Unique Band Research Articles

Visible-light responsive PDI/rGO composite film for the photothermal catalytic degradation of antibiotic wastewater and interfacial water evaporation

A visible-light responsive self-assembled perylenetetracarboxylic diimide (PDI)/reduced graphene oxide (rGO) composite film was obtained and showed excellent photocatalytic performance and efficient interfacial steam generation. The degree of π-π interactions between Perylenetetracarboxylic diimide supramolecular nanofibers (nano-PDI) and rGO regulated the energy band structure and redox potential of the composite film to produce h+ and O2− active species. The photothermal conversion of the composite film under visible light irradiation was realized, which was mainly because the above-bandgap electrons and holes of the upper nano-PDI relaxed to the edge of the band and converted the excess energy into heat. The unique energy band structure of rGO also promotes the effective photothermal conversion of the composite film. The composite film degraded 94.31 % (10 mg/L) of ciprofloxacin hydrochloride (CIP) under 0.5 sun visible light irradiation within 120 min. The corresponding interfacial steam generation efficiency via photothermal conversion of the composite film was 10.92 %. Furthermore, the composite film retained its excellent photothermal performance, when used to remove CIP from real water samples, including Yellow River water, Weihe River water, and tap water.

Ellipsometry Study of Hexagonal Boron Nitride Using Synchrotron Radiation: Transparency Window in the Far‐UVC

The linear optical response of the ultrawide bandgap h‐BN is investigated by spectroscopic ellipsometry. The ordinary dielectric function of h‐BN is determined up to 25 eV on a high‐quality single‐crystal platelet. The direct bandgap and the high‐energy transitions are characterized with the aid of ab initio self‐consistent GW calculations and the optical properties are calculated using the Bethe–Salpeter equation. The dispersion of the ordinary refractive index in the visible and UV part of the spectrum below the bandgap is in excellent agreement with previous transmission experiments. A sharp excitonic peak at 6.1 eV associated with the direct bandgap dominates the absorption spectrum, and a second peak is observed at 6.8 eV. At higher energies, a strong absorption peak emerges at 15 eV associated with higher σ → σ* transitions. As a consequence of the unique electronic band structure of h‐BN, a transparency window is observed in the far‐UV region between 7 and 13 eV, where the light penetration depth reaches a value of 38 nm, as opposed to the value of 0.8 nm at the absorption peak of the fundamental bandgap.

Double band inversion in the topological phase transition of Ge1-x Snx alloys

We use first-principles simulation and alchemical mixing approximation to reveal the unique double band inversion and topological phase transition in GeSn alloys. Wave function parity, spatial charge distribution and surface state spectrum analyses suggest that the band inversion in GeSn is relayed by its first valence band. As the system evolves from Ge to -Sn, its conduction band moves down, and inverts with the first and the second valence bands consecutively. The first band inversion makes the system nontrivial, while the second one does not change the topological invariant of the system. Both of the band inversions yield surface modes spanning the individual inverted gaps, but only the surface mode in the upper gap associates with the nontrivial nature of tensile-strained -Sn.

Growth of two-dimensional material black phosphorus guided by gold substrates and its growth mechanism

