TiOxNy Films Research Articles

Nanoporous Titanium (Oxy)nitride Films as Broadband Solar Absorbers.

Broadband absorption of solar light is a key aspect in many applications that involve an efficient conversion of solar energy to heat. Titanium nitride (TiN)-based materials, in the form of periodic arrays of nanostructures or multilayers, can promote significant heat generation upon illumination thanks to their efficient light absorption and refractory character. In this work, pulsed laser deposition was chosen as a synthesis technique to shift metallic bulk-like TiN to nanoparticle-assembled hierarchical oxynitride (TiOxNy) films by increasing the background gas deposition pressure. The nanoporous hierarchical films exhibit a tree-like morphology, a strong broadband solar absorption (∼90% from the UV to the near-infrared range), and could generate temperatures of ∼475 °C under moderate light concentration (17 Suns). The high heat generation achieved by treelike films is ascribed to their porous morphology, nanocrystalline structure, and oxynitride composition, which overall contribute to a superior light trapping and dissipation to heat. These properties pave the way for the implementation of such films as solar absorber structures.

Optical and structural investigations on titanium oxynitride films for visible-UV photocatalytic applications

We report on the epitaxial growth of titanium oxynitride (TiOxNy) films on α-Al2O3 (0001) substrates by using a pulsed-laser deposition technique and their optical properties. Using TiN as a solid source, N content (y) in the films was tuned by changing the partial pressure of O2 gas. The crystalline phase was found to evolve up to y ≈ 0.4 either from rock-salt type or from rutile-type structures. The optical absorption spectra of the films had two distinct components in regions of 0.44–2.4 eV and 2.4–6 eV, which arise from d–d and charge-transfer transitions, respectively. The former transition decreased with decreasing y and vanished at y ≈ 0.26, where a fundamental absorption edge due to the latter transition was found to be 2.4 eV. The results demonstrate a range of anion compositions in the TiOxNy being suitable for visible-light harvesting applications.

Preparation and characterization of nanostructured titanium oxynitride films for the application in self-cleaning and photoelectrochemical water splitting

Titanium oxynitride (TiOxNy) films capped with 10 nm titanium oxide (TiO2) layer were prepared using reactive direct current magnetron sputtering from pure Ti target. Part of the samples was annealed. Energy dispersive analysis of X-ray revealed that all the samples contain nitrogen and the incorporation of nitrogen into the oxynitrides is not linear. Phase investigation by X-ray diffraction showed structural variation with changing oxygen and nitrogen gas flow rates as well as annealing. Anatase, brookite, rutile and titanium nitride were detected individually or mixed in the as-prepared and annealed samples. The optical properties were found to be controlled by a structure and chemical composition. Transmittance and reflectance measurements were carried out by a high performance double beam ultraviolet-visible-near infrared spectrophotometer. Based on that, the energy band gap, refractive index and extinction coefficient were derived. The obvious difference between the dark and light currents indicated the validity of the TiO2/TiOxNy bilayer samples to act as photoanodes. All the annealed samples have photoelectrochemical water splitting response better than the as-prepared samples. The as-prepared TiO2/TiOxNy bilayer films were hydrophobic (contact angels, 81° - 93°) and their contact angles were independent from the nitrogen content. The annealed samples have lower contact angles than the as-prepared samples. The wettability of the as-prepared and annealed samples was changed from hydrophobic to more hydrophilic with increasing illumination time. These results are of important interest for the self-cleaning surfaces.

Structural, Optical and Electrical Properties of Electron Beam Evaporated Tioxny Films as Selective Solar Absorber Coatings

Titanium oxinitride (TiOx Ny ) solar absorber coatings were deposited at different oxygen partial pressures onto Cu, Si and glass substrates using electron beam evaporation technique. XRD diffraction patterns evidenced (111), (200) and (220) orientation of TiNx phase. The preferred orientation of the films changed with oxygen partial pressure. XPS revealed the intensity of both Ti 2P3/2 and Ti 2P1/2 increases as a function of oxygen flow, and also shifted towards higher binding energy, indicating more oxidized state of Ti species than that of TiO2 due to incorporation of nitrogen atoms. Formation of uniformly distributed spherical like particles and an increase in surface roughness of the TiOx Ny films were observed as a function of oxygen partial pressure as depicted from SEM and AFM, respectively. Ellipsometric and resistivity measurements showed a shift from metallic to semiconductor behaviour of the TiOx Ny films as oxygen flow changed. A solar absorptance value of 0.94 in the solar spectrum region and a low thermal emittance value of 0.05 were achieved for the TiOx Ny solar absorber coatings prepared at the oxygen partial pressure of 7.5x10-5 Torr due to both interference and intrinsic absorption. This study confirmed that a single layer of TiOx Ny film can be a good candidate as selective solar absorber.

