Applications In Electronic Devices Research Articles

Organic Thermoelectric Materials for Wearable Electronic Devices

Wearable electronic devices have emerged as a pivotal technology in healthcare and artificial intelligence robots. Among the materials that are employed in wearable electronic devices, organic thermoelectric materials possess great application potential due to their advantages such as flexibility, easy processing ability, no working noise, being self-powered, applicable in a wide range of scenarios, etc. However, compared with classic conductive materials and inorganic thermoelectric materials, the research on organic thermoelectric materials is still insufficient. In order to improve our understanding of the potential of organic thermoelectric materials in wearable electronic devices, this paper reviews the types of organic thermoelectric materials and composites, their assembly strategies, and their potential applications in wearable electronic devices. This review aims to guide new researchers and offer strategic insights into wearable electronic device development.

Friction Force Mapping of Molecular Ordering and Mesoscopic Phase Transformations in Layered-Crystalline Organic Semiconductor Films.

It is critical to understand molecular ordering processes in small-molecule organic semiconductor (OSC) films in optimizing electronic device applications, although it is difficult to observe and investigate the ordering characteristics at a mesoscopic or device scale. Here, we report that friction force microscopy (FFM) allows visualizing the ordering transformation process from a thermodynamically metastable phase to a stable phase at a mesoscopic scale. We utilized 2-octyl-benzothieno[3,2-b]naphtho[2,3-b]thiophene (2-C8-BTNT) as a typical highly layered-crystalline OSC. We found that the friction force between an AFM tip and spin-coated OSC films significantly depends on whether local film states are in metastable monolayer phase or stable bilayer-type herringbone (b-LHB) phase that exhibits high carrier mobility. The formation of the stable b-LHB phase leads to lower friction than the metastable monolayer phase, clearly visualizing the molecular order. Force map (Fmap) analysis indicates that the lower friction in the b-LHB phase should be associated with the reduction of interfacial adhesion force. Notably, the observed results demonstrate that the spin-coated thin film changes from continuous film with the monolayer phase to rugged microcrystal grains with the b-LHB phase when left at ambient conditions. By contrast, an appropriate post-thermal annealing process facilitates the phase transformation without inducing such morphological changes. The technique provides a unique and effective tool for revealing the relationship between processing conditions and device performance in polycrystalline OSC films.

Change in nonlinear optical response of C24 nanocage upon doping with lithium based superalkalis

Abstract Density functional theory (DFT) calculations are used to analyze the change in nonlinear optical (NLO) response, electronic and geometric properties of the Li based superalkalis doped C24 nanocage. It was observed that the adsorption of Li4N, Li3O and Li2F superalkalis on C24 nanocage results in thermodynamically stable isomers (A-F). The energy gap between the highest occupied and the lowest unoccupied molecular orbitals (GH-L) is reduced after superalkalis doping on carbon (C24) nanocage. Density of states spectra depict the strong contribution of superalkalis in HOMOs of the considered complexes. Natural bond orbital (NBO) charge analysis showed that the charge is being transferred from superalkali toward C24 nanocage. The values of polarizability (αo) and hyperpolarizability (βo) showed that doping of superalkalis on C24 has a significant effect on its NLO response, resulting in a considerable increase in values of αo and βo. Li4N@C24 isomer E showed the highest βo value of 6470.74 au. Time dependent density functional theory (TD-DFT) calculations are implemented to analyze the absorption spectra. This research provides unique and highly efficient superalkalis doped C24 isomers for their applications in future electronic devices.

Enhanced dielectric properties of copper substituted nickel ferrite nanoparticles for energy storage applications

