Reactive Gas Flow Sputtering Research Articles

Hollow Cathode Gas Flow Sputtering of Nickel Oxide Thin Films for Hole‐Transport Layer Application in Perovskite Solar Cells

Nickel oxide (NiO1+δ) is a versatile material used in various fields such as optoelectronics, spintronics, electrochemistry, and catalysis which is prepared with a wide range of deposition methods. Herein, for the deposition of NiO1+δ films, the reactive gas flow sputtering (GFS) process using a metallic Ni hollow cathode is developed. This technique is distinct and has numerous advantages compared to conventional sputtering methods. The NiO1+δ films are sputtered at low temperatures (100 ºC) for various oxygen partial pressures during the GFS process. Additionally, Cu‐incorporated NiO1+δ (Cu x Ni1−x O1+δ) films are obtained with 5 and 8 at% Cu. The thin films of NiO1+δ are characterized and evaluated as a hole‐transporting layer (HTL) in perovskite solar cells (PSCs). The NiO1+δ devices are benchmarked against state‐of‐the‐art self‐assembled monolayers (SAM) ([2‐(3,6‐dimethoxy‐9H‐carbazol‐9‐yl)ethyl]phosphonic acid (also known as MeO2PACz)‐based PSCs. The best‐performing NiO1+δ PSC achieves an efficiency (η) of ≈16% without a passivation layer at the HTL interface and demonstrates better operational stability compared to the SAM device. The findings suggest that further optimization of GFS NiO1+δ devices can lead to higher‐performing and more stable PSCs.

Electrochromic WO3 Films with Controlled High-Rate Deposition By Hollow Cathode Gas Flow Sputtering

An amorphous WO3 is one of the most important materials for electrochromic (EC) devices because of its blue coloration caused by electron injection. For the industrial applications including EC smart windows, there are strong demands for EC devices to be produced with a high deposition rate, with a higher stability and at lower costs. Gas flow sputtering (GFS) has the possibility for very high deposition rate because of using high density hollow cathode discharge and a large amount of sputtering gas (Ar) flow and the stability of the reactive sputtering process in the wide range of the reactive gas (O2) flow, so there is no “transition region” which should appear in the conventional reactive sputtering processes. In this study, reactive GFS was adopted to deposit amorphous WO3 films with the high EC properties with the high deposition rate. WO3 films were deposited on unheated ITO-coated glass substrate by GFS using two W metal targets which were mounted parallel with each other. Sputtering power was fixed at 1000 W. Ar and O2 flows were 5.0 slm and 10-125 sccm, respectively. Total gas pressures during the depositions were 70 Pa and 90 Pa. X-ray diffraction measurements showed that the all films were amorphous. The density of WO3 films were estimated from data measured by X-ray fluorescence and ICP spectroscopy. The films were electrochemically intercalated with protons and lithium ions. The deposition rates were almost constant with O2 flow during depositions. Figure shows the coloration efficiency of proton intercalated WO3 films as a function of O2 flow during depositions. The coloration efficiency had a tendency to decrease with increasing O2 flow during depositions. [1] N. Oka, Y. Shigesato, et al., Thin Solid Films 532, 1-6 (2013). Figure 1

Visible-light active thin-film WO3 photocatalyst with controlled high-rate deposition by low-damage reactive-gas-flow sputtering

A process based on reactive gas flow sputtering (GFS) for depositing visible-light active photocatalytic WO3 films at high deposition rates and with high film quality was successfully demonstrated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process and the process was highly stable. Furthermore, Pt nanoparticle-loaded WO3 films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH3CHO under visible light irradiation. The decomposition time for 60 ppm of CH3CHO was 7.5 times more rapid on the films deposited by the GFS process than on the films deposited by the conventional process. During GFS deposition, there are no high-energy particles bombarding the growing film surface, whereas the bombardment of the surface with high-energy particles is a key feature of conventional sputtering. Hence, the WO3 films deposited by GFS should be of higher quality, with fewer structural defects, which would lead to a decrease in the number of centers for electron-hole recombination and to the efficient use of photogenerated holes for the decomposition of CH3CHO.

