Oxygen Content In Films Research Articles

Properties of NbxTi(1−x)N thin films deposited on 300 mm silicon wafers for upscaling superconducting digital circuits

Scaling superconducting digital circuits requires fundamental changes in the current material set and fabrication process. The transition to 300 mm wafers and the implementation of advanced lithography are instrumental in facilitating mature CMOS processes, ensuring uniformity, and optimizing the yield. This study explores the properties of Nb x Ti(1−x)N films fabricated by magnetron DC sputtering on 300 mm Si wafers. As a promising alternative to traditional Nb in device manufacturing, Nb x Ti(1−x)N offers numerous advantages, including enhanced stability and scalability to smaller dimensions, in both processing and design. As a ternary material, Nb x Ti(1−x)N allows engineering material parameters by changing deposition conditions. The engineered properties can be used to modulate device parameters through the stack and mitigate failure modes. We report characterization of Nb x Ti(1−x)N films at less than 2% thickness variability, 2.4% T c variability and 3% composition variability. Film resistivity (140–375 Ωcm) shows a strong correlation with the film oxygen content, while the critical temperature T c (4.6 K–14.1 K) is strongly affected by film stoichiometry and its microstructure has only a moderate effect on modifying T c. Our results offer insights about the interplay between film stoichiometry, film microstructure and critical temperature.

Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10-6 T). This vacuum contains enough residual oxygen to allow a time-independent gas phase oxidation of the ablated species as well as a time-dependent regulated surface oxidation of TiN to TiON films. The time-dependent surface oxidation is controlled by means of film deposition time that, in turn, is controlled by changing the number of laser pulses impinging on the polycrystalline TiN target at a constant repetition rate. By changing the number of laser pulses from 150 to 5000, unoxidized (or negligibly oxidized) and oxidized TiN films have been obtained with the thickness in the range of four unit cells to 70 unit cells of TiN/TiON. X-ray photoelectron spectroscopy (XPS) investigations reveal higher oxygen content in TiON films prepared with a larger number of laser pulses. The oxidation of TiN films is achieved by precisely controlling the time of deposition, which affects the surface diffusion of oxygen to the TiN film lattice. The lattice constants of the TiON films obtained by x-ray diffraction (XRD) increase with the oxygen content in the film, as predicted by molecular dynamics (MD) simulations. The lattice constant increase is explained based on a larger electrostatic repulsive force due to unbalanced local charges in the vicinity of Ti vacancies and substitutional O. The bandgap of TiN and TiON films, measured using UV-visible spectroscopy, has an asymmetric V-shaped variation as a function of the number of pulses. The bandgap variation following the lower number of laser pulses (150-750) of the V-shaped curve is explained using the quantum confinement effect, while the bandgap variation following the higher number of laser pulses (1000-5000) is associated with the modification in the band structure due to hybridization of O2p and N2p energy levels.

Triplet exciton reactions in MEH-PPV films registered by accompanying magneto-sensitive photoluminescence

Magneto-sensitive delayed photoluminescence (DPL) of the deaerated MEH-PPV films in the presence of an external magnetic field is investigated. The obtained results have shown that the sign of the magnetic field effect on DPL can be inverted by varying molecular oxygen concentration in the films. For explaining the “sign-inversion” of the magnetic field effect on DPL, the mathematical model based on the superposition of exciton-initiated reactions was proposed. The magnetic field dependencies of DPL based on the theoretical model were calculated. The calculations of the magnetic field effects on DPL confirm the “sign-inversion effect”. Also, the critical molecular oxygen concentration when the magnetic field effect on DPL disappears was determined theoretically. The obtained results can be used for the detection of spin-selective exciton-initiated reactions as well as for the determination of molecular oxygen concentration in MEH-PPV films.

Эффект "стабилизации" кислородного содержания в пленках La-=SUB=-0.8-=/SUB=-Sr-=SUB=-0.2-=/SUB=-MnO-=SUB=-3-delta-=/SUB=- при термообработке на воздухе

In a series of epitaxial La0.8Sr0.2MnO3- films 12–75 nm thick on NdGaO3 substrates, the variation in the oxygen content during heat treatment in air at temperatures of 873–1073 K was quantitatively studied. Experimental and calculated time dependences of the change in the oxygen content in films with taking into account the effect of inhomogeneous diffusion of oxygen over the thickness of the films, allowing to make the optimal choice of temperature and duration of the heat treatment procedure. In films 25–75 nm thick, the effect of “stabilization” of the oxygen content is observed, which indicates the presence of an energy barrier that prevents the incorporation of an excess oxygen atom into the surface layer of the film under optimal conditions of heat treatment.

