/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

The purpose of this article is to describe the basic physical processes involved in the nucleation and growth of thin films of materials on solid surfaces. In this introduction the three modes of crystal growth which are thought to occur on surfaces in the absence of interdiffusion are described, and the relationships between the thermodynamics of adsorption and the kinetics of crystal growth are explored in general terms. This is followed by a brief review of atomistic nucleation theory, explaining the relations of such theories to experimental observables. In the next three sections, recent experimental examples of these three growth modes are given, which are interpreted where possible in terms of nucleation and growth theory. The last section discusses observations on the shapes of growing crystallites and the relation of such observations to nucleation and surface diffusion processes.

https://iopscience.iop.org/article/10.1088/0034-4885/47/4/002/pdf

Nucleation and growth of thin films

The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.

/pdf/engineering-atomic-and-molecular-nanostructures-at-surfaces-2sqr7sjd15.pdf

Engineering atomic and molecular nanostructures at surfaces

“Spintronics,” in which both the spin and charge of electrons are used for logic and memory operations, promises an alternate route to traditional semiconductor electronics. A complete logic architecture can be constructed, which uses planar magnetic wires that are less than a micrometer in width. Logical NOT, logical AND, signal fan-out, and signal cross-over elements each have a simple geometric design, and they can be integrated together into one circuit. An additional element for data input allows information to be written to domain-wall logic circuits.

http://science.sciencemag.org/content/sci/309/5741/1688.full.pdf

Magnetic Domain-Wall Logic

The electrostatic interaction between two capacitively coupled metal double-dots is studied at low temperatures. Experiments show that when the Coulomb blockade is lifted by applying appropriate gate biases to both double-dots, the conductance through each double-dot becomes significantly lower than when only one doubledot is conducting. A master equation is derived for the system and the results obtained agree well with the experimental data. The model suggests that the conductance lowering in each double-dot is caused by a single-electron tunneling in the other double-dot. Here, each double-dot responds to the instantaneous, rather than average, potentials on the other double-dot. This leads to correlated electron motion within the system, where the position of a single electron in one double-dot controls the tunneling rate through the other doubledot. @S0163-1829~99!16347-1#

/pdf/conductance-suppression-due-to-correlated-electron-transport-1j8e0tt7c1.pdf

Conductance suppression due to correlated electron transport in coupled double quantum dots

An introduction to quantum-dot cellular automata (QCA) is presented along with experimental implementations. QCA is a transistorless nanoelectronic computation paradigm that addresses the issues of device and power density, which are becoming increasingly important in the electronics industry. Scaling of CMOS is expected to come to an end in the next 10-15 years, with perhaps the most important limiting problem being the power density and the resulting heat generated. QCA offers the possibility of circuitry that dissipates many orders of magnitude less power than CMOS, is scalable to molecular dimensions, and provides the power gain necessary to restore signal levels.

Implementations of Quantum-dot Cellular Automata

Hierarchical self-assembly was used to construct meso-scale DNA objects as eventual templates for molecular electronic circuitry. DNA tiles were assembled from single-stranded precursors. The tiles measure 4 nm/spl times/12 nm/spl times/2 nm. They can be programmed to self-assemble into larger objects, such as a 4-tile raft 37 nm long. The composition and structure of the DNA rafts were characterized in solution by biochemical assays. Rafts were imaged on mica substrates under isopropanol by non-contact mode AFM, or alternately, were deposited on silicon wafers and imaged by non-contact mode AFM in air.

/pdf/nanometer-scale-rafts-built-from-dna-tiles-1q2ev03bz0.pdf

Nanometer scale rafts built from DNA tiles

In addition to bound states, quantum wells also produce resonant states in the continuum. While bound states have received considerable attention and are now the basis of device applications, the corresponding virtual states have hardly been studied. Here, we specifically investigate the influence of these resonant states on hot electron transport in quantum wells. We find that the matrix elements which determine scattering rates exhibit structure at the resonant energies. This leads to suppression of scattering by polar optical phonons relative to non-polar optical and acoustic phonon scattering. We discuss the effect that these states have on the capture and release of carriers by the quantum well.

Effect of continuum resonances on hot carrier transport in quantum wells

This paper examines adiabatic logic for computation, and presents a design for a MIPS processor implemented in CMOS. Adiabatic reversible logic was examined in the 1980s and 1990s but in that era power dissipation was a secondary concern, and the trade-off of reduced computational speed for reduced power was deemed unacceptable. Now, power dissipation and the associated heat are the major obstacles limiting progress in integrated circuits, particularly processors. In modern processors trading performance for reduced power dissipation is already done using techniques such as multi-core and dark silicon, so adiabatic logic may now be an attractive approach. To evaluate the adiabatic approach, this paper uses the figure of merit of the product of switching energy, delay time, and area (EDA). Using this figure of merit, adiabatic logic is shown to be advantageous when additional constraints are considered, such as maximum allowed power density. As a proof of concept circuit, a simplified MIPS microprocessor was designed using adiabatic logic based on split-rail charge recovery logic and Bennett clocking. New design and verification tools were developed using structural Verilog and extensions of ModelSim to provide needed capabilities are not available in commercial packages. The design is implemented using a standard cell design.

Craig S. Lent

Papers

Conductance suppression due to correlated electron transport in coupled double quantum dots

Implementations of Quantum-dot Cellular Automata

Nanometer scale rafts built from DNA tiles

Effect of continuum resonances on hot carrier transport in quantum wells

A Mini-MIPS microprocessor for adiabatic computing