Growth control of stoichiometry in LaMnO3 epitaxial thin films by pulsed laser deposition

We have studied structural, magnetic, and optical transport properties of LaMnO₃ (LMO) thin films grown on SrTiO₃. While the stoichiometric LMO is an insulating antiferromagnet, it tends to be a ferromagnetic insulator when grown as thin films. By exploring the majority of growth parameters, we have found that the bulk-like electronic and magnetic phases can be stabilized by growing thin films under reducing atmospheres and by using more energetic laser processes. These conditions are found to reduce the La deficiency in the film resulting in the greatly improved cation stoichiometry. Since oxides are prone to reduce the oxygen content and to alter the cation ratio under such growth conditions, it suggests that the cation and oxygen stoichiometries in complex oxide thin films can be improved by properly optimizing the growth parameters.     

Effect of Mn concentration and growth temperature on nanostructures and magnetic properties of Ge1−xMnx grown on Si

The nanostructures and magnetic properties of Ge_1−xMn_x thin films grown on Si substrates by molecular beam epitaxy, with different nominal Mn concentrations (1−4%) and different growth temperatures, have been systematically investigated by transmission electron microscopy and superconducting quantum interference device. It was discovered that when Ge_1−xMn_x thin films were grown at 70 °C, with increase in Mn concentration, Mn-rich tadpole shaped clusters started to nucleate at 1% Mn and become dominate in the entire film at 4% Mn. While for the thin films grown at 150 °C, tadpoles was firstly seen in the film with 1% Mn and subsequently Mn-rich secondary precipitates became dominant. The magnetic properties show specific features, which are mainly related to the nature and amount of Mn-rich clusters/precipitates within these thin films.     

Optical properties and chemical bonding characteristics of amorphous SiNX:H thin films grown by the plasma enhanced chemical vapor deposition method

Amorphous silicon nitride (SiN_X:H) thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method are presently the most important antireflection coatings for crystalline silicon solar cells. In this work, we investigated the optical properties and chemical bonding characteristics of the amorphous SiN_X:H thin films deposited by PECVD. Silane (SiH₄) and ammonia (NH₃) were used as the reactive precursors. The dependence of the growth rate and refractive index of the SiN_X:H thin films on the SiH₄/NH₃ gas flow ratio was studied. The chemical bonding characteristics and the surface morphologies of the SiN_X:H thin films were studied using the Fourier transform infrared spectroscopy and atomic force microscopy, respectively. We also investigated the effect of rapid thermal processing on the optical properties and surface morphologies of the SiN_X:H thin films. It was found that the rapid thermal processing resulted in a decrease in the thickness, increase in the refractive index, and coarser surfaces for the SiN_X:H thin films.     

Laser wavelength effect on structural and optical properties of Cd34Se66 nanocrystalline thin film

Cadmium Selenide (Cd₃₄Se₆₆) thin films are deposited on a glass substrate using the thermal evaporation method at room temperature. The Cd₃₄Se₆₆ films are characterized using XRD. The crystallite size of the film is calculated from XRD data, which is found as 29.61 nm as-deposited. It is also found that crystallite size of Cd₃₄Se₆₆ changed after irradiation with N₂ and Nd:YAG laser. The changes in the optical properties of the films after irradiation with N₂ laser and Nd:YAG laser are also studied in the wavelength range of 300-700 nm and it is found that the optical band gap of the Cd₃₄Se₆₆ films changed after laser irradiation.     

Structure of pulsed-laser deposited arsenic-rich As–S amorphous thin films,and effect of light and temperature

Thin amorphous films from As–S system (∼As₅₀S₅₀) were prepared by the pulsed laser deposition technique. Light- and thermally-induced changes of structure of studied films have been investigated using Raman scattering spectroscopy results and interpreted in terms of chemical reactions and/or phase transitions between individual structural units. The irradiation of as-deposited thin films causes light-induced reactions, in which As₄S₃, α- and β-As₄S₄, and pararealgar/χ-As₄S₄ molecules are formed. Thermal-annealing of exposed thin films leads to the formation of β-As₄S₄ molecules.     

Magnetic and magnetotransport behavior of granular FexAg100−x thin films

We present magnetic and magnetotransport properties of Fe_xAg_100−x granular thin films prepared by the pulsed laser deposition technique. Increasing the Fe nanoparticles, x, the interactions among them modify the magnetic response from an interacting superparamagnetism to a ferromagnetic-like behavior with a crossover at x = 25. For this value, an extraordinary Hall effect becomes dominant while magnetoresistance decrease. The appearance of in-plane anisotropies are discussed through the study of extraordinary Hall effect.     

Thin film deposition of Ge33As12Se55 by pulsed laser deposition and thermal evaporation: Comparison of properties

Thin films of Ge₃₃As₁₂Se₅₅ were produced using two deposition techniques, ultra-fast pulsed laser deposition (UFPLD) and thermal evaporation (TE), and their properties have been investigated. The chemical composition of the UFPLD films was virtually identical to the composition of the chalcogenide glass targets, whereas the composition of films deposited by TE was significantly different from the target material. Heating of the substrate with a temperature gradient during deposition produced a gradient in composition in both UFPLD and TE films.     

