Annealing Of Films Research Articles

Templated dewetting of single-crystal sub-millimeter-long nanowires and on-chip silicon circuits

Large-scale, defect-free, micro- and nano-circuits with controlled inter-connections represent the nexus between electronic and photonic components. However, their fabrication over large scales often requires demanding procedures that are hardly scalable. Here we synthesize arrays of parallel ultra-long (up to 0.75 mm), monocrystalline, silicon-based nano-wires and complex, connected circuits exploiting low-resolution etching and annealing of thin silicon films on insulator. Phase field simulations reveal that crystal faceting and stabilization of the wires against breaking is due to surface energy anisotropy. Wires splitting, inter-connections and direction are independently managed by engineering the dewetting fronts and exploiting the spontaneous formation of kinks. Finally, we fabricate field-effect transistors with state-of-the-art trans-conductance and electron mobility. Beyond the first experimental evidence of controlled dewetting of patches featuring a record aspect ratio of sim1/60000 and self-assembled simmm long nano-wires, our method constitutes a distinct and promising approach for the deterministic implementation of atomically-smooth, mono-crystalline electronic and photonic circuits.

Low-Temperature Synthesis of α-SiC Nanocrystals

Thick SiCx films have been deposited on a c-Si surface by radiofrequency (rf) magnetron sputtering (150 W, 13.56 MHz, Ar flow 2.4 L/h, 0.4 Pa) of graphite and silicon targets. The X-ray diffraction study shows that fast annealing of the SiCx film deposited on the c-Si surface for 3 h leads to the low-temperature (970°C) formation of hexagonal structural phases α-SiC (6H-SiC and other) along with the cubic modification of silicon carbide β-SiC. The IR spectroscopy has shown the formation of SiC nanocrystal nuclei due to the energy action of the rf plasma ions on the upper layer of the SiC film during its growth. The data of X-ray reflectometry demonstrate a high density of the films up to 3.59 g/cm2 as a result of formation of dense C and SiC clusters in the layers under action of the rf plasma.

The phase optimization, optical and electrical properties of kesterite Cu2ZnSnS4 thin film prepared by single target RF magnetron sputtering technique for solar cell application

Cu2ZnSnS4 (CZTS) thin film was prepared by RF sputtering technique from a single quaternary target by optimizing RF power, in situ substrate temperature and post deposition annealing temperature. The single phase formation of crystalline CZTS thin film has been verified at a particular optimized condition by characterizing through x-ray diffraction, Raman spectrometer and x-ray photoelectron spectroscopy. The kesterite structure has been further confirmed from the lattice fringes of high resolution transmission electron microscope and selected area electron diffraction study. The surface properties such as particle size, shape and roughness and elemental composition of amorphous and crystalline phase of CZTS studied by atomic force microscope, scanning electron microscope and energy dispersive analysis of x-rays. The optical absorption and photoluminescence studies of post-deposition annealed film prove the defect free and single phase CZTS formation. The band gap calculation for crystalline CZTS showed band gap of 1.49 eV calculated from the Tauc plot. The electrical properties of optimized CZTS thin film has been studied from Hall effect measurement showing P-type conductivity with better carrier concentration and Hall mobility.

Electron-microscopy study of ordered silver nanoparticles synthesized in a ZnO:Al polycrystalline film

The optical absorption spectra and structural properties of samples series consisting of AZO oxide films with an intermediate layer of silver nanoparticles with different sol compounds were investigated. TEM analysis of the obtained coatings showed that the nanoparticles in the AZO film form an ordered structure, and the distance between them depends on the sol composition and the film annealing temperature. Optical measurements showed that a position of the nanoparticle plasmon peak in AZO also depends on them.

Electrochemically and chemically deposited polycrystalline CdSe electrodes with high photoelectrochemical performance by recycling from waste films

