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Nanotechnology in general and molecular nanotechnology in particular received a big boost in the United States when the President announced the National Nanotechnology Initiative (NNI) at the beginning of the year. The NNI identifies nanotechnology as an emerging area of national interest, and has provision for substantial increases in funding levels from US Federal agencies. In addition, several major scientific organizations such as the American Physical, Chemical, and Materials Research Societies have launched focus groups and/or divisions that will sponsor several sessions on nanotechnology-related areas during their future annual meetings. Quite a few smaller conferences, focusing on one or other constituent areas of nanotechnology, have sprung up and also started to draw audiences and speakers. The Foresight Conferences, with their focus on molecular nanotechnology, continue to be the leader in this field by providing a truly multidisciplinary platform for audiences and speakers to gather and discuss the most recent advances in core enabling technologies.

The 7th Foresight Conference (15-17 October 1999), again held in the heart of silicon valley, was no exception. Many recent advances in enabling technologies such as scanning probes, molecular motors and biotechnology, nanomechanics and materials, molecular electronics and self-assembly, and modelling and simulations were covered at the conference. Specific topics discussed included a keynote address by Nobel Laureate John Polanyi who talked about nanoscale precision in laser-induced surface chemistry on silicon surfaces, advances in molecular motors by Montemagno of Cornell and Michl of Colorado, a novel biomechanical switch discussed by Vogel of Washington University, DNA-based nanotechnology by Heller of Nanogen Inc., nanomanipulation of nanotubes by Superfine of North Carolina State University and Ruoff of Washington University at St Louis, and electronic and materials properties of nanotubes and related materials by McEuen from the University of California at Berkeley and Dai of Stanford University. Federal agencies were represented in talks by Warren of the Defense Advanced Research Projects Agency and Meyyappan of NASA Ames summarizing advances in molecular electronics, and Srivastava of NASA Ames and Karna of the Air Force Research Laboratory discussing modelling and simulations of nanomechanics and optical properties. Mirkin of Northwestern discussed advances and possible applications of dip-pen nanolithography, and scanning probe operations/applications were represented in talks by Russell of North Carolina State University and Henderson of Iowa State University. Allara of Pennsylvania State University, Andres of Purdue University and Hoh of Johns Hopkins School of Medicine covered diverse aspects of self-assembly, and the role of modelling and simulations in advancing the frontiers was described in examples shown by Vashishta of Louisiana State University, Brenner of North Carolina State University, and Cho of Stanford University.

The papers submitted for this Special Issue of the journal Nanotechnology reflect the highly multidisciplinary structure and the content of the conference. Papers related to molecular motors, electronics, carbon nanotubes, molecular building blocks, self-assembly, and scanning probes describe some of the advances that are leading the way for molecular nanotechnology. Limberis and Stracke talk about motors and mechanisms in biological systems. Peng, Wei and Jian discuss future electronics, sensor and materials applications of carbon nanotubes and fullerenes, and Hersam, Çagin and Hua describe non-fullerene-derived nanostructured materials. Merkle and Pum consider details of possible molecular building blocks that could be self-assembled or nanomanipulated into larger functional materials and/or devices. The process and examples of self-assembly are topics of papers authored by Chen and Ram, and Morita and Hughes describe atomic force microscopy and electro-kinetics as enabling technologies. Finally, the paper by Toth-Fejel discusses architectural issues related to future assembly of fully functional molecular nanotechnology systems. These papers continue the march of nanotechnology, and give a flavour of topics covered at the conference.

Kinesin motor proteins and the microtubule cytoskeleton function as an intracellular railroad system - a railroad with nanometre-scale engines running on nanometre-scale tracks. Our long-term objective is to take this molecular transport machinery and integrate it into kinesin-powered microdevices. As a step toward this objective, we have coupled kinesin to microscale silicon chips that were patterned photolithographically and etched from silicon membranes. The microchips were observed by light microscopy to move on microtubules aligned and immobilized on the surface of a microscope flowchamber. The microchips translated, rotated, and flipped over. From these examples of microchip movements, it is conceivable that this technology can be extended to moving more elaborate microparts, like gears, or rotors, or levers using kinesin motors. This will allow kinesin forces to be coupled to a useful action in a microdevice. For example, a microrotor turned by kinesin could demonstrate the feasibility of creating a kinesin-powered microgenerator or micropump.

