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The recent advances in the field of gas sensing technology by the introduction of van der Waals (vdW) heterostructures have attracted worldwide attention. The integration of atomically thin layers of 2D materials with other materials significantly improves the molecular detection capability due to high surface area, tunable junction properties, and their synergistic effects. Therefore, a deeper understanding of the exciting physics of vdW heterostructures is of considerable importance for developing advanced and versatile gas sensors. As a result, here we present a critical review highlighting the recent developments in gas sensors with a particular emphasis on vdW heterostructures. We provide a deep understanding of different kinds of 2D/0D, 2D/1D, 2D/2D, and 2D/3D heterostructures and their sensing mechanism towards realizing high-performance practical gas sensors. Finally, we summarize the article by stressing the challenges and giving our perspective on the applications of vdW heterostructures in developing next-generation gas sensors. [ABSTRACT FROM AUTHOR]

Gas sensors that exhibit high sensitivity and possess astonishingly low detection limits are appealing for a wide range of practical applications, such as real-time environmental monitoring, exhaled breath diagnostics, security, medical diagnosis and the quality of food analysis. 2D tungsten disulfide/selenide is extensively investigated as a viable material for the fabrication of chemiresistive gas sensors due to its low price, high stability, high sensitivity, distinct electronics, and catalytic characteristics. To improve the performance parameters of the sensor, such as response, sensitivity, selectivity, and long-term stability, the sensing material layer of 2D-WS2 and WSe2 is modified by decorating it with different metal nanoparticles that form heterojunctions or composites of 2D material or semiconductor and carbon derivatives. In this article, we presented an in-depth review of current advancements in WS2 and WSe2-based chemiresistive gas sensors, with particular prominence on the role played by the various noble metal-decorated 2D materials and composites for high performance characteristics, including enhanced response, faster response and recovery times, reduced operating temperatures, and extremely low detection limits. We also talk about the difficulties that 2D-WS2 and WSe2 chemiresistive sensors face and their potential in the future. [ABSTRACT FROM AUTHOR]

Reduced tin dioxide/copper phthalocyanine (SnOx/CuPc) heterojunctions recently gained much attention in hybrid electronics due to their defect structure, allowing tuning of the electronic properties at the interface towards particular needs. In this work, we focus on the creation and analysis of the interface between the oxide and organic layer. The inorganic/organic heterojunction was created by depositing CuPc on SnOx layers prepared with the rheotaxial growth and vacuum oxidation (RGVO) method. Exploiting surface sensitive photoelectron spectroscopy techniques, angle dependent X-ray and UV photoelectron spectroscopy (ADXPS and UPS, respectively), supported by semi-empirical simulations, the role of carbon from adventitious organic adsorbates directly at the SnOx/CuPc interface was investigated. The adventitious organic adsorbates were blocking electronic interactions between the environment and surface, hence pinning energy levels. A significant interface dipole of 0.4 eV was detected, compensating for the difference in work functions of the materials in contact, however, without full alignment of the energy levels. From the ADXPS and UPS results, a detailed diagram of the interfacial electronic structure was constructed, giving insight into how to tailor SnOx/CuPc heterojunctions towards specific applications. On the one hand, parasitic surface contamination could be utilized in technology for passivation-like processes. On the other hand, if one needs to keep the oxide's surficial interactions fully accessible, like in the case of stacked electronic systems or gas sensor applications, carbon contamination must be carefully avoided at each processing step. [ABSTRACT FROM AUTHOR]

Reduced tin dioxide/copper phthalocyanine (SnOx/CuPc) heterojunctions recently gained much attention in hybrid electronics due to their defect structure, allowing tuning of the electronic properties at the interface towards particular needs. In this work, we focus on the creation and analysis of the interface between the oxide and organic layer. The inorganic/organic heterojunction was created by depositing CuPc on SnOx layers prepared with the rheotaxial growth and vacuum oxidation (RGVO) method. Exploiting surface sensitive photoelectron spectroscopy techniques, angle dependent X-ray and UV photoelectron spectroscopy (ADXPS and UPS, respectively), supported by semi-empirical simulations, the role of carbon from adventitious organic adsorbates directly at the SnOx/CuPc interface was investigated. The adventitious organic adsorbates were blocking electronic interactions between the environment and surface, hence pinning energy levels. A significant interface dipole of 0.4 eV was detected, compensating for the difference in work functions of the materials in contact, however, without full alignment of the energy levels. From the ADXPS and UPS results, a detailed diagram of the interfacial electronic structure was constructed, giving insight into how to tailor SnOx/CuPc heterojunctions towards specific applications. On the one hand, parasitic surface contamination could be utilized in technology for passivation-like processes. On the other hand, if one needs to keep the oxide's surficial interactions fully accessible, like in the case of stacked electronic systems or gas sensor applications, carbon contamination must be carefully avoided at each processing step.