Synthesis of Multishell Nanoplates by Consecutive Epitaxial Growth of Bi2Se3 and Bi2Te3 Nanoplates and Enhanced Thermoelectric Properties

Janus nanoparticles targeting extracellular polymeric substance achieve flexible elimination of drug-resistant biofilms

Safe and efficient antibacterial materials are urgently needed to combat drug-resistant bacteria and biofilm-associated infections. The rational design of nanoparticles for flexible elimination of biofilms remains challenging. Herein, we propose the fabrication of Janus-structured nanoparticles targeting extracellular polymeric substance to achieve dispersion or near-infrared (NIR) light-activated photothermal elimination of drug-resistant biofilms, respectively. Asymmetrical Janus-structured dextran-bismuth selenide (Dex-BSe) nanoparticles are fabricated to exploit synergistic effects of both components. Interestingly, Janus Dex-BSe nanoparticles realize enhanced dispersal of biofilms over time. Alternatively, taking advantage of the preferential accumulation of nanoparticles at infection sites, the self-propelled active motion induced by the unique Janus structure enhances photothermal killing effect. The flexible application of Janus Dex-BSe nanoparticles for biofilm removal or NIR-triggered eradication in vivo is demonstrated by Staphylococcus aureus-infected mouse excisional wound model and abscess model, respectively. The developed Janus nanoplatform holds great promise for the efficient elimination of drug-resistant biofilms in diverse antibacterial scenarios.

Exploring Material Properties and Device Output Performance of a Miniaturized Flexible Thermoelectric Generator Using Scalable Synthesis of Bi2Se3 Nanoflakes

Environmental heat-to-electric energy conversion presents a promising solution for powering sensors in wearable and portable devices. However, the availability of near-room temperature thermoelectric (TE) materials is highly limited, posing a significant challenge in this field. Bi₂Se₃, as a room-temperature TE material, has attracted much attention. Here, we demonstrate a large-scale synthesis of Bi₂Se₃ nanoflakes used for the microflexible TE generator. A high-performance micro-TE generator module, utilizing a flexible printed circuit, has been designed and fabricated through the process of screen printing. The TE generator configuration comprises five pairs of PN TE legs. The p-type TE leg utilizes commercially available Sb₂Te₃ powder, while the n-type TE leg employs Bi₂Se₃ nanoflakes synthesized in this study. For comparative purposes, we also incorporate commercially available Bi₂Se₃ powder as an alternative n-type TE leg. The optimal performance of the single-layer microflexible TE generator, employing Bi₂Se₃ nanoflakes as the active material, is achieved when operating at a temperature differential of 109.5 K, the open-circuit voltage (V_OC) is 0.11 V, the short circuit current (I_SC) is 0.34 mA, and the maximum output power (P_MAX) is 9.5 μW, much higher than the generator consisting of commercial Bi₂Se₃ powder, which is expected to provide an energy supply for flexible electronic devices.

Multifunctional two-dimensional Bi2Se3 nanodiscs for anti-inflammatory therapy of inflammatory bowel diseases

The overexpression of reactive oxygen and nitrogen species (RONS) in the colonic mucosa destroys the mucosa and its barrier, accelerating the occurrence of inflammatory bowel disease (IBD). The elimination of RONS from the inflammatory colon has proven effective in alleviating IBD. Although many nanoantioxidants have been developed, preparing robust and efficient nano-antioxidants remains challenging. Herein, by modifying bismuth selenide (Bi₂Se₃) nanodiscs with polyvinylpyrrolidone (PVP), a multifunctional nanozyme based on 2D nanomaterials was developed for the treatment of IBD. By eliminating multiple RONS, such as hydroxyl radicals (•OH), superoxide anions (O₂^-•), nitric oxide (NO), and Bi₂Se₃ nanodiscs enhanced cellular survival after H₂O₂ stimulation. As evidenced by colonic injury, reduced body weight, spleen index, and proinflammatory cytokine levels in mice, RONS clearance alleviated intestinal inflammation in a prevention and delay model of acute colitis. 16S rDNA amplicon sequencing reveals that Bi₂Se₃ nanodiscs had the potential to regulate intestinal flora, increase the proportion of Firmicutes to Bacteroidetes, inhibit Proteobacteria bacteria, and restore intestinal homeostasis. This study highlights the use of Bi₂Se₃ nanodiscs with excellent biocompatibility, multienzyme functionality, and RONS scavenging ability as treatments for IBD without apparent adverse effects. STATEMENT OF SIGNIFICANCE: RONS were efficiently scavenged by Bi₂Se₃ nanodiscs. Bi₂Se₃ nanodiscs could be as a promising and potentially safe theraeputic agent for IBD. The gut microbiota could be modulated by Bi₂Se₃ nanodiscs.

