Se Nanowires Research Articles

SiX2 (X = S, Se) Nanowire Gate-All-Around MOSFETs for Sub-5 nm Applications.

The gate-all-around (GAA) field-effect transistor (FET) holds great potential to support next-generation integrated circuits. Nanowires such as carbon nanotubes (CNTs) are one important category of channel materials in GAA FETs. Based on first-principles investigations, we propose that SiX2 (X = S, Se) nanowires are promising channel materials that can significantly elevate the performance of GAA FETs. The sub-5 nm SiX2 (X = S, Se) nanowire GAA FETs exhibit excellent ballistic transport properties that meet the requirements of the 2013 International Technology Roadmap for Semiconductors (ITRS). Compared to CNTs, they are also advantageous or at least comparable in terms of gate controllability, device dimensions, etc. Importantly, SiSe2 GAA FETs show superb gate controllability due to the ultralow minimum subthreshold swing (SSmin) that breaks "Boltzmann's tyranny". Moreover, the energy-delay product (EDP) of SiX2 GAA FETs is significantly lower than that of the CNT FETs. These features make SiX2 nanowires ideal channel material in the sub-5 nm GAA FET devices.

2D Self-Assembly of Large-Sized Inorganic Nanosheets Leading to Enhanced Power Factors in Earth-Abundant Cu3SbSe4-Based Flexible Hybrid Films.

Fabrication of large-sized inorganic nanosheets is an efficient strategy to promote carrier transportation in flexible thermoelectric (TE) films. Herein, we report the self-assembly of large-sized Cu3SbSe4 nanosheets by using a Se nanowire template via wet chemical synthesis and then vacuum-assisted filter these plate-like microcrystals on nylon to prepare Cu3SbSe4 flexible thermoelectric (TE) hybrid films. SEM reveals that the as-synthesized Cu3SbSe4 powders by using Se nanowires as selenium sources presented 2D plate-like micron structures uniformly and tightly self-assembled by acute triangle-like nanoparticles. Furthermore, XPS evidences that extra Sb vacancies are generated in the unit cell of Cu3SbSe4 crystals synthesized by using the Se NW template, resulting in the shrinkage of the unit cell and the narrowing interplanar spacing, which are characterized by XRD and TEM. As a result, both carrier concentration and carrier mobility have been significantly improved. The high carrier concentration is proved to originate from the extra carriers induced by Sb vacancies, and the high carrier mobility of the film is mainly ascribed to its continuous grain boundaries in the plate-like microcrystal morphology. The large-sized nanosheet Cu3SbSe4/nylon hybrid film (CSS MPs) exhibits a high power factor (PF) of 235.45 μW m-1 K-2 at 400 K, which is 4.23 times higher than that of the Cu3SbSe4/nylon hybrid film (CSS NPs) where Cu3SbSe4 crystals are synthesized by using raw Se particles. This work reveals a novel approach to prepare plate-like Se-based semiconductors, which requires both high carrier concentration and high carrier mobility.

Nanoengineering approach toward ultrahigh power factor Ag2Se/polyvinylpyrrolidone composite film for flexible thermoelectric generator

Flexible thermoelectric (TE) generators (F-TEGs), able to harvest heat energy from the human body, are considered to be competitive energy supply devices for wearable and implantable electronics. Herein, we fabricate Ag2Se/polyvinylpyrrolidone (PVP) films on nylon membranes via a novel nanoengineering approach: First, small amount Ag nanoparticles decorated Ag2Se nanowires (NWs) coated with a nanolayer of PVP are synthesized via a Se NW template method, and the Ag nanoparticles react with small amount Se residues at the core of the Ag2Se NWs during hot-pressing and form Ag2Se nanograins rich in defects embedded in big Ag2Se grains. The Ag2Se nanograin has a different orientation from the big Ag2Se grain; hence, the interface between the Ag2Se nanograin and the big Ag2Se grain enhances the phonon scattering but almost does not affect the transport of carriers. An optimized film exhibits a maximum power factor of 2478 ± 67 μW m−1 K−2 (corresponding ZT ∼ 1.05) at 300 K, which is one of the highest values reported for flexible Ag2Se films. The excellent TE properties of the film are attributed to its unique microstructure: highly densified, coherent/semi-coherent Ag2Se grains, embedded Ag2Se nanograins, and a very small amount of PVP located at nanopores. Besides, the film shows good flexibility: after 1500 times bending along a rod with a radius of 4.0 mm, the electrical conductivity still maintains 90.9 %. Furthermore, a 6-leg F-TEG assembled with the optimal film generates a maximum power of 4.58 μW (corresponding power density of ∼ 31.2 W m−2) at a temperature gradient of 38.7 K. This work provides an efficient strategy for the fabrication of ultrahigh-performance Ag2Se-based flexible TE films.

