Coulomb blockade behaviors in individual Au nanoparticles as observed through noncontact atomic force spectroscopy at room temperature

Coulomb blockade behaviors in individual Au nanoparticles of 2 nm core diameter in double-barrier structures have been studied by means of noncontact atomic force spectroscopy (NC-AFS) at room temperature. The Au nanoparticles with a 1-decanethiol ligand were chemisorbed by 1,10-decanedithiol molecules of a mixed 1-octanethiol/1,10-decanedithiol self-assembled monolayer coated on a Au(111) surface; these particles were observed through NC-AFS. NC-AFS measurements of the cantilever frequency shift-sample voltage (Δf-V(S)) curves were sequentially conducted on three Au nanoparticles under the same experimental conditions; the Δf-V(S) curves were found to deviate from the parabolic (Δf(N)) curve in the cases where no extra charge existed on the Au core. The experimental Δf(CB)(=Δf-Δf(N)) and Δf(CB)/V curves agree well with the theoretical curves obtained using a golden-rule calculation and the same parabolic parameters. All the results, through NC-AFS, suggest Coulomb blockade behaviors in the Au nanoparticles at room temperature.     

Coulomb blockade induced negative differential resistance effect in a self-assembly Si quantum dots array at room temperature

We report a Coulomb blockade induced negative differential resistance (NDR) effect at room temperature in a self-assembly Si quantum dots (Si-QDs) array (Al/SiO₂/Si-QDs/SiO₂/p-Si), which is fabricated in a plasma enhanced chemical vapor deposition system by using layer-by-layer deposition and in-situ plasma oxidation techniques. Obvious NDR effects are directly observed in the current-voltage characteristics, while corresponding capacitance peaks are also identified at the same voltage positions in the capacitance-voltage characteristics. The NDR effect in dot array, arising from the Coulomb blockade effect in the nanometer-sized Si-QDs, exhibits distinctive scan-rate and scan-direction dependences and differs remarkably from that in the quantum well structure in the formation mechanism. Better understanding of the observed NDR effect in Si-QDs array is obtained in a master-equation-based numerical model, where both the scan-rate and scan-direction dependences are well explained.     

Abnormal structure of titanium formed by ion beam sputtering at room temperature

Stable fcc modification of titanium (a=0.420 nm) has been observed in ion beam sputtered films at room temperature. When the deposition rates are above 0.8 Å/s, the normal hcp structure is obtained.     

Ultraporous monoliths of alumina prepared at room temperature by aluminium oxidation

The oxidation of aluminium through a mercury film usually leads to unorganized filaments or fibrous powders of hydrated alumina. Here, we show that the addition of a small amount of silver in the mercury considerably modifies the growth process, and that large sized monoliths can be obtained through a new process. Regular growth can be maintained at a typical rate of 2.1 μm s⁻¹ (∼0.75 cm/h) for several hours. The samples consist of tangled nanometric fibres and have an open porosity of 99%. The influence of various parameters has been studied and optimal conditions for regular growth have been determined. Anhydrous alumina monoliths with a nanometric microstructure and a high-specific area are obtained after thermal treatments that remove water.     

Manipulation of periodic Coulomb blockade oscillations in ultra-scaled memories by single electron charging of silicon nanocrystal floating gates

Ultra-scaled silicon nanocrystal memories fabricated on a silicon-on-insulator substrate exhibit very periodic Coulomb blockade oscillations at 4.2 K. We control the phase of those oscillations by charging and discharging the floating gate with a single electron. We can distinguish between resonances due to the whole channel area covered by the gate and impurity levels localized in the access regions and less coupled to the gate. Comparison with a reference device without nanocrystals is also reported.     

Noble metal nanoparticles deposited on self-assembled monolayers by pulsed laser deposition show coulomb blockade at room temperature

Nanometer-sized noble-metal clusters are fabricated on top of alkylthiolate self-assembled monolayers (SAMs) on annealed gold by pulsed laser deposition at elevated pressures. The size distribution of the clusters depends on the metal and on the pressure during the deposition. Scanning tunneling microscopy (STM) and conductive probe atomic force microscopy (CP-AFM) showed that the metal clusters are insulated from the substrate on top of the SAM. Coulomb blockades could be measured at room temperature by STM for palladium clusters on decanethiol SAMs.     

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced meta-magnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and mag-netostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn0.983Co1.017Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn0.983Co1.017Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.     

Drawability of AZ31 magnesium alloy sheet produced by equal channel angular rolling at room temperature

The objective of this study is to investigate the possibility of improved drawability of AZ31 magnesium alloy sheet produced by equal channel angular rolling process at room temperature. Although with similar optical microstructure, the limiting drawing ratio of AZ31 magnesium alloy sheet is improved from 1.2 to 1.6 for the specimens before and after equal channel angular rolling, which is due to the changing crystal orientation that induces shear deformation through this process. The enhanced drawability in AZ31 magnesium alloy sheet provides the possibility for drawing at ambient temperature by controlling the crystal orientation in AZ31 magnesium alloy sheet.     

Effects of grain size on compressive behaviour in ultrafine grained pure Mg processed by equal channel angular pressing at room temperature

Ultrafine-grained pure magnesium with an average grain size of 0.8 μm was produced by refining coarse-grained (980 μm) ingot by multi-pass equal channel angular pressing (ECAP) at room temperature with the application of a back pressure. The compressive deformation behaviour at room temperature depended on grain size, with deformation twinning and associated work hardening observed in coarse-grained Mg, but absent in the ultrafine grained material as decreasing grain size raised the stress for twinning above that for dislocation slip. The ultrafine grained Mg showed good plasticity with prolonged constant stress after some initial strain hardening.     