Structure and mechanical properties of ZrO 2 films deposited by gas flow sputtering

ZrO 2 films were deposited by reactive gas flow sputtering (GFS) where voltage is applied to a cyindrical hollow-cathode target from a DC source, the discharge being produced at relatively high sputtering pressure. In this system, secondary electrons form a major component of the total current flow and lead to heating of the substrate which in turn has an effect on the properties of deposited films. The present experiments were carried out under the following conditions: Ar gas flow rate of 200 sccm, O 2 flow rate F O 2 in the range between 0.003 and 1 sccm, and sputtering power ( P S) in the range of 50–800 W. The reults showed that the crystal structure of the films deposited for P S below 200 W was monoclinic but for P S above 400 W, the films included tetragonal cystals of stable structure formed at high temperature by the electron bombardment. The films were formed with grains of 20–100 nm in diameter in a porous structure. The mechanical properties of the films were determined by a nanoindentation technique. Martens hardness ( H M) of the porous films was found to be in the range between 220 and 330 MPa which is substantially less than that of films typically deposited by rf magnetron sputtering.

Preparation and Characterization of Fe–N Nanoparticles by Gas Flow Sputtering

Iron nitride (Fe–N) nanoparticles were prepared by reactive gas flow sputtering. The structure, size distribution, and magnetic properties of these particles were studied as a function of the average atomic ratio of N against Fe (N/Fe ratio). X-ray diffraction analysis revealed that the mixture of α-Fe and γ'-Fe4N was formed at an N/Fe ratio of approximately 0.2 and ε-Fe2–3N began to appear at an N/Fe ratio of approximately 0.4. Using transmission electron microscopy, it was found that α-Fe and γ'-Fe4N crystallites were not formed in one particle; instead, Fe particles and γ'-Fe4N particles coexisted. The size distribution was well fitted by a log–normal distribution; the mean diameter and standard deviation were approximately 50 and 15 nm, respectively, and were independent of the N/Fe ratio. The saturation magnetization decreased monotonously with an increase in the N/Fe ratio.

Influence of Bias Voltage on the Structure of Lead Zirconate Titanate Piezoelectric Films prepared by Gas Flow Sputtering

The work focuses on the influence of ion bombardment on the microstructure of gas flow sputtered lead zirconate titanate (PZT) films. PZT is a well-known piezoelectric material used in many piezoelectric sensor and actuator applications. However, films in the 10 µm thickness region are still in demand for fast and powerful electromechanical drives (e.g. inkjet head). We used the reactive gas flow sputtering technique (GFS) for the high-rate deposition of PZT thin films on platinum- and on Pt/TiO2-coated silicon wafers. The stoichiometry was adjusted to be near the morphotropic phase boundary Pb(Zr0.52Ti0.48)O3 using segmented pure metallic targets. A substrate temperature of 680 °C during growth was applied and the films were prepared with a deposition rate of up to 120 nm · min−1. The perovskite crystalline phase was verified by X-ray diffraction and studies on grain sizes have been performed. The layer morphology was investigated by SEM and films were proved to be mostly crack- and defect-free.

Nanocomposite layers of ceramic oxides and metals prepared by reactive gas-flow sputtering

Thin nanocomposite layers of ceramic oxides in conjunction with a second metallic phase were prepared by reactive gas-flow sputtering. The two nanogranular phases were dispersed into each other by co-deposition from two separate targets. TiO 2 and Al 2O 3 were chosen as ceramic phase, respectively, which was obtained by sputtering one of the metals and reacting with oxygen. In order to investigate the influence of a hard and a ductile metal, either tungsten or copper was chosen as the second metallic phase. Highly compact thin films could be prepared as was revealed by SEM. A low hydrogen content of 1–2 at.% was measured by SIMS indicating a low sample porosity and an effective residual gas displacement from the surface of the growing film. X-Ray diffraction revealed the TiO 2-derived films to contain rutile-phase grains of average grain size of less than 10 nm. Mechanical and tribological properties of the 3- to 4-μm thick coatings were determined by a micro-indenter operating with a Vickers-type diamond and by a pin-on-disk tester. The plastic microhardness HU pl amounted up to 24.1 GPa in case of TiO 2-derived nanocomposite films and up to 14.8 GPa in case of Al 2O 3-based films. Also, with respect to tribological properties TiO 2:Cu and TiO 2:W coatings were superior over Al 2O 3-derived ones. A wear coefficient of 0.35×10 −6 mm 3/Nm was obtained for optimised TiO 2 films against an alumina sphere under unlubricated sliding conditions. In lubricated pin-on-disk tests wear coefficients on the order of 0.1×10 −6 mm 3/Nm were obtained for both metal-doped TiO 2 and Al 2O 3 films.

