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1.
Small ; 16(1): e1906205, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31793750

RESUMO

Plasmonic nanolasers based on wide bandgap semiconductors are presently attracting immense research interests due to the breaking in light diffraction limit and subwavelength mode operation with fast dynamics. However, these plasmonic nanolasers have so far been mostly realized in the visible light ranges, or most are still under optical excitation pumping. In this work, III-nitride-based plasmonic nanolasers emitting from the green to the deep-ultraviolet (UV) region by energetic electron beam injection are reported, and a threshold as low as 8 kW cm-2 is achieved. A fast decay time as short as 123 ps is collected, indicating a strong coupling between excitons and surface plasmon. Both the spatial and temporal coherences are observed, which provide a solid evidence for exciton-plasmon coupled polariton lasing. Consequently, the achievements in III-nitride-based plasmonic nanolaser devices represent a significant step toward practical applications for biological technology, computing systems, and on-chip optical communication.

2.
Glob Chall ; 3(10): 1900040, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31592336

RESUMO

It has long been an aspirational goal to create artificial evaporators that allow omnidirectional energy absorptance, adequate water supply, and fast vapor transportation, replicating the feat of plant transpiration, to solve the global water crisis. This work reveals that magnolia fruits, as a kind of tree-like living organism, can be outstanding 3D tree-like evaporators through a simple carbonization process. The arterial pumping, branched diffusion, and confined evaporation are achieved by the "trunk," "branches," and "leaves," respectively, of the mini tree. The mini tree possesses omnidirectional high light absorptance with minimized heat loss and gains energy from the environment. Water confined in the fruit possesses reduced vaporization enthalpy and transports quickly following the Murray's law. A record-high vapor generation rate of 1.22 kg m-2 h-1 in dark and 3.15 kg m-2 h-1 under 1 sun illumination is achieved under the assistance of the gully-like furry surface. The "absorption of nutrients" enables the fruit to recover valuable heavy metals as well as to produce clean water from wastewater efficiently. These findings not only reveal the hidden talent of magnolia fruits as cheap materials for vapor generation but also inspire future development of high-performance, full-time, and all-weather vapor generation and water treatment devices.

3.
Nanotechnology ; 30(49): 495204, 2019 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-31491775

RESUMO

Metallic cavities show substantial advantages in light confinement, providing opportunities to modulate the optical resonances and absorption. Here, we report on the configuration of horizontally aligned ZnO-nanowires-based metallic cavity ensemble with a light to dark current ratio of ∼1000. An enhanced polarization photodetection ratio of transverse electric (TE) to transverse magnetic (TM) was experimentally observed compared to the single ZnO nanowire photodetector. Finite difference time domain simulation was performed on the metallic cavities, showing the distinct resonance behaviors under TE and TM light. The confinement by the multi-reflection and optical resonances between the metallic claddings contribute to the high anisotropy ratio. Furthermore, the polarized light absorption in the metallic cavity was studied as well as in the naked nanowire, which reveal a significant dependence on the cavity diameter and wavelength. For the metallic cavities, the absorption ratio of TE to TM show an enhanced value in the range of 300-500 nm wavelength and 85-150 diameter and a reversed value in the range of 400-500 nm wavelength and 17-50 diameter. While for the naked nanowires, the ratio show an apparently opposite value in these two regions. The presented metallic cavities demonstrate a specific paradigm of optical engineering in nanoscale and potentially helps the development of optoelectronic devices.

4.
Sci Rep ; 9(1): 8796, 2019 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-31217468

RESUMO

Implementing selective-area p-type doping through ion implantation is the most attractive choice for the fabrication of GaN-based bipolar power and related devices. However, the low activation efficiency of magnesium (Mg) ions and the inevitable surface decomposition during high-temperature activation annealing process still limit the use of this technology for GaN-based devices. In this work, we demonstrate successful p-type doping of GaN using protective coatings during a Mg ion implantation and thermal activation process. The p-type conduction of GaN is evidenced by the positive Seebeck coefficient obtained during thermopower characterization. On this basis, a GaN p-i-n diode is fabricated, exhibiting distinct rectifying characteristics with a turn-on voltage of 3 V with an acceptable reverse breakdown voltage of 300 V. Electron beam induced current (EBIC) and electroluminescent (EL) results further confirm the formation of p-type region due to Mg ion implantation and subsequent thermal activation. This repeatable and uniform manufacturing process can be implemented in mass production of GaN devices for versatile power and optoelectronic applications.

