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Visualization of Local Conductance in MoS 2 /WSe 2 Heterostructure Transistors
The vertical stacking of van der Waals (vdW) materials presents a new degree of freedom to the research of two-dimensional (2D) systems. The interlayer coupling strongly influences the band structure of the heterostructures, resulting in novel properties that can be utilized for electronic and optoelectronic applications. Based on microwave microscopy studies, we report quantitative electrical imaging on gated molybdenum disulfide (MoS 2 )/tungsten diselenide (WSe 2 ) heterostructure devices, which exhibit an intriguing antiambipolar effect in their transfer characteristics. Interestingly, in the region with significant source-drain current, electrons in the n-type MoS 2 and holes in the p-type WSe 2 segments are nearly balanced, whereas the heterostructure area is depleted of mobile charges. The spatial evolution of local conductance can be ascribed to the lateral band bending and formation of depletion regions along the line of MoS 2 -heterostructure-WSe 2 . Our work vividly illustrates the microscopic origin of novel transport behaviors, which is important for the vibrant field of vdW heterojunction research.
Sources and Mechanism of Degradation in p-Type Thiophene-Based Organic Electrochemical Transistors
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Processing, Structure, and Transistor Performance: Combustion versus Pulsed Laser Growth of Amorphous Oxides
Abstract not provided
Influence of Side Chains on the n-Type Organic Electrochemical Transistor Performance
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High-Performing Thin-Film Transistors in Large Spherulites of Conjugated Polymer Formed by Epitaxial Growth on Removable Organic Crystalline Templates
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Unraveling the Mechanism of Interfacial Charge Transfer and Photoresponsivity of WS 2 Quantum Dots/MoS 2 (0D–2D) Heterostructure-Based Transistors
To assess the efficacy of a mixed-dimensional van der Waals (vdW) heterostructure in modulating the optoelectronic responses of nanodevices, the charge transport properties of the transition-metal dichalcogenide (TMD)-based heterostructure comprising zero-dimensional (0D) WS 2 quantum dots (QDs) and two-dimensional (2D) MoS 2 flakes are critically analyzed. Herein, a facile strategy was materialized in developing an atomically thin phototransistor assembled from mechanically exfoliated MoS 2 and WS 2 QDs synthesized using a one-pot hydrothermal route. The amalgamated photodetectors exhibited a high responsivity of ∼8000 A/W at an incident power of 0.05 nW of white light, surpassing that of the pristine MoS 2 devices. Furthermore, the detectivity of pristine MoS 2 , which was on the order of 10 10 , increased to 10 12 Jones for the WS 2 QDs/MoS 2 heterostructure photodetector, outperforming other WS 2 -based materials. The quasiparticle band gap and density of states (DOS) are further analyzed to elucidate the photophysics of the WS 2 QD/MoS 2 hybrid assembly. The difference in the work function between MoS 2 and WS 2 QDs gives rise to an electric field across the 0D–2D interface, facilitating effective charge separation and migration and contributing to the enhancement of photoresponsivity. The analysis of optical responses using density functional theory (DFT) revealed stronger absorption and less reflection over a broader spectrum of wavelengths for the heterostructure compared to the pristine materials. The estimated optical conductivity aligns well with the experimentally predicted maximum photoresponsivity under visible light, which is attributed to the high absorbance of 2D MoS 2 . In conclusion, combining diverse spectroscopic and imaging techniques with quantum simulation provides insights that clarify the pertinence of 0D–2D TMDs in designing phototransistors.
