One-dimensional ZnO Nanowires Research Articles

Synthesis of Ti3C2Tx nanosheets / ZnO nanowires composite material for NO2 gas sensing

NO2 is a toxic gas that poses a significant threat to the environment and human health. In this work, one-dimensional ZnO nanowires and two-dimensional layered titanium carbide (Ti3C2Tx) have been prepared by hydrothermal and selective chemical etching methods, respectively. The Ti3C2Tx/ZnO composites are synthesized by electrostatic self-assembly method. The characterization results indicate that the ZnO nanowires are uniformly dispersed on the surface of layered Ti3C2Tx to form a heterostructure. Meanwhile, the gas sensitive performance of Ti3C2Tx/ZnO composite material is investigated and compared with that of pure Ti3C2Tx. The results reveal that the composite exhibits a high selectivity as well as sensitivity with a response value (S = Rg/Ra) of 18.66 to 100 ppm NO2 at 250 ℃, which is 4.3 times higher than that of pure Ti3C2Tx. This proves that the prepared composite material is an effective sensing material for detecting NO2 gas.

Synergistic Assembly of 1DZnO and Anti-CYFRA 21-1: A Physicochemical Approach to Optical Biosensing.

Objective: We conducted a comprehensive physicochemical analysis of one-dimensional ZnO nanowires (1DZnO), incorporating anti-CYFRA 21-1 immobilization to promote fast optical biomarker detection up to 10 ng ml-1. Impact Statement: This study highlights the effectiveness of proof-of-concept 1DZnO nanoplatforms for rapid cancer biomarker detection by examining the nanoscale integration of 1DZnO with these bioreceptors to deliver reliable photoluminescent output signals. Introduction: The urgent need for swift and accurate prognoses in healthcare settings drives the rise of sensitive biosensing nanoplatforms for cancer detection, which has benefited from biomarker identification. CYFRA 21-1 is a reliable target for the early prediction of cancer formation that can be perceptible in blood, saliva, and serum. However, 1DZnO nanostructures have been barely applied for CYFRA 21-1 detection. Methods: We assessed the nanoscale interaction between 1DZnO and anti-CYFRA 21-1 antibodies to develop rapid CYFRA 21-1 detection in two distinct matrices: PhosphateBuffered Saline (PBS) buffer and artificial saliva. The chemical modifications were tracked utilizing Fourier transform infrared spectroscopy, while transmission electron microscopy and energy dispersive spectroscopy confirmed antigen-antibody interplay over nanostructures. Results: Our results show high antibody immobilization efficiencies, affirming the effectiveness of 1DZnO nanoplatforms for rapid CYFRA 21-1 testing within a 5-min detection window in both PBS and artificial saliva. Photoluminescence measurements also revealed distinct optical responses across biomarker concentrations ranging from 10 to 1,000 ng ml-1. Conclusion: Discernible PL signal responses obtained after 5 min affirm the potential of 1DZnO nanoplatforms for further advancement in optical biomarker detection for application in early cancer prognosis.

A review of flexible lead-free piezoelectric energy harvester

Piezoelectric nanogenerator has emerged as a promising power generation device that converts mechanical energy into electrical energy. Flexible and stretchable piezoelectric energy harvesters can detect low frequencies like heartbeat, footsteps, ambient noise, and airflow, which is promising for further application. Thus, the development of a lead-free piezoelectric nanogenerator is required owing to its less toxic nature. One-dimensional ZnO (nanowire and nanorods) and perovskite-based materials (BaTiO 3 and BiFeO 3 ) have been widely investigated for piezoelectric nanogenerators because of their excellent piezoelectric properties and environmental friendliness. Hitherto, various electrodes, substrates, nanostructures, and polymers have been utilized to improve the efficiency of piezoelectric devices. In this review, we discuss the state-of-the-art achievements, stretchable piezoelectric nanowire, nanocomposite nanogenerators, and future possibilities of lead-free flexible energy harvesting devices.

