/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 model the fundamental behavior of a two-branch quantum interference device. Quantum interference oscillations are visible in the output as the magnetic flux through the paths is varied. Multiple witness systems are field-coupled to each branch. Each witness state entangles with the device state, but for our {\em blind} witnesses which-path information is not transferred to the quantum state of witnesses--they cannot "see" or make a record of which path is traversed. Yet the presence of these minimal witnesses rapidly quenches quantum interference. Thus, it is not the imprinting of which-path information in the witness states that is essential for decoherence, but simply the entanglement that embeds the device degrees of freedom in the larger Hilbert space that includes the witnesses. The loss of interference visibility can be understood as the result of phase cancellations from different paths through the larger state space.

Blind witnesses quench quantum interference without transfer of which-path information

Summary form only given, as follows. New nanodevices which encode information into the geometrical charge distribution of artificial (or natural) molecules have been proposed. Functional units are composed by exploiting the electrostatic coupling between neighboring devices. In these units, processing takes place by reshaping the electron density of the molecules, and not by switching electron currents. It has been proposed and demonstrated that high speed, extremely low loss logic gates (e.g. inverters, majority gates) can be realized. It will be shown that Coulomb-coupled time-invariant or stationary artificial molecules behave like nonlinear locally passive systems for small-signal excitations, thus multiple equilibria cannot be achieved by integrating them. Without multiple equilibrium write-hold-read memories, and thus signal processors, cannot be realized. However, the signal transfer-function of strongly nonlinear molecules can be varied in time by adiabatic control, called clock control. It will be shown that strongly nonlinear time-varying molecules can transform the necessary amount of clock-energy into the flow of signals, thereby enabling the network of molecules to perform multiple equilibria. It is envisaged that, by a proper integration of clock-controlled artificial molecules, universal digital signal processors can be built.

Why is time-varying control necessary for signal processing with locally-connected quantum-dot arrays?

We study quantum entanglement loss due to environmental interaction in a condensed matter system with a complex geometry relevant to recent proposals for computing with single electrons at the nanoscale. We consider a system consisting of two qubits, each realized by an electron in a double quantum dot, which are initially in an entangled Bell state. The qubits are widely separated and each interacts with its own environment. The environment for each is modeled by surrounding double quantum dots placed at random positions with random orientations. We calculate the unitary evolution of the joint system and environment. The global state remains pure throughout. We examine the time dependence of the expectation value of the bipartite Clauser-Horne-Shimony-Holt (CHSH) and Brukner-Paunkovic-Rudolph-Vedral (BPRV) Bell operators and explore the emergence of correlations consistent with local realism. Though the details of this transition depend on the specific environmental geometry, we show how the results can be mapped on to a universal behavior with appropriate scaling. We determine the relevant disentanglement times based on realistic physical parameters for molecular double-dots.

Craig S. Lent

Papers

Blind witnesses quench quantum interference without transfer of which-path information

Why is time-varying control necessary for signal processing with locally-connected quantum-dot arrays?

Entanglement loss in molecular quantum-dot qubits due to interaction with the environment

Quantum Dots in Nanoelectronic Devices