xNx Thin Films Research Articles

Mechanical and tribological properties of (AlCoCrNiSi)100−xNx thin films

High entropy thin films of (AlCoCrNiSi)100−xNx were deposited on silicon wafers using a pulsed DC magnetron sputtering technique, with nitrogen gas flow ratios (RN) of 0, 0.33, and 0.50. The structure and properties of these films were analyzed for elemental composition, surface and cross-sectional morphologies, microstructure, roughness, and mechanical properties. The coatings were primarily composed of an amorphous structure with a minor presence of a BCC structure and exhibited periodic variations in chemical composition from the substrate to the free surface. An increase in RN enhances crystallinity of the materials. Nanoindentation results showed that the films deposited at RN = 0.50 displayed the highest hardness (10.7 ± 0.5 GPa) and reduced modulus (176 ± 5 GPa), which were the highest among the films. Microtribology testing was conducted using a 20 μm radius spherical diamond tip under ambient air and normal loads ranging from 0.5 to 9 mN. Worn surfaces were characterized using atomic force microscopy. The coefficient of friction was evaluated to investigate the elastic and plastic behaviors of films using Schiffmann’s model. The coating without nitrogen displayed a predominant plastic behavior during the initial cycles, while the coating deposited at RN = 0.33 demonstrated a more elastic behavior, particularly at lower loads.

Engineering of Ferroic Orders in Thin Films by Anionic Substitution

AbstractMultiferroics are a unique class of materials where magnetic and ferroelectric orders coexist. The research on multiferroics contributes significantly to the fundamental understanding of the strong correlations between different material degrees of freedom and provides an energy‐efficient route toward the electrical control of magnetism. While multiple ABO3 oxide perovskites are identified as being multiferroic, their magnetoelectric coupling strength is often weak, necessitating the material search in different compounds. Here, the observation of room‐temperature multiferroic orders in multi‐anion SrNbO3−xNx thin films is reported. In these samples, the multi‐anion state enables the room‐temperature ferromagnetic ordering of the Nb d‐electrons. Simultaneously, ferroelectric responses that originate from the structural symmetry breaking associated are found with both the off‐center displacements of Nb and the geometric displacements of Sr, depending on the relative O‐N arrangements within the Nb‐centered octahedra. The findings not only diversify the available multiferroic material pool but also demonstrate a new multiferroism design strategy via multi‐anion engineering.

Varying nitrogen background pressure; an efficient approach to improve electrical properties of MBE-grown GaAs1−xNx thin films with less atomic disorder

Epitaxial GaAs1−xNx thin films were grown on GaAs (001) substrates through solid-source molecular beam epitaxy using an RF plasma source for incorporating nitrogen. We examined the thin films grown under different nitrogen background pressures (NBPs) using various ex-situ techniques. GaAs0.969N0.031 thin films grown under a high NBP of 5.5 × 10−6 Torr exhibited thickness variation-induced Pendellösung fringes, a smooth surface with few Ga droplets, and a high electron mobility of 4020 cm2/(Vs), all of which evidence the high crystal quality. This is attributed to the reduction in surface recombination centers at elevated nitrogen concentrations. A high intensity of the GaAs LO1 and low intensity of the GaN-like local vibrational mode of the relaxed films were observed, attributed to less atomic disorder in the alloys. GaAs0.969N0.031 thin films exhibited near-band emission at 1.14 eV, close to the ideal band gap of (In)GaAsN (∼1 eV). Moreover, the photoluminescence intensity of films annealed at 750 °C exhibited a ∼200-fold improvement over films annealed at 650 °C. Hence, superior-quality epitaxial GaAs0.0969N0.031 thin films grown through SS-MBE are an ideal substitute for (In)GaAsN in high-efficiency multijunction solar cell applications.

Nitrogen incorporation in SnO2 thin films grown by chemical vapor deposition

The influence of nitrogen incorporation in high concentrations on the structural properties and morphology of SnO2–xNx thin films grown by chemical vapor deposition is studied. A decrease in crystallite size and a lattice expansion in SnO2–xNx films with increasing x are found by X‐ray diffraction analysis and Raman spectroscopy. Substitutional nitrogen with a binding energy of 397.15 eV was detected by X‐ray photoelectron spectroscopy, attributed to the N3− ion in the SnN bond. The increase of the N atomic concentration x in SnO2–xNx films from 0 to 7.9 at.% without phase separation with increasing NH3 flow rate during the deposition is accompanied by a decrease of O atomic concentration.

