Single ZnO Research Articles

Optical microcavity based on a single ZnO microwire grown on Si(111) substrate by catalyst-free mist chemical vapor deposition

Optical microcavity based on a single ZnO microwire grown on Si(111) substrate by catalyst-free mist chemical vapor deposition

Modulation of bandgap and electrical conductivity in europium doped single ZnO nanorod device

We investigate the effect of europium doping on the optical properties and electrical conductivity of hydrothermally grown ZnO nanorods. The widening of optical bandgap with europium doping occurs because of the Burstein-Moss effect upto 0.8% and bandgap renormalization is observed at higher concentration. The temperature-dependent resistivity measurements of the individual nanorods reveal that the intrinsic electrical conductivity is a combination of thermally activated and nearest-neighbor hopping conduction processes at high and low-temperature regimes, respectively. We can successfully correlate that the modulation of carrier concentration in the defect D and D− bands can tune both bandgap and electron transport in Eu doped ZnO nanorods.

Production of ZnO-CoOx-CeO2 nanocomposites and their dye removal performance from wastewater by adsorption-photocatalysis

In this paper, a new series of ZnO-CoOx-CeO2 nanocomposites were prepared by impregnation method. The composite nano-catalysts were characterized by SEM, TEM, EDS, XRD, FT-IR, XPS, BET and Zeta potential. The removal rate of degraded CR was used to evaluate the adsorption performance and adsorption-photocatalysis synergistic performance of ZnO-CoOx-CeO2 composites. The results show that ZnO-CoOx-CeO2 nanocomposites have the best adsorption activity and photocatalytic oxidation activity than single metal oxide ZnO and binary metal oxide ZnO-Co3O4. In addition, the adsorption-photocatalysis synergistic process showed better activity than the single adsorption process. Then the effects of operation parameters such as catalyst calcination temperature, initial pH and catalyst dosage on the decomposition efficiency of the catalyst were investigated. Under the optimized conditions, when the concentration of catalyst is 1 g L−1, the initial pH is in the range of 6–7, the roasting temperature is 450 °C and the reaction time is 65 min, the removal rate of CR can reach more than 98.8 %. The stability of the prepared catalyst was tested, and it was found that the sample maintained almost the same removal ability after 4 cycles.

ZnO Nanowire-Based Piezoelectric Nanogenerator Device Performance Tests

Over the past two decades, the quick development of wireless sensor networks has required the sensor nodes being self-powered. Pushed by this goal, in this work, we demonstrated a ZnO nanowire-array-based piezoelectric nanogenerator (NG) prototype, which can convert mechanical energy into electricity. High-quality single crystalline ZnO nanowires, having an aspect ratio of about 15, grown on gold-coated silicon substrate, were obtained by using a low-cost and low-temperature hydrothermal method. The NG-device fabrication process has been presented in detail, and the NG’s performance has been tested in both compression and vibration modes. Peak power of 1.71 µW was observed across an optimal load resistance of 5 MΩ for the ZnO nanowires-based NG, with an effective area of 0.7 cm2, which was excited in compression mode, at 9 Hz, corresponding to ~38.47 mW/cm3 volume-normalized power output. The measured voltage between the top and bottom electrodes was 5.6 V. In vibration mode, at 500 Hz, the same device showed a potential of 1.4 V peak-to-peak value and an instantaneous power of 0.04 μW, corresponding to an output power density of ~0.9 mW/cm3.

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer.

