Synthesis of carbon nitride films by direct current plasma assisted pulsed laser deposition

Carbon nitride films were deposited by pulsed laser ablation of a graphite target under a nitrogen atmosphere at room temperature. A direct current discharge apparatus was used to supply active nitrogen species during the deposition of carbon nitride films. The composition and bonding structure of carbon nitride films were determined by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy. The incorporation of nitrogen atoms in the films is greatly improved by the using of a dc glow discharge. The ratio N/C can reach 0.34 at the discharge voltage of 400 V. Six peaks centered at 1025 cm^-1, 1226 cm^-1, 1381 cm^-1, 1534 cm^-1, 1629 cm^-1, and 2200 cm^-1 can be clearly distinguished from the FTIR spectra of the deposited films, which indicates the existence of C–N, C=N, and C≡N bonds. The fraction of sp² C, C≡N bonds, and C=N bonds in the deposited films increases with increasing discharge voltage. Deconvolution results of C 1s and N 1s spectra also indicate that nitrogen atoms in the films are chemically bonded to sp¹ C, sp² C, and sp³ C atoms. Most of the nitrogen atoms are bonded to sp² C atoms. Increasing the discharge voltage leads to a decrease of the fraction of nitrogen atoms bonded to sp² C and the fraction of amorphous carbon; however, it leads to an increase of the fraction of nitrogen atoms bonded to sp³ C and the fraction of sp² C and sp³ C atoms bonded to nitrogen atoms. Received: 7 June 2000 / Accepted: 19 February 2001 / Published online: 27 June 2001     

SBN thin films growth by RF plasma beam assisted pulsed laser deposition

SBN thin films were grown on MgO and Silicon substrates by PLD and RF-PLD (radiofrequency assisted PLD) starting from single crystal Sr_0.6Ba_0.4Nb₂O₆ and ceramic Sr_0.5Ba_0.5Nb₂O₆ stoichiometric targets. Morphological and structural analyses were performed on the SBN layers by AFM and XRD and optical properties were measured by spectroellipsometry. The films composition was determined by Rutherford Backscattering Spectrometry. The best set of experimental conditions for obtaining crystalline, c-axis preferential texture and with dominant 31° in-plane orientation relative to the MgO (100) axis is identified.     

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     

Reactive pulsed laser deposition of gold nitride thin films

We report on the growth and characterization of gold nitride thin films on Si 〈1 0 0〉 substrates at room temperature by reactive pulsed laser ablation. A pure (99.95%) Au target was ablated with KrF excimer laser pulses in nitrogen containing atmosphere (N₂ or NH₃). The gas ambient pressure was varied in the range 0.1-100 Pa. The morphology of the films was studied by using optical, scanning electron and atomic force microscopy, evidencing compact films with RMS roughness in the range 3.6-35.1 nm, depending on the deposition pressure. Rutherford backscattering spectrometry and energy dispersion spectroscopy (EDS) were used to detect the nitrogen concentration into the films. The EDS nitrogen peak does not decrease in intensity after 2 h annealing at 250 °C. Film resistivity was measured using a four-point probe and resulted in the (4-20) × 10⁻⁸ Ω m range, depending on the ambient pressure, to be compared with the value 2.6 × 10⁻⁸ Ω m of a pure gold film. Indentation and scratch measurements gave microhardness values of 2-3 GPa and the Young's modulus close to 100 GPa. X-ray photoemission spectra clearly showed the N 1s peak around 400 eV and displaced with respect to N₂ phase. All these measurements point to the formation of the gold nitride phase.     

Effect of deposition parameters on structural and mechanical properties of niobium nitride synthesized by plasma focus device

Effects of deposition angle and axial distance on the structural and mechanical properties of niobium nitride synthesized by a dense plasma focus(DPF) system are studied.The x-ray diffraction(XRD) confirms that the deposition parameters affect the growth of multi-phase niobium nitride.Scanning electron microscopy(SEM) shows the granular surface morphology with strong thermally assisted coagulation effects observed at the 5-cm axial distance.The non-porous granular morphology observed at the 9-cm distance along the anode axis is different from those observed at deposition angles of 10°and 20°.Energy dispersive x-ray(EDX) spectroscopy reveals the maximum nitrogen content at the shortest(5 cm) axial position.Atomic force microscopy(AFM) exhibits that the roughness of coated films varies for coatings synthesized at different axial and angular positions,and the Vickers micro-hardness test shows that a maximum hardness value is(08.44 ± 0.01) GPa for niobium nitride synthesized at 5-cm axial distance,which is about 500% more than that of a virgin sample.     