Waste CdSe film electrodes can be recycled into useful films without sacrificing their photoelectrochemical performance. Cd2+ aqueous ions have been recovered from waste CdSe electrodes by soaking in minimal amount of HCl (10.0 M) at 80 °C for 60 min. The Se2− ions, converted into H2Se(g) by the acid, have been trapped in basic NaOH solution for further use. The recovered Cd2+ ions have been used to deposit new (recycled) CdSe film electrodes onto fluorine doped tin oxide films (FTO/Glass) using aqueous Na2SeSO3 solutions by two methods. Electrochemical deposition (ECD) has been performed using applied potential (−1.0 V vs Ag/AgCl). Chemical bath deposition (CBD) has been performed in a basic medium at 70 °C. Both ECD and CBD recycled films have been prepared using recovered Cd2+ solutions, whereas fresh films have been prepared using fresh solutions. In both cases, the recycled CdSe films do not show any inferior characteristics to the freshly prepared counterparts. Effects of annealing at 150 °C and cooling rate on physical and photoelectrochemical (PEC) characteristics have been studied for different CdSe film electrodes. In both recycled and fresh systems, the CBD film electrodes exhibit enhanced uniformity, compactness and photo-electrochemical (PEC) performance by annealing. Upon annealing, the recycled and fresh ECD films exhibit less film uniformity and compactness, and consequently lower PEC performance. In ECD and CBD films, fast cooling is advantageous over slow cooling. Conversion efficiency values of ~8% are observed for the CBD recycled pristine films once carefully annealed and quickly cooled. This is higher than literature values for pristine CdSe (~5%), TiO2/CdS/CdSe (~4%) film electrodes, and resembles that for Tl/CdSe0.65Te0.35 (~8) multi-layer systems. The results show the feasibility of recycling waste CdSe film electrodes.

Effect of annealing temperature on the thermal transformation to cobalt oxide of thin films obtained via chemical solution deposition

An ammonia-free chemical solution deposition formulation is employed to synthesize cobalt hydroxide thin films. The films are subsequently annealed at different temperatures to obtain cobalt oxide (Co3O4). The reaction solution is composed solely of cobalt sulfate and triethanolamine. The annealing temperature has a strong effect on the properties of thin films. X-ray diffraction shows that the films are amorphous despite the thermal treatment; the morphology for both as-deposited and annealed films are found to be homogeneous, compact, with no evident changes. X-ray photoelectron spectroscopy reveals that the as-deposited thin films are mainly composed of cobalt hydroxide. After annealing, the films transform into cobalt oxide (Co3O4) thin films. The optical spectra confirm the X-ray photoelectron spectra, due to the appearance of characteristic features of Co3O4 on both characterization methods. The energy band gap is estimated to lie between 2.1 and 3.0 eV. The resistivity of the annealed films ranges from 4.29 × 103 to 1.46 × 104 Ω⋅ cm. Finally, with the work function and ionization energy, we propose an experimental band diagram as a function of annealing temperature, showing a p-type nature for the cobalt oxide films.

Scale up of microwave annealed FA0.83Cs0.17PbI1.8Br1.2 perovskite towards an industrial scale

Perovskite solar cells (PSCs) efficiency has rapidly increased from the initial 3.8 to recent 24.2%. This high efficiency has attracted serious worldwide researchers and industry attention due to their low material cost, and simple solution-based fabrication process. However, fundamental studies on PSCs are usually produced through lab-scale actions and carried out on small-area devices (≤1 cm2). Here we present the advances of up-scaling using microwave (MW) annealing of perovskite films on large area specimens (~16 cm2), looking forward the industrial-scale. Morphological, structural and optical characterization were performed to confirm the effectiveness of the scaled up MW annealing.

Evidence of weak antilocalization in epitaxial TiN thin films

Defect engineering provides a tremendous opportunity to impart novel functionalities to nanomaterials. This report is focused on TiN metallic system, where the unpaired spin structure and electron-transport are controlled by injecting nitrogen vacancies (VN). The TiN films are epitaxial, with the TiN/Al2O3 epitaxial relationship given by: (1 1 1) TiN//(0 0 0 1) Al2O3 as out-of-plane, and 〈11-0〉 TiN//〈1 0 1- 0〉 Al2O3 and 〈1 1 2-〉 TiN//〈1 1 2-0〉 Al2O3 as in-plane, after 30° rotation. Epitaxy in such a large misfit system (~9.24%) is rationalized to arise via domain matching epitaxy (DME) paradigm. Following the report of room-temperature ferromagnetism [1] in TiN1−x films formed by injecting nitrogen vacancies, we provide direct experimental evidence of weak antilocalization (WAL) effects by plugging VN using nitrogen annealing of TiN films. This evidence with simultaneous loss of magnetization in nitrogen annealed TiN films is the tell-tale sign of VN acting as magnetically active defects in TiN, as their removal facilitates Berry’s phase formation and generation of time-reversal symmetry. Through detailed EELS and Raman analysis, we have explicitly shown the absence of Ti+2 polarons in TiN films on N2 annealing. The resistivity minima in TiN films are attributed to the WAL effect with persistent log T behavior under 0–7 Tesla magnetic fields. The temperature-dependent coherence length analysis also highlights the emergence of WAL under the two-dimensional localization theory. The WAL effect in TiN is similar to topological insulators, quenching on the introduction of magnetically active defects, while stable against non-magnetic defects. Our findings demonstrate the prime importance of nitrogen vacancies in tuning the magentotransport characteristics in epitaxial nitride films for optoelectronic device applications.

