Conduction Band Of ZnO Research Articles

ZnO/g-C3N4 photocatalyst activated by low-pressure ultraviolet for restoring the SWASV signals: A fast pretreatment method for electrochemically detecting Cd2+ and Pb2+ in soil extracts

Soil organic matter (SOM) significantly impacts the detection accuracy of Cd2+ and Pb2+ using square wave anodic stripping voltammetry (SWASV) due to the complexation of SOM to heavy metal ions (HMIs), thereby attenuating SWASV signals. This study explored an effective pretreatment method that combined low-pressure ultraviolet (LPUV) photolysis with the ZnO/g-C3N4 photocatalyst, activating the photocatalyst to generate highly oxidative •OH radicals and O2•− radicals, which effectively disrupted this complexation, consequently restoring the electroactivity of HMIs and achieving high-fidelity SWASV signals. The parameters of the LPUV-ZnO/g-C3N4 photocatalytic system were meticulously optimized, including the pH of photolysis, duration of photolysis, g-C3N4 mass fraction, and concentration of the photocatalyst. Furthermore, the ZnO/g-C3N4 photocatalyst was thoroughly characterized, with an in-depth investigation on the synergistic interaction between ZnO and g-C3N4 and the mechanisms contributing to the restoration of SWASV signals. This synergistic interaction effectively separated charge carriers and reduced charge transfer resistance, enabling photogenerated electrons (e−) from the conduction band of g-C3N4 to be quickly transferred to the conduction band of ZnO, preventing the recombination of e− and hole (h+) and generating more radicals to disrupt complexation and restore the SWASV signals. Finally, the analysis of HMIs in real soil extracts using the proposed pretreatment method demonstrated high detection accuracy of 94.9% for Cd2+ and 99.8% for Pb2+, which validated the feasibility and effectiveness of the proposed method in environmental applications.

Tailoring the electrical and magneto-electric transport properties of ZnO films via Ti ion implantation

A significant development toward semiconductor-based electronic devices is based on the electric and magneto-electric control of the transport properties of the charge carriers. This study unprecedentedly investigates the Ti implantation and thereafter the effect of structural defects on the electrical and magneto-electric transport properties of Ti-implanted RF-sputtered ZnO thin films. Theoretical stopping and range of ions in matter simulations along with the experimental structural and elemental studies reveal that Ti ion implantation generates a significant amount of oxygen vacancy (VO) defects apart from Ti-related impurities in post-implantation annealed films. The film implanted with 8 × 1015 ions/cm2 (TZO815) exhibits the lowest resistivity (4.68 × 10−3 Ω cm) and the highest carrier concentration (6.61 × 1020 cm−3) values. Resistivity measurements over a temperature range of 5-300K indicate semiconducting behavior for all the films implanted up to fluences of 5 × 1015 ions/cm2 identified with a grain boundary dominated thermally activated band, nearest neighbor hopping, and Mott and Efros–Shklovskii (ES) variable range hopping conduction mechanisms at various temperature intervals. Notably, the gradual decrease in both Mott and ES hopping ranges following Ti implantation indicates the formation of more localized states. Interestingly, the TZO815 film exhibits metal-semiconductor transition around 220 K, suggesting the formation of a degenerate band within the ZnO conduction band upon Ti implantation. Remarkably, the magnetoresistance results align with a semiempirical formula proposed by Khosla and Fischer, indicating that a negative magneto resistance in the TZO thin films is attributed to the spin-dependent scattering of conduction electrons by the localized magnetic moments induced mainly by the implantation induced VO defects.

Photo-Fenton efficient degradation of organic pollutants over S-scheme ZnO@NH2-MIL-88B heterojunction established for electron transfer channel

Combining photocatalysts with Fenton technology can improve the catalytic properties of materials and achieve efficient degradation of organic pollutants. However, preparing low-cost catalysts using simple methods remains a challenge. This paper selected a more environmentally friendly and cost-effective semiconductor material, zinc oxide, for the modification of NH2-MIL-88B and prepared a new S-scheme heterojunction photo-Fenton catalyst ZnO@NH2-MIL-88B (ZMFe-x) by a simple solvothermal method. Moreover, the Zn-O-Fe bonds that were formed between the interfaces enabled a fast channel for the photoelectron transport that was created by photoexcitation from the ZnO conduction band to the NH2-MIL-88B valence band. This allowed the ZMFe-x catalysts to have better removal performance for organic pollutants in the photo-Fenton reaction. The dominating role of hydroxyl radicals in the degradation procedure was determined by ESR analysis and free radical trapping experiments, and the degradation mechanisms and pathway of contaminants were predicted by intermediate analysis and DFT calculations. This study provides a stable and effective new strategy for preparing MOFs catalysts for removing various pollutants.

