High‐Performance Micro‐Solid Oxide Fuel Cells Fabricated on Nanoporous Anodic Aluminum Oxide Templates

Micro‐solid oxide fuel cells (μ‐SOFCs) are fabricated on nanoporous anodic aluminum oxide (AAO) templates with a cell structure composed of a 600‐nm‐thick AAO free‐standing membrane embedded on a Si substrate, sputter‐deposited Pt electrodes (cathode and anode) and an yttria‐stabilized zirconia (YSZ) electrolyte deposited by pulsed laser deposition (PLD). Initially, the open circuit voltages (OCVs) of the AAO‐supported μ‐SOFCs are in the range of 0.05 V to 0.78 V, which is much lower than the ideal value, depending on the average pore size of the AAO template and the thickness of the YSZ electrolyte. Transmission electron microscopy (TEM) analysis reveals the formation of pinholes in the electrolyte layer that originate from the porous nature of the underlying AAO membrane. In order to clog these pinholes, a 20‐nm thick Al₂O₃ layer is deposited by atomic layer deposition (ALD) on top of the 300‐nm thick YSZ layer and another 600‐nm thick YSZ layer is deposited after removing the top intermittent Al₂O₃ layer. Fuel cell devices fabricated in this way manifest OCVs of 1.02 V, and a maximum power density of 350 mW cm^?2 at 500 °C.     

Highly Efficient Plasmonic Membrane Flow Reactor

A plasmonic flow reactor, consisting of thin Au film at exits of monolithic anodized aluminum oxide (AAO) membranes under LED illumination is demonstrated. The system shows over 200% quantum efficiency (QE) for peroxide activation and the ability to limit to single oxidation reaction by controlling residence time with flow rate and pore geometry. Periodic pore arrays (20–200 nm diameter) with 25 nm thick Au on AAO are modeled by finite-difference time-domain (FDTD) simulations and predicted largest E-field enhancements for the larger 200 nm pore diameters. Peroxide activation, as measured by O₂ generation is most efficient with a 200 nm pore diameter system under 523 nm LED illumination. The optimal wavelength falls near the absorption peak of Au@AAO with 200 nm pore diameter suggesting that hot electron generated from gold plasmonic response is the primary mechanism for activation of H₂O₂. QE for gold plasmonic flow system calculated from O₂ generation experiments is as high as 250%, which indicates a mechanism of hot-electron activation of peroxide that leaves a still energetic hot-electron to catalytically activate multiple reactions. The formation of Au surface oxides that are catalytically active in dark is also observed and must be accounted for in Au plasmonic photochemical studies.     

Au/STO/Pt三明治结构阻变存储器性质研究

采用脉冲激光沉积法(PLD)在Pt衬底(Pt/TiO2/SiO2/Si)上制备了SrTiO3(STO)薄膜,并对其表面特性,表面组成和结构进行了研究分析。在此基础上制备了具有三明治结构的Au/STO/Pt阻变器件,并测试了其I-V特性。结果显示:空间电荷限制电流(SCLC)机制对SrTiO3薄膜中氧空位的运输起了决定作用;薄膜界面缺陷对载流子的俘获与去俘获导致了SrTiO3薄膜I-V特性的产生。     

Multisegment PtRu Nanorods: Electrocatalysts with Adjustable Bimetallic Pair Sites

Multisegment PtRu nanorods (Pt–Ru, Pt–Ru–Pt, Pt–Ru–Pt–Ru, Pt–Ru–Pt–Ru–Pt, Pt–Ru–Pt–Ru–Pt–Ru) with customizable lengths of the individual metals are obtained by the sequential electrodeposition of the metals into the pores of anodic aluminum oxide (AAO) membranes. Field‐emission scanning electron microscopy (FESEM) shows that the nanorods are about 200 nm in diameter and 1.2 μm long, with 900 nm of total platinum‐segment length. The alternating platinum and ruthenium segments can be easily differentiated using FESEM. X‐ray diffractometry reveals that the platinum and ruthenium in the bimetallic nanorods are polycrystalline with face‐centered cubic and hexagonal close‐packed crystal lattice structures, respectively. The presence of Pt⁰, Pt^II, Pt^IV, Ru⁰, and Ru^VI on the surface of the bimetallic nanorods is demonstrated via X‐ray photoelectron spectroscopy. The nanorods are catalytically active in the room‐temperature electro‐oxidation of methanol. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long‐time (near‐steady‐state) current density and the number of Pt–Ru interfaces. The use of segmented nanorods with a controlled number of Pt–Ru interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts and has provided a direct demonstration of the role of pair sites in bifunctional catalysis.     

