RF Magnetron Sputtering Deposition Research Articles

Enhanced optical gain assisted by the plasmonic effects of Au nanoparticles in Nd³⁺ doped TeO₂-ZnO waveguides produced with the pedestal architecture

Investigation of the signal enhancement of Nd3+ codoped TeO2-ZnO pedestal waveguides, at 1064 nm, due to Au nanoparticles deposited over the core is presented for the first time. Nd3+ doped TeO2-ZnO thin film was obtained by RF Magnetron Sputtering deposition. The resulting core with 500 nm height and widths in the 4–40 μm range, exhibited low roughness average in all area measured (0.48 ± 0.04) nm. Minimum propagation losses of 2.2 dB/cm were observed for waveguide width of 40 μm whereas an increase took place for smaller ones. Scanning electron microscopy (SEM) allowed the waveguide structure inspection and transmission electronic microscopy (TEM) the Au nanoparticles evaluation. The results showed that the Au nanoparticles contributed up to 75 % of relative gain enhancement, under 808 nm excitation. This increase was due to the local field growth in the proximity of the nanoparticles that enhances the density of excited Nd3+. The internal gain that considers the propagation losses reached positive values for larger core widths (above 8 μm).The present study opens possibilities for optical amplifiers with low propagation losses based on different metal-dielectric composites, as well as other waveguide-based devices.

Investigation of crystalline and band alignment properties of NiO/GaN and Ni0.5Co0.5O/GaN heterojunctions using synchrotron radiation based techniques

Epitaxial layers of NiO and Ni0.5Co0.5O have been deposited on GaN templates using RF magnetron sputtering deposition technique. The epitaxial relationship in out-of-plane and in-plane directions for NiO and Ni0.5Co0.5O layers with respect to GaN is [111]NiO(Ni0.5Co0.5O)∥[0001]GaN and [1̅10]NiO(Ni0.5Co0.5O)∥[1̅21̅0]GaN, respectively. The epi-layers are found to have two triangular domain structures oriented along [111] direction with an in-plane rotation of 60° with respect to each other. Photoelectron spectroscopy (PES) has been used to determine the valence band offset (∆EV) and the band alignment at the heterojunctions (HJs). The ∆EV at NiO/GaN and Ni0.5Co0.5O/GaN HJs are 1.2 ± 0.2 eV and 1.8 ± 0.2 eV, respectively. The conduction band offsets (∆EC) have also been estimated using the determined values of optical band gap (NiO: Eg = ∼ 3.5 eV; Ni0.5Co0.5O: Eg = ∼ 3.3 eV) from optical transmission measurements. The values of ∆EC are found to be 1.5 ± 0.2 eV and 1.9 ± 0.2 eV at NiO/GaN and Ni0.5Co0.5O/GaN HJs, respectively. A type-II band alignment is observed at both the HJs. Higher values of valence band and conduction band offsets are observed at Ni0.5Co0.5O/GaN HJ in comparison to NiO/GaN. These experimentally determined values of band offsets can be used to design wide band gap HJ based devices like photodetectors, where higher values of band off-set at the Ni0.5Co0.5O/GaN HJ can be utilized to confine the carriers.

Improving hydrogen isotope permeation resistance of (TiVAlCrZr)O multi-component metal oxide coating by O+ Ion implantation

Oxygen vacancy can greatly affect the performance of metal oxide to hydrogen isotope permeation resistance. In this work, we report a new strategy to improve the permeation resistance by oxygen ion implantation. A (TiVAlCrZr)O multi-component metal oxide film was prepared as a tritium permeation barrier on a 316 L substrate by RF magnetron sputtering deposition, and then implanted by oxygen ions to fill the oxygen vacancies inside. The grazing incidence X-rays (GIXRD) analysis showed that the pristine and the oxygen-implanted coatings were in an amorphous phase. The deuterium permeation resistance of the four coatings was tested by a gas-driven device. The result showed that the pristine coating had a permeation reduction factor (PRF) of 5,610 at 500 °C, while there was a 13.6 times of increase in PRF with an oxygen concentration of 11.4 at.% with the best-reported value of 76,500, and more oxygen ions implanted, the better the deuterium permeation resistance of the coating. The GIXRD showed that after the test the pristine coating remained amorphous, while some crystals were formed in the oxygen-implanted coating with an oxygen concentration of 11.4 at.%. Oxygen ion implantation enhanced the deuterium permeation resistance by filling the oxygen vacancies and forming of more stable state of amorphous multi-component metal oxide, which is expected to be a new type of deuterium permeation barrier.