The widely used ZnO quantum dots (QDs) as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) have one drawback. That the balancing of electrons and holes has not been effectively exploited due to the low hole blocking potential difference between the valence band (VB) (6.38 eV) of ZnO ETL and (6.3 eV) of CdSe/ZnS QDs. In this study, ZnO QDs chemically reacted with capping ligands of oleic acid (OA) to decrease the work function of 3.15 eV for ZnO QDs to 2.72~3.08 eV for the ZnO-OA QDs due to the charge transfer from ZnO to OA ligands and improve the efficiency for hole blocking as the VB was increased up to 7.22~7.23 eV. Compared to the QLEDs with a single ZnO QDs ETL, the ZnO-OA/ZnO QDs double ETLs optimize the energy level alignment between ZnO QDs and CdSe/ZnS QDs but also make the surface roughness of ZnO QDs smoother. The optimized glass/ITO/PEDOT:PSS/PVK//CdSe/ZnS//ZnO-OA/ZnO/Ag QLEDs enhances the maximum luminance by 5~9% and current efficiency by 16~35% over the QLEDs with a single ZnO QDs ETL, which can be explained in terms of trap-charge limited current (TCLC) and the Fowler-Nordheim (F-N) tunneling conduction mechanism.

Improved performance of near UV-blue n-ZnO/p-GaN heterostructure LED with an AlN electron blocking layer

High quality single crystalline n-type ZnO films, with a thickness of 200 nm, were grown on top of AlN/GaN layers under 25 W, 50 W and 100 W sputtering powers. The AlN and p-type GaN layers were deposited by metalorganic chemical vapor deposition (MOCVD). From X-ray diffraction measurements, the samples exhibited the (000l) peaks corresponding to both ZnO, GaN and AlN monocrystalline layers. As the sputtering power was increased, the ZnO grain size increased and the dislocation density decreased. This result is supported by a reduction of the rms values obtained on the ZnO layers from Atomic Force Microscopy (AFM) results. In addition, photoluminescence peaks of ZnO at 372 nm, 375 nm and 380 nm were seen as dependent on the sputtering power. We have used an AlN electron blocking layer between ZnO and GaN films to improve the electroluminescence from the n-ZnO side. Room temperature electroluminescence (EL) of the LEDs demonstrated near UV-blue emission consisting of predominating peaks centred at 405 nm, 390 nm and 380 nm for the device with ZnO deposited at 25 W, 50 W and 100 W sputtering powers, respectively. Moreover, the I-V curves of the LEDs showed a rectifying behavior with 6.8 V, 6.4 V, 5.2 V threshold voltages for 25 W, 50 W and 100 W values.

Synthesis of high photoreactive flower-like ZnO nanoneedles assembly with exposed nonpolar {1010} facets oriented by carbon spheres

In this work, carbon spheres (CSs) derived from glucose by simple eco-friendly process were used to create a multiphase environment for precipitation reaction to obtain flower-like C-doped ZnO (C-ZnO) nanoneedles assembly. It was found that the presence of carbon spheres can affect the crystal orientation and morphology of ZnO. When the additive amount of carbon spheres was 13 wt%, one-dimensional (1D) needle-like single crystal C-doped ZnO were obtained, which exposed with higher proportion of nonpolar {1010} facets (51%) than that of pristine ZnO (46%), and C-Zn and C-O-Zn bonds were formed. Compared with pristine ZnO prepared by direct precipitation method (ZnO-DPM) without carbon spheres, carbon doped ZnO exhibited higher light absorption ability and smaller band gap width due to the formation of surface defects. The photocatalytic degradation rate of methyl orange over 13 %C-ZnO was 99.98% for 3 h under the irradiation of UV lamp (15 W), almost 1.3 times higher than that of pristine ZnO-DPM. Even after repeating use for 3 times, the degradation rate of methyl orange can be kept as high as 99%. The present study offers a new preparation method for high photoreactive ZnO with exposed nonpolar {1010} facets by precipitation reaction.

Resonant defect recombination-localized surface plasmon energy transfer and exciton dominated fluorescence in ZnO-Au-ZnO multi-interfaced heteronanocrystals.