5.
Nanoscale Res Lett ; 14(1): 170, 2019 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31115700

RESUMO

Deep ultraviolet AlGaN-based nanorod (NR) arrays were fabricated by nanoimprint lithography and top-down dry etching techniques from a fully structural LED wafer. Highly ordered periodic structural properties and morphology were confirmed by scanning electron microscopy and transmission electron microscopy. Compared with planar samples, cathodoluminescence measurement revealed that NR samples showed 1.92-fold light extraction efficiency (LEE) enhancement and a 12.2-fold internal quantum efficiency (IQE) enhancement for the emission from multi-quantum wells at approximately 277 nm. The LEE enhancement can be attributed to the well-fabricated nanostructured interface between the air and the epilayers. Moreover, the reduced quantum-confined stark effect accounted for the great enhancement in IQE.

6.
ACS Appl Mater Interfaces ; 11(23): 20956-20964, 2019 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-31046216

RESUMO

We systematically study the device characteristics of the monolayer (ML) blue phosphorene metal-oxide semiconductor field-effect transistors (MOSFETs) by using ab initio quantum-transport simulations. The ML blue phosphorene MOSFETs show superior performances with ultrashort-channel length. We first predict the ultrascaled ML blue phosphorene MOSFETs with proper doping concentration and underlap structures are compliant with the high-performance (HP) and low-power (LP) requirements of the International Technology Roadmap for Semiconductors in the next decade in the aspects of the on-state current, delay time, and power dissipation. Encouragingly, the performances of the ML blue phosphorene MOSFETs are superior to that of the MOSFETs based on arsenene, antimonene, InSe, etc. in terms of the on-state current at similar device size. We also consider the electron-phonon scattering in 10.2 nm gate ML blue phosphorene MOSFET. It is found that the on-state current with the scattering of the blue phosphorene device is degraded by 25.4 and 23.6% for HP and LP applications, which can also fulfill the HP and LP application target. Therefore, we can deduce that ML blue phosphorene is an alternative channel material to silicon for ultrascaled FETs if the large-scale and high-quality blue phosphorene can be achieved.

7.
Opt Express ; 27(4): 4781-4788, 2019 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-30876088

RESUMO

Temperature-dependent ultraviolet (UV) Raman scattering from AlGaN/GaN heterostructure is investigated. Compared to the visible Raman spectrum, four new peaks at 600, 700, 780, and 840 cm-1 are observed in the UV Raman spectrum. The peak at 780 cm-1 is from the AlGaN A1(LO) mode. According to the calculated dispersion relations of the interface phonon modes in the AlGaN/GaN heterostructure, the peaks at 600 and 840 cm-1 correspond to interface phonon modes. Meanwhile, the peak at 700 cm-1 is attributed to the disorder-active mode near the 2DEG interface. Due to the near-resonant enhancement effect, the intensities of the GaN A1(LO) mode, interface phonon modes, disorder active mode and the AlGaN A1(LO) mode exhibit different temperature dependence. Furthermore, the frequencies of the interface phonon modes and the disorder active mode show anomalous temperature dependence, which can be attributed to the strong built-in electric field near the 2DEG interface.

8.
ACS Appl Mater Interfaces ; 11(7): 7131-7137, 2019 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-30676013

RESUMO

To suppress noise from full daylight background or environmental radiation, a spectrally selective solar-blind photodetector is widely required in many applications that need detection of light within a specific spectral range. Here, we present highly narrow-band solar-blind photodetectors by light polarization engineering of the anisotropic transitions in ß-Ga2O3 single crystals. The polarized transmittance characteristics reveal that direct transitions from valance subbands to the conduction band minimum are tuned between 4.53 and 4.76 eV for the light polarized E// c and E// b. The polarization-dependent photoresponsivity verifies that the order of fundamental band-to-band transitions obeys well the selection rules in terms of the valence-band splitting in the ß-Ga2O3 monoclinic crystal band structure. By combining an orthogonally aligned identical ß-Ga2O3 (100) single crystal filter with a detector measured at a chopper frequency of 17 Hz, a highly narrow-band detection is produced with a peak responsivity of 0.23 A/W at 262 nm, an EQE of 110%, a bandwidth of 10 nm, a light rejection ratio over 800, and a response time of 0.86 ms. This provides a new paradigm for a narrow-band solar-blind photodetector with broad applications where background noise emission needs to be suppressed.