Activity and Durability of Mn Binary Oxide-Based Electrocatalyst for an Alternative Anode

Compared with alkaline water electrolysis (AWE), proton exchange membrane water electrolysis (PEMWE) has several advantages such as high current density, compact system and high purity of hydrogen gas. However, a conventional anode of PEMWE utilizes precious metal oxide such as iridium oxide (IrO2) with high cost and low resources. Recently, it has been reported that the performance of low-loading IrO2 anodes deteriorates due to the potential fluctuations simulated variable renewable energies [1-2]. Thus, it is required to develop a low-cost catalyst with high durability against the potential fluctuations. We have focused on the tantalum oxide-based electrocatalyst because of its low cost and high chemical stability in acid. In this study, we have investigated on the catalytic activity and durability of Mn added Ta oxide-based thin film (Mn-TaOx) for the alternative anode of PEMWE. For the purpose of improvement of durability, Mn-TaOx coated with ZrO2 fabricated by the Atomic Layer Deposition (ALD) was also prepared to evaluate the durability of potential cycling.A Ti rod was used as the substrate, and Mn-TaOx was prepared by RF magnetron sputtering deposition. Mn disk was used as the sputtering target, and the Ta plate was placed on the Mn target to prepare Mn-TaOx. Mn addition was fixed at 50 at%, and it was controlled by the area ratio considering sputtering rate of Mn and Ta metal. Partial pressure of Ar and O2 gas were kept constant at 0.23 Pa for 20 min during the sputtering. The substrate heating temperature was constant at 673 K during the sputtering. The prepared Mn-TaOx electrode was coated with ZrO2 fabricated by ALD (ZrO2 coating Mn-TaOx). The thickness of coating ZrO2 was varied in the range of 0.5 to 2.0 nm. All electrochemical measurements such as oxygen evolution reaction (OER) was used by conventional three electrode cell in 1 M H2SO4 at 303 K. In addition, electrochemical impedance spectroscopy (EIS) was also performed to estimate several factors such as charge transfer resistance (R ct), film resistance (R film) and so on. The protocol of potential cycling as a durability test was set the potential in the range of 1.5 to 2.0 V with 50 mV s-1 for 10000 cycles, and the slow scan voltammetry was conducted every 2000 cycle in the range of 1.2 to 2.0 V with 5 mV s-1 to compare the OER activity before and after test.The OER current of ZrO2 coating Mn-TaOx was smaller than that of Mn-TaOx without coating (Mn50-TaOx (0 nm)). In particular, the OER current of Mn-TaOx coated with 2 nm of ZrO2 (“2 nm”) was greatly decreased because the film thickness of ZrO2 is too thick so that it has low electric conductivity. Furthermore, the APD-ZrO2 covered on the surface, and it is also hard to react with reactant at active site. From results of EIS, the R ct and R film of “2 nm” increased. On the other hand, the OER current of Mn-TaOx coated with 1 nm of ZrO2 (“1 nm”) did not drastically decrease compared to Mn-TaOx and it was suggested that “1 nm” relatively maintained its activity.Figure 1 shows the geometric current density (i geo) at 2.0 V of ALD-ZrO2 coated on Mn-TaOx after potential cycling. The i geo at 2.0 V of Mn-TaOx without coating also shows in Fig. 1. The i geo of Mn50-TaOx (0 nm) was decreased about half value after 2000 cycles of durability test, but that of Mn-TaOx coated with ZrO2 did not decrease significantly even after 2000 cycles of potential cycling. In particular, the i geo of “1 nm” was the highest current after the 2000 cycles of potential cycling in this study, and the degradation didn’t observe in this cycle range. According to the results from XPS spectrum, a small amount of ZrO2 was detected on the surface of “1 nm” after the potential cycling. The redox peak of Mn(Ⅲ)/(Ⅳ) [3] observed at the ALD-ZrO2 coated on Mn-TaOx was also detected after the potential cycling, so that the Mn species as an active site of Mn-TaOx for the OER was still remained. Therefore, the reason why the “1 nm” was relatively stable is that the amounts of both active and protect site have maintained during the durability test.AcknowledgementThis work is partially supported by Suzuki Foundation.References(1) Ayers, Curr. Opin. Electrochem., 18, 9 (2019).(2) M. Alia, and G. C. Anderson, J. Electrochem. Soc., 166, F282 (2019).(3) Morita, C. Iwakura, and H. Tamura, Electrochim. Acta, 24, 357 (1979). Figure 1

