Nanomosis

Atomic-Scale Fabrication of a Silicon-based Quantum Computer

Neil Curson, Senior Research Fellow at the Centre for Quantum Computer Technology, at the University of New South Wales, Sydney, Australia, presented the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar is available for viewing and discussion through the Internanotech Community at http://nanotech.colayer.net/

Atomic-Scale Fabrication of a Silicon-based Quantum Computer

Quantum computers have the potential to dramatically reduce computing time for problems such as factoring [1] and database searching [2]. In particular a silicon-based quantum computer [3] shows promise for its potential to scale to a large number of qubits and for its compatibility with standard CMOS processing.

Our group has designed a fabrication strategy for the realisation of a scaleable quantum computer based in silicon using a combination of scanning probe microscopy for single qubit placement and silicon molecular beam epitaxy to encapsulate the qubit array [4]. In order to achieve this goal we have demonstrated the following key steps: we have been able to incorporate single P atoms as the qubits in silicon with atomic precision [5]; we have been able to minimise P segregation and diffusion during Si encapsulation [6] and we have imaged the array of buried P atoms using scanning tunneling microscopy to prove that the array remains intact after the encapsulation stage. Recently we have been able to fabricate a robust electrical device in silicon using the scanning tunneling microscope to lithographically pattern the dopants [7] and have demonstrated that this device can be contacted and measured outside the ultra-high vacuum environment.

We highlight the importance of our results for the fabrication of a Si-based quantum computer and discuss the final stages of the fabrication process required to realize a functional device, including the formation of an electrical isolation barrier and the alignment of surface metal electrodes to the buried P atom array.

[1] P. W. Shor, Proc. of the 35th Annual Symposium on Foundations of Computer Science, Editor: S. Goldwasser (IEEE Computer Society Press, USA, 1994), p. 124.
[2] L. K. Grover, Phys. Rev. Lett. 79, 325 (1997).
[3] B. E. Kane, Nature 393, 133 (1998).
[4] J. L. O'Brien et al. , Phys. Rev. B 64, 161401(R) (2001).
[5] S. R. Schofield et al ., Phys. Rev. Lett. 91, 136104 (2003).
[6] L. Oberbeck et al. , accepted for publication in Appl. Phys. Lett. (2004).
[7] F.J. Ruess et al., submitted to Nano Letters (2004).

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/
Blog On Nanotechnology - Nanomosis: http://barryhardy.blogs.com/nanomosis/

Computational and Theoretical Nanoscience: Essential Enabling Tools for Nanotechnology

Peter T. Cummings, John R. Hall Professor of Chemical Engineering at Vanderbilt University, USA will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/

Computational and Theoretical Nanoscience: Essential Enabling Tools for Nanotechnology

Theory, modeling and simulation (TMS) have been repeatedly identified as key enabling technologies for making fundamental advances in nanoscience and for making nanotechnology a practical reality [1-3]. In this talk, we provide an overview of the role of TMS in nanoscience, as well as an introduction to our ongoing theoretical and simulation-based research programs in nanotribology, nanoscale complexity of the electric double layer, molecular electronics, hybrid organic-inorganic nanocomposites and nanoconfined fluids.

1. Dixon, D.M., P.T. Cummings and K. Hess, Investigative Tools: Theory, Modeling and Simulation, in Nanotechnology Research Directions: IWGN Workshop Report Vision for Nanotechnology in the Next Decade, M.C. Roco, S. Williams, and P. Alivisatos, Editors. 2000, Kluwer Academic Publishers: Dordrecht.
2. McCurdy, C.W., E. Stechel, P.T. Cummings, B. Hendrickson and D. Keyes, Theory and Modeling in Nanoscience: Report of the May 10–11, 2002, Workshop Conducted by the Basic Energy Sciences and Advanced Scientific Computing Advisory Committees to the Office of Science, Department of Energy. 2002.
3. Alivisatos, P., P.T. Cummings, J. De Yoreo, K. Fichthorn, B. Gates, R. Hwang, D. Lowndes, A. Majumdar, L. Makowski, T. Michalske, J. Misewich, C. Murray, S. Sibener, C. Teague and E. Williams, Nanoscience Research for Energy Needs: Report of the March 2004 National Nanotechnology Initiative Grand Challenge Workshop. 2004, National Science and Technology Council, Committee on Technology, Subcommittee on Nanoscale Science, Engineering and Technology and Office of Basic Energy Sciences, Department of Energy.