<p indent=0mm>Two-dimensional (2D) materials are the frontier research direction of material sciences and condensed matter physics in recent years. Among different kinds of 2D materials, black phosphorus (BP) has received extensive attention due to its unique band gap and excellent optical and electrical anisotropy properties. Compared with graphene and transition metal dichalchogenides (TMDCs), BP stands out for its unique properties with widely tunable direct bandgaps ranging from <sc>0.3–1.7 eV,</sc> covering the wavelength from ~600 to <sc>4000 nm,</sc> which fill in the gap between graphene <sc>(0 eV)</sc> and TMDCs (~1.0–2.5 eV) and is considered the ideal material for optoelectronic applications, such as light detection and light modulation. For example, photodetectors are basic devices for optoelectronics, as they transform the information stored in light into electric signals. BP based photodetectors not only stand out for their wide detection range reaching far infrared (IR) region, but also for their high responsivity and high gain, demonstrating their excellent performance for mid-IR detection. In order to achieve above-mentioned applications, few or even monolayer BP flakes or continuous BP films are required. However, how to control the preparation of thin layer of BP is one of the biggest challenges in this field. In this paper, we carried out a systematic study on the growth of BP on different substrates and found that Au can guide and promote the growth of BP, thereby controlling its growth. Based on the above findings, the growth of BP nanosheets on the Au-Si substrate is achieved by using a Si substrate deposited with Au thin film on top, and by designing a strategy with gradient temperature and in confined space. We observed that the BP nanosheets grown by this system exhibited different shapes such as ribbons and flakes, and their thicknesses can be reduced to be about <sc>51 nm</sc> with a lateral size of around <sc>10 µm.</sc> In addition, by systematically tuning the growth parameters in the system, we found that the growth temperatures and the amount of red phosphorous loading are the key parameters for the growth of BP. With certain temperatures and precursor loadings, we achieve the growth of BP nanosheets, while by-products would be obtained on the substrate with other parameters. In our previous work, we found that the temperature gradients play a crucial role in the yield, purity, and crystal quality of bulk BP growth. Therefore, further optimization of temperature distribution is of great importance for the growth of BP nanosheets. In addition, we observed in this paper that Au would guide the nucleation and growth of BP. Therefore, it is important to regulate Au-P compounds during growth of BP, as on the one hand, it can control the by-products during the reaction and on the other hand, it can also improve the controllability of BP nucleation. Based on this, we believe that optimization of the temperature distribution and the growth regulation of Au-P compounds are important research directions, as to precisely control and reduce the thickness of BP nanosheets to grow few layer BP. The growth system proposed in this paper improves the chemical vapor transport (CVT) growth of traditional bulk BP from three aspects: Substrate design, confined space design, and temperature gradient control, which have paved the way for the future controllability growth of BP nanosheets and have deepened the understanding of BP growth mechanism.

Heterostructural (Sr0.6Bi0.305)2Bi2O7/ZnO for novel high-performance H2S sensor operating at low temperature

Exploring novel sensing materials enabling selective discrimination of trace ambient H2S at lower temperature is of utmost importance for diverse practical applications. Herein, heterostructural (Sr0.6Bi0.305)2Bi2O7/ZnO (SBO/ZnO) nanomaterials were proposed. Synergetic effect of promoting analyte adsorption (via multiplying oxygen vacancy defects) and reversible sulfuration-desulfuration reaction induced unique band alignment among SBO/ZnO/ZnS, contributes to the sensitive and selective response toward H2S molecules. Novel SBO/ZnO (10%) sensor possesses excellent sensing H2S performances, including a high response (107.6 for 10 ppm), low limit of detection of 20 ppb, good selectivity and long-term stability. Together with the merits of low operation temperature of 75 °C and weak humidity dependence (endowed by the hydrophobic SBO), present heterostructural SBO/ZnO sensor paves the way for the practical monitoring of trace H2S pollutants in diverse workplaces including petroleum and natural gas industries.

Impurity band assisted carrier relaxation in Cr doped topological insulator Bi2Se3

Topological insulators (TIs) with unique band structures have wide application prospects in the fields of ultrafast optical and spintronic devices. The dynamics of hot carriers plays a key role in these TI-based devices. In this work, using the time- and angle-resolved photoemission spectroscopy technique, the relaxation process of the hot carriers in Cr-doped Bi2Se3 has been systematically studied since the ferromagnetic TI is one of the key building blocks for next-generation spintronics. It is found that electronic temperature (Te) and chemical potential (μ) decrease faster with the increase in the Cr doping concentration. Similarly, the lifetime (τ) of the excited electrons also decreases with more Cr doped into Bi2Se3. The results suggest a mechanism of impurity band-assisted carrier relaxation, where the impurity band within the bulk bandgap introduced by Cr doping provides significant recombination channels for the excited electrons. This work directly illustrates the dynamic process of the photon-generated carriers in Cr-doped Bi2Se3, which is expected to promote the applications of (Bi1-xCrx)2Se3 in photoelectric devices.