Substrate oxygen sponge effect: A parameter for epitaxial manganite thin film growth

The emergent phenomena in complex oxide thin films are strongly tied to the oxygen content, which is often engineered by the oxygen partial pressure during growth. However, such oxygen control by the growth pressure is challenging to synthesize for some oxide films, which requires a subtle control of the oxygen content. A parameter of controlling the oxygen content independent of the growth pressure is desired. Here, we propose a method of controlling the oxygen content of films by engineering the substrate before the growth. The oxide substrate serves as an oxygen sponge, which provides a tunable oxygen environment ranging from oxygen-rich to oxygen-poor for the film growth, depending on the pre-substrate annealing (PSA) conditions. Using manganite as a model system, we demonstrate that this simple PSA method leads to remarkable changes in the structure and physical properties of the as-grown films. This substrate oxygen sponge effect, driven by the large oxygen concentration gradient at high temperatures, can be applied to explore not only emergent interfacial phenomena but also the growth of a variety of functional oxide thin films and nanocomposites.

Effect of substrate bias on the microstructure and properties of (AlCrSiNbZr)Nx high entropy nitride thin film

In this study, AlCrSiNbZr nitride thin films were deposited on Si substrate by reactive radio frequency magnetron sputtering under the substrate bias from 0 V to −100 V at room temperature. The effect of substrate bias on structure, morphology, hardness and resistivity of the films was investigated. The results show that (111) preferred orientation was dominant phases for samples under bias of 0 V, −25 V, −50 V and − 75 V whereas amorphous-like feature was observed for samples under the bias of −100 V. In addition, crystallinity of film was enhanced when the substrate bias increased from 0 V to −50 V, but decreased when substrate bias further increased from −50 V to −100 V, suggesting that the optimized crystallinity of films was achieved under the substrate bias of −50 V. The oxygen contents of the thin films decreased significantly when the substrate bias was higher than −25 V. The hardness of the films was divided into two regions and samples under bias of −75 V and −100 V possessed higher hardness than those under bias of 0 V, −25 V and −50 V, which was mainly attributed to less oxynitride phases for samples under bias of −75 V and −100 V. The resistivity of thin films decreased as the substrate bias increased, which was mainly affected by the concentration of oxygen in films. The optimized substrate bias was −75 V with the maximum hardness and lowest resistivity.

Tailoring Nonstoichiometry and Mixed Ionic Electronic Conductivity in Pr0.1Ce0.9O2-δ/SrTiO3 Heterostructures.

The oxygen deficiency or excess, as reflected in the nonstoichiometry of oxide films, plays a crucial role in their functional properties for applications such as micro solid oxide fuel cells, catalysis, sensors, ferroelectrics, and memristors. High concentrations of oxygen vacancies may be beneficial or detrimental according to the application, and hence there is interest in controlling the oxygen content of films without resorting to compositional changes. Here, we demonstrate that substantial changes in the nonstoichiometry of Pr0.1Ce0.9O2-δ (PCO), a model mixed ionic electronic conductor, can be achieved by fabricating multilayers with an inert material, SrTiO3 (STO). We fabricated heterostructures using pulsed laser deposition, keeping the total thickness of PCO and STO constant while varying the number of layers and thickness of each individual layer, to probe the effects of the PCO/STO interfaces. Conductivity measurements as a function of oxygen partial pressure (PO2) and temperature showed a significant weakening of the PO2 dependence compared to bulk PCO, which scaled with the density of interfaces. We confirmed that this change was due to variations in nonstoichiometry, by optical transmission measurements, and show that the lower oxygen content is consistent with a decrease in the effective oxygen reduction enthalpy of PCO. These results exemplify the dramatic differences in properties between films and their bulk counterparts, achievable by interface engineering, and provide generalized insight into tailoring the properties of mixed ionic electronic conductors at the nanoscale.

Measurements of Microstructural, Chemical, Optical, and Electrical Properties of Silicon-Oxygen-Nitrogen Films Prepared by Plasma-Enhanced Atomic Layer Deposition.

