Tunable Electronic Properties Research Articles

Rippled blue phosphorene with tunable energy band structures and negative Poisson’s ratio

Recent successes in the discovery of novel two-dimensional (2-D) phosphorene allotropes have motivated more in-depth investigations into tuning their properties through precise geometric control. This is also driven by the fact that these materials, particularly blue phosphorene, are highly prone to wrinkling. In this work, we systematically study the mechanical and electronic behaviors of a series of rippled blue phosphorene PN (N = 8, 18, 32, 50, 72, 98) using density functional theory combined with molecular dynamic simulations. A novel approach to tailor the electronic energy band structure of blue phosphorene is proposed by wrinkle engineering, transforming the native indirect bandgap into a direct bandgap, and enabling bandgap tuning by modifying the undulation magnitude ratio. Furthermore, the mechanical behaviors of rippled blue phosphorene differ significantly along the 4-8-4 and 4-4-4 directions. Notably, negative Poisson’s ratio is observed under tension along the 4-4-4 direction. This work demonstrates new techniques for geometrically regulating blue phosphorene and potentially other 2-D materials. The findings also yield valuable insights for the design of novel 2-D auxetic semiconductors with tunable electronic properties.

Heterostructured MoO3 Anchored Defect-Rich NiFe-LDH/NF as a Robust Self-Supporting Electrocatalyst for Overall Water Splitting.

The rational design of inexpensive metal electrocatalysts with exciting catalytic activity for overall water splitting (OWS) remains a significant challenge. Heterostructures of NiFe layered double hydroxides (NiFe-LDHs) with abundant oxygen defects and tunable electronic properties have garnered considerable attention. Here, a self-supporting heterostructured catalyst (named MoO3/NiFe-NF) is synthesized via a hydrothermal method to grow NiFe-LDH with oxygen vacancies (OV) in situ on inexpensive nickel foam (NF). Subsequently, MoO3 is anchored and grown on the surface of NiFe-LDH by electrodeposition. The obtained catalysts achieved outstanding oxygen/hydrogen evolution reaction (OER/HER, 212mV/85mV@10mAcm-2) performance in 1mKOH. Additionally, when MoO3/NiFe-NF is utilized as the cathode and anode in OWS, a current density of 10mAcm-2 can be obtained as an ultralow battery voltage of 1.43V, a significantly lower value compared to the commercial electrolyzer incorporating Pt/C and IrO2 electrode materials. Finally, density functional theory (DFT) calculations and advanced spectroscopy technology are conducted to reveal the effects of heterojunctions and OV on the internal electronic structure of the electrical catalysts. Mainly, the present study provides a novel tactic for the rational design of remarkable, low-cost NiFe-LDH electrocatalysts with heterostructures for OWS.

Direct Z-scheme GaTe/SnS2 van der Waals heterojunction with tunable electronic properties: A promising highly efficient photocatalyst

The production of hydrogen through photocatalytic water splitting offers a secure and eco-friendly approach. In this study, the application of GaTe/SnS2 heterojunction in the field of photocatalysis was studied in depth by using the first-principles calculation method. Based on single-layer GaTe and SnS2, a novel two-dimensional GaTe/SnS2 van der Waals heterojunction (vdwH) was constructed. Through analytical calculations, it is obvious that the GaTe/SnS2 heterojunction has an indirect bandgap of 0.85eV. Furthermore, its type-II band alignment facilitates efficient separation of photogenerated electrons and holes across different layers. The application of Bader charge analysis revealed an intriguing observation: the GaTe layer transferred a charge of 0.058e to the SnS2 layer. This charge transfer led to the creation of a robust built-in electric field, which played a pivotal role in efficiently inhibiting the recombination of photogenerated electrons and holes. Under the condition of pH = 0, GaTe/SnS2 heterojunction can promote redox reaction and realize water splitting. In addition, when the biaxial strain of -3%–3 % is applied to the GaTe/SnS2 heterojunction, the band edge position and light absorption properties are effectively changed, and more photons participate in the water splitting process. More importantly, the solar-to-hydrogen (STH) efficiency of GaTe/SnS2 heterojunction reaches 56.6 %, and when ε = 3 %, ηSTH increases to 58.21 %. Hence, our research showcases the GaTe/SnS2 heterojunction's potential as a highly efficient Z-scheme photocatalyst for water splitting, offering promising prospects for hydrogen production.

