Multiwalled carbon nanotube supported Pt–Sn–M (M = Ru,Ni, and Ir) catalysts for ethanol electrooxidation

In the present study, Pt–Sn–M (M = Ru, Ni, and Ir) nanocatalysts were supported on multiwalled carbon nanotube and their electrocatalytic activity for ethanol oxidation in membraneless fuel cells was investigated. The combination of monometallic Pt/MWCNTs, bi-metallic Pt–Sn/MWCNTs, and tri-metallic Pt–Sn–Ru/MWCNT, Pt–Sn–Ni/MWCNT, and Pt–Sn–Ir/MWCNT nanocatalysts were prepared by the ultrasonic assisted chemical reduction method. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were used for the catalyst characterization. The electrocatalytic activities of the catalysts were investigated in half-cell experiments using cyclic voltammetry (CV), CO stripping voltammetry, and chronoamperometry (CA). During the experiments performed on a single membraneless ethanol fuel cell (MLEFC), the Pt–Sn–Ir/MWCNTs exhibited a better catalytic activity from among all the catalysts prepared, with a power density of 39.25 mW cm^?2.     

Electrochemical characterization of platinum-based anode catalysts for membraneless fuel cells

In the present work, carbon-supported Pt–Sn, Pt–Ru, and Pt–Sn–Ru electrocatalysts with different atomic ratios were prepared by alcohol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cells. The synthesized electrocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrocatalytic activities were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results obtained at room temperature showed that the addition of Sn and Ru to the pure Pt electrocatalyst significantly improved its performance in ethanol electro-oxidation. The onset potential for ethanol electro-oxidation was 0.2 V vs. Ag/AgCl, in the case of the ternary Pt–Sn–Ru/C catalysts, which was lower than that obtained for the pure Pt catalyst (0.4 V vs. Ag/AgCl). During the experiments performed on single membraneless fuel cells, Pt ? Sn ? Ru/C (70:10:20) performed better among all the catalysts prepared with power density of 36 mW/cm². The better performance of ternary Pt–Sn–Ru/C catalysts may be due to the formation of a ternary alloy and the smaller particle size.     

Interplay of strain and interdiffusion in Heusler alloy bilayers

Combining conventional and inverse magnetocaloric materials promises to enhance solid state refrigeration. As a first step here we present epitaxial Ni–Mn–Ga/Ni–Mn–Sn bilayer films. We examine the dependence of the lateral and normal lattice constants on the deposition sequence by combining experimental and ab initio techniques. Structural properties are determined with X‐ray diffraction as well as highresolution transmission electron microscopy, while ab initio calculations explain the interplay of strain, local relaxations and the interdiffusion of atoms. The latter is confirmed by Auger electron spectroscopy and is expected to have a noticeable impact on the functional properties of the Heusler materials. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

锂离子电池Sn-Ti合金负极材料的制备及性能研究

采用磁控溅射沉积技术制备了纳米级Sn-Ti合金负极材料,并用X射线衍射和扫描电子显微镜进行表征,用高精度电池测试系统进行充放电和循环伏安测试.结果表明先镀Sn后镀Ti（Sn/Ti复合膜）和先镀Ti后镀Sn（Ti/Sn复合膜）具有很大的性能差异,其中Sn/Ti复合膜具有优异的循环稳定性和较高的可逆容量.首次放电容量和充电容量分别为9275 mAh/g和6954 mAh/g,首次库仑效率为75％,经30次循环后,该电极的放电容量保持为4152 mAh/g,这主要归因于活性物质Sn与电解液界面之间存在非活 关键词： 锂离子电池 磁控溅射 Sn-Ti合金 电化学性能     

Synthesis of compositionally controllable Cu<Subscript>2</Subscript>(Sn<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript>)S<Subscript>3</Subscript> nanocrystals with tunable band gaps

In this work, we show that compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals can be successfully synthesized by the hot-injection method through careful tuning the Ge/(Sn+Ge) precursor ratio. The band gaps of the resultant nanocrystals are demonstrated to be linearly tuned from 1.45 to 2.33 eV by adjusting the composition parameter x of the Ge/(Sn+Ge) ratio from 0.0 to 1.0. The crystalline structures of the resultant NCs have been studied by the X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), select area electron diffraction (SAED), and Raman spectroscopy. A ligand exchange procedure is further performed to replace the native ligands on the surface of the NCs with sulfur ions. The photoresponsive behavior indicates the potential use of as-prepared Cu₂(Sn_1–xGe_x)S₃ nanocrystals in solar energy conversion systems. The synthesis of compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals reported herein provides a way for probing the effect of Ge inclusion in the Cu-Sn-S system thin films.     

