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Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO 2 processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV. [ABSTRACT FROM AUTHOR]

The growth of hetero-epitaxial ZnO-AlN core–shell nanowires (NWs) and single crystalline AlN films on non-polar ZnO substrate at temperature of 380 °C by atomic layer deposition (ALD) was investigated. Structural characterization shows that the AlN shells have excellent single-crystal properties. The epitaxial relationship of [0002]ZnO//[0002]AlN, and [10−10]ZnO//[10−10]AlN between ZnO core and AlN shell has been obtained. The ZnO NW templates were subsequently removed by annealing treatment in forming gas, resulting in ordered arrays of AlN single-crystal nanotubes. The impact factors on the epitaxial growth of AlN films are thoroughly investigated. It turned out that the growth parameters including lattice mismatch between substrate and AlN, growth temperature, and the polarity of ZnO substrate play important roles on the growth of single-crystal AlN films by ALD. Finally, non-polar AlN films with single-crystalline structure have been successfully grown on m-plane ZnO (10−10) single-crystal substrates. The as-grown hollow AlN nanotubes arrays and non-polar AlN films with single-crystalline structures are suggested to be highly promising for applications in nanoscale devices. Our research has developed a potential method to obtain other inorganic nanostructures and films with single-crystalline structure at fairly low temperature. [ABSTRACT FROM AUTHOR]

The energy band alignment of AlN/β-Ga2O3 heterostructures was investigated by X-ray photoelectron spectroscopy. The valence band offsets were estimated to be −0.09 ± 0.1 eV (type II alignment) for AlN grown by plasma enhanced atomic layer deposition (PEALD) on β-Ga2O3 and 0.72 ± 0.1 eV (type I alignment) for AlN prepared by thermal atomic layer deposition (T-ALD) on β-Ga2O3, which gives the conduction band offsets of 1.39 ± 0.1 eV for PEALD AlN and 0.58 ± 0.1 eV for T-ALD AlN. The large difference in the band alignment for the AlN/β-Ga2O3 heterostructures is dominated by different levels of oxygen incorporation into the AlN films as a result of different deposition techniques. The determination of the band alignment of the AlN/β-Ga2O3 heterostructure has significant implications for the design of electronic and optical devices based on AlN/β-Ga2O3 heterojunctions. [ABSTRACT FROM AUTHOR]

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn 2 SnO 4 was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range. [ABSTRACT FROM AUTHOR]

Development of high-performance ammonia (NH 3) sensor is imperative for monitoring NH 3 in the living environment. In this work, to obtain a high performance NH 3 gas sensor, structurally well-defined WO 3 @SnO 2 core shell nanosheets with a controllable thickness of SnO 2 shell layer have been employed as sensing materials. The prepared core shell nanosheets were used to obtain a miniaturized gas sensor based on micro-electro-mechanical system (MEMS). By tuning the thickness of SnO 2 layer via atomic layer deposition, a series of WO 3 @SnO 2 core-shell nanosheets with tunable sensing properties were realized. Particularly, the sensor base on the fabricated WO 3 @SnO 2 nanosheets with 20-nm SnO 2 shell layer demonstrated superior gas sensing performance with the highest response (1.55) and selectivity toward 15 ppm NH 3 at 200 °C. This remarkable enhancement of NH 3 sensing ability could be ascribed to the formation of unique WO 3 -SnO 2 core-shell heterojunction structure. The detailed mechanism was elucidated by the heterojunction-depletion model with the help of specific band alignment. [ABSTRACT FROM AUTHOR]

• Heterostructured α-Fe 2 O 3 /ZnO core-shell NWs with precisely controlled shell thickness were synthesized by ALD. • The NWs structured MEMS gas sensors with 20 nm ZnO shell layer exhibited enhanced sensitive and selective H 2 S detection. • The maximum response of the α-Fe 2 O 3 /ZnO core-shell NWs gas sensor to 5 ppm H 2 S is 5.98 at an operating temperature of 250 °C. The α-Fe 2 O 3 /ZnO core-shell nanowires (NWs) on micro-electro-mechanical system structure were prepared for hydrogen sulfide (H 2 S) gas sensing. Core α-Fe 2 O 3 NWs were prepared by thermal oxidation and the ZnO shell layer was coated by atomic layer deposition, respectively. The diameter of the obtained α-Fe 2 O 3 /ZnO core-shell NWs increases uniformly with the increase of ZnO shell thickness. When the operating temperature is 250 °C, the maximum response of the α-Fe 2 O 3 /ZnO core-shell NWs gas sensor to 5 ppm H 2 S is 5.98, which is about five times of pure α-Fe 2 O 3 NWs gas sensor (∼1.1). Moreover, α-Fe 2 O 3 /ZnO core-shell NWs-based gas sensors showed good selectivity, response, and recovery properties to H 2 S. The improvement of gas response of core-shell NWs is due to the slender α-Fe 2 O 3 /ZnO core-shell NWs and the appropriate energy band structure between ZnO and α-Fe 2 O 3. Thus, the proposed α-Fe 2 O 3 /ZnO core-shell NWs will be one of ideal sensitive materials for H 2 S high-performance sensor. [ABSTRACT FROM AUTHOR]