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Electrets are dielectric materials that have a quasi-permanent dipole polarization. A single-molecule electret is a long-sought-after nanoscale component because it can lead to miniaturized non-volatile memory storage devices. The signature of a single-molecule electret is the switching between two electric dipole states by an external electric field. The existence of these electrets has remained controversial because of the poor electric dipole stability in single molecules. Here we report the observation of a gate-controlled switching between two electronic states in Gd@C82. The encapsulated Gd atom forms a charged centre that sets up two single-electron transport channels. A gate voltage of ±11 V (corresponding to a coercive field of ~50 mV A–1) switches the system between the two transport channels with a ferroelectricity-like hysteresis loop. Using density functional theory, we assign the two states to two different permanent electrical dipole orientations generated from the Gd atom being trapped at two different sites inside the C82 cage. The two dipole states are separated by a transition energy barrier of 11 meV. The conductance switching is then attributed to the electric-field-driven reorientation of the individual dipole, as the coercive field provides the necessary energy to overcome the transition barrier. A Gd@C82 molecule shows electric polarization switching behaviour under a gate bias voltage, thus demonstrating a single-molecule electret device.

A size-selected beam of Au923±20 clusters is generated in a gas-phase condensation cluster source equipped with a lateral time-of-flight mass selector. The beam current reaches up to 9.13 nA for small clusters and 80 pA for Au923±20 clusters, which are then analyzed using a scanning transmission electron microscope. Four types of metastable structures are observed for the Au923±20 clusters, including ino-decahedron (Dh), cuboctahedron and icosahedron (Ih). The proportion of bulk-favorable cuboctahedron (i.e. face center cubic (Fcc)) structure takes up only 10–20%, while the penta-rotating symmetrical structures (Dh/Ih) are the dominant ones which take up over three quarters. Changing the beam condition may optimize the clusters from Dh-dominant to the Ih-dominant phase, which paves the way towards nanoparticle control beyond the diameters.

Indium selenide (InSe) is a promising two-dimensional photodetector material. However, the photogenerated electron-hole pairs are easy to recombine in simplex InSe semiconductor. Here, we design InSe-based van der Waals heterostructure, InSe/antimonene (β-Sb), based on first-principles. InSe/β-Sb heterostructure possesses intrinsic type-II electronic structure. Simultaneously, the work function of InSe (β-Sb) layer is −5.7 eV (−4.5 eV) which also promotes electrons transfer. In addition, the good optical absorption performance of InSe and β-Sb sublayer is preserved in the heterostructure. Moreover, different stacking mode between InSe/β-Sb does not affect the efficient carrier separation which is convenient to the application of optoelectronics.

Using first-principles calculations, we study the growth process of bismuth (Bi) films on Cu (111) substrate. By analyzing the formation mechanism of single layer α‑bismuthene and stability of multilayered Bi layers, we reveal that Bi atoms show quasi-one-dimensional growth model by developing periodic zigzag chains, and eventually form a Bi atomic layer on Cu (111) surface. Flat surface α‑bismuthene (Fα-Bi) can be formed by depositing two Bi atomic layers on Cu (111) and maintains its stability below 60 K. In the multilayered Bi atomic layers, the stability of Bi films shows an oscillatory behavior. It is more stable for Bi films with even layers. The charge density between even and odd films shows that the stability is associated with the saturation of pz orbital of Bi atoms. Besides, the distorted surface α‑bismuthene (Dα-Bi) can maintain its stability up to 450 K on Cu (111) surface. Further study shows that the Cu substrate strongly affects the properties of Fα-Bi than that of Dα-Bi. Our studies provide guidance for fabricating stable Bi (110) thin films based devices.

Grain boundaries (GBs) in polycrystalline graphene could significantly modulate the physicochemical properties of graphene films, and have attracted intense interest. However, fundamental magnetotransport mechanisms of GBs in bilayer graphene grown by chemical vapour deposition (CVD) are scarcely reported. In this work, we synthesize bilayer graphene bicrystals on polycrystalline Cu foils and measure the electronic properties of such grains as well as of individual graphene grain boundaries. Interestingly, the pronounced metallic character of GB is observed, which is dramatically different from individual grains. Large linear magnetoresistance in graphene bicrystals is observed, which attributes to inhomogeneous charge transport, decorated by quantum interference effects at low temperatures. The measurement data show that individual boundaries between coalesced grains impede electrical transport, suppress the magnetoresistance and enhance intervalley scattering, leading to degradation of electrical performance of CVD graphene. Nevertheless, GBs embedded in a perfect graphene sheet can tune its electronic structure at the nanoscale, act as quasi-one-dimensional metallic wires and can be used as good candidates for strong magnetic field sensors. This work is beneficial to the fundamental understanding of the role of GBs in CVD-grown graphene and opens a potential avenue of application for polycrystalline bilayer graphene in functional devices.