9.
Nanotechnology ; 30(6): 065202, 2019 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-30523917

RESUMO

ZnO nanowire photodetectors have attracted much attention due to their excellent optoelectronic performance. However, operating speed remains a challenge, and scalability is also impeded by uncontrolled transfer methods and sophisticated fabrication process. In this paper, we have fabricated an excellent ZnO nanobridge ultraviolet photodetector array by using a simple one-step method. The faster photoresponse speed and a broader response wavelength (from UV to visible range) have been achieved by constructing a type-II ZnO/rubrene heterointerface. Performance enhancement is believed to arise from the well-matching band alignment and highly efficient separation of photogenerated electron-hole pairs at the heterointerface. Our strategy provides a simple and promising route to develop cost-effective and highly sensitive UV-vis photodetectors.

10.
Nanoscale ; 10(46): 21936-21943, 2018 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-30444231

RESUMO

The sensing properties of an α phase black phosphorus carbide (P2C2) monolayer for the adsorption of CO2, H2, H2O, N2, H2S, NH3, O2 and NO2 gases are theoretically investigated using first-principles calculations. We calculate the adsorption energy, equilibrium distance, Mulliken charge transfer, electron localization function, and work function to explore whether P2C2 is suitable for detecting NO2 gas. The results demonstrate that the P2C2 monolayer is highly sensitive and selective to NO2 gas molecules with robust adsorption energy and superior charge transfer due to the existence of strong orbital hybridization between the NO2 molecule and monolayer P2C2. In addition, the results of the work function calculations indicate that field effect transistor type NO2 gas sensors based on P2C2 monolayers are also feasible. Furthermore, the current-voltage curves reveal that the adsorption of NO2 can greatly modify the resistance of the P2C2 monolayer. Our results show that gas sensors based on P2C2 monolayers could be better than those based on black phosphorene (BP) for detecting NO2 molecules in an air mixture. In addition, the recovery time of the P2C2 sensor at T = 300 K was estimated to be short (and even shorter at higher temperatures) for NO2 which satisfies the demands for sustainable use.

11.
Sci Rep ; 8(1): 15464, 2018 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-30337709

RESUMO

In recent years, various kinds of ZnO-based core@shell nanomaterials have been paid much attention due to their widespread applications in the fields of physics, chemistry and energy conversion. In this work, the electronic and optical properties of a new type of ZnO-based one-dimensional core@shell nanostructure, which is composed of inner ZnO nanowire and outer carbon nanotube (CNT), is calculated based on the first-principles density functional theory (DFT). Calculation results suggest that the ZnO nanowire encapsulated in (9, 9)-CNT is the most stable structure from the view of formation energy. The interaction between the inner ZnO nanowire and the outer (9, 9) CNT belongs to a weak van der Waals type. The complex structure is found to possess metallicity for the outer (9, 9) CNT and maintain the wide band gap nature for the inner ZnO nanowire. Under the different external strains, the charge redistribution between inner ZnO nanowire and outer CNT caused by electron tunneling leads to the shift of Dirac point and the band narrowing of inner ZnO nanowire. The inner ZnO nanowire only has light absorption in the UV region, which is consistent with its optical property originating from its wide bandgap nature.

12.
ACS Nano ; 12(7): 7327-7334, 2018 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-29894159

RESUMO

The ability to manipulate light-matter interaction in semiconducting nanostructures is fascinating for implementing functionalities in advanced optoelectronic devices. Here, we report the tailoring of radiative emissions in a ZnTe/ZnTe:O/ZnO core-shell single nanowire coupled with a one-dimensional aluminum bowtie antenna array. The plasmonic antenna enables changes in the excitation and emission processes, leading to an obvious enhancement of near band edge emission (2.2 eV) and subgap excitonic emission (1.7 eV) bound to intermediate band states in a ZnTe/ZnTe:O/ZnO core-shell nanowire as well as surface-enhanced Raman scattering at room temperature. The increase of emission decay rate in the nanowire/antenna system, probed by time-resolved photoluminescence spectroscopy, yields an observable enhancement of quantum efficiency induced by local surface plasmon resonance. Electromagnetic simulations agree well with the experimental observations, revealing a combined effect of enhanced electric near-field intensity and the improvement of quantum efficiency in the ZnTe/ZnTe:O/ZnO nanowire/antenna system. The capability of tailoring light-matter interaction in low-efficient emitters may provide an alternative platform for designing advanced optoelectronic and sensing devices with precisely controlled response.

