Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2001, Vol.10, No.13
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GENERAL

MANIPULATION OF ATOMS, MOLECULES AND CLUSTERS FOR CONSTRUCTION OF NANOSYSTEMS

F. Moresco, S.W. Hla, J. Repp, K.-F. Braun, S. F?lsch, G. Meyer, K. H. Rieder
Chin. Phys., 2001, 10 (13): 10-18 doi: 10.1088/1009-1963/10/13/003
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Controlled manipulations with the scanning tunneling microscope (STM) down to the scale of small molecules and single atoms allow to built molecular and atomic nanosystems, leading to the fascinating possibility of creating manmade structures on atomic scale. Here we present a short review on atomic scale manipulation investigations. Upon soft lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. We show that even the manipulation of highly coordinated native substrate atoms is possible and we demonstrate how this can be applied as local analytic and synthetic chemistry tools, with important consequences on surface structure research. Vertical manipulation of Xe and CO is demonstrated, leading to improved imaging with functionalized tips. With CO deliberately transferred to the tip, we have also succeeded to perform vibrational spectroscopy on single molecules. Furthermore, we describe how we have reproduced a full chemical reaction with single molecules, whereby all basic steps, namely preparation of the reactants, diffusion and association, are induced with the STM tip. Finally, we have extended the manipulation techniques to large specially designed molecules by performing lateral manipulation in constant height and realizing the principle of a conformational molecular switch.

FOURIER ANALYSIS OF TEMPORAL AND SPATIAL OSCILLATIONS OF TUNNELING CURRENT IN SCANNING TUNNELING MICROSCOPY

Xie Fang-qing, S. Molitor, Th. Koch, P. von Blanckenhagen
Chin. Phys., 2001, 10 (13): 19-26 doi: 10.1088/1009-1963/10/13/004
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Partially oxidized Si(111) surfaces and surfaces of highly oriented pyrolytic graphite (HOPG) were studied by two different ultrahigh vacuum scanning tunneling microscope (UHV-STM) systems and by an STM system working under ambient conditions, respectively. The STM current images of partially oxidized Si(111) surfaces and HOPG surfaces were analyzed by one/two-dimensional fast Fourier transformation (1D-FFT/2D-FFT). The phenomenon of temporal oscillations of tunneling current on the partially oxidized Si(111) surfaces was detected with both UHV-STM systems. Temporal as well as spatial oscillations of tunneling current appeared in highly resolved STM current images of the Si(111) surfaces simultaneously, but both kinds of oscillations could be discriminated according to their different influence on the 2D-FFT spectra of the current images, while varying the scanning range and rate. On clean HOPG surfaces only spatial oscillations of tunneling current induced by the surface structure were observed.

NANOBUBBLES AT THE LIQUID/SOLID INTERFACE STUDIED BY ATOMIC FORCE MICROSCOPY

Lou Shi-tao, Gao Jian-xia, Xiao Xu-dong, Li Xiao-jun, Li Guang-lai, Zhang Yi, Li Min-qian, Sun Jie-lin, Hu Jun
Chin. Phys., 2001, 10 (13): 108-110 doi: 10.1088/1009-1963/10/13/020
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Bubbles on the nanometer scale were produced by a special method on solid surfaces. Atomic Force Microscopy (AFM) was used to detect these bubbles. It shows that nanobubbles can be seen clearly in the interfaces of liquid/graphite and liquid/mica. In AFM images, the nanobubbles appeared like bright spheres. Some of the bubbles kept stable for hours during the experiments. The bubbles were disturbed under high load during AFM imaging. The conformation of the bubbles is influenced by the atomic steps on the graphite substrate. In addition, a shadow was found around the bubbles, which was due to the interactions between a bubble adhered to the tip and a bubble on the substrate.