Investigation of Antibacterial Efficacy of CuCrO2 Delafossite Thin Films Against E. coli

Terminals used in hospitals, information systems displaying patient information, and smartphones use touch panels that incorporate n and p transparent conducting oxide (TCO) layers [1]. There are a lot of pre-existing research present on n-type TCO while at the same time similar research interest related to p-type TCOs has been lacking. This is due to the inherently high electrical resistivity or low optical transparency of p-type TCOs. Recently, there has been a spike in research related to p-type delafossite thin films, owing to their excellent electrical and optical properties as compared to the other p-type counterparts. Cu-based p-type delafossite materials exhibit low resistivity and at the same time good optical transparency in the visible region. Among the Cu-based delafossites, copper chromium oxide (CuCrO2) exhibits the lowest electrical resistivity reported yet. Use of CuCrO2 as the p-type TCO along with a suitable n-type TCO might demonstrates significant potential to be used for optoelectronic applications.In this work, CuCrO2 thin films have been deposited on quartz substrates using dual target RF magnetron sputtering technique. This involved dual sputtering of 3- inch Cu2O and Cr2O3 targets. The substrate temperature was maintained at 400 °C during the deposition with Ar used as the sputtering gas. This was followed by post deposition annealing. Previous research carried out by our group has indicated that single-phase CuCrO2 was obtained at an annealing temperature of 650 °C in N2 ambiance for 4 hours [2, 3]. Successful synthesis of single-phase CuCrO2 has been confirmed using XPS and XRD study. The resistivity of CuCrO2 was obtained as 0.652 Ω-cm, which is the lowest reported so far. The optical study denoted an average optical transmission of > 60% in the visible wavelength spectrum and a high optical bandgap of 3.2 eV. The antibacterial efficacy of different thickness of CuCrO2 thin films was tested against E. coli bacterial strain and compared against the efficacy of plain quartz in this research work. Results showed that with an increase in the thickness of CuCrO2 thin films, the efficacy against E. coli increases. The highest antibacterial efficacy of 78.07 % was shown by 2000 A° CuCrO2 thin film.[1] Chiu T-W, Yang Y-C, Yeh A-C, Wang Y-P, Feng Y-W. Antibacterial property of CuCrO2 thin films prepared by RF magnetron sputtering deposition. Vacuum. 2013;87:174-177.[2] Sundaresh S, Bharath AH, Sundaram KB. Effect of Annealing Temperature on Radio Frequency Sputtered p-Type Delafossite Copper Chromium Oxide (CuCrO2) Thin Films and Investigation of Diode Characteristics Forming Transparent pn-Heterojunction. Coatings2023.[3] Sundaresh S, Bharath AH, Sundaram KB. Effect of Cu2O Sputtering Power Variation on the Characteristics of Radio Frequency Sputtered p-Type Delafossite CuCrO2 Thin Films. Coatings2023.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Electron and hole injection barriers between silicon substrate and RF magnetron sputtered In2O3 : Er films

In2O3 : Er films have been synthesized on silicon substrates by RF magnetron sputter deposition. The currents through the synthesized metal/oxide/semiconductor (MOS) structures (Si/In2O3 : Er/In-contact) have been measured for n and p type conductivity silicon substrates and described within the model of majority carrier thermoemission through the barrier, with bias voltage correction to the silicon potential drop. The electron and hole injection barriers between the silicon substrate and the film have been found to be 0.14 and 0.3 eV, respectively, by measuring the temperature dependence of the forward current at a low sub-barrier bias. The resulting low hole injection barrier is accounted for by the presence of defect state density spreading from the valence band edge into the In2O3 : Er band gap to form a hole conduction channel. The presence of defect state density in the In2O3 : Er band gap is confirmed by photoluminescence data in the respective energy range 1.55–3.0 eV. The band structure of the Si/In2O3 : Er heterojunction has been analyzed. The energy gap between the In2O3 : Er conduction band electrons and the band gap conduction channel holes has been estimated to be 1.56 eV.

