PacSurf2014 Session NM-TuP: Nanomaterials Poster Session

Tuesday, December 9, 2014 4:00 PM in Mauka

Tuesday Afternoon

Time Period TuP Sessions | Topic NM Sessions | Time Periods | Topics | PacSurf2014 Schedule

NM-TuP-1 Electronic Structure of Titanate Nanoribbons Studied by O 1s and Ti 2p X-Ray Absorption and 3-Dimensional Dichroism Measured in a Scanning Transmission X-ray Microscope (STXM)
Adam Hitchcock, Xiaohui Zhu (McMaster University, Canada); Carla Bittencourt (University of Mons, Belgium); Polona Umek (Jožef Stefan Institute, Slovenia); Peter Krüger (Chiba University, Japan)

TiOx-based nanostructures are being used as active materials in lithium ion batteries, gas sensors, photocatalysts, dye synthesized solar cells, etc. Much effort has been directed toward understanding their electronic properties [1] because they exhibit physical and chemical properties different from their bulk counterparts. They are challenging to study by analytical electron microscopy techniques since they are highly sensitive to radiation damage. Their nano-scale prevents the use of conventional X-ray absorption spectroscopy (NEXAFS) to study individual structures. Scanning transmission x-ray microscopy (STXM) allows studies of the electronic structure of individual nanomaterials with high spatial resolution (30 nm) and high energy resolution (0.1 Ev) via NEXAFS spectroscopy and its linear dichroism (spectral variation as a function of the E-vector orientation) [2]. Here we report STXM-NEXAFS studies of individual sodium titanate nanoribbons (NaTiOx-NR) prepared by hydrothermal treatment of anatase TiO2 micro-particles [3]. By measuring the dichroism with the sample at different orientations relative to the X-ray beam, and varying the direction of the linear E-vector by an elliptically polarizing undulator (EPU), the linear dichroism at the O 1s and Ti 2p edges was measured along the 3 principle axes of the anisotropic nanoribbons. Comparison of the spectra and dichroism with high level calculations helps confirm the crystal structure [4] and gives insight into the electronic bonding in these novel layered materials through the orientation dependence of local electronic structure within the crystallite. The methodology for 3D dichroic STXM measurements newly developed in this study is a powerful way to investigate anisotropic nanomaterials.

Research carried out at the Canadian Light Source, which is supported by NSERC, CIHR, NRC and the University of Saskatchewan. Research funded by NSERC, Canada Research Chair.

[1] P. Krüger, Phys. Rev. B 81 (2010) 125121.

[2] A.P. Hitchcock,Soft X-ray Imaging and Spectromicroscopy Ch. 22 in Handbook on Nanoscopy, eds. G. Van Tendeloo, D. Van Dyck and S.J. Pennycook (Wiley, 2012) 745.

[3] P. Umek, R. C. Korošec, B. Jančar, R. Dominko, D. Arčon, J. Nanosci. Nanotechnol.7 (2007) 3502.

NM-TuP-3 VOC Degradation Ability of VOx-TiO2 Mixed Nanoparticles Attached on Glass Fiber in the Flow Chamber Test
Seonmin Kim (KETI, Republic of Korea); JinWoo Cho (KETI)

Vox-TiO2 nanocomposite samples made by one-pot synthesis showed the various catalytic activities depending on the calcination temperature. Photocatalytic activity of VOx-TiO2 nanoparticles fabricated at various temperatures were characterized by the degradation of methylene blue in aqueous solutions under UV irradiation. Nanocomposites show significant enhancement of decomposition of methylene blue and the reason is considered by the synergistic effect between two different materials. In this study, the prepared nanocomposite catalysts were attached on glass fiber by cross-linking method and photodegradation abilities were tested by the change of VOC gas concentration in a closed chamber. For the photocatalytic analysis of the prepared nanoparticles, the absorption spectra are measured by UV-visible spectrophotometer and the bandgap analysis are performed by Kubelka-Munk theory. VOC removal abilities are quantified by the variation of p-xylene concentration in the closed chamber. Obtained results show that the as-prepared Vox-TiO2 nanocomposites have different degradation abilities depending on the calcination temperature and vanadium atomic percentage.

NM-TuP-4 Surface Modification of TiO2 Nanoparticles with Organic Molecule and Their Selective Adsorption Activity Toward Proteins
Xia Zhang (Northeastern University, China)

The nanomaterials have been widely applied in the biomedical area, which play important role in the disease diagnosis and treatment, tissue repair and proteins separation. Nano-TiO2, as a biologically inert material, shows good biocompatibility and bonding biological activity of the protein. In addition, the surface modification of TiO2 can be achieved by the surface bonding between its surface hydroxyl groups and organic molecules. Furthermore, the research on the selective adsorption of proteins on the functionalized nanomaterials has important theoretical significance and application value in the field of protein separation.

In this work, TiO2 nanoparticles were prepared by improved hydrothermal method, and then some organic molecule, such as silane KH560 and oleic acid were used to modify the TiO2 nanoparticles. Some means, such as TEM, XRD, TG-DSC, and FT-IR were used to character the functionalized TiO2 nanoparticles. The results showed that the organic molecules were successfully combined on the surface of TiO2 nanoparticles via chemical bond and physical weak interaction.