The semiconductor-metal heteronanocrystals (HNCs) that possess a perfect epitaxial interface can accommodate novel and interesting physical phenomena owing to the strong interaction and coupling between the semiconductor excitons and metal plasmons at the interface. Here, we fabricate the pyramidal ZnO-Au HNCs and study their unique photophysical properties. Several Au nanospheres are perfectly epitaxially bound with a single ZnO NC owing to the small lattice mismatch between them and there are also ZnO-Au-ZnO sandwiched HNCs. There is a strong coupling between the green defect-associated recombination in the ZnO NC and the localized surface plasmon resonance (LSPR) of the Au nanosphere at the interface of the HNC. This leads to resonant defect recombination-LSPR energy transfer and resultant nearly complete quenching of the green defect luminescence of the ZnO NCs in the HNCs, leaving only the UV exciton luminescence. The lifetimes of both the green and UV emission bands decrease significantly in the ZnO-Au HNCs relative to that of the pure ZnO NCs owing to the combined effect of resonance energy transfer and surface plasmon enhanced radiative transition. The exponent of the luminescence intensity-excitation intensity power function for the green emission band is remarkably smaller than unity, and this suggests that the involved defects have an intermediate concentration.

Switch type PANI/ZnO core-shell microwire heterojunction for UV photodetection

In this study, single crystal ZnO microwires (MW) with size of ∼5.4 mm × 30 μm are prepared through a chemical vapor deposition technique at high temperature (1200 °C). Subsequently, p-type conducting polyaniline (PANI) polymers with different conductivities are densely coated on part of the ZnO MW to construct organic/inorganic core-shell heterojunction photodetectors. The hetero-diodes reach an extremely high rectification ratio (I +3V /I -3V ) of 749230, and a maximum rejection ratio (I 350nm /I dark ) of 3556 (at -3 V), indicating great potential as rectified switches. All the heterojunction devices exhibit strong response to ultraviolet (UV) radiation with high response speed. Moreover, the obvious photovoltaic behavior can also be obtained, allowing the device to operate as an independent and stable unit without externally supplied power. Under 0 V bias voltage, the self-powered photodetector shows a maximum responsivity of 0.56 mA W −1 and a rapid response speed of 0.11 ms/1.45 ms (rise time/decay time). Finally, a finite difference time domain (FDTD) simulation is performed to further demonstrate the interaction mechanism between the incident light field and the hexagonal cavity, which strongly supports the enhancement of the light absorption in whispering-gallery-mode resonator.

Plasmonic enhanced high brightness blue micro-light-emitting devices

Brightness blue micro-light-emitting devices (Micro-LED) play an important role in display and optical communication fields. However, optical loss often occurs in Micro-LEDs, thus preventing the brightness. In this article, a single ZnO microwire (MW) was used to prepare the n-ZnO MW/p-GaN LED, and Ag nanowires were used to fabricate an enhanced plasmonic Micro-LED. Our results showed that the devices presented a typical bule electroluminescence (EL) spectrum and it was enhanced 10 times after the Ag nanowires were bonded. The mechanism of the enhancement was analyzed by theoretical calculation and time resolved photoluminescence (TRPL) results. The work provides a new strategy for the fabrication and enhancement of Micro-LEDs.

Bidirectional Photoresponse in Perovskite‐ZnO Heterostructure for Fully Optical‐Controlled Artificial Synapse

AbstractCompared with electrical synapses, optoelectronic synapses exhibit great potential for ultrafast computing and wireless communication in neuromorphic hardware with advantages of low crosstalk, high bandwidth, and low power consumption. However, due to the unidirectional photoresponse in most of optoelectronic synapses, the related researches still focus on the electrical stimulation of inhibitory behaviors. Herein, a synaptic device based on perovskite−ZnO heterostructure is prepared with the characteristic of bidirectional photoresponse and can realize both the potentiation and depression by ultraviolet (UV) and green light stimuli, respectively. Consecutive UV and green light stimuli for potentiation and depression reveal the reliability and repeatability of the fully optical‐controlled artificial synapse. A series of logic functions including “OR,” “AND,” “NOR,” and “NAND” has also been demonstrated in a fully‐optical pathway. This work not only offers an innovative architecture based on the perovskite single crystal and ZnO for fully optical‐controlled artificial synapse, but also represents a step toward optical wireless neuromorphic systems.

