Band Gap Regulation Research Articles

Construction and Band Gap-Regulation of Ordered Macro-Microporous Single Crystals of an Amine-Linked Covalent Organic Framework.

Heterogeneity engineering provides an effective route to manipulate the chemical and physical properties of covalent organic frameworks (COFs) but is still under development for their single-crystal form. Here, we report the strategy based on a combination of the template-assisted modulated synthesis with a one-pot crystallization-reduction method to directly construct ordered macro-microporous single crystals of an amine-linked three-dimensional (3D) COF (OM-COF-300-SR). In this strategy, the colloidal crystal-templating synthesis not only assists the formation of ordered macropores but also greatly facilitates the in situ conversion of linkages (from imine to amine) in the COF-300 single crystals. The as-synthesized OM-COF-300-SR120 exhibits a reversible symmetry change from a tetragonal I41/a to monoclinic I2/c space group after activation, which was not observed previously. On the other hand, this strategy allows for a flexible control over the degree of amination (from 0 to 100%, as determined by X-ray photoelectron spectroscopy (XPS) analysis) in COF-300 crystals to regulate their band gap (from 2.57 to 2.81 eV) for the optimization of photocatalytic activity. The high degree of amination and the embedded ordered macropores render OM-COF-300-SR120 with superior photocatalytic activity (with a reaction rate constant of 0.9572 min-1) to its nonmacroporous counterpart (NM-COF-300-SR120, 0.2303 min-1) for the degradation of rhodamine B. In addition, the significant contribution of ordered macropores to confront mass transfer resistance in COF single crystals was also confirmed by the much higher catalytic activity of Au/OM-COF-300-SR120 (with an activity parameter of 7.96 × 103 s-1 mol-1) as compared with Au/NM-COF-300-SR120 (1.43 × 103 s-1 mol-1) in the model reduction reaction of 4-nitrophenol by NaBH4.

Thermal Regulation of the Acoustic Bandgap in Pentamode Metamaterials

This study used the finite element method to investigate the acoustic bandgap (ABG) characteristics of three-dimensional pentamode metamaterial (PM) structures under the thermal environment, and a method for controlling the PM ABG based on external temperature variation is also proposed. The results indicate that the complete acoustic bandgap can be obtained for a PM in the thermal environment, which makes the PM combine the bandgap characteristics of phononic crystals. More than that, the bandwidth and locations of ABGs can be effectively manipulated by controlling the temperature. Considering the softening effect of thermal stresses, the ABG gradually moves to lower frequencies as the temperature increases. Based on this, different degrees of ABG tunability can be achieved by changing the thermal environment to propagate or suppress acoustic waves of different frequencies. This work provides the possibility for PMs to realize intelligent regulation of the bandgap.

Band gap regulation of MIL-101(Fe) via pyrazine-based ligands substitution for enhanced visible-light adsorption and its photo-Fenton-like application

Regulating the photo-response region of iron metal-organic frameworks (Fe-MOFs) is a viable strategy for enhancing their practical application in the visible-light driven photo-Fenton-like process. This study developed a novel pyrazine-based Fe-MOFs (MIL-101(Fe)-Pz) by substituting the 1,4-dicarboxybenzene acid ligands in typical MIL-101(Fe) with 2,5-pyrazinedicarboxylic acid (PzDC), in which sodium acetate was used as coordinative modulator to control the crystal size (2–3 µm). The incorporation of Fe-pyridine N coordination structures originated from PzDC ligands gave MIL-101(Fe)-Pz narrowed band gap (1.45 eV) than MIL-101(Fe) (2.54 eV) resulting in improved visible-light adsorption capacity (λ > 420 nm), and also increased the proportion of Fe(II) in the Fe-clusters. Thus MIL-101(Fe)-Pz exhibited a synergistic enhanced photo-Fenton-like catalytic performance under visible-light irradiation. The MIL-101(Fe)-Pz/H2O2/Vis system could degrade 99% of sulfamethoxazole within 30 min, which was 10-fold faster than that of the pristine MIL-101(Fe), it also effectively removed other organic micropollutants with high durability and stability. Mechanistic analysis revealed that the PzDC ligands substitution decreased the band gap of MIL-101(Fe), giving MIL-101(Fe)-Pz appropriate band structure (-0.40 – 1.05 V vs NHE) which can cover several light-driven process for the generation of reactive oxygen species, including Fe(III) reduction and H2O2 activation for accelerating •OH generation, as well as oxygen reduction reaction for generating H2O2, O2•− and 1O2. This study highlights the role of pyridine-N containing ligands in regulating the band structure of Fe-MOFs, providing valuable guidance for the design of Fe-MOFs photocatalysts.