Study of Gallium-Doped Zinc Oxide Thin Films Processed by Atomic Layer Deposition and RF Magnetron Sputtering for Transparent Antenna Applications.

Gallium-doped zinc oxide (GZO) films were fabricated using RF magnetron sputtering and atomic layer deposition (ALD). The latter ones demonstrate higher electrical conductivities (up to 2700 S cm-1) and enhanced charge mobilities (18 cm2 V-1 s-1). The morphological analysis reveals differences mostly due to the very different nature of the deposition processes. The film deposited via ALD shows an increased transmittance in the visible range and a very small one in the infrared range that leads to a figure of merit of 0.009 Ω-1 (10 times higher than for the films deposited via sputtering). A benchmarking is made with an RF sputtered indium-doped tin oxide (ITO) film used conventionally in the industry. Another comparison between ZnO, Al:ZnO (AZO), and Ga:ZnO (GZO) films fabricated by ALD is presented, and the evolution of physical properties with doping is evidenced. Finally, we processed GZO thin films on a glass substrate into patterned transparent patch antennas to demonstrate an application case of short-range communication by means of the Bluetooth Low Energy (BLE) protocol. The GZO transparent antennas' performances are compared to a reference ITO antenna on a glass substrate and a conventional copper antenna on FR4 PCB. The results highlight the possibility to use the transparent GZO antenna for reliable short-range communication and the achievability of an antenna entirely processed by ALD.

Antireflective black coatings comprised of Ag–Fe–O thin films with high electrical resistivity

Black antireflective (AR) coatings with electric insulative properties are required to improve the visibility of touch panel displays in the turned-on state and their appearance in the turned-off state. In this study, multilayer black AR stacks comprised of black insulative Ag–Fe–O, high-n TiO2, and low-n SiOxNy were constructed by optical simulation and prepared using RF magnetron sputtering and pulsed laser deposition. For the stacking model with five layers, the calculations show an excellent low reflectance of below 0.15% over the whole visible range with a transmittance of 0.002%. A simulation of the three-layered model indicated that the average reflectance can be reduced from over 43% for a monolayer to 3% with a reasonable average transmittance of 15% for display applications. RF magnetron sputtering, an industrial friendly method, was used to prepare the black insulative Ag–Fe–O in the AR stack for the first time. The Ag–Fe–O thin films deposited at 200–300 °C show both a large and constant absorption coefficient over the whole visible range and an acceptable high sheet resistance. The black AR stack was comprised of the black insulative Ag–Fe–O prepared at 250 °C by RF magnetron sputtering. The observed reflectance is in good agreement with the simulated model. These results indicate the high potential of the black Ag–Fe–O films for use in AR black coatings in touch panel displays for a visually attractive turn-off appearance.

Fabrication of thin solid electrolytes containing a small volume of an Li3OCl-type antiperovskite phase by RF magnetron sputtering

RF magnetron sputter deposition was performed using an Li2O + LiCl powder target. The resulting solid electrolyte films were found to contain a small volume fraction of an Li3OCl-type antiperovskite phase.

Sputter Deposited Magnetostrictive Layers for SAW Magnetic Field Sensors.