Ionic conductivity of Li2OB2O3 thin films

The ionic conductivity of evaporated Li₂OB₂O₃ thin films has been studied. These thin films were found to show a considerably high ionic conductivity of 1 × 10^?7 Ω^?1 cm^?1 at room temperature. The conductivity increases with increasing Li content and exhibits a maximum value near 3Li₂O·B₂O₃. The structure of these films was determined using infrared absorption and laser Raman scattering spectroscopy. Using the results, the correlation between structure and conductivity is also discussed.     

Influence of pulsed laser deposition rate on the microstructure and thermoelectric properties of Ca3Co4O9 thin films

The effects of deposition rate on the microstructure and thermoelectric (TE) properties of Ca₃Co₄O₉ thin films fabricated by pulsed laser deposition (PLD) technique were investigated. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca_xCoO₂ secondary phase. Formation of Ca_xCoO₂ was inevitable during the thin film growth, and this was discussed from both structural and compositional point of view. With longer deposition interval or with sufficient oxygen at a lower deposition rate, the Ca_xCoO₂ phase was able to transit into the desired Ca₃Co₄O₉ phase during the coalescence process. The quality of the thin films was further analyzed by electrical properties measurements. The Ca₃Co₄O₉ thin film fabricated at a slower deposition rate was found to exhibit a low electrical resistivity of 9.4 mΩ cm and high Seebeck coefficient of 240 μV/K at about 700 °C, indicating a good quality film.     

Effects of oxide buffer layers on the microstructure and electrical properties of PLZST 2/87/10/3 antiferroelectric thin films

In the present work, the effects of oxide buffer layers, such as ZrO₂, CeO₂ and TiO₂, on the microstructure and electrical properties of (Pb_0.97La_0.02)(Zr_0.87Sn_0.10Ti_0.03)O₃ (PLZST 2/87/10/3) antiferroelectric (AFE) thin films were investigated systematically. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) pictures illustrated that the crystalline orientation and surface microstructure of PLZST 2/87/10/3 AFE thin films had a close relation with these oxide buffer layers. As a result, the final electrical properties of AFE films were tuned by these buffer layers. Electrical measurements result showed that the dielectric properties, polarization characteristic and current–field curves of AFE thin films could be tailored by selecting a proper oxide buffer layer.     

Effect of hot-wire passivation on the properties of hydrogenated microcrystalline silicon films to reduce post-deposition oxidation

Hydrogenated microcrystalline silicon (μc-Si:H) films have a large number of grain boundaries that oxidize after deposition, leading to deterioration of device performance. In this study, post-treatment of μc-Si:H thin films was carried out with methane-related radicals generated by a hot wire. The effect of the hot-wire passivation on the properties of the μc-Si:H thin films was investigated using Fourier-transform infrared (FT-IR) transmission spectroscopy. Through post-treatment, hydrogen on the silicon-crystallite surface was substituted with hydrocarbon. Further, an increase in filament temperature (T_ft) was found to enhance passivation. For films treated at T_ft above 1700 °C, post-oxidation and nitridation hardly occurred, whereas films treated at T_ft below 1400 °C were oxidized and nitrided even after post-treatment.     

Growth and structure properties of La1−xSrxMnO3−σ (x=0.2, 0.3, 0.45) thin film grown on SrTiO3 (0 0 1) single-crystal substrate by laser molecular beam epitaxy

La_1−xSr_xMnO_3−σ (LSMO) thin films have been grown on SrTiO₃ (0 0 1) single-crystal substrates using the laser molecular beam epitaxy (MBE) technique. The two-dimensional layer-by-layer growth was in-situ monitored by reflection high-energy electron diffraction (RHEED). Kinetic growth with surface relaxation was also observed, and crystallinity of the thin films was investigated by high-resolution X-ray diffraction. Results of 2θ−ω scans revealed a strong correlation between out-of-plane lattice constant and oxygen content as well as strontium doping concentration. However, further analysis of rocking curve measurements around (0 0 2) plane of thin films grown under different oxygen pressure (P_O2) shown the effects of oxygen content on the crystal structure. An exceptionally low full-width at half-maximum (FWHM) of 0.02° was measured from the sample grown at P_O2 of 5.0 Pa, indicating the almost perfect epitaxial growth of LSMO thin films.     

Epitaxial Mn-doped ZnO diluted magnetic semiconductor thin films grown by plasma-assisted molecular-beam epitaxy

A growth window for the Mn effusion cell temperature (T_Mn) is demonstrated for epitaxial Mn-doped ZnO (MnZnO) thin films grown on sapphire substrates using molecular-beam epitaxy. Within the growth window, the films are ferromagnetic with the largest saturated magnetization occurring at T_Mn=700 °C. The Curie temperature of these MnZnO diluted magnetic semiconductor thin films is above room-temperature. The ferromagnetism is weakly anisotropic. Well-resolved near-band-edge photoluminescence emissions dominate the spectra at both low- and room-temperatures. No evident spin polarization on the carriers was detected with the magneto-photoluminescence studies. Magnetoresistance and anomalous Hall effects of the MnZnO thin films were studied. The anomalous Hall coefficient shows a quadratic dependence on the resistivity.     