A heterojunction film of NiS2 and MnS as an efficient counter electrode for dye-sensitized solar cells

Transition metal sulfides are an important alternative to Pt in dye-sensitized solar cells (DSSCs) to lower the cost and improve the stability. In this letter, we deposited NiS2/MnS and MnS/NiS2 heterojunction films on FTO as the counter electrode (CE) by pulsed laser deposition (PLD) and vapor-phase sulfurization. The heterojunction CE of NiS2/MnS can achieve a power conversion efficiency of 6.44 %, which is close to that of the Pt CE (6.84 %). The unique band gap structure of NiS2 and MnS in this heterojunction can accelerate the transport of electrons in the CE to improve the ability of electro-catalysis. This makes the heterojunction film composed of two inexpensive transition metal sulfides an ideal substitute for Pt film.

Graphene plasmon for optoelectronics

Surface plasmon polaritons (SPPs) can achieve light transmission beyond the diffraction limit due to their special dispersion relationship. As a novel two-dimensional material, graphene has attracted extensive attention in recent years because of its unique band structure, excellent electronic and optical properties, and ability to support SPPs transmission on its surface. Graphene surface plasmon polaritons (GSPPs) are characterized by high carrier mobility, strong localization, low consumption and high tunability. It has functional and future applications in the transmission of optical knowledge, photodetectors, surface plasmon waveguides, metamaterials and nanolasers.

In Situ Corrosion Fabrication of NaNbO3 /Nb3 O7 F Heterojunctions with Optimized Band Realignment for Enhanced Photocatalytic Hydrogen Evolution.

Heterostructured photocatalysis is a significant issue owing to the unique band alignment, improved spectrum absorption, and enhanced photocatalytic activity. However, the construction of uniform, controllable, and effective heterojunctions is still a huge challenge. Herein, NaNbO3 /Nb3 O7 F heterojunctions are fabricated through an in situ corrosion technique for the first time. The influence of phase transformation on the hydrogen evolution reaction (HER) activity is investigated systematically in terms of photocatalytic water splitting for H2 production. Interestingly, the band realignment and good interfacial contact endow the NaNbO3 /Nb3 O7 F heterojunctions with a high HER activity (43.3 mmol g-1 h-1 ), which is about 2.4 times that of pure Nb3 O7 F and 1.36 times that of pure NaNbO3 . The results may provide some new insights into the corrosion technique and HER activity of novel heterostructured catalysts.

Plasmon-induced visible light absorption arising from edge-interfaces of titanium-oxides nanocomposites

The efficient utilization of visible light on wide-bandgap metal-oxides is a long-term goal but is still a grand challenge for plasmon-driven chemistry. The plasmon-induced concentration of photons in adjacent materials provides a strategic pathway to extend the light-harvesting regime to sub-bandgap. With the abundant edge-spots in surface nanostructures, here, we report that the titanium-oxides nanocomposites composed of the metallic titanium coupled with its oxides exhibit significant resonant visible absorption. The experimental characterizations with computational analyses demonstrate that the excited plasmon resonance at edge-interfaces results in the unique visible absorption band. Localized field-enhancement, charge-scattering, and hot-electrons effects conclusively confirm that the visible absorption is derived from the plasmon resonance, rather than the narrowing of bandgap or energy levels of impurities or defects. The plasmon-induced absorption effectively enhances the separation and transfer of photogenerated charge carriers leading to improved photoactivity. Our results help to advance titanium-oxides nanocomposites towards plasmonic chemistry in the visible-light region and highlight a potential general route to harnessing photons beyond the bandgap limitation based on plasmonic metal-oxides nanocomposites.