Gold nanoclusters on GaAs(001) surface: atomic force microscopy and optical spectroscopy of plasmons

Gold nanoclusters of two different kinds are found to occur on annealing of thin Au films deposited on either oxidized or nitridized GaAs(001) surfaces. The morphology of Au/GaAs interfaces is characterized, and the gold nanoclusters are established to cause two resonant peaks in optical reflectance spectra at the energies of 1.6 eV and 2.15 eV. Using the data of reflection spectroscopy and theoretical analysis, we assign the latter peak to localized plasmons of Au nanoislands located on Au/GaAs surface. The former peak is attributed to plasmons of prolate Au nanoclusters buried in GaAs crystal just near its surface. As well, plasmonic anisotropy of Au nanoclusters formed on nitridized GaAs surfaces is detected using reflectance anisotropy spectroscopy.

Strong Disorder in HgCdTe Studied with Optical Methods and X-Ray Diffraction

Optical transmission, photoluminescence, and X-ray diffraction have been used for studying structural disorder in Hg1-xCdxTe (x=0.3–0.4) films grown by Molecular-Beam Epitaxy on GaAs and Si substrates. According to all three methods, studied films immediately after the growth showed quite different scale of the disorder. After thermal annealing films showed similar optical properties, yet their structural properties remained different. It appears that the ability of Hg1-xCdxTe to gain good optical quality under annealing for considerably disordered initial material is not directly structure-related.

Investigating the impact of thermal annealing on the photovoltaic performance of chemical bath deposited SnO2/p-Si heterojunction solar cells

The current work investigates the impact of annealing temperature on the optoelectronic properties of SnO2 thin films grown by chemical bath deposition (CBD) method. The as-grown SnO2 films, on p-Si substrate, are annealed at 200 °C and 400 °C for 10 min in Ar ambient for investigating the impact of such annealing on the performance of SnO2/p-Si heterojunction solar cells. The growth of a uniform SnO2 film on Si surface has been confirmed from SEM studies and the chemical composition and optical properties of the as-grown and annealed films are investigated in detail by employing XRD and ellipsometric measurements. Absorption coefficient of the samples is observed to vary in the range of 24 × 105 – 60 × 105/m, at its band gap (3.0 eV). The current–voltage characteristics under both dark and illuminated conditions suggest superior voltaic performance of the 200 °C annealed SnO2 film. The short-circuit current density, open-circuit voltage and fill-factor are obtained to be 0.45 mA/cm2, 5.41 mA/cm2 and 0.4 V, 0.34 V and 13%, 8% respectively for as-grown and 200 °C annealed samples. The maximum power conservation efficiency (η) of 4.9% is obtained for the 200 °C annealed sample. Thus, the study indicates the potential of CBD-grown SnO2 film for photovoltaic applications.

Physical properties of ZnSe thin films: Air and vacuum annealing evolution to buffer layer applications

In order to develop high efficiency solar cell device by replacing conventional hazardous CdS window layer by environmental friendly Zn-based buffer layer, ZnSe thin films of thickness 100 nm were grown on glass and ITO substrates employing electron beam evaporation technique followed by air and vacuum annealing at temperature 100°C, 200°C and 300°C. As-grown and annealed films were subjected to characterization tools like XRD, UV-Vis spectrophotometer, SEM, EDS and source meter. Structural results reveal the amorphous phase, SEM images indicate uniform deposition without pin holes and EDS patterns confirm the deposition. Transmittance is observed to be high in visible region and band gap is found to change with temperature of the treatment and I-V measurements demonstrate ohmic nature. On the basis of optimized results, the films annealed at 200°C in vacuum may be used as buffer layer to develop high efficiency Cd-based and CIGS thin film solar cells.

Effect of photon annealing and cryogenic temperature on the microstructure, optical and electrophysical properties of Mo thin films

