This paper provides an overview of research developments toward nanometer-scale electronic switching devices for use in building ultra-densely integrated electronic computers. Specifically, two classes of alternatives to the field-effect transistor are considered: 1) quantum-effect and single-electron solid-state devices and 2) molecular electronic devices. A taxonomy of devices in each class is provided, operational principles are described and compared for the various types of devices, and the literature about each is surveyed. This information is presented in nonmathematical terms intended for a general, technically interested readership

While still relatively "new", the quantum-dot cellular automata (QCA) appears to be able to provide many of the properties and functionalities that have made CMOS successful over the past several decades. Early experiments have demonstrated and realized most, if not all, of the "fundamentals " needed for a computational circuit -- devices, logic gates, wires, etc. This study introduces the beginning of a next step in experimental work: designing a computationally useful -- yet simple and fabricatable circuit for QCA. The design target is a QCA Field Programmable Gate Array.

Quantum Cellular Automata (QCA) has been proposed as an alternative architecture to CMOS and in principle should permit the implementation of ultra lower-power, nano-scale logic circuitry working at teraflop frequency. QCA is based on a new paradigm for encoding binary logic into electronic circuitry, where binary 1s and 0s are mapped to spatial configurations of electrons rather than magnitudes of electronic currents. The layout rules for QCA based circuits are radically different from those of CMOS based circuits, and design automation tools for QCA circuit layout are hard to find. This paper discusses the first automatic global placement algorithm for QCA-based circuits. We divide the QCA global placement process into zone partitioning and zone placement, and identify the constraints and objectives that are unique to QCA-based circuits as opposed to the conventional CMOS VLSI. 1.

1 Introduction In the past 40 years, the metal-oxide semiconductor field effect transistor (MOSFET) has become the basic building block for almost all computing devices. The steady growth of their popularity is due to the steady shrinking of the feature size which at present has reached 0.1 micron. However, the laws of quantum mechanics and limitations of fabrication techniques may soon prevent the further decrease of feature size. Hence, researchers are investigating several alternatives to the transistor for ultra-dense circuitry. These new devices whose dimensions are on the order of tens of nanometers are called nano-devices and their science is termed nano-technology.

Nanotubes have numerous potential applications in areas such as biotechnology, electronics, photonics, catalysis and separations. There are several challenges to be overcome in order to realize their potential, such as: (1) Synthesis of monodisperse (in diameter and in length) single-walled nanotubes; (2) Quantitative understanding of the mechanism of formation and growth of nanotubes; (3) Capability to engineer the nanotube size; (4) Low temperature synthesis process; and (5) Synthesis of impurity free nanotubes. Our investigation focuses on a class of metal oxide (aluminosilicate/germanate) nanotubes, which are; single walled nanotubes with monodisperse inner and outer diameters, can be synthesized in the laboratory by a low temperature (95ºC) process in mildly acidic aqueous solutions, and their formation timescales is hours, which makes it convenient as a model system to study the mechanisms of nanotube formation. This work is focused on obtaining a qualitative and quantitative understanding of the mechanism of formation of aluminosilicate and aluminogermanate nanotubes. In order to achieve this overall objective, this thesis consists of the following aspects: (1) A systematic phenomenological study of the growth and structural properties of aluminosilicate and aluminogermanate nanotubes. The constant size and increasing nanotube concentration over the synthesis time strongly suggest that these nanotubular are assembled through self-assembly process. (II) Investigation of the mechanism of formation of single-walled aluminogermanate nanotubes provided the central phenomena underlying the formation of these nanostructures: (1) the generation (via pH control) of a precursor solution containing chemically bonded precursors, (2) the formation of amorphous nanoscale (~ 6 nm) condensates via temperature control, and (3) the self-assembly of short nanotubes from the amorphous nanoscale condensates. (III) Synthesis of mixed metal oxide (aluminosilicogermanate) nanotubes with precise control of elemental composition, diameter and length of the product nanotubes. (IV) Preliminary work towards generalization of the kinetic model developed for aluminogermanate nanotubes to a larger class of metal oxide nanotubes. It was found that the size of nanotubes is dependent on the amount of precursors that can be packed in a single ANP and in turn depends on the size of the ANP.