Evaluation of carbon films electrodeposited on different substrates from different organic solvents

Diamond-like-carbon (DLC) films have been deposited on Si, aluminum and indium tin oxide-coated glass from several organic solvents with pulse-modulated power. The films are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS spectra show that the main composition of the films is carbon and Raman spectra show that the films are typical DLC films and a high potential is preferable in the formation of sp ³-structure carbon. Comparing the results from different solvents and different substrates we deduce that the methyl group of the solvents has a critical function in forming the DLC films. However, the formation process and the characters of the films, such as appearance, resistivity and thickness, are mainly determined by the substrate. We may call this deposition a substrate-controlled reaction. Received: 31 May 2000 / Accepted: 9 January 2001 / Published online: 3 April 2001     

Synthesis of carbon nitride films by low-power inductively coupled plasma-activated transport reactions from a solid carbon source

Thin films of carbon nitride were prepared by low-power inductively coupled plasma chemical vapor deposition from a solid carbon source by utilizing transport reactions. The maximum deposition rate achieved was 10 nm/min and depended mainly on the substrate position in the reactor. The nitrogen fraction in the films was not so sensitive to the process parameters and was at about 0.5 for all experiments as measured by Auger electron spectroscopy (AES) and elastic recoil detection (ERD) analysis. The chemical bonding structure studied by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the presence of triple, double and single bonds between carbon and nitrogen atoms. Received: 12 May 1999 / Accepted: 12 May 1999 / Published online: 24 June 1999     

Laser deposition of amorphous diamond films from liquid aromatic hydrocarbons

6 H₅CH₃, C₆H₆, and C₆H₅CH(CH₃)₂) to pulsed visible laser radiation of a copper vapor laser (λ=510.6 nm). The X-ray Auger electron spectroscopy (XAES), reflection high energy electron diffraction (RHEED), and Raman analysis are employed to characterize the deposited films. The sp³ fraction in deposited films amounts to 60–70% and depends on the precursor. The average film thickness on a glass substrate is about 100 nm. The films show excellent adherence, are transparent in the visible and have microhardness of 50–70 GPa, as measured by nanoindentor. Received: 28 September 1998 / Accepted: 13 January 1999     

Simultaneous interaction of methyl radicals and atomic hydrogen with amorphous hydrogenated carbon films, as investigated with optical in situ diagnostics

Methyl radicals (CH₃) and atomic hydrogen (H) are dominant radicals in low-temperature plasmas from methane. The surface reactions of these radicals are believed to be key steps leading to deposition of amorphous hydrogenated carbon (a-C:H) films or polycrystalline diamond in these discharges. The underlying growth mechanism is studied, by exposing an a-C:H film to quantified radical beams of H and CH₃. The deposition or etching rate is monitored via ellipsometry and the variation of the stoichiometry is monitored via isotope labeling and infrared spectroscopy. It was shown recently that, at 320 K, methyl radicals have a sticking coefficient of 10^-4 on a-C:H films, which rises to 10^-2 if an additional flux of atomic hydrogen is present. This represents a synergistic growth mechanism between H and CH₃. From the interpretation of the infrared data, a reaction scheme for this type of film growth is developed: atomic hydrogen creates dangling bonds by abstraction of bonded hydrogen within a surface layer corresponding to the range of H in a-C:H films. These dangling bonds serve at the physical surface as adsorption sites for incoming methyl radicals and beneath the surface as radicalic centers for polymerization reactions leading to carbon–carbon bonds and to the formation of a dense a-C:H film. Received: 18 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

Development of conductive transparent indium tin oxide (ITO) thin films deposited by direct current (DC) magnetron sputtering for photon-STM applications

Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95% indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10^-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range 3.0–5.7×10^-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities in the range 2.9–4.0×10^-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C, and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h. Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing time have been investigated. Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001     

Amorphous hydrogenated carbon synthesized by pulsed laser deposition from cyclohexane