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Physical Vapor Deposition Features of Ultrathin Nanocrystals of Bi2(TexSe1-x)3

Structural and electronic properties of ultrathin nanocrystals of chalcogenide Bi₂(Te_x Se_1-x)₃ were studied. The nanocrystals were formed from the parent compound Bi₂Te₂Se on as-grown and thermally oxidized Si(100) substrates using Ar-assisted physical vapor deposition, resulting in well-faceted single crystals several quintuple layers thick and a few hundreds nanometers large. The chemical composition and structure of the nanocrystals were analyzed by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, electron backscattering, and X-ray diffraction. The electron transport through nanocrystals connected to superconducting Nb electrodes demonstrated Josephson behavior, with the predominance of the topological channels [Stolyarov et al. Commun. Mater., 2020, 1, 38]. The present paper focuses on the effect of the growth conditions on the morphology, structural, and electronic properties of nanocrystals.

Molten-Salt Processed Potassium Sodium Niobate Single-Crystal Microcuboids with Dislocation-Induced Nanodomain Structures and Relaxor Ferroelectric Behavior

We herein report a facile molten-salt synthetic strategy to prepare transparent and uniform Li, Ba-doped (K,Na)NbO₃ (KNN) single-crystal microcuboids (∼80 μm). By controlling the degree of supersaturation, different growth modes were found and the single-crystal microcuboids were synthesized via island-like oriented attachment of KNN particles onto the growing surface. The distinct relaxor ferroelectric (RFE) properties were achieved in the single-crystal microcuboids, which were different from the normal ferroelectric (FE) properties found in their KNN ceramic counterparts prepared through a solid-state reaction using the same initial precursors. The RFE properties were realized by dislocation-induced nanodomain formation during oriented attachment growth of single-crystal microcuboids, which is different from the current strategies to derive the nanodomains by the local compositional inhomogeneity or the application of an electric field. The dislocations served as nucleation sites for ferroelectric domain walls and block the growth of domains. The KNN single-crystal microcuboids exhibited a higher effective piezoelectric coefficient (∼459 pm/V) compared to that of the bulk KNN ceramic counterpart (∼90 pm/V) and showed the broad diffuse maxima in the temperature dependence dielectric permittivity. The high maximum polarization (69.6 μC/cm²) at a relatively low electric field (30 kV/cm) was beneficial for energy storage applications. Furthermore, the KNN-based transparent, flexible pressure sensor directly monitored the mechanical motion of human activity without any external electric power. This study provides insights and synthetic strategies of single-crystal RFE microcuboids for other different perovskites, in which nanodomain structures are primarily imposed by their chemical composition.

