Band Structure Engineering Research Articles

Band Structure Engineering of Single Pt Atoms on Fe-TiO2 for Enhanced Photocatalytic Performance.

Single atomic site catalysts display the maximal atom-utilization efficiency, unique structural properties, and remarkable enhancements on catalytic activity. Herein, single Pt atoms loaded Fe-TiO2 catalysts were prepared. Fe3+ doping leads to the formation of oxygen vacancies and improve the interaction between TiO2 and Pt. Single Pt atoms are thus anchored and effectively modify the local energy band structure of TiO2 . The optimized local band structures improve the intrinsic photoexcitation of Pt/Fe-TiO2 , promote the separation of photogenerated carriers, and extend the lifetime of photogenerated carriers. Meanwhile, the electrons transfer from the excited dyes to the conduction band edge of Pt/Fe-TiO2 is also facilitated due to the shift-down of the conduction band edge. Therefore, with the increase of the Pt content (till up to 0.6 wt%), the photocatalytic performance of Pt/ Fe-TiO2 with the confined single Pt atoms is significantly boosted in either the intrinsic or the sensitized photocatalytic process.

Phase and Band Structure Engineering via Linear Additive in NBT-ST for Excellent Energy Storage Performance with Superior Thermal Stability.

Lead-free relaxor ferroelectric ceramics with ultrahigh energy-storage performance are vital for pulsed power systems. We herein propose a strategy of phase and band structure engineering for high-performance energy storage. To demonstrate the effectiveness of this strategy, (1 - x)(0.75Na0.5Bi0.5TiO3-0.25SrTiO3)-xCaTi0.875Nb0.1O3 (NBT-ST-xCTN, x = 0.1, 0.2, 0.3, 0.4, and 0.5) samples were designed and fabricated via the solid-state reaction method. The linear dielectric CTN was used as a modulator to tune both phase and band structures of the tested system. Our results show that both rhombohedral phase (R-phase) and tetragonal phase (T-phase) coexist in the samples. The R/T ratio decreases, while the band gap increases with increasing CTN content. The best energy-storage properties with large energy storage density (Wrec = 7.13 J/cm3), a high efficiency (η = 90.3%), and an ultrafast discharge time (25 ns) were achieved in the NBT-ST-0.4CTN sample with R/T = 0.121. Importantly, along with its excellent energy-storage performance, the sample exhibited superior thermal stability with the variations of Wrec ≤ 7% and η ≤ 10% over the wide temperature range of 233-413 K. This work suggests that this engineering of phase and band structures is a promising strategy to achieve superior energy-storage properties in lead-free ceramics.

Enhanced photocatalytic activity for degradation of ofloxacin and dye by hierarchical flower-like ZnS/MoS2/Bi2WO6 heterojunction: Synergetic effect of 2D/2D coupling interface and solid sulfide solutions

To strengthen the photocatalytic degradation of antibiotics and organic dyes, the band structure engineering serves as an efficient approach, which can be realized by constructing heterostucture photocatalysts. Herein, 0D/2D/2D ZnS/MoS2/Bi2WO6 (ZMB) hierarchical flower-like microspheres were smoothly prepared via in-situ growth of Bi2WO6 nanoparticles on ZnS/MoS2 surfaces. The results illustrated that the content of Bi2WO6 played a crucial role in regulating the photocatalytic activity of ZMB heterostructures. ZMB-7 showed a better degradation capacity compared to ZnS/MoS2 and other ZMB composites, and the degradation rates of ofloxacin (OFL) and rhodamine B (RhB) respectively reached 98.5% and 91.1% under light illumination. The enhanced photocatalytic activity could be attributed to the large specific surface, improved separation of photogenerated carriers, as well as rapid charge transfer by combining the advantage of 2D coupling interfaces generated from MoS2/Bi2WO6 and composition-controlled band gap in solid sulfide solutions. On the basis of active species trapping experiments and HPLC-MS tests, a possible photocatalytic mechanism and gradation pathway for OFL were further proposed. The ternary ZnS/MoS2/Bi2WO6 heterojunction with enhanced photocatalytic activities in the work may have vital applications for environmental purification owing to its synergistic effects between composition and microstructure.