Fractal Germanium Patterns: Annealing Strategies and Perspectives of Metal-Induced Crystallization

Semiconductor germanium (Ge) in contact with some metals, such as Al, Pd, and Au, etc., is a class of distinctive materials with non-integer dimensions (D) that differ from integer dimensional materials, such as nanoparticles (0D), nanowires/nanorods//nanotubes/nanoribbons (1D), and thin films (2D). In this article, we describe our efforts toward understanding the annealing strategies and perspectives of metal-induced crystallization for the amorphous Ge embedded in Al, Pd, and Au matrices prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the Al-induced crystallization of amorphous Ge and formation processes of fractal Ge patterns. In addition, the fractal Ge patterns induced by Pd nanoparticles with solid-state reactions will be summarized in detail. Temperature-dependent properties of resistance and fractal dimension in Pd/Ge bilayer films will be expounded. In particular, the nonlinear optical properties are discussed in detail. Finally, we will emphasize the in situ observations by transmission electron microscopy and multi-fractal analysis for the fractal Ge patterns induced by Au nanoparticles. Moreover, the polycondensation-type fractal Ge patterns with non-integer dimensions, thick branches and smooth edges, and metastable gamma-Au_0.6Ge_0.4 are further investigated. The computer simulation indicated that the experimental results are good agreement with the simulation patterns, which were carried out by a ripening mechanism of non uniform grains. This review may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices.     

Formation and structure of a (√19 × √19)R23.4°-Ge/Pt(1 1 1) surface alloy

An ordered (√19 × √19)R23.4°-Ge/Pt(1 1 1) surface alloy can be formed by vapor depositing one-monolayer Ge on a Pt(1 1 1) substrate at room temperature and subsequently annealing at 900-1200 K. The long-range order of this structure was observed by low energy electron diffraction (LEED) and confirmed by scanning tunneling microscopy (STM). The local structure and alloying of vapor-deposited Ge on Pt(1 1 1) at 300 K was investigated by using X-ray Photoelectron Diffraction (XPD) and low energy alkali ion scattering spectroscopy (ALISS). XPS indicates that Ge adatoms are incorporated to form an alloy surface layer at ∼900 K. Results from XPD and ALISS establish that Ge atoms are substitutionally incorporated into the Pt surface layer and reside exclusively in the topmost layer, with excess Ge diffusing deep into the bulk of the crystal. The incorporated Ge atoms at the surface are located very close to substitutional Pt atomic positions, without any corrugation or “buckling”. Temperature Programmed Desorption (TPD) shows that both CO and NO adsorb more weakly on the Ge/Pt(1 1 1) surface alloy compared to that on the clean Pt(1 1 1) surface.     

Structure and strain tunings of topological anomalous Hall effect in cubic noncollinear antiferromagnet Mn_3Pt epitaxial films

Antiferromagnets(AFMs) with chiral noncollinear spin structure have attracted great attention in recent years. However, the existing research has mainly focused on hexagonal chiral AFMs, such as Mn_3Sn, Mn_3Ga, Mn_3Ge with low crystalline symmetry.Here, we present our systematical study for the face-centered cubic noncollinear antiferromagnetic Mn_3Pt. By varying the alloy composition(x), we have successfully fabricated antiferromagnetic Mn_(1-x)Pt_x epitaxial films on MgO substrates and have observed a crystalline structure transition from L1_0 MnPt to L1_2 Mn_3Pt. The Mn_3Pt exhibits a large anomalous Hall effect, which is in the same order of magnitude as those of ferromagnetic materials. Moreover, a large thickness-evolved strain effect is revealed in Mn_3Pt films by X-ray diffraction(XRD) analysis based on the Scherrer method. Our work explores Mn_3Pt as a promising candidate for topological antiferromagnetic spintronics.     