Study of the Thermoelectric Properties of Bi2Te3/Sb2Te3 Core-Shell Heterojunction Nanostructures

Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core-shell Bi₂Te₃/Sb₂Te₃ (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different Bi₂Te₃ core to Sb₂Te₃ shell ratios could be synthesized by controlling the reaction precursors. Scanning electron microscopy images show well-defined hexagonal nanoplates and the distinct interfaces between Bi₂Te₃ and Sb₂Te₃. The similarity of the area ratios with the precursor ratios indicates that the growth of the Sb₂Te₃ shell mostly took place on the lateral direction rather than the vertical. Transmission electron microscopy revealed the crystalline nature of the as-synthesized Bi₂Te₃ core and Sb₂Te₃ shell. Energy-dispersive X-ray spectroscopy verified the lateral growth of a Sb₂Te₃ shell on the Bi₂Te₃ core. Thermoelectric properties were measured on pellets obtained from powders via spark plasma sintering with two different directions, in-plane and out-of-plane, showing anisotropic properties due to the nanostructure alignment in the pellets. All samples showed a degenerate semiconducting character with the electrical resistivity increasing with the temperature. Starting from Sb₂Te₃, the electrical resistivity increases with the increase in amounts of Bi₂Te₃. Thermal conductivity is lowered due to the increase in interfaces and additional phonon scattering. We show that the out-of-plane direction of the BTST 1-3 sample (where 1-3 indicates the ratio of BT to ST) demonstrates a high Seebeck value of 145 μV/K at 500 K which may be attributed to an energy filtering effect across the heterojunction interfaces. The highest overall zT is observed for the BTST 1-3 sample in the out-of-plane direction at 500 K. The zT values increase continuously over the measured temperature range, indicating a probable higher value at increased temperatures.

Filling the gap between topological insulator nanomaterials and triboelectric nanogenerators

Reliable energy modules and higher-sensitivity, higher-density, lower-powered sensing systems are constantly required to develop wearable electronics and the Internet of Things technology. As an emerging technology, triboelectric nanogenerators have been potentially guiding the landscape of sustainable power units and energy-efficient sensors. However, the existing triboelectric series is primarily populated by polymers and rubbers, limiting triboelectric sensing plasticity to some extent owing to their stiff surface electronic structures. To enrich the current triboelectric group, we explore the triboelectric properties of the topological insulator nanofilm by Kelvin probe force microscopy and reveal its relatively positive electrification charging performance. Both the larger surface potential difference and the conductive surface states of the nanofilms synergistically improve the charge transfer behavior between the selected triboelectric media, endowing the topological insulator-based triboelectric nanogenerator with considerable output performance. Besides serving as a wearable power source, the ultra-compact device array demonstrates innovative system-level sensing capabilities, including precise monitoring of dynamic objects and real-time signal control at the human-machine interface. This work fills the blank between topological quantum matters and triboelectric nanogenerators and, more importantly, exploits the significant potential of topological insulator nanofilms for self-powered flexible/wearable electronics and scalable sensing technologies.

Going beyond the equilibrium crystal shape: re-tracing the morphological evolution in group 5 tetradymite nanocrystals

Nanocrystals of group 5 tetradymites M₂X₃ (where M = Bi and Sb, X = Se and Te) are of high technological relevance in modern topological nanoelectronics. However, there is a current lack of a systematic understanding to predict the preferred nanocrystal morphology in experiments where commonly-used equilibrium thermodynamic models appear to fail. In this work, using first-principles DFT calculations with a rationally-extended ab initio atomistic thermodynamics approach coupled to implicit solvation models and Gibbs-Wulff shape constructions, we demonstrate that this absence of predictive power stems from the limitation of equilibrium thermodynamics. By re-tracing and carefully addressing with a more realistic chemical potential definition, we illustrate this shortcoming can be overcome and afford a more rational route to size-engineer and shape-design highly-functional group 5 tetradymite nanoparticles for targeted applications.