Growth of Bi<sub>2</sub>O<sub>2</sub>Se nanowires and their superconducting quantum interference devices

Bi<sub>2</sub>O<sub>2</sub>Se is a new type of semiconductor material, which has the advantages of high carrier mobility, air stability, strong spin-orbit coupling, etc. It has a variety of synthesis methods and a wide range of applications. In the past few years, many explorations have been made in the synthesis, large-size growth, and applications of Bi<sub>2</sub>O<sub>2</sub>Se. It has been applied to field effect transistors, infrared photodetectors, semiconductor devices, heterojunctions, spin electronics, etc. Since nanowire has a larger surface area-to-volume ratio than nano-film, nanowire may have greater advantages in gate regulation and strong spin-orbit coupling, and these properties can play a crucial role in certain fields. However, most of the studies focused on its two-dimensional films, and there are less researches of its one-dimensional counterpart. In this work, a method of growing Bi<sub>2</sub>O<sub>2</sub>Se one-dimensional nanowires by chemical vapor deposition in a three-temperature-zone tubular furnace is introduced. High-quality suspended Bi<sub>2</sub>O<sub>2</sub>Se nanowires are obtained. In addition, the effects on the Bi<sub>2</sub>O<sub>2</sub>Se nanowire growth of the position of the mica substrates, i.e, different horizontal positions and vertical heights in the quartz boat, are studied, and the optimal conditions for the growth are summarized. The nanowires are characterized by atomic force microscope and energy dispersive spectrometer to show the information about the size and component. Then, superconducting quantum interference device based on the Bi<sub>2</sub>O<sub>2</sub>Se nanowires is constructed, and the superconducting quantum interference in a magnetic field is observed, which provides a way to broaden the application of Bi<sub>2</sub>O<sub>2</sub>Se nanowires.

High-Performance Ag 2 Se/Methyl Cellulose Thermoelectric Composites for Flexible Power Generators

Flexible thermoelectric generators (FTEGs) offer a promising solution for powering wearable electronics, while their practical applications are mainly obstructed by the moderate properties of flexible thermoelectric (TE) materials. Here, flexible Ag 2 Se nanowire (NW)/methyl cellulose (MC) composite films were developed via facile screen-printing technology combined with cold pressing and annealing treatment, and a highest power factor of 1,641.58 μW m −1 K −2 at 360 K was achieved. The reasons for the high TE performance of the Ag 2 Se NW/MC composite films were because, after the annealing treatment, the Ag 2 Se NWs were sintered to form conductive network structures, the crystallinity of Ag 2 Se was markedly enhanced, and the content of insulating phase MC in the composite film was decreased. The Ag 2 Se NW/MC composite film held appreciable flexibility, as its room-temperature power factor (1,312.08 μW m −1 K −2 ) can retain ~93% after bending for 1,000 cycles at a radius of 4 mm. Furthermore, the assembled FTEG consisting of 4 strips can generate a maximal power density of 3.51 W m −2 at a temperature difference of 14.1 K. Our results open an effective and large-scale strategy for fabricating high-performance flexible TE materials and energy-harvesting devices.

Rich-grain-boundary Ni–Co–Se nanowire arrays for fast charge storage in alkaline electrolyte

In this work, the one-dimensional (1D) Ni–Co–Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni–Co–Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni–Co–Se electrode sample displayed an area specific capacitance of 242.6 μAh cm−2 at 30 mA cm−2 with a current retention rate of 68.34%. The assembled Ni–Co–Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2 μAh cm−2 and 225.8 μAh cm−2 at 3 mA cm−2 and 30 mA cm−2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg−1 and 3441.33 W kg−1 at the energy densities of 37.62 Wh kg−1 and 25.81 Wh kg−1, respectively. Those results suggested the potentials of the obtained Ni–Co–Se nanowire arrays as electrode material for the high-performance pseudocapacitors.