For the best possible limit of detection of any thin film-based magnetic field sensor, the functional magnetic film properties are an essential parameter. For sensors based on magnetostrictive layers, the chemical composition, morphology and intrinsic stresses of the layer have to be controlled during film deposition to further control magnetic influences such as crystallographic effects, pinning effects and stress anisotropies. For the application in magnetic surface acoustic wave sensors, the magnetostrictive layers are deposited on rotated piezoelectric single crystal substrates. The thermomechanical properties of quartz can lead to undesirable layer stresses and associated magnetic anisotropies if the temperature increases during deposition. With this in mind, we compare amorphous, magnetostrictive FeCoSiB films prepared by RF and DC magnetron sputter deposition. The chemical, structural and magnetic properties determined by elastic recoil detection, X-ray diffraction, and magneto-optical magnetometry and magnetic domain analysis are correlated with the resulting surface acoustic wave sensor properties such as phase noise level and limit of detection. To confirm the material properties, SAW sensors with magnetostrictive layers deposited with RF and DC deposition have been prepared and characterized, showing comparable detection limits below 200 pT/Hz1/2 at 10 Hz. The main benefit of the DC deposition is achieving higher deposition rates while maintaining similar low substrate temperatures.

Optical Characterization of H-Free a-Si Layers Grown by rf-Magnetron Sputtering by Inverse Synthesis Using Matlab: Tauc–Lorentz–Urbach Parameterization

Several, nearly-1-µm-thick, pure, unhydrogenated amorphous-silicon (a-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the normal-incidence transmission of such a samples and on the adoption of the inverse-synthesis method, by using a devised Matlab GUI environment. The so-far existing limiting value of the thickness-non-uniformity parameter, Δd, when optically characterizing wedge-shaped layers, has been suppressed with the introduction of the appropriate corrections in the expression of transmittance. The optical responses of the H-free RFMS-a-Si thin films investigated, were successfully parameterized using a single, Kramers–Krönig (KK)-consistent, Tauc–Lorentz oscillator model, with the inclusion in the model of the Urbach tail (TLUC), in the present case of non-hydrogenated a-Si films. We have also employed the Wemple–DiDomenico (WDD) single-oscillator model to calculate the two WDD dispersion parameters, dispersion energy, Ed, and oscillator energy, Eso. The amorphous-to-crystalline mass-density ratio in the expression for Ed suggested by Wemple and DiDomenico is the key factor in understanding the refractive index behavior of the a-Si layers under study. The value of the porosity for the specific rf-magnetron sputtering deposition conditions employed in this work, with an Ar-pressure of ~4.4 Pa, is found to be approximately 21%. Additionally, it must be concluded that the adopted TLUC parameterization is highly accurate for the evaluation of the UV/visible/NIR transmittance measurements, on the H-free a-Si investigated. Finally, the performed experiments are needed to have more confidence of quick and accurate optical-characterizations techniques, in order to find new applications of a-Si layers in optics and optoelectronics.

Competing tunneling conduction mechanisms in oxygen deficient Hf0.5Zr0.5O2

The direct control of the tunneling current as a function of electric polarization in ferroelectric tunnel junctions has recently attracted noticeable attention through the availability of the CMOS compatible ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2). While a lot of progress has been made in the understanding of ferroelectric tunnel junctions, the control and optimization of the volume fraction of the polar orthorhombic phase are still in its infancy and raise the question whether all observed resistive switching events are necessarily associated with polarization reversal. Trap-assisted tunneling is also able to modulate the current density through a field-induced variation of the oxygen vacancy density across the tunnel junction. The amplitude of the effect should depend on the pre-existing density of oxygen vacancies introduced during the fabrication. Here, by controlling the oxygen partial pressure during the RF magnetron sputtering deposition of the non-polar monoclinic phase of Hf0.5Zr0.5O2 thin films of approximately 3 nm, we demonstrate tuning of its transport mechanism due to the formation of oxygen vacancies. We show that two mechanisms dominate the current transport depending on the average distance between traps. For large oxygen content in the Hf0.5Zr0.5O2 thin film, direct tunneling (DT) is the dominant transport mechanism, while the electrical conductivity in the oxide can be described by the phonon-assisted tunneling between traps (PATTs) for the oxygen deficient Hf0.5Zr0.5O2 thin film. We derive a critical inter-trap distance and a critical thickness value that explains the transition from DT to PATT mechanism in Hf0.5Zr0.5O2 thin films.