TiN-buffered substrates for photoelectrochemical measurements of oxynitride thin films

Developing novel materials for the conversion of solar to chemical energy is becoming an increasingly important endeavour. Perovskite compounds based on bandgap tunable oxynitrides represent an exciting class of novel photoactive materials. To date, literature mostly focuses on the characterization of oxynitride powder samples which have undeniable technological interest but do not allow the investigation of fundamental properties such as the role of the crystalline quality and/or the surface crystallographic orientation toward photo-catalytic activity. The challenge of growing high quality oxynitride thin films arises from the availability of a suitable substrate, owing to strict material and processing requirements: effective lattice matching, sufficiently high conductivities, stability under high temperatures and in strongly reducing environments. Here, we have established the foundations of a model system incorporating a TiN-buffer layer which enables fundamental investigations into crystallographic surface orientation and crystalline quality of the photocatalyst against photo(electro)chemical performance to be effectively performed. Furthermore, we find that TiN as current collector enables control over the nitrogen content of oxynitride thin films produced by a modified pulsed laser deposition method and allows the growth of highly ordered LaTiO3−xNx thin films.

Influence of sputtering pressure on optical constants of a-GaAs1−xNx thin films

Amorphous GaAs1−xNx (a-GaAs1−xNx) thin films have been deposited at room temperature by a reactive magnetron sputtering technique on glass substrates with different sputtering pressures. The thickness, nitrogen content, carrier concentration and transmittance of the as-deposited films were determined experimentally. The influence of sputtering pressure on the optical band gap, refractive index and dispersion parameters (Eo, Ed) has been investigated. An analysis of the absorption coefficient revealed a direct optical transition characterizing the as-deposited films. The refractive index dispersions of the as-deposited a-GaAs1−xNx films fitted well to the Cauchy dispersion relation and the Wemple model.

Pulsed laser deposition and characterisation of perovskite-type LaTiO3−xNx thin films

LaTiO3−xNx films with high nitrogen contents (x≈0.4–0.8) have been grown on (001)-oriented MgO and LaAlO3 substrates by pulsed reactive crossed-beam laser ablation from a La2Ti2O7 target in a one-step process. These films have a perovskite-type structure, similar to bulk polycrystalline LaTiO2N. The nitrogen content in the films can be changed by selecting the nitriding source, i.e. NH3 or N2 gas pulse, and by varying the substrate temperature. Films deposited on MgO show a preferential (001) and (112) orientation, whereas films on LaAlO3 are predominantly (001) oriented. N(2p) orbitals contribute to the top of the valence band, leading to a considerable decrease in the band gap energy from ∼4.0eV for the parent LaTiO3.5 to ∼2.4–2.9eV for LaTiO3−xNx (x≈0.4–0.8) films. This results in a strong visible light absorption at wavelengths below ∼500nm. The band gap energies in LaTiO3−xNx films decrease with increasing nitrogen content. The values of the band gap energies for LaTiO3−xNx as a function of the N content agree well with other titanate-based perovskite-type oxynitrides, which confirms the proposed band gap model.

Electron spin quantum beats and room temperature g factor in GaAsN

We report on the investigation of electron spin quantum beats at room temperature in GaAsN thin films by time-resolved Kerr rotation technique. The measurement of the quantum beats, which originate from the Larmor precession of electron spins in external transverse magnetic field, yields an accurate determination of the conduction electron g factor. We show that the g factor of GaAs1−xNx thin films is significantly changed by the introduction of a small nitrogen fraction.

The use of HI-ERDA/RBS and NRA/RBS to depth profile N in GaAs1−xNx thin films

N profiles of several GaAs1−xNx epitaxial layers with different N mole fractions in the range 0<x<0.14 were obtained by using (1) heavy-ion elastic recoil detection analysis (HI-ERDA) along with Rutherford backscattering spectrometry (RBS) using a 35MeV Si6+ beam, and (2) nuclear reaction analysis (NRA) with the 14N(α,p)17O reaction, also with RBS, using a 3.7MeV 4He+ beam. The results from the two techniques are compared and the advantages, disadvantages and capabilities are discussed.