In this study, it was aimed to obtain copper-substituted nickel ferrite nanoparticles, which are advantageous for use in energy storage devices such as batteries and supercapacitors that provide high energy storage capability with their high dielectric behavior, by co-precipitation method. Nickel ferrite nanoparticles in the form of CuxNi1-xFe2O4 containing copper substitution at ratios for x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 were synthesized. X-ray diffraction Method (XRD) was used to analyze the spinel structure, the purity phase, and the crystalline size of the nanoparticles. Field Emission Scanning Electron Microscopy (FE-SEM), and Fourier Transform Infrared (FTIR) Spectroscopy were also performed to investigate the particle size, morphological distribution, and the functional groups of the samples. The structural analyses confirmed the successfully produced single-phase pure cubic spinel nickel ferrite and copper-substituted nickel ferrites with nanometer-scale particle distribution. The Impedance Spectroscopy technique was used for the characterization of the dielectric properties of the samples. Frequency-dependent complex dielectric, impedance, modulus, and alternating current (AC) conductivity mechanisms of the copper-doped nickel ferrite nanoparticles (CuxNi1-xFe2O4) were determined. The results showed that copper-induced nickel ferrite nanoparticles display a promising dielectric material consisting of grains and grain boundaries which are confirmed by Maxwell-Wagner interface-type polarization, which is in agreement with Koop's theory. Furthermore, a remarkable enhancement is obtained on the dielectric parameters of copper-induced nickel ferrites for x = 0.2, and it is seen that this is a critical value on the doping ratio. In addition, the dielectric parameters decreased between x = 0.2–0.8 ratios but still showed higher values than pure nickel ferrites, confirming that nickel ferrites have a tunable dielectric behavior depending on the stoichiometric copper doping ratios. Therefore, this may make them a promising dielectric medium for further studies in various electronic device applications.

Low contact resistance and high breakdown voltage of AlGaN/GaN HEMT grown on silicon using both AlN/GaN superlattice and Al0.07Ga0.93N back barrier layer

In this study, the growth of a high-quality AlGaN/GaN high electron mobility transistor (HEMT) heterostructure on silicon (Si) by metal–organic chemical vapor deposition was investigated by utilizing both the AlN/GaN superlattice (SL) and Al0.07Ga0.93N back barrier (BB) techniques. An atomic force microscope and high-resolution x-ray diffractometer confirm a low surface roughness of 0.26–0.34 nm and the formation of a high-quality AlN/GaN SL and GaN channel. The AlGaN/GaN heterostructures exhibit a high electron mobility of up to 1700 cm2 V−1∙s and a high carrier concentration density of (1.02–1.06 × 1013 cm−2) for both heterostructures. The AlGaN/GaN HEMT devices demonstrate a low specific contact resistivity (ρ c) of 2.7 × 10−6 Ω·cm2 and a low contact resistance (RC ) of 0.3 Ω·mm for the heterostructure with a BB layer. Furthermore, the DC characteristics demonstrate that incorporating Al0.07Ga0.93N BB in the heterostructure results in a 19.2% increase in lateral breakdown voltage (with a 10 µm spacing) and a 27.5% increase in vertical breakdown voltage (at 1 mA cm−2) compared to heterostructures without Al0.07Ga0.93N BB within the AlN/GaN SL structure. Moreover, an improvement of 10.6% in the maximum saturation current (I DS) and 15.2% in on-resistance (R ON) has been achieved for the device fabricated on an Al0.07Ga0.93N BB structure. The insertion loss of the buffer layer improves to −1.40 dB mm−1 at 40 GHz. Consequently, the proposed heterostructure investigated in this study demonstrates suitability for electronic device applications.

Raman spectrum and phonon thermal transport in van der Waals semiconductor GaPS4

The emergent van der Waals semiconductor GaPS4 is heralding frontiers for gallium-based semiconductors. Despite its potential, the intricacies of its Raman spectrum and phonon heat transport remain elusive. In this research, experimental and theoretical methods are employed to give a comprehensive portrayal. The Raman spectra and phonon calculations obtained were cross-validated, affirming the study's credibility. A total of 28 Raman peaks were identified, with all phonon irreducible representations delineated. Advanced calculations unveiled notable shifts in the transition of GaPS4 from bulk to monolayer. During this process, phonons undergo a red shift, and the vibration contributions of different atoms change. The lifetime and group velocity of low wavenumber phonons are markedly reduced, suppressing the thermal conductivity in the monolayer. The thermal conductivity of GaPS4 bulk at 300 K is 0.5 W/m K, and 0.13 W/m K for monolayer, while the thermal conductivity in the cleavage direction is lower. These findings offer a detailed account of the complex Raman spectra and phonon thermal transport properties of GaPS4, setting the stage for its subsequent exploration and prospective applications in electronic and thermal devices, and contributing to enriching condensed matter theory of phonon thermal transport in van der Waals materials.

High-Performance Tin Oxide Thin-Film Transistors Realized by Codoping and Their Application in Logic Circuits.