Z-Scheme LaFeO3/Cd0.7Zn0.3S heterojunction based on 3DOM LaFeO3 perovskite for enhanced photocatalytic hydrogen activity

The narrow band gap semiconductor LaFeO3 with ABO3 perovskite structure has been deeply studied in the field of photocatalysis due to its good thermal stability, chemical stability, photoelectric properties and suitable band position. The inverse opal structure gives the material a large specific surface area and increases the adsorption area and active site of the catalyst. In this work, it is reported for the first time that perovskite LaFeO3 inverse opal was applied to photocatalytic hydrogen production. The Cd0.7Zn0.3S QDs were deposited on the skeleton wall of LaFeO3 inverse opal to construct LaFeO3/Cd0.7Zn0.3S binary heterojunction catalyst. The LaFeO3 3DOM can effectively increase the contact area with Cd0.7Zn0.3S QDs with an increase in specific surface area, and the multiple scattering effect improves the efficiency of light utilization. The introduction of Zn2+ ions regulate the band gap position of Cd0.7Zn0.3S QDs and increases the thermodynamic reduction ability of photo generated electrons. The Z-type heterojunction effect formed by LaFeO3 inverse opal and Cd0.7Zn0.3S QDs facilitates the separation and transmission of photo generated charges. The LaFeO3/Cd0.7Zn0.3S heterojunction catalysts achieved a hydrogen production performance of 277.48 μmol/g/h due to the large specific surface area of 3DOM, good light capture ability, band gap regulation of element doping, and efficient charge separation synergistic effect of heterojunction. This work provides new insights into the design and manufacture of perovskite-type 3DOM heterojunction photocatalysts.

Ultrafast Laser Printing Green–Red Dual‐Phase Perovskite Quantum Dots in Glass

AbstractFlexible regulation of local chemistry and band gap of perovskite quantum dots (PeQDs) is crucial for exploring their new functionalities and device applications. In this work, a strategy based on the combination of femtosecond (fs) laser‐irradiation and thermal treatment to effectively manipulate chemical composition and emitting wavelength of PeQDs in amorphous glass, is reported. The engineering of ultrafast laser‐induced thermal effect enables to induce in situ nucleation/growth of dual‐phase PeQDs within an individual glass matrix. By elevating heat‐treatment (HT) temperature, I− ions are driven to surmount the diffusion barrier into the PeQDs lattice, leading to a tunable emission wavelength ranging from 613 to 647 nm. Besides, it is verified that the temperature‐dependent diffusion rate of I− ions plays a pivotal role in affecting luminescent efficiency and color of the dual‐phase glass. Finally, fs laser direct writing of multi‐color patterns is presented, which provides a flexible method to develop new encryption/decryption technology for information security and anti‐counterfeiting.

Diamond/cubic boron nitride (111) heterojunction interface: Rational regulation of high two-dimonsional electron gas

Wide-bandgap diamond exhibits excellent physical and chemical properties, making it an ideal substrate material for developing high-temperature and high-power semiconductor devices and broadening its application prospects in the field of microelectronics and optoelectronic devices. However, because of the Fermi pinning effect, it is difficult to achieve n-type diamond with excellent transport properties. Cubic boron nitride (cBN) has similar structural properties and a smaller lattice mismatch with diamond. Thus, making the two-dimensional electron gas of the diamond/cBN heterojunction provides a new idea to solve the problem of diamond n-incorporation difficulty and small bandgap regulation range. The diamond/cBN heterojunction is applied to study the law of influence factors on the heterojunction band structure, band alignment, and polarization strength. Further, a regulation mechanism for two-dimensional electron gas density is established at heterojunction interfaces, which can help solve the core difficulties of diamond n-type doping, small bandgap regulation range, and high impedance, providing a theoretical basis for realizing diamond power devices with high power density and low power consumption.

A Nonbenzenoid 3D Nanographene Containing 5/6/7/8-Membered Rings

Nanographenes (NGs) have attracted continuous attention in recent years owing to their opened bandgaps and optoelectronic applications. Especially, nonbenzenoid NGs containing non-six-membered rings have been developed rapidly due to their unique structures and properties. In this work, we employ nonbenzenoid acepleiadylene (APD) and the cyclooctatetraene (COT) moiety to construct the first three-dimensional (3D) NG containing 5/6/7/8-membered rings in one molecule (COT-APD). The calculated results prove that COT-APD has a saddle-like configuration similar to that of other COT-type molecules. Each APD segment in COT-APD keeps the inherent aromaticity of the APD moiety. Compared with other COT-type molecules, COT-APD shows a narrower bandgap, which indicates the superiority of APD in bandgap regulation. Furthermore, four reversible reductive waves are observed in electrochemical characterizations, demonstrating the excellent electron-accepting capability of COT-APD.