Molecular markers for authentification of Allium sativum L. cultivar ‘Taicangbaisuan’ and genetic relationships among 9 Chinese garlic cultivars

Garlic (Allium sativum L.) is a traditional crop that has long been valued worldwide as food, condiment and medicine. Morphology-based authentication can hardly distinguish one garlic cultivar from other cultivars; however, the molecular markers for the identification of different garlic germplasms are yet to be investigated. The present study aimed to establish a reliable method that can specifically recognise ‘Taicangbaisuan’, a unique landrace in Jiangsu Province, China. We collected nine prevalent accessions of Chinese garlic cultivars, determined the discriminative ability of four DNA fragments (matK, psbA-trnH, nad1 and alliinase) among these cultivars and reconstructed their genetic relationships using inter simple sequence repeat (ISSR) markers. Our results revealed that the nucleotide substitutions of matK, psbA-trnH and nad1 could just divide these cultivars into two groups, while variable sites of alliinase could specifically identify ‘Taicangbaisuan’ from the other eight cultivars. Genetic relationship analysis based on ISSR markers indicated that these nine cultivars grouped into two main clusters that showed high accordance with morphological and agricultural characteristics, suggesting they may have been domesticated from two different ancestors. A unique band of ‘Taicangbaisuan’ was found in the products of ISSR-811 primer and a specific ISSR-SCAR marker was developed successfully according to this unique allele to authenticate ‘Taicangbaisuan’ from related garlic cultivars. The authentication method proposed in this study will be useful in the protection of excellent garlic germplasms and could serve as a reference for the molecular identification of other crops.

Parametric oscillation of electromagnetic waves in momentum band gaps of a spatiotemporal crystal

Photonic crystals have revolutionized the field of optics with their unique dispersion and energy band gap engineering capabilities, such as the demonstration of extreme group and phase velocities, topologically protected photonic edge states, and control of spontaneous emission of photons. Time-variant media have also shown distinct functionalities, including nonreciprocal propagation, frequency conversion, and amplification of light. However, spatiotemporal modulation has mostly been studied as a simple harmonic wave function. Here, we analyze time-variant and spatially discrete photonic crystal structures, referred to as spatiotemporal crystals. The design of spatiotemporal crystals allows engineering of the momentum band gap within which parametric amplification can occur. As a potential platform for the construction of a parametric oscillator, a finite-sized spatiotemporal crystal is proposed and analyzed. Parametric oscillation is initiated by the energy and momentum conversion of an incident wave and the subsequent amplification by parametric gain within the momentum band gap. The oscillation process dominates over frequency mixing interactions above a transition threshold determined by the balance between gain and loss. Furthermore, the asymmetric formation of momentum band gaps can be realized by spatial phase control of the temporal modulation, which leads to directional radiation of oscillations at distinct frequencies. The proposed structure would enable simultaneous engineering of energy and momentum band gaps and provide a guideline for implementation of advanced dispersion-engineered parametric oscillators.

Mechanistic Evaluation of Single-Crystalline Aluminum Nitride Nanowire Synthesis from Plastic Waste

One-dimensional aluminum nitride (AlN) nanowires are of great interest because of their unique large band gap and low dimensionality, which make them promising for novel molecular electronic device...

Thermoelectric properties of α -In2Se3 monolayer

Thermoelectric (TE) properties of monolayered α-In2Se3 are investigated using the first-principles calculations based on the density functional theory and Boltzmann transport theory. The results show that monolayered α-In2Se3 is a great candidate for high-performance thermoelectric materials with the power factor PF and the figure of merit ZT as high as 0.02 W/mK2 and 2.18 at room temperature, respectively. We attribute such great TE performance to the large electrical conductivity and low lattice thermal conductivity, which originate from unique band structures of group III chalcogenides and anharmonic scattering. Furthermore, we prove that the quantum confinement effect can realize up to an order of magnitude enhancement in the PF. Our findings may open up new possibilities for two-dimensional thermoelectric materials in practical applications.

