Tunable Electronic Properties Research Articles

Controlling Thermoelectric Properties of Laser-Induced Graphene on Polyimide

In the field of wearable thermoelectric generators, graphene-based materials have attracted attention as suitable candidates due to their low material costs and tunable electronic properties. However, their high thermal conductivity poses significant challenges. Low thermal conductivity due to porous structure of the laser-induced graphene, combined with its affordability and scalability, positions it as a promising candidate for thermoelectric applications. In this study, thermoelectric properties of the laser-induced graphene (LIG) on polyimide and their dependence on structural modifications of LIG were investigated. Furthermore, it was shown that increasing the laser scribing power on polyimide results in larger graphene flakes and a higher degree of graphitization. Electrical conductivity measurements indicated an increase with increasing laser power, due to a higher degree of graphitization, which enhances charge carrier mobility. Our findings reveal that LIG exhibits p-type semiconducting behavior, characterized by a positive Seebeck coefficient. It was shown that increasing laser power increased the Seebeck coefficient and electrical conductivity simultaneously, which is attributed to a charge carrier energy filtering effect arising from structures occurred on the graphene flakes. Moreover, the porous structure of LIG contributes to its relatively low thermal conductivity, ranging between 0.6 W/m·K and 0.85 W/m·K, which enhances the thermoelectric performance of LIG. It has been observed that with increasing laser power, the figure of merit for laser-induced graphene can be enhanced by nearly 10 times, which holds promising applications for laser-induced graphene due to the tunability of its thermoelectric performance by changing laser parameters.

Tunable electronic and photoelectric properties of Janus group-III chalcogenide monolayers and based heterostructures

Janus group-III chalcogenide monolayers and based heterostructures with breaking vertical structural symmetry offer additional prospects in the upcoming high-performance photoelectric devices. We studied the geometrical, electronic, and photoelectric properties of Janus group-III chalcogenide monolayers and heterostructures. The most energy favorable stacking design of ten vertical heterostructures are considered. The results showed that the Janus Se-In-Ga-S and S-In-Ga-Se monolayers exhibit semiconducting characteristics with the band gaps of 1.295 eV and 1.752 eV, respectively. Furthermore, the different stacking configurations and surface termination at interface can realize the transition of band alignment between type I and type II due to the interlayer coupling. Moreover, we systematically investigated the photoelectric properties of Janus group-III chalcogenide heterostructures and predicated an optimized power conversion efficiency of 16.2%. These findings can aid in comprehending the customized characteristics of Janus group-III chalcogenide heterostructures, offering theoretical guidance for creating innovative photoelectric devices.

Tunable electronic, transport, and optical properties of fluorine- and hydrogen-passivated two-dimensional Ga2O3 by uniaxial strain

Two-dimensional (2D) semiconductors have shown great prospects for future-oriented optoelectronic applications, whereas the applications of conventional 2D materials are significantly impeded by their low electron mobility (⩽200 cm2 V−1 s−1). In this work, strain-mediated fluorine- and hydrogen-passivated 2D Ga2O3 systems (FGa2O3H) have been explored via using first-principles calculations with the Heyd–Scuseria–Ernzerh and Perdew–Burke–Ernzerhof functionals. Our results reveal a considerable high electron mobility of FGa2O3H up to 4863.05 cm2 V−1 s−1 as the uniaxial tensile strain reaches 6%, which can be attributed to the enhanced overlapping of wave functions and bonding features. Overall, when applying uniaxial strain monotonously along the a(b) direction from compressive to tensile cases, the bandgaps of 2D FGa2O3H increase initially and then decrease, which originates from the changes of σ* anti-bonding in the conduction band minimum and π bonding states in the valence band maximum accompanying the lengthening Ga–O bonds. Additionally, when the tensile strain is larger than 8%, the stronger π bonding at the G point leads to an indirect-to-direct transition. Besides the highest electron mobility observed in n-type doped 2D FGa2O3H with 6% tensile strain, the electrical conductivity is enhanced and further elevated as the temperature increases from 300 K to 800 K. The variations of the absorption coefficient in the ultraviolet region are negligible with increasing tensile strain from 0% to 6%, which sheds light on its applications in high-power optoelectronic devices.

BODIPY-Based Macrostructures: A Design Strategy toward Enhancing the Efficiency of Dye-Sensitized Solar Cells.

