in solution-processed 6,13 bis(tri-isopropylsilylethynyl) pentacene thin film transistors

Grain boundaries play an important role in determining the electrical, mechanical, and optical properties of polycrystalline thin films. A side-disubstituted counterpart of pentacene, 6,13 bis(tri-isopropylsilylethynyl) (TIPS) pentacene, has lateral π-π packing and reasonably high solubility in a number of organic solvents. In this paper, the effects of grain boundaries on the effective hole mobility, on/off ratio, threshold voltage, and hysteresis of transistor transfer characteristics were investigated in solution-processed TIPS pentacene thin film transistors with both experiments and simulations. The effects of solvent type, concentration, substrate temperature, and evaporation rate were investigated by optical, electron, and atomic force microscopies. An apparatus for controlled solution casting was designed, fabricated, and used to make TIPS pentacene thin film transistors with more precisely controlled variations in microstructure and defect densities. First, hysteresis in the electrical characteristics was found to correlate directly with grain width WG (the crystal dimension along [12¯0]) in active layers. In addition, since TIPS pentacene crystals with larger grain width (WG>6 μm) generally took a long needle shape and the ones with smaller domain sizes (WG<4 μm) had a more equiaxed geometry, a sharp enhancement in the effective mobility was observed in the larger grains. In devices with active layers cast from toluene solution, the measured field-effect hole mobility for grain width WG smaller than 4 μm was generally ≤0.01 cm2/V s, whereas mobility for films with grain width WG>6 μm was typically 0.1∼1 cm2/V s. A model of boundary-limited transport was developed and used to explain experimental data. Based on the proposed model and an energy barrier (EB) on the order of 100 meV for electrical transport across grain boundary, the effective grain-boundary mobility μGBo was estimated to be approximately 5×10−7 cm2/V s.

Structural and optical properties of polycrystalline thin films of rare earth oxides grown on fused quartz by low pressure MOCVD

We report the structural and optical properties of oriented polycrystalline thin films of rare earth oxides (REO), namely Er 2O 3, Gd 2O 3, Eu 2O 3, and Yb 2O 3 grown on fused quartz by low-pressure metalorganic chemical vapour deposition (MOCVD) in the temperature range of 450–800 °C, using adducted β -diketonate complexes of rare earth metals as precursors. The films were characterized by X-ray diffraction (XRD) and UV–visible spectrophotometry. While the films grown at low temperatures (∼500 °C) are poorly crystalline, those grown on or above 525 °C display a significant (1 1 1) texture. Growth of textured cubic REO in (1 1 1) direction on amorphous substrate is interpreted in terms of minimization of surface energy at the film–substrate interface. The degree of misfit between the interatomic distances in the disordered fused quartz substrate and those in the crystalline REO is invoked to explain the presence (absence) of low-intensity reflections other than (1 1 1). The incorporation of carbon (from the precursor) into the films affects the optical properties of REO, as examined by UV–visible spectroscopy.

417 繊維配向を有した多結晶薄膜の機械的特性の有限要素法予測(応力破壊解析,学術講演)

417 繊維配向を有した多結晶薄膜の機械的特性の有限要素法予測(応力破壊解析,学術講演)

Structural and mechanical properties of well-relaxed amorphous–crystal interface in silicon: molecular dynamics study

Amorphous–crystal interface properties in silicon are key parameters for the control of the mechanical and electrical properties of polycrystalline thin film. We propose a method to calculate the interface properties of the well-relaxed amorphous–crystal interface by using structural parameters to evaluate the interface structures. The amorphous–crystal interface energies, γ I=0.29 and 0.33 J/m 2, are obtained for (0 0 1) and (1 1 1) plane, respectively. Structural relaxation greatly influences those values. It is found that the interface energies are smaller than the surface energies and depend weakly on the crystal orientation. These findings agree very well with the experiments. The interface stress is small as compared with that of metal/metal interface and involves the scattering across a broad range. A critical nucleus size estimated by the calculated interface energy is slightly smaller than that estimated by the direct MD simulation for homogeneous nucleation. That small mismatch is thought to be caused by the limit of the classical nucleation theory.

515 <001> 繊維配向を有する多結晶薄膜における弾性特性の有限要素解析

515 <001> 繊維配向を有する多結晶薄膜における弾性特性の有限要素解析

Statistical methods of investigations on the electrical properties of molybdenum disulphide intercalates

The paper presents the results of testing the electrical properties of polycrystalline thin films of MoS2 obtained and its intercalates of M0.5MoS2; where M=Ga, In or Tl. The investigations were carried out according to a five-level rotational plan. Threefold repeatability of measurement was applied at respective stages of this plan. The experimental results were subjected to statistical analysis in accordance with developed methods. An exponential model of the electrical conductivity was developed for the semiconducting materials obtained. Model coefficients were determined using the least square method. The compounds obtained are semiconductors with energy gap 0.88–0.92eV, activation energy of doping levels 0.009–0.10eV and the specific conductivity at room temperature 2.22–3.67Ω−1cm−1.

Stress and grain growth in thin films

The mechanical properties of polycrystalline thin films with thickness of 1 μm or less depend strongly on the grain geometry, the grain size, and the way in which the crystallographic orientations of the grains are distributed. Grain growth during film formation or during post-deposition annealing can play a dominant role in defining these microstructural characteristics, and therefore, the mechanical properties of films. Stress can suppress or promote grain growth. In the latter case, stress promotes texture evolution during grain growth. Grain growth can serve as a stress relief mechanism in both elastically isotropic and anisotropic materials, and can also promote plastic yielding.

Reentrant transition and spin-glass state in CdCr2xIn2-2xSe4 thin films.

Magnetic properties of polycrystalline thin films of chromium chalcogenide spinels, i.e., ${\mathrm{CdCr}}_{2}$${\mathrm{Se}}_{4}$ lightly doped with indium and ${\mathrm{CdCr}}_{2\mathit{x}}$${\mathrm{In}}_{2\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Se}}_{4}$, are studied. The ferromagnetic- and spin-wave-resonance techniques have been used to investigate the temperature dependences of the spin-wave stiffness constant D, the saturation magnetization ${\mathit{M}}_{\mathit{s}}$, and the resonance linewidth \ensuremath{\Gamma}. The resonance spectra have been recorded in the temperature range extending from 4.2 to 300 K. The influence of indium concentration on ${\mathit{M}}_{\mathit{s}}$(T), D(T), and \ensuremath{\Gamma}(T) is studied. It is shown that lightly doped samples ([In]/[Cd]1%) exhibit ferromagnetic ordering, with ${\mathit{M}}_{\mathit{s}}$(T) and D(T) being linear functions of ${\mathit{T}}^{3/2}$ and ${\mathit{T}}^{5/2}$, respectively. A higher concentration of indium produces the reentrant transition and spin-glass state of magnetic ordering in ${\mathrm{CdCr}}_{2\mathit{x}}$${\mathrm{In}}_{2\mathrm{\ensuremath{-}}2\mathit{x}}$${\mathrm{Se}}_{4}$. A numerical analysis of the saturation magnetization and linewidth temperature dependence has been performed in order to determine the type of magnetic ordering.