RF Sputtering Method Research Articles

Ferroelectric, magnetoelectric and photoelectric properties of BiFeO3 /LaNiO3 heterostructure

BiFeO3/LaNiO3 (BFO/LNO) heterostructure was fabricated on quartz substrate via RF sputtering method. The microstructure and surface morphology of the BFO/LNO heterostructure was demonstrated. BFO layer shows good ferroelectric and weak ferromagnetic characters at room temperature. The dielectric constants of the heterostructure under an applied magnetic field 1.2T and zero field are both decreased with increasing frequency at room temperature and the dielectric constant under the applied magnetic field is larger, which is attributed to the coupling between the electric and magnetic dipoles, and further demonstrated in the framework of the Ginzburg-Landau theory for second phase transition. Additionally, the photoconductivity of the heterostructure under blue-laser illumination was observed, and the photoconductivity increase with the enhanced power of the blue-laser.

Enhanced La0.8Sr0.2CrO3/Pt thin film thermocouple with Al2O3 coating layer for high temperature sensing

Thin film thermocouples (TFTCs) as a kind of passive sensor are used to measure in-situ high temperature and integrated surface devices. In this work, La0.8Sr0.2CrO3/Pt TFTCs were successfully fabricated by RF sputtering method. When the TFTCs were tested below 900 °C for multi-cycles, they showed an excellent stability and reproducibility. By comparing with the thermal responses of uncoated and coated with Al2O3 protection layer, the coated TFTC had a higher measurement temperature than uncoated TFTC, and good durability. The failure of TFTCs was mainly attributed to the volatilization of Pt and 0.2LSCO thin films at high temperature, while 0.2LSCO had a better thermal stability than Pt. The La0.8Sr0.2CrO3/Pt TFTC coated with Al2O3 protection layer may provide a new candidate thermal sensor for high temperature sensing in air.

Charge/Discharge Mechanism of Cu/CuF2 Cathode in All-Solid-State Fluoride Battery

Introduction The all-solid-state fluoride battery, which uses fluoride anion as an ion carrier, is the promising high energy density storage system because multi electron reaction can be used between metal and metal fluoride electrodes [1]. Although CuF2 exhibits as a reversible charging/discharging capacity as the cathode for the fluoride battery [1, 2], the reaction rate is slow and the reaction mechanism has been poorly understood. Herein we prepared for the metal thin-film all-solid-state fluoride battery system using Cu cathode and investigated the phase transition and/or charge compensation mechanism by the electrochemical potential step measurement and the X-ray absorption spectroscopy (XAS). Experimental The thin-film all-solid-state fluoride battery cell was prepared by a RF sputtering method. Cu and Pb thin-films were deposited on LaF3 solid electrolyte substrate and used as the working and reference electrodes, respectively. Pt was deposited on the LaF3 substrate as the counter electrode, in which deposition/dessolution reactions of La occur. The galvanostatic charge/discharge cycling was performed at a rate of 1C (850 mA/g) at 150, 60, and 25°C. These battery assembly and the measurements were conducted in an inert atmosphere. The XAS was carried out at a beam-line of BL37XU at SPring-8 in Japan. The absorption spectra for the Cu K-edge were collected with partial fluorescence mode. Results and Discussion The discharge capacity and average discharge potential at 150°C are 670 mAh/g and 0.664 V vs. Pb/PbF2, respectively. The consequent gravimetric energy density with an assumption of 3 V configuration is 2010 Wh/kg. As the operating temperature decreased, the irreversible capacity and the polarization increased. The X-ray absorption spectra exhibited an isosbestic point upon both the charge and discharge processes, indicating that the electrochemical redox of Cu/CuF2 proceeds via two-phase reaction. The obtained spectra were fitted with Cu and CuF2 spectra in X-ray absorption near edge region. The ratio of Cu and CuF2 from the fitting is consistent with the one from the electrochemically reacted values. Therefore, the Cu/CuF2 fluorinated and defluorinated reaction proceeds via the two phases consisted of Cu and CuF2 and the side reaction did not occur. Our finding provides the potential of the fluoride batteries for the future energy storage system. To investigate the phase formation kinetics of CuF2, we performed the KJMA analysis. The both value of the Avrami exponent n estimated by electrochemically passed current and XRD are approximately 1 which indicates the phase transition is one-dimensional phase-boundary movement.

