AVS2001 Session NS-ThP: Poster Session
Thursday, November 1, 2001 5:30 PM in Room 134/135
Thursday Afternoon
Time Period ThP Sessions | Topic NS Sessions | Time Periods | Topics | AVS2001 Schedule
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NS-ThP-1 Manipulation of Organic Monolayers Confined in Molecule Corrals
A. Schnieders, T.P. Beebe, Jr. (University of Utah) Nanometer-scale organic surface structures have significant potential applications, e. g. in the field of nanoelectronics. Therefore the characterization but also the controlled production of these structures is of increasing importance. In recent years, it has been shown that scanning tunneling microscopy (STM) is, besides its wide use in the characterization of organic monolayers, also well suited for manipulation of these layers. In this study we investigate the possibility to use molecule corrals to confine the effects of manipulation of organic monolayers to small areas. Molecule corrals are nanometer-sized etch pits in the basal plane of highly ordered pyrolytic graphite (HOPG). They are formed by heating HOPG to 650° C in air. This technique produces corrals, which are uniformly circular and one monolayer deep. The radius is easily controlled by the etching time. Molecule corrals have previously been used to contain and study small numbers of molecules in their interiors and as highly controllable surface defects on graphite. We used a home build STM and a commercial STM (Multimode Nanoscope, Digital Instruments) for both, manipulation and characterization of self-organized organic monolayers on HOPG, with and without molecule corrals. Most of the experiments were performed under a liquid droplet of the organic compound in solution at room temperature. In this presentation, we will show, among others, results on diacetylene monolayers. |
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NS-ThP-2 Bistability in Scanning Tunneling Spectroscopy of Ga-Terminated Si(111)
I.B. Altfeder, D. Chen (Rowland Institute for Science) Demonstration of a Tunable Bistable Tunnel Device with a Low Temperature STM and A Self-organized Ga Array on Si(111)1 Bistable electron transport, a phenomenon usually associated with double-barrier structures, has been observed with a conventional STM junction formed between a metal tip and a Ga-terminated Si(111) surface at 77 K. Large hysteresis loops appear in the current-voltage characteristics when electrons are injected from the tip to the surface. The turn-on bias varies from -3.1 to -4.0 V and shows an inverse dependence on the tip-sample distance, indicating a strong field effect. The turn-off bias, however, is essentially pinned at a conductance threshold of -2.7 V. |
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NS-ThP-3 Nanostructures of Si Luminescence Materials Fabricated by Microwave Plasma CVD
H. Kezuka (Tokyo University of Technology, Japan); I. Kato, T. Matsumoto, R. Saito (Waseda University, Japan); T. Suzuki (Tokai University, Japan) The double-tubed coaxial line-type microwave plasma CVD(Chemical Vapor Deposition) system has been developed for obtaining a stable plasma with a low gas pressure in order to fabricate electro-microdevices and photonic devices. In this paper, the microwave plasma CVD is applied for the fabrication of nano-particles of a-Si:H. In this system, the microwave power is confined in the the cavity, and not injected into the plasma in the chamber. Thus,in the deposition chamber,the gas flow forms spatial afterglow plasma with no microwave power injected. He outer discharge tube is composed of fused quartz and the inner tube is made of stainless steel. The Ar gas is fed to the outer discharge tube and the SiH4 gas is fed to to the inner tube.The Ar gas is ionized in the cylindrical cavity region by the microwave power. The SiH4 gas flows into the Ar plasma at the discharge tube end through the inner tube, and then the SiH4 is dissorciated by the microwave power.The substrate table area is 40cm2 and is placed at z = 10 cm. The Ar gas flow rate is 110 ml/min and the SiH4 gas flow rate is 30 ml/mi.After heat-treatments of 72 hrs in air for as-deposited a-Si:H partiles, it is assumed that nano-particles(nanoball) of a-Si:H include nano-crystal(nc) Si characterized from XPS-spectrum of the oxygen 1s region and of the silicon 2p region.From SEM- and AFM-observation of the oxidized surface of nano-particles, the size of nanoballs of a-Si:H is about 20-30nm in diameter. |
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NS-ThP-4 Si Stems Produced by Annealing Au/Si(111) Surface
T. Takami (Visionarts Research); I. Kusunoki (Tohoku University, Japan) Nano-tubes, fibers, and wires are interested as an intelligent material supporting the "nano-technology". Silicon nano-wire1 and other semiconductor nano-wires2,3 had already been produced before the discovery of carbon nano-tube by Iijima.4 Recently, Homma et al.5 succeeded to form Si nano-columns on a Si substrate arranged with Au-islands by using vapor-liquid-solid (VLS) reaction of disilane (Si2H6). In the present work, we have demonstrated the formation of the Si stem (a bundle of nano-fibers) without using VLS reaction. Small Si particles for the seeds of the Si stems were scattered on a Si(111) wafer. After introducing the wafer in an ultrahigh vacuum (UHV) chamber, monolayer-equivalent Au atoms were deposited on the wafer by the vacuum evaporation. After the deposition, the wafer was annealed at 1000°C for 260 minutes. Then the Si stems were formed on the Si surface, which were observed by scanning electron microscope (SEM). The stems looked like tiny mushrooms in micro-meter scale. The Au atoms worked as a catalyst for the stem formation by inducing the surface segregation of the bulk-materials. |
