Nanometer-thick platinum silicide films were obtained by solid-state thermal reaction films in the presence of an interfacial native silicon oxide layer. They were studied using High-Resolution Transmission Electron Microscopy (HRTEM) and selected-area electron diffraction. Ten nm-thick sputtered Pt films reacted with the Si substrate through the oxide pinholes, which influenced the Pt-Si reaction over the whole annealing temperature range examined (165-800 degrees C). Silicide films grown through an interfacial oxide layer consist of two adjacent Pt2Si and PtSi layers in contrast with films obtained on oxide-free wafers, which show only PtSi grains. The continuous PtSi film transforms to an epitaxial, island-type film after annealing at 650 degrees C. The Pt2Si layer, to the contrary, remains unchanged up to 700 degrees C at least. The existence and stability of this layer at higher temperatures, together with the epitaxial relationship at the Pt2Si/PtSi interface help preserve the continuity and the good electrical conductance of silicide films obtained in presence of an interfacial oxide layer even above 700 degrees C. Epitaxial relationships between thin and very thin (3-5 nm) platinum silicide films and the Si substrates have also been studied directly from HRTEM images. Several orientation relationships for the PtSi/Si interface are discussed. (C) 2008 Elsevier B.V. All rights reserved.

The electronic structure of hexagonal β-Nb2N and δ′-NbN, and cubic fcc δ-NbN, grown by magnetron sputtering, have been investigated by X-ray photoemission spectroscopy and ellipsometric measurements. The valence band (VB) energy distribution curves (EDC) of these nitrides significantly differ each from each other. The hybridized N2p–Nb4d bands of β-Nb2N originate a featureless peak centered at 6 eV below the Fermi level, those of the δ′-NbN are characterized by two narrow peaks centered at 5 eV and 6.5 eV. Striking changes are also observed in the EDCs near the Fermi level, these features are associated with the nearly metallic Nb4d states. The dielectrical function of these nitrides reveals structures near the screened plasma edge which correlate well with their associated electronic structure. The dielectric function spectra can be used in the phase identification of the hexagonal and fcc phases. Comparing hexagonal and fcc electronic structures, both β-Nb2N and δ′-NbN are more covalent that the cubic δ-NbN. The prominent covalent bonding in these hexagonal nitrides can be related to their higher hardness values compared to that of the cubic phase.

The optical and electrical properties of NbzSiyNx thin films deposited by dc reactive magnetron sputtering have been investigated as a function of the Si content (CSi). Optical properties were studied by both specular reflectivity and spectroscopic ellipsometry. Electrical resistivity was measured by the van der Pauw method at room temperature and as a function of the temperature down to 10K. Both the optical and electrical properties of NbzSiyNx films are closely related with the chemical composition and microstructure evolution caused by Si addition. For CSi up to 4at.% the Si atoms are soluble in the lattice of the NbN crystallites. In this compositional regime, the optical and electrical properties show little dependence on the Si content. Between 4 and 7at.% the surplus of Si atoms segregates at the grain boundaries, builds an insulating SiNx layer, and originates important modifications in the optical and electrical properties of these films. Further increase of CSi leads to the formation of nanocomposite structures. The electrical properties of these films are well described by the grain-boundary scattering model with low probability for electrons to cross the grain boundary. The appearance of the intragranular-insulating SiNx layer and the reduction of the grain size are noticed in the dielectric function mainly as a strong damping of the plasma oscillation.

The optical properties of sputtered ZrNx films with 0.81≤x≤1.35 have been investigated and interpreted in terms of stoichiometry-related defects and crystal structure. The optical properties were determined by optical reflectivity, transmission and spectroscopic ellipsometry. As x increases from 0.81 to 1.35, the optical properties continuously change from metallic to semiconducting behavior. The experimental results have been fitted with a model dielectric function based on a set of Drude–Lorentz oscillators in order to separate the contributions due to free carriers and interband transitions. The effective density N* of conduction electrons decreases from N*=4.9×1022 cm−3 to N*=2.9×1021 cm−3 as x is increased from 0.81 to 1.29. The charge carrier scattering time increases from 4.9×10−16 to 2.6×10−15 s for 0.811.3 are poorly crystallized. In this composition range, the compounds exhibit a crystal structure close to orthorhombic Zr3N4; they are insulating with optical absorption coefficients in the range of 2×104 cm−1 below 2 eV and an optical absorption onset at 2.3 eV.

