Modification Of Band Structure Research Articles

Energy Band-Modulated SnO Anodes with Improved Rate Capacity and Initial Coulombic Efficiency for Sodium-Ion Batteries.

An efficient interface and composition modification strategy is proposed to significantly increase the rate capacity and initial Coulombic efficiency (ICE) of SnO anodes via energy band structure modulation for Na-ion batteries (SIBs). The as-fabricated SnO@Bi@C material with Bi nanocrystals homogeneously dispersed on and around the SnO surface is prepared by an electrospinning method. The excellently dispersed Bi nanocrystals realize an effective interface contact with SnO and Na2O, which effectively lowers the electron conduction barriers and promotes sodium-ion release and transport upon the desodiation process, increasing the rate capacity and ICE of the SnO anode. The prepared SnO@Bi@C exhibits a much higher rate capacity up to 10 A g-1, except an improved ICE of 80.67%, compared to 57.38% of SnO@C. Importantly, the intercalation of Na+ between layer-structured Bi galleries provides a good basis for excellent cycle stability due to the highways constructed inside the prepared composites. This finding provides an effective tactic to establish ion transport high-speed channels, which essentially increase the rate performance and the ICE of the SnO-based anodes.

Superluminality in parity-time symmetric Bragg gratings

Abstract Parity-time (PT) symmetric Bragg gratings (PTBGs) possess unique features compared to traditional ones. For example, the photonic bandgap of a PTBG can be modified and even closed when the PT symmetry evolves from an exact phase to a broken one, and the complex reflection coefficient of a PTBG is sensitive to the direction of incidence. In this article, we reveal how the superluminal effects of transmission behave following the modified band structure of PTBGs. The superluminality of the directionally sensitive reflection is also discussed. We then investigate the Hartman effect and argue that, to account for the superluminal effects in PTBGs, a directionally sensitive dwell time should be applied. This study offers unique insights into the mechanisms of superluminality and group delay of light in non-Hermitian open systems and contributes to the advancement of PTBGs, which can eventually become an indispensable platform for probing some of the exotic properties of optical wave phenomena and light-matter interactions.

Structural and optical properties of In-doped CdS nanostructures: A comprehensive study

This research offers a comprehensive exploration of the effects of In-doping on the characteristics of CdS nanopowders (NPs). The structural and morphological properties of In-doped CdS nanostructures were investigated, revealing significant changes induced by In-doping. X-ray diffraction (XRD) analysis verified the formation of CdS phase. Determination of crystallite size (D) demonstrated a decrease from 27.0 nm for undoped CdS to 23.0 nm for CdS doped with 12% In-doped. Field-emission scanning electron microscopy (FESEM) imaging showed grain-like structures with sizes of 20 – 35 nm, showing variations in particle size distribution with increasing In-dopant concentration. Photoluminescence (PL) analysis illustrated changes in PL intensity and emission peak wavelengths due to In-doping. PL intensity decreased after In-doping. Additionally, a blue-shift in emission peak wavelengths indicated changes in the bandgap energy of CdS induced by In-doping. UV-Vis spectroscopy assessed the optical properties, revealing shifts in absorption and transmission spectra du to In-doping. In-doping enhanced absorption within the 400 – 500 nm range while decreasing absorption within 600 – 1000 nm. Transmission spectra displayed increased transparency after In-doping, attributed to modifications in band structure and morphology. Reflectance spectra initially increased with In-dopant concentration within 400 – 500 nm, followed by a decrease, suggesting alterations in electronic and structural properties. Estimation of band gap energy (Eg) unveiled an increase in Eg for In-doped CdS nanostructures compared to undoped CdS, likely due to reduced crystallite size and the Burstein-Moss effect induced by In-dopant ions. Raman analysis revealed a shift in peak positions and changes in intensity after In-doping, with a decrease in the 2LO/LO ratio indicating a deterioration in crystalline quality after In-doping. Overall, this comprehensive investigation provides valuable insights into the structural, morphological, optical, and electrical properties of In-doped CdS nanostructures, pivotal for their promising applications in optoelectronic devices and photovoltaics.