Combustion synthesis and characterization of visible-light-driven La/Al co-doped ZnO nanoparticles used for wastewater treatment

Visible-light-driven LaxAl0.03-xZn0.97O (x = 0.01, 0.015 and 0.02) nanoparticles were synthesized by tartaric acid-assisted combustion method. Both ZnO and La/Al co-doped ZnO samples were indexed to the pure hexagonal wurtzite ZnO structure and were composed of nanoparticles with particle size ranges of 100-150 nm and 20-50 nm, respectively. The photocatalytic activities of ZnO and LaxAl0.03-xZn0.97O (x = 0.01, 0.015 and 0.02) nanoparticles were monitored through the degradation of methylene blue (MB) under visible light irradiation. The La0.02Al0.01Zn0.97O nanoparticles have the highest photocatalytic activity in degrading of MB under visible light irradiation because the La/Al co-dopant played the role in creating shallow energy level under the conduction band of ZnO.

Role of defects in tailoring optical, electronic, and luminescent properties of Cu-doped ZnO films

We present a detailed characterization study on copper-doped ZnO films to correlate the films' electronic and optical properties with the existing native defects in the lattice. In addition, we describe the variation in the concentration of these defects with Cu dopant and temperature. The results of XRD confirmed the single-phase würtzite-structure of the synthesized films. The SEM images showed a homogeneous and dense grain morphology with a granular form and a signature for a hexagonal-like shape. The EDX, XPS, and UV–Vis spectra showed the proper doping of Cu ions into the lattice. The XPS analysis indicated mixed electronic states of both Cu2+ and Cu1+ and showed a clear increase in the Cu2+ intensity relative to Cu1+, with Cu dopant. The transmittance spectra exhibited an average value above 80% in all doped films in the visible and infrared regions. The overall results indicated a clear link between the films’ optical and electronic responses and the level of the intrinsic defects in the lattice. By increasing the Cu dopant, we find a slight reduction in the energy bandgap (Eg). This is correlated with a clear reduction in the blue emission luminescence band associated with the VZn and in the yellow emission band associated with the Oi. On the other hand, we observed a clear enhancement in the green emission band originating from the VO, and in the emission band related to possible transitions from Zni levels to Oi levels. The slight reduction in the Eg signals a weak sp-d hybridization between the ZnO conduction band electrons and the Cu2+ ions, which is mediated by the intrinsic defects. With reducing the temperature, the photoluminescence temperature profiles indicated a slight increase in the Eg values and a negligible effect on the distribution of the native defects.

Improving Separation Efficiency of Photogenerated Charges through Combination of Conductive Polythiophene for Selective Production of CH4

In today’s society, mankind is confronted with two major problems: the energy crisis and the greenhouse effect. Artificial photosynthesis can use solar energy to convert the greenhouse gas CO2 into high-value compounds, which is an ideal solution to alleviate the energy crisis and solve the problem of global warming. The combination of ZnO and polythiophenes (PTh) can make up for each other’s drawbacks, thus improving the photoresponse behavior and separation efficiency of the photogenerated carriers. The PTh layer can transfer photogenerated electrons to ZnO, thereby extending the lifetime of the photogenerated charges. The production rate of CH4 from the photoreduction of CO2 with ZnO/PTh10 is 4.3 times that of pure ZnO, and the selectivity of CH4 is increased from 70.2% to 92.2%. The conductive PTh can absorb photons to induce π–π* transition, and the photogenerated electrons can transfer from the LUMO to the conduction band (CB) of ZnO, thus more electrons are involved in the reduction of CO2.

BiOI/ZnO Heterojunction for Increased Photodegradation of Metronidazole under Visible Light Irradiation

AbstractA heterojunction interface with a rational design can overcome the limitation of a single photocatalyst structure and enable the separation and transport of photogenerated carriers. p‐n Heterojunctions of BiOI/ZnO nano‐flake were achieved by a simple one–step hydrothermal process for metronidazole (MNZ) degradation under visible light. The measurements show that the BiOI/ZnO could completely remove MNZ within 180 min, which is 2.6 times and 4.8 times higher than that of pristine ZnO and BiOI, respectively. Under visible light irradiation, the electrostatic field formed within the p‐n heterojunction drives the flow of photogenerated electrons from the conduction band of BiOI to the conduction band of ZnO, while the holes are retained, promoting photogenerated carrier separation and enhancing photocatalytic efficiency. The fact that BiOI/ZnO good stability and reusability demonstrates the importance of heterostructure construction of two different semiconductors in overcoming the defects of traditional semiconductor materials.

