/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

Quantum-dot Cellular Automata (QCA) is a promising architecture which employs quantum dots for digital computation. It is a revolutionary approach which addresses the issues of device density and power dissipation. With a dot size of 20 nm an entire full adder would occupy only one square micron, and the power delay product is as low as a few kT. A basic QCA cell consists of four quantum dots coupled capacitively and by tunnel barriers. The cell is biased to contain two excess electrons within the four dots, which are forced to opposite "corners" of the four-dot system by Coulomb repulsion. These two possible polarization states of the cell represent logic "0" and "1". Properly arranged, arrays of these basic cells can implement Boolean logic functions. We present experimental results from functional QCA devices built of nanoscale metal dots defined by tunnel barriers.

Quantum-dot cellular automata

A numerical algorithm for the solution of the two‐dimensional effective‐mass Schrodinger equation for current‐carrying states, the quantum transmitting boundary method, is extended to magnetotransport problems where a magnetic field is applied Boundary conditions appropriate for such states are developed and a solution algorithm based on the finite‐element method is constructed The algorithm is valid for general device shapes, general potential profiles, and multiple leads of general orientations The technique is applied to a quantum channel with a single scatterer, an antidot, in the channel Magnetic quasibound states (MQBS) are formed around the scatterer and MQBS‐induced resonant reflection is observed

Quantum transmitting boundary method in a magnetic field

We calculate the excess energy transferred into two-dot and three-dot quantum dot cellular automata systems during switching events This is the energy that must eventually be dissipated as heat The adiabaticity of a switching event is quantified using the adiabaticity parameter of Landau and Zener For the logically reversible operations of WRITE or ERASE WITH COPY, the excess energy transferred to the system decreases exponentially with increasing adiabaticity For the logically irreversible operation of ERASE WITHOUT COPY, considerable energy is transferred and so must be dissipated, in accordance with the Landauer Principle The exponential decrease in energy dissipation with adiabaticity (eg, switching time) distinguishes adiabatic quantum switching from the usual linear improvement in classical systems

https://www.mdpi.com/2079-9268/8/3/30/pdf

Exponentially Adiabatic Switching in Quantum-Dot Cellular Automata

Summary form only given, as follows. We investigate the use of nanoelectronic structures in cellular neural network (CNN) architectures, for future high-density and low-power CMOS-nanodevice hybrid circuits. We present simulation results for Single Electron Tunneling (SET) transistors configured as a voltage-to-current transducer for CNN cells. We also present an example of quantum-dot cellular arrays which may be used to realize binary CNN algorithms. Nanoelectronics offers the promise of ultra-low power and ultra-high integration density. Several device structures have been proposed and realized experimentally, yet the main challenge remains the organization of these devices in new circuit architectures. Here, we investigate the use of nanodevices in CNN architectures. Specifically, we focus on nanostructures based on SET devices and Coulomb-coupled quantum-dot arrays, the so-called Quantum-Dot Cellular Automata (QCA). CNN-type architectures for nanostructures are motivated by the following considerations: on the one hand, locally-interconnected architectures appear to be natural for nanodevices where some of the connectivity may be provided by direct physical device-device interactions. On the other hand, CNN arrays with sizes on the order of 1000-by-1000 (which are desirable for applications such as image processing) will require the use of nanostructures since such integration densities are beyond what can be achieved by scaling conventional CMOS devices.

/pdf/modeling-nanoelectronic-cnn-cells-cmos-sets-and-qcas-13bdy5fay4.pdf

Modeling nanoelectronic CNN cells: CMOS, SETs and QCAs

An overview is given of the QCA architecture, along with a summary of experimental demonstrations of QCA devices. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses such challenging issues as device and power density. The basic building blocks of the QCA architecture, such as AND, OR gates and clocked cells have been demonstrated and are presented. The quantum dots used in the experiments are metal islands that are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. A noninvasive electrometer is presented which improves the sensitivity and linearity of dot potential measurements. The operation of this basic cell is confirmed by an externally controlled polarization change of the cell.

Craig S. Lent

Papers

Quantum-dot cellular automata

Quantum transmitting boundary method in a magnetic field

Exponentially Adiabatic Switching in Quantum-Dot Cellular Automata

Modeling nanoelectronic CNN cells: CMOS, SETs and QCAs

Quantum-dot cellular automata: introduction and experimental overview