Room temperature ultrasensitive detection of acetone vapours via noble metal anchored reduced graphene oxide

Developing a low-cost, realistic room temperature operable acetone sensor is highly desirable in industrial and medical sectors for environmental monitoring and diagnostic purposes. The present study focuses on the simple co-reduction route to synthesize noble metal nanoparticle decorated reduced graphene oxide (rGO) and investigating the acetone sensing ability by using them as sensing materials to fulfil the requirements. Various spectroscopic and microscopic tools were employed to probe the structural and morphological details of the prepared materials. Gas sensing tests demonstrated the selective identification of acetone by the developed sensors, with the sensing materials exhibiting remarkable response at room temperature. The decoration of gold nanoparticles on reduced graphene oxide (AurGO) notably enhanced the response (1.87%) compared to pure rGO (0.65%). Despite a decrease in response with silver loading on rGO (AgrGO) (0.20%), sensors based on AgrGO exhibited rapid response and recovery times (49/38 seconds) compared to those of rGO (90/116 seconds) and AurGO (136/150 seconds). The acetone sensing mechanism is discussed in detail by predicting the band structure modification under the acetone exposure. The superior selectivity, repeatability, and long-term stability displayed by all the sensing materials suggest their cutting-edge applicability for real-world applications.

Twist Proximity-Endowed Large Figure of Merit in a Band-Modulated CrI3/1T-MoS2 Moiré Superlattice.

Moiré superlattices with a robust twist proximity effect in the low-dimensional regime can facilitate nanoscale thermoelectric devices. In pristine systems, the low efficiency and lack of proficient control of thermoelectric properties impede desirable advancements in the field of energy conversion. In the present study, we demonstrate remarkable macroscopic thermoelectric response as a consequence of microscopic band structure modulation via the twist proximity in an engineered CrI3/1T-MoS2 moiré superlattice. The local twist effect, which leads to the microscopic phenomena of electron localization, results in a comprehensive electronic structure modulation. Consequently, these local effects convolute the macroscopic thermoelectric effect. Additionally, flat bands and angle-dependent metallic to semiconducting transitions are observed at 10.89, 23.41, and 30° twist angles. We correlate the observed phenomenon with the augmented spin-charge transport and interconversion via the twist proximity effect in its semiconducting phase. The estimated ultralow electronic and lattice thermal conductivities further corroborate with the observed large figure of merit and Seebeck coefficient. The maximum values of the Seebeck coefficient and figure of merit are estimated to be ∼413 μV/K and ∼4.3 at 200 K for 30° under the constant time relaxation approach. The twist-endowed outstanding thermoelectric effect in moiré superlattices with band modulation unveils a distinctive approach to establish efficient thermoelectric devices.

Halides doping in the shallow lattice of BiOBr nanosheets promoting photocatalytic degradation of organic contaminants

The Br− in crystal structure of BiOBr are easily doped by other halides. However, the effect of halides doping degree on the photocatalytic performances of BiOBr is barely known. Herein, the halides (X’=Cl, I) doping degree in BiOBr (X’-BiOBr) nanosheets were regulated by altering the molar concentration of doped halides. The lower concentration of halides was doped into the shallow lattice of BiOBr, while excessive halides were doped into its deep lattices. The doped halides in shallow lattices of BiOBr modified band structure, contributing to efficient charge separation for promoted photodegradation of organic contaminants. Particularly, X’-BiOBr with halides doping in the shallow lattice exhibited superior photocatalytic activities.

Strain-dependent ultrafast carrier dynamics and spin–lattice interaction in LaMnO3 films

We investigate the ultrafast carrier dynamics and spin–lattice interaction in strained and unstrained LaMnO3 films via temperature-dependent femtosecond transient optical spectroscopy. The transient reflectivity measurements show two characteristic relaxation processes in both types of films, which are attributed to electron–phonon coupling and phonon-assisted spin–lattice interaction, respectively. The carrier dynamics and coupling between lattice and spin system are well described with the three-temperature model; the spin–lattice relaxation time constant is dominated by the temperature-dependent spin specific heat. Both the electron–phonon coupling and the spin–lattice interaction are enhanced in the strained film, as a result of the modified band structure and orbital ordering under biaxial compressive strain. Our results reveal the critical role of strain in the photo-induced dynamical interactions in LaMnO3.