CNx films were deposited on various substrates using either dimethylamine (DA) precursor or the reaction between trichloroethylene (TCE) and ammonia with N-2 or 92% N-2+8% H-2 mixtures as background gas. The nature of the chemical bonding in these films was characterized by FTIR spectroscopy, and the film composition was analyzed by RBS. The microstructure and morphology were observed by AFM, STM, TEM and SEM techniques. We found that introducing H-2 into the background gas reduced film adhesion and allowed for lower deposition temperatures. Hydrogen etching causes removal of nitrogen, as well as of C-H and N-H bonds, from the films. Better CNx network connectivity and improved compactness were achieved in our experiment. (C) 2002 Elsevier Science B.V. All rights reserved.

Thin films of titanium oxides TiOx (x=0.7…2) can be produced by DC reactive magnetron sputtering with O2 and/or H2O as a reactive gas. In this work we investigate the deposition of nanometric multilayers and thin films of modulated composition. Samples are characterized by electrical resistivity measurements, optical measurements, X-ray diffraction and atomic force microscopy. The influence of the sputtering parameters on the morphology and on the electrical properties of the multilayers is reported. The analysis of the electrical and optical properties of the TiO2–TiOx multilayer system will contribute to a better understanding of the doping mechanism of nano-crystalline titanium dioxide by the grain boundaries.

The present study of the electronic properties of titanium monoxide thin films is centered on the electrical and optical properties of nano-grain material. TiOx thin films with x ranging from 0.75 to 1.45 have been deposited by r.f. reactive magnetron sputtering in a mixed Ar/O2 or Ar/H2O atmosphere. All films show a negative temperature coefficient of the resistivity. Spectroscopic ellipsometry measurements were performed in the Vis-UV spectral range. The free carrier and interband contributions to the dielectric function have been sorted out. The most striking feature of the free carrier optical response is the very short scattering time of the order of 10−15 s. Such an intense impurity scattering is beyond the validity range of the semi-classical Boltzmann equation and remains an open problem.

X-Ray photoelectron spectroscopy (XPS) and electrical resistivity measurements have been performed to investigate the electronic properties of Cr1−xAlxN films. The films, deposited by reactive magnetron sputtering, crystallize in the fcc rocksalt type of structure (B1-type) in a wide composition range of 0≤x≤0.63. The electrical resistivity was measured from 50 to 320 K. The electrical resistivity at 320 K increases with increasing Al content, and the temperature coefficient of the resistivity is always negative. A detailed study of XPS valence band (VB) spectra shows that the substitution of Cr atoms by Al atoms leads to local modifications of covalent-ionic bonds between N 2p and Cr 3d orbitals. The variations of the VB structure due to the changes in the chemical composition correlate with the electrical and mechanical properties.

The thermal stability against oxidation of Cr1−xAlxN films with 0≤x≤0.63 has been investigated by isochronal (15 min) heating in air at various temperatures up to 1173 K. Cr1−xAlxN thin films were deposited by reactive magnetron sputtering from Cr and Al targets in a mixed Ar/N2 atmosphere at a substrate temperature of 573 K. All the films crystallize in the pseudo binary, rocksalt-type cubic structure, showing a (111) preferential orientation. Oxidation proceeds by de-nitridation and the formation of a pseudo binary, mixed, Cr/Al oxide with the corundum structure. The degree of film oxidation was evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Rutherford backscattering spectroscopy (RBS). The substitution of Cr atoms by Al atoms leads to two oxidation behaviors. Cr1−xAlxN films with low Al content (x<0.2) exhibit poor resistance against oxidation and aluminum alloying is actually detrimental. These films show signs of oxidation at 773 K already. In contrast Cr1−xAlxN films with high Al content (x>0.2) are more resistant to high temperatures compared to pure CrN. Films with the highest Al content (x=0.63) are stable up to 1173 K due to the formation of an amorphous, aluminum-rich oxide which blocks oxygen diffusion and prevents further film oxidation.

CNx films were deposited on various substrates using either dimethylamine (DA) precursor or the reaction between trichloroethylene (TCE) and ammonia with N2 or 92% N2+8% H2 mixtures as background gas. The nature of the chemical bonding in these films was characterized by FTIR spectroscopy, and the film composition was analyzed by RBS. The microstructure and morphology were observed by AFM, STM, TEM and SEM techniques. We found that introducing H2 into the background gas reduced film adhesion and allowed for lower deposition temperatures. Hydrogen etching causes removal of nitrogen, as well as of C-H and N-H bonds, from the films. Better CNx network connectivity and improved compactness were achieved in our experiment.