Cover Picture: Formation of Metal Nano‐ and Micropatterns on Self‐Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition (Adv. Funct. Mater. 10/2006)

The cover illustrates two‐step fabrication of metal micro‐ and nanostructures on self‐assembled monolayers (SAMs) by pulsed laser deposition and electroless deposition. Metal–SAM–metal junctions are a key component of molecular electronic devices. Pt was deposited in a micropattern by pulsed laser deposition through a stencil. XPS maps show how the Pt pattern is developed into a Cu pattern using electroless deposition as reported by Ravoo, Brugger, Reinhoudt, Blank, and co‐workers on p. 1337. The Cu pattern can also be observed by optical microscopy (background). Patterns of noble‐metal structures on top of self‐assembled monolayers (SAMs) on Au and SiO₂ substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano‐ and microstencils. In the second approach, noble‐metal cluster patterns deposited through nano‐ and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO₂ substrates and are subsequently analyzed using X‐ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)‐micrometer‐sized metal structures on top of SAMs. This method minimizes the gas‐phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.     

Local crystal structural modifications in pulsed laser deposited high-k dielectric thin films on silicon and germanium

The thin film growth conditions are correlated with the local structures formed in Hf_xZr_1−xO₂ (x=0.0–1.0) high-k dielectric thin films on Si and Ge substrates during deposition. Pulsed laser deposition (PLD) technique has been used in the synthesis of the thin films with systematic variations of substrate temperature, Zr content of the targets and substrate selection. The local structural information acquired from extended X-ray absorption spectroscopy (EXAFS) is correlated with the thin film growth conditions. The response of the local structure around Hf and Zr atoms to growth parameters was investigated by EXAFS experiments performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The competing crystal phases of oxides of Hf were identified and the intricate relation between the stabilized phase and the parameters as: the substrate temperature; Hf to Zr ratio; have been revealed. Specifically, HfO₂ thin films on Si(1 0 0) exhibit a tetragonal to monoclinic phase transformation upon increase in the substrate temperature during deposition whereas, HfO₂ PLD films on Ge(1 0 0) substrates remain in tetragonal symmetry regardless of the substrate temperature.     

Carbon Electrodes Modified with TiO2/Metal Nanoparticles and Their Application for the Detection of Trinitrotoluene

The preparation of modified, catalytically active, functional carbon electrodes and their application to the electrochemical reduction of trinitrotoluene (TNT) is reported. Modification of the electrodes is performed with composites of nanometer‐sized, mesoporous titanium dioxide, which acts as a support containing inserted/deposited nanoparticles of ruthenium, platinum, or gold. These composites are prepared by a novel sonochemical synthesis using simple and low‐cost precursors. Cyclic voltammetry shows that 2,4,6‐trinitrotoluene can be reduced on thus‐modified carbon‐paper electrodes at potentials of around –0.5 V (vs. Ag/AgCl/Cl^–) in aqueous solutions. Unexpectedly, carbon‐paper electrodes modified with the TiO₂/nano‐Pt composites demonstrate a remarkable electrochemical activity toward the reduction of trinitrotoluene. A significant finding is that the two electrode processes—the reduction of TNT and of oxygen—are quite well separated in potential on the modified carbon‐paper electrodes because of selective electrochemical activity of the TiO₂/nano‐Pt and TiO₂/nano‐Au composites. TiO₂/nano‐Ru composites are found to be much less electrochemically active for the detection of TNT compared to the previous two. It was also established that the titanium dioxide support of TiO₂/nano‐Pt composites plays a specific role for facilitating the TNT‐ and oxygen‐reduction processes.     

Fabrication and characterization of Zr-rich Zr-aluminate films for high-κ gate dielectric applications