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NS-ThP-5 A Simple Method of Forming Small Gold Particles on a Thin Gold Film
M. Xiao (CCMC-UNAM, Mexico) We have produced gold particles whose sizes range from several tenth nanometers up to about one micrometer. The small gold particles are distributed on a gold thin film of thickness $50\sim 80$\AA. The method for the formation is simple. We first evaporated the gold thin film, and then applied DC field along the film. When the field increases from zero to 30 V, and the measured current increases from 0 to 650 mA, the particles were formed. The sizes and the distribution distances could be controlled by the applied DC field. |
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NS-ThP-6 Theoretical Studies on One-dimensional Photonic Band-gap Structures
M. Xiao (CCMC-UNAM, Mexico); D. Soto Puebla (CIFUS and CICESE, Mexico); F. Ramos Mendieta (CIFUS, Mexico) We present numerical results of dispersion relations and transmission spectra for one-dimensional photonic band-gap structures composed of periodic metallic thin films separated by dielectric layers. In the calculation, both published experimental data and the Drude model are used to obtain the refraction index of the silver film. Influences fo various parameters on the quality of the band-gap structures are discussed on the base of the results. |
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NS-ThP-7 CdS Self-assambled Nanostructures Produced by Pulsed Laser Deposition1
C. Manzano, R. Castro (Cinvestav-IPN, México); J.L. Peña (CICATA-IPN, México); M.A. Santana-Aranda, M. Meléndez-Lira (Cinvestav-IPN, México) Low-dimensional structures are very attractive due to their potential application in the production of high-efficiency opto-electronic devices. Until now, most of the semiconductor self-assembled nanostructures (SSN) have been fabricated employing epitaxial deposition techniques. The formation mechanism of SSN has been identified as the misfit strain involved during the heteroepitaxial growth. We report results of the production, and optical and structural characterization of CdS nanostructures deposited by pulsed laser deposition on Corning glass substrates (CGS), two possible mechanisms for the production of these nanostructures are discussed: 1) stress due to differences in the thermal expansion coefficients of the CdS film and CGS; 2) CdS droplets ejected from the target and directly deposited on the CGS. The samples were grown using a Nd:YAG laser focused on a rotating CdS target. Depositions were performed with 50 lasers shots employing substrate temperatures of 250, 350 and 500°C under a pressure of 10-6 Torr. The morphology of the deposited CdS layers was examinated by atomic force microscopy finding the presence of elliptic islands with typical dimensions around 60 and 30 nm for the major and minor axis lengths, respectively. There is no evidence of degradation with time or handling. A clear blue shift, with values up to 100 meV, of the absorption band edge was observed in the room temperature transmission spectroscopy (TS) measurements, and was attributed to quantum confinement. Room temperature modulated transmission spectroscopy (MTS) measurements indicated a blue shift of only 7 meV. The differences between the results from TS and MTS are discussed taking in account the islands size distribution. These results are correlated with those obtained from 10 K photoluminescence, x-ray diffraction and scanning electron microscopy measurements. |
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NS-ThP-8 Atomistic Simulation Studies of Stresses and Grain Boundaries by Cu Nanowire Deformations
J.W. Kang, H.-J. Hwang (Chung-Ang University, Korea) We investigated mechanical properties of Cu nanowires with grain boundary by various mechanical deformations using classical molecular dynamics simulation. We simulated the cases of elongation, shearing, rotation, rotated elongation, and compression. Before the first yielding, nanowires preserve the elastic stages, and after this, the mechanical deformation proceeds in alternating quasi-elastic and yielding stages. For Cu nanowires with grain boundary, most of the slip events occurred in the interfaces of grain boundary. For Cu {100} nanowires in this work, all slips occurred in the [110] directions on the {111} planes. In compression case, whole nanowires region, which has originally {100} planes, was transformed into {111} planes during temporary state. However, in other cases, such as elongation, [100] shear, [110] shear, and rotation, only part of nanowires region were transformed into {111} planes. |
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NS-ThP-9 Micro-Fabrication of Sub-wavelength-Size Aperture for Near-Field Optical Probe
M.Y. Jung, J.W. Kim, D.W. Kim, S.S. Choi (Sun Moon University, Korea) There have been considerable interests about the microfabrication of the submicron size hole due to the potential application of the near field optical sensor array for gigabyte storage device. We have previously reported fabrication of the submicronsize oxide aperture.1 In this report, the 5 micron size dots were photo-lithographically patterned on the Si (100) wafer. After formation of the V-groove shape utilized by anisotropic KOH etching, the orientation dependent oxide growth was performed to have an etch-mask for dry etching. The reactive ion Cl2 etching using inductively coupled plasma (ICP) system will be performed in order to etch thin SiO2 layer on the bottom of the etch stop and to etch the Si on the bottom. After etching, the fabricated submicron-size oxide aperture followed by a proper metal deposition and silicon nitirde deposition procedures can be utilized as a near field optical probe.