Band Structure Engineering of 2D Heterotriangulene Polymers by Incorporating Acetylenic Linkages for Photocatalytic Hydrogen Production

By performing first-principles calculations, we propose to introduce acetylenyl (−C≡C−) into the honeycomb kagome lattices of heterotriangulenes (HT)-based two-dimensional (2D) polymers to construct 2D HT-polyynes with tunable electronic and optical properties for photocatalysis. It is found that the band gap can be effectively reduced to a moderate value of around 2.00 eV by increasing the number of −C≡C– (n = 1, 2, 3) in the skeletons, contributing to enhanced light-harvesting ability in the visible range of the spectrum. Interestingly, the band edges of 2D HT-polyynes shift upward after incorporating with −C≡C– and then shift downward when the number of incorporated −C≡C– increases from 1 to 2 and 3. Possessing moderate band gap and matching band-edge alignments, high carrier mobility, and pronounced light-harvesting capability, the designed 2D HT-polyynes are predicted to be potential candidates for photocatalytic hydrogen production.

An oxide-based heterojunction optoelectronic synaptic device with wideband and rapid response performance

• The device has a wideband (520∼1550 nm) and high sensitive response to light spike • Our device has a rapid response time of 2 ms and presents a stable performance • The synaptic device has the functions of color and light source direction recognition With the rapid development of science and technology, the emergence of new application scenarios, such as robots, driverless vehicles and smart city, puts forward high requirements for artificial visual systems. Optoelectronic synaptic devices have attracted much attention due to their advantages in sensing, memory and computing integration. In this work, via band structure engineering and heterostructure designing, a heterojunction optoelectronic synaptic device based on Cu doped with n-type SrTiO 3 (Cu:STO) film combined with p-type CuAlO 2 (CAO) thin film was fabricated. It is found surprisingly that the optoelectronic device based on Cu:STO/CAO p-n heterojunction exhibits a rapid response of 2 ms, and that it has a wideband response from visible to near-infrared (NIR) region. Additionally, a series of important synaptic functions, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP) to long-term potentiation (LTP) transition, learning experience behavior and image sharpening, have been successfully simulated on the device. More importantly, the performance of the device remains still stable and reliable after several months which were stored at room temperature and atmospheric pressure. Based on these advantages, the optoelectronic synaptic devices demonstrated here provide great potential in the new generation of artificial visual systems.

Self-Induced Dirac Boundary State and Digitization in a Nonlinear Resonator Chain.

The low-energy excitations in many condensed matter and metamaterial systems can be well described by the Dirac equation. The mass term associated with these collective excitations, also known as the Dirac mass, can take any value and is directly responsible for determining whether the resultant band structure exhibits a band gap or a Dirac point with linear dispersion. Manipulation of this Dirac mass has inspired new methods of band structure engineering and electron confinement. Notably, it has been shown that a massless state necessarily localizes at any domain wall that divides regions with Dirac masses of different signs. These localized states are known as Jackiw-Rebbi-type Dirac boundary modes and their tunability and localization features have valuable technological potential. In this study, we experimentally demonstrate that nonlinearity within a 1D Dirac material can result in a self-induced domain boundary for the Dirac mass. Our experiments are performed in a dimerized magnetomechanical metamaterial that allows complete control of both the magnitude and sign of the local material nonlinearity, as well as the sign of the Dirac mass. We find that the massless bound state that emerges at the self-induced domain boundary acts similarly to a dopant site within an insulator, causing the material to exhibit a dramatic binary switch in its conductivity when driven above an excitation threshold.

Effective Charge Carrier Utilization of BiVO4 for Solar Overall Water Splitting.

Solar energy-driven overall water splitting (OWS) is an attractive way for generating clean and renewable green hydrogen. One key challenge is the construction of OWS systems with high solar energy conversion efficiencies, in which how to manipulate photoexcited charge carriers to efficiently participate in the reaction is the top priority. In recent years, bismuth vanadate (BiVO4 ) has emerged as one of the most promising materials for photo(electro)catalytic OWS and considerable progress has been achieved. In this review, recent advances of BiVO4 -constituted OWS systems in both photoelectrocatalytic and photocatalytic approaches are presented in a mainline of effective charge carrier utilization. Various strategies for improved charge carrier utilization, including band structure engineering, improving charge separation, reducing charge recombination, and accelerating reaction kinetics, are summarized and analyzed in detail. Finally, perspective and outlook on further exploring the application potential of BiVO4 are proposed.