Two kinds of Zr-rich Zr-aluminate films for high-κ gate dielectric applications with the nominal composition of (ZrO₂)_0.8(Al₂O₃)_0.2 and (ZrO₂)_0.9(Al₂O₃)_0.1, were deposited on n-type silicon wafer by pulsed laser deposition (PLD) technique at different deposition conditions. X-ray diffraction (XRD) reveals that the (ZrO₂)_0.8(Al₂O₃)_0.2 film could remain amorphous after being rapid thermal annealed (RTA) at the temperature above 800 °C, while the other one displays some crystalline peaks at 700 °C. The energy gap calculated from optical transmittance spectrum of (ZrO₂)_0.8(Al₂O₃)_0.2 film on quartz is about 6.0 eV. Sputtering depth profile of X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that a Zr-Si-O interfacial layer was formed at the near surface of the silicon substrate. The dielectric constant of the (ZrO₂)_0.8(Al₂ O₃)_0.2 film has been determined to be 22.1 by measuring a Pt/(ZrO₂)_0.8(Al₂ O₃)_0.2/Pt MIM structure. An EOT of 1.76 nm with a leakage current density of 51.5 mA/cm² at 1 V gate voltage for the film deposited in N₂ were obtained. Two different pre-treatments of Si substrates prior to depositions were also carried out and compared. The results indicate that a surface-nitrided Si substrate can lead to a lower leakage current density. The amorphous Zr-rich Zr-aluminate films fabricated by PLD have promising structure and dielectric properties required for a candidate material for high-κ gate dielectric applications.     

Effects of annealing technique and TiO2 seed layer on the phase composition of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 film

The lead magnesium niobate–lead titanate (PMN–PT) thin films with and without the TiO₂ seed layer were prepared by a pulsed laser deposition (PLD) deposited on Pt/Ti/SiO₂/Si substrates. The films were treated by two-step annealing and normal annealing with rapid thermal annealing (RTA). The effects of two-step annealing and the TiO₂ seed layer on the phase composition of PMN–PT films were studied. The results show that the PMN–PT film with TiO₂ seed layer can gain a pure perovskite phase with a high (1 0 0) preferential orientation after the two-step annealing technique.     

Tailoring of LaxSr1‐xCoyFe1‐yO3‐δ Nanostructure by Pulsed Laser Deposition

Pulsed Laser Deposition (PLD) was used to prepare thin films with the nominal composition La_0.58Sr_0.4Co_0.2Fe_0.8O_3‐δ (LSCF). The thin film microstructure was investigated as a function of PLD deposition parameters such as: substrate temperature, ambient gas pressure, target‐to‐substrate distance, laser fluence and frequency. It was found that the ambient gas pressure and the substrate temperature are the key PLD process parameters determining the thin film micro‐ and nanostructure. A map of the LSCF film nanostructures is presented as a function of substrate temperature (25–700 °C) and oxygen background pressure (0.013–0.4 mbar), with film structures ranging from fully dense to highly porous. Fully crystalline, dense, and crack‐free LSCF films with a thickness of 300 nm were obtained at an oxygen pressure lower than 0.13 mbar at a temperature of 600 °C. The obtained knowledge on the structure allows for tailoring of perovskite thin film nanostructure, e.g., for solid oxide fuel cell cathodes. A simple geometrical model is proposed, allowing estimation of the catalytic active surface area of the prepared thin films. It is shown that voids at columnar grain boundaries can result in an increase of the surface area by approximately 25 times, when compared to dense flat films.     

Formation of Metal Nano‐ and Micropatterns on Self‐Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition

Patterns of noble‐metal structures on top of self‐assembled monolayers (SAMs) on Au and SiO₂ substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano‐ and microstencils. In the second approach, noble‐metal cluster patterns deposited through nano‐ and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO₂ substrates and are subsequently analyzed using X‐ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)‐micrometer‐sized metal structures on top of SAMs. This method minimizes the gas‐phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.     

Photoisomerisation process of self-assembled monolayers of some novel azobenzenes†

Self-assembled monolayers (SAMs) of four azobenzene derivatives containing a sulphonamide linkage and a thiol group were deposited on both vacuum-evaporated and sputtered gold (Au) thin films. The optically induced switching effect on the surface potential U_s upon alternating irradiation with UV (centred at 360 nm) and visible (centred at 450 nm) light was investigated by the Kelvin probe technique. Changes in surface potential were in the range ΔU_s=4–70 mV for SAM samples, depending on the structure of the molecule. The dependence of surface potential change and decay time upon irradiation on the structure of the Au film was observed. Copyright © 2000 John Wiley & Sons, Ltd.     