In Situ X-ray Measurements to Follow the Crystallization of BaTiO3 Thin Films during RF-Magnetron Sputter Deposition

Here, we report on adding an important dimension to the fundamental understanding of the evolution of the thin film micro structure evolution. Thin films have gained broad attention in their applications for electro-optical devices, solar-cell technology, as well storage devices. Deep insights into fundamental functionalities can be realized via studying crystallization microstructure and formation processes of polycrystalline or epitaxial thin films. Besides the fundamental aspects, it is industrially important to minimize cost which intrinsically requires lower energy consumption at increasing performance which requires new approaches to thin film growth in general. Here, we present a state of the art sputtering technique that allows for time-resolved in situ studies of such thin film growth with a special focus on the crystallization via small angle scattering and X-ray diffraction. Focusing on the crystallization of the example material of BaTiO3, we demonstrate how a prototypical thin film forms and how detailed all phases of the structural evolution can be identified. The technique is shaped to enable a versatile approach for understanding and ultimately controlling a broad variety of growth processes, and more over it demonstrate how to in situ investigate the influence of single high temperature sputtering parameters on the film quality. It is shown that the whole evolution from nucleation, diffusion adsorption and grain growth to the crystallization can be observed during all stages of thin film growth as well as quantitatively as qualitatively. This can be used to optimize thin-film quality, efficiency and performance.

Sputter deposition and structural characterization of BiCuSeO epitaxial films on (001)/(110) SrTiO3 substrates

BiCuSeO epitaxial films were grown on (001)/(110) SrTtO3 (STO) substrates by RF magnetron sputter deposition. A sputter power over 40 W was needed to transfer target composition to substrate, leading to a fast deposition rate over 17.5 nm/min. The films grown on (001) STO at 100−150 °C showed a dominant [110] orientation instead of [001], which was what expected in view of the smallest lattice misfit and perfect match in symmetry between (001) BiCuSeO and (001) STO. This was caused by slow film growth along c-axis that could not follow the fast deposition rate, whereas a fair lattice misfit, combined with strong bonding along directions vertical to c-axis, entails the growth along [110] at low temperature. Preferred [001] orientation only occurred at high temperature (>350 °C) when the kinetic process was accelerated. However, high temperature and the fast deposition rate imposed by the required sputter power led to the growth of multiple orientations. Epitaxial growth of (001) BiCuSeO film on (001) STO was achieved after the deposition rate was reduced to 0.67 nm/min by a periodically opening and closing shutter installed in front of sputter target. Interestingly, (001) BiCuSeO epitaxial film could be grown on (110) STO at a fast deposition rate of 15 nm/min. Such films on (110) STO had to be grown at higher temperature (∼500 °C). In contrast to (001) STO, (110) STO did not had good lattice match with any BiCuSeO orientation other than [001], so fast kinetic process only promoted the growth of single [001] orientation.

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al2O3, Er2O3 and Y2O3, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y2O3 layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y2O3 layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y2O3 thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y2O3 thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.

Enhanced Magneto-Optic Properties in Sputtered Bi- Containing Ferrite Garnet Thin Films Fabricated Using Oxygen Plasma Treatment and Metal Oxide Protective Layers.

Magneto-optic (MO) imaging and sensing are at present the most developed practical applications of thin-film MO garnet materials. However, in order to improve sensitivity for a range of established and forward-looking applications, the technology and component-related advances are still necessary. These improvements are expected to originate from new material system development. We propose a set of technological modifications for the RF-magnetron sputtering deposition and crystallization annealing of magneto-optic bismuth-substituted iron-garnet films and investigate the improved material properties. Results show that standard crystallization annealing for the as-deposited ultrathin (sputtered 10 nm thick, amorphous phase) films resulted in more than a factor of two loss in the magneto-optical activity of the films in the visible spectral region, compared to the liquid-phase grown epitaxial films. Results also show that an additional 10 nm-thick metal-oxide (Bi2O3) protective layer above the amorphous film results in ~2.7 times increase in the magneto-optical quality of crystallized iron-garnet films. On the other hand, the effects of post-deposition oxygen (O2) plasma treatment on the magneto-optical (MO) properties of Bismuth substituted iron garnet thin film materials are investigated. Results show that in the visible part of the electromagnetic spectrum (at 532 nm), the O2 treated (up to 3 min) garnet films retain higher specific Faraday rotation and figures of merit compared to non-treated garnet films.