Metal halide perovskites (MHPs) with highly sensitive photoelectric response and ultrahigh absorption coefficient in the visible range exhibit huge potential as building blocks for optoelectronic devices. However, these perovskites suffer from poor absorption efficiency in the infrared range due to the weak coupling of infrared light. In this work, we report a new class of MHP-based heterostructures by the integration of two-dimensional Cs3+nPbnSb2I9+3n perovskites with GaN nanosheets for the realization of highly efficient carrier separation and broadband absorption. We find that the formation of the Cs/GaN(0001) interface in Cs3+nPbnSb2I9+3n/GaN heterostructures can induce the shift of the vacuum level below the conduction band minimum, resulting in negative electron affinity (NEA). Moreover, the NEA of the heterostructures is not sensitive to the thickness of perovskite and GaN layers. Owing to the type-II band alignment and NEA of these heterostructures, they exhibit highly efficient carrier separation and enhanced optical absorption from the infrared to ultraviolet light region, which result in maximum power conversion efficiency as high as 28.5%. The findings suggest the large potential of Cs3+nPbnSb2I9+3n/GaN heterostructures for optoelectronic applications, such as solar cells, photodetectors, and field emission devices.

Alongside the rise in fully automated equipment and wearable devices, there is currently a high demand for optically transparent and flexible gas sensors operating at room temperature. Nanoparticle films are ideal H2-sensing materials that can be coupled with flexible substrates because of their discrete nanogranular structure and unique interparticle electrical responsiveness. In this work, we present an optically transparent and flexible H2 sensor based on a Pd nanoparticle film, prepared on a polyethylene terephthalate sheet using a straightforward nanocluster deposition technique. Hundreds of bending cycles demonstrated that the sensor has good electrical stability and mechanical robustness without significant degradation in H2-sensing performance. The H2-sensing behaviors under bent state were systematically evaluated. The loading of tensile and compressive strains under bent state produced a positive and negative influence, respectively, on the sensing performances. The possible influence mechanism ...

The plasmonic response of gold clusters with atom number (N) = 100–70 000 was investigated using scanning transmission electron microscopy-electron energy loss spectroscopy. For decreasing N, the bulk plasmon remains unchanged above N = 887 but then disappears, while the surface plasmon firstly redshifts from 2.4 to 2.3 eV above N = 887 before blueshifting towards 2.6 eV down to N = 300, and finally splitting into three fine features. The surface plasmon's excitation ratio is found to follow N0.669, which is essentially R2. An atomically precise evolution picture of plasmon physics is thus demonstrated according to three regimes: classical plasmon (N = 887–70 000), quantum confinement corrected plasmon (N = 300–887) and molecule related plasmon (N

Through the density functional theory, we studied molecular devices composed of single tetrathiafulvalene (TTF) molecules connected with zigzag graphene nanoribbon electrodes by four different junctions. Interestingly, some devices have exhibited half-metallic behavior and can bring out a perfect spin filtering effect and remarkable negative differential resistance behavior. The current–voltage characteristics show that these four devices possess different spin current values. We found that all the TTF molecules were stretched due to interactions with the electrodes in the four devices. This leads to the Fermi levels of the three devices being down-shifted to the valence band; therefore, these devices exhibit half-metallic properties. The underlying mechanisms of the different spin current values are attributed to the different electron transmission pathways (via chemical bonds or through hopping between atoms). These results suggest that the device properties and conductance are controlled by different junctions. Our work predicts an effective way for designing high-performance spin-injected molecular devices.