Kinesin is a microtubule-associated protein, converting chemical into mechanical energy. Based on its ability to also work outside cells, it has recently been shown that this biological machinery might be usable for nanotechnological developments. Possible applications of the kinesin-based motor system require the solution of numerous methodological and technical problems, including the orientation of force generation into a desired direction and the determination of the tolerable roughness of the surfaces used, the minimal free vertical space still enabling force-generating activity, and the temporal stability of the system. This paper reports on the example of microtubules gliding across kinesin-coated surfaces and shows that the force-generating system needs a minimal free working space of about 100 nm height and works up to 3 h with nearly constant velocity. Individual microtubules were observed to cover distances of at least 1 mm without being detached from the surface and to overcome steps of up to 286 nm height. In addition, mechanically induced flow fields were shown to force gliding microtubules to move in one and the same direction. This result is regarded as being an essential step towards future developments of kinesin-based microdevices as this approach avoids neutralization of single forces acting in opposite directions.

The possibility of modifying the electronic properties of nanotubes using gas molecule adsorption is investigated using the first-principles total energy density functional calculations. Detailed analysis of the electronic structures and energetics is performed for the semiconducting (10,0) single-walled carbon nanotube interacting with several representative gas molecules (NO₂, NH₃, CO, O₂, and H₂O). The results elucidate the mechanisms of the adsorption-induced nanotube doping and illustrate an example of the simulation-based design characterization of nanoelectronic components.

We report on a method for self-assembly of integrated carbon nanotube circuits using selective area chemical vapour deposition on pre-patterned catalyst electrodes. The circuits consist of a multi-wall carbon nanotube bridging a pair of electrodes, forming a metal/carbon nanotube/metal structure. Electron-beam lithography was used to define electrode sets separated by a desired distance on a 500 nm thick SiO₂ film on Si substrates. Following metal evaporation and lift-off, chemical vapour deposition was used for selective growth of carbon nanotubes on the catalyst electrodes. The carbon nanotubes eventually form a bridge between nearby electrodes consisting of one, or in some cases more than one, multi-wall nanotube. The resistance of the carbon nanotube circuits at room temperature is typically less than 100 kΩ. For a few high-resistance samples (>>100 kΩ) transport properties were studied in a temperature range from room temperature to 2 K. At room temperature the I-V is linear. The resistance increases with decreasing temperature, and the I-V gradually becomes nonlinear. At low temperatures a gap appears around V = 0 suggesting semiconducting behaviour.

As the sizes of electronic and mechanical devices are decreased to the micron and nanometre level, it becomes particularly important to predict the thermal transport properties of the components. Using molecular level theories, such predictions are particularly important for modelling nano-electronic devices where scaling laws may change substantially but it is most difficult to accurately measure the properties. Hence, using the empirical bond order dependent force field, we have studied here the thermal conductivity of nanotubes' dependence on structure, defects and vacancies. The anisotropic character of the thermal conductivity of the graphite crystal is naturally reflected in the carbon nanotubes. We found that the carbon nanotubes have very high thermal conductivity comparable to diamond crystal and in-plane graphite sheet. In addition, nanotube bundles show very similar properties as graphite crystal in which dramatic difference in thermal conductivities along different crystal axis.

One potential application of molecular nanotechnology is the integration of molecular electronic function with advanced silicon technology. One step in this process is the tethering of individual molecules at specific locations on silicon surfaces. This paper reports the fabrication of arrays of individual organic molecules on H-passivated Si(100) surfaces patterned with an ultrahigh vacuum scanning tunnelling microscope (STM). Feedback controlled lithography (FCL) is used to create templates of individual silicon dangling bonds. Molecules introduced in the gas phase then spontaneously assemble onto these atomic templates. Norbornadiene (NBE), copper phthalocyanine (CuPc), and C₆₀ molecular arrays have been made by this technique and studied by STM imaging and spectroscopy. Both NBE and CuPc molecules appear as depressions in empty states images, whereas in filled states images they are nearly indistinguishable from Si dangling bonds. Furthermore, the fourfold symmetry and central copper atom of CuPc are clearly observed at positive sample bias. Spatial tunnelling conductance maps of CuPc illustrate charge transfer from the surrounding substrate when the molecule is bound to the surface via its central copper atom. On the other hand, when the CuPc molecule interacts with the substrate via an outer benzene ring, molecular rotation is observed. C₆₀ molecules display intramolecular structure in topographic images and spectroscopic data. The local density of states of C₆₀ clearly shows the location of the lowest unoccupied molecular orbital, which suggests that the highest occupied molecular orbital is located within 0.3 eV of the fermi level.

