Post-deposition Annealing In Vacuum Research Articles

Fabrication of conductive Nb-doped anatase TiO2 thin films by mist chemical vapor deposition using aqueous solutions of water-soluble Ti and Nb compounds

Electrically conductive Nb-doped anatase TiO2 (Ti1−x Nb x O2: TNO) films can be fabricated through mist CVD using aqueous precursor solutions of water-soluble oxo-peroxo-glycolato titanium complex and ammonium niobium oxalate. Post-deposition annealing in vacuum crystallizes the as-deposited amorphous films into a conductive anatase phase, leading to the fabrication of conductive TNO films. Notably, the addition of H2O2 to the precursor solutions enhances both the crystallinity and conductivity of the annealed TNO films. A Ti0.77N0.23O2 film, annealed at 700 °C, exhibits a resistivity of 2.0 × 10−2 Ω cm at ambient temperature. In general, the solution-based fabrication of TiO2 films relies on organic solvents, which are sometimes toxic and explosive. Here, we demonstrate for the first time that conductive TNO films can be prepared from less toxic and nonflammable aqueous solutions. These findings mark a significant advancement towards a more environmentally compatible process for fabricating TNO films with sufficient conductivity.

Exploring hafnium oxide's potential for passivating contacts for silicon solar cells

We investigate the potential of ultra-thin HfO2 films grown by atomic layer deposition for passivating contacts to silicon focusing on variations in film thickness and post-deposition annealing temperature. A peak in passivation quality – as assessed by carrier lifetime measurements – is reported for 2.2 nm thick films annealed at 475 °C, for which a surface recombination velocity <1 cm/s is determined. For films <2.2 nm thick, there is a marked decrease in passivation quality. X-ray diffraction highlights a change from crystallised monoclinic to amorphous HfO2 as film thickness decreases from 12 nm to 2.2 nm. Kelvin probe results indicate that as-deposited 2.2–12 nm films have similar effective work functions, although the work function of 1 nm films is considerably lower. Upon post-deposition annealing in vacuum, all films exhibit a reduction in effective work function at temperatures coincident with the onset of passivation in air-annealed samples. An initial investigation into the contact resistivity in a passivating contact structure utilizing HfO2 reveals a strong post-deposition annealing temperature dependence, with the lowest resistance achieved below 375 °C, followed by a decrease in performance as temperature increases towards the optimal temperature for passivation (475 °C). Limitations of the contact structure used are discussed.

Linear and non-linear optical properties of boron carbide thin films

Boron carbide films deposited by PECVD are subjected to post deposition vacuum annealing and plasma treatment for investigation of changes in the structure, linear and non-linear optical properties of the films. Deconvolution of core level XPES spectra of B1s, C1s and O1s indicates changes in the surface chemical states of the constituent atoms after post deposition treatments. Particle size estimated from XRD spectrum is found increasing from 135 to 140 nm after annealing. Envelop method is used to estimate refractive index, extinction co-efficient, and thickness from their measured optical transmission spectra in VIS-NIR region (400–1400 nm). The refractive index value is found to be 1.619, highest for the vacuum annealed boron carbide film. Direct and indirect optical bandgap remains same after vacuum annealing (Eg = 2.84), the plasma treatment causes a slight decrease in the bandgap. 5% decrease in film thickness is observed after post deposition annealing and plasma treatment owing to film densification. Energy loss in the medium measured in terms of tanδ and ELF’s reveals that the vacuum annealing of the film reduces the electromagnetic and electron energy loss in the film. Non-linear refractive index estimated using Ticha and Tichy relation exhibits similar trend as the linear refractive index spectra.

Structure-dependent optical nonlinearity of indium tin oxide

We use post-deposition vacuum annealing of epsilon-near-zero (ENZ) indium tin oxide (ITO) nanolayers in order to modify their structural properties and enhance the third-order optical nonlinear response around the ENZ wavelength. We find that room temperature magnetron sputtering deposition results in polycrystalline thin films with an intrinsic tensile strain and a ⟨110⟩ fiber axis preferentially oriented normal to the substrate. Moreover, we demonstrate that post-deposition vacuum annealing treatments produce a secondary anisotropic phase characterized by compressive strain that increases with the annealing temperature. Finally, we use the Z-scan optical technique to accurately measure the complex nonlinear susceptibility χ(3) and the intensity-dependent refractive index change Δn for samples with different structural properties despite featuring similar ENZ wavelengths. Our intensity-dependent analysis demonstrates that an enhancement of the optical nonlinearity can be achieved by tuning the structure of ENZ nanolayers with values as large as χR(3)=(5.2 ± 0.3)×10−17m2/V2. This study unveils the importance of structural control and secondary phase formation in ITO nanolayers with ENZ optical dispersion properties for the engineering of integrated highly nonlinear devices and metamaterials that are compatible with the scalable silicon photonics platform.