Spray pyrolysis-derived W-doped MoSe2/rGO paper-like microspheres: optimization of microstructure and mesostructure for enhanced lithium storage

Two-dimensional MoSe2 is a promising candidate for lithium-ion battery anodes. However, its conductivity and lithium storage volumetric effect still need to be optimized. In this work, W-doped MoSe2/rGO paper-like microspheres are successfully prepared through ultrasonic spray pyrolysis, achieving optimization at both the microstructure and mesostructure to enhance the lithium storage performance of the material. Firstly, by utilizing the similar two-dimensional structure between MoSe2 and rGO, self-assembly is achieved through spray pyrolysis, resulting in a well-defined van der Waals heterostructure at the interface on the microscale, enhancing the electron and ion transfer capability of the composite. Secondly, the mesoscale paper-like microsphere morphology provides additional volume expansion buffering space. Moreover, W-doping not only increases the interlayer spacing of MoSe2 (0.73 nm), thereby reducing the diffusion resistance of Li+, but also allow for the modulation of the energy band structure of the material. Density functional theory (DFT) calculations confirm that W-doped MoSe2/rGO exhibits the narrowest bandgap (0.892 eV). Therefore, the composite demonstrates excellent lithium storage performance, maintaining a specific capacity of 732.9 mAh·g−1 after 300 cycles at a current density of 1 A·g−1.Graphical abstract

Boosting tetracycline degradation of BaTiO3-based piezo-catalysts via modulating phase boundary and band structure

Piezoelectric catalysis, which converts mechanical energy into chemical activity, has important applications in environmental remediation. However, the piezo-catalytic activity of various piezoelectric materials is limited by the weak piezoelectricity as well as the mismatched band-gap, leading to inefficient electron-hole pair generation and difficult carrier migration. Here, a simple strategy combining phase boundary and energy band structure modulation was innovatively proposed to enhance the piezo-catalytic activity of BaTiO3 ferroelectric by Ce ions selecting different doping sites. Thanks to the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) phases effectively flattened the Gibbs free-energy and thus enhanced the piezoelectric activity, as well as suitable energy bandwidth facilitating the carrier migration were realized in the B-sites doped Ba(Ti0.95Ce0.05)O3. The degradation rate constant k of tetracycline (TC) was high to 30.56 × 10-3 min−1, which was 2.03 times higher than that of pure BaTiO3 and superior to most representative lead-free perovskite piezoelectric materials. Theoretical calculations validated that the charge density and high O2 and OH– adsorption energy on the Ba(Ti0.95Ce0.05)O3 surface promoted more efficient •O2– and •OH radicals conversion and bettered response to piezo-catalytic reaction. This work is important to design high-performance piezo-catalysts by synergistic regulation of phase boundary and energy band structure in perovskite materials for long-term antibiotic tetracycline removal.

Effective redox reaction in a three-body smart photocatalyst through multi-interface modulation of organic semiconductor junctioned with metal and inorganic semiconductor

Forming metal/semiconductor heterojunctions is a well-known strategy to enhance photo-reaction through interface band bending. However, challenges remain in simultaneously minimizing fast charge carrier recombination and avoiding potential photo-corrosion in photocatalysts for high efficiency and long lifetime application in energy, environment, and green chemistry. We here design and propose a new strategy by which multi-interface band structure modulation occurs in a three-body photocatalyst, exemplified by Ag/PDA@Ag2S (PDA: polydopamine). Experimental analyses including in-situ x-ray photoelectron spectroscopy (XPS) and time-resolved photoluminescence (TRPL) spectroscopy together with projected density of states studies suggest an S-scheme heterojunction formation in the PDA@Ag2S, which greatly enhances the separation of photogenerated carriers. Consequently, we demonstrate that this multibody photocatalyst exhibits superior stability and selective oxidation of a series of ionic dyes under solar-simulated irradiation. The hydrogen generation efficiency (reduction) is also remarkably enhanced compared to virgin Ag/Ag2S photocatalysts. We believe this work brings a new insight into catalyst design.

