Papers

AVS2004 Session NS1-ThM: Nanoscale Fabrication

Thursday, November 18, 2004 8:20 AM in Room 213C

Thursday Morning

Start	Invited?	Item
8:20 AM		NS1-ThM-1 Three-Dimensional Nanotechnology by Focused-Ion-Beam Chemical-Vapor-Deposition S. Matsui (Himeji Institute of Technology, CREST-JST, Japan) The deposition rate of focused-ion-beam chemical-vapor-deposition (FIB-CVD) is much higher than that of electron-beam chemical-vapor-deposition (EB-CVD) due to factors such as the difference of mass between electron and ion. Furthermore, FIB-CVD has an advantage over EB-CVD in that it is more easily to make a complicated 3-dimensional nanostructures. Because, a smaller penetration-depth of ion compared to electron allows to make a complicated 3-dimensional nanostructures. For example, when we make a coil nanostructure with 100 nm linewidth, electrons with 10-50 keV pass the ring of coil and reach on the substrate because of large electron-range (over a few µm), so it is very difficult to make a coil nanostructure by EB-CVD. On the other hand, as ion range is less than a few ten-nm, ions stop inside the ring. Three-dimensional nanostructure fabrication using FIB-CVD has following advantages. (1) As a beam diameter of FIB is 5nm, 3 D nanostructures with a few ten nm can be fabricated by FIB. (2) 3D nanostructures made of metal, semiconductor, and insulator etc. can be fabricated by using various source gases. Three-dimensional nanotechnology using FIB can be widely applied to electronics, mechanics, optics, and biology. We have demonstrated the fabrication of free-space-nanowiring, electrostatic nano-actuator, bio-injector and electrostatic nano-manipulator by using FIB-CVD.
9:00 AM		NS1-ThM-3 Integration of Ion Beams with Scanning Probes for Local Doping and Chemical Analysis of Materials T. Schenkel, A. Persaud (E. O. Lawrence Berkeley National Laboratory); I.W. Rangelow (University Kassel, Germany); S.J. Park, F.I. Allen (E. O. Lawrence Berkeley National Laboratory); K. Ivanova (University Kassel, Germany) We describe our newly developed scanning probe instrument which integrates ion beams with imaging and alignment functions of a piezo resistive scanning probe in high vacuum. In the past, Scanning Probe functions have been combined successfully with lasers, excited reactants, as well as neutral beams for surface analysis or materials modification at a nanometer length scale. In our approach, we transport beams of energetic ions (1 to 200 keV) through small (5-30 nm diameters), high aspect ratio holes (>5:1) in the scanning probe tips. Holes are formed by Focused Ion Beam drilling and thin film deposition. Transport of single ions can be monitored through detection of secondary electrons that are emitted when ions impinge on sample surfaces. Secondary electron yield enhancements for highly charged dopant ions (e. g., P15+, or Te36+) allow efficient detection of single ion impacts for single atom device formation. Detection of secondary electrons and ions enables adaptation of a time-of-flight secondary ion mass spectrometry scheme for correlation of scanning probe images with chemical and molecular composition information on a 10 nm length scale. In our presentation we will discuss potential and limits of this approach in ion placement resolution, sensitivity in surface analysis, as well as issues of probe lifetime and effects of ion guiding in dielectric nanoholes. Acknowledgments: We thank the staff of the UC Berkeley Microlab, and the National Center for Electron Microscopy for their technical support. This work was supported by NSA and ARDA under ARO contract number MOD707501, and by the U. S. DOE under contract No. DE-AC03-76SF00098.