Se vacancy-rich NiMoSe@NiAl-LDH hierarchical core-shell structure towards high-performance supercapacitors

As promising electrode materials, transition metal selenides show great potential applications in energy storage devices. Here self-supported Ni0.85Se nanowires with Se vacancies (denoted as NiMoSe) on NF were synthesized by a solvothermal route and post-selenization using NiMoO4 as the precursor, which electrochemical performance was optimized by adjusting the Se feeding during the selenization. Whereas, the supercapacitive properties of the optimal NiMoSe need to be further improved for achieving higher rate capability and electrochemical stability. So, an efficient strategy was proposed to improve the electrochemical performance through welding the NiAl hydrotalcite (NiAl-LDH) nanosheets on the NiMoSe surface to construct a novel 1D-2D-3D hierarchical core-shell material (NiMoSe@LDH), which provided more active sites and ensured a high rate-capability and long-term stability. Benefiting from the synergistic effect between NiMoSe nanowires core and NiAl-LDH shell, the NiMoSe@LDH delivered a favorable specific charge of 1381.1 C g−1 at 1 A g−1 with impressive rate capability and cyclic stability (85.2% retention after 5 000 cycles at 5 A g−1). Furthermore, the as-assembled NiMoSe@LDH//AC afforded a high energy density of 50.2 Wh kg–1 at a power density of 800 W kg–1 and good cycling stability (86.5% retention at 5 A g−1 after 10 000 cycles) compared to the NiMoSe//AC (36.3 Wh kg–1 at 800 W kg–1, 77.3% retention). This work provides a new strategy for the design of high-performance transition metal selenides in next-generation energy storage devices.

Mesoporous Co0.85Se nanowire arrays for flexible asymmetric supercapacitors with high energy and power densities

Transition metal selenides have attracted particular interest in the energy storage field due to their high conductivity, but their low specific capacitances limit their development. Herein, we design the Co0.85Se with an orderly aligned nanowire-arrayed (NWA) structure, which has great micromorphological stability and fast electronic/ionic transport rate, achieving a high specific capacitance of 1800 F g−1 at 1 mV s−1. The asymmetric supercapacitors (ASCs) are built to widen the voltage window to 0– 1.6 V and then increase the energy density, which reaches 71.3 Wh kg−1 at a power density of 800 W kg−1 in the liquid-state electrolyte, and 3.03 mWh cm−3 at the power density of 8.0 W cm−3 in the solid-state electrolyte. It also shows excellent cycling stability of 86 % retention after 10,000 charge/discharge cycles, fast rate capability of 79 % retention at the 15-fold increased current density and little performance degradation even under severe bent deformation. As shown, the Co0.85Se NWAs-based ASCs own high energy and power densities, long cycle life, fast rate capability and stable flexibilities simultaneously, which have significant potential in high-performance wearable energy storage systems.

A supercapacitor electrode with ultrahigh areal capacity by using loofah-inspired bimetallic selenide-incorporated hierarchical nanowires

Nanostructure engineering on the electrodes remains challenging for high-performance supercapacitors to meet the ever-increasing demands. Inspired by the function and structure of the loofah which possesses an inner firm skeleton coupled with the outer crisscrossed fibers, herein, a novel loofah-like core-shell nanostructure is synthesized with well-designed Co0.6Mn0.4Se nanowires dominated as the core, and MnO2 nanoflakes decorated as the shell. The bimetallic selenide exhibits high conductivity and rich electrochemical activity owing to the coexisting metals component. It also serves as a robust support to hinder the agglomeration of MnO2 nanoflakes, forming a unique porous structure with great ability of self-adapting to volumetric changes. The optimized Co0.6Mn0.4Se/MnO2 electrode exhibits an ultrahigh areal capacity (3.91 F cm−2/0.60 mAh cm−2 at 2 mA cm−2) and an exceptional retention of 95.47 % after 8000 cycles. Both performances are superior to the MnCo2O4/MnO2 electrode without the loofah-like networks in our work. Moreover, the assembled Co0.6Mn0.4Se/MnO2//AC (active carbon) hybrid supercapacitor delivers a high energy density of ∼89.67 Wh kg−1 at a power density of 399.98 W kg−1, and a remarkable life span with ∼97.30 % retention after 12,000 charge/discharge cycles. The eye-catching results indicate that the integrated Co0.6Mn0.4Se nanowires show great potential to engineering advanced electrodes. Further demonstration of the all-solid-state flexible cell based on the bio-inspired Co0.6Mn0.4Se/MnO2 structure also proves its practical application in wearable electronics.

