Structure, electrical and chemical properties of zirconium nitride films deposited by dc reactive magnetron sputtering

2 and Ar ambient. X-ray diffraction indicated that growth of ZrN with a preferred (111) orientation over Si(100) was achieved. The resistivity of the films varies from 200 μΩcm to 15 μΩcm depending on the N₂ content in the working gas. The square resistance of the films deposited on 96% Al₂O₃ ceramic wafers is stable below 300 °C. Received: 17 June 1996/Accepted: 9 December 1996     

Excimer laser deposited CuO and Cu<Subscript>2</Subscript>O films with third-order optical nonlinearities by femtosecond <Emphasis Type="Italic">z</Emphasis>-scan measurement

By controlling the oxygen pressure, single-phase CuO and Cu₂O thin films have been obtained on quartz substrates using a pulsed laser deposition technique. The structure properties and linear optical absorption of the films were characterized by X-ray diffraction and UV–VIS spectroscopy. By performing z-scan measurements using a femtosecond laser (800 nm, 50 fs), the real and imaginary parts of the third-order nonlinear susceptibility, Re χ ⁽³⁾ and Im χ ⁽³⁾, of the films were determined. Both CuO and Cu₂O films exhibited large optical nonlinearities, which is comparable to those in some representative semiconductor films such as ZnO and GaN films using femtosecond laser excitation. Compared with Cu₂O films, the CuO films showed larger third-order nonlinear optical effects under off-resonance excitation. Furthermore, the mechanisms of the optical nonlinearities in CuO and Cu₂O films are explained in the main text. It was suggested that the reasons of the difference in their nonlinear refractive effects may be related to the different electronic structure in CuO and Cu₂O materials.     

Transverse Seebeck effect in Bi2Sr2CaCu2O8

2 Cu₃O₇ has been observed in “off-c-axis” grown Bi₂Sr₂CaCu₂O₈ films. The films were prepared by pulsed laser deposition from Bi₂Sr₂CaCu₂O₈ targets and grown with a tilt angle of 10 degrees between the film c-axis and the film surface on off-axis cut SrTiO₃ substrates. From the thermoelectric response upon laser irradiation the anisotropy of the thermopower is estimated. Received: 15 April 1996/ Accepted:19 November 1996     

Pulsed laser deposition of (110) oriented semiconductive SrFeO3−x thin films

 The semiconductive perovskite-type oxide SrFeO_3-x (x<0.16) (SFO) thin films have been directly fabricated on (001)SrTiO₃ and (001)LaAlO₃ single crystal substrates by pulsed laser deposition(PLD) under high oxygen partial pressure of 100 Pa. The SFO thin films were (110) oriented. The x-ray photoelectron spectroscopy (XPS) analysis showed that the surface of SFO thin film has strong gas absorption capability. The resistance versus temperature has been measured in the temperature range from 77 K to 300 K. The SFO thin film showed typical semiconductive property. Dependence of resistance of SFO thin film on oxygen pressure was measured and result showed that the SFO thin film had better oxygen sensitive property. Received: 14 May 1996/Accepted: 15 August 1996     

Deposition and characterization of ITO films produced by laser ablation at 355 nm

Indium tin oxide (ITO) films have been deposited by pulsed laser deposition (PLD) at 355 nm. Even though the absorption of laser light at the wavelength 355 nm is much smaller than that of the standard excimer lasers for PLD at 248 nm and 193 nm, high-quality films can be produced. At high fluence and at high substrate temperatures, the specific resistivity of the films, 2–3×10^-4 Ω cm, is comparable to values obtained with excimer lasers, whereas the resistivities obtained at room temperature are somewhat higher than those of films produced by excimer lasers. The transmission coefficient of visible light, about 0.9, is also comparable to values for films deposited by excimer lasers. The crystalline structure of films produced at 355 nm is similar to that of samples produced by these lasers. Received: 16 January 2001 / Accepted: 24 July 2001 / Published online: 17 October 2001     

Laser-induced desorption of Na-dimers

We find that Na-dimers are desorbed in a thermal process if rough Na surfaces are irradiated with pulsed laser light of λ=532 nm. In contrast, for light of λ=355 nm, Na₂ can be detached in a non-thermal reaction at low laser fluences. This is concluded from the kinetic energy distributions of the dimers determined by time-of-flight measurements using a second laser at λ=248 nm for photoionization. The transition from non-thermal to thermal desorption at large fluences of the laser light can also be identified. Received: 23 July 1996 / Accepted: 26 August 1996     

The role of photoelectronic processes in the formation of a fluorescent plume by 248-nm laser irradiation of single crystal NaNO3