Correlation Between 3-D Surface Topography and Different Deposition Times of Engineered Ni@a-C:H Thin Films

This study is aimed at analyzing the surface micromorphology of amorphous hydrogenated carbon layers containing nickel nanoparticles (Ni-NPs@a-C:H) within their structure, which were sputtered by co-deposition of RF-Sputtering and RF-PECVD method from acetylene gas and nickel target on glass substrates. Prepared films were then used as research material following their deposition time at three different times of 3, 7 and 13 minutes. Series of height samples were taken with the help of atomic force microscopy (AFM) operating in a non-contact mode and examined in order to determine their surface engineering characteristics. The analysis of 3-D surface texture helps to understand their essential characteristics and their implications as well as graphicalmodels and their implementation in computer simulation.

Highly photostable Zn-doped TiO2 thin film nanostructures for enhanced dye degradation deposited by sputtering method

Zn-doped TiO2 thin films were deposited on glass substrates using the RF sputtering method with various Zn-dopant concentrations at a substrate temperature of 300 °C. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), UV–Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to analyze the crystal structure, surface morphology, transmittance, elemental composition, oxidation states, and degradation of the prepared thin films. The anatase phase of TiO2 was observed in the coated thin films. A maximum transmittance of ~77% and the lowest band gap of ~3.12 eV was achieved. The roughness of films increased with the Zn concentration, and a roughness of ~15.23 nm was observed. Photocatalytic degradation activity was tested using phenol red dye, and a maximum dye degradation of ~58% was achieved. In addition, no structural or surface chemical changes were seen in the thin film used for the photocatalytic activity, even after five cycles, which indicates that the films exhibit high photostability.

Dielectric properties, electrical modulus and current transport mechanisms of Au/ZnO/n-Si structures

Au/ZnO/n-Si (MIS) structures were fabricated by using the RF sputtering method and their complex dielectric constant (ε*=ε’-jε’’), electric modulus (M*=M′+ jM’’) and electrical conductivity (σ = σdc+σac) values were investigated as a function of frequency (0.7 kHz-1 MHz) and voltage (−6 – (+6 V)) by capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements to get more information on the conduction mechanisms and formation of barrier height between Au and n-Si. The lnσ-Lnf plots have two different regions corresponding to low-intermediate and high frequencies. Such behavior of lnσ−lnf plots shows that the existence of two different conduction mechanisms (CMs) at low-intermediate and high frequencies. Moreover, the reverse bias saturation current (Io), ideality factor (n), barrier height (ΦBo) were determined from the forward bias I-V data and they were found as a strong function of temperature. The value of n especially at low temperature is considerably higher than unity. The values of Φ̅B0 and standard deviation(σs) were found from the intercept and slope of ΦBo-q/2kT plots as 0.551 eV and 0.075 V for the region I (80–220 K) and 1.126 eV and 0.053 V for the region II (220–400 K), respectively. The values of Φ̅Bo and effective Richardson constant (A*) were found from slope and intercept of activation energy plots as 0.564 eV and 101.084 Acm−2 K−2 for the region I and 1.136 eV and 41.87 Acm−2 K−2 for the region II, respectively. These results confirm that the current-voltage-temperature (I-V-T) characteristics of the fabricated Au/ZnO/n-Si SBDs can satisfactorily be explained on the basis of TE theory with double GD of the BHs.

Enhanced Soft Magnetic Properties of [NiFe/Ta]<italic>n</italic> Laminated Films for Flux Amplification in Magnetic Sensors