Band gap and interface engineering of ZnO@MoSe2heterojunction film and its light-matter coupling

The wide/narrow band gap semiconductor heterojunction promotes the coupling of light with matter and the rapid electron transport, which opens up a new research way for the construction of heterojunctions, photodetectors and quantum phenomena due to their excellent optical properties. Hereon, petal-like ZnO@MoSe2 and worm-like MoSe2 films were prepared by two-step/single-step RF magnetron sputtering method. Combined with the experimental results and the finite difference time domain (FDTD) simulation, it is proven that the 1T and 2H mixed phase MoSe2 can provide low energy growth sites for ZnO. ZnO@MoSe2 longitudinal n-p heterojunctions can form super-fast carrier transfer channels, enhancing the luminescence properties of heterojunctions in near-Gaussian fields. Moreover, both MoSe2 and ZnO@MoSe2 films show saturation absorption phenomenon with the coefficients of 0.43 × 10−7 mW−1 and 0.18 × 10−7 mW−1, respectively. The saturation absorption coefficient of ZnO@MoSe2 films is reduced due to Pauli blocking, which is caused by the electron transfer from the conduction band of MoSe2 to the conduction band of ZnO. The synthesized ZnO@MoSe2 films can be used in all optical switching, passive mode locking and other fields.

Efficiency enhancement of photocatalytic activity under UV and visible light irradiation using ZnO/Fe3O4 heteronanostructures

ZnO/Fe3O4 heteronanostructures (HNSs) have attracted great attention due to their possibility of removing organic pollutants in aqueous solutions, then detaching from aqueous solutions by magnetic fields. However, there is a lack of research on their photocatalytic performance under visible light irradiation and the mechanism for the degradation process is still arguable. We present here the enhancement in the photocatalytic activity of ZnO/Fe3O4 HNSs, synthesized by a facile hydrothermal technique, under both Ultraviolet (UV) and visible light irradiation. Particularly, the methylene blue (MB) degradation efficiency exhibited a great enhancement of up to 99.7% and 79.7% for HNSs with different ZnO:Fe3O4 mole ratios of 16:1 and 8:1 under UV and visible light, respectively. It could be explained by the transfer of electrons (i) from the conduction band (CB) of ZnO to that of Fe3O4 or/and (ii) from the CB of Fe3O4 to new defect states (e.g., Fe2+/Fe3+ levels) below the CB of ZnO. Additionally, ZnO/Fe3O4 HNSs show great stability in their photocatalytic activities when remained 95.1% and 92.1% after 5-reused cycles under UV and visible light irradiation, respectively. Therefore, the fabricated ZnO/Fe3O4 HNSs show great potential for enhancing the MB degradation efficiency under both UV and visible light.

S-scheme ZnO/WO3 heterojunction photocatalyst for efficient H2O2 production

• ZnO/WO 3 step-scheme (S-scheme) H 2 O 2 -production photocatalyst prepared. • The ZnO/WO 3 samples with high photocatalytic H 2 O 2 -production activity. • In-situ irradiated XPS measurements investigation on S-scheme mechanism. • Advantages of S-scheme heterojunction in H 2 O 2 -production discussed. Designing highly efficient photocatalyst for hydrogen peroxide (H 2 O 2 ) production is an ideal strategy to avoid the shortcomings of traditional H 2 O 2 production and to realize the conversion of solar energy to chemical energy. In this work, a step-scheme (S-scheme) heterojunction photocatalyst composed of ZnO and WO 3 is carefully prepared by hydrothermal and calcination method for efficient photocatalytic H 2 O 2 production. The ZW30 composite photocatalysts exhibit enhanced activity with the highest H 2 O 2 -production rate of 6788 μmol L −1 h −1 . The results show that the photocatalytic H 2 O 2 production process is dominated by a direct two-electron O 2 reduction pathway. The enhanced photocatalytic H 2 O 2 -production activity is attributed to the formation of interfacial internal electric field (IEF) in the S-scheme heterojunction, which boosts the spatial separation of charge carriers and enables electrons with the strongest reduction power to participate in H 2 O 2 production. This work provides an in-depth insight of the great advantages of S-scheme heterojunction in photocatalytic H 2 O 2 production. Benefiting from the formation of the S-scheme heterojunction of ZnO and WO 3 , the useful electrons on the conduction band of ZnO and holes on the valence band of WO 3 can be efficiently spatially separated, leading to high photocatalytic production of H 2 O 2 . The S-scheme heterojunction presents great advantages for efficient H 2 O 2 production.