 Visible fluorescent “plumes” are readily produced when nominally transparent ionic materials are exposed to pulsed UV laser irradiation. Over a wide range of laser fluences where plumes are observed, however, the photon and electron densities are inadequate to support multiphoton ionization and inverse bremsstrahlung, which are often used to explain plasma production and excitation of atomic spectral lines. We present evidence that the great majority of charged particles (electrons and positive ions) comprising the plume at the onset of formation in defect-laden NaNO₃ are emitted directly from the surface. A model is described wherein the required electron energy to excite and eventually ionize neutral atoms is provided by electrostatic interactions in the expanding plume. The time evolution of the “overlap” between the expanding charge cloud and thermally emitted neutrals accounts for the time evolution of the atomic line emissions after the laser pulse. Received: 15 August 1996/Accepted: 16 August 1996     

Production and characterization of Nd,Cr:GSGG thin films on Si(001) grown by pulsed laser ablation

Nd,Cr:Gd₃Sc₂Ga₃O₁₂ (GSGG) thin films have been produced for the first time. They were grown on Si(001) substrates at 650 °C by pulsed laser ablation at 248 nm of a crystalline Nd,Cr:GSGG target rod. The laser plume was analyzed using time-of-flight quadrupole mass spectroscopy, and consisted of elemental and metal oxide fragments with kinetic energies typically in the range 10 to 40 eV, though extending up to 100 eV. Although films deposited in vacuum using laser fluences of 0.8±0.1 J cm⁻² reproduced the Nd,Cr:GSGG bulk stoichiometry, those deposited using fluences above ≈3 J cm⁻² resulted in noncongruent material transfer and were deficient in Ga and Cr. Attempts to grow films using synchronized oxygen or oxygen/argon pulses yielded mixed oxide phases. Under optimal growth conditions, the films were heteroepitaxial, with GSGG(001)[100]∥Si(001)[100], and exhibited Volmer–Weber-type growth. Room-temperature emission spectra of the films suggest efficient non-radiative energy transfer between Cr³⁺ and Nd³⁺ ions, similar to that of the bulk crystal. Received: 1 October 1999 / Accepted: 15 October 1999 / Published online: 23 February 2000     

Effect of the growth conditions on infrared upconversion efficiency of CaS: Eu, Sm thin films

High-quality electron-trapping thin films CaS: Eu, Sm with red light output have been successfully deposited on quartz and single-crystal silicon substrates by electron beam evaporation (EBE) and radio frequency (RF) magnetron sputtering in vacuum and H₂S partial pressures. Infrared upconversion efficiency of CaS: Eu, Sm thin films under different growth conditions has been investigated by using ultrashort infrared (IR) laser pulse with 20 ps (full width at half-maximum (FWHM)). The results show that upconversion efficiency of CaS: Eu, Sm thin films depends strongly on growth conditions in spite of the existence of “exhaustion” phenomena. Microstructures identified by X-ray diffraction (XRD) indicate that crystallinity of CaS films relies on both substrate materials and growth conditions. The stoichiometric composition of CaS films was measured by secondary-ion mass spectrometry (SIMS). The post-annealing process was found to promote grain growth and activate strong luminescence so that it could obviously improve upconversion efficiency of CaS: Eu, Sm films, even though it had negative influence on transmittance and spatial resolution of these films. Received: 5 June 2000 / Accepted: 7 June 2000 / Published online: 23 August 2000     

Effect of laser fluence on the deposition and hardnessof boron carbide thin films

We deposited amorphous thin films of boron carbide by pulsed laser deposition using a B₄C target at room temperature. As the laser fluence increased from 1 to 3 J/cm², the number of 0.25–5 μm particulates embedded in the films decreased, and the B/C atomic ratio of the films increased from 1.8 to 3.2. The arrival of melt droplets, atoms, and small molecular species depending on laser fluence appeared to be involved in the film formation. In addition, with increasing fluence the nanoindentation hardness of the films increased from 14 to 32 GPa. We believe that the dominant factor in the observed increase in the films’ hardness is the arrival of highly energetic ions and atoms that results in the formation of denser films. Received: 23 March 2001 / Accepted: 1 July 2001 / Published online: 2 October 2001     

Structural, electrical, and surface characteristics of La0.5Sr0.5CoO3 thin films prepared by pulsed-laser deposition

