KrF Excimer Pulsed Laser Deposition Research Articles

Effects of annealing temperature on amorphous GaN films formed on Si(1 1 1) by pulsed laser deposition

GaN thin films were grown on Si(1 1 1) substrates using a pulsed KrF excimer laser-deposition system, and post-annealing was examined to improve the films' quality. In order to investigate the effect of thermal annealing temperature on the crystalline quality, optical properties and surface morphology of the samples, after deposition, the samples were subsequently annealed at different temperatures in ammonia (NH3) ambience for 15 min. The annealed films were characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), Raman spectra and photoluminescence spectra. The measured results show that annealing temperature plays an important role in improving the quality of GaN films, polycrystalline wurtzite structure GaN thin films with c-axis preferred orientation were successfully obtained by annealing, and the optimum annealing temperature is 1100 °C.

Effects of Temperature on Microstructure and Tribological Performance of a-CN<sub>x</sub> Films Prepared by Pulsed Laser Deposition

a-CNx films were deposited onto silicon wafers at temperatures from RT up to 600 °C by using pulsed KrF excimer laser deposition. The composition, morphology and microstructure of the CNx films were characterized by X-ray photoelectron spectrum (XPS), scanning electron microscopy (SEM) and Raman spectrum. The tribological performance of the films was investigated using a ball-on-disk tribometer. With increasing the deposition temperature ranging from RT to 400 °C, the N content of films dropped from 36 at.% to 22 at.%, the ratio of N-sp3 C bonds, hardness and friction coefficient of the film decreased. Further increase of deposition temperature led to the lack of nitrogen and the increasing degree of order in ringed sp2 C=C bonds of the amorphous carbon film. The mechanical and tribological performances became worse. The film deposited at 300°C showed a low friction coefficient of 0.11 and a preferable wear resistance of 1.65×10–7 mm3 Nm–1 in humid air.

Pulsed-laser deposition of nanostructured Pd/C thin films: A new entry into metal-supported catalysts for hydrogen producing reactions

Carbon-supported palladium thin films were synthesized at room temperature by KrF excimer pulsed laser deposition by using oriented pyrolytic graphite and Pd target. By changing the experimental conditions, a range of structures, from smooth to porous cluster-assembled carbon films were obtained prior to deposition of the Pd films. High amount of sp 2 coordinated graphitic carbon embedded with large degree of disorder is observed in these carbon films. Surface morphology was studied by using scanning electron microscopy, while compositional analysis was performed by using energy dispersive spectroscopy. Structural analysis was performed using Raman spectroscopy and Fourier transform infrared spectroscopy. The importance of morphology and chemical structure of carbon films on their catalytic activity was investigated by using the hydrolysis of aqueous NaBH 4 as a reference process. Pd/C film produced by pulsed laser deposition are here demonstrated to be a better catalyst than Pd/C powder because of the high content of sp 2 bonding carbon atoms arranged into the porous and irregular surface of the carbon film.

Growth of Transparent Conductive Al-Doped ZnO Thin Films and Device Applications

High-purity transparent conductive Al-doped ZnO (AZO) films were grown by KrF excimer pulsed laser deposition. We used ultraviolet and X-ray photoelectron spectroscopes to directly measure the absolute values of the vacuum work function of AZO films. The structure and electrical and optical properties of the as-grown AZO films were studied using X-ray diffraction, room temperature Hall effect measurement and spectro photometer, respectively. Finally, organic light emitting diodes (OLED) were fabricated on these AZO films. OLED device measurement showed that the current of the OLED with AZO was clearly increased. Our AZO thin films showed a higher conductivity (ρ=1.33×10-4 Ω cm, Rs=10.1 Ω/sq) than conventional indium tin oxide films.