Polaron induced ferromagnetism in ZnO

The odd phenomenon of the ferromagnetic moment of n-type ZnO increasing with temperature has been observed in experiments. We proposed an impurity model accompanying the polaron theory to explain this result because the electron-phonon interaction plays a critical role in inducing ferromagnetism in n-type ZnOs. Thus, we propose that the ferromagnetism of ZnOs comes from the polarons in the impurity states, and the strong Coulomb interaction in these states causes the spin of electrons to split. In addition, the proper hybridization interaction between the conduction band and the impurity states promotes the increase of electron density in the impurity states as well as the ferromagnetism. In contrast, a too strong hybridization interaction will delocalize the electrons in the impurity states to suppress the ferromagnetism. The polarons induce the ferromagnetism by the Coulomb excitation in the impurity states. The electron thermal excitation produces the polarons in the impurity states near the ZnO conduction band edge coupling with the phonon. Based on the model, the ferromagnetism increases with the temperature consistent with the experimental results.

Photodegradation of dye using Polythiophene/ZnO nanocomposite: A computational approach

Incorporating nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. Here, we present density functional theory (DFT) study of Polythiophene/Zinc oxide (PTh/ZnO) nanocomposite with high photocatalytic performance and stability which exhibits superior degradation of alizarine dye under the visible light condition with interaction energy of −149.55 kcal/mol between conducting polymer (PTh) and metal oxide, with PTh sponsoring more number of electrons to the conduction band of ZnO. The electrical and optical properties of optimized geometries of PTh/ZnO nanocomposite were studied by frontier molecular orbital analysis, natural bond orbital (NBO) charge simulation, natural electronic configuration, and UV–vis absorption spectra. The modulation of the energy band gap (∽ 2.60 eV) and exciton binding energy (∽ 0.36 eV) causes visible light absorption and hence enhances the photodegradation activity of PTh/ZnO. NBO analysis evidences the electron accepting behavior of ZnO in the composites as it withdraws electron cloud density of about 0.14e from the polymer unit.

B and Au doped ZnO and ZnO/Cu(111) bilayer films: A DFT investigation

AbstractsThe structural and electronic properties of B and Au doped graphite‐like ZnO and ZnO/Cu(111) bilayer films have been investigated by using the DFT + U scheme including dispersion correction and compared to that of undoped materials. The differences in electronic properties of the B and Au doped ZnO and ZnO/Cu(111) films compared to undoped materials were probed by CO adsorption. The same oxidation state of B (+3) was observed for B doped ZnO and ZnO/Cu(111) bilayer films. However, an excess electron associated with B doping is delocalized over the conduction band of ZnO, while it transfers to underlying Cu support of ZnO/Cu(111). This is evidenced by a much large redshift of CO frequency on B doped ZnO versus the small redshift of CO frequency on B doped ZnO/Cu(111). At variance, the oxidation state of Au dopant was reduced from +2 (5d9) for Au doped ZnO to +1 (5d10) for Au doped ZnO/Cu(111) films. This is due to the charge transfer from Cu support to doped Au which results in the stronger binding of CO on Au doped ZnO/Cu(111) compared to ZnO bilayer films. However, a slight difference in CO frequency was found for CO bound to Au doped ZnO and ZnO/Cu(111).

Facile fabrication of novel magnetic 3-D ZnFe2O4/ZnO aerogel based heterojunction for photoreduction of Cr(Ⅵ) under visible light: Controlled synthesis, facial change distribution, and DFT study

A novel magnetic type Ⅱ ZnFe2O4/ZnO aerogel (ZZA) heterojunction photocatalyst is firstly developed for photocatalytic reduction of Cr(Ⅵ) to Cr (III). The optimal ZZA-400 shows typical “pearl-like” nanostructures, with particle diameters at around 20–30 nm. It possesses a large BET specific surface area of 127.5 m2/g and an appropriate bandgap of 1.9 eV. It exhibits an efficiency of 87.0 % for photocatalytic Cr(VI) reduction within 120 min under extremely high Cr(VI) concentration (100 mg/L), with the rate constant up to 7.08 × 10−3 min−1. Density functional theory (DFT) calculations show that the incorporation of ZnFe2O4 (ZFO) introduces an impurity energy level in the gap region of ZnO (ZO), which contributes to the optical absorption in the visible light region. It is energetically favorable for the electrons' migration from ZnO to ZnFe2O4 due to the lower Fermi energy level of ZnFe2O4. However, the electrons migrate from ZnFe2O4 to the conduction band of ZnO with the assistance of the built-in electric field under visible light illumination, therefore, the separation of electron-hole pairs can be greatly promoted. The combination of formed O2–, the electrons in the conduction band of ZnO, and the reductive CO2– radical together enhance the photocatalytic property of the aerogel heterojunction.