Quantifying alignment and quality of graphene nanoribbons: A polarized Raman spectroscopy approach

Graphene nanoribbons (GNRs) are atomically precise stripes of graphene with tunable electronic properties, making them promising for room-temperature switching applications like field-effect transistors (FETs). However, challenges persist in GNR processing and characterization, particularly regarding GNR alignment during device integration. In this study, we quantitatively assess the alignment and quality of 9-atom-wide armchair graphene nanoribbons (9-AGNRs) on different substrates using polarized Raman spectroscopy. Our approach incorporates an extended model that describes GNR alignment through a Gaussian distribution of angles. We not only extract the angular distribution of GNRs but also analyze polarization-independent intensity contributions to the Raman signal, providing insights into surface disorder on the growth substrate and after substrate transfer. Our findings reveal that low-coverage samples grown on Au(788) exhibit superior uniaxial alignment compared to high-coverage samples, attributed to preferential growth along step edges, as confirmed by scanning tunneling microscopy (STM). Upon substrate transfer, the alignment of low-coverage samples deteriorates, accompanied by increased surface disorder. For high-coverage samples, the alignment is preserved, and the disorder on the target substrate is reduced compared to the low-coverage samples. Our extended model enables a quantitative description of GNR alignment and quality, facilitating the development of GNR-based nanoelectronic devices.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector.

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

Roles of MXenes in Photocatalysis

Artificial photocatalysis is beneficial to carbon neutrality, renewable resources generation, and sustainable society development. Due to the unique layered structure, abundant surface functional groups, and tunable electronic properties, MXene is emerging as a promising contender to improve the comprehensive performance of photocatalysts. Much progress has been made in the study of MXene‐based nanomaterials over the past years, and state‐of‐the‐art advances in the rational design, controllable synthesis, characterization techniques, and diverse applications of MXene‐based photocatalysts have been reviewed. However, the roles and perspectives of MXenes in photocatalysis have been less summarized. Based on the analysis of the physical/chemical properties of MXenes and the latest research progress, herein, the multiple roles of MXenes are discussed in promoting photocatalysis, including carrier for active site anchoring, light‐transmitting media, mass transfer medium, cocatalyst, and heat conductor. In addition, the current status and challenges of MXenes in photocatalysis are summarized, and the future directions as well as the bottleneck of development that need to be broken through for MXenes in photocatalysis are also proposed. This review provides a clear and in‐depth understanding of the physical/chemical properties of MXene‐based photocatalysts and their contributions to photocatalysis.

Tunable electronic properties and Schottky barrier in Janus Ti3C2FO and TMD heterostructures by interface atomic species and disorder

In two-dimensional (2D) Janus MXenes materials, asymmetric disordered surface termination can greatly enhance material functionality. In this work, considering surface termination composition and disorder in 2D Janus MXenes, we designed five models of Janus Ti3C2FO, and then systematically investigated the electronic and contact properties of the corresponding Janus Ti3C2FO and TMD (TMD=WS2, MoS2 and WSe2) heterostructures using the density functional theory method. When the top and bottom surfaces of Janus Ti3C2FO are purely occupied by F and O atoms, respectively, Janus Ti3C2FO shows a pseudogap, which disappears in the presence of the mixed F and O atoms. It was found that the surface termination atomic species and disorder of Janus Ti3C2FO can effectively control the contact nature and Schottky barrier height (SBH) of these Ti3C2FO/TMD heterostructures and lead to a different response of their contact properties to the interlayer distance and external electric field. The presence of pure F atoms at the interface induces in the SBHs a strong dependence on the decrease in interlayer distance, while the pure O atoms causes both ΦB,n and ΦB,p to be almost pinned. Our study provides important new insight into the tuning of contact properties of MXenes/TMD heterostructures.

Tunable Electronic Properties, Carrier Mobility, and Contact Characteristics in Type-II BSe/Sc2CF2 Heterostructures toward Next-Generation Optoelectronic Devices.

Conducting heterostructures have emerged as a promising strategy to enhance physical properties and unlock the potential application of such materials. Herein, we conduct and investigate the electronic and transport properties of the BSe/Sc2CF2 heterostructure using first-principles calculations. The BSe/Sc2CF2 heterostructure is structurally and thermodynamically stable, indicating that it can be feasible for further experiments. The BSe/Sc2CF2 heterostructure exhibits a semiconducting behavior with an indirect band gap and possesses type-II band alignment. This unique alignment promotes efficient charge separation, making it highly promising for device applications, including solar cells and photodetectors. Furthermore, type-II band alignment in the BSe/Sc2CF2 heterostructure leads to a reduced band gap compared to the individual BSe and Sc2CF2 monolayers, leading to enhanced charge carrier mobility and light absorption. Additionally, the generation of the BSe/Sc2CF2 heterostructure enhances the transport properties of the BSe and Sc2CF2 monolayers. The electric fields and strains can modify the electronic properties, thus expanding the potential application possibilities. Both the electric fields and strains can tune the band gap and lead to the type-II to type-I conversion in the BSe/Sc2CF2 heterostructure. These findings shed light on the versatile nature of the BSe/Sc2CF2 heterostructure and its potential for advanced nanoelectronic and optoelectronic devices.