Pyrolytic gas exfoliation and template mediation inducing defective mesoporous carbon network from industrial lignin for advanced lithium-ion storage

Enzymatic hydrolysis lignin (EHL) from the biorefinery industry has been considered an ideal carbon source to prepare high-performance carbonaceous electrodes due to its high aromaticity and abundance. However, the severe agglomeration of the directly carbonized EHL results in insufficient lithium storage sites and inferior transfer kinetics. Herein, a delicate strategy of pyrolytic gas exfoliation and template mediation through ZnCO3 and ZnC2O4 decomposition was developed to engineer the microstructure of EHL-derived carbonaceous material (ECM) at 650 °C for robust lithium storage. The mesoporous ECM with an interconnected grape-like (200 nm) network is prepared by single CO2 exfoliation and ZnO templating. Surface micropores are engineered by temporary ZnO activation at 500–650 °C. The blocky ECM with coexisting micro/mesopores is prepared by dual CO/CO2 exfoliation and ZnO templating. The tempestuous release of CO2 produces deep micropores. The developed mesoporous structure boosts fast Li-ion transportation and accessibility for defects. In addition, the nanostructured grape-like (200 nm) network exposes active surface defects and shortens the charge-diffusion distance. Thus, the mesoporous ECM displays a robust capacity (534.1 mAh·g−1 at 0.2 A·g−1), superior rate capability (323.4 mAh·g−1 at 1 A·g−1) and excellent cycling stability. The blocky ECM with coexisting micro/mesopores shows better lithium storage performance than the microporous blocky ECM prepared by ZnCl2 activation.

Fabrication of a Microcavity Prepared by Remote Epitaxy over Monolayer Molybdenum Disulfide.

Advances in epitaxy have enabled the preparation of high-quality material architectures consisting of incommensurate components. Remote epitaxy based on lattice transparency of atomically thin graphene has been intensively studied for cost-effective advanced device manufacturing and heterostructure formation. However, remote epitaxy on nongraphene two-dimensional (2D) materials has rarely been studied even though it has a broad and immediate impact on various disciplines, such as many-body physics and the design of advanced devices. Herein, we report remote epitaxy of ZnO on monolayer MoS2 and the realization of a whispering-gallery-mode (WGM) cavity composed of a single crystalline ZnO nanorod and monolayer MoS2. Cross-sectional transmission electron microscopy and first-principles calculations revealed that the nongraphene 2D material interacted with overgrown and substrate layers and also exhibited lattice transparency. The WGM cavity embedding monolayer MoS2 showed enhanced luminescence of MoS2 and multimodal emission.

Thermoelectric performance of In and Ga single/dual-doped ZnO ceramics fabricated by spark plasma sintering

In single-doped [Zn(1−y)Iny]O (y = 0.005, 0.01, 0.02, 0.03, 0.05) ceramics and In and Ga dual-doped [Zn(1−x−y)GaxIny]O (y = 0.005; x = 0.005, 0.01, 0.02, 0.03, 0.05) ceramics were prepared using a solid-state reaction and spark plasma sintering at 1423 K in vacuum. The microstructural and chemical composition analyses revealed that Zn7In2O10 and ZnGa2O4 existed as the secondary phases in the single-doped ZnO (y ≥ 0.02) and dual-doped ZnO (y = 0.005; x ≥ 0.02) ceramics. Doped (single and dual) ZnO showed a high relative density of 92.5–100% as compared to pure ZnO (91.3%). The dual-doped sample with x = 0.005 and y = 0.005 prepared at 1046 K showed the highest power factor of 1.05 mW K−2 m−1. The dual-doped ZnO ceramics thereby showed an improved thermoelectric performance, attaining the figure of merit of 0.17 as compared to that of pure ZnO (0.12) at 1046 K.