High-resolution transmission electron microscopy (HRTEM) and selectedarea electron diffraction (SAED) were used to study the formation of 20 nm thick platinum silicide films in the presence of an interfacial native silicon oxide layer. Pt films 10 nm thick were sputtered on Si[001] substrates covered by a native oxide layer 0–2.2 nm thick and annealed between 165 and 800°C. HRTEM observations on cross-sections show that, when an interfacial oxide layer is present, the reactants interdiffuse through the oxide pinholes. The pinholes influence the Pt–Si reaction over all the annealing temperature range examined. Up to 250°C their influence is observed by differences in the silicide phases formed and in the silicide–Si interface flatness. In the 350–550°C annealing temperature range. films with or without an interfacial oxide layer are continuous, polycrystalline and quite homogeneous in thickness, being equivalent for electrical uses. Silicide films grown through an interfacial oxide layer consist of two adjacent Pt2Si and PtSi layers in contrast with oxide-free wafers, which show only PtSi grains. The continuous PtSi film transforms to an epitaxial island-type film afer annealing at 650°C. The Pt2Si layer, however, does not follow the same evolution but remains unchanged up to 700°C at least. By these means, the continuity of silicide films obtained in presence of an interfacial oxide layer can be preserved even above 700°C. These results explain the evolution of the resisitivity as a function of the temperature obtained for the same samples.

TiO2 thin films were prepared by direct current (dc) reactive sputtering, using various kinds of supports such as glass, silicon, alumina, and glass coated with indium–tin oxide. Samples were characterized by X-ray diffraction (XRD), and atomic force microscopy (AFM). Different TiO2−x stoichiometries, crystal structures and morphologies were obtained by changing the parameters of the reactive gas. The photocatalytic properties of the samples were tested on the degradation of phenol. The best efficiency in respect with phenol mineralization was obtained for samples prepared using an Ar–H2O mixture as the reactive gas. Indium–tin oxide supports provide the most efficient thin films. The catalytic efficiency per unit area of the sputtered films is at least one order of magnitude better than that of a 50m2g−1, reference TiO2 powder.

Spectroscopic ellipsometry is applied to determine the oxidation resistance of TiN and CrN coatings. This technique proves to provide accurate measurements of the oxide layer thickness in a convenient, fast, and nondestructive manner. The magnetron-sputtered thin films were heated in air in the temperature range between 673 and 925 K. The verification with scanning electron microscopy and x-ray reflectometry shows an excellent agreement between these complementary techniques. The rate constant k of the oxidation is directly related to the film morphology in TiN thin films. While understoichiometric films with a dense fine-grained structure exhibit a moderate k of 4 nm2/s at 773 K, overstoichiometric films with a pronounced columnar structure oxidized over seven times faster. The nonstoichiometry in TiNy and CrNy leads to a reduced activation energy for oxidation compared to stoichiometric compounds.

Thin films of hard materials are of prime importance for wear-resistant, protective and decorative coatings. Besides adhesion, hardness is the most often quoted requirement, even if doubts remain on the experimental determination of the hardness values of thin films, on their theoretical interpretation and on their significance for wear protection. Transition metal interstitial compounds are extensively used because of their broad range of functional properties in the fields of machining, microelectronics, decoration, etc. This article presents a summary of recent relevant results on the structural, mechanical, electronic and optical properties of fee TIN, VN, CrN, NbN, W2N, hexagonal MoN, and some ternary nitrides in the form of sputtered thin films. The process parameters, e.g. the reactive gas partial pressure and the substrate bias, strongly influence the film properties. The composition and growth parameters influence the morphology, the stress state and other physical properties.The systematic investigation of the electronic density of states in valence and core states of comparable nitrides provides indications of the degree of covalency in the chemical bonding in relation to properties such as cohesive energy and hardness. For example, in molybdenum nitride the low stability of the cubic MoN phase is related to an increase in the charge transfer of Mo d electrons to nitrogen with increasing stoichiometric ratio N/Mo.Ellipsometric measurements of the dielectric function interpreted in relation to details of the band structure measure the variation of the density of conduction electrons. Vacancies and interstitials remove or add a specific number of electrons at the Fermi level. This analysis allows one to differentiate the types of defect at various compositions in, for example, TiNgamma films, for which the reported hardness values spread over a wide range. (C) 1999 Elsevier Science S.A. All rights reserved.