A parametric study of the growth of La_0.5Sr_0.5CoO₃ (LSCO) thin films on (100) MgO substrates by pulsed-laser deposition (PLD) is reported. Films are grown under a wide range of substrate temperature (450–800 °C), oxygen pressure (0.1–0.9 mbar), and incident laser fluence (0.8–2.6 J/cm²). The optimum ranges of temperature, oxygen pressure, and laser fluence to produce c-axis oriented films with smooth surface morphology and high metallic conductivity are identified. Films deposited at low temperature (500 °C) and post-annealed in situ at higher temperatures (600–800 °C) are also investigated with respect to their structure, surface morphology, and electrical conductivity. Received: 20 November 1998 / Accepted: 6 July 1999 / Published online: 21 October 1999     

“Cold” CO<Subscript>2</Subscript> laser ablation of green-state LTCC—experimental verification of improved model and comparison of various LTCC materials

New experimental results in support of the universal mechanism of “cold” laser ablation for machining of various commercial green ceramic materials (LTCC) are presented in this paper. The “cold” ablation model was mathematically formulated and employed to derive an ablation curve equation. The model was tested by CO₂ laser ablation of a custom-made green-state alumina ceramic featuring varying binder content. An excellent fit of ablation curve to experimental data was obtained, yielding insight into process energetics and an ablative measurement method of absorption coefficient. The analysis was applied to a sample of commercial LTCC materials. The ablation results were practically identical for all materials in agreement with the prediction of the model, with the high rates of >100 micron/shot at repetition >1 kHz and accuracy comparable with the ceramic grain size. This work provides evidence that the CO₂ laser processing has a great potential to become a key low-cost precision processing method for the existing LTCC-based electronic devices (micro-via drilling, general cutting and scribing) and for the new generation of LTCC-based devices comprising micro-fluidics, micro-mechanics, opto-electronics and meta-material structures.     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Characterization and antibacterial functions of Ag–TiO<Subscript>2</Subscript> and W–TiO<Subscript>2</Subscript> nanostructured thin films prepared by sol-gel/laser-induced technique

A novel sol-gel/laser-induced technique (SGLIT) has been developed to form nanocrystalline titanium dioxide (TiO₂) based thin films with an improved antibacterial performance. TiO₂ precursor films loaded with W⁺⁶ and Ag⁺² ions (W–TiO₂, Ag–TiO₂) were prepared separately by sol-gel method and spin-coated on microscopic glass slides. As-dried films were subjected to KrF excimer laser pulses at optimized parameters to generate mesoporous anatase and rutile phases at room temperature. The anatase phase was obtained after irradiation with 10 laser pulses only at 75–85 mJ/cm² fluence in W–TiO₂ films. However, higher number of laser pulses and higher W⁺⁶ content favored the formation of rutile. Whereas Ag–TiO₂ films exhibited anatase up to 200 laser pulses at the same fluence. The films were characterized by using XRD, FEG-SEM, TEM and UV-Vis spectrophotometer to investigate the crystallographic structure, phase transformation, surface morphology, film thickness and the optical properties. A crystallite size of approximately 20 nm was achieved from the anatase prepared by SGLIT. The films exhibited an enhanced antibacterial function against E-Coli cells under the UV excitation.     

Microstructures and dielectric properties of compositionally graded (Ba1-xSrx) TiO3 thin films prepared by pulsed laser deposition

Compositionally graded (Ba_1-xSr_x)TiO₃ (BST) (x:0.0∼0.25) thin films were grown on Pt (111)/TiO₂/SiO₂/Si (100) substrates using layer-by-layer pulsed laser deposition in the temperature range 550–650 °C. Both downgraded (Ba/Sr ratio varying from 100/0 at the bottom surface to 75/25 at the top surface) and upgraded (Ba/Sr ratio varying from 75/25 at the bottom surface to 100/0 at the top surface) BST films were prepared. Their microstructures were systematically studied by X-ray diffractometry and scanning electron microscopy. A grain morphology transition from large ‘rosettes’ (>0.30 μm) to small compact grains (70–110 nm) was observed in the downgraded BST films as the deposition temperature was increased from 550 to 650 °C. No such grain morphology transition was detected in the upgraded BST films. Dielectric measurements with metal electrodes revealed an enhanced dielectric behavior in the downgraded films. This enhancement is mainly attributed to the large compressive stress field built up near the interface between the downgraded film and substrate. Furthermore, the BaTiO₃ layer in the downgraded BST films not only serves as a bottom layer but also as an excellent seeding layer for enhancing the crystallization of the subsequent film layers in the downgraded films. Received: 10 December 2001 / Accepted: 12 March 2002 / Published online: 19 July 2002 RID="*" ID="*"Corresponding author. Fax: 86-25/359-5535, E-mail: xhzhu@public1.ptt.js.cn     

