Platinum-coated Silicon Research Articles

Synthesis and characterization of strontium-doped barium titanate thin film by dip and dry technique

Thin films of polycrystalline (Ba[Formula: see text][Formula: see text]TiO3 ([Formula: see text] = 0.2 and 0.3) with Perovskite structure were prepared by a dip and dry technique on a platinum-coated silicon substrate. The good quality thin films with uniform microstructure and thickness were successfully produced by dip-coating techniques annealed at 730[Formula: see text]C for 1 h. The resulting thin film shows a well-developed dense polycrystalline structure with more uniform grain size distribution. The BST thin films were characterized for their structural, Raman spectroscopy, morphological properties, and complex impedance properties. The dielectric constant-frequency curve showed the good dielectric constant and loss dielectric loss with low-frequency dispersion. The BST 0.3 thin film reveals that the dielectric constant and dielectric loss at a frequency of 1 kHz were 578 and 0.02, respectively. The obtained results on dielectric properties can be analyzed in terms of the Maxwell–Wagner model.

Ferroelectric and photoluminescence properties of (Ca, Eu)Bi2Ta2O9 thin films prepared by pulsed laser deposition

Thin films of CaBi2Ta2O9 (CBT) and Eu3+ doped CaBi2Ta2O9 (CEBT) were deposited on platinum-coated silicon substrates via the pulsed laser deposition technique. The microstructural, leakage current, ferroelectric behavior and photoluminescence properties of CBT/CEBT films were systematically studied. The CBT/CEBT films form single phase with a polycrystalline perovskite structure is confirmed by X-ray diffraction, and the CEBT films exhibit better crystallinity when doped with a number of Eu3+ ions. Meantime, the ferroelectric hysteresis loops show that enhanced ferroelectric property with a remnant polarization 2Pr = 8 μC/cm2 are obtained from CEBT film when x = 0.15. Leakage current density curves show that the Eu3+ doping could lead to the increase of leakage current of CBT film. Furthermore, under the excitation of 394 nm and 464 nm light, the thin films exhibit yellow and red emission peaks centered at 592 nm and 613 nm, which attributes to the f–f electronic transition of 5D0 → 7F1 and 5D0 → 7F2 of Eu3+ ions. This study suggests that Eu3+ doped CaBi2Ta2O9 films have a potential application in the new multifunctional photoluminescence ferroelectric thin-film devices.

High-temperature crystallized thin-film PZT on thin polyimide substrates

Flexible piezoelectric thin films on polymeric substrates provide advantages in sensing, actuating, and energy harvesting applications. However, direct deposition of many inorganic piezoelectric materials such as Pb(Zrx,Ti1-x)O3 (PZT) on polymers is challenging due to the high temperature required for crystallization. This paper describes a transfer process for PZT thin films. The PZT films are first grown on a high-temperature capable substrate such as platinum-coated silicon. After crystallization, a polymeric layer is added, and the polymer-PZT combination is removed from the high-temperature substrate by etching away a release layer, with the polymer layer then becoming the substrate. The released PZT on polyimide exhibits enhanced dielectric response due to reduction in substrate clamping after removal from the rigid substrate. For Pb(Zr0.52,Ti0.48)0.98Nb0.02O3 films, release from Si increased the remanent polarization from 17.5 μC/cm2 to 26 μC/cm2. In addition, poling led to increased ferroelastic/ferroelectric realignment in the released films. At 1 kHz, the average permittivity was measured to be around 1160 after release from Si with a loss tangent below 3%. Rayleigh measurements further confirmed the correlation between diminished substrate constraint and increased domain wall mobility in the released PZT films on polymers.

Study on leakage current properties of BiFeO3 thin films with Pb(Zr,Ti)O3 buffer layer

ABSTRACTA lead zirconate titanate (PZT) buffer layer was introduced for bismuth ferrite (BFO) thin films on platinum-coated silicon substrate, fabricated by sol-gel process. The enhanced crystallization has been obtained and explained by constraint stress contributed by the PZT buffer layer. The decreased leakage current has also been gained compared with the BFO thin film directly deposited on platinum electrode. The asymmetry of leakage current characteristic was exhibited and analyzed for this structure, which can be attributed to the differences of Schottky barrier height, because it has been proved that the leakage current mechanism is dominated by Schottky emission.

Study of the optical properties of lead zirconate–titanate layers obtained by magnetron sputtering

Lead zirconate–titanate films to be used as the active and adhesion layers in a ferroelectric structure have been studied. The layers are obtained by magnetron sputtering on platinum-coated silicon substrates, and spectral ellipsometry is used to determine their optical characteristics. The ellipsomeric angles were measured in the 250–900-nm wavelength range, and the thicknesses (213 and 54 nm) and the dispersion of the optical constants (the refractive and absorption indices) were determined on the basis of two optical models of the layers.

