Multifunctional two-dimensional glassy graphene devices for vis-NIR photodetection and volatile organic compound sensing

Multifunctional devices are of great interest for integration and miniaturization on the same platform, but simple addition of functionalities would lead to excessively large devices. Here, the photodetection and chemical sensing device is developed based on two-dimensional (2D) glassy-graphene that meets similar property requirements for the two functionalities. An appropriate bandgap arising from the distorted lattice structure enables glassy graphene to exhibit comparable or even improved photodetection and chemical sensing capability, compared with pristine graphene. Due to strong interactions between glassy graphene and the ambient atmosphere, the devices are less sensitive to photoinduced desorption than the ones based on graphene. Consequently, the few-layer glassy graphene device delivers positive photoresponse, with a responsivity of 0.22 A W−1 and specific detectivity reaching ∼1010 Jones under 405 nm illumination. Moreover, the intrinsic defects and strain in glassy graphene can enhance the adsorption of analytes, leading to high chemical sensing performance. Specifically, the extracted signal-to-noise-ratio of the glassy graphene device for detecting acetone is 48, representing more than 50% improvement over the device based on graphene. Additionally, bias-voltage- and thickness-dependent volatile organic compound (VOC) sensing features are identified, indicating the few-layer glassy graphene is more sensitive. This study successfully demonstrates the potential of glassy graphene for integrated photodetection and chemical sensing, providing a promising solution for multifunctional applications further beyond

Soft Nanoelectronic Devices Based on Novel 2D Nanomaterials and Self-assembled Organic Semiconductors

Department of Energy EngineeringRecent advances in electronic device are focused on a fabrication of flexible and stretchable electronic gadgets in a low-cost and sustainable ways. The fabrication of flexible and stretchable electronic devices is highly challenging using inorganic or Si-based electronic materials due to its fragile nature upon a strain. Utilization of solution-processable organic materials including small molecules and polymer in organic field effect transistors (OFETs), light emitting diodes, and solar cells, facilitates a low-cost, large-area, cheap, and environment-friendly mass production for the fabrication of flexible and stretchable electronic devices. Conjugated small molecules and polymers continue to be studied intensively as semiconducting and conducting materials due to its tunability of their electronic and optoelectronic properties. Graphene, a single layer of two-dimensional (2D) carbon atoms in a honeycomb lattice, has attracted enormous attention due to its unique electronic, optical, thermal, and mechanical properties. It has an extremely high charge carrier mobility (~ 200,000 cm2V???1s???1), an optical transmittance of 97.7%, a theoretical sheet resistance of 30 ??/sq, a high fracture strain resistance greater than 20%, and chemical stability. These features make it highly promising for applications in flexible electronics and energy conversion devices, including touch screens, field-effect transistors (FETs), capacitors, batteries, solar cells, and light-emitting diodes (LEDs). However, the zero-band gap, small optical absorption, and chemical inertness have limited its practical application in switching and optoelectronic devices. Similar to graphene, transition metal dichalcogenides (TMDCs) are 2D materials stacked by van der Waals forces. Contrary to graphene, which does not have a bandgap energy, TMDCs have tunable bandgaps unlike to graphene. Typically, bulk TMDCs show indirect bandgap. On the other hand, the bandgap of TMDCs gradually decrease to one monolayer. Herein, I present a forward-looking my research results which are mainly focused on the interface studies between organic electronic materials and 2D nanomaterials including graphene and MoSe2, because of the importance of the mechanism and the behavior of electrical property change when organic electronic materials and 2D nanomaterials comes together in the electronic device system. When it comes to the interface study between heterogeneous electronic materials, doping of organic semiconductor and 2D nanomaterials is one of the important steps to enhance the electrical performance. Especially, n-doping of organic semiconductor is more challenging than p-doping because the n-dopants have to show a very low ionization potential to enable electrons to be transferred effectively, which renders most possible candidates unstable in air. Among the various doping strategies, surface transfer doping technique has been investigated for graphene and MoSe2 to modify or enhance their electrical or optoelectrical properties without severe damage on the surface of matrix. In addition, new carbon-based materials with honey comb structure or graphitic structure applying heterogenous atoms such as nitrogen (nitrogen doped reduced graphene oxide and 2D polyaniline) are explored to figure out their unique electrical properties and potential of electronic application. The experimental results and discussion in this thesis represent a forward-looking insight in charge transport behavior when organic electronic materials and 2D nanomaterials make junction together and pave the way of the applicability of organic semiconductors in conventional microelectronic infrastructures, which will lead to progress in the realization of soft nanoelectronic devices.ope