Gas Sensing Properties of Metal Doped WO3 Thin Film Sensors Prepared by Pulsed Laser Deposition and DC Sputtering Process

Tungsten trioxide (WO3) thin films gas sensors were prepared by the KrF excimer pulsed laser deposition (PLD) method. The films were prepared on the quartz glass, silicon and also on the Al2O3 sensor substrates with platinum interdigitated electrodes. The effect of doping of the platinum (Pt), palladium (Pd) or gold (Au) on the WO3 thin film was also investigated. These metals were doped to the WO3 thin film by the DC sputtering process during the PLD. The substrate temperature and the oxygen pressure were 400 °C and 100 mTorr, respectively, during the deposition. The films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The sensitivity of the prepared sensors to 60 ppm NO gas was examined using the two terminal resistance method in a chamber at atmospheric pressure and operating temperatures of 25–350 °C. The sensitivity of the WO3 thin films doped with Pt, Pd, or Au was found to be higher than that of the undoped WO3 thin film.

Pulsed-laser deposition of carbon: from DLC to cluster-assembled films

Carbon films have been synthesized on (100) Si substrates at room temperature by KrF Excimer Pulsed Laser Deposition (PLD) of highly oriented pyrolitic graphite. Changing laser power density (from 0.5 to 19 MW mm −2) and ambient conditions (vacuum; molecular nitrogen at 1 Pa; helium, from 0.6 Pa to 2 kPa), a range of structures and microstructures, from DLC to nanosized cluster assembled (CA) films were obtained. The microstructure and morphology of the films were studied by Scanning Electron Microscopy. The surface of all films deposited in vacuum and in nitrogen appears uniform, flat, featureless. In CA films, the nature-pressure of ambient gas and the energy deposited by each laser pulse determine threshold fluences of increasing value. These correspond to the sequence of dense columns, followed by nodule-like morphology and by an open dendritic structure. Atomic Force Microscopy on several CA films allowed to estimate the size distribution and relative abundancies of aggregates of carbon clusters. Film morphology is correlated with the ballistic mechanisms that occur when the plasma plume constituents interact with ambient gas atoms. For all films, local carbon coordination was studied by visible Raman spectroscopy. UV Raman spectra were collected for vacuum- and nitrogen-deposited films. The films are hydrogen-free, as shown by Fourier Transform Infra-Red spectroscopy, and result invariably structurally disordered. Vacuum-deposited films undergo a transition from mainly disordered graphitic to up to 80% tetrahedral amorphous carbon (ta-C) above a threshold power density. Transmission Electron Energy Loss spectra on selected samples confirmed ta-C formation. The same transition is absent in films deposited in N 2 atmosphere. All CA films are structurally disordered, sp 2 coordinated, and belong to the family of carbon nanoglasses. The mechanisms underlying the graphite to ta-C transition are discussed with reference to the different atmospheres.

Preparation and Characterization of Thin Films by Pulsed Laser Deposition for NOx gas Sensor

ABSTRACTGas sensors based on WO3 thin films doped with platinum (Pt) or palladium (Pd) were prepared by KrF excimer pulsed laser deposition method combined with dc sputtering. The films were deposited on silicon, quartz and Al2O3 sensor substrate with Pt interdigital electrodes at various substrate temperatures from 300°C to 500 °C, and oxygen pressures from 100 mTorr to 300 m Torr, respectively during the deposition. The morphology and structure of the films were examined by AFM and XRD. The sensor property of the WO3−x thin films was measured by the two terminal resistance method at operating temperatures of 25 °C to 400 °C. The sensitivity of the WO3 thin film gas sensors with doping (platinum or palladium) was found to be higher than that of undoped WO3 thin films gas sensors. The sensitivity of the pt doped WO3 films to different concentration of NO gas was examined and the sensitivity was found to be increased with increasing NO gas concentration.