Novel thermoelectric performance of 2D 1T- Se2Te and SeTe2with ultralow lattice thermal conductivity but high carrier mobility

The design and search for efficient thermoelectric materials that can directly convert waste heat into electricity have been of great interest in recent years since they have practical applications in overcoming the challenges of global warming and the energy crisis. In this work, two new two-dimensional 1T-phase group-VI binary compounds Se₂Te and SeTe₂with outstanding thermoelectric performances are predicted using first-principles calculations combined with Boltzmann transport theory. The dynamic stability is confirmed based on phonon dispersion. It is found that the spin-orbit coupling effect has a significant impact on the band structure of SeTe₂, and induces a transformation from indirect to direct band gap. The electronic and phononic transport properties of the Se₂Te and SeTe₂monolayer are calculated and discussed. High carrier mobility (up to 3744.321 and 2295.413 cm²V^-1S^-1for electron and hole, respectively) is exhibited, suggesting great applications in nanoelectronic devices. Furthermore, the maximum thermoelectric figure of meritzTof SeTe₂for n-type and p-type is 2.88, 1.99 and 5.94, 3.60 at 300 K and 600 K, respectively, which is larger than that of most reported 2D thermoelectric materials. The surprising thermoelectric properties arise from the ultralow lattice thermal conductivityk_l(0.25 and 1.89 W m^-1K^-1for SeTe₂and Se₂Te at 300 K), and the origin of ultralow lattice thermal conductivity is revealed. The present results suggest that 1T-phase Se₂Te and SeTe₂monolayer are promising candidates for thermoelectric applications.

Enhanced Thermoelectric Performance of n-Type Bi2Se3 Nanosheets through Sn Doping

The cost-effective conversion of low-grade heat into electricity using thermoelectric devices requires developing alternative materials and material processing technologies able to reduce the currently high device manufacturing costs. In this direction, thermoelectric materials that do not rely on rare or toxic elements such as tellurium or lead need to be produced using high-throughput technologies not involving high temperatures and long processes. Bi₂Se₃ is an obvious possible Te-free alternative to Bi₂Te₃ for ambient temperature thermoelectric applications, but its performance is still low for practical applications, and additional efforts toward finding proper dopants are required. Here, we report a scalable method to produce Bi₂Se₃ nanosheets at low synthesis temperatures. We studied the influence of different dopants on the thermoelectric properties of this material. Among the elements tested, we demonstrated that Sn doping resulted in the best performance. Sn incorporation resulted in a significant improvement to the Bi₂Se₃ Seebeck coefficient and a reduction in the thermal conductivity in the direction of the hot-press axis, resulting in an overall 60% improvement in the thermoelectric figure of merit of Bi₂Se₃.

Cation Exchange Enabled Cu Dopants Location Tailoring and Photoelectric Properties Regulation in CdS Nanosheets

Doping-related point defect engineering in low-dimensional semiconductor nanostructures is important to regulate their optical and electronic properties. The substitutional or interstitial location of heterovalent dopants is critical and has not been controlled effectively yet. Herein, we carefully control the kinetics of reverse cation exchange between Cu_xS 2D nanosheets and ligand-coordinated Cd²⁺ cations to control the Cu doping sites in CdS nanosheets (NSs). The substitutional and interstitial Cu dopants were directly confirmed by spherical aberration-corrected TEM (SACTEM) and their X-ray absorption spectroscopy (XAS) coordination investigation. Density functional theory (DFT) calculations and their experimental conductivities and dopant luminescence performance demonstrated the dramatic differences that are due to the location of different Cu dopants. These findings provide deeper insights on dopants' location regulation in a nanostructured host semiconductor.

Excellent thermoelectric performance achieved in Bi2Te3/Bi2S3@Bi nanocomposites

A Bi2Te3/Bi2S3@Bi nanocomposite with a network microstructure was successfully synthesized via a hydrothermal method and spark plasma sintering. This composite was constructed from Bi2Te3 nanoparticles and Bi2S3@Bi nanowires, and its network structure is beneficial for obtaining excellent thermoelectric performance. A ZT peak of 1.2 at 450 K was realized for the nanocomposite sample.

Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power. Moreover, the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades. Among these compounds, layered two-dimensional (2D) materials, such as graphene, black phosphorus, transition metal dichalcogenides, IVA-VIA compounds, and MXenes, have generated a large research attention as a group of potentially high-performance thermoelectric materials. Due to their unique electronic, mechanical, thermal, and optoelectronic properties, thermoelectric devices based on such materials can be applied in a variety of applications. Herein, a comprehensive review on the development of 2D materials for thermoelectric applications, as well as theoretical simulations and experimental preparation, is presented. In addition, nanodevice and new applications of 2D thermoelectric materials are also introduced. At last, current challenges are discussed and several prospects in this field are proposed.

Rational construction of a scalable heterostructured nanorod megalibrary

Integrating multiple materials in arbitrary arrangements within nanoparticles is a prerequisite for advancing many applications. Strategies to synthesize heterostructured nanoparticles are emerging, but they are limited in complexity, scope, and scalability. We introduce two design guidelines, based on interfacial reactivity and crystal structure relations, that enable the rational synthesis of a heterostructured nanorod megalibrary. We define synthetically feasible pathways to 65,520 distinct multicomponent metal sulfide nanorods having as many as 6 materials, 8 segments, and 11 internal interfaces by applying up to seven sequential cation-exchange reactions to copper sulfide nanorod precursors. We experimentally observe 113 individual heterostructured nanorods and demonstrate the scalable production of three samples. Previously unimaginable complexity in heterostructured nanorods is now routinely achievable with simple benchtop chemistry and standard laboratory glassware.

Dirac States of 2D Topological Insulators: Effect of Heterovalent Dopant-Content

We have studied Bi2Se3 at its 2D-limit using scanning tunneling spectroscopy (STS). Bulk Bi2Se3 is a well-known topological insulator having gapless surface states. In the 2D limit, the interior of the material exhibits a band gap, whereas the periphery shows a gapless metallic state having a Dirac point. We demonstrate a method to tune the Fermi energy and hence the Dirac point of Bi2Se3 nanoplates through doping at the anionic site. For this purpose, STS measurements were carried out on the Bi2Se3 system. We have used bromide as a dopant, which turns the material to n-type in nature. As a result, STS studies infer that the Fermi energy (EF) shifted toward the conduction band and consequently the Dirac point could be found to move away from Fermi energy. Through STS measurements, we have demonstrated a correlation between the shift of Dirac point position and the dopant content. The size, shape, and compositions of Bi2Se3 nanoflakes and concentration of bromine in the doped nanostructures were determined using transmission electron microscopy, associated energy dispersive X-ray spectroscopy analysis, and X-ray diffraction.

Synergistical Tuning Interface Barrier and Phonon Propagation in Au-Sb2Te3 Nanoplate for Boosting Thermoelectric Performance

Engineering of low-dimensional metal-semiconductor nanocomposites is expected to decouple electrical and thermal property, leading to substantially higher thermoelectric property. In this study, we rationally design a unique 0D-2D Au-Sb₂Te₃ architecture with beneficial interface barrier and strengthened phonon scattering, resulting in synergistically optimized electrical and thermal properties. In-situ growth of Au nanoparticles ∼10 nm on Sb₂Te₃ nanoplates enables better manipulation of electron and phonon transport compared to traditional bulks. The energy barrier between Au and Sb₂Te₃ effectively filters low-energy holes, while the Au nanoparticles competently hinder the propagation of midto-long wavelength phonons. As a result, this unique 0D-2D Au-Sb₂Te₃ composite exhibits a concurrent increase in electrical conductivity and Seebeck coefficient, and a decrease in lattice thermal conductivity, which allows a double of ZT value (∼0.8 at 523 K) for 1 mol % Au-Sb₂Te₃ composites with respect to the pristine Sb₂Te₃ (∼0.39 at 523 K). This self-assembled heterostructure provides a direction to design other low-dimensional metal-semiconductor nanoassemblies for thermoelectric application.

