Visible-light active photocatalytic WO3 films loaded with Pt nanoparticles deposited by sputtering

Visible-Light active photocatalytic tungsten trioxide (WO3) films were deposited at a substrate temperature of 800 degrees C by dc reactive magnetron sputtering using a W metal target. In addition, Platinum (Pt) was deposited on the WO3 film surfaces at room temperature, also by sputtering. In the early stages of Pt growth, formation of Pt nanoparticles could be expected because of the island structure observed in Volmer-Weber-type growth mode. The surface coverage of Pt on the WO3 films was estimated quantitatively by X-ray photoelectron spectroscopy and was found to be approximately 60% after 7 s deposition. High resolution electron microscopy (HREM) demonstrated that Pt nanoparticles with a diameter of about 2.5 nm were generated and dispersed uniformly on the entire surface area of the columnar polycrystalline WO3 films. These Pt-loaded films exhibited high photocatalytic activity in the decomposition of acetaldehyde (CH3CHO) under visible light irradiation.     

表面活性剂对FePt纳米颗粒形貌的影响

分别以乙酰丙酮铁(Fe(acac)3)和氯铂酸(H2PtCl6.6H2O)作为Fe源和Pt源,乙二醇作为还原剂和溶剂,通过多元醇还原法制备出单分散的FePt纳米颗粒,并研究了表面活性剂油酸油胺和CTAB对FePt纳米颗粒形貌和磁性能的影响。通过X射线衍射仪(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)对纳米颗粒进行表征。结果表明,表面活性剂油酸油胺和CTAB修饰的FePt纳米颗粒均为面心立方(FCC)结构,分散性良好,粒径分布较未使用表面活性剂时变窄;油酸油胺修饰的FePt形貌主要是球形,但是有四方形纳米结构出现;而CTAB修饰的FePt形貌有蠕虫状产生。VSM结果显示其矫顽力都趋近于零,呈现超顺磁性。     

Surface modification of carbon nanofibers with platinum nanoparticles using a “polygonal barrel-sputtering” system

Carbon nanofibers (CNFs) modified with Pt nanoparticles have been prepared using a new RF sputtering instrument called a “polygonal barrel-sputtering” system. The prepared samples were characterized by optical microscopy, field emission scanning microscopy (FE-SEM), inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray fluorescence (XRF), X-ray diffraction (XRD), and transmission electron microscopy (TEM) with energy-dispersive X-ray spectrometry (EDS). When only the CNFs were placed in the system, large CNF aggregates with sizes of 5-15 mm were observed and Pt was deposited non-uniformly. In addition, microscopic observations revealed that ca. 40% of the CNFs were still unmodified. In contrast, when pieces of bent columnar stainless steel were placed in the system with the CNFs, large CNF aggregates were not observed in the Pt deposited sample. In this sample, CNFs modified with highly dispersed Pt nanoparticles were obtained successfully, and unmodified CNFs were absent. The sizes of the Pt nanoparticles were in a narrow range of 1.7-3.5 nm, and their mean size was 2.5 nm.     

Mechanisms of current conduction in Pt/BaTiO3/Pt resistive switching cell

The 80-nm-thickness BaTiO₃ (BT) thin film was prepared on the Pt/Ti/SiO₂/Si substrate by the RF magnetron sputtering technique. The Pt/BT/Pt/Ti/SiO₂/Si structure was investigated using X-ray diffraction and scanning electron microscopy. The current-voltage characteristic measurements were performed. The bipolar resistive switching behavior was found in the Pt/BT/Pt cell. The current-voltage curves were well fitted in different voltage regions at the high resistance state (HRS) and the low resistance state (LRS), respectively. The conduction mechanisms are concluded to be Ohmic conduction and Schottky emission at the LRS, while space-charge-limited conduction and Poole-Frenkel emission at the HRS. The electroforming and switching processes were explained in terms of the valence change mechanism, in which oxygen vacancies play a key role in forming conducting paths.     

Microstructural and electrical properties in textured lead calcium lanthanum titanate thin films deposited on a Pt/Ti/SiO2/Si substrate

Textured Ca modified (Pb,La)TiO₃ (PLCT) films were deposited on Pt/Ti/SiO₂/Si substrates using a metal-organic decomposition (MOD) process. The microstructure of the PLCT thin film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Electric properties were measured using the Pt/PLCT/Pt capacitor structure. The PLCT films exhibit good ferroelectric and dielectric properties.     