Measurements of Nonlinear Dielectric Constants of Pb(Zr,Ti)O3 Thin Films Using a Dynamic Measuring Method

The nonlinear dielectric constants of Pb(Zr,Ti)O3 (PZT) thin films were studied using a dynamic measuring method. The 111-oriented PZT thin films with various Zr/Ti ratios were deposited on platinum-coated silicon substrates using a sol–gel method. The ε333 of the films increased with the Zr concentration in the tetragonal region and reached a maximum value of 280 aF/V close to the morphotropic phase boundary (Zr/Ti= 52/48). This measured value is 400 times larger than that of LiTaO3 single crystals.

Ferroelectric and structural instability of (Pb,Ca)TiO3 thin films prepared in an oxygen atmosphere and deposited on LSCO thin films which act as a buffer layer

Structural, microstructural and ferroelectric properties of Pb0.90Ca0.10TiO3 (PCT10) thin films deposited using La0.50Sr0.50CoO3 (LSCO) thin films which serve only as a buffer layer were compared with properties of the thin films grown using a platinum-coated silicon substrate. LSCO and PCT10 thin films were grown using the chemical solution deposition method and heat-treated in an oxygen atmosphere at 700°C and 650°C in a tube oven, respectively. X-ray diffraction (XRD) and Raman spectroscopy results showed that PCT10 thin films deposited directly on a platinum-coated silicon substrate exhibit a strong tetragonal character while thin films with the LSCO buffer layer displayed a smaller tetragonal character. Surface morphology observations by atomic force microscopy (AFM) revealed that PCT10 thin films with a LSCO buffer layer had a smoother surface and smaller grain size compared with thin films grown on a platinum-coated silicon substrate. Additionally, the capacitance versus voltage curves and hysteresis loop measurement indicated that the degree of polarization decreased for PCT10 thin films on a LSCO buffer layer compared with PCT10 thin films deposited directly on a platinum-coated silicon substrate. This phenomenon can be described as the smaller shift off-center of Ti atoms along the c-direction 〈001〉 inside the TiO6 octahedron unit due to the reduction of lattice parameters. Remnant polarization (Pr) values are about 30μC/cm2 and 12μC/cm2 for PCT10/Pt and PCT10/LSCO thin films, respectively. Results showed that the LSCO buffer layer strongly influenced the structural, microstructural and ferroelectric properties of PCT10 thin films.

Fluorescence biosensing micropatterned surfaces based on immobilized human acetylcholinesterase

Human acetylcholinesterase (AChE) is a widely studied target enzyme in drug discovery for Alzheimer's disease (AD). In this paper we report evaluation of the optimum structure and chemistry of the supporting material for a new AChE-based fluorescence sensing surface. To achieve this objective, multilayered silicon wafers with spatially controlled geometry and chemical diversity were fabricated. Specifically, silicon wafers with silicon oxide patterns (SiO(2)/Si wafers), platinum-coated silicon wafers with SiO(2) patterns (SiO(2)/Pt/Ti/Si wafers), and Pt-coated wafers coated with different thicknesses of TiO(2) and SiO(2) (SiO(2)/TiO(2)/Pt/Ti/Si wafers) were labelled with the fluorescent conjugation agent HiLyte Fluor 555. Selection of a suitable material and the optimum pattern thickness required to maximize the fluorescence signal and maintain chemical stability was performed by confocal laser-scanning microscopy (CLSM). Results showed that the highest signal-to-background ratio was always obtained on wafers with 100 nm thick SiO(2) features. Hence, these wafers were selected for covalent binding of human AChE. Batch-wise kinetic studies revealed that enzyme activity was retained after immobilization. Combined use of atomic-force microscopy and CLSM revealed that AChE was homogeneously and selectively distributed on the SiO(2) microstructures at a suitable distance from the reflective surface. In the optimum design, efficient fluorescence emission was obtained from the AChE-based biosensing surface after labelling with propidium, a selective fluorescent probe of the peripheral binding site of AChE.

Apolipoprotein E3 (ApoE3) but Not ApoE4 Protects against Synaptic Loss through Increased Expression of Protein Kinase Cϵ

Synaptic loss is the earliest pathological change in Alzheimer disease (AD) and is the pathological change most directly correlated with the degree of dementia. ApoE4 is the major genetic risk factor for the age-dependent form of AD, which accounts for 95% of cases. Here we show that in synaptic networks formed from primary hippocampal neurons in culture, apoE3, but not apoE4, prevents the loss of synaptic networks produced by amyloid β oligomers (amylospheroids). Specific activators of PKCε, such as 8-(2-(2-pentyl-cyclopropylmethyl)-cyclopropyl)-octanoic acid methyl ester and bryostatin 1, protected against synaptic loss by amylospheroids, whereas PKCε inhibitors blocked this synaptic protection and also blocked the protection by apoE3. Blocking LRP1, an apoE receptor on the neuronal membrane, also blocked the protection by apoE. ApoE3, but not apoE4, induced the synthesis of PKCε mRNA and expression of the PKCε protein. Amyloid β specifically blocked the expression of PKCε but had no effect on other isoforms. These results suggest that protection against synaptic loss by apoE is mediated by a novel intracellular PKCε pathway. This apoE pathway may account for much of the protective effect of apoE and reduced risk for the age-dependent form of AD. This finding supports the potential efficacy of newly developed therapeutics for AD.