Effect of ZnS/C Mass Ratio on the Morphologies and Luminescence Properties of ZnO Nano/Microstructures Synthesized via Thermal Evaporation of ZnS and C Powder Mixtures

ZnO nano/microstructures were grown via a simple thermal evaporation process in air at atmospheric pressure. Mixtures of ZnS and carbon powders were used as the sources. The effects of growth temperature and mass ratio of carbon powder to ZnS on the morphologies and luminescence properties of the ZnO nano/microstructures were investigated in this study. When the growth temperature was 1000 <sup>o</sup>C, ZnO nanowires with a hexagonal wurtzite crystal structure started to be formed and were preferentially grown along the [0001] direction. As the temperature increased to 1200 <sup>o</sup>C, the crystal growth in the lateral direction perpendicular to the [0001] direction was enhanced, which resulted in a decreasing aspect ratio of the onedimensional ZnO nanowires. When source powders with different mass ratios of ZnS:C=2:1, 1:1 and 1:2 were used to grow ZnO nano/microstructures at 1200 <sup>o</sup>C, ZnO microrods with wurtzite crystal structure were formed in all the samples. As the mass ratio of carbon powder to ZnS increased, the aspect ratio of ZnO microrods was reduced, which suggests that the carbon powder enhanced the growth of ZnO microrods in the lateral directions. A strong ultraviolet emission band centered at 380 nm was observed in the ZnO nano/microstructures synthesized using the source powders with the mass ratios of ZnS:C=1:1 and 1:2, indicating that the ZnO nano/microstructures had a high crystalline quality.

Size-controllable zinc oxide nanowires fabricated via the combination of die-casting and oxidation process

Herein, we demonstrate a facile approach in the fabrication of one-dimensional ZnO nanowires (NWs) from the vacuum die-casting method in assistance with anodic aluminum oxide (AAO) template. The casting method enables molten Zn to embed uniformly over the AAO nanomould under high pressure and temperature of 500 °C. Besides, the significant influence of the oxidation time and temperature stimulates the ZnO NWs growth inside the AAO nanochannels. The oxidation in the nanochannels was profoundly controlled by the inward diffusion of oxygen atoms and the ZnO grows perpendicular towards the surface which obeys the parabolic law. The TEM and XRD results revealed the ZnO wurtzite crystalline structure with preferential orientation along the c-axis. The relationship between ZnO geometry and function of oxidation parameters is demonstrated by microscopic and spectroscopic analysis. The obtained NWs from the chemical etching process resulted in high crystalline, homogeneous, and high-aspect ratio ZnO NWs in relationship with the AAO pore dimension. Further, the as-prepared ZnO NWs electrical properties were measured in a four-electrode system through the single nanowire device fabricated by FIB. The obtained current-voltage characteristic curves exhibited hysterias loop in consequence with the space charge limited current effect of ZnO NW, which confirms its potential to be used in practical electronic applications.

Enhanced NO2 sensing performance of ZnO nanowires functionalized with ultra-fine In2O3 nanoparticles

Structure and surface properties of the sensing materials have been recognized as the primary consideration for fabricating metal oxide semiconductor gas sensors. In this study, one-dimensional ZnO nanowires with large length-to-diameter ratio were firstly synthesized by a facile hydrothermal method. Then, different contents of ultra-fine In2O3 nanoparticles were directly grown on their surface. The structural characterization confirmed that the In2O3 nanoparticles were only 3–5 nm in diameter and well dispersed on the surface of ZnO nanowires. The gas sensing results showed that the ultra-fine In2O3 nanoparticles gave rise to a significant improvement in NO2 response at their optimal operating temperature of 150 °C. The highest response of 54.6 to 1 ppm NO2 was obtained for the sensor based on In2O3/ZnO composites with the In/Zn molar ratio of 5 %, which was about 8 times higher than that of pure ZnO nanowires. Importantly, a high response of 18.4 to a relatively low NO2 concentration of 250 ppb was also observed for In2O3-functionalized ZnO nanowires. The enhanced NO2 sensing mechanisms of ZnO nanowires functionalized with ultra-fine In2O3 nanoparticles were discussed.

