Dissociation phenomena of gas molecule on a metal surface, especially, the effect of motion of a gas molecule on dissociation probability of the molecule on a metal surface was analyzed by Molecular Dynamics (MD) method. Platinum (111) surface and hydrogen were chosen as the metal surface and the gas molecule, respectively. Embedded Atom Method (EAM) was used to express the interaction potential as the functional of the electron density. Parameters or functions of the EAM potential were determined so that the characteristics of the interaction potential obtained by the EAM method were consistent with those obtained by Density Functional Theory (DFT). Dissociation probabilities at specific sites (top, brg and fcc) were obtained by MD method against impinging energy. On the other hand, the dissociation probabilities were determined from dissociation barriers of the sites and orientations of hydrogen molecule. These results were compared with each other and the effect of motion of atoms or molecules on dissociation probability was analyzed. [DOI: 10.1380/ejssnt.2010.211]

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The growth of Ge on Ag:Si(111)-√3×√3-R30° has been studied by low-energy electron microscopy (LEEM), low-energy electron diffraction (LEED) and x-ray photoemission electron microscopy (XPEEM). For submonolayer adsorption of Ag at 550°C, the Ag terminated √3×√3-R30° domains decorate the step edges of the substrate. The wetting layer growth and Ge island nucleation on such a step-edge decorated surface is quite similar to Ge growth on bare Si(111)-7×7. During Ge deposition, the √3×√3-R30° domains dissolve and small Ag terminated 3×1 domains are formed that are distributed over the whole surface. Larger 3×1 domains are found only at the circumference of the three-dimensional (3D) Ge islands. From the Ge 3D island morphology, size distribution and density it is concluded that in this submonolayer Ag pre-adsorption scenario there is only little influence of the Ag on the growth kinetics and island geometry. This is completely different for Ge growth on an entirely covered Ag:Si(111)√3×√3-R30° surface. As compared to growth on bare Si(111)-7×7, a strong increase of the diffusion length is observed that leads to a drastic reduction of the island density. Also the island morphology is strongly affected by Ag pre-adsorption in this regime. Instead of triangular islands, we observe huge, irregularly shaped islands that rather resemble a discontinuous Ge film. [DOI: 10.1380/ejssnt.2010.221]

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We have measured the bulk and surface electronic structure of several ionic liquids of alkyl-imidazolium cations with different alkyl chains (EMIm, BMIm, HMIm, OMIm) and bis(trifluoromethylsulfonyl)imide anions (Tf₂N) by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS He I and He II) as well as metastable induced electron spectroscopy (MIES). The results are compared with the densities of states (DOS) calculated by density functional theory (DFT). By XPS we found the stoichiometry of the respective ILs reproduced, and different carbon atom positions reflected by the splitting of the C(1s) - from the trifluor-methyl groups (CF₃) of the anion with highest binding energy to the alkyl chains of the cation with the lowest one. Furthermore with increasing alkyl chain length the peak related to the alkyl group appears at slightly lower binding energy. The more bulk-sensitive XPS spectra reveal only minor differences in the valence band structure for the studied ionic liquids, whereas the more surface-sensitive methods UPS and especially MIES display distinct changes in the peak-intensities for varying the alkyl chain length. This is a strong indication for either a non-stoichiometric composition of the upmost molecular layer of the IL-surface and/or a reorientation of the cations, probably turning the alkyl chains to the surface. [DOI: 10.1380/ejssnt.2010.241]

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The H:Si(113) structure has been studied by scanning tunneling microscopy and ab initio caluculation. After exposing hydrogen atoms on a clean Si(113) surface, 2×n:H (n = 2,3) structures form. High-resolution STM images reveal that these structures show three types of protrusions. Islands growing one-dimensionally are observed on the local surface area. We performed an ab initio calculation for several possible structural models of the 2×2:H structure. Comparison of observed STM images and simulated images obtained by ab initio calculation clarifies that the structural model composed of a pentamer without an interstitial atom and two three-coordinated site atoms is most favorable. Energy analysis indicates that this structural model is most stable. Based on these results, a structural model of the 2×3:H structure is also proposed. The 2×n:H structures are expected to have anisotropic surface strain. [DOI: 10.1380/ejssnt.2010.261]

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To study atomistic behavior of CO oxidation reaction on Pt(332) surface, we used ultra accelerated quantum chemical molecular dynamics method. First, we estimated the CO oxidation reactivity on step and terrace site of Pt(332) surface. Then, we confirmed that the effect of PtO₂ stripe on step site on reactivity of the CO oxidation. It is shown that ultra accelerated quantum chemical molecular dynamics method is available for the analysis of reaction dynamics on metal surface. [DOI: 10.1380/ejssnt.2010.272]