Thin films of lithium tantalate have been deposited by RF sputtering on RuO2- or SiO2-coated silicon substrates. Two electrical contact configurations have been used. The first configuration is a thin capacitor with an RuO2 buried electrode and a gold, nickel or RuO2 upper electrode. The second configuration has recourse to RuO2 interdigitated electrodes fabricated by a photolithographic process. Ferroelectric hysteresis measured with a Sawyer-Tower circuit shows a spontaneous polarization in the range of 20 mu C/cm(2) and an electric coercive field of 3 kV/cm. The dynamic pyroelectric response has been measured as a function of frequency at various temperatures. From 100 Hz to 1 kHz at room temperature, the pyroelectric current and voltage responses are 12 mu A/W and 18 V/W, respectively. The device with interdigitated electrodes shows a higher response due to a larger pyroelectric coefficient. The effects of the poling process have also been investigated and significant improvements of the pyroelectric response have been obtained.

Thin titanium nitride films were deposited by rf reactive sputtering. The N/Ti ratio varied between 0.88 and 1.12. The optical constants have been determined by ellipsometric measurements between 1.5 and 5 eV. The normal reflectivity was measured between 0.5 and 5.5 eV. The results have been fitted by a model dielectric function based on a set of Drude–Lorentz oscillators. In this way the contributions due to free carriers and to interband transitions could be unambiguously sorted out. The analysis of the optical properties sheds light on the nature of the stoichiometry-related defects of TiNx. It is shown that TiN contains one conduction electron per TiN unit, and that in TiNx the square of the plasma frequency varies in a manner indicating a loss of about one electron to each nitrogen interstitial and a gain of about one conduction electron for each nitrogen vacancy. In substoichiometric material the most significant defect is the nitrogen vacancy and in nitrogen-rich TiNx excess nitrogen behaves like an interstitial defect. The occasional presence of titanium defects is also detected.

TiO2 thin films with different thickness (0.4 mu m, 1 mu m, 1.7 mu m) deposited over various substrates (glass, quartz, alumina) were prepared by DC reactive sputtering. The structural characteristics of the films and their morphology, obtained by X-ray diffraction and by atomic force microscopy, are related to the deposition parameters. The catalytic properties of TiO2 thin films in the oxidation of toluene, and in particular their deactivation behavior, show a sensitivity to the morphology of the thin film.

The present study discusses the effect of iron doping in thin films deposited by rf sputtering. Iron doping induces a structural transformation from anatase to rutile and electrical measurements indicate that iron acts as an acceptor impurity. Thermoelectric power measurement shows a transition between n-type and p-type electrical conduction for an iron concentration around 0.13 at.%. The highest p-type conductivity at room temperature achieved by iron doping was .

This paper reports on an investigation on fee TiO1+x thin films with 0<x<1. The films were deposited by r.f. reactive sputtering and characterized by X-ray diffraction, electron probe microanalysis, X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunneling microscopy, and electrical measurements. The films crystallized in the fee phase with a lattice parameter a=0.419 nm, exhibit a gold like color, an electrical resistivity of about 400 mu Omega cm at room temperature, and remarkable nanohardness values of about 23 GPa. The results of these experiments are discussed and compared to the archetypal fee TiN coatings. (C) 1998 Elsevier Science S.A. All rights reserved.

Cerium-doped TiO2 thin films have been prepared by reactive RF sputtering. At low Ce concentration, X-ray diffraction indicates that the films have the anatase structure. Ce concentrations higher than 1.2 at.% result in an amorphization of the film which remains stable up to 873 K. The TiO2 electrical properties have been stabilized and improved by cerium doping, resulting in a lower conductivity (10-9 Ω-1m-1), a higher electrical breakdown strength (2 ×107 V/m), and a high value of the permittivity (45±5). The implementation of amorphous TiO2:Ce thin films as insulator layers in ZnS:Mn alternating current thin film electroluminescent devices (ACTFELD) results in a significant drop in the threshold operating voltage and a notable increase in the device brightness compared with ACTFELD containing Y2O3 or BaTa2O6 insulator layers. Rapid thermal annealing further improves the performance of the electroluminescent device.