Le Duc Toan

Bio: Le Duc Toan is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: Business & Responsivity. The author has an hindex of 1, co-authored 1 publications receiving 135 citations.

Ultrahigh Responsivity in Graphene–ZnO Nanorod Hybrid UV Photodetector

Abstract: Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time-dependent behaviors of hybrid-channel FETs reveal a high sensitivity and selectivity toward the near-UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (RI ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid-channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V Dirac ) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10(10) and 4 × 10(10) per mW, respectively. The maximum values of RI and G infer from the fitted curves of RI and G versus UV intensity are 3 × 10(5) A W(-1) and 10(6) , respectively. Therefore, the hybrid-channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.

Factors Affecting the Efficiency of the Internal Control System, Impact on the Competitiveness of Vietnam Businesses. Case Study in Binh Duong Province

Abstract: The article presents research on the factors affecting the effectiveness of the internal control system, thereby finding out the relationship between the effectiveness of the internal control system and the competitiveness of enterprises. The data was surveyed at 150 enterprises in Binh Duong province and processed through SPSS 20.0 software. The results show that there are 6 factors affecting the effectiveness of the internal control system. The control environment is a factor that strongly influences the effectiveness of internal control. The effectiveness of the internal control system affects the competitiveness of the enterprise. From the research results, the article has proposed some managerial implications for the relevant units.

The physics and chemistry of graphene-on-surfaces

Abstract: Graphene has demonstrated great potential in next-generation electronics due to its unique two-dimensional structure and properties including a zero-gap band structure, high electron mobility, and high electrical and thermal conductivity. The integration of atom-thick graphene into a device always involves its interaction with a supporting substrate by van der Waals forces and other intermolecular forces or even covalent bonding, and this is critical to its real applications. Graphene films on different surfaces are expected to exhibit significant differences in their properties, which lead to changes in their morphology, electronic structure, surface chemistry/physics, and surface/interface states. Therefore, a thorough understanding of the surface/interface properties is of great importance. In this review, we describe the major “graphene-on-surface” structures and examine the roles of their properties and related phenomena in governing the overall performance for specific applications including optoelectronics, surface catalysis, anti-friction and superlubricity, and coatings and composites. Finally, perspectives on the opportunities and challenges of graphene-on-surface systems are discussed.

Zinc oxide ultraviolet photodetectors: rapid progress from conventional to self-powered photodetectors

Abstract: Currently, the development of ultraviolet (UV) photodetectors (PDs) has attracted the attention of the research community because of the vast range of applications of photodetectors in modern society A variety of wide-band gap nanomaterials have been utilized for UV detection to achieve higher photosensitivity Specifically, zinc oxide (ZnO) nanomaterials have attracted significant attention primarily due to their additional properties such as piezo-phototronic and pyro-phototronic effects, which allow the fabrication of high-performance and low power consumption-based UV PDs This article primarily focuses on the recent development of ZnO nanostructure-based UV PDs ranging from nanomaterials to architectural device design A brief overview of the photoresponse characteristics of UV PDs and potential ZnO nanostructures is presented Moreover, the recent development in self-powered PDs and implementation of the piezo-phototronic effect, plasmonic effect and pyro-phototronic effect for performance enhancement is highlighted Finally, the research perspectives and future research direction related to ZnO nanostructures for next-generation UV PDs are summarized

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

Abstract: Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted much attention in the field of optoelectronics due to their tunable bandgaps, strong interaction with light and tremendous capability for developing diverse van der Waals heterostructures (vdWHs) with other materials. Molybdenum disulfide (MoS2) atomic layers which exhibit high carrier mobility and optical transparency are very suitable for developing ultra-broadband photodetectors to be used from surveillance and healthcare to optical communication. This review provides a brief introduction to TMD-based photodetectors, exclusively focused on MoS2-based photodetectors. The current research advances show that the photoresponse of atomic layered MoS2 can be significantly improved by boosting its charge carrier mobility and incident light absorption via forming MoS2 based plasmonic nanostructures, halide perovskites–MoS2 heterostructures, 2D–0D MoS2/quantum dots (QDs) and 2D–2D MoS2 hybrid vdWHs, chemical doping, and surface functionalization of MoS2 atomic layers. By utilizing these different integration strategies, MoS2 hybrid heterostructure-based photodetectors exhibited remarkably high photoresponsivity raging from mA W−1 up to 1010 A W−1, detectivity from 107 to 1015 Jones and a photoresponse time from seconds (s) to nanoseconds (10−9 s), varying by several orders of magnitude from deep-ultraviolet (DUV) to the long-wavelength infrared (LWIR) region. The flexible photodetectors developed from MoS2-based hybrid heterostructures with graphene, carbon nanotubes (CNTs), TMDs, and ZnO are also discussed. In addition, strain-induced and self-powered MoS2 based photodetectors have also been summarized. The factors affecting the figure of merit of a very wide range of MoS2-based photodetectors have been analyzed in terms of their photoresponsivity, detectivity, response speed, and quantum efficiency along with their measurement wavelengths and incident laser power densities. Conclusions and the future direction are also outlined on the development of MoS2 and other 2D TMD-based photodetectors.

All-Printable ZnO Quantum Dots/Graphene van der Waals Heterostructures for Ultrasensitive Detection of Ultraviolet Light

Abstract: In ZnO quantum dot/graphene heterojunction photodetectors, fabricated by printing quantum dots (QDs) directly on the graphene field-effect transistor (GFET) channel, the combination of the strong quantum confinement in ZnO QDs and the high charge mobility in graphene allows extraordinary quantum efficiency (or photoconductive gain) in visible-blind ultraviolet (UV) detection. Key to the high performance is a clean van der Waals interface to facilitate an efficient charge transfer from ZnO QDs to graphene upon UV illumination. Here, we report a robust ZnO QD surface activation process and demonstrate that a transition from zero to extraordinarily high photoresponsivity of 9.9 × 108 A/W and a photoconductive gain of 3.6 × 109 can be obtained in ZnO QDs/GFET heterojunction photodetectors, as the ZnO QDs surface is systematically engineered using this process. The high figure-of-merit UV detectivity D* in exceeding 1 × 1014 Jones represents more than 1 order of magnitude improvement over the best reported previously on ZnO nanostructure-based UV detectors. This result not only sheds light on the critical role of the van der Waals interface in affecting the optoelectronic process in ZnO QDs/GFET heterojunction photodetectors but also demonstrates the viability of printing quantum devices of high performance and low cost.