Tunable electronic and optical properties of GeC/g-C3N4 vdWH by electric field and biaxial strain

van der Waals heterostructures (vdWHs) show great potential for optoelectronic devices and photocatalysis. This work investigates the stability, electronic structure and optical properties of GeC/g-C3N4 using first-principles and considers the role of external electric fields and biaxial strain in the heterostructure. The results show a reduced band gap of GeC/g-C3N4 vdWH with strong optical absorption in the visible light range compared to monolayer GeC and g-C3N4. The heterostructure is a type-II semiconductor that is extremely suitable for the development of optoelectronic devices and photocatalytic materials. The external electric field can flexibly tune the band gap and band alignment of GeC/g-C3N4 vdWH, enabling it to transition between type-I, type-II and type-III. Biaxial strain effectively tunes the band structure of GeC/g-C3N4 vdWH, reducing the band gap and further increasing optical absorption capacity. These results suggest that external electric fields and biaxial strain are effective ways to tune GeC/g-C3N4 vdWH, providing a theoretical basis for relevant experimental preparation.

Covalent Topochemical Photo-Cross-Linking of Diketopyrrolopyrrole-Based Polymers with Polydiacetylenes toward Tunable Mechanical and Electronic Properties

Covalent Topochemical Photo-Cross-Linking of Diketopyrrolopyrrole-Based Polymers with Polydiacetylenes toward Tunable Mechanical and Electronic Properties

Heterointerface manipulation in the architecture of Co-Mo2C@NC boosts water electrolysis

Heterostructures with tunable electronic properties have shown great potential in water electrolysis for the replacement of current benchmark precious metals. However, constructing heterostructures with sufficient interfaces to strengthen the synergistic effect of multiple species still remains a challenge due to phase separation. Herein, an efficient electrocatalyst composed of a nanosized cobalt/Mo2C heterostructure anchored on N−doped carbon (Co−Mo2C@NC) was achieved by in situ topotactic phase transformation. With the merits of high conductivity, hierarchical pores, and strong electronic interaction between Co and Mo2C, the Co−Mo2C@5NC−4 catalyst shows excellent activity with a low overpotential for the hydrogen evolution reaction (HER, 89 mV@10 mA cm−2 in alkaline medium; 143 mV@10 mA cm−2 in acidic medium) and oxygen evolution reaction (OER, 356 mV@10 mA cm−2 in alkaline medium), as well as high stability. Furthermore, this catalyst in an electrolyzer shows efficient activity for overall water splitting and long−term durability. Theoretical calculations reveal the optimized adsorption−desorption behaviour of hydrogen intermediates on the generated cobalt layered hydroxide (Co LDH)/Mo2C interfaces, resulting in boosting alkaline water electrolysis. This work proposes a new interface−engineering perspective for the construction of high−activity heterostructures for electrochemical conversion.

A Novel Biosensing Approach: Improving SnS2 FET Sensitivity with a Tailored Supporter Molecule and Custom Substrate.

The exclusive features of two-dimensional (2D) semiconductors, such as high surface-to-volume ratios, tunable electronic properties, and biocompatibility, provide promising opportunities for developing highly sensitive biosensors. However, developing practical biosensors that can promptly detect low concentrations of target analytes remains a challenging task. Here, a field-effect-transistor comprising n-type transition metal dichalcogenide tin disulfide (SnS2 ) is developed over the hexagonal boron nitride (h-BN) for the detection of streptavidin protein (Strep.) as a target analyte. A self-designed receptor based on the pyrene-lysine conjugated with biotin (PLCB) is utilized to maintain the sensitivity of the SnS2 /h-BN FET because of the π-π stacking. The detection capabilities of SnS2 /h-BN FET are investigated using both Raman spectroscopy and electrical characterizations. The real-time electrical measurements exhibit that the SnS2 /h-BN FET is capable of detecting streptavidin at a remarkably low concentration of 0.5 pm, within 13.2s. Additionally, the selectivity of the device is investigated by measuring its response against a Cow-like serum egg white protein (BSA), having a comparative molecular weight to that of the streptavidin. These results indicate a high sensitivity and rapid response of SnS2 /h-BN biosensor against the selective proteins, which can have significant implications in several fields including point-of-care diagnostics, drug discovery, and environmental monitoring.

