There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15<x<0.5) and thickness between 20 and 65 nm demonstrate the important role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces. Characterization of the electrical properties of nominally undoped transistor structures reveals the presence of high sheet carrier concentrations, increasing from 6×1012 to 2×1013 cm−2 in the GaN channel with increasing Al-concentration from x=0.15 to 0.31. The observed high sheet carrier concentrations and strong confinement at specific interfaces of the N- and Ga-face pseudomorphic grown heterostructures can be explained as a consequence of interface charges induced by ...

/pdf/two-dimensional-electron-gases-induced-by-spontaneous-and-11pht7aexp.pdf

Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures

Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

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

Energy Limits in Computation

We study the generation of thermoelectricity by arrays of antenna-coupled nanothermocouples (ACNTCs) in response to long-wave infrared radiation. An ACNTC is constructed from a dipole antenna and a nanoscale thermocouple (NTC). The NTCs are based on a newly discovered thermoelectric effect in single-metal nanostructures with cross-sectional discontinuity. Dependences on antenna array size and polarization are investigated. We show that large arrays of ACNTCs are capable of converting optical energy to measurable electrical signals. This could open the possibility to use such devices for solar energy harvesting in the IR portion of the spectrum, which is inaccessible to photovoltaics.

Antenna-coupled single-metal thermocouple array for energy harvesting

Infrared detectors in the long-wave infrared range (LWIR) are of special interest since they are sensitive to blackbody radiation of objects at room temperature, with a wide range of applications. In previous work, we have reported bi-metallic antenna-coupled infrared detectors for the LWIR [1], and here we report novel mono-metallic antenna-coupled infrared detectors, as well as a comparison between the two. Such antenna-coupled thermocouples are promising candidates for various applications including energy harvesting [2], target tracking [3], and thermal imaging. These detectors operate without the need of any bias or cooling. The antenna design determines the resonant frequency, directivity, and polarization of these detectors.

Bi-metallic and mono-metallic antenna-coupled nanoscale thermocouples for infrared detection

A single-electron latch is a device that can be used as a building block for quantum-dot cellular automata circuits. It consists of three nanoscale metal ``dots'' connected in series by tunnel junctions; charging of the dots is controlled by three electrostatic gates. One very important feature of a single-electron latch is its ability to store (``latch'') information represented by the location of a single electron within the three dots. To obtain latching, the undesirable leakage of charge during the retention time must be suppressed. Previously, to achieve this goal, multiple tunnel junctions were used to connect the three dots. However, this method of charge leakage suppression requires an additional compensation of the background charges affecting each parasitic dot in the array of junctions. We report a single-electron latch where a granular metal film is used to fabricate the middle dot in the latch which concurrently acts as a charge leakage suppressor. This latch has no parasitic dots, therefore the background charge compensation procedure is greatly simplified. We discuss the origins of charge leakage suppression and possible applications of granular metal dots for various single-electron circuits.

Using granular film to suppress charge leakage in a single-electron latch

We present a real-time measurement of electron switching in clocked Quantum-Dot Cellular Automata (QCA) circuit, a QCA latch. A capacitively coupled radio frequency single electron transistor (RF-SET) with carrier frequency at 991.2 MHz is used as read-out electrometer. Reflection-mode detection of the SET impedance provides a fast response to changes of charge configuration in the latch dots. We demonstrate a QCA latch with operating temperature above 300 milli-Kelvin and clocking speed of 5 µsec.

Alexei O. Orlov

Papers

Energy Limits in Computation

Antenna-coupled single-metal thermocouple array for energy harvesting

Bi-metallic and mono-metallic antenna-coupled nanoscale thermocouples for infrared detection

Using granular film to suppress charge leakage in a single-electron latch

Towards real-time testing of clocked Quantum Dot Cellular Automata