Effect of the plasma parameters on the properties of titanium nitride thin films grown by laser ablation

Titanium nitride thin films were deposited at low temperatures (less than 250 °C) using the laser ablation technique. The effect of both the laser beam energy density and the gas pressure on the plasma parameters was studied. The film structure, mechanical properties and surface morphology were investigated as a function of the plasma parameters. The results showed a strong dependence of these properties on the ion kinetic energy and plasma density. The gas pressure was seen to control the preferred orientation of the films in the (200) and (111) directions. At 1×10^-2 Torr only the (200) direction was observed. In addition, the crystal size for all the films was found to depend on the plasma parameters; generally, an increase of ion energy and plasma density resulted in a decrease of the crystal size. TiN films with hardness as high as 24.0 GPa, which is suitable for many mechanical applications, were obtained. The hardness was strongly affected by the ion energy, increasing as the ion energy increased. These results show that the properties of the deposited material are controlled in part by the degree of ion bombardment and the plasma density. PACS 81.15.Fg; 81.05.Je; 68.55.Jk; 52.70.Ds     

Study of porous carbon thin films produced by pulsed laser deposition

Amorphous carbon is an interesting material and its properties can be varied by tuning its diamond-like (sp³) fractions. The diamond-like fractions in an amorphous carbon films depends on the kinetic energy of the deposited carbon ions. Porous amorphous carbon thin films were deposited onto silicon substrates at room temperature in a vacuum chamber by Glancing Angle Pulsed Laser Deposition (GAPLD). Krypton fluoride (248 nm) laser pulses with duration of 15 ns and intensities of 1-20 GW/cm² were used. In GAPLD, the angles between the substrate normal and the trajectory of the incident deposition flux are set to be almost 90°. Porous thin films consisting of carbon nanowires with diameters less than 100 nm were formed due to a self-shadowing effect. The kinetic energies of the deposited ions, the deposition rate of the films and the size of the nanowires were investigated. The sp³ fraction of the porous carbon films produced at intensity around 20 GW/cm² were estimated from their Raman spectra.     

Pulsed laser deposition of amorphous carbon nitride thin films and their electrical properties

Amorphous carbon nitride thin films were deposited by pulsed laser deposition combined with a nitrogen rf radical beam source. A structural characterization of the deposited films was performed using X-ray photoelectron and Raman-scattering spectroscopy. The Raman spectra showed that the dominant hybridization state of carbon atoms in the deposited film is sp². N 1s electron spectra were deconvoluted into three components, N bonded to pyridine-like N and/or N-sp³C (N1), substitutional N in graphite (N2), and N-O and/or N-N (N3). The proportion of N1 increased with increasing N/C atomic ratio in the film. The electrical conductivity at room temperature decreased and the Tauc optical band gap increased with increasing N/C atomic ratio. The temperature dependence of the electrical conductivity indicated that electronic conduction occurred by variable range hopping between electron localized states. The decrease in electrical conductivity with increasing N/C atomic ratio was caused by a strong electron localization due to the increased proportion of N1. PACS 81.05.Uw; 81-15.Fg; 73.61.Jc     

脉冲激光沉积法制备的Ni1-xFexO稀磁半导体的结构和磁性研究

利用脉冲激光沉积方法制备出了具有室温铁磁性的Ni1-1-xFexO(x=0.02,O.05)稀磁半导体.X射线衍射(XRD)结果表明Ni,1-xFexO的品体结构为Nacl结构,并且在Fe含量较高的Ni095Fe0.05O中出现了少量的a-Fe2O3物相.X射线吸收近边结构谱(XANFS)和X射线光电子能谱(XPs)进一步表明了掺杂的Fe原子替代Ni0日格中Ni原子,并且样品中不存在能够诱导室温磁性的第二相.这些研究结果表明Ni1-xFexO的室温铁磁性是本征的.     

Study of the structure and electrical properties of the copper nitride thin films deposited by pulsed laser deposition

Copper nitride thin films were prepared on glass and silicon substrates by ablating a copper target at different pressure of nitrogen. The films were characterized in situ by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and ex situ by X-ray diffraction (XRD). The nitrogen content in the samples, x = [N]/[Cu], changed between 0 and 0.33 for a corresponding variation in nitrogen pressure of 9 × 10⁻² to 1.3 × 10⁻¹ Torr. Using this methodology, it is possible to achieve sub-, over- and stoichiometric films by controlling the nitrogen pressure. The XPS results show that is possible to obtain copper nitride with x = 0.33 (Cu₃N) and x = 0.25 (Cu₄N) when the nitrogen pressure is 1.3 × 10⁻¹ and 5 × 10⁻² Torr, respectively. The lattice constants obtained from XRD results for copper nitride with x = 0.25 is of 3.850 Å and with x = 0.33 have values between 3.810 and 3.830 Å. The electrical properties of the films were studied as a function of the lattice constant. These results show that the electrical resistivity increases when the lattice parameter is decreasing. The electrical resistivity of copper nitride with x = 0.25 was smaller than samples with x = 0.33.     