It is demonstrated that a liquid hydrocarbon precursor, cyclohexane, is appropriate for laser-induced carbon deposition. Amorphous hydrogenated carbon films (a-C:H) were deposited by KrF excimer laser irradiation of single-crystal silicon surface immersed under cyclohexane. The technique is simple and easy to operate. IR absorption spectra of the deposited films confirmed the presence of carbon in the diamond phase. Raman and XPS studies showed diamond-like character of the deposited films. Moreover, these two studies provided strong evidence that laser fluence played an important role in the formation of DLC bondings and the quality of the deposited films. Received: 15 September 1998 / Accepted: 5 January 1999 / Published online: 5 May 1999     

Al2O3 thin films by plasma-enhanced chemical vapour deposition using trimethyl-amine alane (TMAA) as the Al precursor

2 O₃ thin films by plasma-enhanced chemical vapour deposition (PECVD) using trimethyl-amine alane (TMAA) as the Al precursor. The thin films were deposited on both Si and quartz silica (SiO₂) substrates. Deposition rates were typically 60 Å min^-1 keeping the TMAA temperature constant at 45 °C. The deposited Al₂O₃ thin films were stoichiometric alumina with low carbon contamination (0.7–1.3 At%). The refractive index ranged from 1.54 to 1.62 depending on the deposition conditions. The deposition rate was studied as a function of both the RF power and the substrate temperature. The structure and the surface of the deposited Al₂O₃ thin films were studied using X-ray diffraction, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Received: 20 May 1997/Accepted: 12 June 1997     

Room-temperature epitaxial growth of CeO2(001) films on YSZ buffered Si(001) substrates

2 (001) epitaxial thin films deposited on Si(001) with yttria-stabilized zirconia buffers have been obtained for the first time at room temperature by pulsed-laser deposition. The influence of oxygen pressure on the crystal quality of CeO₂ was studied for the films deposited at 100 °C. The rocking curve full width at half maximum of the CeO₂(002) peak for films deposited at room temperature and 100 °C was between 1° and 2°, for oxygen pressures below 3×10^-2 mbar. The best crystal quality was obtained at around 3×10^-3 mbar. Epitaxial growth at room temperature was confirmed by cross-sectional transmission electron microscopy. Scanning electron microscopy and atomic force microscopy revealed very smooth surfaces for oxygen pressure below 3×10^-2 mbar, with rms roughness values around 0.3 nm over 5 μm×5 μm. Received: 25 September 1997/Accepted: 22 April 1998     

Raman investigation of submicro-grained Si films obtained by incoherent UV photo-CVD of silicon hydrides

Received: 10 February 1998/Accepted: 12 February 1998     

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     

Ferroelectricity of lanthanum-modified lead titanate thin films obtained by a diol-based sol-gel method

Lanthanum-modified lead titanate thin films have been prepared by a diol-based sol-gel method from precursor solutions with a growing excess of PbO. The films were crystallized with thermal treatments at 650 °C and heating rates of 10 °C  min^-1 and higher than 500 °C min^-1 by direct insertion in a pre-heated furnace. The structure, microstructure, and composition of the films were studied by grazing-incidence X-ray diffraction, electron microscopies, and energy-dispersive X-ray spectroscopy. A 20 mole % excess of PbO must be included in the precursor solution in order to compensate PbO volatilization occurring during the thermal treatment and, thus, obtain single-phase perovskite-type structure films. Non-textured porous films were obtained when a 10 °C min^-1 rate is used, whereas [001]/[100] oriented films without porosity were obtained when rapid heating was used. Dielectric permittivity, ac current density, hysteresis loops, and switching curves were measured in the films. Values of remanent polarization and coercive field are comparable to those reported for similar films. The effects on the ferroelectric properties of an electrical and a post-crystallization thermal treatments were characterised. Received: 5 January 1998 / Accepted: 20 November 1998 / Published online: 17 March 1999     