Structural, optical, magnetic and electrochemical properties of hydrothermally synthesized WS2 nanoflakes

Transition metal dichalcogenides (TMDCs) have emerged as highly intriguing materials due to their unique tunable band gap properties with layer number, finding applications in optoelectronic devices. TMDCs have been considered as potential hydrogen evolution reaction (HER) catalysts. Here we describe the hydrothermal synthesis of WS2, a promising TMDC material for efficient HER, under various conditions, and its structural, optical and magnetic and electrochemical studies are discussed in detail. The WS2 nanoflakes have good optical absorption property in region of 400–700 nm and the photoluminescence spectra show the excitation-dependent emission from two peaks corresponding to A and B excitons due to the polydispersity of nanoflakes. WS2 nanoflakes show room temperature ferromagnetism, which is attributed to the presence of zigzag edges in the magnetic ground state at the grain boundaries. The electrochemical results make them a potential candidate in energy conversion. The tunable optical and magnetic properties of WS2 could empower a great deal of flexibility in designing atomically thin optoelectronic and spintronic devices.

Graphdiyne Visible‐Light Photodetector with Ultrafast Detectivity

AbstractTwo‐dimensional (2D) materials have captured a tremendous amount of attention worldwide due to their unique physical and chemical properties. Herein, a mesoscopic graphdiyne (GDY) film is prepared through a facile solution method and directly used to construct an ultra‐fast visible light detector. This GDY thin film‐based photodetector exhibits both stable and repeatable high‐performance photoelectric responses to the visible light with various wavelengths. Among the visible light range, the GDY thin film is discovered to be most sensitive to 640 nm laser, which can enable it to achieve the highest response value of up to 46300%, thus conferring GDY materials an undeniable superiority of application in photoelectric devices. Especially, such GDY‐based detectors demonstrate ultra‐fast response speeds with an ephemeral response/recovery time of only 5.15/19.83 µs, which is far better than most reported photosensitive materials, including inorganic materials, low‐dimensional composites, and heterojunctions. This study suggests that GDY thin films can be regarded as new promising candidates for application as rapid photoelectric sensors. More importantly, this paper reveals the vast potential of such sp‐hybridized carbon as novel carbon‐based semiconductors in future optoelectronic applications due to their unique structure and energy band.

When thermoelectric materials come across with magnetism

Nowadays, thermoelectric materials have attracted a lot of attention as they can directly convert heat into electricity and vice versa. However, while strenuous efforts have been made, those conventional strategies are still inevitably going to meet their performance optimization limits. For this reason, brand new strategies are badly needed to achieve further enhancement. Here, the roles played by magnetism in recent advances of thermoelectric optimization are concluded. Firstly, magnetic thermoelectric materials can just be treated like other normal materials because the use of universal optimization strategies can still get good results. So, it is not a situation which is all or nothing and the tactics of using magnetism for thermoelectric optimization can coexist with other strategies. Besides, through magnetic doping, we can introduce and adjust magnetism in materials for further optimization. Magnetism provides more possibilities in thermoelectric optimization as it can directly influence the spin states in materials. Furthermore, in the form of magnetic second-phase nanoclusters, magnetism can be introduced to thermoelectric materials to conquer the dilemma that the solid solubility of many magnetic ions in thermoelectric materials is too low to have any significant effect on thermoelectric properties. Finally, when exposed to an external magnetic field, topological materials can rely on its unique band structures to optimize.

Development of species-specific SCAR markers for identification and authentication of three rare Peninsular Malaysian endemic Coelogyne (Orchidaceae) orchids.