Tin oxide is a promising channel material, offering the advantages of being low-cost and environmentally friendly and having a wide band gap. However, despite the high electron mobility of SnO2 in bulk, the corresponding thin-film transistors (TFTs) generally exhibit moderate performance, hindering their widespread application. Herein, we proposed a codoping strategy to improve both the electrical property and the stability of SnO2 TFTs. A comparative analysis between doped and undoped SnO2 was conducted. It is observed that taking advantage of the difference in ionic radii between two dopants (indium and gallium) and the tin ions in the host lattice can effectively reduce impurity-induced strain. Additionally, we investigated the effect of codoping content on SnO2 TFTs. The optimal codoped SnO2 (TIGO) TFTs demonstrate high performance, featuring a field-effect mobility of 15.9 cm2/V·s, a threshold voltage of 0.2 V, a subthreshold swing of 0.5 V/decade, and an on-to-off current ratio of 2.2 × 107. Furthermore, the devices show high stability under both positive and negative bias stress conditions with a small threshold voltage shift of 1.8 and -1.2 V, respectively. Utilizing the TIGO TFTs, we successfully constructed a resistor-loaded unipolar inverter with a high gain of 10.76. This study highlights the potential of codoped SnO2 TFTs for advanced applications in electronic devices.

A first-principles prediction of novel Janus ZrGeZ3H (Z = N, P, and As) monolayers: Raman active modes, piezoelectric responses, electronic properties, and carrier mobility.

In this article, an attempt is made to explore new materials for applications in piezoelectric and electronic devices. Based on density functional theory calculation, we construct three Janus ZrGeZ3H (Z = N, P, and As) monolayers and study their stability, piezoelectricity, Raman response, and carrier mobility. The results from phonon dispersion spectra, ab initio molecular dynamics simulation, and elastic coefficients confirm the structural, thermal, and mechanical stability of these proposed structures. The ZrGeZ3H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP3H and ZrGeAs3H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ3H monolayers possess both in-plane and out-of-plane piezoelectric coefficients, revealing that they are potential piezoelectric candidates. In addition, the carrier mobilities of electrons and holes along transport directions are anisotropic. Notably, the ZrGeP3H and ZrGeAs3H monolayers have high electron mobility of 3639.20 and 3408.37 cm2 V-1 s-1, respectively. Our findings suggest the potential application of the Janus ZrGeZ3H monolayers in the piezoelectric and electronic fields.

A systematic first-principles investigation of the structural, electronic, mechanical, optical, and thermodynamic properties of Half-Heusler ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) for spintronics and optoelectronics applications.

This paper is the first to look at the structural, electronic, mechanical, optical, and thermodynamic properties of the ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) half-Heusler (HH) using DFT based first principles method. The lattice parameters that we have calculated are very similar to those obtained in prior investigations with theoretical and experimental data. The positive phonon dispersion curve confirm the dynamical stability of ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The electronic band structure and DOS confirmed that the studied materials ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) are direct band gap semiconductors. The investigation also determined significant constants, including dielectric function, absorption, conductivity, reflectivity, refractive index, and loss function. These optical observations unveiled our compounds potential utilization in various electronic and optoelectronic device applications. The elastic constants were used to fulfill the Born criteria, confirming the mechanical stability and ductility of the solids ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn). The calculated elastic modulus revealed that our studied compounds are elastically anisotropic. Moreover, ANiX (ASc, Ti, Y, Zr, Hf; XBi, Sn) has a very low minimum thermal conductivity (Kmin), and a low Debye temperature (θD), which indicating their appropriateness for utilization in thermal barrier coating (TBC) applications. The Helmholtz free energy (F), internal energy (E), entropy (S), and specific heat capacity (Cv) are determined by calculations derived from the phonon density of states.

Structural, optical, and electrical properties of multi-component P-type oxide-semiconductor Cu-Mn-Sn-O thin films

P-type oxide semiconductors have attracted significant attention as conducting channel layers due to their wide applications in electronic devices. In this study, multi-component oxide-semiconductor Cu1–2xMnxSnxO thin films with x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.33 were prepared on glass substrates using a solution process accompanied by a spin-coating technique. A phase transition between the cupric oxide monoclinic structure and the rock salt structure was observed with increasing concentrations of Mn and Sn, while the concentration of Cu simultaneously decreased in the precursors. The crystallite size decreased throughout the samples, reaching a minimum value of 9.8 nm at an equimolar ratio. Scanning electron microscopy further confirmed this downward trend and indicated an improvement in the quality of the film surfaces. According to the optical absorption measurements, the bandgap energy ranged from 2.68 to 3.44 eV. Interestingly, the sheet resistance of Cu1–2xMnxSnxO films dropped sharply from 5.24 kΩ/sq for CuO to 0.034 kΩ/sq for the film with a molar ratio of Cu:Mn:Sn being 34:33:33.

