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In this work, the effects of noble metal (Au and Pt) incorporation into black phosphorus (BP) were first investigated. Several important sensing results were observed as a result of the incorporation of Au or Pt into the BP surface. First, prior to incorporation, pristine BP only detects paramagnetic molecules, e.g., NO2 or NO. However, after incorporation with Pt, low concentration of H2 can be detected with high response amplitude. Furthermore, the H2 sensing performance reported in this study was found to be most sensitive as compared with that observed for a previously reported 2D H2 gas sensor. The second significant result was obtained after incorporation with Au, where the work function of BP was varied by the transfer of electrons from the Au nanoparticles, thereby inducing the effects of n-doping on p-type pristine BP. Accordingly, the response behavior of BP to oxidizing gas changed from a p-type response (negative resistance variation) to an n-type response (positive resistance variation). In addition, a highly stable, low noise baseline was achieved in the Au-incorporated BP channel material. Finally, because of the high chemical and ambient stability of the Au or Pt, the synthesized Au- or Pt-incorporated BP systems exhibited long-term stability, which is difficult to achieve when using other doping strategies. Overall, a significant step was taken toward the efficient control of the electrical/chemical sensitization level of BP and significant enhancement of superior chemical sensing performance of BP. [ABSTRACT FROM AUTHOR]

The development of high-performance volatile organic compound (VOC) sensor based on a p-type metal oxide semiconductor (MOS) is one of the important topics in gas sensor research because of its unique sensing characteristics, namely, rapid recovery kinetics, low temperature dependence, high humidity or thermal stability, and high potential for p-n junction applications. Despite intensive efforts made in this area, the applications of such sensors are hindered because of drawbacks related to the low sensitivity and slow response or long recovery time of p-type MOSs. In this study, the VOC sensing performance of a p-type MOS was significantly enhanced by forming a patterned p-type polycrystalline MOS with an ultrathin, high-aspect-ratio (∼25) structure (∼14 nm thickness) composed of ultrasmall grains (∼5 nm size). A high-resolution polycrystalline p-type MOS nanowire array with a grain size of ∼5 nm was fabricated by secondary sputtering via Ar+ bombardment. Various p-type nanowire arrays of CuO, NiO, and Cr2O3 were easily fabricated by simply changing the sputtering material. The VOC sensor thus fabricated exhibited higher sensitivity (ΔR/Ra = 30 at 1 ppm hexane using NiO channels), as well as faster response or shorter recovery time (∼30 s) than that of previously reported p-type MOS sensors. This result is attributed to the high resolution and small grain size of p-type MOSs, which lead to overlap of fully charged zones; as a result, electrical properties are predominantly determined by surface states. Our new approach may be used as a route for producing high-resolution MOSs with particle sizes of ∼5 nm within a highly ordered, tall nanowire array structure. [ABSTRACT FROM AUTHOR]

Enhancement of the fluorescence intensityof quantum dot (QD)–polymer nanocomposite arrays is an importantissue in QD studies because of the significant reduction of fluorescencesignals of such arrays due to nonradiative processes in densely packedpolymer chains in solid films. In this study, we enhance the fluorescenceintensity of such arrays without significantly reducing their opticaltransparency. Enhanced fluorescence is achieved by hybridizing ultrathinplasmonic Au nanowalls onto the sidewalls of the arrays via single-steppatterning and hybridization. The plasmonic Au nanowall induces metal-enhancedfluorescence, resulting in a maximum 7-fold enhancement of the fluorescencesignals. We also prepare QD nanostructures of various shapes and sizesby controlling the dry etching time. In the near future, this facileapproach can be used for fluorescence enhancement of colloidal QDswith plasmonic hybrid structures. Such structures can be used as opticalsubstrates for imaging applications and for fabrication of QD–LEDdevices. [ABSTRACT FROM AUTHOR]

Developing hydrogen (H2) sensors with a high sensitivity, rapid response, long-term stability, and high throughput is one of the critical issues in energy and environmental technology [Hübert et al. Sens. Actuators, B 2011, 157, 329]. To date, H2 sensors have been mainly developed using palladium (Pd) as the channel material because of its high selectivity and strong affinity to the H2 molecule [(Xu et al. Appl. Phys. Lett. 2005, 86, 203104), (Offermans et al. Appl. Phys. Lett. 2009, 94, 223110), (Yang et al. Nano Lett. 2009, 9, 2177), (Yang et al. ACS Nano 2010, 4, 5233), and (Zou et al. Chem. Commun. 2012, 48, 1033)]. Despite significant progress in this area, Pd based H2 sensors suffer from fractures on their structure due to hydrogen adsorption induced volumetric swelling during the α → β phase transition, leading to poor long-term stability and reliability [(Favier et al. Science 2001, 293, 2227), (Walter et al. Microelectron. Eng. 2002, 61-62, 555), and (Walter et al. Anal. Chem. 2002, 74, 1546)]. In this study, we developed a platinum (Pt) nanostructure based H2 sensor that avoids the stability limitations of Pd based sensors. This sensor exhibited an excellent sensing performance, low limit of detection (LOD, 1 ppm), reproducibility, and good recovery behavior at room temperature. This Pt based H2 sensor relies on a highly periodic, small cross sectional dimension (10-40 nm) and a well-defined configuration of Pt nanowire arrays over a large area. The resistance of the Pt nanowire arrays significantly decreased upon exposure to H2 due to reduced electron scattering in the cross section of the hydrogen adsorbed Pt nanowires, as compared to the oxygen terminated original state. Therefore, these well-defined Pt nanowire arrays prepared using advanced lithographic techniques can facilitate the production of high performance H2 sensors. [ABSTRACT FROM AUTHOR]