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In Superhydrophobic systems, a spontaneous transition from heterogeneous to homogeneous regime can occur in time. This transition can hinder the sliding motion of a water drop deposited on the surface, then hampering many applications of such coatings. In this paper, we present a detailed study of this phenomenon on a new kind of Superhydrophobic surfaces, characterized by a strong spatial disorder. We demonstrate that disorder can help to prevent the transition, which assumes a peculiar behavior. [DOI: 10.1380/ejssnt.2010.275]

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The structural modifications of insulators after swift heavy ion irradiation are studied by applying a combination of the Monte-Carlo method (MC), used to describe the excitation and relaxation induced by the penetrating ion in the electronic subsystem, with the two temperature model (TTM) describing the temporal evolution of the lattice temperature heated by the hot electronic system. This MC-TTM combination demonstrates that secondary ionizations play a very important role for the track formation process and is capable to compute important material parameters which are often unaccessible by experiments. It is found that the secondary electron generation leads to an additional energy source in the heat diffusion equation related to energy storage in holes. [DOI: 10.1380/ejssnt.2010.278]

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CdSe quantum dots (QDs) were fabricated by using an alternate supply of Se- and Cd-molecular beams on ZnSe (100) films. The reflection high-energy electron diffraction and its specular beam intensity were used to investigate the moment of dot-generation, dot-coalescence and the alloying of the CdSe wetting layer (WL) and QDs due to the Zn beam irradiation. The alloying of CdSe WL under Zn beam irradiation, increased the critical thickness for the CdSe QDs generation, and the composition of the alloy depended on the irradiation period of Zn beam. The alloying speed of CdSe QDs was found to be fairly fast, but the alloying stopped at a certain Zn composition (self-limiting of diffusion). [DOI:10.1380/ejssnt.2010.283]

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We have demonstrated electric field-induced resistance change in a Cr₂O₃/ultra-thin La_0.7Sr_0.3MnO₃ (LSMO) magnetic heterostructure. By the application of an electric field to the Cr₂O₃ gate, the resistance of the LSMO film was changed. The temperature dependence of the resistance change has a maximum around 220 K. Since the temperature dependence of the magneto-electric (ME) susceptibility of Cr₂O₃ has the same tendency, this resistance change is more likely due to the ME effect of the Cr₂O₃ film. [DOI: 10.1380/ejssnt.2010.318]

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In the present study molecular dynamics simulations were performed for collisions of nanoclusters with each other and with the substrate for determining the mechanism of formation of bound states depending on the cluster size and impact velocity. A highly efficient parallel code for three-dimensional molecular dynamics was developed. This code is based on a spatial domain decomposition algorithm with one-dimensional parallelization and involves an additional subdomain load balancing algorithm that can save a considerable amount of computational time. [DOI: 10.1380/ejssnt.2010.331]

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Resistance random access memory (ReRAM) is attractive as a next generation nonvolatile memory. We investigated an electric field induced resistance change of SrFeO_3-x (SFO) film as a candidate of RRAM material. As-deposited SFO film with high oxygen deficiency, which is expected to have a high oxygen percolation, barely showed hysteresis in current-voltage curve. On the other hand, the annealed sample showed a distinct hysteresis. The amount of oxygen in the sample and easiness of oxygen migration play an important role of the resistance switching properties. [DOI: 10.1380/ejssnt.2010.346]

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Photoemission electron microscopy (PEEM) is used to study Ag surface diffusion on vicinal Si surfaces. The diffusion field is represented by Iso-Coverage Zones around Ag islands during desorption. By analyzing the shape and radius of the Iso-Coverage Zone we can determine diffusion parameters. For anisotropic diffusion the zone has an elliptical shape and the aspect ratio gives a measure for the anisotropy. Using this technique, we study the degree of anisotropy of Ag diffusion on vicinal Si(001) and Si(111). With increasing miscut angles, starting from Si(001) as well as from Si(111), we find a gradually increasing anisotropy, caused by the higher step density. On higher index surfaces, like Si(119), Si(115) and Si(113), we find isotropic diffusion for surfaces with comparable dimer and (double) step structure as on Si(001)-4°, where diffusion is strongly anisotropic. [DOI: 10.1380/ejssnt.2010.372]