Structural, electrical and mechanical properties of NiO thin films grown by pulsed laser deposition

Nickel oxide (NiO) thin films were prepared by reactive pulsed laser deposition on thermally oxidized Si substrates in 10 Pa oxygen pressure. The substrate temperature during deposition was varied and its influence on the structural, electrical and nanomechanical properties was studied. It was proved that the structural properties were affected by the increase of substrate temperature improving the crystalline structure. Furthermore, a higher substrate temperature resulted in a thicker NiO film, which was attributed to an increased grain size. This effect influenced the electrical properties, too. Resistivity measurements showed that it increased with the increase of substrate temperature. For the first time, the nanomechanical properties of NiO films were studied. The formation and improvement of crystalline structure affected the nanomechanical properties. Nanoindentation testing of NiO thin films revealed an increase of hardness (H) and elastic modulus (E) and a decrease of surface roughness when increasing the substrate temperature.     

Effect of the laser fluence on structural and optical characterization of thin CdS films synthesized by femtosecond pulsed laser deposition

CdS thin films have been grown on Si(1 1 1) and quartz substrates using femtosecond pulsed laser deposition. X-ray diffraction, atomic force microscopy, photoluminescence measurement, and optical transmission spectroscopy were used to characterize the structure and optical properties of the deposited CdS thin films. The influence of the laser fluence (laser incident energy in the range 0.5–1.5 mJ/pulse) on the structural and optical characterizations of CdS thin films has been studied. The results indicate that the structure and optical properties of the CdS thin films can be improved as increasing the per pulse output energy of the femtosecond laser to 1.2 mJ. But when the per pulse output energy of the femtosecond laser is further increased to 1.5 mJ, which leads to the degradation of the structure and optical properties of the CdS thin films.     

Matrix assisted pulsed laser deposition of light emitting polymer thin films

Matrix assisted laser processing allows for the deposition of functional and fragile materials with a minimum of breakdown and decomposition. In this communication we report on light emitting thin films of ruthenium tris(bipyridine)-centered star-shaped poly(methyl methacrylate), Ru(bpyPMMA₂)₃(PF₆)₂, grown by matrix assisted pulsed laser deposition. A pulsed excimer laser (KrF) operating at 248 nm was used for all experiments. Due to the absorption at 248 nm and the solubility characteristics of [Ru(bpyPMMA₂)₃](PF₆)₂, dimethoxy-ethane (DME) was used as a solvent [1]. Dilute solutions (2 wt.%) of [Ru(bpyPMMA₂)₃](PF₆)₂ and DME were flash frozen in liquid nitrogen producing a solid target. Thin films ranging from 20 to 100 nm were grown on Si in an Ar atmosphere at 200 mTorr at a laser fluence of 0.04 J/cm². The deposited materials were characterized by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) equipped with refractive index (RI), and ultraviolet/visible (UV/vis) detection. PACS 81.15.Fg; 79.20.Ds; 78.66.Qn; 42.70.Jk     

RF-plasma assisted pulsed laser deposition of nitrogen-doped SrTiO3 thin films

Perovskite-type nitrogen substituted SrTiO₃ thin films were deposited with a one-step process by RF-plasma assisted pulsed laser deposition from a SrTiO₃ target using a N₂ plasma, while deposition with a NH₃ plasma yields films with almost no incorporated nitrogen. The deposited films exhibit a cubic perovskite-type crystal structure and reveal oriented growth on MgO(100) substrates. The unit cell parameters of the studied N-doped SrTiO₃ films range within 3.905<a<3.918 Å, which is slightly larger than for SrTiO₃ (a=3.905 Å). The nitrogen content in the deposited films varies from 0.2 to 0.7 atom%. The amount of incorporated nitrogen in the films decreases with increasing RF-power, while the N₂ flow rate does not have any pronounced influence on the N content. Nitrogen incorporation results in an increased optical absorption at 400–600 nm, which is associated with N(2p) energy states that have a higher energy level than the valence band in strontium titanate. The optical band gap energies in the studied N-doped SrTiO₃ films are at 3.2–3.3 eV, which is very similar to that of pure strontium titanate (～3.2 eV). Films deposited with NH₃ for the RF-plasma exhibit a lower degree of crystallinity and reveal almost no nitrogen incorporation into the crystal lattice.     