These functionalized TiO2 nanoparticles were used in the adsorption experiments of bovine hemoglobin (BHb) and bovine serum albumin (BSA). The effects of different conditions on the adsorption capacity were studied systematically, and the optimum adsorption conditions were determined. Compared with the original nano-TiO2, after surface modification, the functionalized TiO2 nanoparticles showed selective adsorption activity toward BHb. For example, under optimum conditions (c0 (BHb or BSA) = 150 mg/L, m (TiO2) =0.8 mg/mL, t = 80 min.), for the pure TiO2 nanoparticles, the adsorption capacity of BHb and BSA was 70.6 mg/g and 40 mg/g respectively. Meanwhile, for the KH560 modified TiO2, the maximum adsorption capacity of BHb was 122.8 mg/g and the adsorption of BSA was almost 0.
NM-TuP-5 Spontaneous Oxidation and Exfoliation of Graphene Oxide using Couette-Taylor Reactor
WonKyu Park, Hyeongkeun Kim (Korea Electronics Technology Institute); WooSeok Yang (Korea Electronics Technology Institute, Republic of Korea)
For the application of reduced graphene oxide to industries, an eco-friendly reduction method and shortening of the pickling and oxidation reaction times in the graphene oxide production process are essential. We dramatically shortened the graphene oxide production time by applying the Couette-Taylor flow, which allows consecutive reactions, to the graphite oxidation process using the modified Hummers method. With a 60-minute oxidation reaction in the Couette-Taylor reactor, the interlayer spacing increased from 0.34 nm to 0.78 nm, and uniform single- to multi-layer graphene oxides were obtained at a high yield of 93%. The properties of fabricated GO was examined by field emission scanning electron microscope, Raman spectra, atomic force microscope, x-ray photoelectron spectroscope and x-ray diffraction.
NM-TuP-6 Field Emission and Anomalous Light Emission from Isolated ZnO Nanorods Array under Lateral Electric Field Application
Takashi Hirate (Kanagawa University, Japan); Yu Miura, Tomomasa Satoh (Kanagawa University)

We study on electrical and luminescent characteristics of ZnO nanorods array when an electric field is applied in lateral direction to the axis of ZnO nanorods.

ZnO nanorods are grown by chemical vapor deposition after laser ablation of gold on substrate. This growth method was developed by us. Glass substrates (26 mm x 26 mm) are coated with SiO2 film of 100 nm thickness by electron-beam deposition. The length of ZnO nanorods is about 1 micron meter and the diameter is from 50 nm to 80 nm. The direction of nanorods is distributed around a vertical axis to substrate surface.

The mean separation between nanorods on the area between electrodes is about 1.5 micron meter, and nanorods are isolated with each other. This is confirmed by SEM images and the measurement of electrical conduction between indium electrodes. Indium electrodes are electron-beam deposited on ZnO nanorods array with 600 nm thick. Shape of anode is rectangular (4 mm x 4 mm) and that of cathode is triangular with 30 degree vertical angle and 3 mm base, and the separation between the side of anode rectangle and the vertex of cathode triangle is 1.5 mm.

DC voltage is applied between electrodes in vacuum. An electrical potential of the metal chamber is same as that of anode. It is gradually increased from 0 volt. When the applied voltage is low, electric current does not flow. When it reaches about 1500 V, however, the current of about 10-6 [A] initiates abruptly to flow and bluish-white light emission is observed at many points along the cathode edge. These beams of light extend along lines with directions nearly vertical to cathode edge as if the anode electrode did not exist or the voltage was not applied on anode. The intensity of emitted light is very high. It is confirmed experimentally that electrons are field-emitted from ZnO nanorods being at the cathode edges and the light beams correspond to trajectories of the field-emitted electrons. We estimate that the light may be generated by collisions of these electrons with ZnO nanorods, and are studying on this mechanisms.

NM-TuP-7 Carbon Nanotube and Graphene Hybrid Thin Film for Transparent Electrodes and Field Effect Transistors
Ki-Seok An, Wooseok Song, Sung Myung, Jongsun Ihm (Korea Research Institute of Chemical Technology, Republic of Korea)

Low-dimensional sp2 carbon materials including single-walled carbon nanotubes (swCNTs) and graphene have recently received a great deal of attention for potential uses in transparent and flexible nanoelectronics due to their remarkable mechanical, electrical, thermal, and optical properties. Especially, there are many interest in hybrid nanostructures including swCNTs and grapehene. Here, we combined swCNTs and graphene hybrid films with complementary properties for use in high-performance transparent electrodes and field effect transistors (FETs). The hybrid films were synthesized by thermal chemical vapor deposition on Cu foil spin-coated with swCNTs. The density and alignment of swCNTs were simply controlled by adjusting the spin-coating speed or swCNT concentration. Evidence for the formation of the hybrid film was provided by the combined G- and 2D-bands intensity and lineshape Raman features of swCNTs and graphene. Based on the transfer characteristics for the hybrid film-based FETs, an improved Ion/Ioff and on-state current are achieved compared with pristine graphene. Notably, the hybrid film had a sheet resistance of 300 Ω/sq with 96.4% transparency, which was comparable to that of hybrid materials in previous reports.

