Properties Of Nb2O5 Thin Films Research Articles

Anomalous thermal conductivity in amorphous niobium pentoxide thin films: A correlation study between structure and thermal properties

Niobium pentoxide (Nb2O5) based thin films are predominantly used in optical filters, solar cells, electrochromic devices, sensors and microelectronic devices. The temperature-dependent thermophysical properties of Nb2O5 films are crucial for the performance and reliability of such devices. Within this work, for the first time, the thermal properties of sputter deposited Nb2O5 films are correlated with their structural properties at different length scales. Thermal measurements were carried out by time-domain thermoreflectance, yielding a thermal conductivity of 3.0±0.3 W/mK at 25 °C for crystalline Nb2O5 films, which decreases to 2.6±0.2 W/mK at 450 °C. In contrast, amorphous Nb2O5 films had a thermal conductivity of 2.2±0.2 W/mK below 275 °C. Above 275 °C, an abrupt increase in thermal conductivity up to a maximum value of 2.8±0.2 W/mK at 325 °C was recorded. The average and local structure are determined by in-situ high-temperature X-ray diffraction and in-situ high-temperature Raman spectroscopy, respectively. These characterization techniques together enable to cross-correlate structural and thermal properties of Nb2O5 thin films highlighting the observed peculiarity of the thermal conductivity. This substantial increase in thermal conductivity cannot be linked to any macroscopic phase change but rather to a local phase rearrangement near the crystallization temperature, evidenced by temperature-dependent Raman spectra analysis. This study serves as a guide to engineering future Nb2O5 based thin film devices and for their reliability optimization.

Electrical conductivity inversion for Nb2O5 nanostructure thin films at different temperatures

The effect of treatment temperature on structural, morphological, and electrical properties of Nb2O5 thin films using the precipitation method is presented in this work. Clear enhancements, such as decreased stress and dislocation density values, are recognized in structural properties after heat treatment. AFM result shows increased average grain size and RMS of the prepared thin film with treatment temperature from 87.87 °C to 110.97 °C and rising temperature from 25 °C to 600 °C. Conductivity type conversion from n- to p-type is observed when the heat treatment is increased from 600 °C to 700 °C based on Hall effect measurement results.

Influence of argon flow rate on structural and optical properties of transparent Nb2O5 thin films

Transparent niobium pentoxide (Nb2O5) thin films deposited on glass substrates by RF sputtering at different argon (Ar) flow rate were contrastively studied. Analytical methods such as X-ray fluorescence, Fourier-transform infrared spectroscopy and field emission scanning electron microscope were utilized to investigate the morphological surface and structural properties of Nb2O5 thin films deposited at different Ar flow rate. UV–Vis–NIR and photoluminescence (PL) spectroscopy were used to explore the optical properties of Nb2O5 thin films deposited at different Ar flow rate. The allowed optical band gap ( $$ {\text{E}}_{\text{g}}^{\text{d}} $$ ) of the Nb2O5 thin films varies from 3.88 to 3.80 eV with increasing Ar flow rate from 30 to 90 sccm. The PL of the Nb2O5 thin films showed strong emission peak around 400 nm. The real values of the refractive index are increase with increasing Ar flow rate. Optical quantities related to the optical constants of Nb2O5 thin films thin films such as single oscillator parameters and third-order nonlinear susceptibility were assessed.

Effect of ammonium concentration on structural, optical and morphological properties of H-Nb2O5 thin films—A novel study

Effect of ammonium concentration on optical, structural and surface roughness properties of Nb2O5 thin films is conducted in this work. Estimated optical band gap and optical constant confirm the dependency of Nb2O5 thin films on ammonium molarity. The band gap in the range of 3.3 to 4.7 eV is directly related to the solution properties. The structural properties are recorded by x-ray diffraction method that display the formation of monoclinic niobium pentoxide (H-Nb2O5) thin films. Optimum molarity at 12 M reveals the prime ammonium concentration for the Nb2O5 thin films formation. The energy gap at optimum preparation state ensures the development of semiconducting material that suits solar cell and other optoelectronics application. AFM results show a highly uniform surface. Grain size is observed to increase with ammonium concentration and recorded to reach its maximum of 85.28 nm at 12 M.

Influence of RF sputtering power on structural and optical properties of Nb2O5 thin films

In this research, Niobium oxide (Nb2O5) films were deposited on glass substrates using RF sputtering technique. The effect of RF sputtering powers (150, 175 and 200 W) on the structural, and optical properties of as-deposited and annealed Nb2O5 thin films were examined using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–vis-NIR double beam spectrophotometer and Photoluminescence (PL) measurements. X-ray diffraction results revealed that the as-deposited and annealed films have polycrystalline structure. The optical parameters such as absorption coefficient, optical band gap energy, refractive index, dielectric constants and oscillators’ parameters are estimated. The dispersion parameters are evaluated and analyzed according to a single oscillator model.

