Antenna enhanced graphene THz emitter and detector

Recent intense electrical and optical studies of graphene have pushed the material to the forefront of optoelectronic research. Of particular interest is the few terahertz (THz) frequency regime where efficient light sources and highly sensitive detectors are very challenging to make. Here we present THz sources and detectors made with graphene field effect transistors (GFETs) enhanced by a double-patch antenna and an on-chip silicon lens. We report the first experimental observation of 1-3 THz radiation from graphene, as well as four orders of magnitude performance improvements in a GFET thermoelectric detector operating at ~2 THz. The quantitative analysis of the emitting power and its unusual charge density dependence indicate significant non-thermal contribution from the GFET. The polarization resolved detection measurements with different illumination geometries allow for detailed and quantitative analysis of various factors that contribute to the overall detector performance. Our experimental results represent a significant advance towards practically useful graphene THz devices

Raman Scattering and Anomalous Stokes-anti-Stokes Ratio in MoTe2 Atomic Layers

Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, and find the effect to be tunable by excitation frequency and number of atomic layers. These observations are interpreted as a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center in the photon-electron-phonon interaction process

Antenna Enhanced Graphene Terahertz Emitter and Detector, and Graphene Microwave Detector

Graphene is a promising candidate for optoelectronic and fast electronics research. In THz and sub-THz frequency regime, sensitive detectors are very difficult to make. This dissertation presents my Ph.D study of THz sources and THz/Microwave (MW) detectors made with graphene. My work demonstrates the emission and detection of 1.9 THz radiation from graphene coupled to a double-patch antenna and a silicon lens. More than 3 orders of magnitude performance improvements are achieved in a half-edge-contacted graphene thermoelectric (TE) detector operating at 1.9 THz by antenna coupling and Si lens coupling. The thermoelectric mechanism is also employed in MW detection. A heterodyne TE microwave mixer at room temperature with 50 GHz (minimum) IF bandwidth is demonstrated. Currently Golay cells and pyroelectric detectors are commonly used as room temperature detectors for THz, my experimental results represent a significant advance toward practically useful graphene THz detectors. By optimizing the device structure, graphene detectors will have similar responsivity, lower NEP and are much faster, thus having a potential to revolutionize THz detection technology and industry. The demonstrated wide band Graphene MW mixer will pave the way for commercializing graphene-based high-speed electronic devices

Single-walled carbon nanotube / polypyrrole thermoelectric composite materials

A single-walled carbon nanotube/polypyrene (SWCNT/PPy) thermoelectric composites were prepared by an in situ oxidative polymerization method. The effect of SWCNT composition on the microstructure of the SWCNT/PPy nanocomposites was investigated. The thermoelectric properties of the composites were measured at different temperatures between 298 K and 398 K. Both of the electrical conductivity and the See beck coefficient of the SWCNT/PPy nanocomposites with 40% SWCNT loading increased simultaneously in the measured temperature. A maximum power factor of 5.46 μWm -1 K -2 was obtained at 398 K for the SWCNT/PPy nanocomposite with 40 wt% SWCNT loading

Thermoelectric properties of graphite-PEDOT:PSS coated flexible polyester fabrics

Flexible thermoelectric (TE) fabrics were prepared by dip coating of a mixture solution of water base colloidal graphite and dimethyl sulfoxide doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) on polyester fabric. The phase composition and morphology of the TE fabrics were investigated by X-ray diffraction and field emission scanning electron microscopy. The TE properties of the graphite-PEDOT:PSS coated fabrics with different graphite loadings were measured in the temperature range from 298 to 398 K. As the content of graphite increased from 5 to 20 wt%, the electrical conductivity of the graphite-PEDOT:PSS coated polyester fabrics decreased, while the Seebeck coefficient increased in the measured temperature range from 298 to 398 K. A maximum power factor of ~0.025 μWm−1K−2 at 398 K was obtained for the graphite-PEDOT:PSS coated fabric with 15 wt% graphite loading

What Determines BIM Competition Results of Undergraduate Students in the Architecture, Engineering and Construction Industry?

Building Information Modeling (BIM) has become the development trend in the architecture, engineering, and construction (AEC) industry. BIM discipline competition is an effective way for students of AEC-related disciplines to integrate theory with practice, and it is a key link to cultivate qualified BIM practitioners. This study takes participants of the 8th National College BIM Graduation Design Innovation Competition as the research objects. The Technology Acceptance Model and the Theory of Planned Behavior are combined to build a driving factor model of the competitions. Contestants of the competition were asked to complete online questionnaires, and 451 valid samples were finally obtained. Structural Equation Modeling was used to fit the theoretical model, and it was found that: Behavioral Intention to use BIM is directly and positively affected by Attitude, Perceived Behavioral Control, and Perceived Usefulness, as well as indirectly and positively affected by Perceived Usefulness and Perceived Eased of Usefulness. Competition Results is directly and positively affected by Behavioral Intention to use BIM, Perceived Behavioral Control, and Facilitating Conditions. It is also indirectly and positively affected by Attitude, Perceived Behavior Control, Perceived Usefulness, and Perceived Eased of Usefulness. The results show that the situation of students’ participation in BIM competition can be optimized by increasing the publicity and promotion of BIM and related policies, strengthening the construction of supporting teaching facilities, building the integrated curriculum system of BIM technology, and strengthening teacher training. This study provides a theoretical reference for further BIM practice, and it would help improve the corresponding teaching organization and enhance the internal drive of students’ BIM learning

Distribution and risk assessment of antibiotics under water level fluctuation in the riparian zone of the Hanjiang River

The riparian zone (RZ) is an important region connecting surface water and groundwater, and it has widely been acknowledged for its pollutant buffering capacity. However, the decontaminating effect of RZ on trace organic compounds such as antibiotics has received little attention. This study explored the distribution of 21 antibiotics and 4 sulfonamide metabolites in river water and groundwater in the lower reaches of the Hanjiang River. The diffusion and exchange of contaminants between the river and riverbanks under the influence of water conservancy projects (Xinglong Dam and the Yangtze-Hanjiang Water Diversion Project) were investigated. Macrolide antibiotics were prevalent in river water (62.5–100%) and groundwater samples (42.9–80.4%). Ofloxacin and chlortetracycline were detected with the highest concentrations in river water (12.2 ng L−1) and groundwater (9.3 ng L−1) respectively. Higher levels of antibiotics were observed in spring and winter than in other seasons. The river-groundwater interaction has a certain interception effect on antibiotics, especially near riverbanks. Redox sensitive element Fe2+ showed significantly positive correlations with some tetracycline and macrolide antibiotics (p < 0.05), and thus the migration mechanism between Fe2+ and antibiotics under the condition of redox change should be investigated further. Environmental risks posed by antibiotics were assessed for algae, daphnids, and fish in surface water and groundwater. Only clarithromycin and chlortetracycline presented a medium risk to algae (0.1 < RQ < 1), and the rest presented low risk (RQ < 0.1). Nevertheless, the risk range may be further extended by interactions between groundwater and surface water. Accurate understanding of antibiotic transport in RZ is critical for developing management strategies aimed at reducing the pollution load on the watershed