CuO-PAA hybrid films: Chemical synthesis and supercapacitor behavior

We report the synthesis of CuO-Poly (acrylic) acid (PAA) hybrid thin films by a cost-effective spin coating technique for supercapacitor application. Coated films were annealed at 300, 400 and 500 °C, to study the annealing effect on the supercapacitor behavior. Further films were characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform-Raman spectroscopy (FT-Raman) and Fourier transform-Infrared spectroscopy (FT-IR) techniques. Energy dispersive spectroscopy (EDS) shows the formation of amorphous blend of CuO and Cu₂O phases at 300 °C. Further, films annealed at 400 and 500 °C exhibit polycrystalline phase pure CuO with monoclinic structure. The scanning electron microscopy (SEM) micrographs show the transition of island-like structure to CuO crystals surrounded by PAA grafted composite ring with increase in annealing temperature. The possible growth mechanism of PAA and CuO bonding is discussed. Cyclic voltammetry (CV) is employed to calculate the specific capacitance (C_sp) in 1 M H₂SO₄ electrolyte. It is observed that the C_sp increases from 41 to136 F g⁻¹ with increase in annealing temperature.     

Raman characteristics of carbon nitride synthesized by nitrogen-ion-beam-assisted pulsed laser deposition

Raman characteristics of carbon nitride films synthesized by nitrogen-ion-beam-assisted pulsed laser deposition were investigated. In addition to the D (disorder) band and G (graphitic) band commonly observed in carbon nitride films, two Raman bands located at 1080–1100 and 1465–1480 cm^-1 were found from our carbon nitride films. These two bands were well matched with the predicted Raman frequencies for βC₃N₄ and the observed Raman bands reported for carbon nitride films, indicating their relation to carbon-nitrogen stretching vibrations. Furthermore, the relative intensity ratio of the two Raman bands to the D and G bands increased linearly with increasing nitrogen content of the carbon nitride films. Received: 30 October 2000 / Accepted: 5 February 2001 / Published online: 2 October 2001     

Growth and characteristics of reactive pulsed laser deposited molybdenum trioxide thin films

Molybdenum trioxide thin films were prepared by reactive pulsed laser deposition on Corning 7059 glass substrates. The influence of oxygen partial pressure and deposition temperature on the structure, surface morphology and optical properties of these films was studied to understand the growth mechanism of MoO₃ thin films. The films formed at 473 K in an oxygen partial pressure of 100 mTorr exhibited predominantly a (0k0) orientation, corresponding to an orthorhombic layered structure of α-MoO₃. The evaluated optical band gap of the films was 3.24 eV. The crystallite size increased with increase of deposition temperature. The films formed at an oxygen partial pressure of pO₂=100 mTorr and at a deposition temperature greater than 700 K exhibited both (0k0) and (0kl) orientations, representing α-β mixed phases of MoO₃. The films formed at an oxygen partial pressure less than 100 mTorr were found to be sub-stoichiometric with α-β mixed phases. The investigation revealed the growth of polycrystalline and single-phase orthorhombic-layered-structure α-MoO₃ thin films with composition nearly approaching the nominal stoichiometry at moderate substrate temperatures in an oxygen partial pressure of 100 mTorr. Received: 9 April 2001 / Accepted: 6 August 2001 / Published online: 17 October 2001     

Femtosecond-laser-induced-crystallization and simultaneous formation of light trapping microstructures in thin a-Si:H films

We report the observation of crystallization and simultaneous formation of surface microstructures in hydrogenated amorphous silicon (a-Si:H) thin films as one step laser processing. Light trapping microstructures of around 300 nm in height were formed on a-Si:H films of thickness in the range of 1.5 μm to 2 μm deposited on soda lime glass after exposure to femtosecond laser pulses. Scanning electron microscope (SEM) images show the formation of spikes that are around 1 μm part and their heights could be controlled by the laser fluences. Atomic force microscope (AFM) images were taken to study the roughness created on the surface. The mean roughness of the textured surface increases with laser fluence at smaller power densities, and for power densities beyond 0.5 J/cm² the film removal deteriorates the texturing. X-ray diffraction results indicate the formation of a nano-crystalline structure with (111) and (311) crystal orientation after the laser treatment. The observed black color and enhanced optical absorption in the near infrared region in laser treated films may be due to a combined effect of light trapping in the micro-structured silicon surface because of multiple total internal reflections, phase change in the film, possible defect sites induced after laser treatment and formation of SiO_x. Demonstration of light trapping microstructures in thin a-Si:H films and simultaneous crystallization could provide new opportunities for optoelectronic devices. PACS 42.55.Px; 42.62.Cf; 81.05.Ge     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.