PIEZOELECTRIC Pb(Zr, Ti)O3 MICRO-DEVICES FOR SCANNING FORCE MICROSCOPY AND ULTRA-DENSITY DATA STORAGE

Chu Jia-ru, Huang Wen-hao, R. Maeda, T. Itoh, T. Suga
Chin. Phys., 2001, 10 (13): 167-173 doi: 10.1088/1009-1963/10/13/031
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In this paper we report two types of micro devices based on Pb(Zr, Ti)O3 (PZT) thin films for improving the throughput of scanning force microscopy (SFM) or data storage using SFM. One is a piezoelectric cantilever array integrated with force sensor as well as z-actuator on each cantilever for parallel operation. The 125-μm-long PZT micro cantilever with a natural resonant frequency of 189 kHz has a high actuation sensitivity of 75 nm/V. Independent parallel images using two cantilevers of the array were obtained. The other is a novel micro-SFM device that is expected to replace the cantilever, the deflection detection unit, and the macro-fabricated scanner which is the bottle neck limiting the single probe acquisition rate. The bridge-structured device has shown a microscopy sensitivity of 0.32 nA/nm in vertical direction and actuation abilities of 70-80nm/±V in the lateral direction.

SETUP AND APPLICATION OF SCANNING NEAR-FIELD OPTICAL MICROSCOPY

Xu Shi-fa, Zhu Xing, Zhou He-tian, Shen Yu-min, Fei Teng, Zhang Yu, Yin Yan, Zhang Bei, Dai Lun, Liu Xiao-ling, Hu Jian-cheng, Lu Ping, Zhai Zhong-he
Chin. Phys., 2001, 10 (13): 195-205 doi: 10.1088/1009-1963/10/13/035
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The research on the setup and application of scanning near-field optical microscopy (SNOM) performed in our laboratory is reviewed in this report. We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near-field imaging and spectroscopy, operating at liquid nitrogen temperature. A special designed coaxial double lens was used to introduce the illumination beam through a 200μm fiber; the detected optical signal was transmitted via a fiber tip to an avalanche photon detector. The performance test shows the stability of the new design. The shear force image and optical image of a standard sample are shown. A system of SNOM working at room temperature and atmosphere was used to characterize semiconductors and bio-molecular samples. It revealed the unique features of semiconductor microdisks in the near-field that is significantly different from that of far-field. The effects of different geographic microstructures on the near-field light distribution of InGaP, GaN, and InGaN multi-quantum-well microdisk were observed.
CLASSICAL AREAS OF PHENOMENOLOGY

LARGE AND EXTREMELY FAST THIRD-ORDER NON-LINEARITY OF Ag NANOPARTICLES EMBEDDED INTO A CsxO SEMICONDUCTOR MATRIX

Zhang Qi-feng, Shao Qing-yi, Hou Shi-min, Zhang Geng-min, Liu Wei-min, Xue Zeng-quan, Wu Jin-lei, Wang Shu-feng, Liang Rui-sheng, Huang Wen-tao, Wang Dan-ling, Gong Qi-huang
Chin. Phys., 2001, 10 (13): 65-69 doi: 10.1088/1009-1963/10/13/013
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The third-order optical nonlinearity of Ag-O-Cs thin films, where Ag nanoparticles are embedded into a CsxO semiconductor matrix, was measured by the femtosecond optical Kerr technique. The third-order nonlinear optical susceptibility, χ(3), of the thin films was estimated to be 1.1×10-9 esu at the incident wavelength of 820 nm. The response time, i.e. the full width at half-maximum of the Kerr signal, is as fast as 114 fs only. The intrinsic third-order optical nonlinearity can be attributed to the intraband transition of electrons from the occupied state near the Fermi level to the unoccupied state. It is suggested that such a nonlinearity is further enhanced by the local field effect that is present in the metallic nanoparticles composite thin films.
ATOMIC AND MOLECULAR PHYSICS

DIAMOND MICRO- AND NANOSTRUCTURING BY ACCELERATED CLUSTER EROSION

C. Becker, J. Gspann, R. Kr?mer, Y. Yamaguchi
Chin. Phys., 2001, 10 (13): 174-178 doi: 10.1088/1009-1963/10/13/032
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Reactive accelerated cluster erosion (RACE) has been used for direct micro- and nanostructuring of bulk diamond. Carbondioxide nanoparticles of about 1000 molecules are accelerated to 100keV energy in order to erode a staircase structure or a toothed wheel into diamond by using appropriate movable or fixed masks. Non-reactive erosion by argon clusters is slower but more effectively polishing. Large-scale molecular dynamics simulations show the nanoparticle impacts to lead to transient craters which relax to a very smooth surface via collective elastic recovery. The enhanced or reduced erosion of the respective cluster material is illuminated.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