Hybrid Materials Based on Carbon Nanotubes and Graphene: Synthesis, Interfacial Processes, and Applications in Chemical Sensing

Development of hybrid nanostructures based on two or more building blocks can significantly expand the complexity and functionality of nanomaterials. For the specific objective of advanced sensing materials, single-walled carbon nanotubes and graphene have been recognized as ideal platforms, because of their unique physical and chemical properties. Other functional building blocks include polymers, metal and metal oxide nanostructures, and each of them has the potential to offer unique advances in the hybrid systems. In any case of constructing hybrid nanostructures, challenges exist in the controlling of composition, morphology and structure of different nanoscale building blocks, as well as the precise placement of these building blocks in the final assembly. Both objectives require systematical exploration of the synthetic conditions. Furthermore, there has been an increasing recognition of the fundamental importance of interface within the nanohybrid systems, which also requires detailed investigation. We have successfully developed several innovative synthetic strategies to regulate the assembly of nanoscale building blocks and to control the morphology of the hybrid systems based on graphitic carbon nanomaterials. We demonstrate the importance of surface chemistry of each building block in these approaches. Moreover, interfacial processes in the hybrid system have been carefully investigated to elucidate their impacts on the functions of the hybrid products. Specifically, we explored the synthesis and characterization of hybrid nanomaterials based on single-walled carbon nanotubes and graphene, with other building blocks including conducting polymers, metal, metal oxide and ceramic nanostructures. We demonstrated the development of core/shell morphology for polyaniline and titanium dioxide functionalized single-walled carbon nanotubes, and we showed a bottom-up synthesis of metal nanostructures that involves directed assembly and nanowelding of metal nanoparticles on the graphitic surfaces. Through electrical, electrochemical and spectroscopic characterizations, we further investigated their surface chemistry, interfacial interaction/processes, as well as their fundamental influence on the performance of the hybrid systems. We showed improved or even synergic properties for each hybrid system. Their chemical sensitivities, material stabilities, and charge separation efficiency were superior to individual components. These properties hold great promise in the real-world sensor applications, and can potentially benefit other research fields such as catalysis and green energy

Spray-Coated Graphene/Quantum Dots Paper-Based Photodetectors

Paper is an ideal substrate for the development of flexible and environmentally sustainable ubiquitous electronic systems. When combined with nanomaterials, it can be harnessed for various Internet-of-Things applications, ranging from wearable electronics to smart packaging. In this study, we present a non-vacuum spray deposition of arrays of hybrid single layer graphene (SLG)-CsPbBr3 perovskite quantum dots (QDs) photodetectors on a paper substrate. This approach combines the advantages of two large-area techniques: chemical vapor deposition (CVD) and spray-coating. The first technique allows for the pre-deposition of CVD SLG, while the second enables the spray coating of a mask to pattern CVD SLG, electrode contacts, and photoactive QDs layers. The prepared paper-based photodetectors achieved an external responsivity of 520 A/W under 405 nm illumination at <1V operating voltage. By fabricating arrays of photodetectors on a paper substrate in the air, this work highlights the potential of this scalable approach for enabling ubiquitous electronics on paper

Environment-Induced Reversible Modulation of Optical and Electronic Properties of Lead Halide Perovskites and Possible Applications to Sensor Development: A Review

none4siLead halide perovskites are currently widely investigated as active materials in photonic and optoelectronic devices. While the lack of long term stability actually limits their application to commercial devices, several experiments demonstrated that beyond the irreversible variation of the material properties due to degradation, several possibilities exist to reversibly modulate the perovskite characteristics by acting on the environmental conditions. These results clear the way to possible applications of lead halide perovskites to resistive and optical sensors. In this review we will describe the current state of the art of the comprehension of the environmental effects on the optical and electronic properties of lead halide perovskites, and of the exploitation of these results for the development of perovskite-based sensors.openDe Giorgi, ML; Milanese, S; Klini, A; Anni, MDe Giorgi, Ml; Milanese, S; Klini, A; Anni,