Some physical properties of Nb2O5 thin films prepared using nobic acid based colloidal suspension at room temperature

This work presents the successful preparation of niobium pentoxide micro structures thin films at room temperature. A chemical colloidal suspension was deposited employing Spin coating method. Nb2O5 thin films were prepared at two different thicknesses before and after ultrasonic vibration processes. Optical, structural, and morphological properties were studied. An enhanced crystalline structure with bigger grain size at both thicknesses was obtained after ultrasonic process; this was ensured by SEM results. The energy gap of the prepared films was estimated and found to be about (2.81, 2.42) eV for (T1 = 325 nm) and (2.59, 2.32) eV at the second thickness (T2 = 425 nm). The I–V characteristic study of prepared heterojunction on silicon substrate show an increase in the rectification ratio after the ultrasonic vibrational process for both thicknesses.

Chemical Vapor Deposition Synthesis and Optical Properties of Nb2O5 Thin Films with Hybrid Functional Theoretical Insight into the Band Structure and Band Gaps.

Nb2O5 is an important material able to exist in many polymorphs with unique optical properties and morphologies that are dependent on the synthetic route. Here we report a novel ambient-pressure chemical vapor deposition route to Nb2O5 via aerosol-assisted chemical vapor deposition. The amorphous as-deposited films were annealed in air to obtain the the three most stable crystal structures: orthorhombic, tetragonal, and monoclinic. The films were thoroughly characterized for their material properties, and an in-depth study into the optical properties was carried out using state-of-the-art hybrid functional theory that allowed more insight into the optical properties of the materials.

Investigation of Antireflection Nb₂O₅ Thin Films by the Sputtering Method under Different Deposition Parameters.

In this study, Nb2O5 ceramic was used as the target to deposit the Nb2O5 thin films on glass substrates with the radio frequency (RF) magnetron sputtering method. Different deposition temperatures and O2 ratios were used as parameters to investigate the optical properties of Nb2O5 thin films. The deposition parameters were a pressure of 5 × 10−3 Torr, a deposition power of 100 W, a deposition time of 30 min, an O2 ratio (O2/(O2 + Ar), in sccm) of 10% and 20%, and deposition temperatures of room temperature (RT), 200, 300 and 400 °C, respectively. We found that even if the deposition temperature was 400 °C, the deposited Nb2O5 thin films revealed an amorphous phase and no crystallization phase was observed. The optical properties of transmittance of Nb2O5 thin films deposited on glass substrates were determined by using a ultraviolet-visible (UV-vis) spectrophotometer (transmittance) and reflectance spectra transmittance (reflectance, refractive index, and extinction coefficient) in the light wavelength range of 250–1000 nm. When the O2 ratio was 10% and the deposition temperature increased from RT to 200 °C, the red-shift was clearly observed in the transmittance curve and the transmission ratio had no apparent change with the increasing deposition temperature. When the O2 ratio was 20%, the red-shift was not observed in the transmittance curve and the transmission ratio apparently decreased with the increasing deposition temperature. The variations in the optical band gap (Eg) values of Nb2O5 thin films were evaluated from the Tauc plot by using the quantity hν (the photon energy) on the abscissa and the quantity (αhν)r on the ordinate, where α is the optical absorption coefficient, c is the constant for direct transition, h is Planck’s constant, ν is the frequency of the incident photon, and the exponent r denotes the nature of the transition. As the O2 ratio of 10% or 20% was used as the deposition atmosphere, the measured Eg values decreased with the increase of the deposition temperature. The reflectance ratio, extinction coefficient, and refractive index curves of Nb2O5 thin films were also investigated in this study. We would show that those results were influenced by the deposition temperature and O2 ratio.

Influence of thickness and calcination under ammonia gas flow on topographical, optical and photocatalytic properties of Nb2O5 thin films prepared by sol–gel: a comparative study

Nb2O5 thin films have been fabricated by spin coating of niobium alkoxide sols on ITO coated glass substrates. The effects of variation in thickness and calcination conditions (i.e. under oxygen and under ammonia gas flow) on optical and photocatalytic properties of the films was investigated. Two sets of Nb2O5 thin films were prepared. One set of the films (N-1a, N-1b, N-1c and N-1d) were calcined under ammonia gas flow and the other (1a, 1b, 1c and 1d) under oxygen gas flow at 500 °C for 1 h. Thicknesses of the films were found to decrease from ≈143.0 to ≈121.0 nm upon increasing the rotation speed of the spin coater from 500 to 2000 rpm. The prepared films were characterized by X-ray diffraction, AFM, Ellipsometry and UV–Vis–NIR spectroscopy. Notably, narrowing of band gaps was observed after calcination under NH3 environment. On account of the observed grain sizes and band gap energies, a comparative evaluation of the efficiencies for photocatalytic degradation of methylene blue under UV irradiation was also done.