NM-TuP-8 Plasmonics Assisted Photoluminescence Enhancement
Jonghyun Park, Doo-Hyun Ko (Korea Institute of Science and Technology, Republic of Korea)
we make nanopatterned device on organic SiO2 substrate including Upconversion material. It appears upconversion property and amplified several times by nanopatterrn. Especially upconversion property is amplified several tens fold at the sandwitch structure.
NM-TuP-9 Electrical Properties of Vertically Integrated Thin Film Transistors using Amorphous-In2Ga2ZnO7 Channel Layer
UnKi Kim, SangHo Rha, JunShik Kim, EunSuk Hwang, SeungJun Lee, Younjin Jang, Cheol Seong Hwang (Seoul National University, Republic of Korea)

Recently, serially connected transistors with vertical configuration have received considerable attention in memory applications due to their potential to increase integration density to ultra-high values. In transistors with the vertically integrated configuration, the semiconductor channel material is usually composed of polycrystalline Si (poly-Si). Although the poly-Si channel has revealed feasible functionality as the semiconductor channel, degraded mobility, uniformity and reliability concerns related to the presence of grain-boundaries have not yet been completely resolved. In this regard, the amorphous nature and high carrier mobility of In2Ga2ZnO7 (a-IGZO) thin films attract a great deal of attention as the channel material for such applications.

In this study, two serially connected and vertically integrated a-IGZO thin film transistors (V-TFTs) were fabricated using a gate-first fabrication process. The V-TFTs were fabricated with a vertical channel length (Lg) of ~500 nm for the top TFT (t-TFT) and ~400 nm for the bottom TFT (b-TFT). Heavily doped p-type silicon was used as the substrate and gate of b-TFT (Gb). A 100-nm-thick SiO2 layer was thermally grown as the isolation layer between the t- and b-TFTs. 500-nm-thick poly-Si was deposited by low-pressure chemical vapor deposition to make the gate of the t-TFT (Gt). Then, the poly-Si/SiO2/Si structure was dry etched sequentially to form the gates. Then, a 100-nm-thick SiO2 layer was deposited by a PECVD as the gate dielectric layer, and an a-IGZO layer was sputter-deposited at room temperature on this structure with a target thickness of 100 nm on the top surface of the sample, which results in a channel thickness of ~40 nm for the t-TFT, and ~50 nm for the b-TFT on the side walls of the SiO2. Finally, the Ti source and drain contacts were fabricated by a lift-off process, as the Ti contact with the a-IGZO is quasi-Ohmic.

The t- and b-TFTs show well-behaved transfer characteristics, with an Ion/Ioff ratio (~ 108) and an SS value of 0.6 V/dec., which are much improved device parameters compared with the previously reported single-layer V-TFT, for which the gate-last fabrication process was adopted. This is due to the favorable distribution of the electric field by the Vd and Vg of the TFTs, where the influence of Vd on the channel can be minimized compared with that from Vg. While the two serially connected TFTs behave well and rather independently of each other, there were certain cross-influence between them. Details for such cross-talk will be discussed in the presentation. Further study results up to four layer V-TFT will also be presented.

NM-TuP-10 Synthesis and Application of Large-Area Transition Metal Dichalcogenides by Chemical Vapor Deposition
Chong-Yun Park, Yooseok Kim, JiSun Kim, Seung-Ho Park, YongHun Ko (Sungkyunkwan University, Korea, Republic of Korea)

Transition metal dichalcogenides (MoS2, WS2, Wse2, MoSe2, NbS2, NbSe2, etc.) are layered materials that would exhibit semiconducting, metallic and even superconducting behavior. In the bulk, it is semiconducting and has an indirect band gap. Recently, these layered systems have attracted a great deal of attention mainly due to their complementary electronic properties when compared to other two-dimensional materials, such as graphene (a semimetal) and boron nitride (an insulator). However, these bulk properties could be significantly modified when the system becomes mono-layered; the indirect band gap becomes direct. Such changes in the band structure when reducing the thickness of a MoS2 and WS2 films has important implications for the development of novel applications, such as valleytronics. In this work, we report for the controlled synthesis of large-area (~cm2) single-, bi-, and few-layer MoS2 and WS2 using a two-step process. MoOx and WOx thin films were deposited onto a Si/SiO2 substrate, and these films were then sulfurized under vacuum in a second step occurring at high temperatures (750 °C). The synthesized MoS2 and WS2 atomic thin films were analyzed by optical microscopy, Raman spectroscopy and TEM, and their photoluminescence properties were evaluated.

NM-TuP-11 Bolometers of Aligned Carbon Nanotubes
Guadalupe Garcia Valdivieso, HugoR. Navarro Contreras, Javier González (Coordinación para la Innovación y la Aplicación de la Ciencia y la Tecnología (CIACyT-UASLP), Mexico); Mildred Quintana Ruiz (Instituto de Física (IF-UASLP), Mexico); Gustavo Vera Reveles (Coordinación para la Innovación y la Aplicación de la Ciencia y la Tecnología (CIACyT-UASLP))

The objective of this work is to report on a study on the preparation of bolometers and their characterization, based on parallel linear arrays of carbon nanotubes (CNTs).

The CNTs present good thermal and electrical properties. That is the reason why they may constitute competitive bolometric devices. A bolometer is a device that absorbs energy, in our case infrared radiation, thus varying its temperature (increasing) and electrical resistance (decreasing). The figure of merit of the bolometers is the temperature coefficient of resistance (TCR).

With the objective of obtaining aligned arrays of CNTs we made a solution in water with polymer (PVP), surfactant (SDBS) and CNTs. For a second group Functionalization was also performed with amino groups (Thymine) to induce better alignment, taking advantage of the hydrogen bonds that form between them.

