Reactive pulsed laser deposition and laser induced crystallization of SnO2 transparent conducting thin films

Transparent conducting SnO₂ thin films with a thickness between 1000–2000 Å were deposited on glass, quartz and silicon substrates using standard pulsed laser deposition techniques with two different targets (Sri and SnO₂) and with three different laser wavelengths (1.06, 0.532 and 0.266 ) from a Q-switched Nd: YAG laser. Tin dioxide films with optical transmission over most of the visible spectrum exceeding 80% were obtained using a Sn target and a background oxygen pressure of 20 Pa. The electrical resistivity () depended strongly on the substrate temperature during deposition, with the lowest values of of about 10^–2 -cm obtained when the substrate was maintained at 400°C during deposition. Using SnO₂ targets, predominantly amorphous phase SnO₂ films were deposited on Si substrates and then transformed into polycrystalline Sn₃O₄ by laser induced crystallization ( = 1.06 m). Whereas these later films were essentially non-conducting as deposited ( > 400 -cm), the electrical resistivity was permanently reduced after laser induced crystallization by a factor greater than 1000 to a value of approximately 4 × 10^–1 -cm.     

Opto-thermal study of the melting transition of benzophenone

We report a series of opto-thermal transient emission radiometry (OTTER) measurements on benzophenone over the temperature range 20–80°C, which includes the melting transition at 48°C. At temperatures sufficiently close, but below the melting point, the form of the opto-thermal decay curves was found to change, when the laser pulse energy was sufficient to cause transient melting near the surface. Such measurements could be useful in the study of re-crystallation dynamics in pulsed laser annealing and similar surface treatments. In addition, the experiment gives a direct measure of ₀, the initial jump in surface temperature, and a comparison of solid and liquid thermal diffusivities. The values found in the present study are ₀, andD(solid)/D(liquid)=2.2±0.2.     

Near Field Observation of a Refractive Index Grating and a Topographical Grating by an Optically-Trapped Gold Particle

We observed the near field for a refractive index grating fabricated on a planar light waveguide circuit (PLC) by scanning an optically-trapped 100 nm diameter gold particle. We demonstrate that stable trapping and scanning occur with a Gaussian laser beam at the scan velocity of 1.6 m/s and Nd:YAG laser power of 25mW. The scattered Ar laser light from the gold particle is strong at high refractive indexes of the grating with periods of 1.06 m and 0.53 m both by s and p polarized illumination. In addition, we observed the surface profile of the optical disk tracking groove with and without the gold particle. © 2004 The Optical Society of Japan     

Pulsed laser crystallization of hydrogen-free a-Si thin films for high-mobility poly-Si TFT fabrication

The possibility to fabricate high-mobility polysilicon TFTs by nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area ( 1 cm²) single ArF excimer laser pulse and a small diameter ( 100 m) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm²/Vs) which are much larger than in polysilicon TFTs fabricated onto the same quartz substrates by low-temperature thermal (630° C) crystallization of amorphous Si films (_fe55 cm²/Vs).     

Low-temperature growth of ZnO epitaxial films by metal organic chemical vapor deposition

ZnO films were grown on Al₂O₃ (0001) substrates by metal organic chemical vapor deposition at temperatures of T_g=150300 °C. Epitaxial growth was obtained for T_g200 °C. The in-plane orientation of the ZnO unit cells was found to change from a no-twist one with respect to that of the substrate at T_g=200 °C to a 30°-twist one at T_g=300 °C. Absorption and photoluminescence were observed from the film grown at 150 °C, although there was no evidence of epitaxial growth. Films grown at T_g200 °C exhibited smoother surfaces. Moreover, all the films grown at T_g=150300 °C revealed acceptor-related emission peaks, indicating the incorporation of acceptors into the films. PACS 81.15.Gh; 78.55.Et; 78.66.Hf     

A sensitive non-destructive method for measuring the Nd doping concentration in Nd : YAG with high spatial resolution

This paper reports on an experimental method for measuring in Nd:YAG the Nd doping concentration (C) with high sensitivity (0.01 at.%Nd) and high spatial resolution (50 m). The method is based on the measurement of the fluorescence lifetime _f of the upper Nd laser level. Additional parameters required to determine C are the intrinsic fluorescence lifetime ₀ and the quenching parameter Q. The measured values of _f, ₀ (256.47±0.14 s) and Q (4.45±0.40×10²⁰ cm^-3) allow us to calculate the Nd concentration C with an absolute accuracy of 0.1 at.%Nd. By using this method C is measured at the outer surfaces of standard laser rods and at the faces of boule slices (with diameters of up to 50 mm). The obtained results demonstrate a detection sensitivity of 0.01 at.%Nd. PACS 42.70.Hj; 81.70.Fy     