Improved Hydrogen Production of Au–Pt–CdS Hetero‐Nanostructures by Efficient Plasmon‐Induced Multipathway Electron Transfer

The design of new functional materials with excellent hydrogen production activity under visible‐light irradiation has critical significance for solving the energy crisis. A well‐controlled synthesis strategy is developed to prepare an Au–Pt–CdS hetero‐nanostructure, in which each component of Au, Pt, and CdS has direct contact with the other two materials; Pt is on the tips and a CdS layer along the sides of an Au nanotriangle (NT), which exhibits excellent photocatalytic activity for hydrogen production under light irradiation (λ > 420 nm). The sequential growth and surfactant‐dependent deposition produce the three‐component Au–Pt–CdS hybrids with the Au NT acting as core while Pt and CdS serve as a co‐shell. Due to the presence of the Au NT cores, the Au–Pt–CdS nanostructures possess highly enhanced light‐harvesting and strong local‐electric‐field enhancement. Moreover, the intimate and multi‐interface contact generates multiple electron‐transfer pathways (Au to CdS, CdS to Pt and Au to Pt) which guide photoexcited electrons to the co‐catalyst Pt for an efficient hydrogen reduction reaction. By evaluating the hydrogen production rate when aqueous Na₂SO₃–Na₂S solution is used as sacrificial agent, the Au–Pt–CdS hybrid exhibits excellent photocatalytic activity that is about 2.5 and 1.4 times larger than those of CdS/Pt and Au@CdS/Pt, respectively.     

Micro Solid Oxide Fuel Cells on Glass Ceramic Substrates

Miniaturized solid oxide fuel cells are fabricated on a photostructurable glass ceramic substrate (Foturan) by thin film and micromachining techniques. The anode is a sputtered platinum film and the cathode is made of a spray pyrolysis (SP)‐deposited lanthanum strontium cobalt iron oxide (LSCF), a sputtered platinum film and platinum paste. A single‐layer of yttria‐stabilized zirconia (YSZ) made by pulsed laser deposition (PLD) and a bilayer of PLD–YSZ and SP–YSZ are used as electrolytes. The total thickness of all layers is less than 1 µm and the cell is a free‐standing membrane with a diameter up to 200 µm. The electrolyte resistance and the sum of polarization resistances of the anode and cathode are measured between 400 and 600 °C by impedance spectroscopy and direct current (DC) techniques. The contribution of the electrolyte resistance to the total cell resistance is negligible for all cells. The area‐specific polarization resistance of the electrodes decreases for different cathode materials in the order of Pt paste > sputtered Pt > LSCF. The open circuit voltages (OCVs) of the single‐layer electrolyte cells ranges from 0.91 to 0.56 V at 550 °C. No electronic leakage in the PLD–YSZ electrolyte is found by in‐plane and cross‐plane electrical conductivity measurements and the low OCV is attributed to gas leakage through pinholes in the columnar microstructure of the electrolyte. By using a bilayer electrolyte of PLD–YSZ and SP–YSZ, an OCV of 1.06 V is obtained and the maximum power density reaches 152 mW cm⁻² at 550 °C.     

UV-O3 treatment effects on structural changes of low-k thin films

The UV-O₃ treatment effects on the structural properties of low-k films as a function of the treatment time were investigated in this study. The thickness of the samples proportionally decreased with the surface treatment time due to highly reactive ozone and the process gradually modified surface layer more SiO₂-like. Excessive treatment of longer than 60 s adversely affected the low-k film, increasing the dielectric constant of underlying low-k film. After the UV-O₃ treatment for the optimized treatment time of 60 s, the poor nucleation problem of Ru deposition was solved and fully-covered Ru film on low-k film was obtained.     

Microgenerator Using BiSbTe-Pt Thermopile and Pt-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Ceramic Combustor

The performance of a microcombustor thermoelectric generator device based on a thermopile using p-type Bi_0.3Sb_1.7Te₃ (BST) and n-type Pt films has been investigated. The BST films were prepared by two different methods—pulsed laser deposition (PLD) and sputter deposition—on Si₃N₄/SiO₂ multilayers on Si substrate. The ceramic catalyst combustor was patterned on the thermopile end on a thin membrane fabricated by back-side bulk etching of the silicon substrate. At 138°C the thermoelectric power factors of the PLD and sputter-deposited films were 3.6 × 10⁻³ W/mK² and 0.22 × 10⁻³ W/mK², respectively. The power from the generator with the sputter-deposited film was 0.343 μW, which was superior to that of the device with the PLD film, which provided 0.1 μW, for combustion of a 200 sccm flow of 3 v/v% hydrogen in air.     

Redox reactions on modified bilayer lipid membranes for biosensing device

Suitably modified bilayer lipid membranes (BLMs) offer exceptionally good opportunities for probing the electric field effects on charge transfer and redox reactions in biosensor and molecular electronics research and development. This work presents an attempt to form an ultrathin electron-conducting matrix for a biosensing redox device on the basis of a BLM modified with tetracyano-p-quinodimethane (TCNQ), a well-known compound forming charge transfer complexes of ‘organic metal’ behavior. The rationale behind the choice of membrane modifier was the reports of its unusual rectifying current–voltage characteristics when incorporated into BLMs alone or as part of an σ-bridged donor–acceptor molecule of C₁₆H₃₃–Q3CNQ (Z-β-(1-hexadecyl-4-quinolinium)-α-cyano-4-styryldicyano methanide) deposited in the form of a Langmuir–Blodgett film.     