Hierarchical ZnO/MXene (Nb2C and V2C) heterostructure with efficient electron transfer for enhanced photocatalytic activity

Recently, MXene has attracted much attention as photocatalysts for efficient pollutant degradation in the field of environmental remediation but a rapid recombination of photogenerated carriers usually leads to a decrease in the photocatalytic performance. Constructing a heterostructure is considered as an effective way to improve the catalytic performance of MXene-based photocatalysts due to the promoted interfacial electron transfer. In this work, the chimeric ZnO nanosheets with good carrier mobility were formed on the accordion-shaped MXene (Nb2C and V2C) surface to construct hierarchical ZnO/MXene heterostructure as a photocatalyst for dye degradation. The obtained ZnO/Nb2C and ZnO/V2C hierarchical structure exhibited excellent photocatalytic performance in the degradation of methylene blue (MB): the degradation rate reached 62.62% and 99.53%, respectively, after irradiation with ultraviolet light for 120 min. Also, the apparent degradation rate constants (k) were 0.00777 min−1 and 0.04317 min−1, respectively, which were 2.92 and 16.23 times higher than those of pure ZnO. This was probably attributed to the heterostructures between ZnO and MXene which could shorten the carrier transfer path, which could facilitate the transfer of photo-generated electrons from conduction band (CB) of ZnO to CB of MXene, thereby significantly improving the photocatalytic degradation efficiency. In addition, the ZnO/Nb2C and ZnO/V2C hierarchical structure showed good photocatalytic stability: the degradation rate remained at 58.6% and 97.3%, respectively, after 4 cycles while it only maintained at 22.0% for pure ZnO because the obtained ZnO/MXene hierarchical structure could provide uniform active sites on the surface and porous structure, preventing the aggregation of ZnO or MXene. Therefore, this work could provide a feasible design strategy to improve the catalytic performance of 2D photocatalysts and shed a light on the design of other photocatalysts.

The Fowler–Nordheim plot behaviour from virtual field emitters arrays of zinc oxide nanorods mixed with carbon nanotubes

ABSTRACT The Fowler–Nordheim plot behaviour is investigated for large area field emitters arrays composed of mixtures of ZnO nanorods and single-wall carbon nanotubes (CNTs). The field emission current–voltage characteristics are calculated using the Murphy-Good equation based on the Fowler–Nordheim model. The influencing factors taken into consideration are the radii of the ZnO rods, the heights of the CNTs, the variation of the onset voltage of the saturation of the ZnO conduction band (CB) emission current and the degradation of the CNTs at high applied voltages. The results show that the FN plots of the mixed arrays exhibit nonlinear behaviour near the high-field region which could be related to the FN plot behaviour of the constituting emitters arrays. The distribution of the emitters geometrical parameters and the onset of saturation of the ZnO CB current are found to affect the FN plot behaviour of the pure ZnO, CNTs arrays as well as mixed arrays. The comparisons between the FN plots from the present work and those measured experimentally are found useful to shed light on the field emission mechanism. This may in turn aid the development of complex field emission arrays for future technological applications. The work also shows the possibility to apply the standard FN model to complex large area field emitters arrays.

Phenol removal and hydrogen production from water: Silver nanoparticles decorated on polyaniline wrapped zinc oxide nanorods

The toxic and carcinogenic organic compounds discharge from industries, contaminate the natural reservoirs of water and air which eventually pose a global threat not only to the aquatic life but also to the humanity. Herein, ternary nanocomposites of silver-nanoparticle (AgNPs)-decorated on polyaniline (Pani)-wrapped zinc oxide nanorods (AgNPs@Pani/ZnO) were prepared via a facile approach. The nanocomposite degraded 97.91% phenol with an optimized dosage and concentration of H2O2. Moreover, the apparent rate constant for phenol degradation was 3.69 times higher than for pure ZnO nanorods. The hydrogen production from AgNPs@Pani/ZnO was 1.58 and 2.74 times higher than Pani/ZnO and ZnO, respectively. The enhanced phenol degradation and hydrogen production is attributed to the transfer of holes to the Pani, from which the electrons were transferred to the conduction band of ZnO and eventually to the conduction band of the AgNPs, where they accelerated the redox reactions for rapid photolysis of water and phenol. The concentration of the catalyst dosage affected the rate of phenol degradation. Further, response surface methodology was also applied in order to design 13 sets of random experiments in which the catalyst dosage and degradation time were varied to predict the phenol degradation.