Abnormal reduction of coercivity on magnetic cobalt–platinum alloy films

Ultrathin Co–Pt alloy films as substrate were studied by the surface magneto-optical Kerr effect. As the growth of Ni, the films show uniquely high polar Kerr responses without any in-plane signals. The coercivity decreased until the thickness of Ni film was higher than 5 ML. A new surface structure was discovered at 7–10 ML Ni/Co–Pt films by the low-energy electron diffraction. Interestingly, polar Kerr signal and coercivity of the 10 ML Ni/Co–Pt(1 1 1) template film reduced rapidly as Co films were further deposited onto only about 1–2 ML. Then the films show a canted magnetization with a rollback hysteresis in the polar configuration during the growth of Co. Coercivity of the 7 ML Co/Ni/Co–Pt film was found unusually down to almost 100 Oe.The corresponding magic number at around 7 ML of Co in the abnormal reduction of coercivity may be attributed to the cluster formations of Co.     

Decorating graphene sheets with Pt nanoparticles using sodium citrate as reductant

In this paper, we proposed a novel and green approach for the synthesis of graphene nanosheets (GNS) and Pt nanoparticles-graphene nanosheets (Pt/GNS) hybrid materials, employing graphene oxide (GO) as precursor and sodium citrate as environmentally friendly reducing and stabilizing agent. The microstructures of GO and Pt/GNS were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and electrochemical measurements. The results confirmed that the uniform size distribution of Pt nanoparticles on the surface of GNS without agglomerates could be easily obtained via using sodium citrate as reductant, moreover the Pt/GNS hybrids exhibited high electrochemical activity.     

Influence of plasma pressure on the growth characteristics and ferroelectric properties of sputter-deposited PZT thin films

PZT thin films of thickness (320-1040) nm were synthesized on Si/SiO₂/Ti/Pt multilayered substrates by radio frequency magnetron sputtering. The influence of plasma pressure in the range of (0.24-4.9) Pa, during deposition, on the structural, electrical and ferroelectric properties of the PZT films was systematically studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and cross-sectional transmission electron microscopy (XTEM) were employed for structural study. Nano-probe Energy Dispersive (EDX) line scanning was employed to investigate the elemental distribution across the film-bottom electrode interface. I-V characteristics and polarization-electric field (P-E) hysteresis loop of the films were measured. The study reveals that the plasma pressure has a strong influence on the evolution and texture of the ferroelectric perovskite phase and microstructure of the films. At an optimum plasma pressure of 4.1 Pa, PZT films are grown with 93% perovskite phase with (1 1 1) preferred orientation and uniform granular microstructure. These films show a saturation polarization of 67 μC/cm², remnant polarization of 30 μC/cm² and coercive field of 28 kV/cm which, according to the literature, seem to be suitable for device applications.Transmission electron microscopy (TEM) study shows that at a plasma pressure of 4.1 Pa, the PZT/bottom Pt interface is sharp and no amorphous interlayer is formed at the interface. At a higher plasma pressure of 4.9 Pa, poor I-V and P-E hysteresis loop are observed which are interpreted as due to an amorphous interlayer at the film-bottom electrode interface which is possibly enriched in Pb, Zr, O and Pt.     

不同衬底上Pb(Zr0.52Ti0.48)O3择优取向铁电薄膜的制备和研究

通过MOD法在Si(100)和Pt(111)/Ti/SiO₂/Si基片上制备出LaNiO₃ ( LNO)薄膜.再通过修 正的Sol-gel法，在Pt(111)/Ti/SiO₂/Si,LNO/Si(100)和LNO/Pt/Ti/SiO_{2< /sub>/Si三种衬底上 制备出具有择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜. 经XRD分析表明，L NO薄膜具有(100)择优取向的类钙钛矿结构；PZT薄膜均具有钙钛矿结构，且在Pt(111)/Ti/S iO2/Si衬底上的薄膜以(110)择优取向，在LNO/Pt/Ti/SiO2/Si和LN O/Si(100)衬底上的 薄膜以(100)择优取向.经场发射SEM分析和介电、铁电性能测试表明，在LNO/Si和LNO/Pt/Ti /SiO2/Si衬底上的PZT薄膜的平均粒径、介电常数以及剩余极化强度均比以Pt/T i/SiO2/Si为衬底的薄膜大. 关键词： 3}薄膜')" href="#">LaNiO₃薄膜 PZT铁电薄膜 择优取向 剩余极化强度     