The Tunable Electronic and Optical Properties of Two-Dimensional Bismuth Oxyhalides.

Two-dimensional (2D) bismuth oxyhalides (BiOX) have attracted much attention as potential optoelectronic materials. To explore their application diversity, we herewith systematically investigate the tunable properties of 2D BiOX using first-principles calculations. Their electronic and optical properties can be modulated by changing the number of monolayers, applying strain, and/or varying the halogen composition. The band gap shrinks monotonically and approaches the bulk value, the optical absorption coefficient increases, and the absorption spectrum redshifts as the layer number of 2D BiOX increases. The carrier transport property can be improved by applying tensile strain, and the ability of photocatalytic hydrogen evolution can be obtained by applying compressive strain. General strain engineering will be effective in linearly tuning the band gap of BiOX in a wide strain range. Strain, together with halogen composition variation, can tune the optical absorption spectrum to be on demand in the range from visible to ultraviolet. This suggests that 2D BiOX materials can potentially serve as tunable novel photodetectors, can be used to improve clean energy techniques, and have potential in the field of flexible optoelectronics.

Tunable magnetic and electronic properties of two intrinsic half-metallic MXene monolayers Sc2Na2CNC and Sc2K2CNC

Magnetic MXenes, especially the half-metallic MXenes, are attracting increasing attention due to their unique crystal characteristics, high strength and flexibility, and then wide applications in spintronics and nano-electronics. In this paper, two intrinsic half-metallic bimetallic MXene monolayers Sc2Na2CNC and Sc2K2CNC were predicted based on the first-principles calculations. Their half-metallicity is stable within a certain biaxial stain range. Their magnetic moments are up to 3.00 μB per unit, which are helpful to their applications in spintronics. The half-metallicity and magnetic moments of these monolayers may be evidently improved by the positive charge states. If the charge states vary from n = 0 to n = +2, the magnetic moments of their 2 × 2 × 1 supercells will increase from 12.00 to 14.00 μB. It was notable that the half-metallic gaps and the magnetic moments of monolayers Sc2Na2CNCF2 and Sc2Na2CNCCl2 are evidently larger than those of the monolayer Sc2Na2CNC, so the F/Cl-absorption bilaterally may improve the performances of the monolayer Sc2Na2CNC. The above magnetic moments agree well with those analyzed by the molecular orbital theory.

Tunable Schottky barrier of in-plane MoSSe/Borophene heterojunctions under electric field and strain

The electronic properties of Janus MoSSe/Borophene in-plane heterojunctions are investigated through the first principle calculations. The constructed MoSSe/Borophene heterojunctions with different structures of Borophene exhibit different electronic properties. All the heterojunctions present the p-type Schottky contact. Furthermore, the electronic properties of MoSSe/Borophene heterojunctions can be modulated by electric field and mechanical strain. Specifically, as the applied electric field changes, the band gap also changes and Ohmic contact is achieved. Additionally, the strain induces a direct to indirect band gap transition of Janus MoSSe and changed contact type. The results demonstrate that the tunable electronic properties of Janus MoSSe/Borophene heterojunction make it become a promising candidate for the electronic devices.

Impact of Molecular Weight on the Ionic and Electronic Transport of Self‐Doped Conjugated Polyelectrolytes Relevant to Organic Electrochemical Transistors

AbstractOrganic electrochemical transistors (OECTs) have gained considerable attention due to their potential applications in emerging biosensor platforms. The use of conjugated polyelectrolytes (CPEs) as active materials in OECTs is particularly advantageous owing to their functional, water‐processable, and biocompatible nature, as well as their tunable electronic and ionic transport properties. However, there exists a lack of systematic studies of the structure‐property relationships of these materials with respect to OECT performance. This study shows how by tuning the molecular weight of self‐doped CPE (CPE‐K) it is possible to fabricate OECTs with a µC* value of 14.7 F cm−1 V−1 s−1, one order of magnitude higher than previously reported CPE‐based devices. Furthermore, OECTs with a transconductance of 120 mS are demonstrated via device engineering. While CPE‐K batches with different molecular weights show good doping behavior and high volumetric capacitance, as confirmed by spectroelectrochemistry and electrochemical impedance spectroscopy, the medium molecular weight possesses the highest carrier mobility of ≈0.1 cm2 V−1 s−1 leading to the highest transconductance. The enhanced charge transport is due to a favorable charge percolation pathway, as revealed by the combination of X‐ray analysis and conductive atomic force microscope. These insights provide guidelines for further improving the performance of CPE‐based OECTs.