Dendrimers are well defined, highly branched macromolecules that radiate from a central core and are synthesized through a stepwise, repetitive reaction sequence that guarantees complete shells for each generation, leading to polymers that are monodisperse. The synthetic procedures developed for dendrimer preparation permit nearly complete control over the critical molecular design parameters, such as size, shape, surface/interior chemistry, flexibility, and topology. Recent results suggest that dendritic polymers may provide the key to developing a reliable and economical fabrication and manufacturing route to functional nanoscale materials that would have unique properties (electronic, optical, opto-electronic, magnetic, chemical, or biological). In turn, these could be used in designing new nanoscale devices. In this paper, we determine the 3D molecular structure of various dendrimers with continuous configurational Boltzmann biased direct Monte Carlo method and study their energetic and structural properties using molecular dynamics after annealing these molecular representations.

One of the most puzzling aspects of fullerenes is how such complicated symmetric molecules are formed from a gas of atomic carbons, namely, the atomistic or chemical mechanisms. Are the atoms added one by one or as molecules (C₂, C₃)? Is there a critical nucleus beyond which formation proceeds at gas kinetic rates? What determines the balance between forming buckyballs, buckytubes, graphite and soot? The answer to these questions is extremely important in manipulating the systems to achieve particular products. A difficulty in current experiments is that the products can only be detected on time scales of microseconds long after many of the important formation steps have been completed. Consequently, it is necessary to use simulations, quantum mechanics and molecular dynamics, to determine these initial states. Experiments serve to provide the boundary conditions that severely limit the possibilities. Using quantum mechanical methods (density functional theory (DFT)) we derived a force field (MSXX FF) to describe one-dimensional (rings) and two-dimensional (fullerene) carbon molecules. Combining DFT with the MSXX FF, we calculated the energetics for the ring fusion spiral zipper (RFSZ) mechanism for formation of C₆₀ fullerenes. Our results shows that the RFSZ mechanism is consistent with the quantum mechanics (with a slight modification for some of the intermediates).

If we are to manufacture products with molecular precision, we must develop molecular manufacturing methods. There are basically two ways to assemble molecular parts: self-assembly and positional assembly. Self-assembly is now a large field with an extensive body of research. Positional assembly at the molecular scale is a much newer field which has less demonstrated capability, but which also has the potential to make a much wider range of products. There are many arrangements of atoms which seem either difficult or impossible to make using the methods of self-assembly alone. By contrast, positional assembly at the molecular scale should make possible the synthesis of a much wider range of molecular structures.

One of the fundamental requirements for positional assembly of molecular machines is the availability of molecular parts. One class of molecular parts might be characterized as molecular building blocks (MBBs). With an atom count ranging anywhere from ten to ten thousand (and even more), such MBBs would be synthesized and positioned using existing (or soon to be developed) methods. Thus, in contrast to investigations of the longer term possibilities of molecular manufacturing (which often rely on mechanisms and systems that are likely to take many years or even decades to develop), investigations of MBBs focus on nearer term developmental pathways.

Crystalline bacterial cell surface layer (S-layer) proteins have been optimized during billions of years of biological evolution as constituent elements of one of the simplest self-assembly systems. Isolated S-layer proteins possess the intrinsic property of being able to recrystallize into two-dimensional arrays at a broad spectrum of surfaces (e.g. silicon) and interfaces (e.g. air-water interface or planar lipid films). The well-defined arrangement of functional groups on S-layer lattices allows the binding of molecules and particles in defined regular arrays. S-layers recrystallized on solid supports can be patterned in the submicrometre range using standard optical lithography. S-layers also represent templates for the formation of inorganic nanocrystal superlattices (e.g. CdS, Au, Ni, Pt, or Pd) as required for molecular electronics and nonlinear optics.