Examination of the kinetics and performance of a catalytically switching (gasochromic) device

The features of a new type of smart window are evaluated. The `gasochromic' device uses a WO3 layer that can be coloured by performing a reaction with gaseous hydrogen via a catalyst.The kinetics of this reaction as a function of several parameters were determined for optimization purposes:•The dependence of the colouration speed on the H2 concentration was found to be linear for the range 0.1–20%.•The temperature dependence is of the Arrhenius type with a Gibbs energy of activation of 27kJ/mol.•For evaporated layers, the kinetics depend strongly on the overall thickness of the catalyst layer.•The shape of the curve for colouration versus time is different for layers with different microstructures i.e. diffusion coefficients.A model accounting for these effects was developed. Within this model the kinetics are described by a surface-controlled process (such as the adsorption) and one-dimensional diffusion of protons and electrons within the bulk material. We found that diffusion limits the speed for dense materials, while the surface process is the limiting one for porous materials.SEM (secondary electron microscopy) images of the examined layers reveal that not only the degree of amorphicity influences the diffusion, but also the strucure on a scale of 100nm (columns formed in the deposition process). The influence of the water content of the atmosphere and the layer on the kinetics and degradation of the device are also discussed. The samples are produced by e-beam evaporation, reactive magnetron sputtering and reactive gas flow sputtering (RGFS) causing the different microstructure of the WO3 layer.

Gas flow sputtering of oxide coatings: practical aspects of the process

On the basis of the principle of reactive gas flow sputtering, advanced sputtering sources for metals and hard coatings have been developed. Main features of these sources, which are based on an intense hollow cathode glow discharge and an inert gas flow supported material transport to the substrate, are the high deposition rates (in the order of 10–20 μm h −1), the operation at a low vacuum level (1 mbar range) and the applicability to a wide range of coating materials. Oxide coatings of aluminum, titanium and zirconium have been deposited; furthermore, corresponding pure metals and high temperature superconductor films (YBaCuO) also. Linear upscaling to 0.5 m source length suggests that there are no principle limits for large area coating. The 3D behavior follows from the directed gas flow and the isotropic out-diffusion from the carrier gas, i.e., it displays characteristics between PVD and CVD. A long-term stability up to 65 h of continuous operation has been demonstrated.

High rate deposition of alumina films by reactive gas flow sputtering

Abstract A new sputter which enables higher deposition rates than standard magnetron sputtering, especially for oxide films, has been developed. The deposition process typically works at several tenths of a millibar and requires no high vacuum environment. It is based on a hollow cathode discharge in combination with a suitable directed gas flow. The particular route of the gas flow also strongly decreases the residual gas influence on the target and substrate. For practical applications a linear sputter source of length 10 cm and width 2 cm which allows the coating of an area of approximately 50 cm2 has been tested. Up to now deposition rates of 10 μm h-1 at 1.4 kW d.c. power have been realized. The total pressure and gas flow were in the region of 0.4 mbar and 800 sccm (standard cm3 min-1) respectively. In spite of the rather high working pressure and the intense argon gas flow towards the substrate, the argon content of the films is very low (0.01 wt.% or less). The concept of the linear hollow cathode with two parallel rectangular targets was found to be simple in construction and operation and can be easily extended in two dimensions for the coating of large areas.

Zirconia thin film deposition on silicon by reactive gas flow sputtering: the influence of low energy particle bombardment

Zirconia (ZrO 2) thin films have been deposited on Si(100) substrates with a new film deposition method, reactive gas flow sputtering, which enables very low energy ion bombardment during film growth. The influence of argon ion bombardment in the energy range 0–30 eV on the film properties was studied by X-ray diffraction, Auger analysis and ellipsometry. Both the structure and stoichiometry of the films were found to respond in a highly sensitive manner to small ion energy shifts in several steps. The ion bombardment effects may be related to differences in bonding strength of the amorphous and crystalline (monoclinic and tetragonal) structures of ZrO 2.