Band gap regulation of LaFeO3 via doping Sr for efficient conversion of coke and steam

Coking is bottleneck problem during steam cracking processes, so strategies for online catalytic conversion of coke are vitally important for ethylene production. In this work, a method for regulating the band bap of perovskites to enhance hydroxyl radical generation is proposed to promote the catalytic conversion of coke. A series of ternary La1-xSrxFeO3 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) perovskites were successfully prepared by sol-gel method. Experimental and DFT calculations show that Sr doped at A sites facilitates a reduction in the band gap and the promotion of electronic transitions in the perovskites. Moreover, water molecule adsorption, decomposition, and intermediate transition state desorption are improved. Using 10 wt% LSF-0.6 catalyst, a water flow rate of 0.167 mL/min, reaction temperature of 900 °C, and reaction time of 120 min, a coke conversion rate of 85.56% is achieved. This work provides a theoretical basis for in-situ high-efficiency coke removal.

A review: Comprehensive investigation on bandgap engineering under high pressure utilizing microscopic UV–Vis absorption spectroscopy

Bandgap engineering plays a vital role in material development and device optimization due to its significant impact on the photovoltaic and photoelectricity properties of materials. Nevertheless, it is still a great challenge to accurately control the bandgap of semiconductors to achieve the targeted properties of materials. Recently, pressure-induced bandgap regulation has emerged as a novel and effective tool to regulate bandgap, reveal the intrinsic band nature, and construct the in-depth structure–property relationships therein. In this review, the unique techniques of microscopic in situ steady-state UV–Vis absorption spectroscopy and high-pressure diamond anvil cell are introduced. This technique provides a powerful method to monitor the bandgap behaviors at high pressure. Then, the pressure-triggered bandgap responses are outlined based on several typical semiconductors, including metal halide perovskites, inorganic quantum dots, piezochromic molecular compounds, and two-dimensional semiconductor materials. The summarized structural effects on bandgap evolution and the general principles for bandgap engineering under high pressure are expected to provide guidance for further material design under ambient conditions. Microscopic absorption spectroscopy detection under high pressure is proven to be an ideal platform for developing functional materials and high-performance devices.

Improve the Charge Carrier Transporting in Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells.

Conventional 3D organic-inorganic halide perovskite materials have shown substantial potential in the field of optoelectronics, enabling the power conversation efficiency of solar cells beyond 26%. A key challenge limiting the further commercial application of 3D perovskite solar cells is their inherent instability over outer oxygen, humidity, light, and heat. By contrast, 2D Ruddlesden-Popper (2DRP) perovskites with bulky organic cations can effectively stabilize the inorganic slabs, yielding excellent environmental stability. However, the efficiencies of 2DRP perovskite solar cells are much lower than those of the 3D counterparts due to poor charge carrier transporting property of insulating bulky organic cations. Their inner structural, dielectric, optical, and excitonic properties remain to be primarily studied. In this review, the main reasons for the low efficiency of 2DRP perovskite solar cells are first analyzed. Next, a detailed description of various strategies for improving the charge carrier transporting of 2DRP perovskites is provided, such as bandgap regulation, perovskite crystal phase orientation and distribution, energy level matching, interfacial modification, etc. Finally, a summary is given, and the possible future research directions and methods to achieve high-efficiency and stable 2DRP perovskite solar cells are rationalized.

Topochemical-like bandgap regulation engineering: A bismuth thiooxide nanocatalyst for breast cancer phototherapy

The physical property tuning of nanomaterials is of great importance in energy, medicine, environment, catalysis, and other fields. Topochemical synthesis of nanomaterials can achieve precise control of material properties. Here, we synthesized a kind of element-doped bismuth-based nanomaterial (BOS) by topochemical-like synthesis and used it for the phototherapy of tumors. In this study, we employed bismuth fluoride nanoflowers as a template and fabricated element-doped bismuth oxide nanoflowers by reduction conditions. The product is consistent with the precursor in crystal structure and nanomorphology, realizing topochemical-like synthesis under mild conditions. BOS can generate reactive oxygen species, consume glutathione, and perform photothermal conversion under 730 nm light irradiation. In vitro and in vivo studies demonstrate that BOS could suppress tumor growth by inducing apoptosis and ferroptosis through phototherapy. Therefore, this study offers a general regulation method for tuning the physical properties of nanomaterials by using a topochemical-like synthesis strategy.