Development of highly reliable BiFeO3/HfO2/Silicon gate stacks for ferroelectric non-volatile memories in IoT applications

We have investigated the structural, electrical, and ferroelectric properties of metal–ferroelectric-high-k-silicon capacitors with BiFeO3 ferroelectric films deposited on the HfO2/Si substrate. BiFeO3, HfO2 films, and their stack were deposited on the silicon substrate using RF magnetron sputtering and plasma-enhanced atomic layer deposition (PEALD). Film crystal orientation, refractive index, and absorption constant parameters were extracted from X-ray diffraction and ellipsometric analysis. Electrical characterization of metal/ferroelectric/metal (MFM), metal/ferroelectric/silicon (MFS), metal/dielectric/silicon (MIS), and metal/ferroelectric/insulator/silicon (MFIS) capacitor structures provide memory window, leakage current density, hysteresis, fatigue, and data retention time. The metal/ferroelectric/silicon structure exhibits clockwise capacitance–voltage characteristics with the memory window of 5.04 V for the bias voltage of ± 10 V. The electrical and ferroelectric characteristics of MFIS structures were studied for different thicknesses of HfO2 layer, which shows that the introduction of high-k dielectric film between ferroelectric and silicon improves the interface quality. The memory window of the MFIS structure was found to significantly increase to 9.65 V with the introduction of a 10 nm HfO2 layer between the ferroelectric layer and the silicon substrate. Two-order reduction in the leakage current density was also observed in the MF(200 nm)I(10 nm)S structure as compared to the MF(200 nm)S structure. The fabricated MF(200 nm)I(10 nm)S gate stack shows fatigue resistance for read/write operations greater than 1012 cycles and data retention time for greater than 104 s. To the best of author’s knowledge, this is the first investigation to integrate pure BiFeO3 on PEALD-HfO2 dielectric for the gate stack of ferroelectric field effect transistors.

A novel TiC-TiN based spectrally selective absorbing coating: Structure, optical properties and thermal stability

A novel TiC-TiN/Al2O3 tandem solar selective absorbing coating was successfully deposited on Si (1 0 0) and stainless steel (SS) substrates by reactive RF magnetron sputtering deposition. The spectral characteristics, microstructure, thermal stability and solar-thermal conversion efficiency of the coating before and after a long annealing in vacuum were investigated systematically. The optical constants of the coating are measured by an Ultraviolet–visible-near-infrared (UV/Vis/NIR) spectrometer, and the chemical composition analysis, structure information and surface morphology are investigated using XRD, XPS and FESEM. An excellent absorptance (α = 0.92) and a low emittance (ε = 0.11) at 82 °C are obtained by the as-prepared coatings. After annealed at 500 °C for 100 h in vacuum, there is no significant change in micromorphology and optical properties of the coating, which produces a good solar-thermal conversion efficiency. These results indicate that it can be applied as a potential coating material to a high temperature concentrated solar power (CSP) system.

The role of morphology in all-dielectric SERS: A comparison between conformal (T-rex) and non conformal TiO2 shells

All-dielectric optical nanoantennas and resonators are attracting an ever increasing interest for enhanced Raman spectroscopy. These systems can take advantage of many factors that concur to determine their Raman response, including the type of material, refractive index contrast between interfaces, size, shape, roughness and geometrical configuration. However, the relative impact of each one of those terms on the Raman enhancement is still unclear.Here we report the Raman characterization of SiO2@TiO2 semishell microspheres obtained by rf-magnetron sputtering deposition of a TiO2 thin layer on SiO2 cores. The samples were able to significantly amplify Raman scattering in comparison to planar counterparts, however the overall enhancement was very limited with reference to that observed in conformal, smooth and compact TiO2 shell layers obtained by atomic layer deposition. These results demonstrated that geometry is a key factor to maximize the Raman response of these systems and, in general, it is more important than other parameters, such as the surface roughness or even refractive index of the shell layer, which are usually considered crucial for achieving Raman enhancement.