The effects of heat treatment on optical, structural, electrochromic and bonding properties of Nb2O5 thin films

Nb2O5 thin films were deposited onto heated glass substrates by RF magnetron sputtering using a Nb2O5 target. The films were annealed in air at temperatures between 400 and 700 °C for 6 h. Effects of the crystalline structure on optical, structural, electrochromic and bonding properties of the Nb2O5 thin films were investigated by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, optical spectrophotometry and electrochemical measurements. The film refractive index varied between 2.09 and 2.22 at the wavelength of 550 nm depending on the annealing temperature. The decrease of the optical band gap revealed for the films with increasing annealing temperature is attributed to oxygen-ion vacancies in the film structure. The orthorhombic structure of Nb2O5 films resulted in good electrochromic properties with high colouration efficiencies of 19.56 cm2/C and 53.24 cm2/C at 550 nm and 1000 nm, respectively. The optical, structural and electrochromic properties of the different crystalline polymorphic forms of the Nb2O5 films make them attractive for optical applications.

Determination of optical and mechanical properties of Nb2O5 thin films for solar cells application

In this paper investigation results of niobium pentoxide thin films deposited by microwave assisted reactive magnetron sputtering process were described. Surface of prepared coatings was examined with the aid of atomic force microscope (AFM) operating in the contact-mode and in ultra high vacuum conditions. The surface of thin films was homogenous, crack free and exhibit low root mean square (RMS) roughness of about 0.34nm. X-ray photoelectron spectroscopy (XPS) studies were performed to determine the chemical states of the niobium at the surface of thin films. Contact angle and surface free energy were additionally investigated to examine the surface properties of the deposited coatings. Optical properties of the Nb2O5 thin films showed, that prepared coatings were well transparent from 350nm to longer wavelength range. Based on transmission and reflection measurements the values of refractive index and extinction coefficient were determined. The antireflective coating based on Nb2O5 thin films for solar cells application was proposed. The hardness and Young's modulus measurements were performed by the nanoindentation technique. These investigations revealed that the hardness of the deposited coatings was ca., 7GPa. Also scratch tests were applied, which have shown that the Nb2O5 thin films were scratch resistant.

Optical and Dielectric Characterization of Atomic Layer Deposited Nb2O5 Thin Films

Nb2O5 films were grown by atomic layer deposition using (tert-butylimido)tris(diethylamido)niobium as the niobium source and ozone as the oxygen source. The effects of deposition and post-deposition annealing conditions, physical thickness as well as the phase composition on the dielectric properties of Nb2O5 thin films have been investigated. In addition, the optical properties of the films have been evaluated. It was found that by tuning the deposition parameters and post deposition treatments it was possible to obtain high k-values up to 120 with reasonably low leakage current.

06/01323 Effect of TiO 2 mixtures on the optical, structural and electrochromic properties of Nb 2O 5 thin films : Pehlivan, E. et al. Solar Energy Materials and Solar Cells, 2005, 87, (14), 317–322

06/01323 Effect of TiO 2 mixtures on the optical, structural and electrochromic properties of Nb 2O 5 thin films : Pehlivan, E. et al. Solar Energy Materials and Solar Cells, 2005, 87, (14), 317–322

Study of surface morphology and optical properties of Nb2O5 thin films with annealing

Nb2O5 films have been deposited on variety of substrates using the sol-gel dip coating technique. As-deposited films on all substrates are amorphous. Films were annealed under controlled ambience at 300, 400 and 600°C for 5 h. As-deposited films on glass substrate show uniform surface structure. The crystal structure and surface topography are found to depend strongly on the annealing temperature and nature of the substrates. The average grain size of 40 nm is observed in films annealed at 300°C. On annealing at 400°C increasing grain size and resulting fusing of them, enhanced surface roughness. Films deposited on NaCl substrates crystallized into a stable monoclinic phase and those deposited on single crystal Si substrates crystallized into hexagonal phase after annealing at 600°C. The as-deposited films show very high transmittance (>90%) in the visible region. The optical band gap is observed to increase from 4.35 eV when the films are in amorphous state to 4.87 eV on crystallization.

Effect of TiO2 mixtures on the optical, structural and electrochromic properties of Nb2O5 thin films

Abstract Metal oxide films are important for various optical devices and especially for solar energy materials. TiO 2 -mixed Nb 2 O 5 thin films have been produced by sol–gel dip-coating method. Several parameters such as heat treatment, thickness, and mixture percentages are studied for the effect of the optical, structural and electrochromic properties of the materials. Optical parameters of the films were calculated through transmission and reflection measurement by a refractive index, extinction coefficient and thickness analyzer. Structural, electrochromic and surface analyses of the films were done by X-ray diffractometer, potentiostat/galvanostat and atomic force microscope systems.

Internal stress and optical properties of Nb2O5 thin films deposited by ion-beam sputtering.

The influence on the internal stress and optical properties of Nb2O5 thin films with ion-beam energy was investigated. Nb2O5 thin films were deposited on unheated glass substrates by means of ion-beam sputtering with different ion-beam voltage, Vb. The refractive index, extinction coefficient, and surface roughness were found to depend on the ion-beam energy. The stresses in thin films were measured by the phase-shifting interferometry technique. The film stress was also found to be related to Vb, and a high compressive stress of -0.467 GPa was measured at Vb = 850 V. The Nb2O5-SiO2 multilayer coatings had smaller average compressive stress as compared with single-layer Nb2O5 film.