Effect of Al doping on structural,optical and electrical properties of SnO2 thin films synthesized by pulsed laser deposition

Aluminium-doped (Al = 0–5?wt.%) SnO₂ thin films with low-electrical resistivity and high optical transparency have been successfully synthesized by pulsed laser deposition technique at 500 °C. Structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated. X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content. The root mean square (R_q) surface roughness parameter, determined by atomic force microscopy decreases upon annealing of the as-deposited film. While resistivity of the film is the lowest (9.49 × 10^?4 Ω-cm) at a critical doping level of 1?wt.% Al, optical transparency is the highest (nearly 90%) in the as-deposited condition. Temperature dependence of the electrical resistivity suggests that the Mott’s variable range hopping process is the dominant carrier transport mechanism in the lower temperature range (40–135 K) for all the films whereas, thermally activated band conduction mechanism seems to account for conduction in the higher temperature region (200–300 K).     

Influence of assisted ion energy on surface roughness and mechanical properties of boron carbon nitride films synthesized by DIBSD

The BCN thin films were produced by dual ion beam sputtering deposition (DIBSD). The influence of assisted ion energy on surface roughness and mechanical properties of BCN films were investigated. The surface roughness was determined by atomic force microscopy (AFM) and the mechanical properties of BCN firms were evaluated by nano-indentation in N₂ gas. The composition, structure and chemical bonding of the BCN thin films were analyzed by using energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), laser Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). These films appeared as amorphous structure. As a result, the BCN films with the smoothest surface (R_a = 0.35 nm and R_p-v = 4.4 nm) and the highest nano-hardness of 30.1 GPa and elastic modulus of 232.6 GPa were obtained at 200 eV and 12 mA with N₂:Ar = 1:1, and the chemical composition of this BCN film was 81 at.% B, 14 at.% C and 5 at.% N. Moreover, several bonding states such as B-N, B-C and C-N were observed in BCN thin films.     

Dielectric properties of SrZrO3 thin films prepared by pulsed laser deposition

SrZrO₃ (SZO) thin films have been prepared on Pt-coated silicon substrates and directly on Si substrates by pulsed laser deposition (PLD) using a ZrSrO target at a substrate temperature of 400 °C in 20 Pa oxygen ambient. X-ray –2 scans showed that the as-deposited films remain amorphous at a substrate temperature of 400 °C. The dielectric constant of SZO has been determined to be in the range 24–27 for the Pt/SZO/Pt structure. Capacitance–voltage (C–V) characteristics of a metal-oxide-semiconductor (MOS) structure for SZO films deposited in 20 Pa oxygen ambient and 20 Pa nitrogen ambient (SZON) indicated that incorporation of nitrogen during the substrate heating and film deposition can suppress the formation of an interfacial SiO₂ layer, and the SZON films have a lower equivalent oxide thickness (EOT) than that of the SZO films. However, the leakage current of the SZON films is larger than that of the SZO films. The EOT is about 1.2 nm for a 5-nm SZON film deposited at 400 °C. The leakage-current characteristics of as-deposited SZON films and SZON films post-annealed in oxygen ambient by rapid thermal annealing (RTA) have been studied comparatively. The films post-annealed with RTA have a lower leakage current than the as-deposited SZON films. Optical transmittance measurements showed that the band gap of the films is about 5.7 eV. It is proposed that SrZrO₃ films prepared at 400 °C are potential materials for alternative high-k gate-dielectric applications. PACS 77.84.Bw; 77.84.-s; 77.55.+f     

Laser deposition of cryoglobulin blood proteins thin films by matrix assisted pulsed laser evaporation

We report the first successful deposition of type II cryoglobulin blood protein thin films by matrix assisted pulsed laser evaporation (MAPLE) using a KrF^* excimer laser source (λ = 248 nm, τ_FWHM ≈ 20 ns) operated at a repetition rate of 10 Hz. We demonstrate by AFM and FTIR that MAPLE-deposited thin films consist of starting type II cryoglobulin only, maintaining its chemical structure and biological functionality, being properly collected and processed. The dependence on incident laser fluence of the induced surface morphology is presented. The presence of type II cryoglobulin was revealed as aggregates of globular material in the MAPLE-deposited thin films and confirmed by standard cryoglobulin tests.     

Optical properties of zinc phthalocyanine thin films prepared by pulsed laser deposition

ZnPc thin films were prepared by pulsed laser deposition (KrF laser, λ = 248 nm, τ = 5 ns, f = 50 Hz) on suprasil substrates in vacuum. Optical properties in UV–Vis spectral region were analyzed as functions of laser fluence from 40 to 100 mJ/cm² by spectrophotometric and spectral ellipsometry measurements. The spectral ellipsometry data were treated using a three-layer model (substrate, film, roughness). The best results of data fitting were obtained when Q band was characterized by two Lorentz oscillators, while two Gaussian oscillators were used for B and C band fitting. We derived the band gap using Tauc plot considering ZnPc a direct band gap semiconductor. The band gap values were found decreasing from 3.13 to 3.09 eV with increasing laser fluence, which might be related with formation of trapping sites at higher fluence.