Localized surface plasmon and transferred electron enhanced UV emission of ZnO by periodical aluminum nanoparticle arrays

Periodical Al nanoparticle (NP) arrays were applied to enhance the ultraviolet (UV) light emission of ZnO by localized surface plasmon resonance (LSPR) effect and electron transfer mechanism. By applying corresponding anodic aluminum oxide (AAO) templates, periodical Al NP arrays with different diameters (D) and spaces (S) were manufactured by magnetron sputtering. Theoretical simulation by FDTD-solution indicates that local electric field around Al NPs is significantly enhanced, and the surface plasmon resonance wavelength is determined by D and S. Al NP arrays with D of 70 nm and S of 125 nm enhanced near band-edge emission of ZnO by 2.4 times. By adding Al NP arrays, the photonic lifetime of ZnO decreased by 0.09 ns according to time-resolved photoluminescence spectra, indicating that the enhancement in UV luminescence intensity of ZnO is ascribed to the coupling between surface plasmons of Al NPs and ZnO excitons. Deep-level emission spectra analysis indicates that there lies another mechanism of electron transfer from the Al NPs to surface plasmon resonance (SPR) level and then further to ZnO conduction band.

Electron-hole plasma Fabry-Perot lasing in a Ga-incorporated ZnO microbelt via Ag nanoparticle deposition.

In this work, individual ZnO via Ga-doped (ZnO:Ga) microbelts with excellent crystallinity and smooth facets can enable the realization of lateral microresonator Fabry-Perot (F-P) microlasers, and the F-P lasing action originates from excitonic state. Interestingly, introducing Ag nanoparticles (AgNPs) deposited on the microbelt can increase F-P lasing characteristics containing a lower threshold and enhanced lasing output. Especially for the large size AgNPs (the diameter d is approximately 200 nm), the lasing features also exhibit a significant redshift of each lasing peak and an observable broadening of the spectral line width with an increase of the excitation fluence. And the remarkable lasing characteristics are belonging to the electron-hole plasma (EHP) luminescence. The behavior and dynamics of the stimulated radiation in an AgNPs@ZnO:Ga microbelt are studied, suggesting the Mott-transition from the excitonic state to EHP state that is responsible for the F-P lasing. These features can be attributed to the working mechanism that the hot electrons created by the large size AgNPs through nonradiative decay can fill the conduction band of nearby ZnO:Ga, leading to a downward shift of the conduction band edge. This novel filling influence can facilitate bandgap renormalization and result in EHP emission. The results provide a comprehensive understanding of the transition between excitonic and EHP states in the stimulated emission process. More importantly, it also can provide new scheme to developing high efficiency and ultra-low threshold microlasing diodes.

Low-Operating-Temperature NO2 Sensor Based on a CeO2/ZnO Heterojunction.

CeO2/ZnO-heterojunction-nanorod-array-based chemiresistive sensors were studied for their low-operating-temperature and gas-detecting characteristics. Arrays of CeO2/ZnO heterojunction nanorods were synthesized using anodic electrodeposition coating followed by hydrothermal treatment. The sensor based on this CeO2/ZnO heterojunction demonstrated a much higher sensitivity to NO2 at a low operating temperature (120 °C) than the pure-ZnO-based sensor. Moreover, even at room temperature (RT, 25 °C) the CeO2/ZnO-heterojunction-based sensor responds linearly and rapidly to NO2. This sensor’s reaction to interfering gases was substantially less than that of NO2, suggesting exceptional selectivity. Experimental results revealed that the enhanced gas-sensing performance at the low operating temperature of the CeO2/ZnO heterojunction due to the built-in field formed after the construction of heterojunctions provides additional carriers for ZnO. Thanks to more carriers in the ZnO conduction band, more oxygen and target gases can be adsorbed. This explains the enhanced gas sensitivity of the CeO2/ZnO heterojunction at low operating temperatures.