For both sets of prepared CNT’s copper was evaporated on them to have proper ohmic metal contacts to characterize the bolometers thus created.

The samples morphology and alignment were characterized by Scanning Electron Microscopy (SEM). Kaiser Test was performed to check on the degree of functionalization. The TCR of the constructed bolometers was electrothermally measured.

The results obtained with SEM were in some case alignments as long as 3 mm in length. The functionalization degree obtained was 1100 µmol/g. We obtain values of TCR in the range of -1.7 to -3.0 % K-1 for non-functionalized CNTs and from -0.4 to -5.4% K-1 for functionalized CNT’s.These last values are the largest reported for CNTs so far in the literature.

The authors acknowledge the financial support from Consejo Nacional de Ciencia y Tecnología (CONACyT) México, through grant 09-133428, CB-166014, Project CeMIESol 22 from FRC-UASLP, and the access to Laboratorio Nacional de Análisis Físicos, Químicos y Biológicos-UASLP, during the course of this research. MGGV acknowledges the financial support of CONACYT through a Ph.D. scholarship 422974/259064.

NM-TuP-12 Effect of Oxidation of Graphene on Electrical and Optical Properties in Nanocomposites
Alejandra Moreno, Francisco Pérez, Luzmaría Aviles (Centro de Investigación y de estudios avanzados del instituto politécnico nacional, Mexico)

Graphene is one of the latest generation of multifunctional materials considered to be applied to a large number of research areas. However, its structure is often modified to anchor it to different polymeric bases. The effect of anchoring groups such as C = O and C-OH, are necessary for the good dispersion of graphene in solution. However the presence of those chemical groups, greatly affect the electrical and optical properties of the final nanocomposite. The present study shows the relationship between the functionalization of graphene and the optoelectronic effect on the nanocomposites obtained. % functionalization Vs Electrical conductivity is reported. Graphene dispersion in the polymer was observed by SEM and UV-Vis and the functional groups are identified by FTIR.

NM-TuP-13 Mechanical Deformation in Si/ge Quantum Dots
JoséLuis González Arango (Universidad de Pamplona, Colombia); Paulo Freitas Gomes (Universidade Federal de Goias, Campus Jataí, Brazil)

Mechanical deformation (strain) plays an important role in the electronic, optical and transport properties of semiconductor quantum dots (SQDs). Epitaxial SQDs have a spatial deformation profile caused by the mismatch of the lattice parameters of the materials involved. This deformation creates an elastic energy which is one determinant fact in the SQDs grown on Stranski-Kastranow mode. The deformation also changes the potential profiles experienced by the carriers (electron and hole), requiring consideration of them when one calculates the electronics eingenstates. This shows the importance of the deformation profile on the properties of the nanostructures for future applications in electronic and optical devices.

In this work we show one more tool for the calculation of mechanical deformation on Si/Ge semiconductor quantum dots. We used a numerical simulation package to solve the differential equations for the deformation, using Continuous Elasticity Theory. We studied two systems: capped and uncapped. The cap layer is the Si layer grown above the Ge QDs layer. On the capped system, we observed a larger biaxial deformation on the Ge layer plane, when compared with the uncapped system. We also observed the deformation on the Si layer underneath the Ge layer. Again, on the capped system this biaxial deformation was also larger. With these deformation profile, we can also calculate the stress tensor and the elastic energy profiles.

NM-TuP-14 Synthesis of of Pt-based Bimetallic Nanoparticles using Pulsed Plasma Discharge in Water
SangYul Lee (Korea Aerospace University, Republic of Korea); SungMin Kim (Korea Aerospace University, Kora); Jung-Wan Kim (InCheon University, Korea)
The synthetic approach for electrocatalysts is one of the most important methods determining the electrocatalytic performance. In this work, we synthesized Pt and Pt-M (M=Cu, Ag, and Pd) bimetallic nanoparticles using a pulsed plasma discharge in water. A morphological investigation revealed that the as-synthesized Pt and Pt-M bimetallic nanoparticles constituted a nanochain network structure interconnected with primary nanoparticles, and the nanochains grew from the primary nanoparticles via the oriented attachment. The Z-contrast, EDX line scanning, and XRD analysis confirmed that the Pt was alloyed with M without elemental segregation or phase segregation. Furthermore, it was found that the composition difference was dependent on the electrode temperature determined by the power density and thermal parameters. The Pt-Pd bimetallic nanoparticles showed the largest electrochemical surface area due to a crystalline size of less than 5nm, whereas the Pt-Ag bimetallic nanoparticles showed superior electrocatalytic activity, stability, and durability with respect to the methanol oxidation reaction, which could be attributed to the downshift of the d-band center via electronic modification.
NM-TuP-15 Crystal Structure and Surface Orientation dependence of Hydrogen Adsorption on Iron Surfaces
Yuji Kunisada (Hokkaido University, Japan); Norihito Sakaguchi (Hokkaido University)

Introduction

In order to utilize hydrogen as new clean energy resources, we have to realize safe, efficient, and low cost hydrogen transportation and storage. One of the current transport methods is the one with high-pressure hydrogen tanks. However, hydrogen is one of the most important elements in the damage process of materials. Many recent studies have reported that hydrogen atoms absorbed in materials can stabilize vacancies[1], which cause reduction of their ductility. From this point, the atomic- and electronic-scale understanding of hydrogen embrittlement process is necessary to develop new long-life materials for hydrogen transportation and storage.