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NS-ThP-11 An Apparatus for Deposition of Size-selected Clusters and Fabrication of Cluster-assembled Films
N. Tarras-Wahlberg, M. Andersson, A. Rosén (Chalmers Univ. of Tech. and Göteborg Univ., Sweden) We present the design of an apparatus for deposition of size-selected metal clusters. The clusters are fabricated in a laser vaporization source. It consists of a cavity where pulsed light from a Nd:YAG or excimer laser vaporizes metal atoms into a continuous flow of He atoms at a pressure of 10 - 50 mbar and clusters are formed. The cluster-buffer gas mixture exits the cavity through a nozzle (0.5 - 1 mm diameter) and the beam passes a differential pumping stage until it reaches the vacuum chambers for characterization and deposition. At several positions along the cluster beam quartz crystal microbalances and Faraday cups can be inserted to measure the total mass and ion yields. In the first vacuum chamber, just outside the nozzle the deposition rate is high, e.g. 4 Å/s of non size-selected Fe-clusters at 10 Hz repetition rate. A time-of-flight mass spectrometer is used to monitor the cluster production and to characterize the cluster size distribution, and a quadrupole mass filter will be used for size selection and deposition of monodisperse clusters. In previous deposition experiments we have made iron cluster films on HOPG and characterized their magnetic properties [C. Johansson et al., Nanostr. Mater. 12 (1999) 287]. |
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NS-ThP-13 Gas-Phase Purification of Single-Wall Carbon Nanotubes using H2S and O2 Mixture
T. Jeong (LG Innotek, Korea); Y.B. Hahn (Chonbuk National University, Korea) A purification process combining both a gas-phase purification using H2S and O2 mixture to remove impurity carbon particles and an acid treatment to remove metal particles has been developed for single-wall carbon nanotubes (SWNTs), synthesized by an arc-discharge method. Acid solution of 3 M HCl was used to remove catalyst metal particles out of the as-grown SNWTs. Thermal oxidation using the H2S-O2 gas mixture was followed to preferentially remove unwanted carbon particles. Hydrogen sulfide played a role of enhancing the removal of carbon particles as well as controlling the oxidation rate of oxygen with carbon. The optimum gas ratio was 10 ml H2S/min and 20 ml O2/min. After the acid treatment and thermal oxidation at 500 °C for 1 h, we achieved carbon nanotubes purity of > 90 % with yield of 20 - 50 %, depending on the purity of starting material. |
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NS-ThP-14 Growth of Spherical Diamond Tips on Small Cylindrical Substrates
V. Baranauskas, A.C. Peterlevitz, H.J. Ceragioli, S.F. Durrant (Faculdade de Engenharia Eletrica e Computacao - UNICAMP, Brazil) This work demonstrates the possibility of growing spherical diamond tips on the top of metallic rods using chemical vapor deposition (CVD). Spherical diamond tips are of interest for diverse applications, including micro-drilling tools, waveguides, field-emission devices, biomedical instruments and so on. A hot-filament CVD system fed with ethanol highly diluted in hydrogen was used. The nucleation and growth parameters for such spherical diamond tips differ from those for deposition on flat surfaces since there is no competition for space between the neighboring grains to growth in their preferred crystalline direction, which often results in columnar structured materials on flat surfaces. A model for scaling-down or scaling-up the diameter of the diamond tips will be presented. Morphological data obtained by scanning electron microscopy (SEM) and results of Raman spectroscopic analyses of the samples produced with different diameters are discussed. |
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NS-ThP-15 The Carbonitride Nanostructures Synthesized by Microwave Plasma Enhanced Chemical Vapor Deposition in an Acetylene / Ammonia Plasma System
S.-H. Lai, K.-H. Hong, H.C. Shih (National Tsing Hua University, Taiwan) The carbonitride nanostructures consisting of nanotubes and nanofibers have been synthesized on Pd-coated porous silica by microwave plasma enhanced chemical vapor deposition (MPECVD) at a temperature of about 600°C and the precursors are H2, C2H2, NH3, and N2. The condition of Pd clusters was varied with the power density and the bias to the substrate during the plasma immersion ion implantation (PIII) process. Samples were analyzed by SEM, HRTEM, EELS, and XPS. It was found that carbonitride nanostructures are strongly affected by the surface morphology of the Pd implant layer and the N content. HRTEM and EELS studies showed that the degree of linearity and graphitization of the nanostructure decreases as the N content increases. Nevertheless, the field emission properties of the nanostructures are enhanced due to the N doping. Form the XPS results, N is either bonded to two C atoms (sp2 pyridine-like type) or to three (sp3 bridgehead-nitrogen type) in the hexagonal sheets. |