Nanoscale self-assembly of thermoelectric materials: a review of chemistry-based approaches

This review is concerned with the leading methods of bottom-up material preparation for thermal-to-electrical energy interconversion. The advantages, capabilities, and challenges from a material synthesis perspective are surveyed and the methods are discussed with respect to their potential for improvement (or possibly deterioration) of application-relevant transport properties. Solution chemistry-based synthesis approaches are re-assessed from the perspective of thermoelectric applications based on reported procedures for nanowire, quantum dot, mesoporous, hydro/solvothermal, and microwave-assisted syntheses as these techniques can effectively be exploited for industrial mass production. In terms of energy conversion efficiency, the benefit of self-assembly can occur from three paths: suppressing thermal conductivity, increasing thermopower, and boosting electrical conductivity. An ideal thermoelectric material gains from all three improvements simultaneously. Most bottom-up materials have been shown to exhibit very low values of thermal conductivity compared to their top-down (solid-state) counterparts, although the main challenge lies in improving their poor electrical properties. Recent developments in the field discussed in this review reveal that the traditional view of bottom-up thermoelectrics as inferior materials suffering from poor performance is not appropriate. Thermopower enhancement due to size and energy filtering effects, electrical conductivity enhancement, and thermal conductivity reduction mechanisms inherent in bottom-up nanoscale self-assembly syntheses are indicative of the impact that these techniques will play in future thermoelectric applications.

Bi2Se3 topological insulator at the 2D-limit: role of halide-doping on Dirac point

2D topological insulators exhibit insulating bulk and conducting edge states with a Dirac point, which at times is within the energy gap and could be on either side of the Fermi energy. In this study, we demonstrate a method to tune the energy of the Dirac edge state by introducing halides as dopants in Bi₂Se₃. We chose halides to substitute the anion, so that due to higher atomic number (of iodine, for example) with respect to selenium, the spin-orbit coupling parameter could be enhanced, leading to the significant separation of the Dirac point from the Fermi energy. With different halogens having different atomic numbers on either side of selenium, the Dirac point could hence be tuned towards both directions. The dopants, due to their heterovalent nature with respect to selenide, introduce carriers in the lattice and consequently, also shift the Fermi energy. We show that the Dirac point with respect to Fermi energy could be correlated to the dopant's atomic number and thus the atomic-number-induced spin-orbit coupling parameter. Strains developed in the lattice due to a mismatch in the effective ionic radii of the dopants and the host anion affected distribution of band energies, leaving the (distribution of) Dirac point unaffected due to its topologically protected nature.

Ultrathin silver telluride nanowire films and gold nanosheet electrodes for a flexible resistive switching device

We demonstrated a flexible resistive switching device based on ultrathin Ag₂Te nanowire (NW) films and Au nanosheet (NS) electrodes by exploiting a monolayer assembly on the water surface for macroscale two-dimensional structures. Firstly, ultrathin TeNWs (diameter ≈ 10 nm) are rapidly assembled on the water surface as a form of monolayer and transferred to fabricate TeNW films on various substrates with any available size. An assembled TeNW film was used as a template to produce a Ag₂TeNW film through chemical transformation. A well-aligned Ag₂TeNW film device showed reversible resistive switching properties when the Ag composition of the silver telluride NW becomes stoichiometric Ag₂Te. Additionally, a non-stoichiometric Ag_2+δTeNW film shows an increased On/Off ratio. For a flexible memory device, ultrathin AuNSs (thickness ≤20 nm) were adopted as working electrodes, since thermally deposited gold electrodes tend to crack under strain, which can fail to maintain the electrical properties. A paper-like flexibility of AuNS proved its capability as optimal electrodes of ultrathin Ag₂TeNW film-based resistive memory devices.