Realizing High Thermoelectric Performance in GeTe‐Based Supersaturated Solid Solutions

AbstractAs a highly promising thermoelectric material in the mid‐temperature region, pristine GeTe shows deteriorated thermoelectric properties due to the low Seebeck coefficient and the intrinsic high thermal conductivity. Herein, it is discovered that the introduction of strongly correlated d, f electrons by alloying rare‐earth atoms at Ge sites will increase the band effective mass and promote band convergency, which can largely improve the electric transport property. Moreover, the heavy atoms (Pb, Bi) doping induces optical phonon softening and the avoided crossing between acoustic and optical phonon branches, decelerating both optical and acoustic phonon velocities. The modulated composition wave from the fluctuated multi‐component distribution introduces a complicated hierarchical structure including point defects and nanoprecipitates, which provides all‐scale scattering sources for heat‐carrying phonons and results in low lattice thermal conductivity. Consequently, a high zT of 2.4 at 800 K can be obtained in the Ge0.86Pb0.09Bi0.03Ce0.005Te sample due to the combination of strong correlation for d, f electrons and the full‐spectrum scattering for phonons. This work provides an effective strategy to increase the thermoelectric performance of IV–VI compounds by combining the modulated band structure and the softening phonon dispersion.

Covalently-Bonded Laminar Assembly of Van der Waals Semiconductors with Polymers: Toward High-Performance Flexible Devices.

Van der Waals semiconductors (vdWS) offer superior mechanical and electrical properties and are promising for flexible microelectronics when combined with polymer substrates. However, the self-passivated vdWS surfaces and their weak adhesion to polymers tend to cause interfacial sliding and wrinkling, and thus, are still challenging the reliability of vdWS-based flexible devices. Here, an effective covalent vdWS-polymer lamination method with high stretch tolerance and excellent electronic performance is reported. Using molybdenum disulfide (MoS2 )and polydimethylsiloxane (PDMS) as a case study, gold-chalcogen bonding and mercapto silane bridges are leveraged. The resulting composite structures exhibit more uniform and stronger interfacial adhesion. This enhanced coupling also enables the observation of a theoretically predicted tension-induced band structure transition in MoS2 . Moreover, no obvious degradation in the devices' structural and electrical properties is identified after numerous mechanical cycle tests. This high-quality lamination enhances the reliability of vdWS-based flexible microelectronics, accelerating their practical applications in biomedical research and consumer electronics.

Structure evolution and energy band modulation in Ba-doped BiFeO3 thin films

Bi1−xBaxFeO3 (BBFO, x = 0, 0.03, 0.1) thin films were epitaxially grown on SrRuO3-buffered SrTiO3 (001) substrates by pulsed laser deposition. With increasing Ba content, the BBFO thin films show significantly reduced leakage currents but suppressed ferroelectric polarization. X-ray diffraction reciprocal space mappings and Raman spectra indicate a structural evolution from a rhombohedral-like to tetragonal-like phase in the BBFO thin films. Optical absorption and photoelectron spectroscopy measurements demonstrate a modulation of energy band structures in the BBFO thin films. With A-site Ba acceptor doping, the BBFO thin films exhibit a blue-shift of optical bandgap and an increase in work function. The energy positions of conduction and valence bands of the BBFO thin films have been modulated, and the Fermi level shifts down to the center of the forbidden band, but acceptor-doped BFO thin films still show n-type conduction. The presence of extra oxygen vacancies by acceptor doping is supposed to make contribution to conduction behavior. This study provides a method to manipulate the functional properties and gives insights into the physics of Ba doping in BFO thin films.

Promoted Na Solubility and Modified Band Structure for Achieving Exceptional Average ZT by Extra Mn Doping in PbTe.