Reactive Magnetron Sputter Deposition of Titanium Oxynitride TiNxOy Coatings: Influence of Substrate Bias Voltage on the Structure, Composition, and Properties

TiOxNy films were grown onto 316L stainless steel substrate using radiofrequency (rf) magnetron sputtering from a pure titanium nitride target in Ar–O2 gas mixture with various substrate bias voltages. The aim of this work is to investigate the effect of applied substrate bias Vs, varied from 0 to –100 V, on the deposition rate, structure, hardness and optical properties of the TiNxOy films. The characterization of the coatings by grazing incidence X-ray diffraction exhibited a crystalline structure of a mixture of TiN, rutile and anatase. The indirect and direct bad gap were found to decrease for unbiased substrate voltage to Vs = −100 V from 3.84 to 3.20 eV. In addition, the coatings exhibit high transparency (transmittance over 80%). The hardness of the coatings were found in the range of 6.2 to 12.5GPa.

Long-term ambient surface oxidation of titanium oxynitride films prepared by plasma-enhanced atomic layer deposition: An XPS study

The surface oxidation of a titanium oxynitride (TiOxNy) film after long-time storage of 25 month in ambient conditions is investigated. The TiOxNy film is prepared by plasma-enhanced atomic layer deposition using tetrakis(dimethylamino)titanium and nitrogen plasma, and the film is characterized by Ar+ ion sputtering of the film surface in combination with x-ray photoelectron spectroscopy (XPS) as well as by angle-resolved XPS. The total thickness of an oxygen-enriched layer at the surface of the TiOxNy films is found to be about 0.7 nm and it consists of a sequence of a 0.4 nm thick TiON/TiO2 enriched layer followed by a 0.3 nm thick TiO2 enriched layer underneath compared to the bulk composition of the film which shows constant values of 29% TiN, 29% TiO2, and 42% TiON. The results suggest that the TiON enrichment takes place initially at the surface followed by a surface and subsurface oxidation.

Titanium Oxynitride Thin Films with Tunable Double Epsilon-Near-Zero Behavior for Nanophotonic Applications.

Titanium oxynitride (TiOxNy) thin films are fabricated using reactive magnetron sputtering. The mechanism of their growth formation is explained, and their optical properties are presented. The films grown when the level of residual oxygen in the background vacuum was between 5 nTorr to 20 nTorr exhibit double epsilon-near-Zero (2-ENZ) behavior with ENZ1 and ENZ2 wavelengths tunable in the 700-850 and 1100-1350 nm spectral ranges, respectively. Samples fabricated when the level of residual oxygen in the background vacuum was above 2 × 10-8 Torr exhibit nonmetallic behavior, while the layers deposited when the level of residual oxygen in the background vacuum was below 5 × 10-9 Torr show metallic behavior with a single ENZ value. The double ENZ phenomenon is related to the level of residual oxygen in the background vacuum and is attributed to the mixture of TiN and TiOxNy and TiOx phases in the films. Varying the partial pressure of nitrogen during the deposition can further control the amount of TiN, TiOx, and TiOxNy compounds in the films and, therefore, tune the screened plasma wavelengths. A good approximation of the ellipsometric behavior is achieved with Maxwell-Garnett theory for a composite film formed by a mixture of TiO2 and TiN phases suggesting that double ENZ TiOxNy films are formed by inclusions of TiN within a TiO2 matrix. These oxynitride compounds could be considered as new materials exhibiting double ENZ in the visible and near-IR spectral ranges. Materials with ENZ properties are advantageous for designing the enhanced nonlinear optical response, metasurfaces, and nonreciprocal behavior.