Field-electron emission from polyimide-ablated films

Polyimide-ablated film was deposited by using pulsed laser ablation of a polyimide target, and field-electron emission from the film was observed for the first time. The turn-on field of the polyimide-ablated film is 12 V/μm. The current density is 0.725 mA/cm², and the emission sites density is on the order of 10⁶/cm² at the applied field of 24 V/μm. The field-electron emission measurements indicate that this kind of film could be a new cold cathode material. It is suggested that the graphite-like clusters contained in the film play an important role in the field-electron emission. Received: 2 February 2000 / Accepted: 13 March 2000 / Published online: 9 August 2000     

Dielectric and ferroelectric properties of pulsed-laser deposited BaTiO3 films

3 films were produced by KrF excimer-laser ablation. Films deposited on fused silica substrates were polycrystalline without preferential orientation and had cubic rather than tetragonal structure. BaTiO₃/Au/Ti/fused silica films showed a large dielectric constant, which increased with the thickness of the film, but poor ferroelectric properties. This behavior seems to be related to the small size of grains. On (100)MgO substrates oriented films were obtained. BaTiO₃/YBa₂Cu₃O_7-δ/(100)MgO films showed a large dielectric constant also and improved ferroelectric properties. Although this indicates a larger degree of tetragonality, the tetragonal structure of single crystal BaTiO₃ has not yet developed. Localized reduction and metallization of BaTiO₃/(100)MgO films by means of Ar⁺-laser radiation was demonstrated. This technique allows to produce conducting patterns in a single-s tep process. Received: 6 January 1997/Accepted: 21 April 1997     

Core-level and valence-band characteristics of carbon nitride films with high nitrogen content

Carbon nitride films with high nitrogen content were prepared by reactive pulsed-laser deposition at nitrogen partial pressures varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increase of the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at. % at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning the core-level and valence-band structures. Some fingerprint information, which shows the role of nitrogen in controlling the electronic structure of carbon nitride films, was found based on the XPS studies. With enhancing the nitrogen incorporation, both the binding energy and the peak intensity of the core-level and the valence-band spectra vary systematically as a function of nitrogen content in the films. Received: 26 June 2000 / Accepted: 26 June 2000 / Published online: 20 September 2000     

Structural and dielectric properties of Bi4Ti3O12 thin films prepared by metalorganic solution deposition

Ferroelectric Bi₄Ti₃O₁₂ thin films with single phase and nanosized microstructure were prepared on Pt/Ti/SiO₂/Si(111) substrate by metalorganic solution deposition using titanium butoxide and bismuth nitrate at relatively low annealing temperatures. The internal strain in Bi₄Ti₃O₁₂ thin films was calculated from the peak shifts and broadening of XRD patterns. With increase in annealing temperature, the uniform strain decreased from positive to zero and then to negative, and the non-uniform strain decreased and was negative. The total strain was negative and in the range of -0.2%–-1.0%, from which the stress of the films was calculated to be about -1.4×10⁹ N/m². The mode values of strain decreased with increase in annealing temperature and increased with increase in film thickness. The dielectric constant increased with increase in annealing temperature and film thickness. The dielectric properties were interpreted by considering the influence of strain, grain size, and grain boundaries. The strain lowered the polarization and increased the dielectric constant. The larger the grain size and the thinner the grain boundary, the greater the dielectric constant. The influence of grain size and grain boundary was stronger than that of the strain. Received: 23 September 1998 / Accepted: 6 January 1999 / Published online: 24 March 1999     

Structural and ferroelectric properties of Bi4Ti3O12 thin films on IrO2 prepared by rf magnetron sputtering

Bismuth titanate, Bi₄Ti₃O₁₂, thin films were grown on IrO₂/SiO₂/Si substrates by radio-frequency magnetron sputtering. Crystallinity and microstructure of the films were characterized over a wide range of oxygen mixing ratio (OMR) during deposition. X-ray fluorescence spectra reveal that the cation content of the films is dependent upon the OMR, suggesting that control of Bi to Ti ratio is possible by the oxygen content in the sputtering atmosphere. Rutherford backscattering spectrometry measurements also show that oxygen content of the BTO film grown with an OMR = 0.5is close to a stoichiometric phase. In addition, Bi–O bonding chemistry is studied by X-ray photoelectron spectroscopy. Polarization vs. voltage loop shows that remnant polarization, P_r, is +12 μC/cm². Received: 26 November 1999 / Accepted: 26 November 1999 / Published online: 9 August 2000     