Mo films were deposited on a polyimide substrate by dual magnetron sputtering in an UniCoad 200 vacuum unit with an unbalanced magnetic system. The dependence of the characteristics of the obtained Mo films on photon annealing and cryogenic temperature was studied. The photonic annealing of Mo films was carried out at temperatures of 200 °C and 300 °C. For cooling Mo films, liquid nitrogen was used (t = -190°С). The characteristics of the films were investigated using X-ray diffraction, scanning electron microscopy and scanning probe microscopy. The results are presented on the change in specific electrical resistance, diffuse reflection spectra and adhesion strength of Mo films. It is shown that photon annealing at different temperatures does not affect the intensity of the X-ray diffractogram peaks of the Mo coating. After exposure, at a cryogenic temperature, an insignificant change in the X-ray diffractogram occurs, a shift of the diffractogram peak (110) is observed to large angles 2θ from 40.72° to 40.89°. The obtained Mo coating has a columnar structure in the form of tightly packed polycrystallites, oriented perpendicular to the substrate of the polyimide film. Mo coating on a polyimide substrate is resistant to sudden thermal exposure at temperatures not higher than 300 °C. Processing the resulting coating with liquid nitrogen leads to strong cracking of the Mo coating. At the same time, on samples with a coating thickness of 380–400 nm, exfoliation of the Mo coating, in the place of fracture, is not observed. The adhesive strength of the Mo coating with a polyimide film is quite high – 1.11 ± 0.05 GPa. Photon annealing does not reduce the adhesive strength of the Mo coating. The Mo film under conditions of cryogenic temperature (0.89 ± 0.08 GPa) has the worst adhesion strength.

Hillocks formation in the Cr-doped Ni thin films: growth mechanisms and the nano-marker experiment

Stress relaxation in thin metal films often results in formation of hillocks—high grains protruding from the rest of the film. Their formation is discussed in terms of surface diffusion and accumulation of the film material, as well as in terms of material accretion at the film–substrate interface and grain boundary sliding. We employed an ultrathin film of Cr oxide embedded in the middle of a thin nickel (Ni) film deposited on sapphire substrate as a marker tracking the material flow during film annealing. We found that during annealing at the temperature of 700 °C the marker under the growing hillocks remains largely immobile, indicating the negligible role played by grain boundary sliding in hillock formation, and the lack of material accretion below the hillock and along the film–substrate interface. We suggest that the hillocks grew by lateral diffusion of Ni, either along the grain boundaries or on the film surface covered by Cr oxide, and material accumulation on the top of the hillock by surface diffusion. We discuss the hillock nucleation and growth in terms of defects in the layer of Cr oxide formed on the surface of the Ni film.

Surface Roughness Variation and Microstrucural Evolution of AU Thin Films in Rapid Annealing by Microwave and Furnace Heating

Microstructural evolution of Au thin film in post-annealing by microwave and by electric furnace heating was compared. Wave number spectra of film surface roughness were analyzed to characterize their roughness variation by annealing. Coarsening of film microstructure occurred consistently as the increase of the annealing temperature in both methods. Labyrinth-shaped morphologies consisting of bump-ridge crystals were formed by annealing, which might be originated from the fine-grained colonies existed in the as-deposited state. Bumps were formed through coalescence and growth within the colony and increased their height as the increase of annealing temperature. Eventually, microstructures and crystal morphologies became similar by both annealing methods above 800~850°C. However, there are following differences observed in the low temperature annealing cases: 1. While a temporal variation of the film microstructure was observed in furnace annealing, microwave annealing exhibited smaller tendency of this feature. 2. Fine roughness (higher wave number range) of the films was reduced more in the temperature below 720oC by microwave annealing than by furnace annealing. 3. Bump height increase was pronounced more by microwave annealing between 600~800°C, corresponding to the roughness increase (RMS, root mean square value of the roughness). On the other hand, film coverage decreased. The reasons for the difference was discussed by consideration of the competition among the capillary driven surface diffusion, contribution of electro-migration and the thermodynamic equilibrium shapes of the film grain structures.

High-temperature oxidation behavior of HiPIMS as-deposited Cr–Al–C and annealed Cr2AlC coatings on Zr-based alloy

Protective coatings of Zr-based claddings have been proposed for the development of Accident Tolerant nuclear Fuel (ATF). Coatings forming stable oxides at high temperature such as MAX phases are attractive candidates for these applications. In this study Cr–Al–C coatings were deposited on coupons of Zr-based alloy (Zr702) by High Power Impulse Magnetron Sputtering (HiPIMS). Cr2AlC coatings were then obtained by annealing of the as-deposited films at a temperature below metallurgical degradation of Zr alloys. The behavior of as-deposited Cr–Al–C and annealed Cr2AlC coatings with respect to high-temperature oxidation slightly differ for short oxidation times but converge for longer durations. Oxidized coatings are made of (i) an external dense, covering, adherent and thin scale of aluminum and chromium oxides, (ii) an intermediate thicker, porous layer of chromium carbide and (iii) an interdiffusion layer. Both coatings are protective in dry and wet air (up to 1473 K for 2 h in air-28% H2O for an initial thickness of 7 μm), and are thermal shock-resistant. Self-healing capability is observed for submicronic defects. The top oxide scale acts as a barrier against oxygen diffusion, thus efficiently protecting the Zr702 substrate from extended oxidation except near coupon edges. The results indicate that Cr–Al–C thin films grown by HiPIMS process and annealed Cr2AlC coatings are both promising candidates for ATF cladding coatings.