In-gap states in titanium dioxide and oxynitride atomic layer deposited films

Valence band (VB) spectra of titanium dioxide (TiO2) and oxynitride (TiOxNy) films prepared by different atomic layer deposition (ALD) processes are compared and related to electrical characterization [current–voltage (JV) and capacitance–voltage (CV)] results. By increasing the nitrogen amount in the TiO2 film, band-gap narrowing is observed. The band-gap decrease is related to the contribution of the nitrogen density of states, which induces defects within the band-gap and thus reduces its optical band-gap. In-gap states are found in the VB spectra at 1 eV below the Fermi energy in all investigated ALD samples, i.e., in TiO2 as well as in TiOxNy films. An exponential correlation between leakage current density and in-gap state intensity is derived by the combination of JV measurements and VB spectra, whereas the in-gap states seem to have no influence on hysteresis and fixed oxide charges found in the CV data. It is argued that the in-gap states in TiO2 and TiOxNy have an excitonic or polaronic origin. Both, band-gap narrowing and in-gap state intensity can be tuned by the ALD process selection and the variation of its parameters.

Analysis of titanium species in titanium oxynitride films prepared by plasma enhanced atomic layer deposition

A comparative study of thin titanium oxynitride (TiOxNy) films prepared by plasma enhanced atomic layer deposition using tetrakis(dimethylamino)titanium (TDMAT) and N2 plasma as well as titanium(IV)isopropoxide and NH3 plasma is reported. The comparison is based on the combination of Ti2p core level and valence band spectroscopy and current-voltage measurements. The TDMAT/N2 process delivers generally higher fractions of TiN and TiON within the Ti2p spectra of the films and stronger photoemissions within the bandgap as resolved in detail by high energy resolution synchrotron-based spectroscopy. In particular, it is shown that higher TiN contributions and in-gap emission intensities correlate strongly with increased leakage currents within the films and might be modified by the process parameters and precursor selection.

Plasma-enhanced atomic layer deposition of titanium oxynitrides films: A comparative spectroscopic and electrical study

The process parameters' impact of the plasma-enhanced atomic layer deposition (PE-ALD) method on the oxygen to nitrogen (O/N) ratio in titanium oxynitride (TiOxNy) films was studied. Titanium(IV)isopropoxide in combination with NH3 plasma and tetrakis(dimethylamino)titanium by applying N2 plasma processes were investigated. Samples were characterized by the in situ spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and electrical characterization (current–voltage: I-V and capacitance–voltage: C-V) methods. The O/N ratio in the TiOxNy films is found to be very sensitive for their electric properties such as conductivity, dielectric breakdown, and permittivity. Our results indicate that these PE-ALD film properties can be tuned, via the O/N ratio, by the selection of the process parameters and precursor/coreactant combination.

Titanium oxynitride thin films as high-capacity and high-rate anode materials for lithium-ion batteries

Titanium oxynitride (TiOxNy) was synthesized by reactive magnetron sputtering in a mixed N2/O2/Ar gas at ambient temperature. TiOxNy thin films with various amounts of nitrogen contents were deposited by varying the N2/O2 ratios in the background gas. The synthesized TiOxNy films with different compositions (TiO1.837N0.060, TiO1.890N0.068, TiO1.865N0.073, and TiO1.882N0.163) all displayed anatase phase, except TiO1.882N0.163. The impedances and grain sizes showed obvious variations with the nitrogen contents. A wide potential window from 3.0V to 0.05V, high-rate charge–discharge testing, and long cycle testing were applied to investigate the performances of synthesized TiOxNy and pure TiO2 as anodes for lithium-ion batteries. These TiOxNy anodes can be cycled under high rates of 125μA/cm2 (10°C) because of the lower charge–transfer resistance compared with the TiO2 anode. At 10°C the discharge capacity of the optimal TiOxNy composition is 1.5 times higher than that of pure TiO2. An unexpectedly large reversible capacity of ~300μAh/cm2μm (~800mAh/g) between 1.0V and 0.05V was recorded for the TiOxNy anodes. The TiOxNy anode was cycled (3.0V to 0.05V) at 10°C over 300 times without capacity fading while delivering a capacity of ~150μAh/cm2μm (~400mAh/g).