Control over Memory Performance of Layer-by-Layer Assembled Metal Phthalocyanine Multilayers via Molecular-Level Manipulation

We herein report on the nonvolatile memory properties of iron phthalocyanine multilayers prepared using an electrostatic layer-by-layer assembly method. Cationic poly(allylamine hydrochloride) (PAH) and anionic iron(III) phthalocyanine-4, 4,′ 4″, 4′″-tetrasulfonic acid (Fe-TsPc) were alternately deposited onto quartz glass, indium tin oxide (ITO), or platinum-coated silicon substrates via electrostatic interactions. The electrochemical response of the PAH/Fe-TsPc, which was obtained from cyclic voltammograms (CV) in solution, indicated that redox reactions occurred at the phthalocyanine unit and at the metallic center. It was found that these redox reactions of the PAH/Fe-TsPc multilayer films in solution could be extended to resistive switching nonvolatile memory based on a charge trap/release mechanism in air. The PAH/Fe-TsPc multilayers sandwiched between the bottom (platinum) and top (Ag or tungsten) electrodes exhibited the characteristics of a resistive switching memory at a relatively low operating...

Fabrication of Large-Area Platinum-Coated Silicon Nanowire Arrays and Its Application to Enhanced Electrocatalytic Activity for Methanol Oxidation

Abstract An effective route was developed for the fabrication of the platinum-coated silicon nanowire arrays (Pt/SiNWAs). By judiciously combining the seed-growth method and the electroless deposition technique, high-quality three-dimensional (3D) Pt nanostructure was created on the surface of large-area SiNWAs. Owing to their unique 3D structure, the as-prepared Pt/SiNWAs exhibited excellent electrocatalytic activity towards methanol oxidation in comparison with the Si wafer-supported Pt nanoparticle film and could be used as a promising nanoelectrocatalyst.

Investigations on the influence of the substrate on the crystal structure of sputtered LiCoO2

The influence of the uppermost substrate layer on the structural properties of sputtered lithium cobalt oxide (LiCoO2) is discussed in this work. For this purpose, bare, oxidized, and platinum-coated silicon wafers, as well as stainless steel and titanium sheets, were used as substrates. The resulting crystal structure of LiCoO2 deposited on these substrates was analyzed and discussed. The LiCoO2 thin films were deposited by RF magnetron sputtering with different film thicknesses. A subsequent annealing step at 700 °C was performed to induce the crystallinity of LiCoO2. The crystal orientation was determined by X-ray diffraction. The obtained results show a strong dependency of LiCoO2's crystal structure on the surface the film is deposited on. However, the strong influence of the film thickness reported in previous publications could not be observed. If LiCoO2 is deposited on the substrates with a metallic surface, a strong (003) preferential orientation is obtained for a wide range of film thicknesses. In contrast, sputtering of LiCoO2 on bare and on oxidized silicon wafers results in a (101) dominated crystal structure for the different film thicknesses. These experiments show the importance of the characterization of LiCoO2's crystal structure in the intended battery setup.

Direct nano-in-micropatterning of TiO2 thin layers and TiO2/Pt nanoelectrode arrays by deep X-ray lithography

Nano-in-micro-patterned heterogeneous substrates and Pt electrodes are prepared via organic/inorganic self-assembly combined with deep X-ray lithography. Nanoperforated titania membranes are obtained through dip coating from a sol–gel solution using block copolymer micelles as templating agent. Such thin films are selectively exposed to the X-ray radiation that leads to the structural local densification and permits the selective etching of the unexposed layer. Structural as well as electrochemical characterizations demonstrate that the final materials are micrometric features of a sub-10 nm thick perforated titania membrane that guarantees the accessibility to the substrate. This system was also applied to a conductive platinum-coated silicon surface to achieve micrometric features of nanoelectrode arrays. This scalable strategy of combining bottom-up and top-down approaches is thereby promising for various applications involving smart functional devices.