Background:Coelogyne kaliana, Coelogyne stenochila and Coelogyne tiomanensis are three valuable rare orchid species endemic to Peninsular Malaysia, currently rampantly traded illegally via the internet and through local nurseries, which label them as hybrids to avoid enforcement detection. Drastic measures to ensure the continued existence of their populations in the wild should be introduced as they are rapidly diminishing into extinction, including the development of rapid and accurate species-specific identification tools. These three orchid species are highly similar morphologically and currently it is impossible to distinguish among them without their reproductive structures. Methods: RAPD-based species-specific SCAR markers were developed to distinguish and authenticate the identity of these three endemic Peninsular Malaysian Coelogyne species. Results: Three SCAR markers were successfully developed in this study. SCAR marker primer pair , CKL_f / CKL_r was specific to C. kaliana as it produced a unique single band of 271 bp but not in C. stenochila and C. tiomanensis. SCAR marker primer pair CST_f / CST_r amplified a single band of 854 bp in C. stenochila and two bands of different sizes (372 bp and 858 bp) in C. tiomanensis, but no amplification in C. kaliana. The third SCAR marker primer pair, CTI_f / CTI_r produced a single band (about 500 bp) for both C. stenochila and C. tiomanensis, but showed no amplification in C. kaliana. Conclusions: Although not all these SCAR markers were species amplification specific, they could be used to discriminate among the three Coelogyne species effectively. Accurate species identification is one of the most important steps to allow a proper management plan to be established in the effort to conserve these three endangered orchid species of Peninsular Malaysia. Besides, it could effectively put a stop to the illegal trading of these rare endangered orchid species worldwide.

Molecular Characterization of Sewage Bacteriophage and Their Efficiency in Treatment of Antibiotic Resistant Bacteria

Background: The increasing prevalence of multi-drug resistant of bacteria strains, has become a globalproblem and therefore alternative method to antibiotics must be found. Bacteriophages are considered analternative agent to control infection and contamination of the bacteria. Method: We used RAPD-PCRtechnique in present study, and used restriction endonuclease conformed presence unknown DNA fragments.Results: In this study, we described the isolation and character development of lytic bacteriophages capableof infecting bacteria specifically. Lytic bacteriophages, specific to Escherichia coli, Klebsiella pneumonia,Salmonella typhi, clinical strains, was first isolated from sewage. We have analyzed the DNA (RAPD)-PCR technique to produce unique and reproducible band from 21 different bacteriophages infecting E.coli,K. pneumonia, S. typhi . Used restriction endonuclease conformed presence unknown DNA fragments.Conclusion: Phages was capable of eliciting efficient lysis of studied bacteria, revealing its potential as anon-toxic sanitizer for controlling bacterial infection and contamination in both hospital and other publicenvironments.

Recent advances in plasmonic Prussian blue-based SERS nanotags for biological application.

The reliability and reproducibility of surface-enhanced Raman scattering (SERS) technology is still a great challenge in bio-related analysis. Prussian blue (PB)-based SERS tags have attracted increasing interest for improving these deficiencies due to its unique Raman band (near 2156 cm−1) in the Raman-silent region, providing zero-background bio-Raman labels without interference from endogenous biomolecules. Moreover, the stable PB shell consisting of multiple layers of CN− reporters ensure a stable and strong Raman signal output, avoiding the desorption of the Raman reporter from the plasmonic region by the competitive adsorption of the analyte. More importantly, they possess outstanding multiplexing potential in biological analysis owing to the adjustable Raman shift with unique narrow spectral widths. Despite more attention having been attracted to the structure and preparation of PB-based SERS tags for their better biological applications over the past five years, there is still a great challenge for SERS suitable for applications in the actual environment. The biological applications of PB-based SERS tags are comprehensively recounted in this minireview, mainly focusing on quantification analysis, multiple-spectral analysis and cell-imaging joint phototherapy. The prospects of PB-based SERS tags in clinical diagnosis and treatment are also discussed. This review aims to draw attention to the importance of SERS tags and provide a reference for the design and application of PB-based SERS tags in future bio-applications.