The soft magnetic properties of single-layer NiFe and multilayer [NiFe/Ta] n thin films were investigated and presented in this paper. The NiFe films were prepared by RF sputtering method on thermally oxidized Si substrates at room temperature. The thickness dependence of coercivity ( $H_{c}$ ) of single-layer NiFe was revealed by the fact that the $H_{c}$ increased with the thicker films of 25, 50, 100, and 200 nm. In order to enhance the softness of the NiFe films, the non-magnetic spacer tantalum (1 nm) was introduced in the laminated structures leading to a decrease in $H_{c}$ with increase in the number of separated layers ( $n$ ). Notably, with the tantalum spacer of 1 nm at $n = 3$ , $H_{c}$ decreased dramatically from 35 down to 0.3 Oe. A minimum $H_{c}$ of 0.14 Oe was achieved at $n = 3$ and the Ta thickness of 3 nm. A possible application for the designing flux concentrator (FC) in magnetic sensor was simulated using the finite-element method. The obtained favorable results of the multilayer structures envisaged that the microfabrication of laminated [NiFe/Ta] n films would be appropriately used in magnetic sensor applications, such as the flux guide films, FC parts, and the integrated core of fluxgate sensors.

Granular-composite-like electrical transport properties of polycrystalline cubic TaNx thin films prepared by rf sputtering method

We have systematically investigated the electrical transport properties of polycrystalline TaNx (0.83 ≲ x ≲1.32) films with rocksalt structure from 300 down to 2 K. It is found that the conductivity varies linearly with lnT from ∼6 to ∼30 K, which does not originate from the conventional two dimensional weak-localization or electron-electron interaction effects, but can be well explained by the intergrain Coulomb effect which was theoretically proposed in the granular metals. While the fluctuation-induced tunneling conduction process dominates the temperature behaviors of the conductivities (resistivities) above ∼60 K. Normal state to superconductive state transition is observed in the x ≳1.04 films in low temperature regime. The superconductivity can still be retained at a field of 9 T. The upper critical field increases linearly with decreasing temperature in the vicinity of the superconductive transition temperature, which is the typical feature of granular superconductors or dirty type-II superconductors. The granular-composite-like electrical transport properties of the polycrystalline TaNx films are related to their microstructure, in which the TaNx grains with high conductivity are separated by the poorly conductive amorphous transition layers (grain boundaries).

Magnetic and electronic structures of Co ion implanted CeO2 thin films

Present study reports an enhancement of room-temperature ferromagnetism by Co ion implantations in CeO2 thin films and these Co ions exist in divalent state. These films were deposited on Si (111) substrates using RF sputtering method. The X-ray diffraction and Raman measurements confirmed the FCC structure corresponding to phase of CeO2 in these films. The Raman studies also show the presence of defects mainly of oxygen vacancies. The Rutherford backscattering spectrometry shows the thickness of the films as 300 nm and also the presence of Co ions in the implanted films. From the Atomic Force Microscopy, it is found that the surface roughness of the films is modified after Co ion implantation. While the magnetic measurements exhibit an increase in the saturation magnetization from ∼7 to 21 emu/cm3 after Co ion implantation at the fluence of 6 × 1016 ions/cm2, the coercivity value is found to decrease. The Ce ions exhibit both trivalent and tetravalent states as confirmed by X-ray photoelectron spectroscopy measurements. The enhancement in the ferromagnetic properties of these films after Co ion implantation is directly correlated with the magnetic Co ions, oxygen vacancies and the amount of Ce3+ ions. The oxygen vacancies based F-Center exchange model is discussed to understand the enhancement of ferromagnetism in these films.

Selector-Less Graphite Memristor: Intrinsic Nonlinear Behavior with Gap Design Method for Array Applications