700℃退火下铝调制镍硅锗薄膜的外延生长机理

文章研究了在700℃退火下,铝插入层调制镍和硅锗合金反应形成单相镍硅锗化物的生长机理.透射电镜测试结果表明,镍硅锗薄膜和硅锗衬底基本达到赝晶生长;二次质谱仪和卢瑟福沟道背散射测试结果表明,在镍硅锗薄膜形成的过程中,铝原子大部分移动到镍硅锗薄膜的表面.研究结果表明,铝原子的存在延迟了镍和硅锗合金的反应,镍硅锗薄膜的热稳定性和均匀性都得到了提高.最后,基于上述实验结果给出了铝原子调制形成外延镍硅锗薄膜的生长机理.     

Synthesis and characterization of Pt–Sn–Ce/MC ternary catalysts for ethanol oxidation in membraneless fuel cells

The present work represents the mesoporous carbon-supported Pt–Sn and Pt–Sn–Ce catalysts with different mass ratios have been prepared by co-impregnation reduction method. The prepared catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigation. The XRD patterns of prepared Pt/MC (100) Pt–Sn/MC (75:25), Pt–Ce/MC (75:25), and Pt–Sn–Ce/MC (75:20:05) catalysts showed that Pt metal was the predominant material in all the samples, with peaks attributed to the face-centered cubic (fcc) crystalline structures. Additionally changes in the lattice parameters observed for Pt suggest the incorporation of Sn into the Pt crystalling structure with the formation of an alloy mixture with the SnO₂ phase. The TEM analysis designates that the prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrochemical studies showed that ternary catalyst shows best performance for oxidation of ethanol molecule at normal temperature. The enhanced ethanol oxidation activity for the ternary Pt–Sn–Ce catalyst is mainly attributed to the synergistic effect of bifunctional mechanism with electronic effect. Additionally, chemical nature of ceria affords oxygen-containing molecule to oxidize acetaldehyde to acetic acid. In this present context, 1 M ethanol was used as a fuel, 0.1 M sodium perborate was used as an oxidant, and 0.5 M sulfuric acid was used as an electrolyte. In mesoporous carbon-supported binary Pt–Sn and ternary Pt–Sn–Ce anode catalysts were effectively tested in a single membraneless fuel cell at normal temperature. The presence of Sn and Ce enhances the CO oxidation; they produced an oxygen-containing species to oxidize acetaldehyde to acetic acid.     

Sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size formed by laser irradiation

SiGe spheres with different diameters are successfully fabricated on a virtual SiGe template using a laser irradiation method. The results from scanning electron microscopy and micro-Raman spectroscopy reveal that the diameter and Ge composition of the SiGe spheres can be well controlled by adjusting the laser energy density. In addition, the transmission electron microscopy results show that Ge composition inside the Si Ge spheres is almost uniform in a well-defined, nearly spherical outline. As a convenient method to prepare sphere-shaped SiGe micro/nanostructures with tunable Ge composition and size, this technique is expected to be useful for Si Ge-based material growth and micro/optoelectronic device fabrication.     

Room temperature oxidation of Cu(3)Ge films grown on Si and Si(1-x)Ge(x) substrates

Room temperature oxidation of Cu3Ge films grown on Si, Si(0.85)Ge(0.15) and Si(0.52)Ge(0.48) substrates, respectively, at a temperature of 200-300 degrees C was studied using transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM). For Cu(3)Ge films grown at 200 degrees C and subsequently exposed in air for 1 week oxide protrusions and oxide networks appeared in the film surface and grain boundaries of Cu(3)Ge, respectively. At room temperature O from air and Si from the substrate, diffused along the grain boundaries of Cu(3)Ge to react with Cu(3)Ge grains, initiating the Cu(3)Si-catalyzed oxidation. Cu(3)Ge films are superior to Cu(3)(Si(1-x)Gex) films in retarding Cu(3)Si-catalyzed oxidation. Annealing at 300 degrees C allowed Si diffusion from the substrate into the Cu(3)Ge overlayer to form Cu(3)(Si(1-x)Gex), enhancing the Cu(3)Si-catalyzed oxidation rate. In the present study, Cu(3)Ge films grown on Si(0.52)Ge(0.48) at 200 degrees C show the best resistance to room temperature oxidation because higher Ge concentration in the substrate and lower temperature annealing can more effectively retard Si diffusion from the substrate into the Cu(3)Ge overlayer, and hence reduce the Cu(3)Si-catalyzed oxidation rate.     