Calculation Methods

In this study, we investigated the adsorption properties of hydrogen isotopes on iron surfaces with the aid of first principles calculations based on spin-polarized density functional theory, in order to understand hydrogen behaviors in commonly-used iron-based materials, for instance, ferritic and austenitic stainless steels. We also adopted the quantum mechanics calculations of hydrogen nuclei, because the importance of delocalization and zero-point energy of hydrogen nuclei has been reported in various papers. [2, 3] Furthermore, we considered hydrogen(H), deuterium(D), tritium(T), and muonium(μ+-e-) as hydrogen isotopes.

Results and Discussion

At first, we investigated the potential energy surfaces of hydrogen on bcc-Fe(110) and fcc-Fe(111) surfaces. These surface orientations are the most stable ones for each crystal structure, respectively. Furthermore, in order to reveal the surface orientation dependence of hydrogen adsorption, we investigated the potential energy surfaces of hydrogen on fcc-Fe(100) surfaces. We revealed that the most stable adsorption sites on bcc-Fe(110), fcc-Fe(111), and fcc-Fe(100) surfaces are the long-bridge, fcc-hollow, and short-bridge site, respectively. The corresponding adsorption energies with these adsorption configurations are 2.99, 2.78, and 2.82 eV, respectively. Thus, we can point that the adsorption energies on bcc-Fe(110) and fcc-Fe(100) surfaces are slightly lager than the one on fcc-Fe(111) surfaces. We also investigated the hydrogen adsorption states on these surfaces by calculating shrödinger equation for hydrogen nuclei. We found the delocalization of H atoms in the ground state. In addition, we clarified the non-negligible isotope effects in delocalization and zero-point energy of hydrogen isotopes.

References

[1] Y. Tateyama and T. Ohno, Phys. Rev. B 67 (2003) 174105.

[2] N. Ozawa, T. A. Roman, H. Nakanishi, and H. Kasai, Surf. Sci. 600 (2006) 3550.

[3] Y. Kunisada and H. Kasai, J. Phys. Soc. Jpn. 82 (2013) 023601.

NM-TuP-16 Synthesis and Evaluation of Nanocrystalline Diamond Powder Prepared by Coaxial Arc Plasma Gun
Hiroshi Naragino, Aki Tominaga (Kyushu University, Japan); Kazushi Sumitani (Kyushu Synchrotron Light Research Center, Japan); Satoru Hattori (Kyoto Prefectural Technology Center for Small and Medium Enterprises, Japan); Tsuyoshi Yoshitake (Kyushu University, Japan)
Diamond possesses several superior physical properties including high hardness, wide bandgap, and chemical inertness. Furthermore, it is possible to impart functionalities by doping and surface modification. Nano-sized diamond powder shows different properties from bulk diamond. Nanodiamond has mainly been produced by detonation method so far. However, high-purity nanodiamond powder has been difficult to be fabricated by detonation. Moreover, the functionalization of nanodiamond is made after growth, because of in-situ doping being impossible. Our research group has proposed a new novel method that employs a coaxial arc plasma gun (CAPG), which enables us to fabricate nanodiamond crystallites. The specifics to this method are as follows: i) the growth is made using a simple apparatus equipped with a coaxial arc plasma gun, ii) high-purity nanodiamond can be fabricated in principle, iii) doping can be easily made by using doped targets, and iv) the grain size is expected to be changed by controlling the discharge condition of coaxial arc plasma gun. In this work, we experimentally proved the generation of nanodiamond by powder X-ray diffraction (XRD) and transmission electron microscope (TEM) and that the grain size is evidently enlarged with the electric power applied to an arc plasma gun. Moreover, the density of nanodiamond powder was measured using a sink-float method. Nanodiamond powder was fabricated using CAPG (ULVAC, APG-1000) equipped with a graphite target. The inside of the chamber fitted with CAPG was evacuated to < 10-6 Pa and hydrogen was introduced at 5 sccm. The head of the arc plasma gun was pointed at quartz plate heated at 550deg. C. The powder that quickly and automatically exfoliated from the quartz plate was gathered in the collection cell located under the quartz plate. In order to confirm the formation of diamond, the films were structurally investigated by TEM and powder XRD using synchrotron radiation at beamline 15 of the SAGA-LS. The films exhibited diamond-111 and -220 diffraction rings in the electron diffraction patterns and the existence of diamond grains was confirmed from the dark-field TEM images. The XRD patterns also exhibited diffraction peaks due to diamond. The grains size was increased from 2 to 80 nm with increasing electric power applied to an arc plasma gun. From the density measurement, the density of nanodiamond powder was estimated to be approximately 1.77 g/cm3. This value is smaller than that of diamond (3.5 g/cm3), and indicates that the nanodiamond contains the non-diamond phase such as an amorphous carbon. The details of preparation apparatus and preparation mechanism are explained in the conference.
NM-TuP-17 Surface Structure and Local Valence Electronic States of Si(110)-16×2 Surface after Exposure to Water: XPS and Auger-Photoelectron Coincidence Study
Takuhiro Kakiuchi, Shingo Nishiura, Junji Kawamoto (Ehime University, Japan); Shin-ichi Nagaoka (Ehime University); Kazuhiko Mase (KEK, Japan)