Preparation of multiwalled carbon nanotubes-platinum-Nafion-glucose oxidase nanobiocomposite and its application to glucose biosensor

Platinum (Pt) nanoparticles were electrodeposited within multiwalled carbon nanotubes-Nafion-glucose oxidase (MWNTs-Nafion-GOx) nanobiocomposite by a potentiostatic method. The morphology and nature of the resulting MWNTs-Pt-Nafion-GOx nanobiocomposite were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic properties of the MWNTs-Pt-Nafion-GOx nanobiocomposite film modified glassy carbon electrode were characterized by cyclic voltammetry and amperometry in the presence of hydrogen peroxide. The glucose biosensor sensitivity was strongly influenced by the deposits of Pt nanoparticles and amount of GOx concentration within the MWNTs-Pt-Nafion-GOx nanobiocomposite film. The optimized glucose biosensor displayed a sensitivity of 640 nA mM(-1), a linear range of up to 4 mM, a detection limit of 4 microM, and a response time of less than 4 s at an operating potential of +500 mV versus Ag/AgCl (3 M KCl).     

Integration of stacked capacitor module with ultra-thin ferroelectric SrBi2Ta2O9 film for high density ferroelectric random access memory applications at low voltage operation

The crystallization route of thin SrBi₂Ta₂O₉ (SBT) films deposited on Pt(100 nm)/Ti(10 nm)/SiO₂/Si substrate is investigated at different annealing temperatures by atomic force microscopy (AFM) and X-ray diffractometry (XRD). To evaluate the SBT film properties for low voltage operation and for high storage density (>16 MBit), SBT is deposited at different film thicknesses. Furthermore, the performance of a Pt/SBT/Pt capacitor on a barrier-/contact-layer/polysilicon-plug architecture suitable for stacked capacitor memories is investigated by transmission electron microscopy (TEM)/energy dispersive X-ray analysis (EDX) and electrical measurements. It is shown that an oxidized and highly resistive contact layer can be recovered by electrical pulses. Finally, a process solution for a successful integration of 38 nm thin SBT films into this structure is provided.     

NiO-based nanostructured thin films with Pt surface modification for gas detection

Nanocrystalline NiO thin films were prepared by dc reactive magnetron sputtering in a mixture of oxygen and argon and subsequently coated by Pt on an NiO film surface. Very thin Pt overlayers with a thickness of about 3 and 5 nm have been deposited by magnetron sputtering. Then, the modified NiO films have been analyzed by TEM, EELS and AES. NiO thin films showed a polycrystalline structure (fcc NiO phase) with the size of nanocrystals ranging from a few nanometres to 10 nm. TEM observations both of unmodified and Pt-modified NiO films revealed that they were formed by nanocrystals and an amorphous phase. Uniformly distributed Pt particles were produced on top of the NiO surface. According to AES measurements, the presence of Ni in the spectra recorded from Pt pad indicated that the Pt layer has discontinuous nature. Electrical responses of NiO-based sensor structures towards hydrogen have been measured.     

The effect of argon pressure, residual oxygen and exposure to air on the electrical and microstructural properties of sputtered chromium thin films

Chromium thin films were deposited on SiO₂/Si wafers using two sputtering systems with different levels of cleanliness, and at argon sputtering pressures varying between 0.13 and 0.93 Pa. Films from the two systems grown under identical sputtering conditions had significantly different resistivity values that are shown to be due to differences in residual oxygen in the chambers. Electrical transport measurements were conducted on the series of grown films to investigate the influence of argon pressure on film electrical resistivity. The films morphology, microstructure and composition were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. Significant differences were found in Cr thin films sputtered at different sputtering pressures; differences in resistivity performance and microstructure were noted. This change was shown to be due to the transition from porous structure to a denser microstructure. The Cr films sputtered at high pressure contained large quantities of oxygen when exposed to air. Some of the oxygen is added to the film during the deposition depending on the deposition rate and the base pressure of the sputtering system. The rest is incorporated into the film once it is exposed to air. The amount of oxygen added at this stage depends on the structure of the film and would be minimal for the films deposited at low sputtering pressures.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Nanoporous YSZ film in electrolyte membrane of Micro-Solid Oxide Fuel Cell