Among the metal-free dyes, boron dipyrromethene (BODIPY) has attracted much attention in the solar cell industry due to its thermal stability and tunable electronic and photophysical properties. However, the low power conversion efficiency of dye-sensitized solar cells based on BODIPY has limited their widespread application. Accordingly, different types of structural modifications have already been proposed to improve the photophysical properties of the BODIPY dyes. In this study, we used the strategy of constructing BODIPY-based covalent macrostructures by integrating two BODIPY subunits via a π-linker in linear and cyclic configurations. To this end, various types of the π-linkers including butadiyne, phenyl, and thiophene derivatives are considered. The structural, electronic, and optical properties as well as the photovoltaic performance of BODIPY dimers are theoretically calculated within DCM solvent. The results indicate that for a given linker, the BODIPY dimers with a linear configuration show better performance as compared to their macrocyclic counterparts. The reason is the enhancement of π-conjugation length, higher light harvesting ability, and proper charge carrier separation in linearly linked BODIPYs. In the cyclic series, the dyes incorporating phenyl linkers exhibit greater power conversion efficiency of up to 9%. For the dyes with a linear configuration, the involvement of a thienyl-thiophene bridge results in lower charge recombination and enhances the efficiency by up to 15%, which are expected to be potential candidates for organic dyes applied in DSSCs.

Construction of Co1-xZnxFe2xGa2-2xO4 (0

Solid solutions are garnering substantial attention in the realm of solar energy utilization due to their tunable electronic properties, encompassing band edge positions and charge-carrier mobilities. In this study, we designed and synthesized Co1-xZnxFe2xGa2-2xO4 (0<x≤0.6) as a photocatalyst for CO2 conversion using H2O. Careful optical and photo/electrochemical characterizations unveiled that the relative content of CoGa2O4 and ZnFe2O4 not only substantially influences light absorption in the full solar spectrum but also modulates valence and conduction band positions. We thoroughly assessed the photocatalytic activity of Co1-xZnxFe2xGa2-2xO4 and found that when x=0.35, the solid-solution catalyst achieved a remarkable CO2 reduction rate to CH4 and CO (31.5 μmol g-1 h-1). Furthermore, this optimized solid-solution catalyst demonstrated impressive photostability. Characterization and DFT calculations revealed that the formation of a solid solution not only reduces the band gap and promotes the separation of electron-hole pairs to accelerate efficient CO2 photoreduction, but also the introduction of more FeO6 octahedral active sites in Co1-xZnxFe2xGa2-2xO4 solid solutions enhanced the effective photoreduction of CO2. This design results in high conversion efficiencies for producing solar fuels through CO2 reduction with H2O.

A First-Principles Investigation of InSiN2 Monolayer: A Novel Two-Dimensional Material with Enhanced Stability and Tunable Vibrational and Electronic Properties

A First-Principles Investigation of InSiN₂ Monolayer: A Novel Two-Dimensional Material with Enhanced Stability and Tunable Vibrational and Electronic Properties

Highly tunable electronic properties in γ-XSe (X = Ge and Sn) bilayer with strain and electric field

The recent experimental synthesis of the monolayer γ-GeSe, characterized by its unique Mexican-hat band dispersion, has attracted considerable research interest. However, the exploration of band gap engineering in bilayer γ-GeSe and γ-SnSe through the application of strain and electric fields remains under-investigated. In this study, we demonstrate that both strain and electric fields are effective methods for band gap engineering in bilayer γ-GeSe and γ-SnSe. We have discovered that strain can not only tune the band gap but also induce a transition from an indirect to a direct band gap. Furthermore, it is observed that the band gap of bilayer γ-GeSe and γ-SnSe can be modulated by an electric field, potentially leading to a transition from semiconductor to metal. Our findings suggest that band gap engineering via strain and electric fields is a promising approach for designing nanoelectronic and optoelectronic devices based on bilayer γ-GeSe and γ-SnSe.

Tunable Electronic and Optical Properties of MoGe2N4/AlN and MoSiGeN4/AlN van der Waals Heterostructures toward Optoelectronic and Photocatalytic Applications

Tunable Electronic and Optical Properties of MoGe2N4/AlN and MoSiGeN4/AlN van der Waals Heterostructures toward Optoelectronic and Photocatalytic Applications

Confined and spontaneously transformed oxidation structures due to the intrinsic heterogeneous surface morphology of C3N monolayer.

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and abinitio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen-C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation.

Vacancy Engineering in 2D Transition Metal Chalcogenide Photocatalyst: Structure Modulation, Function and Synergy Application.