13.
ACS Appl Mater Interfaces ; 10(26): 22513-22519, 2018 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-29879837

RESUMO

Organic field-effect transistors (OFETs) are the most fundamental device units in organic electronics. Interface engineering at the semiconductor/dielectric interface is an effective approach for improving device performance, particularly for enhancing charge transport in conducting channels. Here, we report flat-lying molecular monolayers that exhibit good uniformity and high crystallinity at the semiconductor/dielectric interface, deposited through slow thermal evaporation. Transistor devices achieve high carrier mobility up to 2.80 cm2 V-1 s-1, which represents a remarkably improvement in device performance compared with devices that are completely based on fast-evaporated films. Interfacial flat-lying monolayers benefit charge transport by suppressing the polarization of dipoles and narrowing the broadening of trap density of states. Our work provides a promising strategy for enhancing the performance of OFETs by using interfacial flat-lying molecular monolayers.

14.
Sensors (Basel) ; 18(5)2018 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-29695112

RESUMO

The AlInN/GaN high-electron-mobility-transistor (HEMT) indicates better performances compared with the traditional AlGaN/GaN HEMTs. The present work investigated the pH sensor functionality of an analogous HEMT AlInN/GaN device with an open gate. It was shown that the Al0.83In0.17N/GaN device demonstrates excellent pH sense functionality in aqueous solutions, exhibiting higher sensitivity (−30.83 μA/pH for AlInN/GaN and −4.6 μA/pH for AlGaN/GaN) and a faster response time, lower degradation and good stability with respect to the AlGaN/GaN device, which is attributed to higher two-dimensional electron gas (2DEG) density and a thinner barrier layer in Al0.83In0.17N/GaN owning to lattice matching. On the other hand, the open gate geometry was found to affect the pH sensitivity obviously. Properly increasing the width and shortening the length of the open gate area could enhance the sensitivity. However, when the open gate width is too larger or too small, the pH sensitivity would be suppressed conversely. Designing an optimal ratio of the width to the length is important for achieving high sensitivity. This work suggests that the AlInN/GaN-based 2DEG carrier modulated devices would be good candidates for high-performance pH sensors and other related applications.

15.
J Phys Chem Lett ; 9(6): 1318-1323, 2018 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-29493240

RESUMO

In organic field-effect transistors, the first few molecular layers at the semiconductor/dielectric interface are regarded as the active channel for charge transport; thus, great efforts have been devoted to the modification and optimization of molecular packing at such interfaces. Here, we report organic monolayers with large-area uniformity and high crystallinity deposited by an antisolvent-assisted spin-coating method acting as the templating layers between the dielectric and thermally evaporated semiconducting layers. The predeposited crystalline monolayers significantly enhance the film crystallinity of upper layers and the overall performance of transistors using these hybrid-deposited semiconducting films, showing a high carrier mobility up to 11.3 cm2 V-1 s-1. Additionally, patterned transistor arrays composed of the templating monolayers are fabricated, yielding an average mobility of 7.7 cm2 V-1 s-1. This work demonstrates a promising method for fabricating low-cost, high-performance, and large-area organic electronics.

16.
Nanotechnology ; 29(11): 115204, 2018 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-29345248

RESUMO

Recently, ZnO nanowire field effect transistors (FETs) have received renewed interest due to their extraordinary low dimensionality and high sensitivity to external chemical environments and illumination conditions. These prominent properties have promising potential in nanoscale chemical and photo-sensors. In this article, we have fabricated ZnO nanowire FETs and have found hysteresis behavior in their transfer characteristics. The mechanism and dynamics of the hysteresis phenomena have been investigated in detail by varying the sweeping rate and range of the gate bias with and without light irradiation. Significantly, light irradiation is of great importance on charge trapping by regulating adsorption and desorption of oxygen at the interface of ZnO/SiO2. Carriers excited by light irradiation can dramatically promote trapping/detrapping processes. With the assistance of light illumination, we have demonstrated a photon-assisted nonvolatile memory which employs the ZnO nanowire FET. The device exhibits reliable programming/erasing operations and a large on/off ratio. The proposed proto-type memory has thus provided a possible novel path for creating a memory functionality to other low-dimensional material systems.