Thermal‐Triggered Phase Separation and Ion Exchange Enables Photoluminescence Tuning of Stable Mixed‐Halide Perovskite Nanocrystals for Dynamic Display

AbstractFlexible regulation of bandgap of perovskite nanocrystals (PNCs) is fundamentally critical for desirable optoelectronic functions and applications. Here, regulating chemical composition and emission wavelength of PNCs in glass by a simple heat‐treatment process are reported, which is established to rely on the thermal‐trigger phase separation and ion exchange. The first principle calculations are overall performed to reveal the mechanism of bandgap engineering and optimization of emission performance. The PNCs exhibit excellent stability against thermal, ultraviolet irradiation, and organic molecules. The bandgap of PNCs in the heat‐treated glass can also be re‐modulated by ultrafast laser irradiation. Ultrafast laser direct writing of multi‐color patterns and holographic dynamic displays are achieved, which hold great potential in the application of encryption‐decryption and emissive devices.

Regulation of band gap and localized surface plasmon resonance by loading Au nanorods on violet phosphene nanosheets for photodynamic/photothermal synergistic anti-infective therapy.

In the face of the serious threat to human health and the economic burden caused by bacterial antibiotic resistance, 2D phosphorus nanomaterials have been widely used as antibacterial agents. Violet phosphorus nanosheets (VPNSs) are an exciting bandgap-adjustable 2D nanomaterial due to their good physicochemical properties, yet the study of VPNS-based antibiotics is still in its infancy. Here, a composite of gold nanorods (AuNRs) loaded onto VPNS platforms (VPNS/AuNR) is constructed to maximize the potential of VPNSs for antimicrobial applications. The loading with AuNRs not only enhances the photothermal performance via a localized surface plasmon resonance (LSPR) effect, but also enhances the light absorption capacity due to the narrowing of the band gap of the VPNSs, thus increasing the ROS generation capacity. The results demonstrate that VPNS/AuNR exhibits outstanding antibacterial properties and good biocompatibility. Attractively, VPNS/AuNR is then extensively tested for treating skin wound infections, suggesting promising in vivo antibacterial and wound-healing features. Our findings may open a novel direction to develop a versatile VPNS-based treatment platform, which can significantly boost the progress of VPNS exploration.

Bandgap regulation and doping modification of Ga2-x Cr x Se3 nanosheets.

Ga2Se3, an important direct wide bandgap semiconductor with excellent optoelectronic properties, has wide application potential in the fields of photodetectors, photoelectric sensors and solar cells. Herein, we describe the synthesis of Ga2Se3 semiconductor nanoparticles using a high temperature organic liquid phase method. Post-annealing treatment at different temperatures can not only improve the crystallinity of Ga2Se3 nanoparticles, but also regulate its optical band gap ranging from 2.50 to 2.80 eV. We further synthesized Ga2-x Cr x Se3 nanosheets by doping CrCl3·6H2O in the reaction process. By adjusting the Cr doping concentration, Ga2-x Cr x Se3 nanosheets can achieve a continuously tunable band gap in the range of 2.23 eV to 2.42 eV. Both Ga2-x Cr x Se3 nanosheets and Ga2Se3 nanoparticles exhibit excellent and stable photoelectric switching performance. With Cr doping, Ga2-x Cr x Se3 exhibits reduced Nyquist impedance and enhanced electrocatalytic activity, which is attributed to its ultrathin nanosheet morphology and large specific surface area. In addition, the diamagnetic behavior of pure Ga2Se3 changes to ferromagnetism with different Cr doping concentrations, and its magnetization is as high as 18.0 emu g-1 at x = 0.4. These findings demonstrate that Ga2-x Cr x Se3 nanosheets have significant potential in future optoelectronic and magnetoelectric applications.

1D Pb halide perovskite-like materials for high performance X-ray detection.

The strategy of bandgap regulation is important for X-ray detection, but has not been reported for 1D Pb halide perovskite materials. In this work, three such materials, 1, 2 and 3, with a tunable bandgap, were fabricated for application in X-ray detection. 3 shows high sensitivity, far superior to commercial X-ray detectors.