Transition metal chalcogenides (TMCs) are widely used in photocatalytic fields such as hydrogen evolution, nitrogen fixation, and pollutant degradation due to their suitable bandgaps, tunable electronic and optical properties, and strong reducing ability. The unique 2D malleability structure provides a pre-designed platform for customizable structures. The introduction of vacancy engineering makes up for the shortcomings of photocorrosion and limited light response and provides the greatest support for TMCs in terms of kinetics and thermodynamics in photocatalysis. This work reviews the effect of vacancy engineering on photocatalytic performance based on 2D semiconductor TMCs. The characteristics of vacancy introduction strategies are summarized, and the development of photocatalysis of vacancy engineering TMCs materials in energy conversion, degradation, and biological applications is reviewed. The contribution of vacancies in the optical range and charge transfer kinetics is also discussed from the perspective of structure manipulation. Vacancy engineering not only controls and optimizes the structure of the TMCs, but also improves the optical properties, charge transfer, and surface properties. The synergies between TMCs vacancy engineering and atomic doping, other vacancies, and heterojunction composite techniques are discussed in detail, followed by a summary of current trends and potential for expansion.

Facile fabrication and tunable electronic properties of Azure A chloride/Si heterojunction for photoelectrical application

In this study, the fabrication, structural, and photoelectrical properties of AZACl on Si heterojunction (AZACl/Si HJ) were examined. The morphology of the thin film of AZACl was analyzed using SEM, while XRD studied the crystal structure. The UV spectrophotometer displayed three distinct absorption regions at 194, 260, and 605 nm due to their complex chemical structure. The electrical characteristics of the AZACl/Si HJ were investigated in dark circumstances at various temperatures. The J-V technique was used to derive the diode properties of AZACl/Si HJ. The photoelectric properties of the AZACl/Si HJ, such as photocurrent, sensitivity, and responsivity, were estimated. At - 0.5 V and light irradiance equals 100 mW/cm2, the calculated photocurrent equals 4.76 × 10−5 A/cm2, the sensitivity equals 20, and the responsivity equals 476 × 10−4. These results indicated that the fabricated AZACl/Si HJ exhibits photodiode characteristics.

Tunable electronic structure and optical properties of GaN monolayer via substituted doping and strain

In this study, the stability, optical properties and electronic structure of transition metal (TM) (Cr, Mn, Fe) doped GaN monolayers is investigated within the first-principles calculation methods. Additionally, the influence of biaxial strain on the aforementioned system is explored. The results demonstrate that substitutional doping effectively adjusts the electronic structure of GaN monolayer, enhancing its performance. The TM-doped GaN monolayer structures exhibit strong dynamic stability: doping with Cr and Fe bring magnetic properties, while Mn doping results in a half-metallicity property. In terms of optical absorption, the GaN:Mn system exhibits significant absorption in the infrared region, while GaN:Cr and GaN:Fe systems show stronger absorption in the visible light and ultraviolet regions compared to the pristine GaN monolayer. Under the biaxial strain from −3% to +12%, with increments of 3%, the band gap types of GaN:Cr, GaN:Fe, and GaN:Mn systems undergo minimal changes, with gradual reduction in gap values. Meanwhile, the optical absorption of doped systems exhibits systematic growth and redshift, particularly evident in the infrared-visible-ultraviolet spectral regions for the GaN:Mn system. These results indicate the controllability and variability of two-dimensional GaN materials, providing new avenues for the potential use of GaN as a material for optoelectronic devices.

Selective modulation of electronic transport in VO2 induced by 10 keV helium ion irradiation

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping.

Tunable electronic and optical properties of BAs/WTe2 heterostructure for theoretical photoelectric device design

The geometric structure of the BAs/WTe2 heterojunction was scrutinized by employing ab initio calculations grounded on density functional theory. Multiple configurations are constructed to determine the equilibrium state of the heterojunction with optimal stability. The results show that the H1-type heterojunction with interlayer distance of 3.92 Å exhibits exceptional stability and showcases a conventional Type-II band alignment, accompanied by a direct band gap measuring 0.33 eV. By applying external electric field and introducing strain, one can efficaciously modulate both the band gap and the quantity of charge transfer in the heterojunction, accompanied by the transition of band alignment from Type-II to Type-I, which makes it expected to achieve broader applications in light-emitting diodes, laser detectors and other fields. Ultimately, the heterojunction undergoes a transformation from a semiconducting to a metallic state. Furthermore, the outstanding optical characteristics inherent to each of the two monolayers are preserved, the BAs/WTe2 heterojunction also serves to enhance the absorption coefficient and spectral range of the material, particularly within the ultraviolet spectrum. It merits emphasis that the optical properties of the BAs/WTe2 heterojunction are capable of modification through the imposition of external electric fields and mechanical strains, which will expand its applicability and potential for future progression within the domains of nanodevices and optoelectronic apparatus.