Effects of thickness on the infrared optical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films

Using infrared spectroscopic ellipsometry (IRSE), the optical properties of the Ba_0.9Sr_0.1TiO₃ (BST) ferroelectric thin films with different film thicknesses on Pt/Ti/SiO₂/Si substrates prepared by a modified sol-gel method have been investigated in the 2.5–12.6 m wavelength range. By fitting the measured ellipsometric parameter ( and ) data with a three-phase model (Air/BST/Pt) and the classical dispersion relation for the BST thin films, the optical constants and thicknesses of the thin films have been obtained. The average thickness of the single layer decreases with increasing film thickness. The refractive index of the BST films decreases with increasing thickness in the wavelength range 2.5–11 m, and increases with increasing thickness in the wavelength range 11–12.6 m. However, the extinction coefficient of the BST films monotonously decreases with increasing thickness. It is closely associated with the crystallinity of the thin films, the crystalline size effect and the influence of the interface layer. The absorption coefficient of the BST films with different thicknesses decreases with increasing thickness. PACS 77.55.+f; 78.20.Ci; 78.30.Am; 81.70.Fy; 81.40.Tv     

The influence of plastic deformation on the magnetostriction constant of nickel

The magnetostriction constant of nickel was measured as a function of plastic deformation up to an elongation of 30%. The values of the magnetostriction constant in deformed samples deviate considerably, a fact which cannot be explained by errors of measurement. The absolute value of the magnetostriction constant decreases with increasing plastic deformation (by around 5%).

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30% . , . ( 5%).

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In conclusion the authors thank J. Kaczér, C. Sc. and B. esták, C. Sc. for carefully reading the paper and for their remarks, J. Míová for help in the measurements and workers of the chemical department of our Institute for careful preparation of the samples.     

Properties of RF sputtered ZnxCd1−xS thin films

Zn _x Cd_1–x S thin films (0x0.20) were prepared using rf sputtering in argon atmosphere and characterized using X-ray diffraction, optical transmission, electrical resistivity and photoconductive decay measurements. The films were found to possess hexagonal structure. The crystallite size and degree of preferential orientation were found to decrease with the increase ofx and to improve upon annealing in vacuum at 250 °C. The transmission edge shifted towards shorter wavelengths with the increase ofx in agreement with the expected shift in the energy band gap. The films were found to exhibit room temperature resistivity in the range 100–1000 cm. The obtained values of long wavelength transmission (70–80%) and minority carrier diffusion length (30 m) are high enough for the application of these films in the field of solar cells.     

Tunable UV radiation at short wavelengths (188–240 nm) generated by sum-frequency mixing in lithium borate

Sum-frequency mixing (₃=₁+₂) of UV laser radiation (₁=266 nm and 213 nm) and tunable coherent infrared light (₂=1.2–2.6 m) in lithium borate (LBO) generates radiation at short wavelengths (₃=188–242 nm). The UV radiation at ₁ is produced by the fourth and fifth harmonic of a pulsed Nd-YAG laser. The infrared light is generated with an optical parametric oscillator of beta barium borate. The phase-matching angle is measured as function of ₃ and compared with calculated values. For UV laser radiation at shorter wavelengths (173 nm₁213 nm) the calculations predict an extension of the tuning range of the sum-frequency generated at ₃ to wavelengths as short as the LBO transmission cutoff at 160 nm.     

Microstructure Observations for Diffusion Induced Recrystallization and Diffusion Induced Grain Boundary Migration on Surfaces of Zincified Cu Bicrystals With [1 1 0] Twist Boundaries