Structural and interfacial stabilities of epitaxial (11-20)-oriented wurtzite AlN films grown on lattice-matched MnS buffered Si(100)

Epitaxial growth of non-polar wurtzite (11-20) AlN thin films was achieved on a Si(100) substrate by inserting an MnS buffer layer. The a-plane AlN film and MnS buffer layer were fabricated by pulsed KrF excimer laser deposition, and their micro- and interfacial atomic structures were investigated by transmission electron microscopy. The epitaxial relationship between films and substrate was found to be AlN(11-20)∥MnS(100)∥Si(100) with in-plane alignment of AlN[1-101]∥MnS[011]∥Si[011]. AlN[11-20] grown on Si is perpendicular to AlN[0001] and parallel to MnS[100]. The MnS/Si interface is abrupt enough to inherit the orientation of the Si(100) surface. A sharp interface was also observed for AlN/MnS without any intermediate layer.

Pulsed laser deposited WO 3 thin films for gas sensor

WO 3 has attracted attention because of its potential for NO x gas sensing. Thin films of WO 3− x were prepared by KrF excimer pulsed laser deposition technique on quartz and Al 2O 3 with Pt electrode. The films were deposited at various substrate temperature, oxygen pressure and conditions of the post-annealing. The substrate temperature over 400 °C was needed for the crystallization of the WO 3− x thin film. The crystal structure of the WO 3− x thin film deposited at oxygen pressure of 100 mTorr and the substrate temperature of 400 °C was tetragonal phase, however, the films deposited at the oxygen pressure over 200 mTorr showed triclinic phase. The atomic force microscopy image of the WO 3− x thin film post-annealed in oxygen atmosphere for 30 min showed an average grain size of 268 nm. It was approximately two times larger than that of the as-deposited film. The maximum sensitivity ( R NO/ R N 2 ) of the as-deposited triclinic WO 3− x thin film gas sensor in the NO gas (60 ppm in N 2) was 4.2 at an operating temperature of 200 °C.

WO3 Thin Films Prepared by Pulsed Laser Deposition

We report the structural and gas sensing properties of tungsten trioxide (WO3) thin films prepared by the KrF excimer pulsed laser deposition technique. The WO3 thin films having amorphous, crystallized tetragonal and triclinic structures were fabricated at the oxygen pressure of 10–300 mTorr and the substrate temperature of 150–800°C. We revealed the effect of the oxygen pressure and substrate temperature during the deposition on the crystal phases of the WO3 thin films. The atomic force microscopy measurement shows that the average grain size and the average number of grains are approximately 200 nm and 8/µm2, respectively. The triclinic WO3 thin film with a thickness of 1 µm showed high sensitivity of 254 in NO (60 ppm) gas at a low operating temperature of 150°C.

Preparation of boron carbide thin film by pulsed KrF excimer laser deposition process

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties. Boron carbide (B 4C) thin films are recognized to have potential for applications like hard coating and electron field emission devices. B 4C is the third hardest material after diamond and cBN, with a highest hardness of HV ∼5000. Furthermore, B 4C is interesting from the point of view of wear resistance and stability at high temperature. We have deposited B 4C thin films by KrF excimer laser (λ=248 nm) ablation of a stoichiometric B 4C target in high vacuum. In this paper, we have prepared the B 4C thin films on Si(100) substrates under various conditions, such as substrate negative DC bias voltage from between 0 to −800 V, substrate temperatures from room temperature up to 550 °C, and laser fluence between 2 and 8 J/cm 2 on the target. The typical absorption of B–C stretching bonds was detected from the infrared absorption measurement by FTIR of the deposited B 4C thin films. We concluded that the hardness of the B 4C thin films increases as the boron/carbon (B/C) ratio increases. The B/C ratio depends on the laser fluence. We obtained the maximum B/C ratio of 3.42 at 5 J/cm 2. The hardness of that sample reached 5.84 times of that of the Si(100) substrate.