Flexible thermoelectric Cu–Se nanowire/methyl cellulose composite films prepared via screen printing technology

Cu–Se nanowires (NWs) have been successfully synthesized by a wet chemical method and then flexible Cu–Se NW/methyl cellulose (MC) composite films have been prepared via a screen printing technology. The thermoelectric properties of the composite films were enhanced by a cold-pressing combining annealing treatment. A power factor of 121.87 μWm−1K−2 has been achieved for the Cu–Se NW/MC composite films at 380 K. A flexible thermoelectric generator (f-TEG) assembled by 4-leg of the as-prepared composite films can generate an output voltage of 0.83 mV and a maximum output power of 6.71 nW at a ΔT = 9.5 K. After being bent for 500 cycles, the resistance change ratio of the f-TEG along the strip length direction was only 3.69%, indicating that the f-TEG has a favorable stability. The screen printing process has many advantages, such as low cost, large-scale production, easy for operation, and therefore, it has a great potential for fabrication of flexible inorganic-organic thermoelectric composite films.

Quantitative analysis of the blue-green single-photon emission from a quantum dot in a thick tapered nanowire

Quantum dots (QDs) acting as single-photon emitters in the blue-green range are fabricated and characterized at cryogenic temperature. They consist in CdSe dots inserted in (Zn,Mg)Se nanowires with a thick shell. Photoluminescence spectra, decay curves, and autocorrelation functions were measured under nonresonant continuous-wave and pulsed excitation. An analytical approach is applied simultaneously to the decay curves and correlation functions. It allows a quantitative description of how these two quantities are affected by the exciton rise due to biexciton feeding, the bright exciton decay, the effect of the dark exciton, and the reexcitation between two laser pulses. Linewidths at our limit of resolution (200 $\ensuremath{\mu}\mathrm{eV}$) are recorded. The reported correlation counts vary from a full control by reexcitation from traps, to a small contribution of reexcitation by mobile carriers or other QDs, as low as 5%.

Selenium Nanowire Formation by Reacting Selenate with Magnetite.

The mobility of 79Se, a fission product of 235U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se(VI)O42-) and selenite (Se(IV)O32-) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids. Here, we investigated the sorption and reduction capacity of synthetic nanomagnetite toward Se(VI) at neutral and acidic pH, under reducing, oxygen-free conditions. The additional presence of Fe(II)aq, released during magnetite dissolution at pH 5, has an effect on the reduction kinetics. X-ray absorption spectroscopy analyses revealed that, at pH 5, trigonal gray Se(0) formed and that sorbed Se(IV) complexes remained on the nanoparticle surface during longer reaction times. The Se(0) nanowires grew during the reaction, which points to a complex transport mechanism of reduced species or to active reduction sites at the tip of the Se(0) nanowires. The concomitant uptake of aqueous Fe(II) and Se(VI) ions is interpreted as a consequence of small pH oscillations that result from the Se(VI) reduction, leading to a re-adsorption of aqueous Fe(II) onto the magnetite, renewing its reducing capacity. This effect is not observed at pH 7, where we observed only the formation of Se(0) with slow kinetics due to the formation of an oxidized maghemite layer. This indicates that the presence of aqueous Fe(II) may be an important factor to be considered when examining the environmental reactivity of magnetite.

Vanadium-doped Co0.85Se nanowire arrays with high areal capacitance for hybrid supercapacitor electrodes

The continuous exploration of advanced electrode materials is noteworthy to reform next-generation high-performance energy storage technology toward a green future. Benefiting from their abundant redox centers and electrochemically active sites, transition metal selenides (TMSs) have emerged as promising electrode materials for supercapacitors, which present massive potential in bridging a gap between the high power density and enhanced energy density. In this paper, we provide a two-step approach for constructing vanadium-doped Co0.85Se (V-doped Co0.85Se) nanowires on nickel foam that have outstanding electrochemical performance. In the three-electrode system, the areal specific capacity of the V-doped Co0.85Se was found as high as 1.28 mAh cm−2 (127.78 mAh g−1) at 5 mA cm −2, which is 1.97 times of that of the Co0.85Se electrode. The assembled quasi-solid-state hybrid supercapacitor also exhibits impressive electrochemical performance, possessing an energy density of 5.30 mWh cm−3 at a power density of 51.15 mW cm−3, and an excellent cycling stability (with capacitance retention of 84.2% after 5000 cycles). The enhanced electrochemical performance of the V-doped Co0.85Se is caused by a unique nanowire-like morphology with high specific surface area, and low charge transfer resistance and ion diffusion resistance. This work provides a feasible strategy for combining metallic element vanadium with selenide electrodes.