In Situ Growth of COF/PVA-Carrageenan Hydrogel Using the Impregnation Method for the Purpose of Highly Sensitive Ammonia Detection.

Flexible ammonia (NH3) gas sensors have gained increasing attention for their potential in medical diagnostics and health monitoring, as they serve as a biomarker for kidney disease. Utilizing the pre-designable and porous properties of covalent organic frameworks (COFs) is an innovative way to address the demand for high-performance NH3 sensing. However, COF particles frequently encounter aggregation, low conductivity, and mechanical rigidity, reducing the effectiveness of portable NH3 detection. To overcome these challenges, we propose a practical approach using polyvinyl alcohol-carrageenan (κPVA) as a template for in the situ growth of two-dimensional COF film and particles to produce a flexible hydrogel gas sensor (COF/κPVA). The synergistic effect of COF and κPVA enhances the gas sensing, water retention, and mechanical properties. The COF/κPVA hydrogel shows a 54.4% response to 1 ppm NH3 with a root mean square error of less than 5% and full recovery compared to the low response and no recovery of bare κPVA. Owing to the dual effects of the COF film and the particles anchoring the water molecules, the COF/κPVA hydrogel remained stable after 70 h in atmospheric conditions, in contrast, the bare κPVA hydrogel was completely dehydrated. Our work might pave the way for highly sensitive hydrogel gas sensors, which have intriguing applications in flexible electronic devices for gas sensing.

Photo‐Directed Growth of Surface Micro‐Patterns on Photosensitive Semicrystalline Polymers

AbstractPatterning polymeric materials with controllable microstructures can meet diversified requirements and realize promising applications. Exploring micro‐/nano‐pattern methodology offers possibilities for future techniques, however, the self‐organized growth of polymeric materials has some limitations and the development of direct and noncontact patterning processes is still challenging. In this work, the study presents a facile strategy for endowing polymers with spatially regulated microstructures by direct photo‐printing, which incorporates both advantages of typical top‐down and bottom‐up approaches. By employing the photodimerization of anthracene‐containing semi‐crystallized polymers, the gradient crosslinking results in a mismatch of thermal expansion coefficients between the crosslinked surface and the uncrosslinked bottom layer. After heating treatment, constrained by the crosslinked surface, the uncrosslinked bottom polymer of the molten state in the exposed region tends to flow and migrate toward the unexposed region, similar to a volcanic eruption, which accurately determines the height and morphology of pattern. Besides, the well‐defined patterns can controllably grow upon thermal treatment due to phase transformation and migration. The versatility of the proposed strategy not only provides a brand‐new reliable platform to pattern functional materials with photo‐regulated and reversible microstructures, but also promotes the development of smart materials that can find applications in information safety, reversible microfluidics, and electronic devices.

N/S‐Doped Hierarchical Porous Bamboo Carbon Fibers with Ultra‐Large Surface Area and Highly Exposed Active Sites for Flexible Zinc‐Air Battery†

Comprehensive SummaryFacile mass transport channel and accessible active sites are crucial for binder‐free air electrode catalysts in rechargeable flexible zinc‐air battery (ZAB). Herein, a ZnS/NH3 dual‐assisted pyrolysis strategy is proposed to prepare N/S‐doped hierarchical porous bamboo carbon cloth (HP‐NS‐BCC) as binder‐free air electrode catalyst for ZAB. BCC fabric with abundant micropores is firstly used as flexible carbon support to facilitate the heteroatom‐doping and construct the hierarchical porous structure. ZnS nanospheres and NH3 activization together facilitate the electronic modulation of carbon matrix by N/S‐doping and optimize the macro/meso/micropores structure of carbon fibers. Benefiting from the highly‐exposed N/S‐induced sites with enhanced intrinsic activity, the optimized mass transport of biocarbon fibers, as well as the ultra‐large specific surface area of 2436.1 m2·g–1, the resultant HP‐NS‐BCC catalyst exhibits improved kinetics for oxygen reduction/evolution reaction. When applied to rechargeable aqueous ZABs, it achieves a significant peak power density of 249.1 mW·cm−2. As binder‐free air electrode catalyst, the flexible ZAB also displays stable cycling over 500 cycles with a minimal voltage gap of 0.42 V, showcasing promising applications in flexible electronic devices.