Ligand-mediated band structure engineering and physiochemical properties of UiO-66 (Zr) metal-organic frameworks (MOFs) for solar-driven degradation of dye molecules

In this study, Zr-based metal organic frameworks (Zr-MOFs) with different ligands such as terephthalic acid (UiO-66), 2-aminoterephthalic (UiO-66-NH2) and 2-methylimidazole (UiO‐66‐2M) are synthesized using hydrothermal method in order to investigate their ligand-dependent properties towards photocatalytic degradation of dyes molecules under solar light. The structural analysis by XRD revealed the fundamental cubic-topology of the UiO-66 structure for all the synthesized MOFs, and the presence of respective functional groups is confirmed via their ART-IR spectra. A spherical morphology with average size of ~80 and 200 nm are observed for UiO-66 and UiO-66-NH2 MOFs, respectively, whereas, bricks-like morphology is observed for UiO‐66‐2M, which is attributed to the binding habit of the respective ligands. Band gap energy of the synthesized UiO-66, UiO-66-NH2 and UiO‐66‐2M is estimated to be ~3.85, 2.92 and 2.77 eV, respectively. Among the synthesized MOFs, the photocatalytic degradation efficiency of UiO-66-NH2 MOFs is found to be greater towards the cationic rhodamine B (RhB) dye (~95% in 120 min), while it is relatively less efficient in degrading the anionic Congo red (CR) dye, (~64% in 120 min). The insights gained from the fundamental characterizations, Mott-Schottky, scavenger and electrochemical impedance analysis revealed that the amino-groups in UiO-66-NH2 MOFs offered the band edge potentials suitable for the effective generation of energetic radical species with the improved carrier delocalization, recombination resistance and charge transfer properties in the MOFs. The further parametric studies revealed that the UiO-66-NH2 MOFs can be effectively scaled-up and used for dye degradation applications in real-time.

Graphene Infrared Radiation Management Targeting Photothermal Conversion for Electric-Energy-Free Crude Oil Collection.

Graphene has been widely used as a solar absorber for its broad-band absorption. However, targeting a higher photothermal efficiency, the intrinsic infrared radiation loss of graphene requires to be further reduced. Herein, band structure engineering is performed to modulate graphene infrared radiation. Nitrogen-doped vertical graphene is grown on quartz foam (NVGQF) by the plasma-enhanced chemical vapor deposition method. Under the premise of keeping high solar absorption (250-2500 nm), graphitic nitrogen doping effectively modulates the infrared emissivity (2.5-25 μm) of NVGQF from 0.96 to 0.68, reducing the radiation loss by ∼31%. Based on the excellent photothermal properties of NVGQF, a temperature-gradient-driven crude oil collecting raft is designed, where the crude oil flows along the collecting path driven by the viscosity gradient without any external electric energy input. Compared with a nondoped vertical graphene quartz foam raft, the NVGQF raft with a superior photothermal efficiency shows a significantly enhanced crude oil collecting efficiency by three times. The advances in this work suggest broad radiation-managed application platforms for graphene materials, such as seawater desalination and personal or building thermal management.

Band Structure Engineering within Two-Dimensional Borocarbonitride Nanosheets for Surface-Enhanced Raman Scattering.

Herein, with two-dimensional (2D) borocarbonitride (BCN) as a metal- and plasmon-free surface-enhanced Raman scattering (SERS) platform, we demonstrate a band structure engineering strategy to facilitate the charge transfer process for an enhanced SERS response. Especially, when the conduction band of the BCN substrate is tuned to align with the LUMO of the target molecule, remarkable SERS performance is achieved, ascribed to the borrowing effect from the vibronic coupling of resonances through the Herzberg-Teller coupling term. Meanwhile, fluorescence quenching is achieved due to the efficient charge transfer between the BCN substrate and target molecule. Consequently, BCN can accurately detect 20 kinds of trace chemical and bioactive analytes. Moreover, BCN exhibits excellent thermal and chemical stability, which can not only withstand high-temperature (300 °C) heating in the air but also resist long-term corrosion in harsh acid (pH = 0, HCl) and base (pH = 14, NaOH). This work provides new insight into band structure engineering in promoting the SERS performance of plasmon- and metal-free semiconductor substrates.

Infrared Transparent and Electromagnetic Shielding Correlated Metals via Lattice-Orbital-Charge Coupling.

Despite being a requisite for modern transparent electronics, few metals have a sufficiently high infrared transmittance due to the free electron response. Here, upon alloying the correlated metal SrVO3 with BaVO3, the medium wavelength infrared transmittance at a wavelength of 4 μm is found to be 50% higher than those for Sn-doped In2O3 (ITO) and La-doped BaSnO3 (BLSO). The room temperature resistivity of the alloy of ∼100 μΩ cm is 1 order of magnitude lower than those of ITO and BLSO, guaranteeing a profound electromagnetic shielding effectiveness of 22-31 dB at 10 GHz in the X-band. Systematic investigations reveal symmetry breaking of VO6 oxygen octahedra in SrVO3 due to the substitution of Sr2+ with larger Ba2+ ions, localization of electrons in the lower energy V-dyz and dzx orbitals, and stronger correlation effects. The lattice-orbital-charge-coupled engineering of the electronic band structure in correlated metals offers a new design strategy to create super-broad-band transparent conductors with an enhanced shielding capability.

