Interesting Web Sites on Nanotechnology

• Wikipedia definition of nanotechnology.
  This is an interesting web page on nanotechnology. However, in its description of technologies it doesn't mention the research on nanowire-based crossbars, an area of great importance.

• This NASA web site has some nice photos and videos highlighting NASA's interest in nanotechnology.

• Charles Lieber's website has a nice demo of the steps that can be taken to assemble a nanocomputer.

Nanotechnology and Molecular Electronics

• Nanomaterials: Synthesis and Assembly Part I and (Part II), 2000 Foresight Conference tutorial by Thomas Mallouk.
  This set of slides is has many useful references. They were prepared for a chemisty and materials science audience.

• Molecular Electronics: Devices, Systems and Tools for Gigagate, Gigabit Chips, by M. Butts, A. DeHon and S.C. Goldstein, Int. Conference on Computer-Aided Design (2002).
  A survey article on the state of the art of computational nanotechnology (a.k.a.\ molecular electronics) as of 2002. It is written for the electrical engineering and computer science audiences and is very accessible.

• Extending the Road Beyond CMOS, by J.A. Hutchby, G.I. Bourianoff, V.V. Zhirnov and J.E. Brewer, IEEE Circuits and Devices Magazine, p.28 (March 2002).
  An accessible paper written for the circuits and devices audience that describes new technologies that are expected to allow for the extension of Moore's Law beyond CMOS.

• The Future of Nanocomputing, by George Bourianoff, Computer Magazine, p. 44 (August 2003).
  An accessible overview of the future of nanotechnology for computation.

• Molecular Electronics, by J.R. Heath and M.A Ratner, Physics Today, vol. 56, no. 5, p. 43 (2003).
  The authors examine "the relationship between molecular structure and electrical conductance and on the use of molecules for computational applications."

Modulation Doping of Nanowires

• Growth of nanowire superlattice structures for nanoscale photonics and electronics by M.S. Gudiksen, L.J. Lauhon, J. Wang, D.C. Smith and C.M. Lieber, Nature, vol. 415, p. 617 (2002).
  This is a readable seminal paper on modulation-doped nanowires written for the physical chemistry audience. Two other contemporaneous articles on the same subject are listed below.

• Block-by-Block Growth of Single-Crystaline Si/SiGe Superlattice Nanowires, by Y. Wu, R. Fan, and P. Yang, Nano Letters, Vol. 2, No. 2, pp. 83-86 (2002).

• One-Dimensional Steeplechase for Electrons Realized, by M.T. Gjork, B.J. Ohlsson, T. Sass, A.I. Persson, C. Thelander, M.H. Magnusson, K. Deppert, L.R. Wallenberg, and L. Samuelson, Nano Letters, Vol. 2, No. 2, pp. 87-89 (2002).

The Integration of Nanowires Into Arrays

• Array-Based Architecture for FET-Based, Nanoscale Electronics, by A. DeHon, IEEE Trans. Nanotechnology, Vol. 2, No. 1, p. 23-32 (2003).
  It's title is descriptive of its content.

• Stochastic Assembly of Sublithographic Nanoscale Interfaces, by A. DeHon, P. Lincoln, and J.E. Savage , IEEE Trans. Nanotechnology, Vol. 2, No. 3, p. 165-174 (2003).
  Describes and analyzes an interface (decoder) for controlling nanowires with lithographic wires. It assumes that nanowires are modulation-doped and explores that issues that this assumption implies.

• Nanoscale Molecular-Switch Crossbar Circuits, by Y. Chen, G.-Y. Jung, D.A.A. Ohlberg, X. Li, D.R. Stewart, J.O. Jeppesen, K.A. Nielsen, J.F. Stoddart, and R.S. Williams, Nanotechnology, vol. 14, p. 462-468 (2003).
  Describes fabrication of an 8x8 crossbar within a 1 micron squared area in which the switches are rotaxane molecules.

Fluidic Assembly of Nanowires

• Langmuir-Blodgett Nanorod Assembly, by F. Kim, S. Kwan, J. Akana, and P. Yang, J. Am. Chem. Soc., vol. 123, p. 4360-4361 (2001).
  One of the first papers to show fluidic assembly of nanorods/nanowires.

• Directed Assembly of One-Dimensional Nanostructures into Functional Networks, by Y. Huang, X. Duan, Q. Wei, and Charles M. Lieber, Science, vol. 291, p. 630-633 (2001).
  One of the first papers to show fluidic assembly of nanorods/nanowires.

• Large-Scale Hierarchical Organization of Nanowire Arrays for Integrated Nanosystems, by D. Whang, S. Jin, Y. Wu, and C.M. Lieber, Nano Letters, Vol. 3, No. 9, p. 1255-1259 (2003).
  A more comprehensive study of the fluidic assembly of nanowires.