Large-Scale Fabrication of Ordered Silicon Nanotip Arrays Used for Gas Ionization in Ion Mobility Spectrometers

The 9/11 events have led to an increase in the request for sensors and sensor systems that can detect rapidly, efficiently, and at moderate cost trace explosives and a whole range of toxic substances at diverse control points, e.g., at airports and inside air conditioning systems in aircraft and public buildings. To date, the security screening instruments of choice are ion mobility spectrometers (IMS), which are basically time-of-flight mass spectrometers (Sielemann, 1999 and Stach, 1997). Such instruments allow for the detection of explosives, chemical warfare agents, and illicit drugs. Widespread adoption of the IMS technology in civilian security screening applications, for instance, at airports, has been hindered due to the fact that state-of-the-art spectrometers employ radioactive ion sources. We report on fabrication and measurements of large-scale-ordered silicon nanotip arrays, used to replace the radioactive source for IMS gas ionization. Surface ionization mechanisms on the platinum-coated silicon surface can be significantly increased compared to flat structures due to the strong field enhancement at the tips. We will show measurements of the ion current of planar surfaces compared to microstructured surfaces as well as a photoelectrochemical etching process that allows to etch flat tips with a low aspect ratio as well as long tips with high aspect ratios with exact control about the tip profile.

10.1007/s11455-008-1006-x

A contact force spectrometry technique was used to measure the van der Waals and electrostatic forces acting on platinum-coated silicon probes contacting with metal films on silicon substrates. It is shown that the results of such measurements can be used for determining the geometric characteristics of probes and the Hamaker constant of contacting materials. The experimental data well agree with the theoretical values.

Synthesis of Ag microparticles with hierarchical nanostructure on the anode of a galvanic cell

In this work, three-dimensional (3D) hierarchical silver microparticles (HSMP) composed of 2D nanoflakes were synthesized on the anode of a galvanic cell. A copper plate immersed in CuSO 4 solution and a platinum-coated silicon plate immersed in AgNO 3 solution served as the cathode and anode, respectively. The two half-cells were linked by a salt bridge. The presence of poly(N-vinyl pyrrolidone) (PVP) in the AgNO 3 electrolyte, an optimum AgNO 3 concentration and an appropriate reaction time are crucial for the formation of a hierarchical nanostructure. The evolution of the products during growth was tracked to study the formation and metamorphosis mechanisms. The catalytic activity of HSMP was studied via promotion of Rhodamine B reduction by NaBH 4.

The Influence of Ni Doping on the Properties of BST Ferroelectric Thin Film

Undoped and Ni-doped barium strontium titanate (BST) thin films have prepared by sol-gel method on a platinum-coated silicon substrate. The structure and dielectric properties of Ni-doped BST thin films were investigated. Results show that grain size of the BST thin films decrease with the increase of Ni content. Dielectric constant and dielectric loss also decrease. As the content of Ni-doped reaches 10 mol%, the dielectric constant, dielectric loss, tunability and FOM are 230.25, 0.015, 30.8% and 20.53, respectively. Ni-doped BST thin films were suitable for tunable microwave devices.

The Influence of Ni Doping on The Properties of BST Ferroelectric Thin Film

Undoped and Ni-doped barium strontium titanate(BST) thin films have prepared by sol-gel method on a platinum-coated silicon substrate. The structure and dielectric properties of Ni-doped BST thin films were investigated. Results show that grain size of the BST thin films decrease with the increase of Ni content. Dielectric constant and dielectric loss also decrease. As the content of Ni-doped reaches 10mol%, the dielectric constant, dielectric loss, tunability and FOM are 230.25, 0.015, 30.8% and 20.53, respectively. Ni-doped BST thin films were suitable for tunable microwave devices.

In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb(0.92)Sr(0.08))(Zr(0.65)Ti(0.35))O(3)] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350 degrees C and 750 degrees C for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750 degrees C. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature-activating significant grain growth for the room-temperature-deposited films is about 275 degrees C and the Curie point lies between 325 and 400 degrees C. This relatively high Curie point makes these films suitable for wide temperature range applications.

Polymeric precursor method to the synthesis of XWO 4 (X = Ca and Sr) thin films—Structural, microstructural and spectroscopic investigations

Stoichiometric XWO 4 (X = Ca, and Sr) thin films were synthesized using the polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. Through the polyesterification reaction, evidences of the formation of the W-citrate complex and the strontium were obtained by 13C NMR and FT-Raman spectroscopy. The thin films were deposited on silicon and platinum-coated silicon substrates through the spinning technique. The surface morphology and crystal structure of the thin films were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), specular reflectance infrared Fourier transform spectroscopy, and micro-Raman spectroscopy. Nucleation stages and surface morphology evolution of the thin films on silicon substrates were studied by atomic force microscopy. X-ray diffraction characterization of these films showed that the XWO 4 (X = Ca, and Sr) thin film phases crystallize at 500 °C from an inorganic amorphous phase, given that no intermediate crystalline phase was identified.