Memristive devices based on single ZnO nanowires—from material synthesis to neuromorphic functionalities

Memristive and resistive switching devices are considered promising building blocks for the realization of artificial neural networks and neuromorphic systems. Besides conventional top-down memristive devices based on thin films, resistive switching devices based on nanowires (NWs) have attracted great attention, not only for the possibility of going beyond current scaling limitations of the top-down approach, but also as model systems for the localization and investigation of the physical mechanism of switching. This work reports on the fabrication of memristive devices based on ZnO NWs, from NW synthesis to single NW-based memristive cell fabrication and characterization. The bottom-up synthesis of ZnO NWs was performed by low-pressure chemical vapor deposition according to a self-seeding vapor-solid (VS) mechanism on a Pt substrate over large scale (∼cm2), without the requirement of previous seed deposition. The grown ZnO NWs are single crystalline with wurtzite crystal structure and are vertically aligned respect to the growth substrate. Single NWs were then contacted by means of asymmetric contacts, with an electrochemically active and an electrochemically inert electrode, to form NW-based electrochemical metallization memory cells that show reproducible resistive switching behaviour and neuromorphic functionalities including short-term synaptic plasticity and paired pulse facilitation. Besides representing building blocks for NW-based memristive and neuromorphic systems, these single crystalline devices can be exploited as model systems to study physicochemical processing underlaying memristive functionalities thanks to the high localization of switching events on the ZnO crystalline surface.

High-brightness Yellow Light-emitting Diode in A Single Ga-doped ZnO∶Ga Microwire Heterojunction

åŸºäºŽåŠå¯¼ä½“ä½Žç»´å¾®çº³ç»“æž„æž„ç­‘çš„å¯è§å ‰å‘å ‰å™¨ä»¶ï¼Œç‰¹åˆ«æ˜¯ä½äºŽ500 ~ 600 nmæ³¢æ®µçš„é»„ç»¿å ‰å ‰æºï¼Œå› å ·æœ‰è¾ƒé«˜çš„å‘å ‰æ•ˆçŽ‡ã€é•¿å¯¿å‘½å’Œä½ŽåŠŸè€—ç­‰ç‰¹ç‚¹ï¼Œåœ¨è¶ é«˜åˆ†è¾¨çŽ‡æ˜¾ç¤ºä¸Žç §æ˜Žã€å•åˆ†å­ä¼ æ„Ÿå’Œæˆåƒç­‰é¢†åŸŸæœ‰ç€å¹¿æ³›çš„åº”ç”¨ä»·å€¼ã€‚ç”±äºŽé«˜æ€§èƒ½ä½Žç»´é»„ç»¿è‰²å‘å ‰å™¨ä»¶åœ¨å‘å ‰ææ–™åˆ¶å¤‡ã€å™¨ä»¶ç»“æž„ä»¥åŠå‘å ‰å™¨ä»¶çš„ “Green/yellow gap”和 “Efficiency droopâ€ç­‰æ–¹é¢å—åˆ°ä¸¥é‡é™åˆ¶ï¼Œæžå¤§åœ°å½±å“äº†ä½Žç»´å¾®çº³ç»“æž„é»„ç»¿å ‰å‘å ‰å™¨ä»¶çš„å¼€å‘å’Œåº”ç”¨ã€‚æœ¬æ–‡é‡‡ç”¨å•æ ¹é•“æŽºæ‚æ°§åŒ–é”Œï¼ˆZnO∶Ga）微米线和p型InGaNè¡¬åº•æž„ç­‘äº†å¼‚è´¨ç»“åŸºé»„å ‰å‘å ‰äºŒæžç®¡ï¼Œå ¶è¾“å‡ºæ³¢é•¿ä½äºŽ580 nm附近，半峰宽大约为50 nmã€‚éšæ³¨å ¥ç”µæµçš„å¢žåŠ ï¼Œå ‰è°±çš„å³°ä½å’ŒåŠå³°å®½å‡ ä¹Žæ²¡æœ‰ä»»ä½•å˜åŒ–ï¼Œä¹Ÿæ²¡æœ‰è§‚å¯Ÿåˆ°InGaNåŸºå ‰æºä¸­å¸¸è§çš„é‡å­æ–¯å¡”å ‹æ•ˆåº”ã€‚å™¨ä»¶ç›¸åº”çš„è‰²åæ ‡å§‹ç»ˆå¤„äºŽé»„å ‰è‰²åŸŸèŒƒå›´ã€‚æ›´ä¸ºé‡è¦çš„æ˜¯ï¼Œå™¨ä»¶çš„å¤–é‡å­æ•ˆçŽ‡åœ¨å¤§ç”µæµæ³¨å ¥ä¸‹å¹¶æ²¡æœ‰å‡ºçŽ°è¾ƒå¤§çš„ä¸‹é™ã€‚ç»“åˆå•æ ¹ZnO∶Ga微米线和InGaNçš„å ‰è‡´å‘å ‰å ‰è°±ï¼Œä»¥åŠn‐ZnO∶Ga/p‐InGaNå¼‚è´¨ç»“èƒ½å¸¦ç»“æž„ç†è®ºï¼Œå¯ä»¥æŽ¨æ–­è¯¥åˆ¶å¤‡å™¨ä»¶çš„å‘å ‰æ¥è‡ªäºŽZnO∶Ga微米线和InGaN结区界面处载流子的辐射复合，器件的Droop效应得到明显抑制。实验结果表明，n‐ZnO∶Ga微米线/p‐InGaNå¼‚è´¨ç»“å¯ç”¨äºŽåˆ¶å¤‡é«˜æ€§èƒ½ã€é«˜äº®åº¦çš„ä½Žç»´é»„å ‰å‘å ‰äºŒæžç®¡ã€‚