The preparation of nanoporous gold electrodes by electrochemical alloying/dealloying process at room temperature and its properties

A novel method of preparing nanoporous gold has been developed: nanoporous gold materials have been prepared on the bulk gold substrates by galvanostatic electrochemical alloying and galvanostatic electrochemical dealloying processes at 0.05 mA in 1 M LiPF₆, EC/DMC(1:1, v/v) solution at room temperature. The result shows that the particle size ranges from 50 nm to 100 nm on the surface of the prepared nanoporous gold by Quanta 200FEG scanning electron microscope. And it is determined that the maximum anodic current for the nanoporous gold electrode is 50 times higher than that of the polished gold electrode in 0.5 M KOH by the cyclic voltammograms.     

Desulfurization from thiophene by SO(4)(2-)/ZrO(2) catalytic oxidation at room temperature and atmospheric pressure

Thiophene, due to its poison, together with its combustion products which causes air pollution and highly toxic characteristic itself, attracted more and more attention to remove from gasoline and some high concentration systems. As the purpose of achieving the novel method of de-thiophene assisted by SO(4)(2-)/ZrO(2) (SZ), three reactions about thiophene in different atmosphere at room temperature and atmospheric pressure were investigated. SO(4)(2-)/ZrO(2) catalyst were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The products were detected by gas chromatography-mass spectrometry (GC-MS). XP spectra show that ozone-catalyst system (SZO) have two forms of sulfur element (S(6+) and S(2-)) on the catalyst surface, which distinguished from that of air-catalyst system (SZA) and blank-catalyst system (SZB) (S(6+)). And the results of GC-MS exhibited that some new compounds has been produced under this extremely mild condition. Especially, many kinds of sulfur compounds containing oxygen, that is easier to be extracted by oxidative desulfurization (ODS), have been detected in the SZA-1.5h and SZB-3h system. In addition, some long chain hydrocarbons have also been detected. While in SZO-0.5h system, only long chain hydrocarbons were found. The results show that total efficiency of desulfurization from thiophene with ozone near to 100% can be obtained with the SO(4)(2-)/ZrO(2) catalytic oxidation reaction.     

Growth of silicon nanowires of controlled diameters by electrodeposition in ionic liquid at room temperature

Silicon nanowires were fabricated for the first time by electrochemical template synthesis at room temperature. This innovative, cheap, and simple process consists of electroreduction of Si ions using a nonaqueous solvent and insulating nanoporous membranes with average pore diameters from 400 to 15 nm which fix the nanowires diameters. Characterization techniques such as scanning and transmission electron microscopies, infrared absorption measurements, X-ray diffraction experiments, energy dispersive X-ray, and Raman spectrometries show that the as-deposited silicon nanowires are amorphous, composed of pure Si and homogeneous in sizes with average diameters and lengths well matching with the nanopores' diameters and the thicknesses of the membranes. Thanks to annealing treatments, it is possible to crystallize the Si nanowires, demonstrating the potentiality for this innovative electrochemical process to obtain a wide range of Si nanowires with well controlled diameters and lengths.     

Determination of water in room temperature ionic liquids by cathodic stripping voltammetry at a gold electrode

An electrochemical method based on cathodic stripping voltammetry at a gold electrode has been developed for the determination of water in ionic liquids. The technique has been applied to two aprotic ionic liquids, (1-butyl-3-ethylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate), and two protic ionic liquids, (bis(2-hydroxyethyl)ammonium acetate and triethylammonium acetate). When water is present in an ionic liquid, electrooxidation of a gold electrode forms gold oxides. Thus, application of an anodic potential scan or holding the potential of the electrode at a very positive value leads to accumulation of an oxide film. On applying a cathodic potential scan, a sensitive stripping peak is produced as a result of the reduction of gold oxide back to gold. The magnitude of the peak current generated from the stripping process is a function of the water concentration in an ionic liquid. The method requires no addition of reagents and can be used for the sensitive and in situ determination of water present in small volumes of ionic liquids. Importantly, the method allows the determination of water in the carboxylic acid-based ionic liquids, such as acetate-based protic ionic liquids, where the widely used Karl Fischer titration method suffering from an esterification side reaction which generates water as a side product.     

The effect of grain refinement by warm equal channel angular extrusion on room temperature twinning in magnesium alloy ZK60

The effect of the grain structure produced by warm equal channel angular extrusion (ECAE) on twinning under subsequent room temperature deformation of magnesium alloy ZK60 was investigated. It was shown that a bi-modal grain structure, characteristics of which are determined by the ECAE temperature and the number of passes, has a strong effect on the tendency to room temperature twinning. The highest density of twins generated during room temperature deformation was found in material pre-strained by ECAE at 300C that exhibited a uniform recrystallised grain structure with an average grain size large enough for twinning to occur.     

Induced forming modes in a pre-consolidated woven polypropylene composite during stretch forming process at room temperature: I. Experimental studies

In the current study, rectangular specimens of pre-consolidated woven Self-Reinforced Polypropylene (SRPP) possessing different fibre orientations and aspect ratios were stretch formed in an open die. Induced displacements were recorded by an in-situ 3D photogrammetric measurement system. Resultant principal strains were investigated to clarify the role of different deformation modes during stamp forming. The dependency of induced deformation modes to the specimens’ geometries was studied. A novel path/deformation dependent failure criterion was established to distinguish between safe and failed regions of SRPP in a stamping process and to elucidate the dependency between failure and induced forming modes in a woven composite. The experimental results highlighted the suitability of consolidated SRPP to be formed into complex doubly curved geometries by the stamp forming process at room temperature. It was found that required forming depths could be achieved if a proper combination of specimen size, boundary condition, and fibre orientation was selected.