One-dimensional ZnO nanowires grown on three-dimensional scaffolds for improved photocatalytic activity

In this paper, ultralong ZnO nanowires were prepared on the surfaces of nickel foams and zinc foils by a hydrothermal method. The photocatalytic activities of ZnO nanowires grown on nickel foams have been tested by the degradation of Rhodamine B solution and using ZnO nanowires grown on zinc foils as the reference. The results indicate that the photocatalytic performance of ZnO nanowires grown on nickel foams is better than those grown on zinc foils. The results are mainly due to the fact that nickel foam is a three-dimensional scaffold structure, which provides large surface area for ZnO nanowire growth. More importantly, the photocatalytic circulation experiments indicate that ZnO nanowires grown on nickel foams are stable and reusable. In addition, the photocatalytic reaction rates can be enhanced by the use of multi-layer of nickel foams with ZnO nanowires grown on their surfaces.

Effects of N implantation on defect formation in ZnO nanowires

One-dimensional ZnO nanowires are a promising material system for a wide range of optoelectronic and photonic applications. Utilization of ZnO, however, requires high-quality ZnO with reliable n-type and p-type conductivity, with the latter remaining elusive, so far. In this work we report on effects of N doping via ion implantation on defect formation in ZnO nanowires studied by optically detected paramagnetic resonance (ODMR) spectroscopy complemented by photoluminescence spectroscopy. After N implantation, zinc interstitial shallow donors, which are formed as a result of ion implantation, are observed in addition to effective mass type shallow donors. Additionally, ODMR signals related to oxygen vacancies can be observed. Implantation also causes formation of a new nitrogen related defect center, which acts as an acceptor. The present findings are of importance for understanding impacts of different defects and impurities on electronic properties of nanostructured ZnO and achieving p-type conductivity via nitrogen doping.

Stability evaluation of ZnO nanosheet based source-gated transistors

Semiconducting nanostructures are one of the potential candidates to accomplish low-temperature and solution-based device assembly processes for the fabrication of transistors that offer practical solutions toward realizing low-cost flexible electronics. Meanwhile, it has been shown that by introducing a contact barrier, in a specific transistor configuration, stable device operation can be achieved at much reduced power consumption. In this work, we investigate both one-dimensional ZnO nanowires (NWs) and two-dimensional nanosheets (NSs) for high performance and stable nano-transistors on conventional Si/SiO2 substrates. We have fabricated two variant of transistors based on nanoscale single-crystalline oxide materials: field-effect transistors (FETs) and source-gated transistors (SGTs). Stability tests are performed on both devices with respect to gate bias stress at three different regimes of transistor operation, namely off-state, on-state and sub-threshold state. While in the off-state, FETs shows comparatively better stability than SGTs devices, in both sub-threshold and on-state regimes of transistors, SGTs clearly exhibits better robustness against bias stress variability. The present investigation experimentally demonstrates the potential advantages of SGTs over FETs as driver transistor for AMOLEDs display circuits which require very high stability in OLED driving current.

Wet-Chemical Synthesis of ZnO Nanowires on Low-Temperature Photo-Activated ZnO-rGO Composite Thin Film with Enhanced Photoconduction

A homogeneous dispersion of graphene oxide (GO) and zinc acetate was dip-coated and subsequently photo-annealed by deep UV irradiation to form ZnO-rGO (DUV) nanocomposite thin film. ZnO nanowires were then grown by wet-chemical synthesis on the ZnO-rGO (DUV) thin film. For comparison, ZnO nanowires were also grown on bare ZnO and ZnO-rGO (HT) thin films thermally annealed at 500°C. X-ray diffraction and Raman spectroscopy of ZnO-rGO (DUV) thin film revealed crystallization of ZnO and reduction of GO. The photoluminescence spectra of ZnO nanowires grown on ZnO-rGO (DUV) thin film showed high crystallinity. The current–voltage characteristics of ZnO nanowires grown on ZnO-rGO (DUV) thin film in dark and under UV showed a 15-fold increase in photocurrent as compared to ZnO nanowires grown on ZnO and ZnO-rGO (HT) thin films. The low-temperature photo-activated ZnO-rGO thin films can be used as a template to grow one-dimensional ZnO nanowires with improved structural and optical properties and can pave the way for high-performance flexible device fabrication.