Yttria stabilized zirconia (YSZ) with 8 mol% Y was deposited by reactive magnetron sputtering onto oxidized (100) silicon substrates. It was possible to switch film texture from (111) to (200) by applying a strong RF substrate bias. Transmission electron microscopy showed that the film deposited under bias is porous and exhibits nanoscaled grains, whereas the film deposited without bias is dense and columnar. The ionic conductivity as a function of temperature revealed an activation energy of 1.04 eV. The mechanical stress could be tuned to low values by thermal post-annealing. Using the dense (111) film as electrolyte layer, and the porous (200) film as an interlayer to a porous Pt anode, an open circuit voltage of 0.85 V was obtained in a micro machined fuel cell structure.     

Synthesis of Pt-containing ordered mesoporous carbons and their catalysis for toluene hydrogenation

Highly ordered Pt-containing mesoporous carbons (Pt-OMCs) have been synthesized by a multi-component co-assembly method followed by pyrolysis at high temperature. In this synthesis, resorcinol, formaldehyde and chloroplatinic acid were used as the carbon and Pt precursors. The triblock copolymer Pluronic F127 was used as the template. X-ray diffraction, N₂-adsorption measurements and transmission electron microscopy revealed that the Pt nanoparticles in about 1–3 nm were embedded in the highly ordered mesostructure carbon. The Pt3.1-OMC was used as the catalyst in the hydrogenation of toluene. By comparing with the traditional impregnated 3.3Pt/OMC catalyst to our catalyst, Pt3.1-OMC, the sample exhibited a much higher selectivity to methylcyclohexane.     

Characteristics of SrTiO3 thin films deposited under various oxygen partial pressures

SrTiO₃ thin films were deposited by rf-magnetron sputtering under various sputtering conditions followed by conventional furnace annealing at 600 and 700 °C. The amorphous SrTiO₃ thin films crystallized into polycrystals at 600 °C. The leakage current of the SrTiO₃ thin films decreased with increasing oxygen partial pressure in the sputtering gas. On the contrary, the dielectric constant increased with increasing the oxygen content in the sputtering gas. The leakage current and dielectric constant increased with increasing substrate temperature and post-annealing temperature. The ratio of SrTi approached 11 with increasing oxygen content in the sputtering gas and substrate temperature during deposition. The oxygen content in the film decreased with increasing the substrate temperature. The capacitance-voltage (C-V) curves showed that the capacitance was nearly independent of the applied voltage. Scanning electron microscopy (SEM) micrographs showed that interdiffusion between the bottom electrode (Pt) and the buffer layer (Ti) occurred during post-annealing, but that the interface between SrTiO₃ and Pt was stable.     

Deposition and structural properties of RF magnetron-sputtered ZnO thin films on Pt/Ti/SiNx/Si substrate for FBAR device

This work investigates high-quality bottom electrode and piezoelectric film used in a thin-film bulk acoustic resonator (TFBAR) device. The titanium (Ti) seeding layer and platinum (Pt) bottom electrode were deposited on silicon substrates by DC sputtering using a dual-gun system. Zinc oxide (ZnO) was then deposited onto the Pt bottom electrode by RF magnetron sputtering. Field-emission scanning electron microscopy (SEM), atom force microscopy (AFM) and the four-point probe method showed that the Pt bottom electrode deposited on the Ti seeding layer exhibited favorable characteristics, such as a crystallite size of less than 10 nm, a surface roughness of 0.69 nm and a sheet resistance of 2.27 Ω/□. The ZnO thin film with a highly c-axis-preferred orientation (FWHM = 0.28°) and a roughness of 6.22 nm was investigated by X-ray diffraction (XRD) and AFM analysis, respectively. The bottom electrode with a low resistance and the highly crystalline ZnO thin film will contribute significantly to the favorable characteristics of the FBAR devices.     