NANOSTRUCTURED MULTI-COMPONENT MATERIALS BY MECHANICAL ALLOYING

C. Politis, A.D. Spiliotis, V. Kapaklis, S. Baskoutas
Chin. Phys., 2001, 10 (13): 27-30 doi: 10.1088/1009-1963/10/13/005
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We have shown that nanostructured multi-component materials like TaC, Nb78Ge22, Mo70Si20B10, Mo60Os20B20, Ru52Zr6B42, (NbC)20Co80 and (WC)80-(Ti90Cu10)20 with an effective length size reduced to atomic level (a few nanometers) can be produced by mechanical alloying of the elemental and/or alloy powders in a high-energy ball mill. All process steps and samples preparation for characterization were done under glove box conditions.

NANOSTRUCTURED AND AMORPHOUS MATERIALS BY MECHANICAL ALLOYING

C. Politis
Chin. Phys., 2001, 10 (13): 31-35 doi: 10.1088/1009-1963/10/13/006
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Mechanical Alloying is particularly attractive because it can be used to process structurally uniform and isotropic bulk quantities of powdered materials that have a fine length scale. Furthermore, it appears to be applicable to many combinations of elements. Here experimental results regarding the synthesis and characterization of several binary and ternary nanocrystalline and amorphous alloys of Ti, Zr, Hf, V, Nb and Fe with other transition elements and with B, C and Si are reported. The nanocrystalline and amorphous powders, with effective particle size between 7 and 30nm, were prepared by mechanical alloying in a high-energy ball-mill using commercial elemental powders and/or alloy powder.

SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF TITANIUM DIOXIDE NANOPARTICLES AND NANOPARTICLES-DYE COMPOSITES

Wang Xin, Zhang Yü, Deng Hui-hua, Shen Yao-chun, Lu Zu-hong, Cui Yi-ping
Chin. Phys., 2001, 10 (13): 54-58 doi: 10.1088/1009-1963/10/13/011
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Hyper-Rayleigh Scattering (HRS) technique was used to study the second-order nonlinear optical (NLO) responses of aqueous titanium dioxide (TiO2) nanoparticles of 10nm in size, and two nanoparticles-dye composites prepared by adding rhodamine B (Rh610) or the organic tosylate salt of dimethylaminostilbazolium (DAST). Results showed that the "per particle" first hyperpolarizability β for TiO2 nanoparticles is very large, in the range of 1026 esu. With adding Rh610 and DAST, the HRS signals of the composites were further enhanced. And in TiO2/Rh610 composite the enhancement was obviously greater than that of TiO2/DAST composite. It has proved that non-centrosymmetry of the nanocrystal/solution interface contributes mainly to its large "per particle" β, overwhelming the nanocrystal core. So the interactions between nanoparticles surfaces and adsorbed dyes were very important for their second-order NLO responses. HRS technique provides a useful new NLO method to characterize the surface structures and microenvironment of nanoscale materials.

HIGH-YIELD PRODUCTION OF MULTI-WALLED CARBON NANOTUBES BY CATALYTIC DECOMPOSITION OF BENZENE VAPOR

Wang Xi-zhang, Hu Zheng, Wu Qiang, Chen Yi
Chin. Phys., 2001, 10 (13): 76-79 doi: 10.1088/1009-1963/10/13/015
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Multi-walled carbon nanotubes (CNTs) have been synthesized on γ-Al2O3 supported unitary, binary or trinity metal (Fe, Co, Ni) catalysts with benzene as carbon source in the range of 600 to 810 ℃. The growth of CNTs was carried out in a fixed bed flow reactor and the quality of carbon deposits was characterized by transmission electron microscopy. The preparation was optimized and the high-yield production of CNTs has been achieved for three mixture catalysts with the yield of high-quality CNTs higher than 200% within 60 min, reaching a maximum of 278% for 1.51 mmol/g Fe-1.51 mmol/g Co/γ-Al2O3 catalyst. This provides a good alternative for future large scale and low cost production of CNTs for applications.