In this study, silicon nitride (SiNx) thin films with different oxygen concentration (i.e., SiON film) were precisely deposited by plasma enhanced atomic layer deposition on Si (100) substrates. Thus, the effect of oxygen concentration on film properties is able to be comparatively studied and various valuable results are obtained. In detail, x-ray reflectivity, x-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry are used to systematically characterize the microstructural, optical, and electrical properties of SiON film. The experimental results indicate that the surface roughness increases from 0.13 to 0.2 nm as the oxygen concentration decreases. The refractive index of the SiON film reveals an increase from 1.55 to 1.86 with decreasing oxygen concentration. Accordingly, the band-gap energy of these films determined by oxygen 1s-peak analysis decreases from 6.2 to 4.8 eV. Moreover, the I-V tests demonstrate that the film exhibits lower leakage current and better insulation for higher oxygen concentration in film. These results indicate that oxygen affects microstructural, optical, and electrical properties of the prepared SiNx film.

APCVD prepared TiNxOy films with energy-saving and self-cleaning functions

In this study, titanium oxynitride (TiNxOy) films were assessed for their potential as energy saving and self-cleaning coatings on window glass. The coatings were obtained through heat treatment of titanium nitride (TiN) films deposited by atmospheric pressure chemical vapor deposition (APCVD). The effects of heat treatment temperature on the properties of the films such as chemical composition, structure, surface morphology, sheet resistance, optical absorption, transmittance, reflectance and self-cleaning performance were investigated. Oxygen content of films increased with increasing the heat treatment temperature, and anatase TiO2 crystalline formed in the films. Hence, the transmittance in the visible light region of the films was well improved, though the electrical conductivity and reflectance in the near infrared region decreased slightly. The results also showed that the treated films exhibited excellent hydrophilic property and gained photocatalytic property. It reveals that after heat treatment at relatively low temperature, such as 450 °C, TiN film turned into TiNxOy film and achieved self-cleaning properties, while energy saving property was remained as well.

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH4), argon (Ar) and oxygen (O2) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp2 to sp3 sites was changed by the variation of oxygen content in the film structure. The sp2/sp3 ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp2 CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6GPa) and residual stress (0.29GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1GPa) and residual stress (0.16GPa) were obtained for un-doped DLC films. The increase of sp3 CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.

Plasma-modified nitric oxide-releasing polymer films exhibit time-delayed 8-log reduction in growth of bacteria.

Tygon(®) and other poly(vinyl chloride)-derived polymers are frequently used for tubing in blood transfusions, hemodialysis, and other extracorporeal circuit applications. These materials, however, tend to promote bacterial proliferation which contributes to the high risk of infection associated with device use. Antibacterial agents, such as nitric oxide donors, can be incorporated into these materials to eliminate bacteria before they can proliferate. The release of the antimicrobial agent from the device, however, is challenging to control and sustain on timescales relevant to blood transport procedures. Surface modification techniques can be employed to address challenges with controlled drug release. Here, surface modification using H2O (v) plasma is explored as a potential method to improve the biocompatibility of biomedical polymers, namely, to tune the nitric oxide-releasing capabilities from Tygon films. Film properties are evaluated pre- and post-treatment by contact angle goniometry, x-ray photoelectron spectroscopy, and optical profilometry. H2O (v) plasma treatment significantly enhances the wettability of the nitric-oxide releasing films, doubles film oxygen content, and maintains surface roughness. Using the kill rate method, the authors determine both treated and untreated films cause an 8 log reduction in the population of both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Notably, however, H2O (v) plasma treatment delays the kill rate of treated films by 24 h, yet antibacterial efficacy is not diminished. Results of nitric oxide release, measured via chemiluminescent detection, are also reported and correlated to the observed kill rate behavior. Overall, the observed delay in biocidal agent release caused by our treatment indicates that plasma surface modification is an important route toward achieving controlled drug release from polymeric biomedical devices.

Structure evolution in reactively sputtered molybdenum oxide thin films

The current work investigates structure and property relations of molybdenum oxide thin films deposited by reactive dc magnetron sputtering from a molybdenum target with varying oxygen/argon gas flow ratio during deposition. With increasing oxygen partial pressure, the film growth rate decreased from 90 to 7 nm/min, whereas the oxygen content in the films increased up to 75 at.%. The dominating phases found by X-ray diffraction and Raman spectroscopy were MoO2, different polymorphs of Mo4O11, and MoO3. The optical appearance changed from metallic to yellowish transparent with increasing oxygen content in the thin film, while the electrical properties varied from electrically conductive to insulating. In general, structure and properties of the deposited molybdenum oxide thin films are tuneable by adjusting the oxygen/argon gas flow ratio during deposition, which enables the use of these films in a wide range of optical and electronic applications.