The formation behavior of the fine-grain region alloyed with Zn due to diffusion induced recrystallization (DIR) in the Cu(Zn) system was experimentally examined for the surfaces polished in different manners using a Cu bicrystal containing a [1 1 0] twist boundary with a misorientation angle of = 46° zincified at 673 K for 2.88 × 10⁴ s with Cu-15 wt% Zn and Cu-30 wt% Zn alloys by a capsule zincification technique. The extent and morphology of the fine-grain DIR region vary depending on the surface conditions and the composition of the Zn-source Cu-Zn alloy. For the specimen with the surface electrolytically polished in an etchant consisting of 20 vol% of nitric acid and 80 vol% of methanol, no DIR region was formed on the whole surface when the Cu-15 wt% Zn alloy was used as a Zn source.In order to observe the morphology of the moving grain boundary owing to diffusion induced grain boundary migration (DIGM) without influences of DIR, Cu bicrystals with [1 1 0] twist boundaries of = 32 ( 27), 39 ( 9), 46, 51 ( 11) and 55° were electrolytically polished in the etchant mentioned above. The polished Cu bicrystals were zincified at 673 K for 2.88 × 10⁴ s using the Cu-15 wt% Zn alloy as a Zn source. Remarkable surface relief and clear slip bands were recognized on the surfaces due to DIGM for the specimens with the 32 ( 27) and 46° boundaries. The moving boundary became zigzag owing to the slip bands parallel to the moving direction. On the other hand, such surface relief and slip bands were not observed for the specimens with the 39 ( 9), 51 ( 11) and 55° boundaries. The moving boundary was considerably irregular for = 39° whereas rather smooth for = 51 ( 11) and 55°. The migration behavior of the grain boundary was not affected by the interruption of the zincification.     

Structural and optical properties of evaporated Zn oxide,Ti oxide and Zn-Ti oxide films

Zn oxide, Ti oxide and Zn-Ti oxide thin films were prepared by vacuum evaporation. Their structural and optical properties have been obtained by X-ray diffractometry (XRD), the energy-dispersive X-ray fluorescence (EDXRF) method and spectrophotometry. The EDXRF method was used to study the stoichiometry of the deposited Zn-Ti oxide films. The XRD patterns show that the prepared ZnO and Zn-Ti oxide films were polycrystalline, while Ti oxide films were amorphous. Spectroscopic optical constants n() and k() as well as the energy gap E_g were evaluated from spectrophotometry in the interband transition energy region. It was discovered that ZnO–TiO thin films remain transparent in a shorter wavelength range than the ZnO thin films, resulting from the slight increase of their band gap. It was found that n, k and transmittance values for the mixed-oxide film vary smoothly between the values of the pure constituent oxides in the fundamental energy gap region. PACS 68.60.Wm; 68.55.-a; 78.66.-w     

The influence of tensile stress on grain and cell boundary precipitation in supersaturated Al-Zn alloys during creep

The results are presented of the optical microscopic and X-ray diffraction study of the stress-induced nucleation and growth of (Zn) precipitates at grain and cell boundaries (GB's and CB's) during uniaxial creep at 200 °C of supersaturated AlZn20 and AlZn30 alloys. The rate of precipitation is increased mainly owing to the modifying effect of tensile stress on diffusion processes in alloy samples during their anneal. The diffusion of Zn atoms toward GB's and CB's from adjacent regions of grains is accompanied during creep by diffusive flux of Zn along boundaries parallel or nearly parallel to the tensile creep axis toward boundaries with near to normal orientation to that axis. Enhanced precipitation of results then preferentially at the latter and is supressed at the former boundaries where even the dissolution of preexisting has been found during a later application of tensile stress. The stress-induced precipitation of at GB's gradually ceases with prolonged creep exposures due to the lengthening of duffusion paths of Zn atoms from grain interior to GB's.Dissolution of lamellae by their regress toward GB's and CB's is assisted with the stress-induced diffusion of Zn along epitaxial / lamellar interfaces. Copious precipitation of at the parts of GB's and/or CB's with near to normal orientation to the creep axis is then observed on account of Zn from dissolved lamellae. Creep strain also leads to the fragmentation of lamellae and thus also to breaking down of the paths for diffusion of Zn along / interfaces. Spheroidization of fragmented parts of lamellae is then observed. Spheroids of remain embedded within the former lamellar regions.Large creep strains and high strain rates observed on fine-grained alloy samples may be associated with an enhanced viscous GB sliding due to the stress-dependent flow of Zn along GB's and/or CB's.     

Deposition of biopolymer thin films by matrix assisted pulsed laser evaporation

We report on the successful deposition of high quality type I fibrilar collagen thin films by Matrix assisted pulsed laser evaporation (MAPLE). Thin films deposition was performed in a N₂ ambient (20 Pa) using a KrF* laser source (=248 nm,20 ns) operated at a repetition rate of 3 Hz, the incident laser energy at a value within the range (20-35)mJ , and the laser spot area was (3.5-18.5)±0.1 mm². The collagen films were deposited on double face polished 100 single crystalline Si wafers and characterized by Fourier transform infrared spectroscopy, atomic force microscopy and high-resolution transmission electron microscopy. We demonstrate that our thin films are composed of collagen, with no impurities and the roughness can be controlled by the deposition conditions. PACS 52.38.Mf; 82.35.Pq; 83.80.Lz     