Tailoring plasmonic resonances in Cu-Ag metal islands films

The plasmonic response of Cu-Ag metal islands films is investigated. Films are obtained by subsequent electron beam deposition of Ag and Cu using different fabrication conditions: deposited mass thickness, substrate temperature and post-deposition annealing in vacuum. Optical properties of films are investigated by spectroscopic ellipsometry and correlated with the structural characterization results obtained by electron microscopy. It is observed that Ag enhances island growth and increases the percolation threshold of Cu films. The localized surface plasmon resonance of isolated particles shows signatures of both Cu and Ag. Moderate thermal annealing enhances island growth and favours Janus-like morphology, increasing the Ag contribution to the surface plasmon resonance. In case of percolated films, annealing-induced dewetting can lead to the appearance of large and irregular particles with a remarkable absorption peak in the near-infrared range. Composition and optical properties of the films can be further modified by Ag partial evaporation upon annealing at high temperatures. The variation of optical properties with aging is related to Cu oxidization and follows different trends depending on the sample morphology. Overall, it is shown that Cu-Ag island films are compelling systems for plasmonic applications, as their optical response can be widely and easily tuned by adjusting fabrication conditions.

Double-plasmon broadband response of engineered titanium silicon oxynitride

Titanium nitride is a CMOS-compatible alternative material to conventional metals for plasmonics and metamaterials applications. We demonstrate complete tunability at visible and near-infrared frequencies of the optical dispersion of titanium nitride nanolayers deposited on Si (100) substrates from metallic to dielectric behavior by alteration of reactive magnetron sputtering growth conditions and, via co-deposition, the addition of Si and/or O2 elemental components. The dielectric function and region of metallic character is found to be further modified by post-deposition vacuum annealing. We categorize this dispersion behavior as anomalous due to a distinctive line shape that allows for double-plasmon resonances, which we investigate analytically using Mie scattering theory.

Annealing effect on the fracture toughness of CrN/TiN superlattices

Superlattice films are generally known for their exceptional high hardness compared to their monolithic constituents. Recently, we have shown that CrN/TiN superlattice films exhibit a peak in fracture toughness for a bilayer period of 6.0nm, similar to the former reported peak in hardness. We propose that a dominating factor for obtaining such favourable material properties is the interface constitution between the individual layers.To proof this notion, we have intentionally modified the interface sharpness by post-deposition vacuum annealing of the samples at different temperatures. This promotes interdiffusion of Ti or Cr into its adjacent layers and gradually changes the interfaces to interphases (because TiN and CrN form a solid solution). In order to obtain reliable KIC fracture toughness values as a function of the annealing temperature, in-situ micromechanical cantilever bending tests on ex-situ vacuum annealed freestanding films were performed. High temperature loads take also place during machining processes like dry cutting or high-speed cutting, and are thus of high practical relevance.

Effect of vacuum annealing on the photoconductivity of CuO thin films grown using sequential ionic layer adsorption reaction

Using sequential ionic layer adsorption reaction technique, Cupric Oxide (CuO) thin films were deposited on a glass substrate at relatively low bath temperature of 338 ± 5 K. The as deposited films were polycrystalline in nature with preferential orientation along the (200) plane. The films were found to exhibit negative photoconductivity. Vacuum annealing of the films resulted in preferential growth along the (111) and (200) plane for temperatures 373 K, 473 K and 573 K. Vacuum annealing at 673 K resulted in preferential growth along the (200) plane. The vacuum annealed films showed normal photoconductivity behavior. The optical band gap of the films was found to increase from 1.57 eV for the as prepared films to 2.06 eV for films annealed in vacuum at 673 K. Surface photo voltage measurements indicate that the direction of band bending is reversed when the as deposited CuO thin films are subjected to vacuum annealing. We conclude that surface state passivation is leading to change in the photoconductive behavior of the thin film samples when subjected to post deposition vacuum annealing.