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/
Blog On Nanotechnology - Nanomosis: http://barryhardy.blogs.com/nanomosis/

Nanolithography with a Modified Scanning Electron Microscope

Grahame Rosolen, nanofabrication expert at CSIRO, Sydney, Australia, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/

Nanolithography with a Modified Scanning Electron Microscope

Electron Beam lithography offers the ability to expose patterns with nanoscale dimensions. It may be used to directly fabricate individual nanostructures or to make nanoscale masters for mass production of nanoscale devices. A direct-write electron beam lithography instrument has been developed based around the electron optics, sample stage and vacuum system of a scanning electron microscope (SEM). The instrument has been used to write a variety of devices with nanoscale dimensions including nanowires, optical detectors, surface acoustic wave devices, high electron mobility transistors, diffraction gratings and optically variable devices. A computer controlled pattern generator and pattern alignment system has been developed and interfaced to the deflection coils, electron detector and beam blanking of the SEM. This provides digital control of the electron beam for exposing patterns and also allows images to be acquired for use in pattern alignment prior to exposure. A novel image correlation technique is used to align the exposed patterns with structures already on the sample. The ability to prepare the pattern data, exposure the nanoscale patterns and subsequently image the fabricated devices, all with the one instrument, enables rapid prototyping and study of a wide range of nanoscale devices.

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/
Blog On Nanotechnology - Nanomosis: http://barryhardy.blogs.com/nanomosis/

Simulating Nanoflows in Nanopores

Nick Quirke, Professor of Physical Chemistry and Head of the Computational, Theoretical and Structural Chemistry group at Imperial College, University of London, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/:

Simulating Nanoflows

The way fluids flow into and fill regular nanopores is of wide interest, however there are currently no experimental data or validated theoretical models for this nanoscale process. Nanoscale flow is dominated by surface properties and these can be studied using molecular simulation.

We first consider equilibrium and steady state flow in nanopores [1] and show using molecular dynamics that the tracer diffusivity depends only weakly on the conditions at the fluid–solid interface, whereas the collective diffusivity is a strong function of the hydrodynamic boundary conditions. A relationship between the collective diffusivity and the Maxwell coefficient describing wall collisions is obtained [2]. The Maxwell coefficient is related to the surface friction and interfacial viscosity.

Turning to transient flows we have carried out molecular dynamics simulations of carbon nanotubes imbibing oil at an oil/vapour interface at 300K [3,4]. We find that the smallest (7,7) nanotubes imbibe extremely rapidly ( < or = 800 m/ s) along the inner tube surface with the penetration length L a linear function of time. We derive expressions for the penetration length L and the velocity of the imbibing oil and relate both to the solid-fluid surface tensions and interfacial friction via the Maxwell coefficient. The imbibition of oil by nanotubes is contrasted with the wetting of their external surfaces and that of planar surfaces. Density profiles (and the molecular structure) of the imbibing fluid in the pores are analysed as a function of time. We present [5] analytical expressions for the density profiles (in x and t) of the imbibing fluid as a function of the minimum decane-pore potential and the pore surface friction. We are therefore able to provide a complete description of imbibition of decane for a wide range of nanopores.

Finally we discuss nanopore- surface junctions and present molecular dynamics results for flow in such systems[6]

1. V. P. Sokhan, D Nicholson and N Quirke, J Chem Phys, 117 ,8531, (2002)
2. V. P. Sokhan and N Quirke, Mol Sim, 30 , 217 (2004),
3. S Supple and N Quirke, Phys Rev Letts, 14501, 90 (2003)
4. S Supple and N Quirke, J Chem Phys (in press)
5. S Supple and N Quirke, J Chem Phys (submitted)
6. S Supple, PhD Thesis, Imperial College (submitted)

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/
Blog On Nanotechnology - Nanomosis: http://barryhardy.blogs.com/nanomosis/

Theoretical Nanoscale Design of Self-Cleaning Surfaces

David Henry, Postdoctoral Fellow in Applied Physics at RMIT University, Victoria, Australia, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/ both during the conference and after the conference.

Theoretical Nanoscale Design of Self-Cleaning Surfaces

In the last few years there has been a considerable amount of work on the development of contamination resistant coatings. One approach is based on the ‘lotus effect' which is observed in nature. Leaves of lotus plants are known to stay clean even in dirty environments and it is now clear that this cleanliness is caused by the extreme non-wetting character of the leaves, with water contact angles greater than 150º. This super-non-wetting character is a result of the leaf surface being covered by a layer of low surface energy wax that is extremely rough on a nano-scale. One of the difficulties involved in using this effect in a synthetic system is that the low surface energy, rough surfaces are easily damaged and can be contaminated by higher surface energy organic contaminants. The lotus plant solves this problem by continually exuding wax to the surface, but this may be difficult to reproduce in a synthetic system. An alternative approach is to produce a strongly hydrophilic surface for which hydrophobic contaminants have little or no affinity and where water would easily remove any contaminants coming in contact with the surface.