The LB technique is an important way to obtain the ordered aggregate of nanometre-sized particles. However, with the usual LB technique only those particles capped by short-chain molecules (<C₁₂) can form a highly ordered two-dimensional (2D) arrangement. When the capping molecules become longer, it is difficult to obtain ordered aggregates. This has been considered to be caused by the hydrophobic interaction of the large organic shells, which has possibly hindered the procedure of self-assembly. Motivated by this, we modified the LB technique by using the multistep creeping method and increasing the subphase temperature during compression. With these modifications, we obtained the long-range ordered 2D arrangement of gold nanoparticles capped by octadecylamine.

An in situ self-assembly technique with nanometre control over thicknesses and multilayered structures was used to manufacture the ultrathin films of polypyrrole (PPY). The PPY film was deposited on a polyanion, poly(styrene sulfonate) (PSS) modified surface as a function of time, previously PSS had been deposited on various substrates (glass, mica, indium-tin-oxide coated glass plates). Later, alternate PPY and PSS films were fabricated on such substrates using a layer-by-layer (LBL) technique. The glucose oxidase (GOD) molecules were also deposited on such self-assembled PPY films by the LBL technique. The PSS/PPY/GOD, PPY/PPY/GOD/poly(ethylene imine) (PEI)/GOD etc, film configurations were fabricated, and functionally as well as structurally characterized by UV-visible, electrochemical and scanning probe microscopy techniques, respectively. The results of a scanning probe microscopic study on the films were analysed to understand the molecular orientation of GOD on the PPY surface, and the dependence of the enzyme concentration for the depositing solutions. Moreover, the electrochemical studies performed provided information with respect to the electron transfer processes on the spatial arrangement of GOD molecules on the PPY surfaces. The immobilization of GOD on a conductive PPY represented a crucial and important step, and allowed us to construct the glucose-responsive biosensors.

We succeeded in obtaining site-dependent frequency-shift curves on an atomic scale as a function of the tip-sample surface distance between a clean Si(111)7×7 surface and a clean active Si tip with a dangling bond using noncontact atomic force microscopy (NC-AFM). As a result, we found a discontinuous jump in the frequency-shift curve measured above active Si adatoms with a dangling bond, in contrast to a continuous frequency-shift curve measured above gaps between adjacent Si adatoms. These results suggest the possibility that the NC-AFM can be developed into a kind of spectroscopic tool, i.e. atomic force spectroscopy, which can measure the three-dimensional force-related map with true atomic resolution. Furthermore, we succeeded in suppressing the discontinuous jump in the frequency-shift curve by replacing the clean active Si tip apex with an oxidized inactive Si tip apex. This result suggests the possibility that we can control the interaction force between the tip and sample atoms on an atomic scale by placing a suitable atom on the tip apex.

The phenomena of dielectrophoresis and electrorotation, collectively referred to as AC electrokinetics, have been used for many years to study, manipulate and separate particles on the cellular (1 µm or more) scale. However, the technique has much to offer the expanding field of nanotechnology, that is the precise manipulation of particles on the nanometre scale. In this paper we present the principles of AC electrokinetics for particle manipulation, review the current state of AC electrokinetic techniques for the manipulation of particles on the nanometre scale, and consider how these principles may be applied to nanotechnology.

Nanoscale assemblers will need robust, scalable, flexible, and well-understood mechanisms such as software agents to control them. This paper discusses assemblers and agents, and proposes a taxonomy of their possible interaction. Molecular assembly is seen as a special case of general assembly, subject to many of the same issues, such as the advantages of convergent assembly, and the problem of scheduling. This paper discusses the contract net architecture of ANTS, an agent-based scheduling application under development. It also describes an algorithm for least commitment scheduling, which uses probabilistic committed capacity profiles of resources over time, along with realistic costs, to provide an abstract search space over which the agents can wander to quickly find optimal solutions.