Ternary TiO2/MoS2/ZnO hetero-nanostructure based multifunctional sensing devices

Discover Nano Research Ternary TiO2/MoS2/ZnO hetero‑nanostructure based multifunctional sensing devices Andrew F. Zhou1 · Soraya Y. Flores2 · Elluz Pacheco2 · Xiaoyan Peng3 · Susannah G. Zhang4 · Peter X. Feng2 Received: 20 December 2023 / Accepted: 16 September 2024 © The Author(s) 2024  OPEN Abstract Novel sensing applications benefit from multifunctional nanomaterials responsive to various external stimuli such as mechanics, electricity, light, humidity, or pollution. While few such materials occur naturally, the careful design of synergized nanomaterials unifies the cross-coupled properties which are weak or absent in single-phase materials. In this study, 2D M oS2 integrated with ultrathin dielectric oxide layers forms hetero-nanostructures with significant impacts on carrier transport. The ternary T iO2/MoS2/ZnO hetero-nanostructures, along with their individual properties, improve the performance of multifunctional sensing devices. The synthesized hetero-nanostructure exhibits a responsivity of up to 16 mA/W to 700 nm light and responds to 5 ppm ammonia gas at room temperature. These enhancements are attributed to interface charge transfer and photogating effects. The ternary TiO2/MoS2/ZnO hetero-nanostructure is compatible with existing semiconductor fabrication technologies, making it feasible to integrate into flexible, lightweight semiconductor devices and circuits. These results may inspire new photodetectors and sensing devices based on two-dimensional (2D) layered materials for IoT applications. Keywords Photodetector · Gas sensor · Two-dimensional material · Molybdenum disulfide · Zinc oxide · Titanium dioxide · Ternary hetero-nanostructure · Multifunctional sensor 1 Introduction The Internet of Things (IoT) is a rapidly growing field that connects physical devices to the Internet, enabling them to collect and exchange data for various applications [1]. Sensors play a crucial role in IoT by capturing real-world data and transforming it into digital information, including temperature sensors, humidity sensors, light sensors, and gas sensors [2]. However, traditional battery-powered sensors require frequent battery replacements or recharging, which can be impractical in largescale IoT deployments. Addressing this limitation, current research delves into the self-powered sensors which can reduce the need for external power sources and become more sustainable and environmentally friendly, especially in remote or inaccessible locations due to their self-sufficiency [3–6]. On the other hand, in the rapidly evolving Internet of Things (IoT) landscape, the development of multifunctional sensing extending beyond conventional applications aligns seamlessly with the demands of IoT devices. This innovative facet capitalizes on the unique properties of synergized and carefully engineered * Andrew F. Zhou, ; * Peter X. Feng, ; Soraya Y. Flores, ; Elluz Pacheco, ; Xiaoyan Peng, ; Susannah G. Zhang, | 1Department of Chemistry, Biochemistry, and Physics, Indiana University of Pennsylvania, Indiana, PA 15705, USA. 2Department of Physics, University of Puerto Rico, San Juan, Puerto Rico 00936, USA. 3Chongqing Key Laboratory of Brain‑Inspired Computing and Intelligent Control, College of Artificial Intelligence, Southwest University, Chongqing 400715, China. 4Physics and Astronomy Department, Vassar College, Poughkeepsie, NY 12604, USA. Discover Nano (2024) 19:157 | https://doi.org/10.1186/s11671-024-04112-7 Vol.:(0123456789) Research Discover Nano (2024) 19:157 | https://doi.org/10.1186/s11671-024-04112-7 2D nanoheterostructures. Moreover, the photoconductivity, coupled with the electrical conductivity of 2D hetero-nanostructures, contributes to the efficient charge transport within the hetero-nanostructure, thereby amplifying its sensitivity and responsiveness in photoinduced scenarios. This intrinsic ability not only ensures the sustainability of the multiple functional sensing devices but also contributes to the overall energy autonomy of IoT systems. For example, in outdoor or remote IoT deployments, where access to traditional power sources may be limited, the self-powered photodetector option enables continuous and uninterrupted operation, eliminating the need for external power sources in certain sensing modalities. The significant research and development of photodetectors based on two-dimensional (2D) materials, such as graphene [7–11] transition metal dichalcogenides [12, 13] (molybdenum disulfide, tungsten disulfide, and others), coordination polymer nanosheets [14] and hexagonal boron nitride [15–19] have been witnessed in the past decade. 2D Molybdenum disulfide ( MoS2)-based photodetectors [20, 21] have been successfully demonstrated. One particular advantage of this material is that, in its monolayer form, M oS2 undergoes a transition from an indirect to a direct bandgap. This feature makes it a direct bandgap semiconductor with a broad absorption spectrum ranging from ultraviolet to visible [22, 23]. Hence its electronic properties can be optimized by controlling the number of layers or by introducing defects for specific application customization. MoS2 also exhibits fast carrier dynamics and, as a result, MoS2-based photodetectors can have relatively fast response times [24]. In addition, MoS2 is a 2D material with a thin atomic structure, allowing for the fabrication of flexible and wearable photodetector devices, or integration with other materials to form heteronanostructures or hybrid nanocomposites [25]. On the other hand, gas sensing devices employing 2D MoS2 materials have emerged as a promising technology with notable sensitivity and selectivity for various gases such as nitrogen dioxide ( NO2), ammonia ( NH3), methane ( CH4), and hydrogen (H2) [26, 27], which is particularly valuable for environmental monitoring and industrial safety applications [28]. Additionally, the tunable bandgap of M oS2 enables tailored sensor responses for specific gases, enhancing its applicability across diverse detection scenarios [29]. Meanwhile, the research on 2D titanium dioxide ( TiO2) materials has garnered attention in detecting gases such as nitrogen dioxide ( NO2), ammonia ( NH3), carbon monoxide (CO), methane (CH4), and volatile organic compounds (VOCs) [14, 30], and research on two-dimensional zinc oxide (2D ZnO) materials has demonstrated their effectiveness in detecting gases such as nitrogen dioxide ( NO2), carbon monoxide (CO), methane (CH4), and volatile organic compounds (VOCs) [31, 32]. To enhance its performance or enable new functionalities in photodetector and gas sensor devices based on one material-based devices, M oS2 has been integrated with other 2D materials or nanostructures [33–38] to form binary heterostructures based sensor devices, including 2D MoS2/ZnO nanowire heterojunctions [39] and MoS2/TiO2 heterostructure phototransistors [40]. However, the binary sensors have limitations in terms of the specific wavelengths they (...truncated)