Influences of oxygen incorporation on the structural and optoelectronic properties of Cu2ZnSnS4 thin films

This study used the sol–gel method to prepare Cu2ZnSnS4 thin films containing oxygen and explored the composition, structural, and optoelectronic properties of the films. The non-vacuum process enabled the oxygen content of the Cu2ZnSnS4 films to be 8.89at% and 10.30at% for two different annealing conditions. In the crystal structure, oxygen was substituted at the positions of sulfur and appeared in the interstitial sites of the lattice. The compositions of the thin films deviated from the stoichiometric ratio. Both films had kesterite structures with no secondary phase structure. The kesterite CZTS film possessed a composite microstructure of crystallite and crystalline states. The microstructure of the Cu2ZnSnS4 film with higher oxygen content was denser and the average grain size was smaller. Incorporating oxygen atoms into crystalline Cu2ZnSnS4 changed the energy band structure: the direct energy band gaps were, respectively, 2.75eV and 2.84eV; the thin films mainly adsorbed photons with wavelengths less than 500nm; and the absorption coefficients increased from 104cm−1 to 105cm−1. The films had a comparatively high absorptive capacity for photons less than 350nm. Increasing the oxygen content of the film lowered the resistivity. Thus, the oxygen-containing Cu2ZnSnS4 thin film could be a candidate for the p-type absorber layer material required in multi-junction solar cells.

Application of n-type microcrystalline silicon oxide as back reflector of crystalline silicon heterojunction solar cells

We investigated the application of n-type hydrogenated microcrystalline silicon oxide (n-µc-Si1−xOx:H) as an alternative back reflector material for n-type heterojunction solar cells. The effect of the CO2 and PH3 flow rates on the refractive index, oxygen content, conductivity, and crystalline fraction (Xc) of n-µc-Si1−xOx:H films was evaluated. By controlling the film oxygen content, the refractive index could be widely changed, while the absorption coefficient at wavelengths exceeding 800 nm was practically zero. We found that the insertion of an n-µc-Si1−xOx:H layer between the back surface field and the rear electrode improves the reflectance at long wavelengths. The improvement in reflectance resulted in higher internal quantum efficiency in the IR range, suggesting that the application of n-µc-Si1−xOx:H as a back reflector is promising for reducing long-wavelength losses in heterojunction solar cells.

Yttrium oxide thin films prepared under different oxygen-content atmospheres: microstructure and optical properties

Yttrium oxide films were prepared on silicon wafers by reactive magnetron sputtering at different oxygen flow rates to investigate the microstructure and optical properties for desirable planar optical waveguiding applications. Under the different conditions of target surface, the deposition rate, structure, and optical properties have great changes. The deposition rate increases to the maximum, and then monotonically decreases. Oxygen content in films increases and the composition of films transforms from stoichiometry to an oxygen-rich state. Y2O3 films grow with the (222) preferred growth orientation at low oxygen flow rate, and then turn into the (622) orientation; the microstructure evolves from crystal structure to amorphous state as oxygen flow rate increases from 2 to 12 sccm. Sufficient oxygen makes films low-order structure and oxygen-rich films have poor crystallinity. Very smooth film has been obtained at oxygen flow rate of 12 sccm. The refractive index can be greatly modulated by the oxygen-content factor. It is convincing that the controllable structure and optical properties of Y2O3 films can be achieved by adjustment the oxygen flow rate for desired optical design and applications.

Atomic layer deposition of GaN at low temperatures

The authors report on the self-limiting growth of GaN thin films at low temperatures. Films were deposited on Si substrates by plasma-enhanced atomic layer deposition using trimethylgallium (TMG) and ammonia (NH3) as the group-III and -V precursors, respectively. GaN deposition rate saturated at 185 °C for NH3 doses starting from 90 s. Atomic layer deposition temperature window was observed from 185 to ∼385 °C. Deposition rate, which is constant at ∼0.51 A/cycle within the temperature range of 250 – 350 °C, increased slightly as the temperature decreased to 185 °C. In the bulk film, concentrations of Ga, N, and O were constant at ∼36.6, ∼43.9, and ∼19.5 at. %, respectively. C was detected only at the surface and no C impurities were found in the bulk film. High oxygen concentration in films was attributed to the oxygen impurities present in group-V precursor. High-resolution transmission electron microscopy studies revealed a microstructure consisting of small crystallites dispersed in an amorphous matrix.