Study of Mos2 and Graphene-Based Heterojunctions for Electronic and Sensing Applications

Since the discovery of graphene, there has been an increase in two-dimensional (2D) materials research for their scalability down to atomic dimensions. Among the analogs of graphene, transition metal dichalcogenides (TMDs) are attractive due to their exceptional electronic and optoelectronic properties. MoS2, a TMD, has several advantages over graphene and the industry workhorse Si, and has been reported to demonstrate excellent transistor performances. The key obstacle in the commercialization of MoS2 technology is low carrier mobility over large areas for top-down devices. Although there were several early reports on synthesis of atomically thin MoS2 with moderate mobility, transferring large area grown films to a substrate of choice leads to interface charges that degrade mobility. In our work, a top-down growth technique for synthesizing large area, 3-5 monolayers (ML) thick MoS2 film have been presented by pre-oxidation of metallic Mo instead of direct sulfidation. The growth temperature was significantly reduced in this method, eliminating free sulfur-induced degradation of the SiO2 gate dielectric. As a result, the leakage current was suppressed by a factor of \u3e108, when compared to a single step direct sulfidation method. Using these thin films, back-gated field effect transistors have been demonstrated with accumulation electron mobility \u3e80 cm2/Vs, on/off \u3e105, and subthreshold swing of 84 mV/dec; which are among the best results for MoS2 based transistors on SiO2 substrate. A hypothesis on current saturation has also been presented, attributing it to charge control rather than velocity saturation. The second part of our work aims at utilizing the best properties both graphene and MoS2 simultaneously by forming a heterojunction of these two atomically thin materials. Interestingly, these two materials have certain contrasting properties, for example, graphene based FETs have poor switching performance while MoS2 based FETs can outperform many state-of-the-art ultra-low power transistors. Fabricating a Schottky diode made of graphene and MoS2 allows the unique properties of these two materials to be combined and has been shown to be useful. A key property of these 2D heterojunctions is that each constituent of the heterojunction is so thin that it may not be able to completely screen an electric field from the second constituent, i.e. the Debye screening length can be greater than the layer thicknesses, so that voltage-induced interfacial tuning is achievable. This capability is unique to thin layers, most practically achieved in 2D heterojunctions, and has been exploited in recent “barristors”, which are 3-terminal devices with Schottky diodes where the barrier height can be tuned by an insulated gate. Such a tunable Schottky diode, similar to a triode vacuum tube is attractive for applications in RF circuits, photodetection and chemical sensing, analog and digital electronics, etc, with all the advantages of solid state devices e.g. high speed, low-cost and compactness. In this work, a graphene/MoS2 heterojunction on SiO2 dielectric has been fabricated to demonstrate a functional barristor device. By varying the gate bias between -20 V and +10 V, the barrier height could be modulated by \u3e0.65 eV, potentially enabling current control over 10 orders of magnitude at room temperature. Using the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of this device, we have also extracted the Richardson’s coefficient and electronic effective mass in MoS2 using a thermionic emission model, which are very important parameters required for proper engineering of these devices. After that, various applications of the barristor device have also been explored. The high optical response of the barristor has demonstrated the presence of photoconductive gain, and has been consistent with the changes in Schottky barrier height caused by the back-gate. The barristor has also been successful as gate-tunable toxic gas sensors, with lowest level detection lying around 100 ppb (parts per billion) for NO2 and 1 ppm (parts per million) for NH3. These observations highlight the potential applications of the graphene/MoS2 barristor for various electronic, optoelectronic and sensing applications. Finally, a mixed dimensional barristor made of graphene/InN nanowire heterojunction with a backgate has been demonstrated. The surface passivation of InN and the tunnel barrier formation at the graphene/NW interface have been achieved through controlled O2 plasma exposure, which has allowed an otherwise ohmic contact to turn into a gate tunable Schottky junction with \u3e1 eV barrier height. This device has been demostrated to perform sub-ppb level trace gas detection, photo-detection with very high sensitivity and a novel gate-controllable memristive action through longer O2 plasma exposure