Field emission properties of a-CN<Subscript>x</Subscript> films prepared by pulsed laser deposition

Amorphous carbon nitride (a-CN_x) films were grown on silicon substrates by ArF excimer laser ablation of a graphite target in the presence of nitrogen at various gas pressures. By working at elevated pressures (up to 100 Pa), large amounts of nitrogen can be incorporated into the films (up to 40 at. %, which leads to a strong enhancement of their field emission properties. This behaviour was demonstrated to be mainly related to changes in the surface morphology of the samples, in connection with the development of graphite-like structures. Received: 22 February 2002 / Accepted: 3 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +33-(0)/388-106-230, E-mail: fogarassy@phase.c-strasbourg.fr     

Growth by laser ablation of Ti-based oxide films with different valency states

x La_2/3+yTiO_3-δ perovskite (with δ≤0.5) were deposited by the laser ablation technique from Li_0.33La_0.56TiO₃ targets. Their growth onto MgO substrateswas studied as a function of the oxygen pressure. For films grown in vacuum (10^-6 mbar), a La_0.63TiO_2.5 composition was obtained, meaning that Ti³⁺ alone is present in the films, while Li ions are not incorporated under these conditions. This material shows good electric conductivity (ρ=500 mΩ cm). By contrast, insulating films with a Li_0.1La_0.70TiO₃ composition corresponding to the Ti⁴⁺ species were obtained at high oxygen pressures (>0.05 mbar). For all conditions, textured films were grown with different orientations depending on the temperature and the oxygen pressure. Received: 10 September 1997/Accepted: 24 November 1997     

Thermal stability of amorphous carbon films deposited by pulsed laser ablation

Diamond-like carbon (DLC) films have been grown on Si substrates at ambient temperature by the pulsed-laser ablation technique, using pulses of different durations both in the nano- and picosecond ranges and at various energy fluences. The stability of these films was investigated as a function of thermal anneals performed in UHV conditions up to 1273 K. Their physico-chemical properties have been characterized by different techniques including X-ray photo-emission, Auger electron and electron-energy-loss spectroscopies, Raman scattering, spectroscopic ellipsometry and atomic-force microscopy. The thermal stability of the films has been demonstrated to be related to their initial structural (sp³/sp² ratio) and chemical (contaminant) properties. DLC layers prepared under optimized conditions have been found to show a very good thermal stability up to 900 K. Received: 4 Jule 2000 / Accepted: 6 July 2000 / Published online: 6 September 2000     

Preparation and crystallization of Pb(Zr0.95Ti0.05)O3 thin films deposited by radio-frequency magnetron sputtering with a stoichiometric ceramic target

0.95 Ti_0.05)O₃ (PZT 95/5) thin films of perovskite structure were prepared on various substrates by the radio-frequency magnetron sputtering with a stoichiometric ceramic target. The crystal structure of the films showed a strong dependency on the crystal structure of the substrates. After conventional-furnace annealing at 750 °C, crack-free and transparent epitaxial PZT 95/5 films were successfully obtained on SrTiO₃(100) substrates, and highly oriented films on LaAlO₃(012). The films on r-sapphire exhibit slightly preferred orientation along both the (040) and (122) axes of the orthorhombic PZT 95/5 phase. The films on YSZ(100) consist principally of the perovskite PZT 95/5 phase with random orientation with a small portion of unknown phase. However, the formation of the perovskite PZT 95/5 phase was not observed in the films on Si(110) or (111)Pt-coated Si substrates. The crystallization of the perovskite PZT 95/5 on these substrates could be improved by rapid thermal annealing (RTA). Single perovskite phase was obtained in the films on (111)Pt/Si which had RTA at 750 °C for 1 min. No tangible loss of Pb from the films occurred during either the sputtering or annealing. Received: 17 April 1997/Accepted: 18 November 1997