Erratum to: Heterojunction between bimetallic metal-organic framework and TiO2: Band-structure engineering for effective photoelectrochemical water splitting

The article Heterojunction between bimetallic metal-organic framework and TiO2: Band-structure engineering for effective photoelectrochemical water splitting, written by Ji Won Yoon et al., was erroneously originally published electronically on the publisher’s internet portal (currently SpringerLink) on 17 May 2022 with the Acknowledgements.

Heterojunction between bimetallic metal-organic framework and TiO2: Band-structure engineering for effective photoelectrochemical water splitting

Heterojunction between bimetallic metal-organic framework and TiO2: Band-structure engineering for effective photoelectrochemical water splitting

Endoepitaxial growth of monolayer mosaic heterostructures.

The controllable growth of two-dimensional (2D) heterostructure arrays is critical for exploring exotic physics and developing novel devices, yet it remains a substantial synthetic challenge. Here we report a rational synthetic strategy to fabricate mosaic heterostructure arrays in monolayer 2D atomic crystals. By using a laser-patterning and an anisotropic thermal etching process, we create periodic triangular hole arrays in 2D crystals with precisely controlled size and atomically clean edges, which function as robust templates for endoepitaxial growth of another 2D crystal, to obtain monolayer mosaic heterostructures with atomically sharp heterojunction interfaces. Systematic microstructure and spectroscopic characterizations reveal periodic modulation of chemical compositions, lattice strains and electronic band gaps throughout the mosaic heterostructures. The robust growth of the monolayer mosaic heterostructures with a high level of synthetic control opens a pathway for band structure engineering and spatially modulating the potential landscapes in the atomically thin 2D crystals, establishing a designable material platform for fundamental studies and development of complex devices and integrated circuits from 2D heterostructures.

Influence of numerous Moiré superlattices on transport properties of twisted multilayer graphene

Band structure engineering by changing the parameters of Moiré superlattices enables creation of materials with outstanding properties for twistronics, straintronics and quantum nanoelectronics applications. Herein, twisted multilayer graphene (tMLG) with various combinations of twist angles (θ) and numerous Moiré superlattices was synthesized. The strong dependence of the transport properties of tMLG on the structural characteristics was demonstrated using synchrotron-based core-level spectroscopy methods combined with micro-Raman spectroscopy. It has been shown that tMLG with a large content of the twisted phase with the twist angles between the adjacent graphene layers of θ = 26–30° over the entire tMLG thickness is characterized by a perfect structure of the single layer graphene (SLG) and extraordinary transport characteristics. At low temperatures, the asymmetry of charge carriers and atypical temperature dependence of average carrier mobility μ were observed. In such tMLG, μ was higher than 105 cm2V−1s−1. Decrease in the content of the twisted phase with θ = 26–30°, as well as increase in the contents of other twist angles and AB-stacked phase (θ = 0°), leads to a significant decrease in μ. Hence, tMLGs are a better choice for the nanoelectronics industry because, having outstanding transport properties, they are, contrary to SLG, insensitive to the specific features of process procedures.

In-plane resonant excitation of quantum dots in a dual-mode photonic-crystal waveguide with high β-factor

A high-quality quantum dot (QD) single-photon source is a key resource for quantum information processing. Exciting a QD emitter resonantly can greatly suppress decoherence processes and lead to highly indistinguishable single-photon generation. It has, however, remained a challenge to implement strict resonant excitation in a stable and scalable way, without compromising any of the key specs of the source (efficiency, purity, and indistinguishability). In this work, we propose a novel dual-mode photonic-crystal waveguide that realizes direct in-plane resonant excitation of the embedded QDs. The device relies on a two-mode waveguide design, which allows exploiting one mode for excitation of the QD and the other mode for collecting the emitted single photons with high efficiency. By proper engineering of the photonic bandstructure, we propose a design with single-photon collection efficiency of β > 0.95 together with a single-photon impurity of ϵ < 5 × 10−3 over a broad spectral and spatial range. The device has a compact footprint of and would enable stable and scalable excitation of multiple emitters for multi-photon quantum applications.

Covalent Patterning of Graphene for Controllable Functionalization from Microscale to Nanoscale: A Mini-Review.