Solution Growth of Two-Dimensional Bi₂Se₃ Nanosheets for Two-Color All-Optical Switching

Two-dimensional Bi₂Se₃ nanosheets with hexagonal shape are synthesized by a solution synthetic route. The Bi₂Se₃ nanosheets are 120 nm in edge width and 7 nm in thickness. The size of the Bi₂Se₃ nanosheets can be controlled by choosing different kinds of reducing agents including hydroxylamine and ethylenediamine. Subsequently, we demonstrate a configuration of two-color all-optical switching based on plasma channels effect using the as-synthesized Bi₂Se₃ nanosheets as an optical media. The signal light can be modulated as two states including dot and ring shape by changing the intensity of control light. The modulated signal light exhibits excellent spatial propagation properties. As a type of interesting optical material, ultrathin two-dimensional Bi₂Se₃ nanosheets might provide an effective option for photoelectric applications.

1D Colloidal Hetero-Nanomaterials with Programmed Semiconductor Morphology and Metal Location for Enhancing Solar Energy Conversion

A new kind of multitetrahedron sheath ternary ZnS-(CdS/Au) hetero-nanorod is prepared, in which one 1D ultrathin ZnS nanorod is integrated with segmented tetrahedron sheaths made of CdS, and more importantly, Au nanoparticles can be decorated in a targeted manner onto the vertexes and edges of CdS tetrahedron sheaths solely, for achieving performance improvement in photoelectric and photochemical conversion applications.

Two-Dimensional Nanomaterials for Cancer Nanotheranostics

Emerging nanotechnologies show unprecedented advantages in accelerating cancer theranostics. Among them, two-dimensional nanomaterials (2DNMs) represent a novel type of material with versatile physicochemical properties that have enabled a new horizon for applications in both cancer diagnosis and therapy. Studies have demonstrated that 2DNMs may be used in diverse aspects, including i) cancer detection due to their high propensity towards tumor markers; ii) molecular imaging for guided tumor therapies, and iii) drug and gene loading, photothermal and photodynamic cancer therapies. However, their biomedical applications raise concerns due to the limited understanding of their in vivo metabolism, transformation and possible toxicities. In this comprehensive review, the state-of-the-art development of 2DNMs and their implications for cancer nanotheranostics are presented. The modification strategies to enhance the biocompatibility of 2DNMs are also reviewed.

Efficient Photothermoelectric Conversion in Lateral Topological Insulator Heterojunctions

Tuning the electron and phonon transport properties of thermoelectric materials by nanostructuring has enabled improving their thermopower figure of merit. Three-dimensional topological insulators, including many bismuth chalcogenides, attract increasing attention for this purpose, as their topologically protected surface states are promising to further enhance the thermoelectric performance. While individual bismuth chalcogenide nanostructures have been studied with respect to their photothermoelectric properties, nanostructured p-n junctions of these compounds have not yet been explored. Here, we experimentally investigate the room temperature thermoelectric conversion capability of lateral heterostructures consisting of two different three-dimensional topological insulators, namely, the n-type doped Bi₂Te₂Se and the p-type doped Sb₂Te₃. Scanning photocurrent microscopy of the nanoplatelets reveals efficient thermoelectric conversion at the p-n heterojunction, exploiting hot carriers of opposite sign in the two materials. From the photocurrent data, a Seebeck coefficient difference of ΔS = 200 μV/K was extracted, in accordance with the best values reported for the corresponding bulk materials. Furthermore, it is in very good agreement with the value of ΔS = 185 μV/K obtained by DFT calculation taking into account the specific doping levels of the two nanostructured components.

Simultaneous observation of surface- and edge-states of a 2D topological insulator through scanning tunneling spectroscopy and differential conductance imaging

Gapless edge-states with a Dirac point below the Fermi energy and band-edges at the interior observed in 2D topological insulators.

Solvothermal synthesis and electrochemical properties of S-doped Bi2Se3 hierarchical microstructure assembled by stacked nanosheets

Hierarchical S-doped Bi₂Se₃ microspheres assembled by stacked nanosheets were successfully synthesized as the anode of a lithium ion battery, which shows an initial discharge capacity of 771.3 mA h g⁻¹ with great potential in energy storage.