SURFACE PLASMON OF Ag CLUSTERS ON ALUMINA FILMS

Guo Qin-lin, D. W. Goodman
Chin. Phys., 2001, 10 (13): 80-83 doi: 10.1088/1009-1963/10/13/016
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The deposition of silver on an ordered alumina film prepared on Re(0001) surface has been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The results show that Ag grows initially as clusters at 90K and 300K. A red shift of the Ag surface plasmon as a function of decreasing coverage is observed, which is related to the cluster size effect. A surface plasmon characteristic of metallic Ag appears at coverages higher than 2.8 monolayer equivalent.

IDENTIFICATION OF MEMBRANE PROTEINS IMAGED BY ATOMIC FORCE MICROSCOPY USING A TEMPLATE MATCHING ALGORITHM

Oliver Enders, Enrico Martinoia, Carsten Zeilinger, Hans-Albert Kolb
Chin. Phys., 2001, 10 (13): 100-107 doi: 10.1088/1009-1963/10/13/019
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The atomic force microscope allows to image biological samples in their native environment. But the identification and the topography of individual randomly distributed membrane proteins is still a challenge. We used membranes of isolated vacuoles of barley mesophyll cells. Images at low resolution indicate that vacuoles spontaneously attach, rupture and finally adsorb completely as planar membrane to mica. Height profiles indicate that the membrane at the peripheral boundary exposes the extravacuolar surface to the scanning tip. At molecular resolution a template matching correlation algorithm was used to identify the most abundant membrane protein, the vacuolar H+-ATPase by the characteristic extravacuolar head of the transport molecule. The data indicate the possibility to analyse single randomly distributed membrane proteins in their native environment with the knowledge of a suitable template.

ON THE STUDY OF SILICON NANO-WIRES SELF-ASSEMBLED AS PARTICLES

Zhang Ze, S.T.Lee
Chin. Phys., 2001, 10 (13): 111-116 doi: 10.1088/1009-1963/10/13/021
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Two different types of Silicon nano-wires (SiNWs) have been observed by scanning and transmission electron microscopy. One are of free standing SiNWs deposited uniformly on the surface of silicon substrates, and the other are self-assembled into special shaped particles. These SiNWs were synthesized by thermal evaporation of SiO amorphous powders without any metal catalysts in the temperature range of 900-1250℃. Growth history reveals that the self-assembled SiNWs are formed by original nucleation from the surface of amorphous SiOx particle matrices through phase separation and silicon precipitation followed by further growth through oxide-assisted vapor-solid reactions. The above results provide a solid experimental support for the oxide-assisted growth model of SiNWs.

PREPARATION OF NANOWIRES AND MICROARRAYS

Zhang Li-de, Meng Guo-wen, F. Phillipp
Chin. Phys., 2001, 10 (13): 117-123 doi: 10.1088/1009-1963/10/13/022
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We report on the synthesis of one-dimensional (1D) solid nanostructures and ordered microarrays consisting of nanowires and carbon nanotubes. For 1D nanostructures, several synthesis methods, such as, carbothermal reduction of silica xerogels containing carbon nanoparticles, chemical vapor deposition on mesoporous active carbon with transition metal catalyst nanoparticles inside the pores, and simple physical evaporation with the help of transition metal nanoparticles as catalysts, have been used. For microarrays, anodic alumina membranes (AAMs) with highly ordered honeycomb structure were used as templates, chemical vapor reaction inside the nanochannels, Sol-gel technique, and selective electrodeposition in the channels, have been used to prepare microarrays embedded in AAMs.