9:20 AM		NS1-ThM-4 Fabrication and Electrical Characterization of 2D Dopant Nanoelectronic Devices in Si J.S. Kline, S.J. Robinson, J.R. Tucker (University of Illinois at Urbana-Champaign); J.-Y. Ji, T.-C. Shen (Utah State University); C. Yang, R.-R. Du (University of Utah) The integration of nanoscale devices with Si-based microelectronics presents a major challenge in nanotechnology. We address this issue by employing STM patterned P donors as the building block for all-epitaxial nanoscale devices on pre-fabricated templates. To preserve the As-implanted contacts, we have developed a low-temperature UHV process using 300eV Ar ion sputtering and sub-700°C annealing to prepare atomically flat and clean surfaces for STM lithography. Differences in surface features and tunneling spectroscopy allow the registration of the STM to the template. After STM nanolithography, P donors are selectively deposited onto the patterned area by phosphine exposure. Subsequent Si low-temperature deposition and 500°C annealing forms an epitaxial overlayer and activates the dopant atoms. Electron transport measurements at 4.2K for several 2-terminal devices including two-dimensional P wires 10-50nm wide and 30-700nm long indicate resistivity of the wires is in the order of 20kΩ/sq. Quantum coherence length and the implication of the oscillations in the magnetoresistance at 0.3K will be discussed. In addition, the fabrication and measurement of tunnel junctions is currently in progress and will also be reported. This work is supported by DARPA-QuIST program under ARO contract DAAD 19-01-1-0324.
9:40 AM		NS1-ThM-5 Scanning Tunneling Microscopy Electronic Characterization of a Nano Device for Quantum Computing M.E. Hawley, G.W. Brown, H. Grube (Los Alamos National Laboratory) Quantum computation is a revolutionary new paradigm that has seen tremendous growth since 1994. The quest to build a quantum computer (QC) has been inspired by its recognized formidable computational potential. The long-term goal in this quest is a large scale, fast, parallel and easily fabricated QC. Although a number of ingenious schemes have been proposed, silicon-based solid-state proposals, using nuclear or electron spins of dopants such a phosphorus as qubits, are attractive because of the long spin relaxation times and their scaleability and integratability with existing silicon technology. We have been working on such a device based on a proposal by B. Kane (Nature 393, 133 (1998), in which buried P atoms placed 20 nm apart act as quantum bits entangled through exchange interactions, atomically placed using Scanning tunneling microscope (STM) lithographic techniques on a hydrogen resist layer. This effort requires dosing the Si(100) surface with phosphine molecules and annealing the phosphorus into the silicon surface. STM-based atomic level lithography methods provides us with the added capability of characterizing the local electronic environment of the dopants. In this talk, Iâ?Tll describe our particular effort to fabricate a QC and the charge imaging technique we are using to image buried phosphorus dopants and charged defects that could potentially interfere with the operation of such a QC device as well as any other nano scale device on the silicon surface.}
10:00 AM		NS1-ThM-6 Nanotip Arrays Fabricated by One-step and Self-masked ECR-Plasma Etching and Their Applications for Field Emission, Antireflection and Sensing L.C. Chen, J.S. Hsu (National Taiwan University, Taiwan); H.C. Lo (Academia Sinica, Taiwan); I.F. Huang (National Taipei University of Technology, Taiwan); K.H. Chen (Academia Sinica, Taiwan); C.R. Lin (National Taipei University of Technology, Taiwan); C.F. Chen (National Chiao-Tung University, Taiwan) Well-aligned nanotip arrays with a nanotip density as high as 10^12 cm^-2 were achieved by a single-step electron cyclotron resonance plasma process using gas mixtures of silane, methane, argon and hydrogen. Formation of SiC cap was observed on each individual nanotip, implying a self-mask etching mechanism. This dry-etching technique was applied to a variety of substrates such as Si, GaN, GaP, Al, sapphire and glass, indicating its general applicability. The nanotip arrays so produced showed superior field emission as well as antireflection properties. The extremely sharp tip geometry provides large field enhancement, therefore a low turn-on field (<1V/micron), while the sub-wavelength nanostrutured surface exhibits an ultra low reflectivity (<0.1%) in visible and IR. The latter property can be explained by a simple gradient index model. Furthermore, the nanotip arrays dispersed with Ag nanoparticles also showed excellent surface enhancement in Raman scattering (SERS). By optimizing the size of Ag nanoparticle and inter-particle distance, SERS of 8-order has been achieved, suggesting potential application of nanoparticle-dispersed nanotip arrays in molecular sensors.