Strain modulation on graphene/ZnO nanowire mixed-dimensional van der Waals heterostructure for high-performance photosensor

The mixed-dimensional van der Waals (vdW) heterostructure is a promising building block for strained electronics and optoelectronics because it avoids the bond fracture and atomic reconstruction under strain. We propose a novel mixed-dimensional vdW heterostructure between two-dimensional graphene and a one-dimensional ZnO nanowire for high-performance photosensing. By utilizing the piezoelectric properties of ZnO, strain modulation was accomplished in the mixed-dimensional vdW heterostructure to optimize the device performance. By combining the ultrahigh electrons transfer speed in graphene and the extremely long life time of holes in ZnO, an outstanding responsivity of 1.87 × 105 A/W was achieved. Under a tensile strain of only 0.44% on the ZnO nanowire, the responsivity was enhanced by 26%. A competitive model was proposed, in which the performance enhancement is due to the efficient promotion of the injection of photogenerated electrons from the ZnO into the graphene caused by the strain-induced positive piezopotential. Our study provides a strain-engineering strategy for controlling the behavior of the photocarriers in the mixed-dimensional vdW heterostructure, which can be also applied to other similar systems in the future.

Controllable preparation of 1-D and dendritic ZnO nanowires and their large area field-emission properties

Large-scale one-dimensional (1-D) and dendritic ZnO nanowires were synthesized on Si substrates using a catalyst-free thermal oxidation technique. By adjusting the stress of the starting Zn thin film for the growth using an Ar ion bombardment process, controllable syntheses of samples composed of only one or a mixture of these two morphologies were achieved. Different nucleation mechanisms were proposed by detailed observations of nucleation and growth process of 1-D and dendritic ZnO nanowires. The strain-induced mass diffusion model and self-catalytic gas-liquid-solid model were used to explain the growth of 1-D and dendritic ZnO nanowires, respectively. In addition, the field-emission characteristics of ZnO nanowires were measured, which showed that dendritic ZnO nanowires have stable emission current.

Mimicking the Heteroleptic Dyes for an Efficient 1D-ZnO Based Dye-Sensitized Solar Cell Using the Homoleptic Ruthenium(II) Dipyridophenazine Complex as a Photosensitizer

Mimicking the properties of heteroleptic ruthenium dyes, a dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylic acid (dppz-COOH) ligand based homoleptic complex, Ru(dppz-COOH)2(NCS)2, with a molar extinction coefficient of 14.3 × 103 M–1 cm–1 has been demonstrated as an efficient photosensitizer for the one-dimensional (1D) ZnO nanowire (NW) and ZnO nanoparticle (NP) based dye-sensitized solar cells (DSSCs) employing cobalt complexes as the redox mediators. The as-synthesized homoleptic dye achieves an intense metal-to-ligand charge transfer (MLCT) absorption band throughout the visible region due to the optimal π-conjugated dipyridophenazine ring extension and concomitantly retains an efficient dye loading tendency as confirmed by the chemisorption results. Electron density distributions of the frontier molecular orbitals obtained from density functional theory (DFT) indicated a characteristic MLCT transitions of the dye molecule as well as a favorable charge transfer feasibility from the lowest unoccupied mol...

Highly efficient one-dimensional ZnO nanowire-based dye-sensitized solar cell using a metal-free, D-π-A-type, carbazole derivative with more than 5% power conversion.