Si(110)-16×2 is a favorable candidate for a next-generation semiconductor substrate because it takes a single domain (SD) structure with high hole-mobility, which is larger than that of the other Si crystal faces. Recently, Adatom-Buckling (AB) model has been proposed as the surface structure model for clean Si(110)-16×2 surface [1]. The AB model consists of five Si surface components of SC1: the buckled upper atoms, SC2: the unbuckled atoms and the second layer atoms with dangling bonds (DBs), SC3: the first layer and second layers atoms without DBs, SC4: the adatoms, and SC5: buckled lower atoms. In the AB model, the surface states S1, S2, S3, and S4 with binding energies of 0.2 eV 0.4 eV, 0.7 eV, and 1.0 eV are reported to be located at specific surface sites of SC4, SC1, SC5, and SC3, respectively [1]. However, the SD structure of Si(110)-16×2 disappears when it is exposed to atmospheric air. In this study, we investigated a water-terminated Si(110)-16×2 SD surface with XPS and Auger-photoelectron coincidence spectroscopy. Si-2p photoelectron spectra indicate that water is dissociatively adsorbed and forms Si-H and Si-OH components after exposure to water of 0.1 Langmuir (L). When Si(110)-16×2 surface is exposure to water form 1.0 L to 5.0 L, there is little change in these Si-2p intensity ratio. This result indicates that clean Si(110)-16×2 surface is saturated with water of less than 1.0 Langmuir (L). In addition, water is preferentially dissociative-adsorbed at surface components of the SC1, the SC2, and the SC3 on step edge of SD structure, but is hardly adsorbed at surface components of the SC4 and the SC5 on the terrace of the SD structure. The SD structure of Si(110)-16×2 surface after the exposure to water of 5.0 Langmuir is kept under ultra-high vacuums condition and atmosphere pressure of N2 gas. This result indicates that Si(110)-16×2 SD surface is inactivated by water dissociative-adsorption. On the other hand, Si-L23VV-Si-2p coincidence spectra suggest that the surface states S1, S2, S3, and S4 disappear after exposure to water. The valence band maximum energy of water adsorbed Si(110)-16×2 surface is shifted to deeper binding energy side in comparison with that of clean Si(110)-16×2 surface. The water adsorbed Si(110)-16×2 SD surface may be used as a unique semiconductor substrate.

[1] K. Sakamoto, M. Setvin, K. Mawatari, P. E. J. Eriksson, K. Miki, and R. I. G. Uhrberg, Phys. Rev. B 79, 045304 (2009).

NM-TuP-19 Study on Tracking Resistance of Silicone Rubber Nanocomposite under DC Voltage
JungHun Kwon, JiSung Park (Chungbuk National University Korea, Republic of Korea)

One of the problems is tracking of outdoor polymeric silicone rubber(SIR) insulation used in HVDC or HVAC transmission lines. These problem are more serious with dc than with ac voltage, due to the electrostatic attraction of airborne contaminants to the insulator surface. In order to improve the tracking resistance of SIR, inclined plane(IP) tracking test similar to IEC 60587 was conducted under positive and negative dc voltages for SIR filled with micro sized silica and nano sized alumina trihydrate(ATH) fillers. The results show that tracking resistance of SIR nanocomposites were more increased than SIR unfilled micro or nano filler. It was also seen that the tracking resistance of SIR showed polarity effect under dc voltage.

NM-TuP-20 Decay Processes of Si 2s Core Holes in Si(111)-7×7 Revealed by Si Auger Electron Si 2s Photoelectron Coincidence Measurements
Kazuhiko Mase (KEK, Japan); Kenta Hiraga, Sadanori Arae (Yokohama National University, Japan); Rui Kanemura (Yokohama National University); Yusaku Takano, Kotaro Yanase, Yosuke Ogashiwa (Gunma University); Nariaki Shohata (University of Tsukuba); Noritsugu Kanayama (Chiba University); Takuhiro Kakiuchi (Ehime University, Japan); Shinya Ohno (Yokohama National University); Daiichiro Sekiba (University of Tsukuba); Koji Okudaira (Chiba University); Makoto Okusawa (Gunma University); Masatoshi Tanaka (Yokohama National University)

The filling of an initial core hole by an electron from a higher subshell of the same shell is known as a Coster–Kronig transition, and Auger photoelectron coincidence spectroscopy (APECS), in which Auger electrons are measured in coincidence with photoelectrons with a fixed kinetic energy (KE), is an ideal tool for probing Coster–Kronig transitions because Auger electrons originating from a specific core ionization are detected .

However, studies of Coster–Kronig transitions have mainly been restricted to metal surfaces, even though Si surfaces are crucial for surface science applications and the semiconductor industry. Issues such as the assignments of the Si L1VV Auger peaks, experimental determination of the branching ratio of the Si L1L23V and Si L1VV Auger decays, and competition between the delocalization of the valence hole and the Si L23V-VVV Auger decay are, to the best of our knowledge, largely unexplored. In this paper, we report on the decay processes of Si 2s core holes in a clean Si(111)-7×7 surface studied using coincidence measurements of the Si Auger electron and the Si 2s photoelectron.

