Anomalous enhancement of thermoelectric power factor in multiple two-dimensional electron gas system.

Toward drastic enhancement of thermoelectric power factor, quantum confinement effect proposed by Hicks and Dresselhaus has intrigued a lot of researchers. There has been much effort to increase power factor using step-like density-of-states in two-dimensional electron gas (2DEG) system. Here, we pay attention to another effect caused by confining electrons spatially along one-dimensional direction: multiplied 2DEG effect, where multiple discrete subbands contribute to electrical conduction, resulting in high Seebeck coefficient.

High-endurance micro-engineered LaB nanowire electron source for high-resolution electron microscopy.

The size tunability and chemical versatility of nanostructures enable electron sources of high brightness and temporal coherence, both of which are important characteristics for high-resolution electron microscopy. Despite intensive research efforts in the field, so far, only conventional field emitters based on a bulk tungsten (W) needle have been able to yield atomic-resolution images. The absence of viable alternatives is in part caused by insufficient fabrication precision for nanostructured sources, which require an alignment precision of subdegree angular deviation of a nanometre-sized emission area with the macroscopic emitter axis.

Patchwork metasurface quantum well photodetectors with broadened photoresponse.

Complex lightwave manipulation such as broadband absorption has been realized with metasurfaces based on laterally arranged metal-dielectric-metal cavities with different geometries. However, application of these metasurfaces for optoelectronic devices by incorporating functional dielectrics remains challenging. Here, we integrate a quantum well infrared photodetector (QWIP) with a metasurface made of a patchwork of square cavities with different dimensions arranged in a subwavelength unit cell.

Synchronously wired infrared antennas for resonant single-quantum-well photodetection up to room temperature.

Optical patch antennas sandwiching dielectrics between metal layers have been used as deep subwavelength building blocks of metasurfaces for perfect absorbers and thermal emitters. However, for applications of these metasurfaces for optoelectronic devices, wiring to each electrically isolated antenna is indispensable for biasing and current flow. Here we show that geometrically engineered metallic wires interconnecting the antennas can function to synchronize the optical phases for promoting coherent resonance, not only as electrical conductors.

Double-Sided Nonalloyed Ohmic Contacts to Si-doped GaAs for Plasmoelectronic Devices.

There is increasing demand for the ability to form ohmic contacts without lossy intermediate layers on both the top and bottom sides of metal-semiconductor-metal plasmoelectronic devices such as quantum cascade lasers and metasurface photodetectors. Although highly Si-doped n-GaAs surfaces can allow an ohmic contact without alloying, conditions for realizing nonalloyed ohmic contacts to other n-GaAs surfaces, originally buried inside but exposed by removing the substrate, have yet to be studied. We discovered that nonalloyed ohmic contacts to initially buried surfaces with a practically low contact resistivity down to 77 K can be realized by fulfilling certain requirements, specifically keeping the Si-doping concentration within a narrow range of 7.

Ultraviolet-nanoimprinted packaged metasurface thermal emitters for infrared CO sensing.

Packaged dual-band metasurface thermal emitters integrated with a resistive membrane heater were manufactured by ultraviolet (UV) nanoimprint lithography followed by monolayer lift-off based on a soluble UV resist, which is mass-producible and cost-effective. The emitters were applied to infrared CO sensing. In this planar Au/AlO/Au metasurface emitter, orthogonal rectangular Au patches are arrayed alternately and exhibit nearly perfect blackbody emission at 4.

Diffraction-unlimited optical imaging of unstained living cells in liquid by electron beam scanning of luminescent environmental cells.

An environmental cell with a 50-nm-thick cathodoluminescent window was attached to a scanning electron microscope, and diffraction-unlimited near-field optical imaging of unstained living human lung epithelial cells in liquid was demonstrated. Electrons with energies as low as 0.8 - 1.

Graphical template software for accurate micromanipulation in a scanning electron microscope.

Micromanipulation techniques in a scanning electron microscope (SEM) have been utilized for assembling micrometer-sized structures. The precision of the assembled microstructures has been limited by the poor accuracy of the SEM image. We have developed a software to assist the operator in the accurate assembly of microstructures in a SEM, in which computer-generated outlines of the target structure [graphical templates (GTs)] are superimposed on the monitor.