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Single layers of carbon (graphene) and hexagonal boron nitride may be grown on transition metal surfaces. The substrates take the role of the support and allow due to their catalytic activity the growth of perfect layers by chemical vapor deposition. The layers are sp² hybridized honeycomb networks with strong in plane σ- and weaker out of plane π-bonds to the substrate and to the adsorbates. This hierarchy in bond strength causes anisotropic elastic properties, where the sp² layers are stiff in plane and soft out of plane. A corrugation of these layers imposes a third hierarchy level in bond energies (α-bonds), with lateral bonding of molecular objects with sizes between 1 and 5 nanometer. The lateral extra bond energies due to the polarizability α of the adsorbates are in the range of thermal energies kT_R at room temperature and are particularly interesting for nanotechnology. The concomitant template function will be discussed. The peculiar bond hierarchy also imposes intercalation as another property of sp² layer systems. Last but not least sp² layer systems are particularly robust, i.e. survive immersion into liquids, which is a promise for sp² layers being useful outside ultra high vacuum. [DOI: 10.1380/ejssnt.2010.62]

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Organic molecule system supported on metal substrate was analyzed by atom probe with two-dimensional ion detector and scanning extractor electrode (3D-SAP). The comparison of angular distribution of detected ions between molecular system and common metal tip showed a significant difference when AP analysis was performed by voltage pulsing. The influence of catalytic property of metal substrate also demonstrated by changing the substrate material. [DOI: 10.1380/ejssnt.2010.69]

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Carbon nanotubes (CNTs) are known as one of the ideal electron emitter material. However, there are many challenges to solve for actual use such as emission current enhancement, emission current stability, life time extension, etc. In this work, methane and ethane gases are used to improve emission characteristics from CNT emitters. A CNT emitter used in this study is a bundle of multi-walled CNTs. In situ field emission microscopy is used to investigate gas effects on emission characteristics. From comparative experiments under different exposure conditions, it is found that gas exposure during field emission is effective to increase emission currents and the effects are comparable between two gases. It is also found that the effect caused by ethane gas has longer life time than that by methane gas. [DOI: 10.1380/ejssnt.2010.77]

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We employed bias-voltage-application in hard x-ray photoelectron spectroscopy (BA-HXPES) to detect electronic states of materials in operating devices. To demonstrate the versatility of this method, we used a metal/SiO₂/Si(100) structure as an ideal platform and found that electronic states at the SiO₂/Si(100) interface were changed depending on the bias-application to the structure. By analyzing the change as a function of bias-voltage, the interface electronic states in the whole Si gap have been directly obtained in which these states cannot be detected without the bias-application. BA-HXPES is a new method to characterize electronic states for advanced materials under device operation. [DOI: 10.1380/ejssnt.2010.81]

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The strains in GaAs/GaAsP superlattices used in spin-polarized photocathodes grown on GaAs and GaP (001) substrates were determined by X-ray diffraction. The thicknesses of the GaAs wells and GaAsP barrier layers were also determined. The band structures of the superlattices were calculated on the basis of these experimentally determined strains and layer thicknesses. The thicknesses and band structures were in good agreement with those observed by transmission electron microscopy and photoluminescence, respectively. The strains induced in the GaAs well layers were approximately linearly dependent upon the phosphorous fraction in the GaAsP layer, and the splitting between the heavy hole band and the light hole band of the superlattices grown on GaP substrates was larger than that of superlattices grown on GaAs substrates. In photocathodes grown on GaP substrates, low polarizations were observed, not due to a lack of band splitting, but to depolarization scattering caused by crystal defects, which were different from that induced in superlattices grown on GaAs substrates. [DOI: 10.1380/ejssnt.2010.125]

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In our previous study, we introduced a new specimen preparation method for the three-dimensional atom probe in which the materials were pared off from oblique back by Ga-FIB. It was suggested that there was a possibility of reducing the gallium implantation in the analyzable regions by using the method. In this study, the gallium implantation level of the method was evaluated with better statistical accuracy by extending the analyzed volume and improving the mass resolution. The specimens were fabricated by means of the conventional and our new methods, and analyzed by atom probe with voltage or laser pulses. The mass spectra with the larger analyzed volume or counts of detected ions and the higher mass resolution than those of our previous study were obtained. Then, the ratio of gallium ions to all detected ions was calculated with better statistical accuracy and it was confirmed that the gallium ion concentration at the surface area was reduced close to or less than the detection limits of our instrument by our new method. [DOI: 10.1380/ejssnt.2010.141]