Covalent patterning of graphene opens many application possibilities in the field of photonics, electronics, sensors, and catalysis due to order-dependent optical properties, band structure engineering, and processibility and reactivity improvement. Owing to the low reactivity of the graphene basal plane, harsh reagents (e.g., radicals) used for covalent functionalization normally result in poor spatial control, which largely compromises the intrinsic properties of graphene. Therefore, precisely spatial control on covalent patterning of graphene is of great importance. Herein, we summarize recent advances for covalent patterning of graphene from the microscale to nanoscale resolution using different techniques such as laser or electrochemical writing, template-directed growth, and tip-induced nanoshaving.

Band Structure Engineering and Defect Passivation of Cu x Ag1-x InS2/ZnS Quantum Dots to Enhance Photoelectrochemical Hydrogen Evolution.

The AgInS2 colloidal quantum dot (CQD) is a promising photoanode material with a relatively wide band gap for photoelectrochemical (PEC) solar-driven hydrogen (H2) evolution. However, the unsuitable energy band structure still forms undesired energy barriers and leads to serious charge carrier recombination with low solar to hydrogen conversion efficiency. Here, we propose to use the ZnS shell for defect passivation and Cu ion doping for band structure engineering to design and synthesize a series of CuxAg1–xInS2/ZnS CQDs. ZnS shell-assisted defect passivation suppresses charge carrier recombination because of the formation of the core/shell heterojunction interface, enhancing the performance of PEC devices with better charge separation and stability. More importantly, the tunable Cu doping concentration in AgInS2 CQDs leads to the shift of the quantum dot band alignment, which greatly promotes the interfacial charge separation and transfer. As a result, CuxAg1–xInS2/ZnS CQD photoanodes for PEC cells exhibit an enhanced photocurrent of 5.8 mA cm–2 at 0.8 V versus the RHE, showing excellent photoelectrocatalytic activity for H2 production with greater chemical-/photostability.

Analytical Modeling and Band-Structure Engineering of Resonant Tunneling Diode for Biased Terahertz Detector

A new strategy to significantly enhance the nonlinearity of double-barrier resonant tunneling diode (RTD) in the positive differential resistance region is theoretically proposed and experimentally demonstrated. An analytical model containing physical insight into the resonant tunneling process is established to bridge the nonlinearity of the current–voltage curve and the band-structure information of RTD. It intuitively shows that the intrinsic current responsivity of RTD as well as its nonlinearity can be greatly improved via band-structure engineering, as enhancing the resonant energy level of the well and reducing the current before the resonant tunneling process. The validation of the proposed model and the associated band-structure engineering strategy are verified by both device simulation and experiments. A RTD device with intrinsic current responsivity of 6.74 A/W is realized, while the peak-to-valley current ratio (PVCR) is also as large as 8.92. This method provides a new pathway to design high-performance terahertz (THz) detectors using double-barrier RTD and may share new perspective on the potential of RTD-based THz transceivers.

Strategies for boosting thermoelectric performance of PbSe: A review

• General physical properties of typical IV-VI compounds are summarized. • Phase diagram, crystal and electrical band structures of PbSe are presented. • Recent ways of adjusting charge and phonon transport processes in PbSe are updated. • Typical preparation methods for PbSe and their scalability are discussed. • Key challenges and future research directions of PbSe are discussed. Thermoelectric materials enable the direct conversion between waste heat and electric energy, playing an important role in alleviating energy crisis. Many excellent thermoelectrics developed so far contain expensive and scarce Te element, largely limiting their applications. Therefore, exploring Te-free compounds with extraordinary thermoelectric performance becomes a vital topic in thermoelectric community in recent years. PbSe is an ideal candidate that meets above criteria and has advanced rapidly in the last decade with reported peak ZT s close to 2.0. Herein we review the recent research progress of PbSe-based thermoelectric materials. This review article starts with a general introduction of the properties of IV-VI semiconductors as advanced thermoelectric materials by comparing their cost, crustal abundance, mechanical strength and chemical bonding. Following that, phase diagram, crystal and electronic band structures of PbSe are comprehensively summarized. Then we discuss how the frequently used dopants regulate its carrier concentrations. Subsequently, electronic band structure engineering (including resonant levels, band flattening, band convergence, band inversion, etc. ) and microstructural architecturing (including atomic arrangements, dislocation arrays, nanoscale precipitates, etc. ) approaches and their impacts on charge and phonon transport properties of PbSe are elaborated. Finally, we summarize the typical production processes of PbSe and comment on their scalability. The future directions for how to further improve the thermoelectric properties of PbSe and promote its applications are discussed at the end of this article.