We measured a coincidence spectrum measured by scanning the ASMA over a KE range of 20­–150 eV, with the DP-CMA fixed at a KE of 76.5 eV (Si-L23VV-Si-2p APECS spectrum). Distinct Auger peaks are observed in a KE region of 50–92 eV with the maximum peak located at KE = 88 eV. We assigned these peaks to Si L23VV Auger electrons emitted in the decay processes of Si 2p holes. Another coincidence spectrum was measured by scanning the ASMA over a KE range of 20­–150 eV with the DP-CMA fixed at KE = 26.3 eV, which corresponds to Si 2s photoelectrons (Si-Auger-Si-2s APECS spectrum). The maximum peak position and shape of the Si-Auger-Si-2s APECS spectrum in the AeKE = 50–92 eV region are almost identical to those of the Si-L23VV-Si-2p APECS. Therefore, we assigned these Auger peaks to Si L23VV Auger processes. This is direct evidence of Si L23VV Auger processes being induced by Si 2s ionization.

The peaks of Si-Auger-Si-2s APECS in the AeKE = 20–50 regions were assigned to Si L1L23V Auger decays, while the peaks of Si-Auger-Si-2s APECS in the AeKE = 100–150 eV regions were assigned to Si L1VV Auger decays. These results indicate that there are two nonradiative decay processes of the Si 2s core hole. The first is the Si L1L23V Coster–Kronig transition followed by delocalization of the valence hole and Si L23VV Auger decay, while the second is Si L1VV Auger decay. From the integrated intensity of the normalized Si L23VV and Si L1VV Auger peaks, we estimated the branching ratio of Si L1L23VV to Si L1VV Auger processes to be (96.8 ± 0.4):(3.2 ± 0.4).

NM-TuP-21 Pulsed Laser Assisted Synthesis of NaLa(MoO4)2:Ho3+/Tm3+/Yb3+ Nanocrystals and their White Upconversion Luminescence
Jeong Ho Ryu, Jung-Il Lee (Korea National University of Transportation, Korea)
In recent years, lanthanide ion doped upconversion (UC) luminescence from near infra-red radiation to visible or UV light has received many attention for their various applications in phosphors, solar cell, flat-panel displays, scintillators, solid state lasers and fluorescent bio-medicals. In the fields of industries, it is required that UC luminescent materials should be engineered to emit wide ranges of white colors. Also, high chemical, physical and mechanical stabilities should be achieved through engineering UC materials. Although multi-color UC luminescence with high efficiency was reported using lanthanide doped fluorides emitting bright blue emission of Tm3+ and green or red of Er3+ under laser excitation (980 nm), fluorides can decompose easily with moisture in air which makes the application difficult in the fields of industries. Conventionally, solid state reaction, precipitation, hydrothermal and sol-gel methods were used for synthesis of nanocrystalline NaLa(MoO4)2 particles However, those methods need long processing time and steps for fabrication. Also, chemical additives in procedure may be incorporated to NaLa(MoO4)2 particles as impurities, which results in bad influence to human body clinically. One novel technique for fabrication of NaLa(MoO4)2 nanocrystals is pulsed laser ablation (PLA) in liquid medium. PLA of solid target in liquid has been a promising technique for producing nanocrystals for analytical and bioanalytical applications as well as the rapid synthesis of complex materials because the experimental procedure is simple and above all, chemical additive is unnecessary. However, to date, there is little report on the preparation of upconverting NaLa(MoO4)2 nanocrystals by laser ablation in liquid medium. In this study, we report a novel synthetic approach to produce Ho3+, Tm3+, Yb3+ tri-doped NaLa(MoO4)2 nanocrystals using PLA in liquid medium without any surfactant. The fabricated NaLa(MoO4)2:Ho3+/Tm3+/Yb3+ nanocrystals were characterized in terms of their crystallinity, microstructure and white upconverting property. Moreover, the laser ablation process was discussed by a thermally induced explosive ejection mechanism.
NM-TuP-22 DFT Study of Surface Passivation of Silicon Carbide Nanowires by Halogens
A. Miranda (Universidad Nacional Autónoma de México); A. Trejo (Instituto Politécnico Nacional, México); M. Cruz-Irisson, Luis A. Pérez (Universidad Nacional Autónoma de México)
The use of silicon carbide nanowires (SiCNWs) as chemical sensors stands out among their many possible applications. At present, SiCNWs are usually coated with SiO2. To further extend and customize their applications, surface modification of nanowires (NWs) by different chemical species is one of the feasible ways to achieve it. An insightful understanding of the effects of such passivating functional groups is thus important to understand the electronic properties of surface modified NWs. In this work, by using density-functional calculations, we study the stability and the electronic structure of SiCNWs passivated with halogen atoms such as F, Cl, Br or I, considering different surface covering schemes. We show that the stability of SiCNWs strongly depends on both the passivating element and the percentage of surface covering, in an otherwise fully hydrogen passivated NW. Moreover, when going from the most stable system to the less stable one, the following stability trend is obtained: F-SiCNW> Cl-SiCNW>Br-SiCNW>I-SiCNW>H-SiCNW, which can be attributed to the different electronegativities of the passivating elements considered. Finally, the effects of chemical decoration on the size and nature of the NW band gaps are discussed.
NM-TuP-23 Diode on Diamond-like Coated Silicon Cathode with Nonresonant Emission
Nina M. Goncharuk, N.F. Karushkin (Research Institute “Orion," Ukraine)
Terahertz diode on base non-resonant emission of silicon cathode with diamond like coating (DLC) was investigated in small-signal approach. Negative conductance of the diode results from comparable time delays of electron emission and transit [1]. Closeness of the delays and sufficiently small their values cause multiband structure of frequency spectrum of negative conductance of the diode and location of the spectrum in terahertz frequency range. Owing to nonzero both electron affinity energy in DLC and difference of the energy in emitter and DLC ϕ potential profile of the diode consists of two triangular potential barriers divided by triangular quantum well (QW). Contribution of emitter accumulation layer in voltage drop of the diode was only considered disregarding emission from it. DLC width b and operating direct electric field F are selected so that a top of the first barrier is lower and a top of the second one is higher than emitting electron energy supposed equal to Fermi energy. In the case non-resonant emission when electron tunnels under the second potential barrier only occurs with it ballistic transit in DLC. Positive emission conductivity  equal to derivative of non-resonant emission current on electric field in vacuum and emission frequency fe equal inverse time of electron tunneling under the second barrier were calculated applying the model of tunnel resistance of single potential barrier [2]. Model of diode microwave impedance [1] is based on a model of semiconductor transit-time diode [3] but considering emission delay, electron acceleration in vacuum transit layer. The diodes with 300K temperature, 5∙1018 emitter doping, ϕ = 0.25 eV, b from 1.5 to 3.5 nm at electric field values little more than corresponding with the first barrier top and emitter conduction band bottom coinciding were studied. At the electric field value maximal  is reached which value is from 0.1 to 0.4 Om-1cm-1 and fe is from 1.27 to 4.29 THz for the diodes. In multiband spectrum of negative conductance of the diode n-th frequency band is situated at fn ≈ (n-1/2) fe. A width of the bands increases with fe increasing. Maximum of the spectrum envelope Gmax reached in the band closest to optimal transit frequency is more at more σ. It decreases and its frequency increases when transit angle go away from optimal closed to 0.05π. The greatest Gmax value of 80 kS/cm2 is reached at frequency fm ≈ fe/2 for the diode with the most σ and fe which admittance reactive and components are the same order. Conducted investigations show a possibility of creation of new type terahertz diodes based on non-resonant emission.