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The emitter shape dependence of the ion current from a gas field ion source (GFIS) was examined using numerical simulations. The simulator is constructed by an electric field calculation program and the spread sheets which were developed by authors based on the gas supply model. The gas supply for Ar was examined in this article, and was compared with that for He. As a result, when using the same emitter, it demonstrated that the effective capture area of Ar gas is 6.8-8.0 times larger than that of He. For a gas temperature of 300K, the effective capture area of Ar and He were estimated to be 0.0814 and 0.0107 μm², respectively. It was also estimated that the ion current of Ar was 2-2.3 times larger than that of He. Through an actual experiment, a similar tendency was confirmed. For Ar, the influence of the shank taper angle to the ion current was confirmed and that influence is more effective than He. The emitter of small shank angle is capable of higher ion current. Therefore, it was concluded that the ion current can be increased through optimization of the emitter configuration. [DOI: 10.1380/ejssnt.2010.174]

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This paper describes a method for automatic acquisition of a high-resolution transmission electron microscope (TEM) tilt series over the full angular range from −90° to +90° for TEM tomography. The goniometer controller of a conventional TEM was modified to allow external computer control over specimen position along the three translational and one rotational axis. The TEM parameters, stage motion, and image acquisition were synchronously controlled by home-coded software. The shift in the specimen position with each step of rotation was determined at low magnification by the cross-correlation function and then compensated by moving the stage. The image shift coil and objective lens were only used for fine-tuning. As a result, a tilt series over a full angular range was automatically collected at a magnification of around ×200k. The specimen position remained within less than around ±100 nm in the three directions during image collection. [DOI: 10.1380/ejssnt.2010.178]

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We have developed a home-made low-energy Ne scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. To avoid the charging effects, low energy atom particle beams (2keV-²⁰Ne⁰) were projected onto the sample surfaces. As an example of data measured by the developed system, a time of flight spectrum obtained from MgO (001) crystal is presented. [DOI: 10.1380/ejssnt.2010.194]

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Carbon nanotube (CNT) synthesis by arc discharge in water can yield high-crystallinity CNTs using simple equipment. However, it is difficult to control the morphology of CNTs, such as their length, diameter, and number of layers, because the mechanism of CNT production by arc discharge method is complicated. We describe how the morphology of CNTs depends on the cathode metal used in arc discharge. When a nickel or tungsten cathode was used, the layer number distribution was narrower than when a graphite electrode was used. Additionally, the peak position of the inner diameter distribution was downshifted in the case of tungsten. The downshift is considered to be caused by the presence of tungsten nanoparticles as a catalyst. [DOI: 10.1380/ejssnt.2010.203]

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We have observed the laser wavelength (1064, 532, 355 nm) and power (2, 10, 20 nJ per pulse) dependence of field evaporation of carbonaceous material on a tungsten needle by a three dimensional atom probe (3DAP). Carbonaceous materials were deposited by gallium focused ion beam-chemical vapor deposition. Several peaks corresponding to low mass carbon compounds were highest at 355 nm. On the other hand, predominant gallium peaks were observed with 20 nJ per pulse. These results indicate that incident photon energy and tip temperature rising should be taken into consideration when using a femtosecond pulsed-laser atom probe. [DOI: 10.1380/ejssnt.2010.217]

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We have studied the adsorption reaction of dimethyl sulfide (DMS) on the Rh-polyvinylpyrrolidone (Rh(PVP)) nanoparticles by using AFM, XPS and NEXAFS techniques. The AFM images show the morphology of the Rh(PVP) nanoparticles depends on the amount of them. The XPS results indicate that the dissociation reaction of DMS into atomic S does not depend upon the existence of the Rh(PVP) nanoparticles. The NEXAFS results show that there is a strong chemical bonding between Rh(PVP) nanoparticle and atomic S. [DOI: 10.1380/ejssnt.2010.233]

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Shave-off depth profiling utilizes a focused ion beam (FIB) micro-machining process to provide the depth profile. This method is a very unique depth profiling for acquiring a depth profile by the shave-off scanning mode (The fast horizontal sweep of FIB is combined with the very slow vertical sweep). Shave-off depth profiling has its own features, absolute depth scale, pin point depth profiling and application for rough surface and hetero interface. However, the shave-off depth profile is affected by the long tail of FIB because shave-off scanning mode has the distinctive position of the primary ion beam against the sample. In this study, we acquired the different shave-off depth profiles by changing the speed of shave-off scan. Then, we estimated the approximate intensity profile of FIB by the change of the depth resolution of experimental depth profiles. By using this estimated intensity profile of FIB, we carried out the deconvolution to remove the influence of the long tails of FIB. As a result, this new data analysis method enables us to reconstruct highly precise calculated depth profile that reflects not the intensity profile of FIB but the true elemental distribution. [DOI: 10.1380/ejssnt.2010.237]