Nb-doped TiO2 thin films for photovoltaic applications

Abstract Polycrystalline titania and Nb:TiO 2 thin films were deposited by RF magnetron sputtering. The influence of post-deposition annealing in vacuum and hydrogen atmosphere on the structure, morphology, oxidation states and optical properties was studied by X-ray diffraction, atomic force microscopy, XPS and UV–VIS spectroscopy. The heat treatment of titanium dioxide thin films in vacuum and H 2 atmosphere induces structural and morphological changes. The band gap narrowing was observed for the transparent as-deposited Nb:TiO 2 films, while annealing at 420 °C in H 2 atmosphere resulted in an enhancement of the electrical conductivity. Further on, TiO 2 / p -CdTe photovoltaic devices with efficiency of 1.8% were fabricated and their characteristic ‘enhancement’ is discussed.

Current transport analysis of ZrO2 thin films: Effects of post-deposition annealing

We report on the effects of post-deposition annealing on the electrical properties and the dielectric performance of atomic layer-deposited ZrO2 thin films investigated by using capacitance-voltage and current-voltage measurements. ZrO2 films crystallized by post-deposition annealing in vacuum showed an enhanced dielectric constant and energy band gap, but the leakage current was increased. The Poole-Frankel and the trap assisted tunneling mechanisms were considered to be the major leakage current conduction processes and the charge trap energy level was reduced from 1.09–1.13 eV to 0.81–0.84 eV by post-deposition annealing. The increase in the leakage current in the crystallized films can be explained by considering structural defect relaxation or grain boundary formation.

Microstructural evolution and magnetic properties in Fe50Pd50 sputtered thin films submitted to post-deposition annealing

Fe50Pd50 thin films (t=50nm) have been deposited on Si substrates covered with a native oxide layer by sputtering technique. As-prepared films consist of a disordered Fe–Pd A1 phase, being deposited without heating the substrate. The order–disorder transformation towards the L10-ordered tetragonal phase has been induced by post deposition annealing in vacuum (annealing temperature ranging in the interval Ta=550–625°C for 1200s). Samples microstructure has been studied by means of X-ray diffraction, SEM and AFM microscopy. Room-temperature hysteresis loops have been measured by AGFM (Alternating Gradient Field Magnetometer) in parallel and perpendicular configuration. All produced systems have been observed to display tunable microstructure and, consequently, various magnetic properties. To study the magnetic properties evolution with annealing temperature, magnetic domain patterns have been measured by MFM. In particular, the domain-period dependence on the magnetocrystalline anisotropy constant has been analyzed.

Annealing effect of ZnO/Au/ZnO transparent conductive films

Au intermediate ZnO (ZAZ) thin films were prepared by radio frequency and direct current magnetron sputtering on glass substrates and then vacuum annealed. The thickness of each layer of the ZAZ films was set at 50 nm, 3 nm, and 47 nm, respectively. The structural, electrical, and optical properties of ZAZ films were investigated with respect to the variation of annealing temperature.As-deposited AZO films showed X-ray diffraction peaks corresponding to ZnO (002) and Au (111) planes and those peak intensities increased with post-deposition vacuum annealing. The optical and electrical properties of the films were strongly influenced by post-deposition annealing. Although the optical transmittance of the films deteriorated with an Au interlayer, as-deposited ZAZ films showed a low resistivity of 2.0 × 10−4 Ω cm, and the films annealed at 300 °C had a lower resistivity of 9.8 × 10−5 Ω cm. The work function of the films increased with annealing temperature, and the films annealed at 300 °C had a higher work function of 4.1 eV than the films annealed at 150 °C. The experimental results indicate that vacuum-annealed ZAZ films are attractive candidates for use as transparent electrodes in large area electronic applications such as solar cells and large area displays.