• Ultrahigh-Density Nanowire Lattices and Circuits, by N.A. Melosh, A. Boukai, F. Diana, B. Gerardot, A. Badolato, P.M. Petroff, J.R. Heath, Science, vol. 300, p.112-115 (2003).
  

• Fabrication of Conducting Si Nanowire Arrays, by R.A. Beckman, E. Johnston-Halperin, N.A. Melosh, Y. Luo, J.E. Green, and J.R. Heath, J. Appl. Physics, vol. 96, no. 10, p. 5921-5923 (2004).
  The SNAP method is used to create Si nanowires using nanolithography.

Memories Based on Arrays of Atomic-Force Microscopes

• The "Millipede" -- Nanotechnology Entering Data Storage by P. Vettiger, G. Cross, M. DEspont, U. Dreschler, U. Durig, B. Gotsmann, W. Haberle, M.A. Lantz, H.E. Rothuizen, R. Stutz and G.K. Binnig, IEEE Trans. Nanotechnology, vol. 1, no. 1 (2002).
  The authors "present a new scanning-probe-based data-storage concept" ... "that combines ultrahigh density, terabit capacity, small form factor, and high data rate." The system uses "large two-dimensional (2D) atomic force microscope (AFM) arrays that have been batch-fabricated by silicon suface-micromachining techniques."

Systems: Self Assembly

• Langmuir-Blodgett Nanorod Assembly by Franklin Kim, Serena Kwan, Jennifer Akana, and Peidong Yang, J. Am. Chem. Soc. , Vol. 123, pp. 4360-4361, (2001).
  Abstract... Herein, we report 2-dimensional nanorod monolayer assembly using the Langmuir-Blodgett technique. Pressure-induced isotropic- nematic-smectic phase transitions as well as transformation from monolayer to multilayer nanorod assembly were observed.

• Directed Assembly of One-Dimensional Nanostructures into Functional Networks by Yu Huang, Xiangfeng Duan, Qingqiao Wei, Charles M. Lieber, Science, Vol. 291, pp. 630-633 (2001).
  Abstract One-dimensional nanostructures, such as nanowires and nanotubes, represent the smallest dimension for efÞcient transport of electrons and excitons and thus are ideal building blocks for hierarchical assembly of functional nanoscale electronic and photonic structures. We report an approach for the hierarchical assembly of one-dimensional nanostructures into well-deÞned functional networks. We show that nanowires can be assembled into parallel arrays with control of the average separation and, by combining ßuidic alignment with surface-patterning techniques, that it is also possible to control periodicity. In addition, complex crossed nanowire arrays can be prepared with layer-by-layer assembly with different ßow directions for sequential steps. Transport studies show that the crossed nanowire arrays form electrically conducting networks, with individually addressable device function at each cross point.

• Self-Assembled Computer Architecture: Design and Fabrication Theory by Christopher L. Dwyer, PhD, U. North Carolina, (2003)
  Abstract This dissertation explores the design and fabrication of massively-parallel computers using self-assembling electronic circuitry. A DNA-guided self-assembly method, inspired by discoveries in chemistry, materials science, and physics, is used to develop an argument for the feasibility of constructing complex circuitry. The fabrication yield of such a process is calculated. Together, these form the foundation for a discussion of the computer architectures and implementations that this self-assembling process enables.

• Large-Scale Hierarchical Organization of Nanowire Arrays for Integrated Nanosystems by Dongmok Whang, Song Jin, Yue Wu, and Charles M. Lieber, Nano Letters , Vol. 3, No. 9 pp. 1255-1259 (2003).
  Abstract The assembly of nanowires and nanotubes into arrays patterned on multiple length scales is critical to the realization of integrated electronic and photonic nanotechnologies. A general and efficient solution-based method for controlling organization and hierarchy of nanowire structures over large areas has been developed. Nanowires were aligned with controlled nanometer to micrometer scale pitch using the Langmuir- Blodgett technique and transferred to planar substrates in a layer-by-layer process to form parallel and crossed nanowire structures. The parallel and crossed nanowire structures were efficiently patterned into repeating arrays of controlled dimensions and pitch using photolithography to yield hierarchical structures with order defined from the nanometer through centimeter length scales. In addition, electrical transport studies show that reliable electrical contacts can be made to the hierarchical nanowire arrays prepared by this method. This solution-based process offers a flexible pathway for bottom-up assembly of virtually any nanowire material into highly integrated and hierarchically organized nanodevices needed for a broad range of functional nanosystems.

• Guided self-assembly of metallic nanowires and channels by B. Erdem Alaca, Huseyin Sehitoglu, and Taher Saif, Applied Physics Letters, Vol. 84, No. 23, pp. 4669-4671 (2004).
  Abstract A method is presented to form metallic nanowires and nanochannels by guided self-assembly. The method relies on an initial plasma-enhanced chemical vapor deposition of a silicon oxide film with altered chemistry on a silicon wafer, and the cracking of the film due to tensile stresses upon annealing. The fabricated stress concentration features on the Si substrate control the number of cracks and their orientation. These cracks are then filled with electroless nickel, and the subsequent removal of SiO2 produces a controlled network of nanowires of about 100 nm in dimension. In addition to nanowires, nanobridges, and nanocantilevers have also been fabricated by releasing the wires, confirming that the resulting structures are rather robust.

