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• 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]

Atomic scale control of the thickness of thin film makes atomic layer deposition highly advantageous in the preparation of high quality super-lattices. However, precisely controlling the film chemical stoichiometry is very challenging. In this study, we deposited SiOx film with different stoichiometry by plasma enhanced atomic layer deposition. After reviewing various deposition parameters like temperature, precursor pulse time, and gas flow, the silicon dioxides of stoichiometric (SiO2) and non-stoichiometric (SiO1.8 and SiO1.6) were successfully fabricated. X-ray photo-electron spectroscopy was first employed to analyze the element content and chemical bonding energy of these films. Then the morphology, structure, composition, and optical characteristics of SiOx film were systematically studied through atomic force microscope, transmission electron microscopy, X-ray reflection, and spectroscopic ellipsometry. The experimental results indicate that both the mass density and refractive index of SiO1.8 and SiO1.6 are less than SiO2 film. The energy band-gap is approved by spectroscopic ellipsometry data and X-ray photo-electron spectroscopy O 1s analysis. The results demonstrate that the energy band-gap decreases as the oxygen concentration decreases in SiOx film. After we obtained the Si-rich silicon oxide film deposition, the SiO1.6/SiO2 super-lattices was fabricated and its photoluminescence (PL) property was characterized by PL spectra. The weak PL intensity gives us greater awareness that more research is needed in order to decrease the x of SiOx film to a larger extent through further optimizing plasma-enhanced atomic layer deposition processes, and hence improve the photoluminescence properties of SiOx/SiO2 super-lattices. [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]