We are involved in the nano-scale design and modification of organic coating surfaces for contamination resistance using theoretical techniques. Simulations are performed to gain a better understanding of the nature of the interaction between carbonaceous contaminants and polymer surfaces. The figure illustrates a fully atomistic model of an interface between a polymer surface and graphite which approximates common carbonaceous contaminants. Using classical potentials we calculate the adhesion energy as a function of interfacial separation (shown) for such interfaces with varying polymer surface composition. With this knowledge we are then able to propose surface modifications that will lead to reduced adhesion of contaminants prior to costly experimental testing.

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotech Hub: http://nanotech.colayer.net/
Nanomosis Blog: http://barryhardy.blogs.com/nanomosis/

Pacific Rim Conference in Nanoscience brought from Australia to your PC

The Nanotech Hub presents over the Internet the Program from the Pacific Rim Conference in Nanoscience, Broome, Australia to be held 7-12 September 2004. The conference is chaired by Professor Nick Quirke, Imperial College London, and includes contributions from leading researchers in the Pacific Region, in addition to invited top speakers from Europe and the USA.

All lectures including slides and audio from the conference will be available through the Web site located at http://nanotech.colayer.net/, starting during the conference week and continuing through September and October.

All virtual registrants may present a poster through the Web site for viewing and discussion.

This conference is multidisciplinary, includes the disciplines of physics, chemistry, biology and engineering, and contains a significant amount of leading chemistry research in nanoscience.

The program covers current key research areas in nanoscience including nanofluidics, nanobio interfaces, nanofabrication, water, energy and minerals, nanoparticles, and computational nanoscience. Lectures on hot topics and workshops will also accompany the invited speaker program.

The virtual conference provides an opportunity to those unable to attend the physical conference in Broome, Australia to access and listen to all talks from the conference and to post questions and discussion items.

Conference Speakers

N. Quirke, Imperial College London; T. Becker, Universitaet Ulm, Ulm, Germany; C. Amatore, Universite de Paris, France; M. Sastry, National Chemical Laboratory, India; M. Pettitt, University of Houston, USA; S. Chou, Princeton University, USA; M. Y. Simmons, University of NSW, Australia; T. Turney, CSIRO Nanotechnology Centre, Australia; D. Evans, Australian National University; B. Hobbs, Chief Scientist, WA, Australia; K. Y. Chan, University of Hong Kong, HK; G. Parkinson, Curtin University, Australia; M. Lu , University of Queensland, Australia; J. Gale, Curtin University, Australia; F. Caruso, University of Melbourne, Australia; K. Kaneko, Chiba University, Japan; P. Cummings, Vanderbilt University and Oak Ridge National Laboratory, USA; A. Fuchs, Universite de Paris Sud, France; B. Todd, Swinburne, University of Technology, Melbourne; P. McCormick, University of Western Australia, Perth; F. Stellacci, MIT, USA; I. Snook, RMIT , Melbourne, Australia; N. Kanellopoulos, NOE Coordinator, NCSR Demokritos, Greece; B. Hobbs, APNF; A. Appleton, Accelrys; J. R. Henderson, Univ. of Leeds, UK; Y. Kaneko, Kyoto University, Japan; D.J. Henry, RMIT University, Australia

Conference abstracts and news and views will be made available on an ongoing basis through the Blog located at http://barryhardy.blogs.com/nanomosis/

Please visit http://nanotech.colayer.net/ for further program information and to signup.

Barry Hardy, Ph.D.
Douglas Connect, Switzerland
www.douglasconnect.com
+41 61 851 0170 (office)
Blogs:
On Nanotechnology - Nanomosis: http://barryhardy.blogs.com/nanomosis/
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Hydrogen storage in nanotubes – has it all gone pear-shaped?: A computational perspective

Julian Gale, Professor of Computational Chemistry at Curtin University of Technology in Perth, Australia will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/

Hydrogen storage in nanotubes – has it all gone pear-shaped?: A computational perspective

Hydrogen has been proposed as the clean energy source of the future, since the combustion product is only water. However, this requires both the efficient generation of hydrogen and an effective means of transportation. There has been considerable interest in the possibility of employing carbon nanotubes for hydrogen storage, as an alternative to compression or metal hydrides.