A comparative research on magnetron sputtering and arc evaporation deposition of Ti–Al–N coatings

Ti–Al–N coating has been proven to be an effective protective coating for machining applications. Here, the differences of cubic Ti–Al–N coatings with a similar Ti/Al atomic ratio of 1 deposited by magnetron sputtering and cathodic arc evaporation have been studied in detail. Main emphasis was laid on the characterization of thermal stability and cutting performance. Both coatings during annealing exhibit a structural transformation into stable phases c-TiN and h-AlN via an intermediate step of spiondal decomposition with the precipitation of c-AlN, however, a difference in decomposition process. Compared to sputtered coating inserts, an increase of tool life-time by 42% is obtained by evaporated coating inserts at the higher speed of 200m/min, whereas the similar cutting life is observed at the speed of 160m/min. It is attributed to the better stability of evaporated coating due to its later structural transformation at elevated temperature. A post-deposition vacuum annealing of both coated inserts in their corresponding temperature range of spiondal decomposition improves their cutting performance due to an increase in hardness arising from the precipitation of coherent cubic-phase nanometer-size c-AlN domains. Additionally, the sputtered coating behaves in worse oxidation resistance due to its more open structure. These behaviors can be understood considering the difference in microstructure and morphology of as deposited coatings originating from adatom mobility of deposited particles, where arc evaporation technique with higher ion to neutral ratio shows higher adatom mobility.

Behavior of oxygen in zinc oxide films through thermal annealing and its effect on sheet resistance

Behavior of oxygen in sputtering deposited ZnO films through thermal annealing and its effect on sheet resistance of the films were investigated. The crystallinities of the ZnO film were improved by post-deposition annealing in vacuum. However, the sheet resistance of ZnO film was dramatically decreased after post-deposition annealing in vacuum at more than 300°C, while O2 desorbed from the film. The oxygen vacancies which acted as donors were formed by the thermal annealing in vacuum. The sheet resistance of the films was recovered by annealing in oxygen ambient. In this paper, 18O2 gas as an oxygen isotope was used as the annealing ambient in order to distinguish from 16O, which was constituent atom of the ZnO films. SIMS analysis revealed that 18O diffused into the ZnO film from the top surface by 18O2 annealing. Therefore oxygen vacancies formed by the post-deposition annealing in vacuum could be compensated by the annealing in oxygen ambient.

Effect of annealing on the electrical, optical and structural properties of cadmium stannate thin films prepared by spray pyrolysis technique

Polycrystalline thin films of cadmium stannate (Cd 2SnO 4) were deposited by spray pyrolysis method on the Corning substrates at substrate temperature of 525 °C. Further, the films were annealed at 600 °C in vacuum for 30 min. These films were characterized for their structural, electrical and optical properties. The experimental results showed that the post-deposition annealing in vacuum has a significant influence on the properties of the films. The average grain size of the film was increased from 27.3 to 35.0 nm on heat treatment. The average optical transmittance in the visible region (500–850 nm) is decreased from 81.4% to 73.4% after annealing in vacuum. The minimum resistivity achieved in the present study for the vacuum annealed films is the lowest among the reported values for the Cd 2SnO 4 thin films prepared by spray pyrolysis method.

Optical properties of sputter deposited transparent and conducting TiO 2:Nb films

Transparent and conducting thin films of TiO 2:Nb were prepared on glass by reactive dc magnetron sputtering in Ar + O 2. Post-deposition annealing in vacuum at 450 °C led to good electrical conductivity and optical transparency. The optical properties in the sub-bandgap region were in good agreement with Drude free electron theory, which accounts for intraband absorption. The band gap of the films was found to be in the range of 3.3 to 3.5 eV and signifies the onset of interband absorption. Electrical conductivities in the 10 − 3 Ω cm range were obtained both from dc electrical measurements and from analysis of the optical measurements.

Comparative study of photocatalytic activity in CdS–TiO2 thin films prepared by two different techniques

In this study, CdS layer in CdS–TiO2 bilayer films was fabricated by two different chemical bath deposition techniques: one with an ammonium complex as complexing agent and the other with sodium citrate as a substitute for the ammonium complex. The TiO2 upper layer was deposited by dc magnetron sputtering technique for both the CdS underlayers. The effect of postdeposition vacuum annealing was studied for both samples. The photocatalytic activity was evaluated by measuring the decomposition of methanol in gas phase under ultraviolet-visible irradiation. The CdS thin films, prepared by both techniques, show a highly oriented hexagonal structure. The optical transmission edge of the CdS thin films deposited by the ammonia-free technique is in lower wavelength than that of the other technique. For both techniques, vacuum annealing extends the absorption edge to higher wavelength, but this effect is more pronounced for the ammonia-content technique. The decomposition efficiency of the as-deposited CdS–TiO2 thin film prepared by the ammonia-free technique is much higher than the as-deposited CdS–TiO2 prepared by ammonia-content technique. In case of the ammonia-content technique, high-vacuum annealing improves the photocatalytic activity but it has minimal influence in the other technique. The surface morphology of all the CdS thin films was studied by field emission scanning electron microscopy and atomic force microscopy in order to find out the possible inherent reason that leads to a huge difference in the photocatalytic decomposition activity of CdS–TiO2 thin films.