Resistive random access memory (RRAM) using various binary metal oxide structures have attracted attentions since the current nonvolatile memory (NVM) has been approaching the scaling limit. RRAMs has excellent scalability, high speed and low power operation ability which is desired for current hardware needs. Meanwhile, selector devices are essential to suppress the sneak path issue which causes reading errors and hinders the implementation of RRAM in high-density cross-bar array architecture. However, additional selector device as commonly proposed one selector-one resistor (1S-1R) design, rises the process complexity and cost. In this work, selectorless graphite-based memristor devices have been demonstrated by utilizing the nonlinear (NL) resistive switching (RS) characteristics with gap design method for RRAM array applications. The starting substrates are heavily-doped N+ Si wafers, and titanium nitride of 200 nm thickness was deposited on N+ Si substrate as bottom electrode. Then, 5 nm of graphite and 7 nm of HfOx were deposited as RS dielectric layers for bilayer (HfOx/C) structures by RF sputtering method. Pt (165nm) was deposited as top electrodes for RRAM devices (not showed here). Fig. 1 shows bipolar I-V characteristics during DC voltage sweeps for single-layer HfOx and HfOx/C stacked devices. Both SET and RESET voltages are around 1 V/-1 V in single-layer HfOx devices as the bilayer devices possibly owing to inserting a HfOx stack layer, which has higher oxygen concentration and potentially be beneficial for low voltage operating applications. Comparing the bilayer structure to the single-layer HfOx structure, where dI/dV increases indicating that there was significantly increased resistance at low voltage region for sneak path current suppression. The graphite-stacked memristor has been confirmed with the nonlinearity than HfOx single layer structure and was proposed as a solution for sneak path issue in crossbar array applications. Nonlinearity (NL) is defined as the ratio of the current at full read voltage (i.e. -0.6 V) to the current at 1/3 read voltage (-0.2 V). The higher nonlinearity, the better ability is to avoid the sneak current interference. Fig. 2 shows the NL for graphite-stacked RRAM with varied graphite thickness i.e. 0, 3, 5, 8, 10 nm (30 DC cycles). The NL is increasing with the portions of graphite thickness in the bilayer stacks. The single layer and bilayer devices with narrow SET/RESET voltage variation and have been found to exhibit low operating voltage (~1 V), which are independent on the graphite thickness in the bilayer structures (Fig. 3). Fig.4 shows the HRS and LRS of all graphite memristors as compared to HfOx layer device. The memory window i.e. ratio of ILRS /IHRS enlarges in the graphite memristors, which is suggested to the graphite oxide (GO) formation caused HRS current reduction. The NL characteristics in ILRS of all the devices under different SET compliance current limits (CCL) as showed in Fig. 5. With a thin graphite layer (5 nm) on the bottom of HfOx (7 nm) layer, the NL is ~3x of the single-layer HfOx layer devices. This makes graphite-stacked bilayer devices a potential candidate for 1R selectorless RRAMs. The NL of graphite-stacked RRAM can be optimized by adjusting SET CCL, as called “gap design method” for memristors. To eliminate device-to-device (D2D) variation in RRAM, three graphite-stacked memristors in distanced region have been demonstrated with the gap migration with increasing the SET CCL. Also, the RESET current is critical for overall switching power in RRAM applications, is ~1 mA and has been found to be independent of the thickness ratio of stacks (not showed here). Fig. 6 as the schematic of single layer and graphite-stacked structures shows the graphite memristor is the candidate of selectorless RRRAM since the formation of GO as the low-k material in gap modulation. The graphite layer has been confirmed by the XRD pattern in graphite (400) phase direction with resistivity of 0.2643kΩ as the switching layer in stacks, not as the electrode. In this study, build-in NL characteristics have been realized for the graphite selectorless memristors without an diode/selector. The graphite-based memristor are promising for high-density, low-power, selectorless RRAM array applications. The formation of GO with low dielectric constant of 4.3 is beneficial for high NL. The highly NL characteristics observed in graphite-based bilayer devices are desirable in suppressing sneak-path currents in crossbar arrays. Figure 1

(Invited) Fabrication and Characterization of β-Ga2O3 Heterojunction Rectifiers

Copper Oxide and Nickel Oxide were deposited and investigated for their electrical and optical properties as a wide bandgap p-type oxide semiconductor. Heterojunctions of CuxOy/β-Ga2O3 were fabricated with a rectification ratio of 2.5x104 at ±2 V. NiO films were deposited using both RF sputtering and atomic layer deposition methods, resulting in rectifying heterojunctions in both cases. A 3.6 eV bandgap was measured upon a 500 °C post-deposition anneal for the sputtered films.

The effect of initial pressure on growth of FeNPs in amorphous carbon films

Iron nanoparticles in amorphous hydrogenated carbon films (FeNPs@a-C:H) were prepared with RF-sputtering and RFPECVD methods by acetylene gas and Fe target. In this paper, deposition and sputtering process were carried out under influence of different initial pressure gas. The morphology and roughness of surface of samples were studied by AFM technique and also TEM images show the exact size of FeNPs and encapsulated FeNPs@a-C:H. The localized surface plasmon resonance peak (LSPR) of FeNPs was studied using UV–vis absorption spectrum. The results show that the intensity and position of LSPR peak are increased by increasing initial pressure. Also, direct energy gap of samples obtained by Tauc law is decreased with respect to increasing initial pressure.