Structural, morphological, optical and electrical characterization of MgO thin films grown by sputtering technique on different substrates

Magnesium Oxide (MgO) thin film structures were deposited on glass and n-Si substrates by means of RF magnetron sputtering technique. Structural, morphological, optical characteristics of MgO thin film were determined by XRD, AFM and UV–Vis spectrometer techniques. The optical properties like absorption coefficient and optical band gap were extracted using optical transmittance and absorption spectra. The band-gap of MgO thin film was determined for direct electronic transition. Additionally, electric parameters like ideality factor, saturation current and barrier height of the Au/MgO/n-Si device were computed from the forward I–V data in dark state. The ideality factor was found to be greater than one. This indicates that the I–V characteristics of the device exhibits non-ideal attitude. The results show that the MgO thin film can be applied to both optical and electronic device applications.

Electrical conductivity of polyvinyl alcohol/carboxymethyl cellulose doped by zinc oxide and hematite nanoparticles for optoelectronics devices

This research explores polymer nanodielectrics, a category of materials where nanoceramic fillers are incorporated into polymers. These hybrid materials are gaining significant interest due to their tunable optical and electrical properties, making them potentially well-suited for applications in flexible optoelectronic and organic electronic devices. Polyvinyl alcohol (PVA), Carboxymethyl cellulose (CMC), zinc oxide (ZnO), and hematite (Fe2O3) nanoparticles (NPs) have been used to create nanocomposite materials in order to improve their optical and electrical characterization. Physical methods have been used to investigate the effects of varying hematite nanoparticle contents on the optical and electrical characterization of the prepared films. XRD analysis indicated a reduction in the crystalline character of the PVA/CMC blend following the incorporation of ZnO/Fe2O3 nanoparticles (NPs). FTIR data approved the interaction between the PVA/CMC composite and the ZnO/Fe2O3, leading to a decrease in intermolecular interactions within the polymeric matrix and coordination with the ZnO/Fe2O3. Electrical analysis obtained an enhancement in σac values with the rise of ZnO/Fe2O3 NPs content up to 30 min of laser ablation times in the polymeric nanocomposite due to the high content of ZnO/Fe2O3 NPs that were added to the PVA/CMC hybrid polymer matrix. The findings from this study suggest the promise of these materials for applications in high-performance batteries, supercapacitors, or other next-generation energy storage and conversion devices.

Study of the effects of heating on the physical, optical, and electrical properties of NiO thin films synthesized using a low-cost sol-gel method

Developments in low-cost techniques for growing high-quality nickel oxide thin films (NiOTFs) are critical enablers for the fabrication of NiO-based devices, particularly solar cells, light-emitting diodes, lasers, and many other applications. In this study, it has been demonstrated that the optical, electrical, and structural characteristics of NiOTFs coated on glass substrate employing a low-cost solution method are strongly influenced by post-thermal annealing treatments in ambient air. A comprehensive study was carried out on the characteristics of the deposited NiOTFs. X-ray diffraction (XRD) measurements indicate the enhancement of the crystal quality of films after annealing. There is a noticeable change and improvement in coated NiOTFs with heat treatment at 300 and 600 ℃ due to clear shifts in density. During the heating temperature increment, the energy of the band gap was shifted from 3.63 to 3.44 eV, and the electrical resistance of the NiOTFs varied from 1020 to 700 Ω-cm. Furthermore, the results indicate that the low-cost sol-gel (SG) deposition technique has a greater potential for producing high-quality p-type NiOTFs with minimal defects for electronic device applications.

Tuning the structural, optical, and dielectric properties of europium-doped barium titanate ceramics

This study explores the optical and dielectric properties of pure and europium-doped barium titanate ceramics with formula Ba1−3x/2EuxTiO3 (x=0,0.005,0.015and0.025\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x=0,0.005, 0.015\ ext{ and }0.025$$\\end{document}). The materials were synthesized using the solid-state reaction method. The influence of Eu + 3 ion incorporation on the crystal structure was examined using XRD, which indicated the formation of a cubic phase. Lattice parameter measurements showed excellent agreement with various theoretical models for predicting the lattice constant, with an average error of only 0.20%. UV–visible spectroscopy analysis is utilized to investigate optical characteristics, revealing a decrease in the optical band gap from 2.65 to 2.77 eV post-Eu doping, which is notably lower than the bulk barium titanate value of 3.2 eV. Materials with smaller band gaps are more suited for optoelectronic applications like photodetectors and light-emitting diodes (LEDs). The dielectric response of europium-doped barium titanate was studied across a frequency range of 1 kHz to 2 MHz and a temperature range of 77 to 300 K, showing remarkable stability. The frequency-dependent dielectric analysis revealed that the dielectric constant initially increased with increasing doping concentration, but decreased at higher concentrations. These results suggest that europium-doped barium titanate holds significant promise for future electronic device applications due to its enhanced optical and dielectric properties.