Solution processed Ge20Sb5S75 thin films: the effect of solution concentration and multiple layers stacking

Ge20Sb5S75 thin films with high chemical resistance to aliphatic amines were deposited from solutions of various glass concentrations (0.015-0.09 g of grinded glass material/ml of n-butylamine) by the spin-coating technique. As-prepared and annealed thin films were analyzed by spectroscopic ellipsometry and EDS (energy-dispersive X-ray spectroscopy). Results proved that the refractive index of thin films was not affected by the solution concentration (within studied range), and the studied optical properties of deposited samples were homogenous in their volume. The Ge20Sb5S75 solution of the highest concentration (0.09 g/ml) was chosen for deposition of thicker chalcogenide glass material using multiply deposition/thermal stabilization procedure. Prepared multilayers proved to have good optical quality and homogenous chemical resistance through the whole thickness. No interfaces between layers were observed from etching kinetics and SEM scans. Thus, the results confirmed that multiple layers stacking procedure is suitable for deposition of thick homogenous Ge20Sb5S75 thin films.

Rapid fabrication of perovskite solar cells through intense pulse light annealing of SnO2 and triple cation perovskite thin films

Rapid evolution of perovskite solar cells (PSCs) performance and stability has inclined the research focus towards scalable bulk fabrication through high speed and cost-effective automated methods. For the first time, intense pulsed light (IPL) is utilized to rapidly fabricate efficient PSCs through swift annealing of both the SnO2 electron transport layer (ETL) and mixed triple cation perovskite thin films. The addition of di-iodomethane (CH2I2) alkyl-halide could enhance the PSC efficiency by retarding the crystallization and improving the surface morphology of the perovskite photoactive film through supplying iodine cleaved by ultraviolet energy during IPL process. The maximum efficiency and fill factor of the PSCs fabricated by IPL annealing were 12.56% and 78.3% for the rigid glass-FTO slides, and 7.6% and 64.75% for flexible PET-ITO substrates when processed in the ambient with relative humidity of 60%, respectively. The annealed materials were characterized through Scanning electron microscopy (SEM), UV–Vis, photoluminescence (PL), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. In addition, impedance spectroscopy (IS) and current-voltage measurements were conducted to study the functionality of fabricated cells. Our results delineated the feasibility of sequential step IPL annealing on rapid fabrication of efficient PSCs which is directly applicable for scalable roll-to-roll manufacturing.

Kinetic approach to defect reduction in directed self-assembly

As a potential solution to next-generation nanolithography, directed self-assembly (DSA) of block copolymers (BCPs) is still restrained in high-volume manufacturing primarily due to its defectivity issue. Though defects possess greater free energies than aligned morphologies and are highly energetically unfavorable, they can be kinetically trapped by the energy barriers and persist for a long time during annealing. Therefore, understanding the kinetics of defect annihilation is crucial in revealing the mechanism of defect formation and in further reducing defectivity in DSA. We focus on two types of predominant defects in DSA—dislocation and bridge. A kinetic model of each defect type is developed through statistical analysis of experimental data, providing insight into possible approaches of further defect reduction. We also investigate the impact of annealing temperature and film thickness on annihilation kinetics and discuss the reasons behind the observed results. By simply optimizing annealing conditions and film thickness, we have successfully reduced the total defect density by 1 order of magnitude. Though these findings are based on polystyrene- b -poly(methyl methacrylate) (PS- b -PMMA), we anticipate they could be readily applied to other BCP platforms as well.

Structural, morphological and optical properties of Yb2Cu2O5 thin films

The Yb2Cu2O5 thin films have been fabricated by ultrasonic spray pyrolysis followed by a high temperature annealing process. The as-deposited and annealed films are analyzed by well-known tools such as x-ray diffraction (XRD) and scanning electron microscope (SEM). The crystal structure of the Yb2Cu2O thin films is orthorhombic and their crystal size is 35.9 nm. The SEM images show that the surface of the Yb2Cu2O thin films is porous as a consequence of the high temperature treatment. The optical properties of Yb2Cu2O5 firstly deposited in a thin film form is also investigated by means of UV–Vis measurements. From Tauc plot, the indirect band gap value of 1.079 ± 0.003 eV is reported for Yb2Cu2O thin films.