Na doping strategy provides an effective avenue to upgrade the thermoelectric performance of PbTe-based materials by optimizing electrical properties. However, the limited solubility of Na inherently restricts the efficiency of doping, resulting in a relatively low average ZT, which poses challenges for the development and application of subsequent devices. Herein, to address this issue, the introduced spontaneous Pb vacancies and additional Mn doping synergistically promote Na solubility with a further modified valence band structure. Furthermore, the induced massive point defects and multiscale microstructure greatly strengthen the scattering of phonons over a wide frequency range, leading to a remarkable ultralow lattice thermal conductivity of ∼0.42 W m-1 K-1. As a result, benefiting from the significantly enhanced Seebeck coefficient and superior thermal transports, a high peak ZT of ∼2.1 at 773 K and an excellent average ZT of ∼1.4 between 303 and 823 K are simultaneously achieved in Pb0.93Na0.04Mn0.02Te. This work proposes a simple and constructive method to obtain high-performance PbTe-based materials and is promising for the development of thermoelectric power generation devices.

The relationship between the plasma edge and topological properties of Sb2Te3 under pressure

Topological insulators have garnered considerable attention in recent years due to their unique electronic properties. However, pressure-induced topological materials often located in the middle of the two diamonds and cannot be detected by Angle resolved electron spectra. Such topological materials only stay in theoretical calculated. Since diamond has a high optical transmittance, its optical properties have been extensively studied to probe the band structure of topological insulators under pressure. In this paper, we determine the high-pressure infrared (IR) properties by measuring the transmittivity and reflectivity of Sb2Te3 up to 23.2 GPa. The plasma edge shows jumping at 4.2 GPa and 8.5 GPa, where is caused by the change of charge carrier features and a new phase appears at 8.5 GPa. Furthermore, by analyzing the position of plasma edge under pressure, we find that the absence of plasma edge at high pressure corresponds to the disappearance of the Sb2Te3 topological structure. Therefore, utilizing the plasma edge to investigate the modification of band structure in materials under high pressures is highly effective.

Photocatalytic activity enhancement with 4-trifluoromethylphenylacetylene-functionalized Cu2O cubes and rhombic dodecahedra from band structure modulation and use in boronic acid hydroxylation

4-Trifluoromethylphenylacetylene-functionalized Cu2O cubes and rhombic dodecahedra show greatly enhanced photocatalytic activity from surface band structure change. The modified cubes can photocatalyze arylboronic acid hydroxylation reactions.

Effect and mechanism analysis of surface hydrogenation and fluorination on the electronic properties of th-GeC2.

A two-dimensional (2D) tetrahex-GeC2 nanosheet demonstrates excellent electronic properties such as a finite direct band gap and high carrier mobilities, as predicted from theoretical calculations. To further expand its potential applications, various strategies can be employed to tailor its electronic properties. These strategies include alloying, strain application, and edge and surface functionalization. This work specifically focuses on the impact of surface functionalization with hydrogen and fluorine adsorption on the 2D tetrahex-GeC2 nanostructures. It was discovered that the electronic properties of these nanostructures undergo significant alterations through surface functionalization by adjusting the adsorption sites and coverage of H/F species. The underlying mechanisms responsible for these property changes have been thoroughly analyzed and discussed in detail. Our calculations, based on density functional theory, reveal that the band gap of tetrahex-GeC2 widens as the surface coverage of H atoms increases. Conversely, the band gap narrows in the case of F adsorption. Additionally, the indirect-direct band gap transition can be triggered through surface functionalization. Such modifications in the electronic band structure are primarily due to the disappearance of the π bond when the C atom is converted from sp2 to sp3 hybridization through the adsorption of surface functionalized species. Furthermore, the results indicate that surface adsorption can regulate the effective mass of carriers, electron affinity, and work function in the 2D tetrahex-GeC2 nanostructure.