Ultrahigh Power Factor of Ternary Composites with Abundant Se Nanowires for Thermoelectric Application.

In this work, ultrahigh-performance single-walled carbon nanotube (SWCNT)/Se nanowire (NW)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) ternary thermoelectric (TE) nanocomposite films are successfully designed by rational design of CNT/Se/PEDOT:PSS ternary nanocomposites. The addition of CNTs apparently improves the electrical conductivity of composite films, resulting in a relatively huge growth of the power factor. The PEDOT:PSS interface layers uniformly attach on both sides of the Se NWs and CNTs effectively, forming a tightly interleaving and interconnected three-dimensional network. As a consequence, a maximum power factor of 863.83 μW/(m·K2) has been achieved for the sample containing 26 wt % CNTs at 434 K. Ultimately, a flexible TE generator prototype consisting of 5-unit freestanding composite film strips is fabricated using the optimized composite films, which can generate a maximum output power of 206.8 nW at a temperature gradient of 44.7 K. Therefore, the present work has a further potential to be used for the flexible polymer/carbon TE nanocomposite films and devices.

Fabrication and characterization of Se/WO3 heterojunctions designed as terahertz/gigahertz dielectric resonators

In this work, Selenium (Se) thin film substrates are coated with tungsten oxide thin layers. The Se/WO3 interfaces are fabricated using a vacuum deposition technique. The substrates displayed stable polycrystalline structure of hexagonal selenium when coated with amorphous WO3. The surface morphology revealed preferred growth of Se nanowires. The coating of Se with WO3 enhanced the light absorbability in the visible and infrared ranges of light spectrum. In addition, the Se/WO3 heterojunctions exhibited conduction and valence band offsets of values of 1.31 eV and 0.0.09 eV, respectively. The band offsets are sufficiently large to force quantum confinement at the interface. It was observed that Se/WO3 behaves as good dielectric resonator revealing resonance peaks in the infrared, visible and ultraviolet ranges of light. Moreover, computing the optical conductivity parameters for these dielectric oscillators revealed drift mobility and plasmon frequency values that are suitable for optical communications. Furthermore, as a terahertz resonator, the Se/WO3 dielectric media displayed terahertz cutoff frequency values in the range of 0.6–75 THz depending on the exciting photon energy. As practical application, when photo-excited with daylight light, the carbon contacted planner Se/WO3 interfaces displayed a light power dependent photosensitivity. The photosensitivity increases 38 times upon irradiation of 0.9 W. With these features, the Se/WO3 heterojunction devices can be nominated for applications in optical communications.

Modulation of electronic bandgaps and subsequent implications on SQ efficiencies via strain engineering in ultrathin SnX (X = S, Se) nanowires

The SQ efficiencies of ultrathin SnX NWs can be fine-tuned via strain engineering. They are more suitable for photovoltaic applications under compressive strain due to their stability under the same. Ultrathin SnS ultrathin NW shows an ultrahigh electron mobility of 9.84 × 105 cm2 V−1 s−1.

High performance Ag2Se/Ag/PEDOT composite films for wearable thermoelectric power generators

Herein, we report a Ag2Se/Ag/PEDOT (poly (3,4-ethylenedioxythiophene) composite film with a high thermoelectric performance and superior flexibility. First, we used PEDOT: poly (styrenesulfonate) (PSS) coated Se nanowires (NWs) as templates to prepare PEDOT:PSS coated Ag2Se/Ag composite powders, then Ag2Se/Ag/PEDOT composite films supported on porous nylon membrane were fabricated by vacuum assisted filtration and then hot pressing. An optimum composite film exhibits a high power factor of ∼1442.5 μW m−1 K−2, ultrahigh electrical conductivity (σ) of ∼5957.3 S cm−1 and superior flexibility (only 5.5% decrease in σ after 1000 times bending around a 4 mm radius rod) at RT. A certain amount of Ag phase in the composite film leads to an ultrahigh σ, while the PEDOT located at the interface between Ag and Ag2Se grains and at the surface of the Ag2Se grains causes the composite film with a low thermal conductivity. The excellent flexibility is due to the synergistic effect of the nylon membrane and PEDOT. Moreover, a 4-leg flexible thermoelectric power generator (f-TEG) assembled with the composite film shows a low internal resistance of ∼8 Ω, which makes it very possible to be integrated with a DC/DC converter for continually outputting power. The f-TEG produces a voltage of 5.6 mV and a maximum power of 1.8 μW (power density of 7.47 W m−2) at a temperature gradient of 27 K. This work provides an effective avenue for preparing high-performance flexible thermoelectric film with ultrahigh electrical conductivity.