SPONTANEOUS TRANSFORMATIONS OF NANOCLUSTERS

M. Rieth, W. Schommers, S. Baskoutas, C. Politis
Chin. Phys., 2001, 10 (13): 132-136 doi: 10.1088/1009-1963/10/13/024
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It is well-known that nano-systems can have properties which are distinctly different from macroscopic systems. In this study we point out the following specific behaviour: if the particle number is decreased so that the size of the system is in the nanometer-realm, new effects emerge which reflect certain features of biological systems although the system is inorganic in nature. This behaviour is shown by realistic molecular dynamics calculations in connection with aluminum-nanoclusters at various temperatures. The clusters can transform without external influence from a metastable into a stable state, and there can be more than one stable state, that is, we observe a bifurcation in the sense of chaos-theory. The stable states can differ in both the atomic structure and the outer shape.

NOVEL FORMATION AND DECAY MECHANISMS OF NANOSTRUCTURES ON THE SURFACE

Wand En-ge, Liu Bang-gui, Wu Jing, Li Mao-zhi, Yao Yu-gui, Zhu Wen-guang, Zhong Jian-xin, John Wendelken, Niu Qian, Zhang Zhen-yu
Chin. Phys., 2001, 10 (13): 144-150 doi: 10.1088/1009-1963/10/13/027
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For decades the research on thin-film growth has attracted considerable attention as these kinds of materials have the potential for a new generation of device application. It is known that the nuclei at the initial stage of the islands are more stable than others and certain atoms are inert while others are active. In this paper, by using kinetic Monte Carlo simulations, we will show that, when a surfactant layer is used to mediate the growth, a counter-intuitive fractal-to-compact island shape transition can be induced by increasing deposition flux or decreasing growth temperature. Specifically, we introduce a reaction-limited aggregation (RLA) theory, where the physical process controlling the island shape transition is the shielding effect of adatoms stuck to the stable islands on the incoming adatoms. Moreover, the origin of a transition from triangular to hexagonal and then to inverted triangular as well as the decay characteristics of three-dimensional islands on the surface and relations of our unique predictions with recent experiments will be discussed. Furthermore, we will present a novel idea to make use of the condensation energy of adatoms to control the island evolution along a special direction.

ATOMIC FORCE MICROSCOPY STUDIES AND MODELING OF SURFACE STRUCTURES PATTERNED DURING OSTWALD RIPENING AT Fe/Mo MULTILAYER SYSTEMS

Shen Dian-hong, Luo Guang-ming, Kang Ning, Lai Wu-yan, A. Berlinger, P. von Blanckenhagen
Chin. Phys., 2001, 10 (13): 163-166 doi: 10.1088/1009-1963/10/13/030
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Fe/Mo multilayers which were grown by sputtering, annealed in high vacuum and analyzed by means of Atomic Force Microscopy and Scanning Electron Microscopy. Concentric circle-1ike patterns were observed after annealing. Two-dimensional Ostwald ripening mechanisms in immiscible systems of Fe/Mo may explain the formation of these structures. We simulated pattern formation in a late stage of the phase separation by applying the Thomas-Freundlich thermodynamic relation. Based on a two-dimensional mode1 in the framework of the Lifshitz-Slyozov theory, our modeling has been extended to include the diffusion limitation in a multi-cluster system.

SPIN-DEPENDENT TUNNELING EFFECTS ON MAGNETIC NANOSTRUCTURES

M. Getzlaff, M. Bode, A. Kubetzka, O. Pietzsch, R. Wiesendanger
Chin. Phys., 2001, 10 (13): 186-194 doi: 10.1088/1009-1963/10/13/034
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The contrast mechanism of spin-polarized scanning tunneling spectroscopy (SP-STS) is demontrated on in-plane magnetized Gd islands grown on W (110) using Fe-coated tips. The use of Gd-coated tips enables the imaging of the antiferromagnetic domain structure of Fe nanowires being perpendicularly magnetized grown on a stepped W(110) substrate. The influence of an external magnetic field on the nanowire domain structure is demonstrated. It is shown that the antiferromagnetic domain structure of the Fe nanowires strongly depends on the miscut of the W(110) substrate. While at high miscut the magnetization direction alternates between adjacent DL stripes it was found to alternate within single Fe DL stripes at low miscut. Nanoscale Fe islands with a height of two atomic layers were found to be single domain particles.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