The g-ZnO/PtSe2 S-scheme heterojunction with controllable band structure for catalytic hydrogen production

The structural, photo-electronic catalytic properties, and the biaxial strain modulation of band structure for the g-ZnO/PtSe2 S-scheme heterojunction are studied by First-principles calculation. The stability for the heterojunction is verified by negative generation energy and ab-initio molecular dynamic simulation. The photo-generated carrier motion and band structure are in accordance with the S-scheme, and the electron mobility of up to 2023 cm2/Vs is obtained in the Zigzag direction. The absorption of visible light is improved, and an absorption peak of 2.893 × 105 cm−1 at 434.337 nm is observed. Due to a higher redox potential, photocatalytic water splitting can occur in the pH range of 0∼14, and a high solar to hydrogen (STH) efficiency of 30.7 % is obtained. The over-potential of hydrogen evolution reaction (HER) (3.719 V) is lower than oxygen evolution reaction (4.128 V), which tends to proceed at the g-ZnO interface. When the strain ≥4 %, the bandgap alignment of the g-ZnO/PtSe2 heterojunction changes from a staggered gap (Type-Ⅱ) to straddling gap (Type-Ⅰ). The g-ZnO/PtSe2 heterojunction exhibits high electron mobility, high STH efficiency, strong absorption of visible light, strong HER ability, and a tunable band structure, expecting as a promising candidate material for catalytic water splitting.

Interfacial electric field construction of hollow PdS QDs/Zn1-xCdxS solid solution with enhanced photocatalytic hydrogen evolution.

The regulation of hollow morphology, band structure modulation of solid solution, and introduction of cocatalysts greatly promote the separation of electron-hole pairs in photocatalytic processes, which is of great significance for the process of photocatalytic hydrogen evolution (PHE). In this study, we constructed Zn1-xCdxS hollow solid solution photocatalysts using template and ion exchange methods, and successfully loaded PdS quantum dots (PdS QDs) onto the solid solution through in situ sulfidation. Significantly, the 0.5 wt% PdS QDs/Zn0.6Cd0.4S composite material achieved a H2 production rate of 27.63 mmol g-1 h-1 in the PHE process. The hollow structure of the composite material enhances processes such as light reflection and scattering, the band structure modulation of the solid solution enables the electron-hole pairs to reach an optimal exciton recombination balance, and the modification of PdS QDs provides abundant sites for oxidation, thereby promoting the proton reduction and hydrogen evolution rate. This work provides valuable guidance for the rational design of efficient composite PHE catalysts with strong internal electric field.

Achieving high quality factor and enhanced thermoelectric performance in polycrystalline SnS by Ag doping and Se alloying

The polycrystalline SnS with a similar layered crystal structure and band structure to SnSe exhibits enormous commercial thermoelectric potential due to its lower cost and environmentally friendly characteristics. However, the wider bandgap of SnS leads to low carrier concentration and inferior electrical transport performance. The two-dimensional interlayer hinders carrier transport, leading to interesting and mysterious anisotropic thermoelectric properties. Herein, we reported the optimized electron–phonon transport in anisotropic polycrystalline SnS by Ag doping and Se alloying, realizing a high quality factor B by multiple strategies of optimizing carrier concentration, modifying band structure, and introducing various defects; further potential performance is predicted by the single parabolic band model. Specifically, Ag-doped SnS not only significantly increases the carrier concentration and weighted mobility μw in both directions but also induces multi-scale precipitates proven by the Debye–Callaway model to suppress phonon transport. Moreover, additional Se alloying optimizes the electronic band structure and increases the Seebeck coefficient, further improving μW and boosting the maximum power factor to ∼3.72 μW cm−1 K−2 at 873 K in the out-of-plane direction. Consequently, the synergistic optimization of carrier and phonon transport achieved a high B of 0.7 and a maximum zTmax of ∼0.8 at 873 K in Ag0.02Sn0.98S0.99Se0.01. Additionally, the high B predicted a high zTmax∼1.5 based on optimized carrier transport characteristics, demonstrating the potential great-performance polycrystalline SnS. This work provides a promising avenue for optimizing the zT of polycrystalline SnS by transport engineering.