While it is likely that the majority of hydrogen will be physisorbed, either within the nanotubes, or in the space between them, there is also the possibility that some hydrogen may be chemisorbed. The thermodynamics of the reactivity of carbon nanotubes with respect to this process has been investigated using non-local density functional theory, as implemented within the SIESTA approach [1]. The variation with respect to the radius of a one-dimensional infinite nanotube has been examined, as well as the trend with successive hydrogenations. In addition, the influence of the termination of the nanotube has been investigated. Chemisorption is found to strongly perturb the shape of nanotubes, which will have important consequences for their physisorption capacity and other properties.

In order to extend the configuration space accessible, the reactivity of nanotubes with respect to hydrogen has been further explored through the use of bond-order potentials of the form proposed by Brenner et al [2], as implemented within the program GULP3 [3]. Through this approach, a preliminary evaluation of the kinetics of the process has also been made. Finally, the influence of doping of the nanotube has been considered to see if it would assist in improving the characteristics of such materials for hydrogen storage.

References:

[1] J.M. Soler, E. Artacho, J.D. Gale, A. Garcia, J. Junquera, P. Ordejon, D. Sanchez-Portal, J. Phys.: Condens. Matter , 14 , 2745 (2002)
[2] D.W. Brenner, O.A. Shenderova, J.A. Harrison, S.J. Stuart, B. Ni, and S.B. Sinnott, J. Phys.: Condens. Matter , 14 , 783 (2002)
[3] J.D. Gale and A.L. Rohl, Mol. Simul. 29 , 291 (2003)

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/

Nanostructured Nanoparticles: a new dimension in self-assembly

Francesco Stellacci, Finmeccanica Career Development Professor of Materials Science, Department of Materials Science and Engineering, MIT, USA, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/ .

Nanostructured Nanoparticles: a new dimension in self-assembly

Francesco Stellacci, MIT

Ligand coated metal nanoparticles are promising nanosize materials for novel electronic and optical devices. Their main strength is in the fact that they combine the advantages of small metals, such as single electron transistor (SET) behavior, together with most of the advantages of the organic ligands that are used to coat them, such as solubility in organic solvents and processability for example via self-assembly methods. Moreover, even complex nanoparticles coated with multiple types of ligands can be synthesized in just one step.

Here we present a new family of mixed ligand nanoparticles that shows sub-nanometer patterns (e.g. ridges) on their ligand shell. This unique sub-nano-structuring of their ligand shell provides new properties to the particles. In particular, we focus on silver and gold particles that have ridges composed of hydrophilic valleys and hydrophobic peaks. For the first time we show the ability to control the supramolecular ordering of the ligands on the nanoparticle surfaces. Indeed, by systematically varying the mixture of ligands introduced during nanoparticle synthesis, one can control the resulting surface properties of the nanoparticles. Scanning tunneling microscopy images show ridges 3 Å deep and 6 Å wide on the ligand shell of nanoparticles. Control of both these parameters is provided by the choice of the ligands and of their molar ratio respectively. We also demonstrate that the nanoparticle ligands interact so as to align the stripes of neighboring nanoparticles over large length scales. The synthetic mechanism that leads to the formation of this supramolecular ordering will be discussed. These particles show unique and unexpected wettability, solubility, self-assembly and surface chemistry properties, in fact they show a remarkable resistance to protein nonspecific adsorption.

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotechnology Hub: http://nanotech.colayer.net/

Poly-electrolytes at the liquid solid interface: Biochips

B. Montgomery Pettitt, Cullen Distinguished Professor of Chemistry at the University of Houston and Director of the Institute for Molecular Design and the Keck Center for Computational Biology will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/

Poly-electrolytes at the liquid solid interface: Biochips

Biochips are becoming important tools in biochemistry and genetics laboratories. The interface between high-tech media like silicon or silicon dioxide and biotech media like protein or nucleic acids forms a new hybrid technology area with immense possibilities for the future in the areas of combinatorial analysis and synthesis. Interfaces between disparate phases of matter offer large electrostatic field and density gradients changing the local free energy surface and therefore form a challenging set of problems in current chemical physics. The current state of theory and computer simulations of polyelectrolytes (DNA) near surfaces will be presented and compared with recent experiments. Recent results will be discussed in terms of their implications for the design of the next generation of chips.

Barry Hardy
Douglas Connect
www.douglasconnect.com
Nanotech Hub: http://nanotech.colayer.net/

Nanomosis Blog

This Nanomosis Blog has been created to provide news and views from the world of nanotechnology and nanoscience and is a companion to our newly launched nanotech community and conferencing site (http://nanotech.colayer.net/).

Barry Hardy
Douglas Connect
www.douglasconnect.com