Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

Plasma-induced oxygen vacancies enabled ultrathin ZnO films for highly sensitive detection of triethylamine.

Heterostructures of metal oxide semiconductors have a great promise for chemical gas sensors due to the peculiar properties at the heterointerface. In this work, a highly sensitive and selective gas sensor for detecting formaldehyde is reported based on SnO2/ZnO heterospheres designed by atomic layer deposition (ALD). The electronic properties at the SnO2/ZnO heterointerface can be modulated by optimizing the loading of ZnO through changing ALD cycles. Gas sensing tests indicate that the ZnO ALD significantly improved the sensor properties including higher responses, faster response-recovery dynamics and better selectivity. The response of the SnO2/ZnO sensor to 1 ppm formaldehyde (Ra/Rg = 9.7) shows 4 times enhancement compared to pristine SnO2 at a working temperature of 200 °C. ZnO ALD of 10 cycles leads to the best response and recovery dynamics (12 and 24 s), and that of 15 ALD cycles results in the highest response (Ra/Rg = 38.2) to 20 ppm formaldehyde. The SnO2/ZnO sensor also registers a low detection limit of 70 ppb, which allows for reliable detection of sub-ppm formaldehyde. The remarkable sensor performances indicate the ALD surface engineering is promising for the design of new materials for reliable detection of harmful molecules.

Atomic layer deposition of ZnO on SnO2 nanospheres for enhanced formaldehyde detection

Thin film technology shows high promise in fabrication of electronic devices such as gas sensors. Tungsten trioxide (WO3), as one of the best-known metal oxide semiconductors (MOS) sensing materials, has attracted significant interest for application in gas sensors. In this review, WO3 thin films and their promising utilization as the sensing layers are overviewed to highlight their potential in gas sensors. First, the sensing mechanism for WO3 materials is briefly discussed. Then, several methods for WO3 film preparation are summarized. Following we discuss the specific gas sensing performances of WO3 film sensors to NO2, H2, NH3, and H2S. Strategies to improve the sensor properties such as sensitivity, response-recovery speed and selectivity are also discussed. Finally, the future perspectives and challenges of WO3 thin film sensors are addressed.

Thin films of tungsten oxide materials for advanced gas sensors

Anionic defects engineering of Co3O4 catalyst for toluene oxidation

Current gas sensors based on metal oxide semiconductors still suffer greatly from the poor selectivity and low tolerance to the high relative humidity (RH) Herein, we report a highly selective and humidity-resistant gas sensor based on SnO2/ZrO2 porous thin films with a three-dimensionally ordered microstructure (3DOM) The 3DOM ZrO2 fabricated by a template method serves as a hydrophobic layer and SnO2 deposited on ZrO2 by atomic layer deposition (ALD) acts as the transducer layer Gas sensing tests reveal the SnO2/ZrO2 sensor has a decent response to triethylamine (TEA), a highly toxic and flammable chemical widely used in industry The sensor exhibits an ultrafast response and recovery (∼ 1 s) speed to 20 ppm TEA at an optimum operating temperature of 190 °C When the RH increases from 50 % to 90 %, the response of SnO2/ZrO2 sensor shows a minor decrease of 18 %, which to our best knowledge surpasses the existing reports on TEA detection under high RH The humidity resistance is attributed to continuous 3DOM ZrO2 layers, which forms an air hydrophobic layer to suppress water adsorption Furthermore, the SnO2/ZrO2 sensor also possesses superior selectivity, long-time stability and a low detection limit of 40 ppb, thereby endowing a potential toward practical TEA detection

Rational design of ordered porous SnO2/ZrO2 thin films for fast and selective triethylamine detection with humidity resistance

Atomically thin layers of transition metal dichalcogenides (TMDs) have attracted numerous attentions for innovative sensor application. However, the sensing capability of WSe2-based sensors such as the modulation of the selectivity and sensitivity are still to be optimized. Herein, we report a highly selective and flexible gas sensor based on exfoliated WSe2 nanosheets for detection of trace concentration NO2 under ultraviolet (UV) activation at room temperature (25 °C). The high quality few-layer WSe2 nanosheets are prepared via a simple liquid-phase exfoliation method, and their structure and electrical properties have been comprehensively investigated by various characterizations and gas sensing measurements. Results reveal that the WSe2 nanosheets- based sensor exhibits a bifunctional selectivity, showing high sensitivity to triethylamine without UV illumination and NO2 under UV illumination. Remarkably, an ultralow limit of detection (LOD) of 8 ppb is registered for NO2 detection under UV. Moreover, the gas sensor demonstrates robust flexibility and bendability without altering the sensor response. This work sheds some light on the integration of WSe2 nanosheets into flexible sensor devices with optimized detection performances.

Chengming Lou

Papers

Plasma-induced oxygen vacancies enabled ultrathin ZnO films for highly sensitive detection of triethylamine.

Atomic layer deposition of ZnO on SnO2 nanospheres for enhanced formaldehyde detection

Thin films of tungsten oxide materials for advanced gas sensors

Rational design of ordered porous SnO2/ZrO2 thin films for fast and selective triethylamine detection with humidity resistance

Flexible NO2 sensors based on WSe2 nanosheets with bifunctional selectivity and superior sensitivity under UV activation