Characterizing the stress and electrical properties of superconducting molybdenum films

In the process of minimizing stress in sputtered Molybdenum (Mo) films for fabricating transition-edge sensor (TES) devices, we have investigated correlations between the stress and film deposition parameters. At a fixed sputtering power, the tensile stress of our film samples decreases toward both low and high ends of Ar pressure, suggestive of two physical mechanisms at work: an “atomic peening” effect at low Ar pressure and the development of voids at high Ar pressure. We have also carried out correlative studies of the stress and electrical properties (including superconducting critical temperature and residual resistivity) of the film samples, and found that the results are complex. We have made extensive comparisons with the published results, and attempted to explain the discrepancies in terms of film deposition techniques, sample preparation and treatment, and dynamical ranges of measurements. It is fairly clear that the microscopic properties, including porosity and disorder, of Mo films may have significant impact on the correlations.

Ultra-high thermal stability of sputtering reconstructed Cu-based catalysts

The rational design of high-temperature endurable Cu-based catalysts is a long-sought goal since they are suffering from significant sintering. Establishing a barrier on the metal surface by the classical strong metal-support interaction (SMSI) is supposed to be an efficient way for immobilizing nanoparticles. However, Cu particles were regarded as impossible to form classical SMSI before irreversible sintering. Herein, we fabricate the SMSI between sputtering reconstructed Cu and flame-made LaTiO2 support at a mild reduction temperature, exhibiting an ultra-stable performance for more than 500 h at 600 °C. The sintering of Cu nanoparticles is effectively suppressed even at as high as 800 °C. The critical factors to success are reconstructing the electronic structure of Cu atoms in parallel with enhancing the support reducibility, which makes them adjustable by sputtering power or decorated supports. This strategy will extremely broaden the applications of Cu-based catalysts at more severe conditions and shed light on establishing SMSI on other metals.

Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response S11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.

A Study on the Characteristic and Antibacterial Activity of Ti3Ox Thin Films

A pure Ti target in Ar/O2 gas mixture was used to synthesize Ti3Ox thin film on a glass substrate by Reactive High-Power Impulse Magnetron Sputtering (HiPIMS) under different sputtering power (2 and 2.5 kW). The influence of HiPIMS parameters on thin films’ structural, morphological, chemical composition, optical and photocatalytic, and antibacterial properties was investigated. In this study, Ti3Ox thin films can be synthesized using the HiPIMS method without the post-annealing process. Two co-existence phases (hexagonal Ti3O and base-centered monoclinic Ti3O5 phases) existed on the Ti3Ox films. It is found that the peak intensity of (006) Ti3O hexagonal slightly increased as the sputtering power increased from 2 to 2.5 kW. The Ti3Ox thin-film bandgap values were 3.36 and 3.50 eV for 2 and 2.5 kW, respectively. The Ti3Ox films deposited at 2.5 kW showed good photocatalytic activity under UV light irradiation, with a higher methylene blue dye degradation rate than TiO2 thin films. The antibacterial study on Ti3Ox thin films exhibited a high inhibition percentage against E. coli and S. aureus. This study demonstrates that Ti3Ox thin films can promote high photocatalytic and antibacterial activity.

High Seebeck coefficient in PVD-WS2 film with grain size enlargement

A high Seebeck coefficient of 1.17 × 103 μV/K was achieved using an on-chip thermoelectric device for a WS2 atomic-layer film, which was synthesized by ultra-high vacuum RF-magnetron sputtering as a function of sputtering power. A layered structure in parallel to SiO2/Si substrate was confirmed from the transmission electron microscopy and X-ray diffraction spectra. The grain size and peak intensities of the Raman spectra increase with a decrease in the sputtering power. Accordingly, the resistivity and activation energy also increase. This WS2 film can be used in thermoelectric generators, such as energy harvesters in LSIs and wearable devices.

Room-Temperature Formation of Hard BCx Films by Low Power Magnetron Sputtering

Boron carbide is one of the most important non-metallic materials. Amorphous BCx films were synthesized at room temperature by single- and dual-target magnetron sputtering processes. A B4C target and C target were operated using an RF signal and a DC signal, respectively. The effect of using single- and dual-target deposition and process parameters on the chemical bonding and composition of the films as well as their functional properties were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray energy dispersive analysis, X-ray diffraction, ellipsometry, and spectrophotometry. It was found that the film properties depend on the sputtering power and the used targets. EDX data show that the composition of the samples varied from B2C to practically BC2 in the case of using an additional C target. According to the XPS data, it corresponds to the different chemical states of the boron atom. A nanoindentation study showed that the film with a composition close to B2C deposited with the highest B4C target power reached a hardness of 25 GPa and Young’s modulus of 230 GPa. The optical properties of the films also depend on the composition, so the band gap (Eg) of the BCx film varied in the range of 2.1–2.8 eV, while the Eg of the carbon-rich films decreased to 1.1 eV.

SURFACE-ENHANCED RAMAN SCATTERING ACTIVITY OF PLASMONIC Ag–Ti NANOISLAND FILMS

Bimetallic nanostructure of noble metals is an alternative material that can provide the tenability of plasmonic performance. In this study, the plasmonic silver–titanium nanoisland (Ag–Ti NI) films deposited on a silicon wafer and glass slide substrates were prepared by magnetron co-sputtering of high-purity Ag target (99.99%) operated at 100 W-DC source, and Ti target (99.99%) operated at 50–250 W-DC pulsed source. The surface morphologies of the prepared films revealed a noncontinuous island Ag–Ti according to the formation of thin film growth based on the Volmer–Weber model. An increase in the sputtering power of the Ti target caused an evident increase in the Ag–Ti NIs diameter. The localized surface plasmon resonance (LSPR) was evaluated by UV–Vis–NIR spectrophotometry. The LSPR peak shift disappears with an increase of the sputtering power of the Ti target.In addition, the results confirmed that the surface-enhanced Raman scattering (SERS) activity of the bimetallic Ag–Ti NIs significantly improved in performance and stability, which is promising for the application in analytical chemistry.

In Situ Sputtering Silver Induction Electrode for Stable and Stretchable Triboelectric Nanogenerators

Triboelectric nanogenerators (TENG) can convert mechanical energy into electricity and exhibit unique advantages in the field of low-frequency and discrete energy harvesting. However, the interfacial state and stability between the triboelectric layer and electrode layer influence the output and applications of TENG. Herein, an in situ sputtering Ag process for fabricating induction electrodes is proposed to match with TENG. The sputtering Ag process is optimized by a variety of parameters, such as sputtering power, single-cycle time, number of cycles, cycle interval, and vacuum degree. In addition, the chemical state of Ag as a function of air placement is investigated, showing the sputtered Ag has excellent conductivity and stability. Moreover, four kinds of polymers are selected for fabricating TENGs based on the sputtered Ag induction electrodes, i.e., nylon 66, polyimide (PI), fluorinated ethylene propylene (FEP), and polydimethylsiloxane (PDMS), which shows great applicability. Considering the demand of flexible power suppliers, the sputtered Ag is integrated with a PDMS substrate, and shows good adhesion, flexibility, and ductility after severe deformation of the PDMS. Finally, the developed induction electrode processing technology is used in flexible TENG and shows great prospects in self-powered electronics for practical applications.