The icosahedral CuxAg13−x (x = 0–13) clusters are calculated using an effective sampling method and first-principle calculations based on density functional theory. And the segregation effect and its influence on the stability and electronic properties of the clusters are investigated. The calculation results show that the stability of CuxAg13−x greatly depends on the occupation position of Cu atoms and their segregation degree. The HOMO–LUMO gap of CuxAg13−x is closely related to the segregation degree of Cu atoms as well as the composition ratio between Cu and Ag. And an optimized Cu7Ag6 cluster, in which Cu atoms have the largest segregation degree, is found to be the largest HOMO–LUMO gap. By analyzing the local density of states, bond strength, bond length and bond ratio, we reveal the origin of the segregation effect and its influence on the HOMO–LUMO gap of CuxAg13−x. The results presented in this work are helpful to design the bimetallic clusters with stable structures and desired electronic properties.

The effect of in-plane uniaxial strain on band structures and electronic properties of graphene/blue phosphorene (Gr/BPh) bilayer has been investigated by using first-principles calculations. The results show that the intrinsic electronic properties of graphene and blue phosphorene are preserved well in the unstrained bilayer. Upon the application of in-plane uniaxial strain, the band gap of the Gr/BPh bilayer can be easily opened by ∼120 meV near ±2%, and the value of band gap increases with increasing the strain value. A maximum gap value ∼240 meV is obtained around ±4% strain. By analyzing the projected density of states and charge density differences, we reveal that the opened band gap under strain is closely related to the change in electronic structure of Gr/BPh bilayer, which is greatly influenced by the electron redistribution between graphene and BPh layers as well as the orbital hybridizations between carbon and phosphorus atoms. Further study finds that the band gap can not be opened when the in-plane biaxial strain is applied to the Gr/BPh bilayer. The present work provides us an effective avenue to tune the electronic structures and band gap for Gr/BPh bilayer.

Pd nanoparticles with a mean diameter of 6.7 nm are prepared by gas phase cluster beam deposition. The Pd nanoparticle films exhibit excellent catalytic activity and stability for methanol oxidation. 3D hybrid nanostructures combined with multi-walled carbon nanotubes and few-layer graphene sheets are used as supports to further enhance the methanol electro-oxidation activity of the Pd nanoparticle catalysts by a factor of more than 2.7. The catalytic activity towards methanol electro-oxidation is characterized with cyclic voltammetry measurements. An ultrahigh electrochemical active surface area (ECSA) as large as 311 m 2 g −1 pd and a mass specific current corresponding to methanol oxidation levels as high as 4038 mA mg −1 pd are realized. These results can be attributed to the high electrochemical activity of the Pd nanoparticles and the unique conductive structure of the multi-walled carbon nanotubes/few-layer graphene sheets.

In this article, we present a modified Velocity-Verlet algorithm that makes cluster system converge rapidly and accurately. By combining it with molecular dynamics simulations, we develop an effective global sampling method for extracting isomers of bimetallic clusters. Using this method, we obtain the isomers of icosahedral PdxAg13−x (x = 0–13). Additionally, using the first-principle spin-polarized density functional theory approach, we find that each isomer still retains its icosahedral structure because of strong s-d orbital hybridization, and the cluster is more stable when a Pd atom is at the center of the cluster. With increasing x value, the magnetic moment decreases linearly from 5.0 μB at x = 0, until reaching zero at x = 5, and then increases linearly up to 8.0 μB at x = 13. By calculating the atom-projected density of states (PDOS), we reveal that the magnetic moment of PdxAg13−x mainly originates from s electrons of Ag when 0 ≤ x d electrons of Pd when 5 xAg13−x tends to transform from a semiconductor state to semi-metallic state when x gradually increases from 0 to 13.

In this work, we proposed a novel three-dimensional (3D) plasmonic nanostructure based on porous graphene/nickel foam (GNF) and gas-phase deposited Ag nanoparticles (NPs). Ag NPs with high density were directly deposited on the surface of 3D GNF by performing a novel cluster beam deposition approach. In comparison with traditional Ag substrate (SiO2/Ag), such hot-spots enriched 3D nanostructure showed extremely high electromagnetic field enhancement under incident light irradiation which could be used as a sensitive chemical sensor based on surface enhanced Raman scattering (SERS). The experimental results demonstrated that the proposed nanostructure showed superior SERS performance in terms of Raman signal reproducibility and sensitivity for the probe molecules. 3D full-wave simulation showed that the enhanced SERS performance in this 3D hierarchical plasmonic nanostructure was mainly obtained from the hot-spots between Ag NPs and the near-field coupling between Ag NPs and GNF scaffolds. This work can provide a novel assembled SERS substrate as a SERS-based chemical sensor in practical applications.