Controlled crystal growth of ZnO nanobelts by chemical vapor deposition method

With the development expansion of environmental sensors in recent years, nanogenerators utilizing small amounts of mechanical energy in surrounding environment to generate electricity have been frequently studied. In order to convert mechanical energy into electrical energy more efficiently, it is necessary to fabricate single crystal ZnO nanostructures with specific crystal facet that exhibits piezoelectricity in the direction of applied strain. Since ZnO nanobelts have three pairs of crystal facets, controlling crystal growth can increase the size of specific crystal facet and their piezoelectricity is greater than that of ZnO nanowires, which is advantageous for power generation using piezoelectricity. ZnO nanobelts have been fabricated by chemical vapor deposition method, and we attempted to control the crystal growth by changing the heating temperature and pressure. Morphologies were observed by field emission scanning electron microscopy. Diffraction patterns were observed by transmission electron microscopy. ZnO nanobelts with the growth direction of [0001] and [0110] have been successfully fabricated in this research.

Interfacial modulation and plasmonic effect mediated high-brightness green light sources in a single Ga-doped ZnO microwire based heterojunction

High-brightness, stable and nearly droop-free green LEDs based on a carefully constructed n-AuNPs@ZnO:Ga MW/MgO/p-InGaN heterojunction were proposed and investigated experimentally.

Modulation of Bandgap and Electrical Conductivity in Europium Doped Single Zno Nanorod Device

Modulation of Bandgap and Electrical Conductivity in Europium Doped Single Zno Nanorod Device

Easy-plane magnetic anisotropy of a single dopant in a single semiconductor nanowire

The magnetic anisotropy of an isolated substitutional Co impurity in a single ZnO nanowire is studied by performing density-functional supercell calculations with the Hubbard U correction. The variation of the magnetic anisotropy energy with the location of the Co atom in different regions of the nanowire is explored. Contrary to usual expectation, it is found that single Co-doped ZnO nanowire possess an easy plane (as opposed to easy axis) of magnetization, which is neither parallel nor perpendicular to the nanowire axis; the orientation of the easy plane is determined by the local geometry around the dopant. Our results also show that the magnetic anisotropy energy is enhanced by almost an order of magnitude when the Co impurity moves to a surface site from an interior site. This enhancement is elucidated on the basis of local bonding characteristics, because a pronounced variation of the orbital moment of Co with the magnetization direction is observed only when Co is located at the nanowire surface. The complementary analysis of these findings shows that the magnetic anisotropy of a single dopant in a single nonmagnetic semiconductor nanowire can be directionally manipulated and substantially enhanced by controlling the local chemical environment of the dopant in the absence of magnetic coupling. Our findings thus imply that the directional control of magnetic anisotropy needs to be achieved for applications of magnetic ion doped semiconductor nanowires.