Multilevel metal/Pb(Zr0.52Ti0.48)O3/TiOxNy/Si for next generation FeRAM technology node

Metal–Ferroelectric–Insulator–Semiconductor (MFIS) thin film capacitors with lead zirconate titanate (Pb(Zr0.52Ti0.48)O3) as ferroelectric layer and ultrathin high-κ titanium oxynitride (TiOxNy) as insulating buffer layer on p-Si are fabricated by RF magnetron sputtering for non-volatile multilevel ferroelectric random access memory (FeRAM). Micro Raman analysis of the proposed systems confirmed the existence of most stable tetragonal rutile phase in ultrathin TiOxNy and perovskite phase of PZT thin films. AFM analysis showed that surface roughness of ultrathin TiOxNy and thin PZT films are ∼2.54nm and ∼1.85nm, respectively and result the uniform interface between substrate and metal. The maximum C–V memory window of ∼1.25V was obtained at cyclic sweep voltage of ±6V and starts to decrease when the sweep voltage exceeds 6V due to charge injection. The fabricated structure possesses good data retention measured till 1.5h and high, low capacitance states remain distinguishable even if extrapolated to 15years. The proposed system exhibited excellent TiOxNy–Si interface, incomparable high breakdown field strength ∼11.15MV/cm and low leakage current density (J) ∼5μA/cm2 at +4V. Thus, Au/PZT/TiOxNy/Si MFIS based FeRAM devices with multilevel operation, high breakdown field and excellent retention are prospective contender for next generation multilevel FeRAM technology node.

Controllable nitrogen doping in as deposited TiO2 film and its effect on post deposition annealing

In order to narrow the band gap of TiO2, nitrogen doping by combining thermal atomic layer deposition (TALD) of TiO2 and plasma enhanced atomic layer deposition (PEALD) of TiN has been implemented. By altering the ratio between TALD TiO2 and PEALD TiN, the as synthesized TiOxNy films showed different band gaps (from 1.91 eV to 3.14 eV). In situ x-ray diffraction characterization showed that the crystallization behavior of these films changed after nitrogen doping. After annealing in helium, nitrogen doped TiO2 films crystallized into rutile phase while for the samples annealed in air a preferential growth of the anatase TiO2 along (001) orientation was observed. Photocatalytic tests of the degradation of stearic acid were done to evaluate the effect of N doping on the photocatalytic activity.

Sputtering characteristics, crystal structures, and transparent conductive properties of TiOxNy films deposited on α-Al2O3(0 0 0 1) and glass substrates

Adding N2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO1−xNx having a face-centered cubic (fcc) structure to TiO2−xNx having an anatase structure. Titanium oxynitride films deposited on an Al2O3(0001) substrate were epitaxial with major orientations toward the (111) and (200) directions for fcc-TiO1−xNx and (112) for anatase-TiO2−xNx. Intermediately oxidized films between TiO1−xNx and TiO2−xNx were amorphous on the glass substrate but crystallized into a Magneli phase, TinO(N)2n−1, on the Al2O3(0001) substrate. Partially substituting oxygen in TiO2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO2−xNx films on Al2O3(0001) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiOxNy films vary continuously with changing N2 flow rate, their transparent conductive properties can be controlled more easily than TiOx. Nb5+ ions could be doped as donors in TiO2−xNx anatase crystals.

Interfacial and Electrical Properties of GaAs Metal-Oxide-Semiconductor Device with TiOxNy High-k Gate Dielectrics

Fermi level pinning attributed to oxides at the GaAs/high-k interface is a major obstacle to develop GaAs-based metal-oxide-semiconductor devices. In this paper, plasma nitridation of GaAs surface prior to the high-k deposition is shown to solve the issue of interface pinning. X-ray photoelectron spectroscopy (XPS) study confirms that nitridation passivation effectively suppresses the oxides formation and minimizes the Fermi level pinning at the interface between the GaAs and TiO2. Plasma-nitrided TiO2 (TiOxNy) films on n-GaAs show better metal-oxide-semiconductor (MOS) capacitor characteristics, such as interface state density, accumulation capacitance, hysteresis, and leakage current.