Influence of deposition pressure and power on characteristics of RF-Sputtered Mo films and investigation of sodium diffusion in the films

Mo films deposited by DC sputtering are widely used as back contact in CIGS and CZTS based thin film solar cells. However, there have been only a few studies on the deposition of Mo films by RF sputtering method. In this context, Mo films on SLG substrates were prepared as a function of deposition pressure and power by using RF magnetron sputtering method to contribute to this shortcoming. Mo films were deposited at 250 °C substrate temperature by using 20, 15, 10 mTorr Ar pressures at 120 W RF power and 10 mTorr Ar pressure at 100 W RF power. Structural, morphological and reflectivity properties of RF-sputtered Mo films were clarified by XRD, AFM, FE-SEM and UV–Vis measurements. In addition, due to sodium incorporation from SLG substrate to the absorber layer through Mo back contact layer is so essential in terms of improving the conversion efficiency values of CIGS and CZTS thin film solar cell devices, the effects of Na diffusion in the films were analyzed with SIMS depth profile. The electrical properties of the films such as mobility, carrier density and resistivity were determined by Hall Effect measurements. It was found that Mo films prepared at 120 W, 10 mtorr and 250 °C substrate temperature and then annealed at 500 °C for 30 min, had resistivity as low as 10−5 Ω cm, as well as higher amount of Na incorporation than other films.

RFスパッタリング法によるGaAs(111)基板上へのGaN薄膜成長に関する研究

RFスパッタリング法によるGaAs(111)基板上へのGaN薄膜成長に関する研究

RF sputtered CdS films as independent or buffered electron transport layer for efficient planar perovskite solar cell

Metal sulfide has the potential to take the place of high temperature sintered TiO2 as electron transportation layer for perovskite solar cell (PSC) with improved light stability and suppressed hysteresis. In this work, CdS films were used as independent or buffered electron transport layer for planar perovskite solar cell by a low-temperature RF sputtering method for the first time. The effects of surface roughness and optical absorption of CdS films on the photovoltaic performance of PSCs were discussed. The PSC with sputtered CdS film shows a higher open-circuit voltage (Voc) and efficiency of 13.17% than high temperature sintered TiO2 ETL (12.71%). Moreover, a RF sputtered CdS buffer layer between TiO2 and perovskite could tune the conduction band edge of TiO2 and perovskite and passivating the surface defects. Time resolved photoluminescence results indicate the RF sputtered CdS film buffer layer could accelerate charge transportation and a higher conversion efficiency over 16% has thus been achieved, with enhanced air stability and minimized hysteresis. These findings offer new research directions for low-temperature sputtered metal sulfide film as a promising electron transport material for stable and high efficient planar perovskite solar cell.

Vertical growth of MoS2 layers by sputtering method for efficient photoelectric application

The 2D layers of MoS2 were deposited at RT, 200 °C and 400 °C over p-Si substrates using RF sputtering method. When the deposition temperature is increased beyond 200 °C, the MoS2 layers were grown in vertical direction. XRD studies revealed that the prominent peak is shifted from 2θ = 24° to 13.5° and become narrow while increasing the temperature to 400 °C. The average absorption of 53.68% was exhibited by the sample deposited at 400 °C whereas it was reduced to 28.47% for the sample prepared at 200 °C. When the MoS2/p-Si photodetector was exposed to the red color wavelength, the high photocurrent of 130 μA was produced even at zero bias. The response and recovery times were measured as 38.78 μs and 43.07 μs respectively for λ ≈ 455 nm. The detectivity was found to be in the range of 109–1010 Jones. The proposed MoS2 based photodetector is more beneficial in terms of quick transport of photogenerated carriers and fast response. The growth control and large-scale production of 2D materials would induce the enhanced photoelectric performances and practical device applications.