10:20 AM		NS1-ThM-7 Nanoscale Integration of NanoCarbons Based on Ultrananocrystalline Diamond and Carbon Nanotubes X.C. Xiao, O.H. Auciello, J.A. Carlisle (Argonne National Laboratory) Nanostructured carbon materials exhibit excellent physical, chemical, mechanical, tribological, and electrical and thermal transport properties that are dictated by the many different bonding configurations available to carbon. Ultrananocrystalline diamond (UNCD) films, and carbon nanotubes (CNTs) are recently discovered nanocarbons with unique properties, and are of particular research interest and have many potential applications. Novel properties and applications could also be expected from the nanoscale integration of these two materials. We report in this study our approaches to strategically combine and control the carbon nanostructure consisting of UNCD and CNTs. Two approaches to the integration of UNCD and CNTs have been developed and the material properties evaluated. The first type is the self-assembly of carbon nanostructure based on UNCD and CNTs which were synthesized simultaneously using a single Ar/CH₄ plasma chemistry in a microwave plasma chemical vapor deposition system. The ease to tailor the nanostructure through adjustment of the nucleation conditions (the relative fraction of nanodiamond seeds for growing UNCD and transition metal catalyst for growing CNTs) as well as the growth temperatures offers a new possibility to form carbon based self assembly nanostructures with unique combined mechanical and electronic properties. In the second approach CNTs are grown directly on UNCD thin films, again through the use of transition metal catalyst dispersed on the UNCD surface and the use of Ar/CH₄ plasmas. The robust integration of vertically aligned CNTs on UNCD combined two desirable electrochemical properties of CNTs and UNCD, i.e. the high specific surface area from CNTs and electrochemical stability from UNCD. Preliminary structure characterization and property studies illustrated the potential of this structure to be used as electrochemical electrodes for chemical sensing applications and in supercapacitors.
10:40 AM		NS1-ThM-8 The Role of Hydrogen in Ultrananocrystalline Diamond Thin Film Growth J.P. Birrell, J.E. Gerbi, O.H. Auciello, J.A. Carlisle (Argonne National Laboratory) A great deal of recent experimental studies and computer simulations have been performed to try to understand the surface stability of diamond nanocrystals. These results have yielded a number of striking conclusions that and the size of the crystallite. This study can help explain the transition of diamond thin film structure from microcrystalline to nanocrystalline with the reduction of hydrogen in the gas phase during microwave plasma enhanced chemical vapor deposition; namely, that the stability of the surface of the diamond nanoparticle is a strong function of both the hydrogen coverage uses TEM, Raman scattering, and XRD to investigate the role of hydrogen in the growth of ultrananocrystalline diamond (UNCD) thin films in two different regimes. First, we add hydrogen to the normal Ar/CH₄ gas mixture used during growth, and observe that rather than a monotonic increase in the grain size from nanocrystalline to microcrystalline, the films are clearly mixed-phase, with microcrystalline diamond inclusions that become much more prominent with added hydrogen. Second, we remove hydrogen from the plasma by changing the hydrocarbon precursor from CH₄ to C₂H₂. We observe that there is a lower limit to the amount of hydrogen that needed to sustain ultrananocrystalline diamond growth, below which a significant amount of disordered graphitic carbon is nucleated. We suggest that the reasons for these observed changes are that large amounts of hydrogen (in the form of H⁺ ) in the plasma enables the more rapid growth of diamond microcrystals, while low concentrations of hydrogen result in unstable diamond nanocrystals and thus the nucleation of disordered carbon material. This work was supported by the DOE-Office of science-Materials Science under Contract No. W-31-109-ENG-38.
11:00 AM		NS1-ThM-9 Surface-Templated Assembly of Nanoparticles on Solid Surfaces for Nano-Optical Applications S. Myung, N. Cho, J. Kim, D. Kim, S. Hong (Seoul National University, South Korea) Nanoparticles made of CdSe or Au have been extensively utilized for optical labeling and other nano-optical applications. In this case, one technological challenge can be positioning nanoparticles onto desired locations on solid substrates with a nanometer scale precision. We utilized surface-templated assembly strategy to position Au and CdSe nanoparticles onto specific locations on Au and silicon oxide substrates. In our method, thiol-terminated self-assembled monolayer (e.g. MPTMS) patterns are utilized to capture nanoparticles from the solution, while methyl-terminated SAM (e.g. 1-octadecanethiol) patterns are utilized to avoid any unwanted assembly of nanoparticles. We also explored the possibility of assembling fluorescent nanoparticles onto 3D structures such as AFM tip for nano-optical applications.