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We have fabricated the Mg nanoparticles by the gas evaporation method. The AFM observation shows Mg nanoparticles fabricated under the several gas pressures of He have the average diameter of 3.6 nm to 8.0 nm. We have studied the influence of the atmospheric oxidation for the chemical state of the Mg nanoparticles by the Mg K-edge NEXAFS technique. The NEXAFS measurement shows that the chemical state of MgCO₃ exists on the most lateral surface of the Mg nanoparticles and the degree of atmospheric oxidation depends on the size of Mg nanoparticles. [DOI: 10.1380/ejssnt.2010.246]

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We have developed an electron optical instrument for evaluation of multi emitters. The instrument is a versatile emission microscope and is capable of operating as a secondary electron emission microscope (SEEM), a photo electron emission microscope (PEEM) and a field electron emission microscope (FEEM) imaging modes. The most important feature of the instrument is the capability of simultaneous observation of SEEM and FEEM images as well as PEEM and FEEM images in real time and in-situ mode. The operating condition of the multi emitters can be observed in DC mode as well as pulse mode. Thus, the instrument enables us to obtain quantitative knowledge as to the percentage of actually working emitters out of the whole emitters and to evaluate the stability of the emission current from each individual working emitter. [DOI: 10.1380/ejssnt.2010.266]

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We investigated the Verwey transition in field-emitted electrons from <110>-oriented magnetite whisker through the measurements of spin polarization. On temperature dependences varying tip voltage as a parameter from 850 V to 950 V, a rapid increase of spin polarization around 100 K due to the Verwey transition was observed more clearly with increase of applied voltage. This results indicates that t_2g band of Fe₃O₄ at surface becomes narrower and possesses lower energy than an ideal bulk state. [DOI: 10.1380/ejssnt.2010.321]

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The phase transition between √3×√3 and 3×3 structures on Sn adsorbed Ge(111) surface is discussed in terms of an order-disorder structural transition. The Monte Carlo calculation is performed to obtain the surface electronic states with a tight-binding model. The calculated reciprocal-space-projected density of states can reproduce both experimental results of the high and low temperature phases by the angle resolved ultraviolet photoemission spectroscopy measurements. [DOI: 10.1380/ejssnt.2010.349]

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The initial adsorption of C₆₀ molecules on an Al nanocluster array template, an Si(111)-7× 7 surface with an Al nanocluster array, was observed at various temperatures using a variable temperature scanning tunneling microscope (STM). STM images showed that C₆₀ molecules stay above the dimer lines near the corner hole, with one of the 6—6 bonds facing toward the adsorbing surface and forming chemical bonds with two neighboring corner Si adatoms. The strong interaction immobilized C₆₀ molecules on the adsorbing template. [DOI: 10.1380/ejssnt.2010.354]

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The exciton-photon matrix elements, exciton-phonon matrix elements, and resonance Raman intensity for radial breathing mode are calculated as a function of a dielectric constant κ which represents surrounding materials of single wall carbon nanotubes using the extended tight binding method. Since the exciton wave function in the real space becomes more delocalized with increasing κ, the exciton-photon matrix elements and resonance Raman intensity for radial breathing mode decrease with increasing κ, while the exciton-phonon matrix elements are not so sensitive to the change of the exciton wave function. [DOI: 10.1380/ejssnt.2010.358]

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he confinement of excitons in a single wall carbon nanotube (SWNT) is discussed based on an analysis of the environmental effect on the optical transition energies, E_ii, measured by photoluminescence spectroscopy. We use the effective dielectric constant κ as a function of nanotube diameter and exciton size that has also been used to reproduce excitonic transition energies E_ii from resonance Raman spectroscopy experiments. When we focus our attention to the lowest transitions, E₁₁ region, we find a systematic deviation of the κ values for semiconducting type-I and type-II carbon nanotubes. We suggest that the E₁₁ energies observed by photoluminescence are upshifted to the calculated E₁₁ energies due to the confinement of excitons in the SWNTs. Considering this effect, the same energy shift formula for the environmental effect as that for the the Raman spectroscopy results can be used to reproduce experimental E_ii values from photoluminescence spectroscopy within a good accuracy, hence providing an accurate assignment of many nanotube chiralities. [DOI: 10.1380/ejssnt.2010.367]

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