Inclined ZnO thin films produced by pulsed-laser deposition

ZnO thin films with a uniformly inclined structure are grown by pulsed-laser deposition on SrTiO₃. The c-axis of ZnO films is inclined by an angle =20±0.5° and =42±0.5° against the surface normal of 25° miscut (100) SrTiO₃ and (110) SrTiO₃ single crystal substrates, respectively. The inclined structure is due to epitaxial growth of hexagonal ZnO on cubic SrTiO₃ as evidenced by X-ray diffraction and high-resolution transmission electron microscopy investigations. The range of deposition parameters (substrate temperature, oxygen background pressure) to achieve epitaxial growth is determined. The inclined films are smooth with an rms surface roughness of 1.5 nm for layer thicknesses up to 700 nm. PACS 61.10.-i; 68.37.-d; 81.15.Fg     

Fabrication of Nd:KGW film on a Si substrate with a CeO<Subscript>2</Subscript> buffer layer

Highly textured single-oriented (110)Nd-doped potassium gadolinium tungstate [Nd:KGd(WO₄)₂ or Nd:KGW] thin films were successfully fabricated on (100)Si substrate by introducing a (100)CeO₂ buffer layer using KrF-excimer-laser pulsed laser deposition (PLD) at precisely controlled experimental conditions. The CeO₂ buffer layer was also prepared by PLD. Home-made potassium-enriched ceramic targets were prepared and used in order to prevent K deficiency in the film during the deposition. Depositions were performed in both Ar and O₂ environments. The optimal growing conditions achieved from the viewpoint of best crystallinity, optical properties and surface morphology were: d_T–S=4 cm, P(O₂)=0.08 mbar and T_sub=700 °C, respectively. Improvement of the properties of the as-grown films was examined by post-deposition annealing between 700 °C and 900 °C in air. Optical waveguide loss and the photoluminescence spectrum in the 800–1400-nm range were measured. PACS 81.15.Fg; 42.79.Gn; 42.79.Hj     

Pulsed laser deposition of non-stoichiometric silicon nitride (SiNx) thin films

Silicon nitride (SiN_x) thin films of various stoichiometries (x) were prepared on Si (100) substrates applying the Nd:YAG (=1064 nm) pulsed laser deposition (PLD) process in the shaded off-axis technique at room temperature. The specific arrangement of this technique with perpendicular target (Si) and substrate surfaces and a metallic screen in between guarantees very low particulate (droplet) deposition and, thus, excellent surface qualities. Compared to the usually used on-axis deposition technique consisting of a parallel arrangement of the target and substrate surface, the coating surface covered with particulates is about 100 times lower reaching a maximum of 0.2% on 400 nm thick films. The variation the N₂ partial pressure affects the nitrogen content and the silicon bonding structure of the films analysed by means of SIMS and XPS, respectively. As a consequence the optical properties (e.g.m refractive index) are tailorable in a wide spectral range between 250 and 1200 nm. PACS 81.15.Fg; 78.20.Ci     

The growth of crystalline vapor deposited carbon-60 thin films

Thin films (25-2500 Å) of C₆₀ molecules have been deposited on both (001) NaCl and mica substrates at varying temperatures by resistive evaporation. Both electron diffraction and high resolution microscopy have been used to assess the degree of crystallinity, the orientational ordering and the nature of the defects present in these face-centered-cubic films. For NaCl, optimum conditions yielded polycrystalline films with a tendency towards a 110 orientation, while for mica, extended single crystal films have been fabricated which exhibit a 111 direction normal to the film surface.     

Influence of Thermal Annealing and Deposition Conditions on the Structure and Optical Properties of GRS‐Active Substrates Based on Silver Films

Using the methods of atomicforce microscopy, xray diffractometry, and spectrophotometry, we have studied the morphological, structural, and optical characteristics of GRSactive substrates based on original and annealed silver films. We show that the backing temperature during deposition is the factor which exerts the most substantial effect on the morphological and optical properties of silver films and also on their stability with time. The coefficients of the correlation of the deposition rate with the characteristics of the optical density spectra of silver films are calculated. It is found that hightemperature (350°C) annealing of a silver film leads to the selforganization of its surface into a quasiperiodic structure with semiellipsoidal islets. The contribution of the processes of excitation of plasma resonances to the formation of the optical density spectra is discussed. It is shown that as a result of thermal modification the concentration of the crystalline phase of silver in a silver film increases 2–3 times and also the dispersion of the orientation of crystallites decreases.