Stimuli‐Responsive Color/Fluorescence Dual‐Switching Behaviors of 1,10‐Phenanthroline‐Based Viologen Derivatives with Halogen Anions

AbstractRecently, stimuli‐responsive color/fluorescence dual‐switchable materials have attracted great attention, whereas most of them respond to monostimulus. Therefore, it is essential to design two or multi‐stimuli‐responsive color/fluorescence dual‐switchable materials and develop their applications. Viologens, which respond to the electric potential, light irradiation, pH, and heat, are suitable for the construction of two‐ or multi‐stimuli‐responsive materials. Moreover, their easily modified chemical structure, tunable electronic properties, and excellent electrochemical characteristics can endow viologens with the desired color/fluorescence dual‐switching behaviors. Herein, novel electro‐ and photo‐stimuli responsive color/emission dual‐switchable viologen derivatives phen‐Vio[Cl− I−], phen‐Vio[2Cl−] and phen‐Vio[2I−] employing fluorophore 1,10‐phenanthroline as an N‐aryl substituent and halogen ions as anions are designed and synthesized. The introduction of 1,10‐phenanthroline groups onto the viologen skeleton can endow viologen derivatives with the color/fluorescence dual‐switching properties under electrical or light stimulus. While the introduction of halogen ions allows viologen derivatives to respond to both electrical and light stimuli simultaneously. Multifunctional devices fabricated with phen‐Vio[Cl− I−], phen‐Vio[2Cl−] or phen‐Vio[2I−] as active materials exhibit excellent electrochromic/electrofluorochromic and photochromic/photofluorochromic performance. Additionally, anti‐counterfeiting applications are successfully demonstrated by employing a commercial printer with self‐made ink and papers. It is believed that this work has important guiding significance for the design and development of multifunctional materials and devices.

Isothianaphthene quinoids: pyrazine-annelated structures for tuning electronic properties

Abstract The development of quinoidal systems with extended π-conjugation has elucidated the influence that diradical characteristics exert on structure–property relationships, which is significant because it broadens the possibilities for the use of organic semiconducting materials in organic electronics. However, the chain-length elongation of such quinoidal molecules has resulted in low chemical stability due to the large contribution of diradical characteristics and to the high level of the highest occupied molecular orbital (HOMO), both of which limit the synthesis of π-extended quinoidal molecules. Here, we describe solving this problem via aromatic stabilization. To accomplish this, we designed a system that utilizes electron-accepting pyrazine-fused thieno[3,4-b]pyrazine following the development of the isothianaphthene quinoids of thiophene 3-mer and 6-mer. Theoretical calculations indicate that the introduction of a pyrazine-annelated structure suppresses the diradical characteristics and stabilizes the HOMO energy level of quinoidal oligothiophenes. The thermal, photophysical, and physicochemical properties of newly synthesized quinoidal molecules with full annelation of the benzene and pyrazine rings were investigated. Quinoidal thiophene 3-mer functioned as an acceptor in organic solar cells with a power conversion efficiency of 1.04%. This study demonstrates that the introduction of pyrazine-fused rings is an effective molecular design to extend the chain length of quinoidal oligothiophenes.

Uniting Synergistic Effect of Single-Ni Site and Electric Field of B- Bridged-N for Boosted Electrocatalytic Nitrate Reduction to Ammonia.

Electrochemical conversion of nitrate, a prevalent water pollutant, to ammonia (NH3) is a delocalized and green path for NH3 production. Despite the existence of different nitrate reduction pathways, selectively directing the reaction pathway on the road to NH3 is now hindered by the absence of efficient catalysts. Single-atom catalysts (SACs) are extensively investigated in a wide range of catalytic processes. However, their application in electrocatalytic nitrate reduction reaction (NO3 -RR) to NH3 is infrequent, mostly due to their pronounced inclination toward hydrogen evolution reaction (HER). Here, Ni single atoms on the electrochemically active carrier boron, nitrogen doped-graphene (BNG) matrix to modulate the atomic coordination structure through a boron-spanning strategy to enhance the performance of NO3 -RR is designed. Density functional theory (DFT) study proposes that BNG supports with ionic characteristics, offer a surplus electric field effect as compared to N-doped graphene, which can ease the nitrate adsorption. Consistent with the theoretical studies, the as-obtained NiSA@BNG shows higher catalytic activity with a maximal NH3 yield rate of 168µgh-1cm-2 along with Faradaic efficiency of 95% and promising electrochemical stability. This study reveals novel ways to rationally fabricate SACs' atomic coordination structure with tunable electronic properties to enhance electrocatalytic performance.