Hydrothermally grown one-dimensional ZnO nanowire (1D ZnO NW) and a newly synthesized metal-free, D-π-A type, carbazole dye (SK1) sensitizer-based photovoltaic device with a power conversion efficiency (PCE) of more than 5% have been demonstrated by employing the cobalt tris(2,2'-bipyridyl) redox shuttle. A short-circuit current density (Jsc) of ∼12.0 mA/cm(2), an open-circuit voltage (Voc) of ∼719 mV, and a fill factor (FF) of ∼65% have been afforded by the 1D ZnO NW-based dye-sensitized solar cell (DSSC) incorporating [Co(bpy)3](3+/2+) complex as the one-electron redox mediator. In contrast, the identical DSSC with traditional I3(-)/I(-) electrolyte has shown a Jsc ≈ 12.2 mA/cm(2), a Voc ≈ 629 mV, and a FF ≈ 62%, yielding a PCE of ∼4.7%. The persuasive role of the inherent superior electron transport property of 1D ZnO NWs in enhancing the device efficiency is evidenced from the impoverished performance of the DSSCs with photoanodes fabricated using ZnO nanoparticles (NPs). The DSSCs having ZnO NP-based photoanodes have achieved the PCEs of ∼3.6% and ∼3.2% using cobalt- and iodine-based redox electrolytes, respectively. The electronic interactions between the SK1 sensitizer and ZnO (NWs and NPs) to induce the photogenerated charge transfer from SK1 to the conduction band (CB) of ZnO are evidenced from the significant quenching of photoluminescence and exciton lifetime decay of SK1, when it is anchored onto the ZnO architectures. The energetics of the SK1 dye molecule are estimated by combining the spectroscopic and electrochemical techniques. The electronic distributions of SK1 dye molecule in its HOMO and LUMO energy levels are interpreted using density functional theory (DFT)-based calculations. The electron donor-π linker-acceptor (D-π-A) configuration of SK1 dye provides an intramolecular charge transfer within the molecule, prompting the electron migration from the carbazole donor to cyanoacrylic acceptor moiety via the oligo-phenylenevinylene linker group. The D-π-A-mediated electron movement witnesses the favorable photoexcited electron transfer from the LUMO of SK1 dye to the CB of ZnO through the carboxyl anchoring group.

Growth of vertically aligned one-dimensional ZnO nanowire arrays on sol–gel derived ZnO thin films

Vertically aligned one-dimensional ZnO nanowire arrays have been synthesized by a hydrothermal method on sol–gel derived ZnO films. Sol–gel derived ZnO films and corresponding ZnO nanowire arrays have been characterized by X-ray diffraction and field-emission scanning electron microscopy. The effect of sol–gel derived ZnO film surface on the morphology of ZnO nanowire arrays has been investigated. The authors suggest from our investigation that sol–gel derived ZnO films affect the growth of one-dimensional ZnO nanostructures. Not only crystalline ZnO films but also amorphous ones can act as a scaffold for ZnO nucleus. Tilted ZnO micro-rods are grown on ZnO gel films, whereas vertically aligned ZnO nanowire arrays are grown on nanometer-sized ZnO grains. The average diameter of ZnO nanowire arrays are correlated strongly with the grain size of sol–gel derived ZnO films.

High Density ZnO Nanowire Arrays for Dye-Sensitized Solar Cells Fabrication

Dye-sensitized solar cells (DSSCs) have been extensively studied for the past few years because of their low-cost and high-efficiency. The surface area of the photoanode, which determines the amount of photons absorbed, is one of the most critical factors to improve the efficiency of DSSCs. Although conventional TiO2 nanoparticle-based DSSCs have shown promising results, their performance has been limited to ~11% because of diffusion and back reaction problems. Due to its excellent band gap (3.37 eV) and high exciton binding energy (60 meV) properties, one-dimensional ZnO nanowire arrays are capable of overcoming the limitation of nanoparticle-based DSSCs by improving electron injection and axial electron diffusion. Based on models proposed by our group, the efficiency of DSSCs based on TiO2 core-shell ZnO nanowire arrays (40 µm in lengths, 40 nm in diameter and ~1011 /cm2 of density) can significantly surpass current efficiencies. To reach our objective, we focused on pH value control and using two-step anodized aluminum oxide (AAO) as a template to control the dimension of ZnO nanowire arrays. The synthesis was carried out using both hydrothermal and CVD methods. SEM, TEM, and XRD were applied to characterize these ZnO nanowire arrays. This technique provides a new approach to obtain vertically-aligned ZnO nanowire arrays with both high density and aspect-ratio through a large-scale process. Keywords: Dye sensitized solar cell (DSSC), ZnO Nanowire Arrays, AAO Template, Hydrothermal, CVD