Growth and electrical properties of flash evaporated AgGaTe2 thin films

Thin films have been prepared by flash evaporation technique of a stoichiometric bulk of AgGaTe₂ compound in vacuum and analysed using X‐ray diffraction, transmission electron microscopy, selected area diffraction and energy dispersive analysis of X‐rays. The effect of substrate temperature on the structural properties – grain size, film orientation, composition, and stoichiometry of the films have been studied. It was found that the polycrystalline, stoichiometric films of AgGaTe₂ can be grown in the substrate temperature range of 473K < Ts < 573K. The influence of substrate temperature (Ts) on the electrical characteristics‐ Resistivity, Hall Mobility, Carrier concentration of AgGaTe₂ thin films were studied. The electrical resistivity was found to decrease with increase in substrate temperature up to 573K and then increases. The variation of activation energy of AgGaTe₂ thin films were also investigated. The implications are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of temperature on the microcrystalline structure of thermally evaporated Sb2S3 thin films

Thin films of antimony trisulfide (Sb₂S₃) were prepared by thermal evaporation under vacuum (p=5×10^–5 torr) on glass substrates maintained at various temperatures between 293 K and 523 K. Their microstructural properties have obtained by transmission electron microscopy (TEM). The electron diffraction analysis showed the occurrence of amorphous to polycrystalline transition in the films deposited at higher temperature of substrates (523 K). The polycrystalline thin films were found to have an orthorhombic structure. The interplanar distances and unit‐cell parameters were determined by high‐resolution transmission electron microscopy (HRTEM) and compared with the standard values for Sb₂S₃. The surface morphology of Sb₂S₃ thin films was investigated by scanning electron microscopy (SEM). The optical transmission spectra at normal incidence of Sb₂S₃ thin films have been measured in the spectral range of 400–1400 nm. The analysis of the absorption spectra revealed indirect energy gaps, characterizing of amorphous films, while the polycrystalline films exhibited direct energy gap. From the photon energy dependence of absorption coefficient, the optical band gap energy, E_g, were calculated for each thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TiO2 thin films as sensing gas materials

TiO₂ thin films were prepared by DC reactive magnetron sputtering on heated Si, quartz and glass substrates using O₂ and water vapor as reactive gases. The percentage of anatase and rutile as well as the grain size strongly depend on the deposition conditions, as revealed by X-ray diffraction patterns. The films deposited on Si substrates are pure rutile, while a mixed anatase/rutile structure occurs in the films deposited on glass and quartz substrates. Smaller grain rutile and anatase films were prepared in a water vapor atmosphere, in contrast to the films grown in oxygen. The former choice considerably increases the sensing properties of titanium dioxide films. The gas sensitivity was investigated for some reducing gases (methane, acetone, ethanol and liquefied petroleum gas) and the optimum operating temperatures were found.     

RbxK1-xTiOPO4 Thin Films Grown on KTiOPO4 Substrates by Liquid Phase Epitaxy

The properties of Rb_xK_1-xTiOPO₄ thin films grown on KTiOPO₄ substrates are reported. High quality films were obtained using the flux liquid phase epitaxy method, and optical waveguiding was observed in these epitaxial films. X-ray analysis shows that the epitaxial films are single crystals films. Their cell constants are different from those of the substrates. The epitaxy growth rate and other film properties were compared for films grown on different faces. Two different surface morphologies were observed for films grown on (100) faces. The morphologies on (201) and (201) faces were also different. The quality of films grown on the (201) face was better. The reason for a structure inversion for films grown on the z⁻ face is discussed.     

Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

DC magnetron power dependence of a-SiC:H IR absorption properties

The infrared absorption properties of a-SiC:H thin films dependence with the dc magnetron power density were investigated. The films were deposited in a mixture of CH₄, H₂ and Ar. The target used was polycrystalline Si. We found that the dc magnetron power density has an important contribution to the film composition. There is a strong dependence of the Si-H and Si-C bonds with the dc power density.     

Synthesis of epitaxial Y-type magnetoplumbite thin films by quick optimization with combinatorial pulsed laser deposition

Y-type magnetoplumbite (Ba₂Co₂Fe₁₂O₂₂:Co₂Y) epitaxial thin films with such a huge lattice parameter as 43.5 Å have been synthesized for the first time. Combinatorial thin film technology was successfully employed to eliminate an impurity phase in the film by quickly optimizing such reaction parameters as the deposition temperature and the thickness of pre-deposition of CoO layer. The coupling of combinatorial pulsed laser deposition and subsequent concurrent X-ray diffraction, both of which we have developed, is a promising way to high throughput optimization of thin film growth and properties.