Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenom...

Prospects of Nanoscience with Nanocrystals

External driving is emerging as a promising tool for exploring new phases in quantum systems. The intrinsically nonequilibrium states that result, however, are challenging to describe and control. We study the steady states of a periodically driven one-dimensional electronic system, including the effects of radiative recombination, electron-phonon interactions, and the coupling to an external fermionic reservoir. Using a kinetic equation for the populations of the Floquet eigenstates, we show that the steady-state distribution can be controlled using the momentum and energy relaxation pathways provided by the coupling to phonon and Fermi reservoirs. In order to utilize the latter, we propose to couple the system and reservoir via an energy filter which suppresses photon-assisted tunneling. Importantly, coupling to these reservoirs yields a steady state resembling a band insulator in the Floquet basis. The system exhibits incompressible behavior, while hosting a small density of excitations. We discuss transport signatures and describe the regimes where insulating behavior is obtained. Our results give promise for realizing Floquet topological insulators.

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Controlled Population of Floquet-Bloch States via Coupling to Bose and Fermi Baths

Additive manufacturing has provided a pathway for inexpensive and flexible manufacturing of specialized components and one-off parts. At the nanoscale, such techniques are less ubiquitous. Manufacturing at the nanoscale is dominated by lithography tools that are too expensive for small- and medium-sized enterprises (SMEs) to invest in. Additive nanomanufacturing (ANM) empowers smaller facilities to design, create, and manufacture on their own while providing a wider material selection and flexible design. This is especially important as nanomanufacturing thus far is largely constrained to 2-dimensional patterning techniques and being able to manufacture in 3-dimensions could open up new concepts. In this review, we outline the state-of-the-art within ANM technologies such as electrohydrodynamic jet printing, dip-pen lithography, direct laser writing, and several single particle placement methods such as optical tweezers and electrokinetic nanomanipulation. The ANM technologies are compared in terms of deposition speed, resolution, and material selection and finally the future prospects of ANM are discussed. This review is up-to-date until April 2014.

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Additive nanomanufacturing – A review

In this review, we describe recent progress made in the study of nanoparticles characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Basic principles of STM measurements and single-electron tunneling phenomena through a single NP are summarized. We highlight the results of electrical and photonic properties on NPs studied by STM and STS. Because nanoparticles are single-digit nanometre in diameter, a single-electron transport on individual nanoparticles such as Coulomb blockade and resonant tunneling through discrete energy levels are investigated. Photon-emission from NPs is also introduced based on STM measurements. Novel single-nanoparticle functions such as stochastic blinking and one-write erasing behaviours are presented. This review provides an overview of nanoparticle characterization methods based on STM and STS that include the detailed understanding of the electrical and photonics properties of nanoparticles.

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Nanoparticle characterization based on STM and STS

Double-gate single-electron transistors (SETs) were fabricated by chemical assembling using electroless gold-plated nanogap electrodes and chemisorbed chemically synthesized gold nanoparticles. The fabricated SET showed periodic and stable Coulomb oscillations under application of voltages of both gates. The sole SET also exhibited all two-input logic operations—XOR, XNOR, NAND, OR, NOR, and AND—with an on/off ratio of 102. This demonstrates the potential of chemical assembling to give highly stable SETs exhibiting all logic operations.

Logic operations of chemically assembled single-electron transistor.

Single-electron devices offer many advantages over traditional devices, but it is a challenge to fabricate them in large numbers. A novel geometry in which the source and drain electrodes are vertically separated by thin dielectric films, and nanoparticles attached to the sidewall of the dielectric films act as Coulomb islands, can now be used for the CMOS-compatible fabrication of single-electron devices that operate at room temperature.

CMOS-compatible fabrication of room-temperature single-electron devices

Electrons can behave as if they are at a temperature different from that of the solid in which they are embedded. Here, the authors demonstrate a room temperature device that can generate electrons with an effective temperature of 45 K by using quantum wells to filter out energetic particles.

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Energy-filtered cold electron transport at room temperature

This letter reports single-particle placement in which exactly one nanoparticle is electrostatically guided and placed onto a target location. Using an ∼20 nm Au nanoparticle colloid as a model system, we demonstrate that self-limiting interactions between a charged nanoparticle and a charged substrate surface are extremely effective in positioning a single Au nanoparticle on each target location. Detailed theoretical calculations revealed that the self-limiting capability in the nanoparticle positioning is due to an increase in the free energy barrier after the first nanoparticle lands on a target position, effectively blocking the approach of other nanoparticles.

Pradeep Bhadrachalam

Papers

CMOS-compatible fabrication of room-temperature single-electron devices

Energy-filtered cold electron transport at room temperature

Single-particle placement via self-limiting electrostatic gating