Compositional and Structural Properties of TiO2−xNx ThinFilms Deposited by Radio-Frequency Magnetron Sputtering

TiO2−xNx thin films are deposited ontoSi(100) and quartz substrates by a rf magnetron sputtering method usinga titanium metal disc as a target in Ar, N2, andO2 atmospheres. The substrate temperature is kept at300°C. The O2 and Ar gas flow rates are kept to beconstants and the N gas flow rate is varied. TiO2−xNx filmswith different N contents are characterized by x-ray diffraction andx-ray photoelectron spectroscopy. The results indicate that theTiO2−xNx thin films can be obtained at 13% N and 15% N contentsin the film, and the films with mixed TiO2 and TiN crystalcan be obtained at 13% N and 15% N contents in the film. In terms ofthe results of x-ray photoelectron spectroscopy, N 1s of β-N (396 eV)is the main component in the TiO2−xNx thinfilms. Because the energy level of β-N is positioned above thevalence-band maximum of TiO2, an effectiveoptical-energy gap decreases from 2.8 eV (for pure TiO2film deposited by the same rf sputtering system) to 2.3 eV, which isverified by the optical-absorption spectra.

Growth of GaP1–xNx thin films by rf sputtering

AbstractWe have deposited GaP1–xNx thin films on glass substrates by rf sputtering employing a nitrogen–argon atmosphere. The films properties were studied as a function of the growth temperature in the range of 420–520 °C. The films characterization was carried out by absorbance, X‐ray diffraction and Raman spectroscopy. The GaP1–xNx films have a cubic polycrystalline structure with a preferential orientation along the [111] direction; the structural properties of the films are improved by increasing the growth temperature up to 500 °C. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

SiCi_xNxthin films preparation by TEA-Co2 Laser induced Vapor-phase reaction and study of the nature of chemical bonds and some their electrical and optical properties

A pulsed (TEA-0O2) laser was used to dissociate molecules of silane ethylene (C2I-14) and ammonia (NH3) gases, through collision assisted multiple photon dissociation (MPD) to deposit(SiC i_xNx) thin films, where the X-values are 0, 0.13 and 0.33, on glass substrate at T,----648 K. deposition rate of (0.416-0.833) nm/pulse and thickness of (500-1000)nm .Fourier transform infrared spectrometry (FT-IR) was used to study the nature of the chemical bonds that exist in the films. Results revealed that these films contain complex networks of the atomic (Si, C, and N), other a quantity of atomic hydrogen and chemical bonds such as (Si-N, C-N, C-14 and N-H).Absorbance and Transmittance spectra in the wavelength range (400-1100) nm were used to study the optical properties of the deposited films. It was found the optical nergy ap E0) of these films is indirect and increases with increasing (X) while the width of localized states decreases.The study of the electrical properties of the deposited films revealed that their electrical conductivity at any constant temperature decreases with increasing (X) and the films have two activation energies both increase with increasing (X).

Nitrogen-induced decrease of the electron effective mass in GaAs1−xNx thin films measured by thermomagnetic transport phenomena

Thin films of GaAs1−xNx were grown on insulating GaAs substrates and subjected to temperature-dependent resistivity, Hall, Seebeck, and Nernst coefficient measurements. Density of states, effective-mass values, which are calculated from the transport data, decrease from 0.084me to 0.029me as x increases from 0 to 0.004.

Transport properties of GaAs1−xNx thin films grown by metalorganic chemical vapor deposition

A series of devices with the structure GaAs/GaAs1−xNx/GaAs and 0.01&amp;lt;x&amp;lt;0.03 have been grown by metalorganic chemical vapor deposition. The transient photoconductive decay of these structures is measured as a function of excitation wavelength and injection level. The decay process is generally described by a stretched exponential function with anomously large decay times. The photoconductive excitation spectrum extends into the infrared, well beyond the bandgap of the given alloy. The processes here can be explained by nitrogen clusters that produce charge separation.

Amorphous GaAs1 − xNx thin films on crystalline Si substrates: growth and characterizations

Abstract This work deals with the growth and study of a new nitride in thin films: GaAs 1 − x N x . The material is deposited in its amorphous form on crystalline Si substrates by means of RF sputtering of a GaAs target in an atmosphere of argon and ammonia. Raman spectroscopy used to study the physico-chemical properties of the film structure pointed out that GaAs 1 − x N x is a wide gap material which is formed by the substitution of arsenic by nitrogen in the GaAs network (J. Bandet, K. Aguir, D. Lollman, A. Fennouh, H. Carchano, Jpn. J. Appl. Phys., 36 (1997) 11. In order to investigate the electrical properties of GaAs 1 − x N x in view of potential applications in optoelectronic systems, J—V and C—V characteristics have been performed. J—V results show that the heterostructures exhibit a drastic increase in resistivity with nitrogen incorporation. The conduction passes from a diode-type one for x = 0 to an approximately symmetrical one with nitridation, i.e. for x > 0. The films present convenient high resistivity values for insulating character consideration. Furthermore, C—V results obtained present a manifest MIS-like behaviour with however the existence of a flat-band voltage ( V FB ).