Spectroscopic characterisation of DLC films deposited on polycarbonate by pulsed laser ablation

Diamond-like carbon (DLC) films have been synthesised by KrF-excimer pulsed laser deposition (PLD) at a wavelength of 248 nm, with laser fluences between 1 and 37 J cm −2, in vacuum and in a nitrogen atmosphere. The substrates were (100) Si wafers coated with a polycarbonate (PC, LEXAN type) layer a few μm thick. Structural analysis was performed by combined visible and UV Raman spectroscopy. In visible Raman spectra, D and G bands are found; in UV Raman spectra, the blue-shifted G band and the T peak are observed. A further band at approximately 1400 cm −1 is found in spectra from vacuum-deposited films at low fluences. The evolution of Raman fitting parameters with increasing laser fluence shows that in the films deposited in vacuum, a structural transition from mainly disordered graphitic to predominantly amorphous, tetrahedrally bonded carbon (ta-C) has occurred at 10 J cm −2. In the presence of an N 2 atmosphere during deposition, important modifications of the Raman spectra, associated with changes in the expansion dynamics of the carbon plasma plume are observed. Fourier-transform infrared (FTIR) spectroscopy on such films gave evidence of bands due to vibrations of the CN, CH and NH groups. Mechanical properties of the films were measured by nanoindentation; the hardness H of vacuum-deposited films with the highest sp 3 content was 8 GPa. The hardness of DLC films prepared in a nitrogen atmosphere at the highest fluence was 5 GPa.

On the structure of thin amorphous carbon films

Abstract Diamond-like carbon films have been prepared by KrF excimer pulsed-laser deposition at a wavelength of 248 nm, with power densities ranging from 0.05 to 1.85 GW cm−2, in vacuum and in a nitrogen atmosphere. Structural analysis was performed first by Fourier transform infrared spectroscopy, which shows that the films are hydrogen free and become transparent above a threshold power density. The band features indicate that the structure of the films is disordered. Combined visible and ultraviolet (UV) Raman spectroscopies allowed us to enhance the scattering cross-section from sp3-coordinated carbon with respect to the sp2 signals. In visible Raman spectra the D and G peaks are found; in UV Raman spectra, besides the blue-shifted G peak and the T peak, a further peak, not reported before, at about 1400 cm−2 is evident in spectra from films deposited in vacuum at low fluences. An analysis of the evolution of Raman fitting parameters with increasing deposition power density shows that above a threshol...

On the structure of thin amorphous carbon films

Abstract Diamond-like carbon films have been prepared by KrF excimer pulsed-laser deposition at a wavelength of 248 nm, with power densities ranging from 0.05 to 1.85 GW cm−2, in vacuum and in a nitrogen atmosphere. Structural analysis was performed first by Fourier transform infrared spectroscopy, which shows that the films are hydrogen free and become transparent above a threshold power density. The band features indicate that the structure of the films is disordered. Combined visible and ultraviolet (UV) Raman spectroscopies allowed us to enhance the scattering cross-section from sp3-coordinated carbon with respect to the sp2 signals. In visible Raman spectra the D and G peaks are found; in UV Raman spectra, besides the blue-shifted G peak and the T peak, a further peak, not reported before, at about 1400 cm−2 is evident in spectra from films deposited in vacuum at low fluences. An analysis of the evolution of Raman fitting parameters with increasing deposition power density shows that above a threshold value of about 0.5 GW cm−2 a structural transition occurs in the films deposited in vacuum from mainly disordered graphitic to predominantly amorphous tetrahedrally bonded carbon. The presence of nitrogen during deposition results in relevant modifications of the Raman spectra, associated with changes in the expansion dynamics of the carbon plasma plume.