Dithieno[3,2-c:3′,2′‑ h ][2,6]naphthyridine-4,9(5H,10H)-dione-Based Conjugated Polymers for High Stable n‑Type Organic Electrochemical Transistors
Amide/imide-based conjugated polymers have been utilized as n-type OECT materials and have demonstrated promising device performance. However, their performance remains insufficient in terms of both efficiency and stability, which limits their practical applications. The development of conjugated polymers based on amide and imide groups represents a promising approach to address this issue. Here, in this study, we introduced dithieno[3,2-c:3′,2′-h][2,6]naphthyridine-4,9(5H,10H)-dione (TVTDA) into the design of the OECT materials for the first time. By copolymerizing it with (E)-2,2′-(ethene-1,2-diyl)bis(thiophene-3-carbonitrile), we prepared two polymers, TVTDA-2CNTVT-ST and TVTDA-2CNTVT-BR, which contain linear or branched ethylene glycol side chains, respectively. OECT devices based on these polymers demonstrate n-type charge transport characteristics, achieving promising μC* values of 7.17 and 26.5 F cm –1 V –1 s –1 for TVTDA-2CNTVT-ST and TVTDA-2CNTVT-BR, respectively. The higher electron mobility and μC* of TVTDA-2CNTVT-BR can be attributed to its mixed edge-on and face-on stacking mode, larger crystalline coherence length, and larger domain size in the thin film. To our delight, the OECT devices based on both polymers exhibit good operational stability after operating in an aqueous solution for 2000 s, with current retention rates exceeding 93%, representing the high level among the OECT devices based on amide/imide-conjugated polymers. Our study demonstrates that the TVTDA unit holds great potential for constructing high-performance n-type OECT materials.
P-Type Electrochemical Doping Can Occur by Cation Expulsion in a High Performing Polymer for Organic Electrochemical Transistors
We investigate the mechanism of ion-dependent charge compensation during electrochemical oxidation (doping) of the model mixed ionic/electronic transporting polythiophene derivative poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT). Using a combination of electrochemical quartz microbalance gravimetry and glow discharge optical emission spectroscopy, we show that charge compensation during polymer redox processes proceeds via a cation-dependent mechanism. For p-type polymer oxidation in certain electrolytes, charge compensation is achieved by both eventual injection of anions into the film, as well as initial expulsion of cations from the film. We compare doping mechanisms for a variety of electrolyte salts including potassium chloride, tetrabutylammonium chloride, potassium hexafluorophosphate (KPF6), and tetrabutylammonium hexafluorophosphate. For the electrolyte KPF6, both the cations and anions coexist in the water-swelled polymer even prior to application of electrical bias. Our data indicate that electrochemical doping (hole injection into the polymer and ionic charge compensation) proceeds via the following mechanism: (1) hydration of the neutral film by electrolyte (water, cations, anions), (2) cation (K+) expulsion from the film upon initial application of an oxidative bias, and (3) anion injection into the film at higher oxidation/doping levels (>~2 × 1020/cm3). Understanding the mechanism of charge compensation during the doping process should allow for the design of improved mixed ionic/electronic conductors for use in applications ranging from organic supercapacitors and redox flow batteries to bioelectronic sensors, thermoelectrics, and devices for neuromorphic computing.
Reply to “Comment on ‘Gate-Controlled Metal–Insulator Transition in TiS 3 Nanowire Field-Effect Transistors’”
The Comment of Gorlova et al. makes some important observations regarding the nature of temperature-dependent conduction in nanostructured TiS 3 . Their assertion that carriers condense into a well-formed CDW below ~60 K and that robust fluctuations out of this state are possible at significantly higher temperatures than this appears consistent with many of the aspects of our experiment. It needs to be noted here that TiS 3 differs significantly from TaS 3 or NbSe 3 , other trichalcogenide materials that have been widely used to study CDW physics. The latter materials are metallic, and thus CDWs or 2D Peierls’ distortions are to be expected. Nonetheless, we disagree with the assertion that there is no MIT in our system and argue instead for the presence of a degenerate semiconductor in TiS 3 at T > ~220 K. Finally, in this state, the material is essentially metal-like, with a conductivity that is limited by phonon scattering and no obvious indication of localization effects. Rather, the dominant source of scattering in this regime is believed to be due to the low-energy polar optical phonons of this material.
Transient Response of h-BN-Encapsulated Graphene Transistors: Signatures of Self-Heating and Hot-Carrier Trapping
Not Available
High Crystalline Dithienosilole-Cored Small Molecule Semiconductor for Ambipolar Transistor and Nonvolatile Memory
Abstract not provided