LiNbO_3/ZnO:Al集成结构的外延生长及电性能研究

采用脉冲激光沉积(PLD)法在蓝宝石衬底上先后外延生长了ZnO:Al(ZAO)和LiNbO3(LN)薄膜。通过X射线衍射分析(XRD)可知二者之间的外延关系为:LN(001)//ZAO(001)、LN[110]//ZAO[110]、LN[100]//ZAO[120]。制备了Au/LN/ZAO和ZAO/LN/ZAO两种电容器结构,对其进行了电流-电压(J-E)测试和铁电(P-E)分析,结果表明:LN/ZAO集成结构具有整流作用,ZAO/LN/ZAO结构表现出较好的绝缘性能,所制备的LN薄膜在室温下的剩余极化强度(Pr)约为1×10–6C/cm2,温度的升高能够促进电畴的翻转,使Pr增加为3×10–6C/cm2。     

Investigations on phosphorus doped amorphous/nanocrystalline silicon films deposited by a filtered cathodic vacuum arc technique in the presence of hydrogen gas

Phosphorus doped amorphous/nanocrystalline silicon (a-Si:H/nc-Si:H) thin films have been deposited by a filtered cathodic vacuum arc (FCVA) technique in the presence of hydrogen gas at different substrate temperatures (T_s) ranging from room temperature (RT) to 350 °C. The films have been characterized by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dark conductivity (σ_D), activation energy (ΔE), optical band gap (E_g) and secondary ion mass spectroscopy. The XRD patterns show that RT grown film is amorphous in nature but high temperature (225 and 350 °C) deposited films exhibit nanocrystalline structure with (111) and (220) crystal orientations. The crystallite size of higher temperature grown silicon film evaluated was between 13 and 25 nm. Raman spectra reveal the amorphous nature of the film deposited at RT, whereas higher temperature deposited films show crystalline nature. The crystalline volume fraction of the silicon film deposited at higher temperatures (225 and 350 °C) was estimated to be 58 and 72%. With the increase of T_s, the bonding configuration changes from mono-hydride to di-hydride as revealed by the FTIR spectra. The values of σ_D, ΔE and E_g of silicon films deposited at different T_s were found to be in the range of 5.37×10⁻⁴–1.04 Ω⁻¹ cm⁻¹, 0.05–0.45 eV and 1.42–1.83 eV, respectively. Photoconduction of 3.5% has also been observed in n-type nc-Si:H films with the response and recovery times of 9 and 12 s, respectively. A n-type nc-Si:H/p-type c-Si heterojunction diode was fabricated which showed the diode quality factor between 1.6 and 1.8.     

Novel Diffusion‐Barrier Materials Against Oxygen for High‐Density Dynamic Random Access Memory Capacitors

A new design concept for diffusion barriers in high‐density memory capacitors is suggested, and both RuTiN (RTN) and RuTiO (RTO) films are proposed as sacrificial oxygen diffusion barriers. The newly developed RTN and RTO barriers show a much lower sheet resistance than various other barriers, including binary and ternary nitrides (reported by others), up to 800 °C, without a large increase in the resistance. For both the Pt/RTN/TiSi_x/n⁺⁺poly‐plug/n⁺ channel layer/Si and the Pt/RTO/RTN/TiSi_x/n⁺⁺poly‐plug/n⁺ channel layer/Si contact structures, contact resistance—the most important electrical parameter for the diffusion barrier in the bottom electrode structure of capacitors—was found to be as low as 5 kohm, even after annealing up to 750 °C. When the RTN film was inserted as a glue layer between the bottom Pt electrode layer and the TiN barrier film in the chemical vapor deposited (Ba,Sr)TiO₃ (CVD–BST) simple stack‐type structure, the RTN glue layer was observed to be thermally stable to temperatures 150 °C higher than that to which the TiN glue layer is stable. Moreover, the capacitance of the physical vapor deposited (PVD)–BST simple stack‐type structure adopted TiN glue layer initially degraded after annealing at 500 °C, and, thereafter, completely failed. In the case of the RTN and RTO/RTN glue layers, however, the capacitance continuously increased up to 550 °C. Thus, the new RTN and RTO films, which act as diffusion barriers to oxygen, are very promising materials for achieving high‐density capacitors.