First-principles investigations of structural and electronic properties of SnAs/SnAsCl heterostructure

In this work, we investigate the tunable structural and electronic properties of SnAs monolayer through chlorinated functionalization and the SnAs/SnAsCl heterostructure construction. Through chlorinated functionalization, we observe a remarkable transformation of the SnAs monolayer into a semiconducting SnAsCl monolayer with a direct band gap of 1.32 eV. This demonstrates the potential for controlling and tuning the electronic properties of SnAs through surface functionalization. Moreover, depending on the specific stacking patterns in the SnAs/SnAsCl heterostructure, we observe the formation of either Ohmic contact or Schottky contact. Particularly noteworthy is the presence of ultra-low Schottky barriers, measured at 0.03 eV, charge transport efficiency and improving device performance. The SnAs/SnAsCl heterostructure exhibits small tunneling probability, indicating a relatively low electron transparency. These findings pave the way for the development of high-performance electronic devices utilizing these heterostructures and offer promising opportunities for future technological advancements.

Structural Diversity of Single-Walled Transition Metal Dichalcogenide Nanotubes Grown via Template Reaction.

Monolayers of transition metal dichalcogenides (TMDs) are an ideal 2D platform for studying a wide variety of electronic properties and potential applications due to their chemical diversity. Similarly, single-walled TMD nanotubes (SW-TMDNTs)-seamless cylinders of rolled-up TMD monolayers-are 1D materials that can exhibit tunable electronic properties depending on both their chirality and composition. However, much less has been explored about their geometrical structures and chemical variations due to their instability under ambient conditions. Here, the structural diversity of SW-TMDNTs templated by boron nitride nanotubes (BNNTs) is reported. The outer surfaces and inner cavities of the BNNTs promote and stabilize the coaxial growth of SW-TMDNTs with various diameters, including few-nanometers-wide species. The chiral indices (n,m) of individual SW-MoS2 NTs are assigned by high-resolution transmission electron microscopy, and statistical analyses reveals a broad chirality distribution ranging from zigzag to armchair configurations. Furthermore, this methodology can be applied to the synthesis of various TMDNTs,such as selenides and alloyed Mo1- x Wx S2 . Comprehensive microscopic and spectroscopic analyses also suggest the partial formation of Janus MoS2(1- x ) Se2 x nanotubes. The BNNT-templated reaction provides a universal platform to characterize the chirality-dependent properties of 1D nanotubes with various electronic structures.

A first principles investigation on strain tuned electronic properties of Janus ReXY (X, Y = Cl, Br, I) monolayers

Transition metal dichalcogenides (TMDs) are a promising class of two-dimensional (2D) materials with tunable electronic and transport properties. In this paper, a first principles calculation of ReClI, ReClBr, and ReIBr Janus 2D materials was carried out in view of structural design and electronic properties. In addition, the structural stability and electronic characteristics of ReClI, ReClBr, and ReIBr were explored under the condition of tensile strain. The conclusions are described as follows: ReIBr maintains excellent lattice structural stability under external forces and possesses the strongest resistance to strain; ReClBr has the highest surface activity, and electrons are more likely to escape and participate in surface chemical reactions; ReClI, ReClBr, and ReIBr are two-dimensional materials that exhibit semiconductor properties while showing varying degrees of tuning under strain conditions.

Strong Electron–Phonon and Phonon–Phonon Interactions Lead to High Thermoelectric Performances in Lead Phosphorene via Symmetry Breaking

AbstractUnderstanding the full electron–phonon and phonon–phonon interaction effects in semiconductors is crucial for tuning electronic and phonon transport properties with the purpose to the enhancement of thermoelectric performances. In this work, based on the detailed investigations on 2D lead phosphorene (PbP) by using the first‐principle calculations, it is demonstrated that, in , , and PbP, the electron–phonon interactions are significantly stronger than conventional group‐IV monolayers such as silicene by five orders in magnitude, and intravalley scatterings dominate over the intervalley scattering due to less degenerate band extrema near Fermi level. Based on the selection‐rule analysis, it is found that the symmetry breaking in the janus γ phase compared to the higher‐symmetry α phase allows fewer symmetry operations, leading to more allowed scattering channels for electrons and phonons, subsequently suppressing the electron and phonon transport in PbP. Due to the low Debye temperatures, and strong four‐phonon interactions, the lattice thermal conductivities at room temperature in these monolayers are sharply decreased. Finally, it is found that the maximum thermoelectric figure of merits for these three monolayers reach 0.90/0.24/1.25 at room temperature, respectively. This work not only paves the way for the promising applications of PbP monolayers in thermoelectric devices, but also suggests that symmetry breaking and strong high‐order phonon–phonon interactions are crucial to identifying excellent thermoelectric materials.