• Magnetically Assembled Multiwalled Carbon Nanotubes on Ferromagnetic Contacts by Sandip Niyogi, Carlos Hangarter, Ramesh M. Thamankar, Yueh-Feng Chiang, Roland Kawakami, Nosang V. Myung, and Robert C. Haddon, J. Phys. Chem. B, Vol. 108, pp. 19818-19824 (2004).
  Abstract A facile method for assembling carbon nanotubes (CNT) on ferromagnetic metal contacts is described. Multiwalled carbon nanotubes (MWNT) with a magnetic cap were fabricated by thermally evaporating nickel on top of a vertical array of MWNTs grown on silicon. Magnetic interaction between the magnets on the nanotubes and lithographically patterned ferromagnetic electrodes caused the relative alignment and directed placement of nanotubes. The lithographically patterned electrodes were further modified using electrochemical deposition to form asymmetric ferromagnetic electrodes as well as improve the electrical and magnetic interactions at the contacts. MWNTs thus assembled showed characteristics that have been established for various nanotube device configurations. This validates the assembling technique for exploring charge- and spin-based electronic devices.

• Large-Scale Hierarchical Organization of Nanowires for Functional Nanosystems by Dongmok WHANG, Song JIN and Charles M. LIEBER, Japanese Journal of Applied Physics, Vol. 43, No. 7B, pp. 4465–4470, (2004).
  Abstract We review recent studies of solution-based hierarchical organization of nanowire building blocks. Nanowires have been aligned with controlled nanometer to micrometer scale separation using the Langmuir-Blodgett technique, transferred to planar substrates in a layer-by-layer process to form parallel and crossed nanowire structures over centimeter length scales, and then efficiently patterned into repeating arrays of controlled dimensions and pitch using photolithography. The hierarchically-organized nanowires open up key opportunities in several general areas of nanoscale science and technology. First, hierarchically-assembled nanowire arrays have been used as masks to define nanometer scale metal lines and surface features over large areas. Second, hierarchically-assembled nanowire arrays have been used to fabricate fully-scalable centimeter size arrays of field-effect transistors in high yields without requiring alignment of individual nanowires to output electrodes. Diverse applications of this approach for enabling a broad range of functional nanosystems, including macroelectronic and sensing applications, are described.

• Scalable Interconnection and Integration of Nanowire Devices without Registration by Song Jin, Dongmok Whang, Michael C. McAlpine, Robin S. Friedman, Yue Wu, and Charles M. Lieber, Nano Letters, Vol. 4, No. 5, pp. 915-919 (2004).
  Abstract A general strategy for the parallel and scalable integration of nanowire devices over large areas without the need to register individual nanowire-electrode interconnects has been developed. The approach was implemented using a Langmuir-Blodgett method to organize nanowires with controlled alignment and spacing over large areas and photolithography to define interconnects. Centimeter-scale arrays containing thousands of single silicon nanowire field-effect transistors were fabricated in this way and were shown to exhibit both high performance with unprecedented reproducibility and scalability to at least the 100-nm level. Moreover, scalable device characteristics were demonstrated by interconnecting a controlled number of nanowires per transistor in “pixel-like” device arrays. The general applicability of this approach to other nanowire and nanotube building blocks could enable the assembly, interconnection, and integration of a broad range of functional nanosystems.

• Magnetic Alignment of Nanowires by Carlos M. Hangarter and Nosang V. Myung, Chem. Mater., Vol. 17, pp. 1320-1324 (2005).
  Abstract Spatial manipulation and ability to assemble and position nanostructures in a controlled manner so they are registered to lithographically defined contacts is a critical step toward scalable integration in high-density nanodevices. By integrating ferromagnetic ends on nanostructures and using the magnetic interaction between ferromagnetic ends and electrodes, we demonstrated assembling, positioning, and spatial manipulating of nanostructures on ferromagnetic contacts. Segmented nickel/gold/nickel (Ni/Au/ Ni) and nickel/bismuth/nickel (Ni/Bi/Ni) nanowires with controlled dimensions were fabricated by template-directed electrodeposition. One hundred percent magnetic alignment of nanostructures to the imposed magnetic fields was achieved by applying a low external magnetic field of 200 Oe. In addition, directional controllability of the magnetic assembling technique was demonstrated by assembling nanostructures with angles from 45° to 135° with respect to the electrodes. This magnetic assembly technique was shown to have potential for high-density interconnects without registration and individually addressable nanostructures with the use of different substrate architectures for two-dimensional control of nanostructures placement.