SINGLE-ELECTRON TRANSISTORS FOR FUTURE APPLICATIONS

Li Hong-wei, Zhou Jun-ming
Chin. Phys., 2001, 10 (13): 1-3 doi: 10.1088/1009-1963/10/13/001
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Single electron transistors with wire channels are fabricated by a nanoelectrode-pair technique. Their characteristics strongly depend on the channel widths and the voltages on the in-plane gates. A few dips in the Coulomb blockade oscillations were observed at the less positive gate voltages for a device with a 70nm-wide wire due to Coulomb blockade between the coupled dots. By applying negative voltages to the in-plane gates, the oscillations became periodic, which indicated the formation of a single dot in the conducting channel. These gates facilitate fabricating single-electron transistors with single dot structures, which have potential applications on its integration.

RESONANT ANDREEV REFLECTION IN HYBRID SUPERCONDUCTING-NORMAL NANOSTRUTURES

Lin Tsung-han
Chin. Phys., 2001, 10 (13): 4-9 doi: 10.1088/1009-1963/10/13/002
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After a brief description of hybrid superconducting-normal nanostructures and a brief introduction of the Andreev reflection, we present a theoretical investigation of the electron tunneling through a normal-metal/quantum-dot/superconductor (N-QD-S) system where multiple discrete levels of the QD is considered. By using the nonequilibrium-Green-function (NGF) method, the current I is obtained and studied in detail. We find that the Andreev tunneling shows clear resonant behavior, as obtained in previous works. Moreover, the current I versus the gate voltage Vg exhibits different kinds of peaks, depending on the bias voltage, the level-spacing of the QD, and the energy gap of the superconducting electrode. Besides, in I-V characteristics extra peaks superimposed on the conventional current plateaus emerge, which stem from the resonant Andreev reflections.

PHOTOLUMINESCENCE OF NANOCRYSTALLINE SiC FILMS PREPARED BY RF MAGNETRON SPUTTERING

Liu Ji-wen, Xie Fang-qing, Zhong Ding-yong, Wang En-ge, Liu Wen-xi, Li Shun-feng, Yang Hui
Chin. Phys., 2001, 10 (13): 36-39 doi: 10.1088/1009-1963/10/13/007
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Amorphous SiC films are deposited on Si (111) substrates by rf magnetron sputtering and then annealed at 1200℃ for different times by a dc self-heating method in a vacuum annealing system. The crystallization of the amorphous SiC is determined by Raman scattering at room temperature and X-ray diffraction. The experimental result indicates that the SiC nanocrystals have formed in the films. The topography of the as-annealed films is characterized by atomic force microscopy. Measurements of photoluminescence of the as-annealed films show blue or violet light emission from the nanocrystalline SiC films and photoluminescence peak shifts to short wavelength side as the annealing time decreases.

INVESTIGATION ON THE STRUCTURE AND ELECTRIC PROPERTIES OF BUCKY ONIONS

Xue Zeng-quan, Liu Hong-wen, Hou Shi-min, Tao Cheng-gang, Zhang Geng-min, Zhao Xing-yu, Liu Sai-jin, Du Min, Liu Wei-min, Wu Jin-lei, Peng Lian-mao, Wu Quan-de, Shi Zu-jin, Gu Zhen-nan
Chin. Phys., 2001, 10 (13): 50-53 doi: 10.1088/1009-1963/10/13/010
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Bucky onions were fabricated by the DC discharge method and their behaviors and electric properties on Highly Oriented Pyrolytic Graphite (HOPG) were studied by using an atomic force microscope (AFM), a scanning tunneling microscope (STM) and a transmission electron microscope (TEM). Small-sized Bucky onions demonstrated the properties of semiconductors and as the size increased their metallicity became stronger. AFM and STM images revealed the tendency of Bucky onions to form dimers.