Electrochromic WO3-x and Colossal Magnetoresistive (La, Sr)MnO3 Perovskite Oxide Thin Films by Pulsed Laser Deposition

AbstractThe functional oxide thin films of electrochromic WO3-x and colossal magnetoresistive La0.8Sr0.2MnO3 were prepared by a KrF excimer pulsed laser deposition technique. Optical transparency and electrical conductivity of the WO3-x film were changed by the oxygen content in the lattice. Triclinic, tetragonal and amorphous WO3-x films were prepared by adjusting the oxygen atmosphere during the deposition. We revealed the relationship between the crystal structure and the gas sensing property of the films. The triclinic WO3-x film (1 μm) showed the high sensitivity to NO (60 ppm) gas at an operating temperature of 150°C. The colossal magnetoresistive La0.8Sr0.2MnO3 thin film having the MR ratio of 15 % (H=7 kG) was deposited under the conditions of the laser energy density of 2 J/cm2 (5Hz), substrate temperature of 850°C and oxygen pressure of 500 mTorr. The magnetic sensor composing of the La0.8Sr0.2MnO3 thin film responded to the AC magnetic field (1 kHz).

Highly c-axis oriented LiNbO 3 thin film grown on SiO 2/Si substrates by pulsed laser deposition

Highly c-axis oriented LiNbO 3 thin film has been deposited on the SiO 2/Si substrate by KrF excimer pulsed laser deposition (PLD) technique under optimized conditions of 30-Pa oxygen pressure and 600 °C substrate temperature. The amorphous SiO 2 buffer layer was coated on the Si (001) wafer by thermal oxidation in situ. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements confirm that the film shows superior crystalline quality and highly c-axis oriented texture. Neither the Li-enriched LiNbO 3 target nor a biased electric field was applied during the deposition.

Preparation of (0 0 1)-oriented PZT thin films on silicon wafers using pulsed laser deposition

Completely (001)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) thin films deposited on (100)-silicon wafers with SrTiO3 (STO)/MgO as a buffer layer system and YBCO as a electrode, were prepared by using KrF excimer pulsed-laser deposition. The epitaxial relationships, i.e. PZT(001)∥YBCO(001)∥SrTiO3(100)∥MgO(100)∥Si(100) and PZT(110) ∥YBCO(110)∥SrTiO3(011)∥MgO(011) were detected using X-ray θ–2θ scans and pole figures or ϕ-scans. Grain size and surface morphologies of the as-prepared films were examined using atomic force microscopy and scanning electron microscopy.

Colossal magnetoresistive and ferroelectric thin films deposited by excimer laser induced plasma

We prepared the colossal magnetoresistive La0.8Sr0.2MnO3 thin films on single crystal MgO, SrTiO3 and LaAlO3 substrates by KrF excimer pulsed laser deposition technique. The thickness dependence of the structural, electric and magnetic properties of the LSMO films on different substrates is reported. The integration of the ferroelectrics with the colossal magnetoresistance thin film was achieved. The plasma plume ablated from target was investigated by intensified charge coupled device and optical emission spectroscopy.

Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part I. Optical emission spectroscopy

A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensity ratio. It is suggested that for both the SCG and a-C target cases, the C2 molecule in the ablated plasma plume may not play an important role in producing high quality DLC films. It is further proposed that the threshold of laser fluence for the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm2(0.84×108 W/cm2) for the a-C target and 3.0 J/cm2(1.2×108 W/cm2) for the SCG target. The C2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spectroscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG plasma plume, especially at relatively lower laser energy density below 3.0 J/cm2.

Crystalline and optical properties of PLZT films prepared by pulsed laser deposition

The PLZT (3/66/34), PLZT (3/46/54), PLZT (9/65/35) and PLZT (28/0/100) thin films were deposited on MgO (100), Sapphire (0001) and fused silica substrates by using pulsed KrF excimer laser deposition technique. The conventional in-situ and 2-step heating processes were utilized to facilitate the synthesis of a large area of uniform PLZT thin film. Pure perovskite phase can be obtained only under very narrow process conditions, the highly textured PLZT films can be easily obtained by in-situ heating process. For PLZT (28/0/100) material, epitaxial films were successfully coated on MgO (100) substrates by 600°C in-situ and RTA 650°C 2-step heating processes. The latter was found to possess higher refractive index and lower extinction coefficient.