Study of TiOxNy MOS Capacitors

A set of MOS capacitors with TiOxNy films deposited by reactive r.f. magnetron sputtering varying the nitrogen partial pressure in an Ar/N2 gaseous mixture, as gate dielectric layer, was fabricated and characterized. These films were annealed at 550 and 1000oC in N2 environment. The TiOxNy films were characterized by Raman, Rutherford Backscattering (RBS), and High Resolution Transmission Electron Microscopy (HRTEM). Capacitance-voltage (1MHz) and current-voltage measurements were used to obtain the effective dielectric constant, the effective oxide thickness (EOT), the leakage current density, and the interface quality. MOS capacitors results show that the TiOxNy films present a dielectric constant varying from 15 to 35, good interface quality with silicon and leakage current density varying from approximately 1 to 10 mA/cm2 for VG = -1V and for EOT of approximately 2 nm. The leakage current density is reduced in 2 orders of magnitude with an increase in nitrogen concentration.

Transparent Conductor: TiOxNy

We propose the feasibility of using TiOxNy films as transparent conductors. The TiOxNy films deposited by electron cyclotron resonance plasma sputtering from a Ti target in the metal mode had a face-centered cubic crystal structure. As deposited films incorporated larger numbers of O and N atoms, their crystallinity approached an amorphous state and optical transparency improved, reflecting the decrease in carrier concentration. Our TiOxNy films extended the controllable range of resistivity and optical transmittance more than that with TiOx and TiNx films and outperformed those produced by conventional magnetron sputtering.

Study of metal‐oxide‐semiconductor capacitors with r.f. magnetron sputtering TiOxNy films dielectric layer

AbstractA set of MOS capacitors with TiOxNy films as gate dielectric layer was fabricated and characterized. The TiOxNy films were deposited by reactive r.f. magnetron sputtering varying the nitrogen and oxygen partial pressure in a Ar/N2/O2 gaseous mixture.The TiOxNy films were characterized by, Rutherford Backscattering (RBS), X‐ray absorption near edge spectroscopy (XANES) in oxygen K‐edge (O‐K), optical absorption and High Resolution Transmission Electron Microscopy (HRTEM). Capacitance‐voltage (1MHz) and current‐voltage measurements were performed to obtain the effective dielectric constant, the effective oxide thickness (EOT), the leakage current density, and the interface quality. MOS capacitors results show that the TiOxNyfilms dielectric constant varies from 28 to 80, present a good interface quality with silicon, and the leakage current density values are in the order of 0.25 mA/cm2 for VG = –2V, which is acceptable for high performance logic circuits and low power circuits fabrication. The leakage current density is reduced in 2 orders of magnitude for increasing nitrogen concentration (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

TiOxNy anti‐resonant layer ARROW waveguides

AbstractARROW waveguides with sputtered‐TiOxNy anti‐resonant layers obtained with different nitrogen concentration in the gaseous mixture were fabricated and characterized. A study of the influence of this parameter on the losses of the waveguides is presented in this work. TiOxNy films have very high refractive indexes, which is a very important characteristic for the first ARROW layer, since this layer behaves like a Fabry‐Perot resonator in anti‐resonance. Optical and compositional properties of the TiOxNy films were also studied and the results are presented. These films were characterized by Rutherford Backscattering Spectroscopy (RBS), FTIRs, optical absorption and ellipsometry. The second anti‐resonant layer and the core of the waveguides were composed of thermally grown SiO2 and PECVD‐SiOxNy, respectively. Optical characterization results show propagation losses as low as 1.18 dB/cm for single‐mode waveguides fabricated with TiOxNy films obtained with 25% of nitrogen in the gaseous mixture. (© WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The reactive gas pulsing process for tuneable properties of sputter deposited titanium oxide, nitride and oxynitride coatings

TiOx, TiNy and TiOxNy thin films were deposited by reactive sputtering. The reactive gas pulsing process was implemented to tune the chemical composition and consequently, the characteristics of the films. For TiOx coatings, oxygen concentration was progressively modified from pure titanium to TiO2 compound. Similarly, a gradual decrease of the deposition rate and a controlled modulation of the chemical composition of TiNy films (y between 0 and 1.05) were easily reached. A reverse evolution of the oxygen and nitrogen contents was produced in TiOxNy films, which was correlated with the smooth transition from metallic to semiconducting behaviours.