Ultrafast Charge Transfer Cascade in a Mixed-Dimensionality Nanoscale Trilayer.

Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron-hole pairs) in specified directions for doing useful work, e.g., for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) and one-dimensional (1D) semiconducting single-walled carbon nanotubes (s-SWCNTs) make them good quantum confined model systems for fundamental studies of charge and exciton transfer across heterointerfaces. Here we demonstrate a mixed-dimensionality 2D/1D/2D MoS2/SWCNT/WSe2 heterotrilayer that enables ultrafast photoinduced exciton dissociation, followed by charge diffusion and slow recombination. Importantly, the heterotrilayer serves to double charge carrier yield relative to a MoS2/SWCNT heterobilayer and also demonstrates the ability of the separated charges to overcome interlayer exciton binding energies to diffuse from one TMDC/SWCNT interface to the other 2D/1D interface, resulting in Coulombically unbound charges. Interestingly, the heterotrilayer also appears to enable efficient hole transfer from SWCNTs to WSe2, which is not observed in the identically prepared WSe2/SWCNT heterobilayer, suggesting that increasing the complexity of nanoscale trilayers may modify dynamic pathways. Our work suggests "mixed-dimensionality" TMDC/SWCNT based heterotrilayers as both interesting model systems for mechanistic studies of carrier dynamics at nanoscale heterointerfaces and for potential applications in advanced optoelectronic systems.

High‐performance BCN‐C heterostructured electrocatalyst derived from covalent triazine frameworks for nitrogen reduction

AbstractDesigning and synthesizing heterostructure‐based catalysis combining two‐dimensional (2D) materials has attracted enormous attention in materials chemistry, especially for electrocatalysis, due to their tunable electronic properties and structure. In this work, a boron carbon nitride (BCN)‐coupled carbon (BCN‐C) heterostructure with improved electronic performance was synthesized starting from C‐ and N‐enriched 2D covalent triazine frameworks (CTFs) via a simple thermal transformation process using NaBH4 as the B source. The characterizations results showed that the B released from NaBH4 reacted with N and C in CTF, forming the BCN‐C heterostructure coupling the BCN and carbon with a strong interfacial effect. The electrocatalytic NRR experiments and density functional theory (DFT) calculation revealed that the interfacial electronic properties and large numbers of active sites of the BCN‐C heterostructure benefited the NRR. The BCN‐C‐1 catalyst showed a high Faradaic efficiency of 27.8% and an NH3 yield of 4.3 μg h−1 mgcat.−1 in 0.1 M HCl electrolyte, owing to its high specific surface area (288 m2/g) with a large number of exposed active sites and the Mott–Schottky effect from the BCN‐C heterostructure. This work highlights the design and synthesis of metal‐free catalysts with high activity and selectivity and makes them excellent candidates for electrocatalytic applications.

Edge modified zigzag GeS nanoribbon devices with tunable electronic properties and significant negative differential resistance effect: A first principle study

Using density functional theory (DFT) in combination with non-equilibrium Green's function (NEGF), we study the effects of edge modification on the structural, electronic, and transport properties of zigzag germanium sulphide nanoribbons (ZGeSNRs). Two different types of modification by H, F, and Cl atoms are considered, i.e., the unilateral edge modification (Ge or S edge) and the bilateral edge modification. The addition of modification atoms eliminates the dangling bonds at the edges and enhances the stability in general though the edge structure may be significantly modulated. The unilateral edge modifications do not change the metallic characteristics of ZGeSNRs but the bilateral edge modifications make them semiconductor. In addition, structures with one half-filled energy band separated from other bands can be realized to obtain strong negative differential resistance effects. A maximal peak-to-valley current ratio of 1.01×105 in the bias range 0.49–1.07 V is predicted in a H modified ZGeSNR, which should be promising for applications in low power and high performance nanoelectronic devices.