Growth mechanism, microstructure and transport properties of Sr1−x La x CuO2 (x=0.10−0.15) thin films

Sr1−xLaxCuO2 (x=0.10−0.15) thin films with an infinite-layer type structure were grown on BaTiO3 buffered (001) SrTiO3 substrates by pulsed laser deposition (PLD). The evolution of the growth front was monitored, in-situ, by high-pressure reflection high-energy electron diffraction (RHEED), while the surface morphology was analyzed by means of atomic force microscopy (AFM), ex-situ. X-ray diffraction (XRD) was used to determine the evolution of the film structure with deposition and cooling parameters, as well as to study the type and level of epitaxial strain in the Sr1−xLaxCuO2 films. The RHEED data showed that the Sr1−xLaxCuO2 films grow on BaTiO3/SrTiO3 following a 2D or Stranski-Krastanov mechanism, depending on the La doping level. The transition point (critical thickness dc) from layer-by-layer like (2D) to island (3D) growth depends on the film stoichiometry: decreasing the La doping concentration x from 0.15 to 0.10, the critical thickness dc increases from ∼45 nm to ∼75 nm. In order to induce superconductivity, the Sr1−xLaxCuO2 films were cooled down under reduction conditions. The as-deposited films showed semiconducting or metallic behavior, the resistivity decreasing with increasing La concentration. Post-deposition vacuum annealing resulted in a superconducting transition onset (but no zero resistance down to 4.2 K) only for some of the x=0.15 Sr1−xLaxCuO2 films.

Do the grain boundaries of β-In2S3 thin films have a role in sub-band-gap photosensitivity to 632.8nm?

Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8nm. Photoresponse to excitation wavelength of 632.8nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.

A Surface Modification of Hastelloy X by a SiC Coating and an Ion Beam Irradiation for a Potential use for Iodine-Sulfur Cycle in Nuclear Hydrogen Production System

ABSTRACTThe materials used for the SO3 decomposer in Iodine-Sulfur (IS) cycle for Nuclear Hydrogen Production System require excellent mechanical properties as well as a high corrosion resistance in SO2/SO3 environment at an elevated temperature up to 950°C. So far, no metallic materials have been suggested to be useful in such an environment. A surface modification of Hastelloy X by a SiC coating processed by an electron beam evaporative deposition has been studied in combination with an ion beam mixing (IBM) and an ion beam hammering (IBH). The simply deposited SiC film on the Hastelloy X substrate is easily peeled-off during an annealing at a high temperature due to a huge difference in their coefficients of thermal expansion (CTE), however the SiC coating on Hastelloy X prepared with IBM is sustained above 900 °C when the heating rate is less than 10 °C/min. The process of coating and IBM consists of a thin SiC film deposition, a subsequent N ion beam bombardment, and then an additional deposition of the film to the designed thickness. IBM plays a role of fastening the SiC film on the Hastelloy X substrate until the interfacial reaction takes place. Once the reaction takes place, new phases are developed at the interface under the consumption of the film and the substrate materials, producing a buffer layer. Without IBM, the SiC film tends to be easily detached during an annealing before the interfacial reaction initiates. The SiC film prepared with IBM requires a post-deposition annealing in vacuum for the interfacial reaction. However, the sublimation of SiC film prepared by an electron beam evaporative deposition occurs at the temperature above 900 °Cdecreasing the thickness of the deposited film. The sublimation of the SiC film can be prevented by IBH in which ion beams are bombarded onto the deposited film. This may be attributed to an ion beam bombardment induced densification of the deposited film. The resultant SiC coated Hastelloy X prepared by IBM and IBH exhibits a high corrosion resistance in a sulfuric acid at 300 °C, suggesting a possible application for the IS cycle.