SURFACE CAPPING OF TiO2 COLLOIDAL NANOPARTICLES STUDIED BY FOURIER TRANSFORM RAMAN SPECTRA

Deng Hui-hua, Wang Xin, Yu Tsing, Mao Hai-fang, Suzuki Toshishige, Lu Zu-hong
Chin. Phys., 2001, 10 (13): 59-64 doi: 10.1088/1009-1963/10/13/012
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Surface capping of TiO2 colloid nanoparticles with tetrasulfonated gallium phthalocyanine chloride (GaTsPc) was studied by Fourier Transform (FT) Raman spectra. A striking FT-Raman signal enhancement of GaTsPc is observed, indicating that a surface complex is formed during surface capping of GaTsPc dye molecules on TiO2 colloid via sulfonate groups. This effect is attributed to a strong Raman resonance with the charge transfer transition in the surface complex. Surface complexation also have considerable influences on the FT-Raman signals for TiO2 nanoparticles.

SELF-ASSEMBLY AND POLARIZABILITY OF CAPPED CdS NANOCRYSTALS ON SILICON SURFACES

Ba Long, Zhang Yu, Lu Zu-hong
Chin. Phys., 2001, 10 (13): 70-75 doi: 10.1088/1009-1963/10/13/014
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The zinc-blende CdS nanocrystals with particle size less than 10nm were prepared in solution with a molecular surfactant. The particle surface was modified with capping molecules, bis(2-ethylhexyl) sulfosuccinate disodium salt (AOT) or hexametaphosphate (HMP). The colloid solution was deposited on silicon wafer and the assembly of these nanocrystals was studied by atomic force microscopy. It was found that the CdS/AOT formed a monolayer by simply dropping the colloid solution on silicon surface, while CdS/HMP exhibited 3D structure with prefered orientation in the similar deposition process. A dynamic electric force microscopy was performed and the polarizability was measured from the resonance of cantilever under applied alternating voltage between tip and substrate. The dielectric constant of CdS nanocrystal was estimated by comparing the different electric capacitance of Au and CdS nanocrystals.

ON THE THERMAL STABILITY AND MELTING TEMPERATURE OF NANO-SYSTEMS

M. Rieth, W. Schommers, S. Baskoutas, C. Politis, A. Jannussis
Chin. Phys., 2001, 10 (13): 137-139 doi: 10.1088/1009-1963/10/13/025
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Various material properties which are well defined and clearly fixed for macroscopic systems, get a modified significance in nano-physics and nano-technology. It is shown, as an example, that the temperature behaviour of material systems is considerably changed when we go from macroscopic to nanometersize. It is pointed out that the standard model of solid state physics (ordered structure, harmonic approximation) is in general not sufficient for the description of nano-systems.

ULTRAHIGH DATA DENSITY STORAGE WITH SCANNING TUNNELING MICROSCOPY

Gao Hong-jun, Shi Dong-xia, Zhang Hao-xu, Lin Xiao
Chin. Phys., 2001, 10 (13): 179-185 doi: 10.1088/1009-1963/10/13/033
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Ultrahigh density data storage devices made by scanning probe techniques based on various recording media and their corresponding recording mechanisms, have attracted much attention recently, since they ensure a high data density in a non-volatile, erasable form in some kinds of ways. It is of particular interest to employ organic polymers with novel functional properties within a single molecule (or a single molecular complex) for fabricating electronic devices on a single molecular scale. Here, it is reported that a new process for ultrahigh density and erasable data storage, namely, molecular bistability on an organic charge transfer complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine (NBMN-pDA) switched by a scanning tunneling microscope (STM). Data density exceeds 1013 bits/cm2 with a writing time per bit of ~1μs. Current-voltage (I/V) measurements before and after the voltage pulse from the STM tip, together with optical absorption spectroscopy and macroscopic four-probe I/V measurements demonstrate that the writing mechanism is conductance transition in the organic complex. This mechanism offers an attractive combination of ultrahigh data density coupled with high speed. The ultimate bit density achievable appears to be limited only by the size of the organic complex, which is less than 1nm in our case, corresponding to 1014 bits/cm2. We believe that provided the lifetime can be improved, molecular bistability may represent a practical route for ultrahigh density data storage devices.
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