Effects of annealing temperature on the structural and photoluminescence properties of nanocrystalline ZrO 2 thin films prepared by sol–gel route

Highly transparent nanocrystalline zirconia thin films were prepared by the sol–gel dip coating technique. XRD pattern of ZrO 2 thin film annealed at 400 °C shows the formation of tetragonal phase with a particle size of 13.6 nm. FT-IR spectra reveal the formation of Zr–O–Zr and the reduction of OH and other functional groups as the temperature increases. The transmittance spectra give an average transmittance greater than 80% in the film of thickness 262 nm. Photoluminescence (PL) spectra give intense band at 391 nm and a broad band centered at 300 nm. The increase of PL intensity with elevation of annealing temperature is related to reduction of OH groups, increase in the crystallinity and reduction in the non-radiative related defects. The luminescence dependence on defects in the film makes it suitable for luminescent oxygen-sensor development. The “Red shift” of excitation peak is related to an increase in the oxygen content of films with annealing temperature. The “Blue shift” of PL spectra originates from the change of stress of the film due to lattice distortion. The defect states in the nanocrystalline zirconia thin films play an important role in the energy transfer process.

Effect of Ar-gas-pressure on oxygen content of Co–Si–O granular film sputter-deposited by using sintered targets

A systematic study of the effect of Ar-gas-pressure (PAr) in Co–Si–O granular film by sputter deposition using sintered targets is carried out for applications in CoPtCr–SiO2 perpendicular media. Detailed analyses of composition, phase formation and microstructure of granular films revealed that: (1) Co–Si–O granular films with similar compositions could be prepared by different sintered targets, (Co)+(SiO2), (Co)+(CoSi)+(CoO), (Co)+(Si)+(CoO), and (Co)+(Si)+(Co3O4), (2) oxygen content in film increases with increasing PAr, (3) oxygen content in film could be adjustable by the target composition (e.g. (CoO)/(CoSi)). Taking these results into account, we tried low PAr deposition of Co–Si–O granular film. Under PAr = 0.6 Pa, oxygen-poor Co–Si–O granular film was obtained using a conventional (Co)+(SiO2) target, while by using a new type of sintered (Co)+(CoSi)+enriched(CoO) target, the oxygen composition in the granular film could be adjusted to be O/Si= 2 with grain isolated structure.

Influence of oxygen deficiency on the out-of-plane tilt of epitaxial Y2O3 films on Ni–5%W tapes

We analyzed the crystallographic c-axis tilt of (001) Y2O3 films grown on biaxially textured Ni–5%W tapes under different oxygen flux conditions. Results show that different tilting mechanisms were effective in films with different oxygen stoichiometry. Moreover, the structure of the film/substrate interface investigated by transmission electron microscopy, and the residual strain of the film investigated by x-ray diffraction were also dependent on the film oxygen content. Although the oxygen stoichiometric Y2O3 sample exhibited a coherent film/substrate interface and the sharpest out-of-plane texture, the films grown under reduced oxygen pressure exhibited a smaller overall c-axis tilt due to formation of interface dislocations and regions in which the film oxygen vacancies ordered to form a lattice superstructure.

Comparative study of gasochromic and electrochromic effect in thermally evaporated tungsten oxide thin films

Substoichiometric tungsten oxide films (WO 3 − y , 0.49 ≥ y ≥ 0.15) were prepared by non-reactive thermal evaporation of WO 3 powder in vacuum. The thin film composition, structure and optical properties were investigated with the purpose to establish their dependence on the deposition conditions and to prove a possible correlation between electrochromic and gasochromic colouration. An analogy in the dependencies of the maximum achievable optical density on the thin film oxygen content for gasochromically and electrochromically coloured films was observed. In-situ performed XPS measurements suggested that the main mechanism of gasochromic colouration is charge transfer between W 6+ and W 5+ states, i.e., similar to the electrochromic effect.