[1] N. Goncharuk, V. Malyshko, V. Orehovskiy, N. Karushkin, EuMW2013 Proceedings.

[2] S. Luryi, Applied Physics Letters, vol. 47(5), pp. 490–492, 1985.

[3] S. M. Sze, Physics of Semiconductor Devices, Vol. 2, Chapt. 10, Sect. 7, J. Wiley & Sons, 1981.

NM-TuP-24 Resonant Emission Diode on Diamond-like Coated Silicon Cathode
Nina M. Goncharuk, N.F. Karushkin (Research Institute “Orion," Ukraine)
Small-signal microwave impedance of a diode based on resonant electron emission of silicon cathode with diamond like coating (DLC) was investigated. Negative conductance of the diode is caused by both negative conductivity of electron emission and delay of electron transit in vacuum transit layer. Energy diagram of the diode includes triangular quantum well (QW) between two triangular potential barriers caused by nonzero electron affinity energy in DLC and difference of the energy in emitter and DLC ϕ. Electron emission from emitter conduction band to an anode through n-th energy level in the QW was only considered regardless the same from accumulation layer. Diode impedance was calculated in framework of models [1], [2] at direct emission characteristics as parameters considering difference of potential profile of the diode with triangular QW from the same with rectangular QW [2]. The emission characteristics are maximal negative conductivity σ on dropping part of resonant dependence of direct current on electric field in vacuum and resonant emission time equal electron dwelling time on the n-th resonant level n. It is supposed 300K diode temperature, 5∙1018 cm-3 emitter doping and contact resistance the same as in [2]. For the diodes with DLC width from 5 to 6.5 nm and ϕ from 0.5 to 0.6 eV values of σ from -0.2 to -1.2 Om-1∙cm-1 and n from 3 to 37 fs have been obtained. Frequency of resonant emission is noticeably more than optimal transit frequency for studied diodes and so their negative conductance takes place in two single bands when transit angle is in interval (0, θ1up) or (1.4π, θ2up) accordingly. Characteristics of the frequency bands and of corresponding transit angle intervals depend on as σ so n. When σ increases in above mentioned its interval θ1up decrease from 0.55π to 0.2π. When n increases in above mentioned its interval θ2up decreases from 2.75π to 2.5π. The bands of negative conductance are situated at frequencies from 0.1 to 0.9 THz and from 1 to 6.5 at transit angle in the first and the second interval accordingly. Negative conductance maximum in any band is the more than more negative emission conductivity. In lower band it more than two orders exceeds the same in the upper band and its frequency is order less. Frequency of the maximum in the lower band decreases and in the upper band increases with negative emission conductivity increasing. Optimal transit angle corresponded with the maximum in the lower band is near 0.05π and in the upper band it decreases from 2.35π to 2.05π with n increasing in its interval. Reactive and active components of diode impedance are the same order at optimal diode parameters.

[1] N. M. Goncharuk, Materials Science & Engineering, A353 , pp. 36−40, 2003.

[2] A. Evtukh, V. Litovchenko, N. Goncharuk, H. Mimura, J. Vac. Sci. Technol. B vol. 30(2), pp. 022207-1 ̶ 022207-8, Mar/Apr 2012.

[3] F. Stern, Phys. Rev. B, vol. 5, pp. 4891−4899, (1972).

[4] Evtukh, V. Litovchenko, Yu. Litvin, D. Fedin, N. Goncharuk, V. Chaika, A. Chakhovskoi, T. Felter, Physics of Low-Dimensional structures, pp. 117 ̶ 127, № 5/6, May/June 2001.

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