Synthesis of High Density ZnO Nanowire Arrays for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have been extensively studied for the past few years because of their low-cost and high-efficiency. The surface area of the photoanode, which determines the amount of photons absorbed, is one of the most critical factors to improve the efficiency of DSSCs. Although conventional TiO2 nanoparticle-based DSSCs have shown promising results, their performance has been limited to ~11% because of diffusion and back reaction problems. Due to its excellent band gap (3.37 eV) and high exciton binding energy (60 meV) properties, one-dimensional ZnO nanowire arrays are capable of overcoming the limitation of nanoparticle-based DSSCs by improving electron injection and axial electron diffusion. Based on models proposed by our group, the efficiency of DSSCs based on TiO2 core-shell ZnO nanowire arrays (40 µm in lengths, 40 nm in diameter and ~1011 /cm2 of density) can significantly surpass current efficiencies. To reach our objective, we focused on pH value control and using two-step anodized aluminum oxide (AAO) as a template to control the dimension of ZnO nanowire arrays. The synthesis was carried out using both hydrothermal and CVD methods. After that, SEM, TEM, and XRD were applied to characterize these ZnO nanowire arrays. By using this technique, it provides a new approach to obtain vertically-aligned ZnO nanowire arrays with both high density and aspect-ratio through a large-scale process. Keywords: Dye sensitized solar cell (DSSC), ZnO Nanowire Arrays, AAO Template, Hydrothermal, CVD

Fabrication of one-dimensional ZnO nanotube and nanowire arrays with an anodic alumina oxide template via electrochemical deposition

In this work, two kinds of one-dimensional ZnO nanowires (NWs) and nanotubes (NTs) were synthesized by using electrochemical deposition with the aid of a high aspect ratio anodic alumina oxide (AAO) template. ZnO NWs and NTs were characterized by using X-ray diffraction, field emission scanning microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. An AAO template was fabricated by two-step anodization in 0.3M oxalic acid with a voltage of 80V. The thickness and channel diameter of the AAO template were about 150μm and 120–150nm, respectively. The morphologies of the ZnO nanostructures synthesized under 20vol.% H2O2 with various electrolyte concentrations of 0.1M and 0.5M ZnSO4, were NTs and NWs, respectively. Both NTs and NWs were uniform in size, which corresponded to the sizes of AAO pores. The thickness of the NTs walls can be controlled based on the deposition time and current density. The crystallinity of the ZnO NTs and NWs annealing in the air were restricted by AAO pore. The growth of the ZnO NTs and NWs was caused by heterogeneous nucleation, and different growth rates through the wall of the AAO will result in different nanostructures, with the growth of the NTs being slower than that of the NWs.

H2 sensing properties of two-dimensional zinc oxide nanostructures

In this work we have grown particular zinc oxide two-dimensional nanostructures which are essentially a series of hexagonal very thin sheets. The hexagonal wurtzite crystal structure gives them their peculiar shape, whose dimensions are few microns wide, with a thickness in the order of 25 nm. Such kind of nanostructure, grown by thermal oxidation of evaporated metallic zinc on a silica substrate, has been used to fabricate conductometric gas sensors, investigated then for hydrogen gas detection. The "depletion layer sensing mechanism" is clarified, explaining how the geometrical factors of one- and two-dimensional nanostructures affect their sensing parameters. The comparison with one-dimensional ZnO nanowires based structures shows that two-dimensional nanostructures are ideal for gas sensing, due to their tiny thickness, which is comparable to the depletion-layer thickness, and their large cross-section, which increases the base current, thus lowering the limit of detection. The response to H₂ has been found good even to sub-ppm concentrations, with response and recovery times shorter than 18s in the whole range of H₂ concentrations investigated (500 ppb-10 ppm). The limit of detection has been found around 200 ppb for H₂ gas even at relatively low working temperature (175 °C).

Giant enhancement of the Raman response due to one-dimensional ZnO nanostructures

We observed giant enhancement of the Raman intensity from 4-Mpy molecules adsorbed on semiconducting one-dimensional ZnO nanostructures, nanowires and nanocones, without involving any noble metals. Interestingly, the enhancement is strongly dependent on the geometry of ZnO nanostructures and can mainly be explained by the cavity-like structural resonance of the electric field. Our results can be applied to systematically create hot spots for Raman signal enhancement using one-dimensional semiconducting nanomaterials.