One-stone, two birds: Alloying effect and surface defects induced by Pt on Cu2−xSe nanowires to boost C-C bond cleavage for electrocatalytic ethanol oxidation

The high-efficient C-C bond cleavage is the key for ethanol electrooxidation. In this work, PtCu/Cu 2−x Se nanowires (NWs) with abundant surface defects were constructed and exhibited remarkable activity of 5.03 A mg −1 Pt as well as 5.29 A mg −1 Pt for ethanol oxidation and methanol oxidation, respectively, which are 5.0 and 5.3 fold of commercial Pt/C. ex situ, in situ experiments and calculation results reveal that the formation of PtCu alloys lowered the d -band level to promote the adsorption of hydroxyl species. The abundant defects created high density of low-coordinated atoms to boost the reaction kinetics. Thus, PtCu/Cu 2−x Se NWs displayed enhanced C-C bond cleavage ability and high selectivity for C1 products (CO 2 ). The assembled direct ethanol fuel cells (DEFCs) with PtCu/Cu 2−x Se NWs as anode provided an open-circuit voltage (OCV) of 0.773 V and a peak power density of 7.8 mW cm −2 . This work not only give us a potential catalyst for C-C bond cleavage, but also provides an effective strategy to enhance the electrocatalytic activity of ethanol/methanol oxidation. • To boost the C-C bond cleavage for ethanol oxidation, a one-stone, two birds strategy was demonstrated. • PtCu/Cu 2-x Se NWs displayed 5.0 and 5.3-fold mass activity than commercial Pt/C for ethanol and methanol oxidation reaction. • PtCu/Cu 2-x Se NWs displayed higher efficiency to break C-C bond to produce more C1 intermediates than commercial Pt/C.

Revisiting the Chemical Stability of Germanium Selenide (GeSe) and the Origin of its Photocatalytic Efficiency

AbstractRecently, germanium selenide (GeSe) has emerged as a promising van der Waals semiconductor for photovoltaics, solar light harvesting, and water photoelectrolysis cells. Contrary to previous reports claiming perfect ambient stability based on experiments with techniques without surface sensitivity, here, by means of surface‐science investigations and density functional theory, it is demonstrated that actually both: i) the surface of bulk crystals; and ii) atomically thin flakes of GeSe are prone to oxidation, with the formation of self‐assembled germanium‐oxide skin with sub‐nanometric thickness. Surface oxidation leads to the decrease of the bandgap of stoichiometric GeSe and GeSe1−x, while bandgap energy increases upon surface oxidation of Ge1−xSe. Remarkably, the formation of a surface oxide skin on GeSe crystals plays a key role in the physicochemical mechanisms ruling photoelectrocatalysis: the underlying van der Waals semiconductor provides electron–hole pairs, while the germanium‐oxide skin formed upon oxidation affords the active sites for catalytic reactions. The self‐assembled germanium‐oxide/germanium‐selenide heterostructure with different bandgaps enables the activation of photocatalytic processes by absorption of light of different wavelengths, with inherently superior activity. Finally, it is discovered that, depending on the specific solvent‐GeSe interaction, the liquid phase exfoliation of bulk crystals can induce the formation of Se nanowires.

The influence of Ga doping on preparation and thermoelectric properties of flexible Ag2Se films

Herein, we prepared Ga doped Ag2Se flexible films on porous nylon membrane. First, Se nanowires (NWs) were wet chemically synthesized, then different amounts of Ga doped Ag2Se (Ag2-xGaxSe, x = 0.01, 0.02, 0.04) NWs were prepared using the Se NWs as templates in solution at 80 °C, and finally the Ga doped Ag2Se films on porous nylon membrane were fabricated by vacuum assisted filtration and then hot pressing at 230 °C and 1 MPa for 30 min. The Ag1.98Ga0.02Se film exhibits a higher power factor of ~1162 μW m−1 K−2 at 300 K and a superior flexibility: after bending for 1000 cycles around a 4-mm-radius rod, about 97% of the initial electrical conductivity is maintained.