Band Gap Regulation with Imino Groups in Graphdiyne: A Promising Photocatalyst for Water-Splitting and CO2 Reduction

Band Gap Regulation with Imino Groups in Graphdiyne: A Promising Photocatalyst for Water-Splitting and CO₂ Reduction

Variation in properties of double-walled zigzag and armchair silicon nanotubes depending on SW defects and applied electric fields by SCC-DFTB method

The geometric structure and electrical properties of the zigzag DWSiNT (8,0)@(12,0) and armchair DWSiNT (5,5)@(7,7) perfect tubes with the same diameter are simulated by self-consistent charge density functional tight binding method (SCC-DFTB). We considered the defective tubes by introducing three types of Stone-Wales (SW) defects, and further investigated the impact of both strong and weak electric fields on these defective tubes. Calculations demonstrate that the atomic arrangement regularity, degree of buckling, stability, energy gap, and charge distribution strongly depend on the type of perfect tubes. Following the introduction of the SW defects, the symmetry of the tubes disappeared, and there is a obvious atomic aggregation occurring at the defects. The armchair tubes demonstrate a higher stability compared to zigzag tubes and all exhibit metallic properties. SWⅡ and SWⅢ defects in zigzag tubes result in a transition from semiconductor to semi-metallic properties. The number of charge transfer increases, and the degree of atomic aggregation is more dispersed. The effect of applied electric field strength on perfect zigzag tubes is more obvious. The weak field has minimally impacted on the stability, and the strong field makes the stability improved to some extent. The presence of a strong field caused the energy gap values of (8,0)@(12,0) tube decrease sharply, and all tubes are transformed into semi-metal or metal. The weak electric field has a more pronounced regulation of band gap within the range of 0 V/nm - 0.3 V/nm on the inner tube. The consequences of this investigation can certainly be helpful in future experimental studies.

Study of the growth mechanism of a self-assembled and ordered multi-dimensional heterojunction at atomic resolution

Multi-dimensional heterojunction materials have attracted much attention due to their intriguing properties, such as high efficiency, wide band gap regulation, low dimensional limitation, versatility and scalability. To further improve the performance of materials, researchers have combined materials with various dimensions using a wide variety of techniques. However, research on growth mechanism of such composite materials is still lacking. In this paper, the growth mechanism of multi-dimensional heterojunction composite material is studied using quasi-two-dimensional (quasi-2D) antimonene and quasi-one-dimensional (quasi-1D) antimony sulfide as examples. These are synthesized by a simple thermal injection method. It is observed that the consequent nanorods are oriented along six-fold symmetric directions on the nanoplate, forming ordered quasi-1D/quasi-2D heterostructures. Comprehensive transmission electron microscopy (TEM) characterizations confirm the chemical information and reveal orientational relationship between Sb2S3 nanorods and the Sb nanoplate as substrate. Further density functional theory calculations indicate that interfacial binding energy is the primary deciding factor for the self-assembly of ordered structures. These details may fill the gaps in the research on multi-dimensional composite materials with ordered structures, and promote their future versatile applications.Graphical

Strain-induced electronic structures and band-gap of few-layer AgInP2S6

The band gap and mechanical control ability of two-dimensional materials largely determine the application value of two-dimensional devices in optical and electronic properties, so the bandgap controllability of two-dimensional materials broadens the application range of multi-functional devices. In the layered van der Waals (vdW) material AgInP2S6, the band gap can be adjusted by the number of layers and flexible strain, and the few layers AgInP2S6 have discrete band gap values, which are also relevant for optoelectronic applications. In the strain range of up to 2.7% applied, the band gap can be adjusted, and the film is relatively stable under strain. We further analyzed the physical mechanism of flexible strain band gap regulation and found that strain-regulation reduced the band gap and increased the chemical bond length. These studies open up new opportunities for the future development of vdW material photoelectric resonators represented by AgInP2S6, and have important reference value.

Broadband high-performance vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode

Vertical semiconductor van der Waals heterojunctions are essential for fabricating high-performance photodetectors. However, the range of the spectral response and defect states of semiconductor materials are two critical factors affecting the performance of photodetectors. In this work, the spectral response range of WS2 was changed through WS2 band gap regulation, and a self-powered vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode was prepared by synthesizing WS1.08Se0.92 film on Si substrate and vertically stacking Ti3C2T x MXene on the film. Due to the electron collection of MXene and the wonderful junction quality of WS1.08Se0.92/Si, the photodetector can detect near-infrared light in the range of 980–1310 nm, which exceed the detection limit of WS1.08Se0.92. And the device had high sensitivity in the broadband. The responsivity was 4.58 A W−1, the specific detectivity was 4.58 × 1011 Jones, the on/off ratio was 4.95 × 103, and the fast response time was 9.81/9.03 μs. These properties are superior to previously reported WS2-based photodetectors. Vertical structure, Energy band tuning, and MXene electrode provide a new idea for preparing broadband high-performance and self-powered photodetector.