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NS-ThP-16 STM Observation of Nanoscale Defects Formed by Annealing the 6H-SiC Surface
M. Yoshimura, K. Ojima, K. Ueda (Toyota Technological Institute, Japan) It was recently reported that the carbon nanotube can be produced on the SiC surface by annealing at high temperature around 1800K. Carbon-terminated surface is considered to be more appropriate for the growth of nanotube than the Si-terminated surface. The transimission electron microscopy (TEM) has been utilized to investigate the growth mechanism for both surfaces. However the determination of the precise atomic structure, such as the location of the pentagons and defects, is difficult only by TEM observation. Here we demonstrate scanning tunneling microscopy (STM) study of the elucidation of Si-terminated SiC surface by annealing. A commercially available 6H-SiC wafer (CREE) was used as a specimen. It was annealed up to 2000K in UHV. STM observation was performed at room temperature with a tungsten tip. After annealing at 1600K, following defect structures were observed on the flat graphite layer; (1)Protruded particles with 4-5nm in diameter were observed and its surface showed /3x/3 superstructure. (2) Nanotube-like structures lie on the surface. They are probably formed by rolling of a graphite layer from the step. (3) Star-shaped defects of 3nm size were frequently observed. The surrounding graphite area also shows the /3x/3 superstructure. The surface was then annealed to 2000K, however, the surface structure was basically unchanged and no nanotube formation normal to the surface was detected. We discuss detailed structure of the defects and its formation mechanism. |
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NS-ThP-17 Scanning Spreading Resistance Microscopy of MOCVD Grown InP and GaAs Optoelectronic and Microelectronic Structures
St.J. Dixon-Warren, G. Pakulski, A.J. SpringThorpe, G. Hillier, D. Macquistan, R. Streater (Nortel Networks, Canada); R.P. Lu, K.L. Kavanagh (Simon Fraser University) Scanning spreading resistance microscopy (SSRM) is a new scanning probe microscopy technique that provides localized resistance profiling over a semiconductor surface. The technique, which is based on contact-mode atomic force microscopy (AFM), provides information on the two dimensional distribution of charge carriers and on the position of pn junctions in semiconductor structures. We have used SSRM to examine the cleaved edge of a number of MOCVD grown InP and GaAs optoelectronic and microelectronic structures, such as heterojunction bipolar transistors and buried heterojunction laser structures. We have also performed careful measurements on dopant staircase structures. Information on the spatial distribution of dopants in the epitaxial layers was obtained, and the effect of the applied tip voltage was investigated. We will also compare the SSRM results with those obtained using Scanning Capacitance Microscopy (SCM) on the same samples. Finally, we plan to report preliminary results for SSRM and SCM measurements for devices under operating bias conditions. |
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NS-ThP-18 Active Feedback Noise Cancellation Low Temperature Scanning Tunneling Spectroscopy
D. Chen, S.L. Pryadkin (The Rowland Institute for Science); B. Wang, H. Wang (University of Science and Technology of China) A scanning tunneling microscope (STM) is one of the most sensitive mechanical and acoustical noise sensors. This in turn makes it difficult to perform fine resolution spectroscopy. Here, we describe a novel UHV and low temperature (4.2K) STM consisting of two tips which can be actuated independently. In the spectroscopy mode, one of the tips serves as the noise sensor whose signal is phase inverted and fed to the second tip to lock the tip-to-sample separation during an I-V measurement. This active feedback method effectively improves the signal-to-noise ratio. More importantly, under the low thermal drift conditions, such as in low temperature operation, it allows the long-time averaging of the measurement while avoiding artifacts due to residual mechanical instability of STM. Examples o the tunneling electron spectroscopy performed on quantized nano-structure will be demonstrated. |