A new type of nanoscale field emitter array, consisting of carbon nanonecklaces and nanotentacles, has
been produced by a novel multi-level self assembly process employing flexible porous alumina films. The
field emission characteristics of the carbon nanostructures were measured using a scanning field emission
microscope (SAFEM) and they exhibited strong Fowler-Nordheim emission. This new synthetic approach
could find potential applications in flexible and inexpensive arrays of nanoscale cold cathode emitters.
This paper details our experimental progress towards the synthesis of self-assembled nanostructures that may exhibit collective computational activity. Self assembled two dimensional networks of heterostructured quantum dots, linked by resistive and capacitive connections, can function as Boolean logic circuits, associative memory, image processors, and combinatorial optimizers. Computational or signal processing activity is elicited from simple charge interactions between the dots which act as non-linear resistors. Such circuits could be massively parallel, fault-tolerant, ultrafast, ultradense and dissipate very little power.
This paper presents a review of our theoretical work on non- linear magneto-optical properties of semiconductor quantum wires. We have studied both second- and third-order non- linearities. The former arises from dipole transitions within the quantized magneto-electronic subbands in a quantum wire, and the latter arises from phase-space filling and saturation of the excitonic state followed by the formation of biexcitons. A magnetic field causes non-zero second-order non-linearity in a geometrically symmetric quantum wire by breaking inversion symmetry and inducing forbidden transitions between electronic subbands. It also enhances third-order non-linearity by adding magnetostatic confinement to the spatial and dielectric confinement of excitons and biexcitons, thereby further constricting the phase space for these entities. Additionally, we find that a magnetic field can be used to modulate the non-linear differential refractive index and absorption coefficient of quantum wires thus allowing efficient polariton transport, optical waveguiding without a concomitant high absorption or insertion loss, and the possibility to realize magneto- optical devices such as frequency modulators, tunable couplers, limiters and mixers.
Conventional nanosynthesis involves film growth followed by direct-write nanolithography. The last step has two major shortcomings in that (a) it causes material damage to the nanostructures and (b) it is always serial in nature whereby each wafer has to be patterned one at a time. The latter makes it impractical for large-scale commercial applications. To overcome these drawbacks, we have developed a novel and `gentle' electrochemical process for fabricating quantum dot arrays that allows parallel processing of millions of wafers. It causes minimal damage, is much cheaper than conventional nanolithography, and yet has the spatial resolution (approximately 1 nm) of state-of-the-art techniques. Semiconductor quantum dot arrays produced by this process show strong signatures of quantum confinement in their photoluminescence spectra. Superconducting quantum dots show a significant transition- temperature shift arising from an interplay of superconductivity with quantum confinement, while ferromagnetic quantum dots give rise to a novel giant magnetoresistance effect caused by remote spin-dependent scattering of electrons. These structures have also been characterized by a variety of analytical techniques--all of which attest to their high quality.
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