Synthesis of Ag metallic nanoparticles by 120 keV Ag− ion implantation in TiO2 matrix

ABSTRACTTiO2 thin film synthesized by the RF sputtering method has been implanted by 120 keV Ag− ion with different doses (3 × 1014, 1 × 1015, 3 × 1015, 1 × 1016 and 3 × 1016 ions/cm2). Further, these were characterized by Rutherford back Scattering, XRD, X-ray photoelectron spectroscopy (XPS), UV–visible and fluorescence spectroscopy. Here we reported that after implantation, localized surface Plasmon resonance has been observed for the fluence 3 × 1016 ions/cm2, which was due to the formation of silver nanoparticles. Ag is in metallic form in the matrix of TiO2, which is very interestingly as oxidation of Ag was reported after implantation. Also, we have observed the interaction between nanoparticles of Ag and TiO2, which results in an increasing intensity in lower charge states (Ti3+) of Ti. This interaction is supported by XPS and fluorescence spectroscopy, which can help improve photo catalysis and antibacterial properties.

Structural and optical properties of Ni-embedded hydrogenated diamond-like carbon (Ni-DLC) prepared by co-deposition of RF-Sputtering and RF-PECVD method

The composite nickel incorporated diamond-like carbon (Ni-DLC) thin films were produced by using RF-Sputtering and RF-Plasma enhanced chemical vapor deposition(RF-PECVD) from acetylene gas and nickel target in various RF powers. The structural and optical properties of thin films with increasing nickel content were investigated. X-Ray Diffraction (XRD) study shows completely an amorphous structure. The presence of Ni and carbon content were confirmed by Energy dispersive X-ray (EDX) Spectra. The optical band gap energy decreases from 4.58 to 3.66eV with increasing applied power. The Urbach energy displays a decreasing trend from 0.472 to 0.189eV. It is shown that the Ni content and the size of nanoparticles could be controlled by adjusting RF applied power.

EUROPIUM SILICATE THIN FILMS FABRICATED BY RF MAGNETRON SPUTTERING AND THERMAL TREATMENT

We report the fabrication and optical characteristics of europium silicate thin films. Layer structures of Eu2O3/SiOX/Si (100) were deposited by an rf-sputtering method and annealed at 1100°C by rapid thermal annealing (RTA). Two methods were used for the deposition of SiOX layer: One was deposited by sputtering using SiO2 target (Ar gas at a rate of 50 sccm) and the other was deposited by reactive sputtering using Si target (Ar gas at a rate of 45 sccm, with an O2 gas at a rate of 5 sccm). Photoluminescence peak at 430 nm was observed in the sample composed of SiOx interlayer sputtered from SiO2 target. In comparison, PL peak at 570 nm was observed in the other sample, the SiOx layer of which was deposited by reactive sputtering from Si target. The compositional distributions of these samples were analyzed by X-ray photoelectron spectroscopy (XPS).

Improvement of flux pinning in GdBa2Cu3O7−δ thin film by nanoscale ferromagnetic La0.67Sr0.33MnO3 pretreatment of substrate surface

The present paper presents the effects of ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on the pinning characteristics of an epitaxial GdBa2Cu3O7−δ ((Gd) BCO) film deposited on top. LSMO nanoparticles with the size between 10 and 20nm were obtained on a (001) STO substrate by RF sputtering method. The analyses of magnetic measurements revealed that the presence of a complex vortex pinning mechanism within the (Gd) BCO film deposited on the undecorated substrate. With respect to a reference (Gd) BCO film, two additional pinning effects in LSMO decorated (Gd) BCO film were observed. One is the effect of the threading dislocations due to LSMO nanoparticles, and the other one is the LSMO nanoparticles itself. Like other nanosized particles, the LSMO nanoparticles on substrate will induce threading dislocations passing through the (Gd) BCO film. These threading dislocations serve as correlated pinning centers along the c-axis, which lead to the improvement of flux pinning properties in LSMO decorated (Gd) BCO film. According to the ferromagnetic property of LSMO material, a magnetic pinning mechanism was proposed to explain the significant increase of Jc and Fp values. The flux pinning abilities of LSMO nanoparticles were evaluated. The enhanced pinning characteristics in the high field region and high temperature together with the movement of H Fpmax (the corresponding field of Fpmax) also suggest a magnetic pinning mechanism for LSMO nanoparticles existed in LSMO decorated (Gd) BCO film.