Novel penta-GeC5 nanosheet as potential candidate for efficient thermoelectric application: A DFT approach

Under the framework of density functional theory, we systematically explore the geometric, electronic, transport, and thermal properties of a novel 2D pentagonal monolayer of GeC5. Our calculations show that the structure is dynamically and mechanically stable. Simulated results indicate that the predicted monolayer is an indirect semiconductor with a band gap of 1.77 eV. Using the Bardeen and Shockley formula, the carrier mobility of the electrons is found to be 824.41 cm2 V−1 S−1, while that of holes registers a more significant value of 4433.84 cm2 V−1 S−1. The lattice thermal conductivity for the undoped system was calculated using the Slack model, recording values of 13.46 W/(m.K), 6.73 W/(m.K), and 4.49 W/(m.K) at 300K, 600K, and 900K, respectively. In the case of electron doping, the figure of merit (ZT) is only significant along the x-direction. ZT reaches a maximum value of 2.97 at T = 300K for an energy of 0.79 eV above the Fermi level. Hole doping, however, does not lead to exciting results due to the shallow ZT values. All reported results are vacuum-free, enabling an accurate and direct comparison with experimental data whenever available. The obtained electronic properties suggest that the penta-GeC5 monolayer is a promising candidate for new electronic device applications. Additionally, when appropriately doped, the figure of merit of penta-GeC5 is expected to increase with temperature, thus making it a key ingredient in producing thermoelectric devices on the nanoscale.

The impact of S vacancies on the modulation of the work function and Schottky barrier at the Au/MoS2 interface

The S vacancy at metal/MoS2 interface plays a much important role than the semiconductor itself. In this work, the influence of different configurations of S vacancy concentrations on the effective work function and band structure of the Au/MoS2 interface has been investigated systematically using first-principles calculations. The study specifically explores the effective work function of the Au/MoS2 interface, the deviation of interface effects from the vacuum work function, and the dipole moment caused by interface charge transfer. The results reveal that the electronic work function of Au/MoS2 increases with the increase in S vacancy concentration, but the rate of increase tends to slow down with higher S concentrations. The variation in the effective work function of the Au/MoS2 interface may be attributed to the presence of S vacancies and the exposure of Mo atoms. S vacancies lead to a reduction in the Schottky barrier, resulting in increased leakage current. The Fermi pinning caused by S vacancy concentration and location is also observed. The results obtained in this study can serve as a theoretical foundation for applications in electronic devices that rely on metal/MoS2 contact.

Enhanced n-Type Thermoelectric Properties and Structure Evolution of Carbonized Metal-Coordination Polydopamine.

Carbonized polydopamine (cPDA) exhibits a nitrogenous graphite-like structure with n-type semiconductor property. However, the low electrical conductivity and Seebeck coefficient of cPDA cannot meet the needs of flexible thermoelectric devices. In this study, a series of metal ions were coordinated with cPDA to enhance n-type thermoelectric properties. At 300 K, all metal-coordination cPDA (metal-cPDA) samples obtain lower thermal conductivity compared to cPDA. Mn-cPDA exhibits the greatest Seebeck coefficient of -25.94 μV K-1, which is almost six times higher than cPDA. Fe-cPDA shows the best electrical conductivity of 2.45 × 105 S m-1. An optimal power factor (PF) value of 11.93 μW m-1 K-2 is achieved in Ca-cPDA with the enhanced electrical conductivity of 9.5 × 104 S m-1 and Seebeck coefficient of -11.24 μV K-1. Using Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM), we revealed the structural characterization of metal-cPDA. Our results indictate that the different metal ions (Mn2+, Zn2+, Mg2+, Al3+, Ca2+, and Fe3+) exert varying influences on the growth of graphite-like structure within metal-cPDA, which lead to the evolution of electrical conductivity. We observe that the carrier density and carrier mobility depend on both the degree of graphitization and the metal-ion coordination, which work together on electrical conductivity and Seebeck coefficient. These findings and understanding of the thermoelectric properties of PDA-based materials will help to realize high-performance n-type thermoelectric materials for flexible electronic device applications.