17.
Opt Express ; 26(24): 31965-31975, 2018 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-30650775

RESUMO

Wide-bandgap inorganic semiconductors based ultraviolet lasers bring versatile applications with significant advantages including low-power consumption, high-power output, robustness and long-term operation stability. However, flexible membrane lasers remain challenging predominantly due to the need for a lattice matched supporting substrate. Here, we develop a simple laser liftoff process to make freestanding single crystalline ZnO membranes that demonstrate low-threshold ultraviolet stimulated emissions together with large sized dimension (> 2 mm), ultralow-weight (m/A<15 g/m2) and excellent flexibility. The 2.6 µm-thick crack-free ZnO membrane exhibits well-retained single crystallinity and enhanced excitonic emissions while the defect-related emissions are completely suppressed. The inelastic exciton-exciton scattering stimulated emissions with increased spontaneous emission rate is obtained with a reduced threshold of 0.35 MW/cm2 in the ZnO membrane transferred onto a flexible polyethylene naphthalate substrate. Theoretical simulations reveal that it is a synergetic effect of the increased quantum efficiency via Purcell effect and the improved optical gain due to vertical directional waveguiding of the membrane, which functions as a Fabry-Perot photonic resonator due to the refractive index contrast at ZnO-air boundaries. With simple architecture, efficient exciton recombination and easy fusion with waveguide system, the ZnO membranes provide an alternative platform to develop compact low-threshold ultraviolet excitonic lasers.

18.
Sci Rep ; 7(1): 17695, 2017 12 18.
Artigo em Inglês | MEDLINE | ID: mdl-29255145

RESUMO

We systematically synthesized mixed-halide hybrid perovskite CH3NH3Pb(BrxI1-x)3 (0 ≤ x ≤ 1) crystals in the full composition range by a solvothermal method. The as-synthesized crystals retained cuboid shapes, and the crystalline structure transitioned from the tetragonal phase to the cubic phase with an increasing Br-ion content. The photoluminescence (PL) of CH3NH3Pb(BrxI1-x)3 crystals exhibited a continuous variation from red (768 nm) to green (549 nm) with increasing the volume ratio of HBr (VHBr%), corresponding to a variation in the bandgap from 1.61 eV to 2.26 eV. Moreover, the bandgap of the crystals changed nonlinearly as a quadratic function of x with a bowing parameter of 0.53 eV. Notably, the CH3NH3Pb(BrxI1-x)3 (0.4 ≤ x ≤ 0.6) crystals exhibited obvious phase separation by prolonged illumination. The cause for the phase separation was attributed to the formation of small clusters enriched in lower-band-gap, iodide-rich and higher-band-gap, bromide-rich domains, which induced localized strain to promote halide phase separation. We also clarified the relationship between the PL features and the band structures of the crystals.

19.
ACS Appl Mater Interfaces ; 9(42): 36997-37005, 2017 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-28975779

RESUMO

The metastable α-phase Ga2O3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga2O3 remains challenging. To this end, single crystalline α-Ga2O3 epilayers are achieved on nonpolar ZnO (112̅0) substrates for the first time and a high performance Au/α-Ga2O3/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 103 and a detectivity of 9.66 × 1012 cm Hz1/2 W-1. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W-1 at -5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga2O3 and Ga2O3/ZnO heterointerfaces. The device also allows avalanche multiplication processes initiated by pure electron and hole injections under different illumination conditions. High avalanche gains over 103 and a low ionization coefficient ratio of electrons and holes are yielded, leading to a total gain over 105 and a high responsivity of 1.10 × 104 A W-1. Such avalanche heterostructures with ultrahigh gains and bias-tunable UV detecting functionality hold promise for developing high performance solar-blind photodetectors.

20.
Sci Rep ; 7(1): 7830, 2017 08 10.
Artigo em Inglês | MEDLINE | ID: mdl-28798302

RESUMO

Two dimensional (2D) molecular crystals have attracted considerable attention because of their promising potential in electrical device applications, such as high-performance field-effect transistors (FETs). However, such devices demand high voltages, thereby considerably increasing power consumption. This study demonstrates the fabrication of organic FETs based on 2D crystalline films as semiconducting channels. The application of high-κ oxide dielectrics allows the transistors run under a low operating voltage (-4 V). The devices exhibited a high electrical performance with a carrier mobility up to 9.8 cm2 V-1 s-1. Further results show that the AlOx layer is beneficial to the charge transport at the conducting channels of FETs. Thus, the device strategy presented in this work is favorable for 2D molecular crystal-based transistors that can operate under low voltages.

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