Synthesis,Structural, and Magnetic Properties of Nanocrystalline Ti 0.95Co0.05O2-Diluted Magnetic Semiconductors

With a view to investigate the influence of nanometric size on the structural, surface, and magnetic properties of nanocrystalline Ti_0.95Co_0.05O₂-diluted magnetic semiconductors, prepared by a novel simple controllable peroxide-assisted reflux chemical route followed by annealing at different temperatures, a systematic investigation has been undertaken. Structural characterizations such as X-ray diffraction followed by Rietveld refinement, electron diffraction pattern, Fourier transform infrared, Raman scattering, and X-ray photoelectron spectroscopy (XPS) measurements have shown anatase phase formation in nanocrystalline Ti_0.95Co_0.05O₂ without any additional impurity phases. The modified reflux chemical route was effective in obtaining pure phase Ti_0.95Co_0.05O₂ nanoparticles. Surface morphological investigations by using transmission electron microscopy and atomic force microscopy measurements showed the predominant effect of random distribution of nanoparticles on the aggregation behavior and local microstructural changes. The deconvoluted XPS core level Co 2p spectral study manifested the oxidation state of Co as + 2 and is found to be stable with varying particle size and annealing temperature. The ferromagnetic behavior was investigated by vibrating sample magnetometer, magnetic force microscopy, and electron spin resonance measurements. These magnetization studies showed all the samples are ferromagnetic at room temperature without any magnetic clusters. The correlation between structure, surface condition of the nanoparticles and local electronic interactions, and magnetization of the samples was analyzed and explored the origin of ferromagnetism.     

Preparation Ru,Bi monolayer modified Pt nanoparticles as the anode catalyst for methanol oxidation

Platinum nanoparticles were successfully electrodeposited on indium tin oxide (ITO) surface in the solution with hexachloroplatinic acid and copper ion by cyclic voltammogram method. The micrographs and structure of Pt nanoparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of Pt nanoparticles/ITO or modified by Ru, Bi underpotential deposition (UPD) for methanol oxidation have been investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High electroactivity and good long-term stability can be observed. These results indicate that Pt nanoparticles modified by UPD may have potential applications in designing noble metal catalysts of fuel cells with low loading and high activity at the atomic level.     

The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films prepared by RF magnetron sputtering

(Ba_{1 − x} Sr _x )TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering. The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy and dielectric frequency spectra. It was found that the preferred orientation of BST thin films could be tailored by insertion of YSZ interlayer and adjusting the thickness of YSZ interlayer. The BST thin films deposited on YSZ interlayer exhibited a more compact and uniform grain structure than that deposited directly on Pt electrode. Dielectric measurement revealed that the BST thin films deposited on 10 nm YSZ interlayer have the largest dielectric constant and a low dielectric loss tangent. The enhanced dielectric behavior is mainly attributed to the YSZ interlayer which serves as an excellent seeding layer to enhance the crystallization of subsequent BST films layer, and a smaller thermal stress field built up at the interface between YSZ interlayer and BST film layer.     

Copper and iron based thin film nanocomposites prepared by radio frequency sputtering. Part I: elaboration and characterization of metal/oxide thin film nanocomposites using controlled in situ reduction process

Copper and iron based thin films were prepared on glass substrate by radio-frequency sputtering technique from a delafossite CuFeO₂ target. After deposition, the structure and microstructure of the films were examined using grazing incidence X-ray diffraction, Raman spectroscopy, electron probe micro-analysis and transmission electron microscopy coupled with EDS mapping. Target to substrate distance and sputtering gas pressure were varied to obtain films having different amount and distribution of copper nanoparticles and different composition of oxide matrix. The overall reaction process, which starts from CuFeO₂ target and ends with the formation of films having different proportion of copper, copper oxide and iron oxide, was described by a combination of balanced chemical reactions. A direct relationship between the composition of the metal/oxide nanocomposite thin film and the sputtering parameters was established. This empirical relationship can further be used to control the composition of the metal/oxide nanocomposite thin films, i.e. the in situ reduction of copper ions in the target.     

Superhydrophilic anatase TiO2 film with the micro- and nanometer-scale hierarchical surface structure

Nanosized anatase TiO₂ film on the ITO glass has been fabricated via spin coat process, with sodium dodecylbenzenesulfonate modified TiO₂ nanoparticles, which is synthesized by a sol-hydrothermal method, and also characterized mainly by means of field emission scanning electron microscopy (FESEM). The results show that the as-prepared anatase TiO₂ film exhibits superhydrophilic characteristic although it is not exposed to ultraviolet irradiation. The high roughness resulting from hierarchical surface structure is responsible for its superhydrophilicity. This work would provide a new route to fabricate newly nanostructured semiconductor films.     

Decoration of single-walled carbon nanotubes with Pt nanoparticles from an organometallic precursor

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt₂(dba)₃ (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2?C3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs.