/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

We study the operation of quantum cellular automata (QCA) devices in the presence of stray charge. The operation of linear arrays of QCA cells, called binary wires, relies on Coulombic interaction between the cells, which is affected by the presence of such stray charge. The position of the charge determines whether or not the devices function properly, and it is possible to determine the "forbidden" region near the array in which the presence of stray charge causes device failure. We calculate this forbidden region by directly diagonalizing the Hamiltonian for the system including the stray charge. We find that the QCA binary wire is unaffected by stray charge at a distance greater than the intercellular repeat distance of the wire.

Effect of Stray Charge on Quantum Cellular Automata

Reply to Comment on ‘Bennett clocking of quantum-dot cellular automata and the limits to binary logic scaling’

The electrostatic interaction between two capacitively coupled, series-connected metal double dots is studied at low temperatures. Experiment shows that when the Coulomb blockade is lifted, by applying appropriate gate biases, in both double dots simultaneously, the conductance through each double dot becomes significantly lower than when only one double dot is conducting a current. The conductance lowering seen in interacting double dots is compared to that caused by an external ac modulation applied to the double-dot gates. The results suggest 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 single electron in one double dot controls the tunneling rate through the other double dot.

/pdf/correlated-electron-transport-in-coupled-metal-double-dots-zw1h2je8uk.pdf

Correlated electron transport in coupled metal double dots

The computation approach known as quantum-dot cellular automata (QCA) is based on encoding binary information in the charge configuration of quantum-dot cells. This paradigm provides a possible route to transistor-less electronics at the nano-scale. QCA devices using single-electron switching in metal-dot cells have been fabricated. Here we examine the limits of switching speed and temperature in QCA circuits. We calculate the dynamic behavior of a semi-infinite shift register. We employ the orthodox, theory of Coulomb blockade and a master-equation approach for the dynamics. A complete phase diagram of the operational space of the circuit as a function of clock speed and temperature is constructed. The crucial role of power gain as a function of temperature is evident.

High-speed metallic quantum-dot cellular automata

In this work, we study the dynamics of molecular quantum-dot cellular automata (QCA) devices by combining the technique of quantum chemistry and coherence vector formalism. First, we apply the quantum chemistry ab initio calculation on the single molecule, and construct a simple model Hamiltonian for each QCA cell based on the calculation. For a three-dot molecule discussed in this work, we show a 3×3 Hamiltonian is sufficient to describe its switching behavior. The second step is to use the model Hamiltonian to calculate the coherence vector evolved as time, from which we will investigate the dynamic behavior of various QCA devices and circuits. Finally, we discuss the structure-functionality relation between the molecular structure and circuit dynamics.

http://ieeexplore.ieee.org/iel5/11219/36118/01717017.pdf

Craig S. Lent

Papers

Effect of Stray Charge on Quantum Cellular Automata

Reply to Comment on ‘Bennett clocking of quantum-dot cellular automata and the limits to binary logic scaling’

Correlated electron transport in coupled metal double dots

High-speed metallic quantum-dot cellular automata

Molecular electronics–from structure to circuit dynamics

Craig S. Lent

Papers

Effect of Stray Charge on Quantum Cellular Automata

Reply to Comment on ‘Bennett clocking of quantum-dot cellular automata and the limits to binary logic scaling’

Correlated electron transport in coupled metal double dots

High-speed metallic quantum-dot cellular automata

Molecular electronics&#8211;from structure to circuit dynamics

Molecular electronics–from structure to circuit dynamics