Terahertz (THz) radiation has uses from security to medicine [1]; however, sensitive roomtemperature detection of THz is notoriously difficult [2]. The hot-electron photothermoelectric effect in graphene is a promising detection mechanism: photoexcited carriers rapidly thermalize due to strong electron-electron interactions [3,4], but lose energy to the lattice more slowly [3,5]. The electron temperature gradient drives electron diffusion, and asymmetry due to local gating [6,7] or dissimilar contact metals[8] produces a net current via the thermoelectric effect. Here we demonstrate a graphene thermoelectric THz photodetector with sensitivity exceeding 10 V/W (700 V/W) at room temperature and noise equivalent power less than 1100 pW/Hz 1/2 (20 pW/Hz 1/2 ), referenced to the incident (absorbed) power. This implies a performance which is competitive with the best room-temperature THz detectors [9] for an optimally coupled device, while time-resolved measurements indicate that our graphene detector is eight to nine orders of magnitude faster than those [7,10]. A simple model of the response, including contact asymmetries (resistance, work function and Fermi-energy pinning) reproduces the qualitative features of the data, and indicates that orders-of-magnitude sensitivity improvements are possible.Graphene has unique advantages for hot-electron photothermoelectric detection. Gapless graphene has strong interband absorption at all frequencies. The electronic heat capacity of single-layer graphene is much lower than in bulk materials, resulting in a larger change in temperature for the same absorbed energy. The photothermoelectric effect has a picosecond response time, set by the electronphonon relaxation rate. [10,11]. Hot electron effects have been exploited in graphene for sensitive bolometry in THz and millimeter-wave at cryogenic temperatures, by using temperature-dependent resistance in gapped bilayer graphene [12], which is sizable only at low temperature, or noise thermometry [13], which requires complex RF electronics. In contrast, our photothermoelectric approach is temperature insensitive and produces an observable dc signal even under room temperature conditions.To realize our graphene hot electron thermoelectric photodetector we generate an asymmetry by contacting graphene with dissimilar metals using a standard double-angle evaporation technique as shown in Figs. 1a-e (also see Methods). Fig. 1f shows optical and atomic-force micrographs of our monolayer graphene device. Two metal electrodes, each consisting of partially overlapping Cr and Au regions, contact the monolayer graphene flake. The 3 µm × 3 µm graphene channel is selected to be shorter than the estimated electron diffusion length [14]. Fig. 1g shows the schematic of our detector in cross section. Figs. 1h-k illustrate the principle of operation: Electrons in graphene are heated by the incident light and the contacts serve as a heat sink, resulting in a non-uniform electron temperature T(x)as a function of position x within the device (Fig. 1h)...

Atomic-layer 2D crystals have unique properties that can be significantly modified through interaction with an underlying support. For epitaxial graphene on SiC(0001), the interface strongly influences the electronic properties of the overlaying graphene. We demonstrate a novel combination of x-ray scattering and spectroscopy for studying the complexities of such a buried interface structure. This approach employs x-ray standing wave-excited photoelectron spectroscopy in conjunction with x-ray reflectivity to produce a highly resolved chemically sensitive atomic profile for the terminal substrate bilayers, interface, and graphene layers along the SiC[0001] direction.

We report a large area terahertz detector utilizing a tunable plasmonic resonance in subwavelength graphene microribbons on SiC(0001) to increase the absorption efficiency. By tailoring the orientation of the graphene ribbons with respect to an array of subwavelength bimetallic electrodes, we achieve a condition in which the plasmonic mode can be efficiently excited by an incident wave polarized perpendicular to the electrode array, while the resulting photothermal voltage can be observed between the outermost electrodes.

InN thin films possessing either a novel cubic or a hexagonal phase were grown by plasma-assisted atomic layer epitaxy on an a-plane sapphire, Si(111), and GaN/sapphire templates, simultaneously. Two ALE growth temperature windows were found between 175–185 °C and 220–260 °C, in which the growth process is self-limiting. In the lower temperature ALE window, InN on an a-plane sapphire crystallized in a face-centered cubic lattice with a NaCl type structure, which has never been previously reported. InN grown on other substrates formed the more common hexagonal phase. In the higher temperature ALE window, the InN films grown on all substrates were of hexagonal phase. The NaCl phase and the epitaxial nature of the InN thin films on the a-plane sapphire grown at 183 °C are confirmed independently by X-ray diffraction, transmission electron microscopy, and numerical simulations. These results are very promising and demonstrate the tremendous potential for the PA-ALE in the growth of crystalline III-N materials with novel phases unachievable by other deposition techniques.

The sensitivity to water vapour of one-, two-, and three-layer epitaxial graphene (1, 2, and 3LG) is examined in this study. It is unambiguously shown that graphene's response to water, as measured by changes in work function and carrier density, is dependent on its thickness, with 1LG being the most sensitive to water adsorption and environmental concentration changes. This is furthermore substantiated by surface adhesion measurements, which bring evidence that 1LG is less hydrophobic than 2LG. Yet, surprisingly, it is found that other contaminants commonly present in ambient air have a greater impact on graphene response than water vapor alone. This study indicates that graphene sensor design and calibration to minimize or discriminate the effect of the ambient, in which it is intended to operate, are necessary to insure the desired sensitivity and reliability of sensors. The present work will aid in developing models for realistic graphene sensors and establishing protocols for molecular sensor design and development.