Validation and traceability of XRF and SEM‐EDS elemental analysis results for solder in high‐reliability applications

A procedure and calibration samples were developed for X‐ray fluorescence spectrometry and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) analysis methods for Sn and Pb amounts in solder and coatings. Test methods are needed by laboratories that perform destructive physical analysis of high‐reliability electronics for MIL‐STD‐1580B. Calibrants are prepared by evaporative deposition of multiple, alternating quantities of pure Sn and pure Pb having mass per unit area proportional to mass fractions of Sn and Pb in a solder being mimicked. Validation reference materials are prepared by evaporative deposition of thin films of SRM 1729 Tin Alloy (97Sn–3Pb). Films are created on high‐purity Ni foil to mimic some actual electronics structures and prevent charging during SEM‐EDS measurements. Maximum thickness of films prepared this way must be kept below approximately 1 µm to ensure that the entire thickness is probed by the primary X‐ray or electron beam and that measured X‐rays come from the entire thickness of all films. Detailed procedures are presented, and method performance was characterized. The primary purpose is to create calibrations for Sn and Pb that are simple to implement and establish traceability to the international system of units. The secondary purpose is to validate calibrations using a certified reference material to prove that, for simpler structures of thin solder coatings on metal, both X‐ray fluorescence and SEM‐EDS provide accurate results. Keeping films thin may be unrealistic in comparison with some, if not many, electronic structures, but this approach enables a laboratory to demonstrate competence in a controlled manner. Copyright © 2014 John Wiley & Sons, Ltd.     

Growth and alloy formation of ultrathin Ni films on Co/Pt(1 1 1)

Low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) were used to study the growth and the structural evolution of Ni/Co/Pt(1 1 1) following high-temperature annealing. From the oscillation of the specular beam of the LEED and Auger uptake curve, we concluded that the growth mode of thin Ni films on 1 ML Co/Pt(1 1 1) is at least 2 ML layer-by-layer growth before three-dimensional island growth begins. The alloy formation of Ni/1 ML Co/Pt(1 1 1) was analyzed by AES. The temperature for the intermixing of Ni and Co layers in the upper interface without diffusing into the bulk of Pt is independent of the thickness of Ni when a Co buffer is one atomic monolayer. After the temperature was increased, formations of Ni-Co-Pt alloy, Ni-Pt alloy and Co-Pt alloy were observed. The temperature required for the Ni-Co intermixing layer to diffuse into Pt bulk increases with the thickness of Ni. The interlayer distance as a function of annealing temperature for 1 ML Ni/1 ML Co/Pt(1 1 1) was calculated from the I-V LEED. The evolution of LEED patterns was also observed at different annealing temperatures.     

Minute SiGe quantum dots on Si(001) by a kinetic 3D island mode

We investigated the initial growth stages of Si(x)Ge(1-x)/Si(001) by real time stress measurements and in situ scanning tunneling microscopy at deposition temperatures, where intermixing effects are still minute (< or =900 K). Whereas Ge/Si(001) is a well known Stranski-Krastanow system, the growth of SiGe alloy films switches to a 3D island mode at Si content above 20%. The obtained islands are small (a few nanometers), are uniform in shape, and exhibit a narrow size distribution, making them promising candidates for future quantum dot devices.     

Synthesis and size differentiation of Ge nanocrystals in amorphous SiO2

Germanosilicate layers were grown on Si substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed at different temperatures ranging from 700–1010 °C for durations of 5 to 60 min. Transmission electron microscopy (TEM) was used to investigate Ge nanocrystal formation in SiO₂:Ge films. High-resolution cross section TEM images, electron energy-loss spectroscopy and energy dispersive X-ray analysis (EDX) data indicate that Ge nanocrystals are present in the amorphous silicon dioxide films. These nanocrystals are formed in two spatially separated layers with average sizes of 15 and 50 nm, respectively. EDX analysis indicates that Ge also diffuses into the Si substrate. PACS 68.73.Lp; 61.46.Hk; 61.46.-w; 68.65.Hb; 61.82.Rx