We report a nonenzymatic H2O2 sensor based on a glassy carbon electrode modified with bilayer graphene films (BGFs) that were decorated with well-defined Pd nanoparticles. The BGFs were synthesized with a chemical vapor deposition process, and the Pd nanoparticle films were produced by gas phase cluster beam deposition. The BGFs provide great accessible active surface area and excellent conductive interfaces for electron transfer, which largely enhance the electrocatalytic performance of the modified electrodes. A rapid response time of less than 3 s and a wide linear range from 4 μM to 13.5 mM was exhibited in the amperometric detection of H2O2.

Based on the first principles calculations, we have investigated the magnetic properties of Irn+1 clusters modulated by Co atoms. The research conclusions show that the amplitude of magnetic anisotropy energy (MAE) and magnetization direction of the small Irn+1 can be manipulated by Co atom if we can control the size very precisely. Such regulatory mechanism of MAE is ascribed to the distributing variation of Ir-5d orbits around the Fermi level induced by Co atom. More importantly, the colossal MAE values, 67.4 meV/atom, 40.26 meV/atom and 91.37 meV/atom, can be obtained for Ir2, Ir4, and CoIr clusters, respectively. Such high values provide a promising avenue for developing high-density magnetic storage units at sub-nanometer size.

Single-crystal bilayer graphene is attractive for functional electronic and photonic devices because of its high carrier mobility as well as a tunable band gap induced by a perpendicular electric field. Chemical vapor deposition (CVD) has been increasingly reported for the production of single-crystal bilayer graphene, but it is limited with respect to grain size because of nonsynchronic growth between the second layer and the first layer of bilayer graphene. In this research, we established a nonisothermal atmosphere CVD (NI-APCVD) system to realize synchronization of nucleation and growth of single-crystal bilayer graphene that contains the surface adsorption for the decomposed carbons and the shallow bulk phase segregation for the dissolved carbons. Based on the above process engineering, we successfully produced large hexagonal single-crystal bilayer graphene (∼1.0 mm) on the polycrystalline Cu foils. This work paves a pathway to the synchronous growth of wafer-scale single-crystal bilayer graphene, w...

To solve the fundamental dilemma in data storage applications, it is crucial to manipulate the magnetic anisotropy energy (MAE). Herein, using first-principles calculations, we predict that the system of double-vacancy graphene decorated by iridium atoms possesses high stability, giant MAE, perpendicular-anisotropy and long-range ferromagnetic coupling. More importantly, the amplitude of MAE can be manipulated by electric fields. This is due to the change in the occupation number of Ir-5d orbitals. The present hybrid system could be a high-performance nanoscale information storage device with ultralow energy consumption.

Pd clusters were generated with a DC magnetron plasma gas aggregation cluster source. The dependence of the size distribution and ionization degree of the Pd clusters on the discharge power was studied. By tuning the discharge power from 15W to 50W, the mean size of the Pd clusters decreased from 13.8 nm to 4.2 nm, and the ratio of neutral and charged Pd clusters to the total rose from about 16.7% to about 76.7%. The effect was explained with a model by considering the enhanced production of Pd ions at higher magnetron discharge power. A simulation based on Direct Simulation Monte Carlo (DSMC) method verified the proposed mechanism of cluster growth.

Indium selenide (InSe) is a promising two-dimensional photodetector material. However, band-gap and work-function of low-dimension InSe are too large to act as photodetector devices. Here, we design InSe-based vdWs heterostructure, InSe/hBN (hexagonal boron nitride), using first-principles. InSe/hBN possesses rather low work-function (~3.0 eV) compared with that of isolated InSe monolayer due to strong interlayer coupling. Besides, strong interlayer coupling induces extra emerging states, markedly reducing band-gap of InSe/hBN. Meanwhile, these emerging states ensure red-shift of optical absorption, from infrared to ultraviolet light-harvesting. Moreover, different heterostructure stacking mode doesn’t affect optical absorption and electron emission, convenient to the application of optoelectronics.

A lateral heterojunction of topological insulator Sb2Te3/Bi2Te3 was successfully synthesized using a two-step solvothermal method. The two crystalline components were separated well by a sharp lattice-matched interface when the optimized procedure was used. Inspecting the heterojunction using high-resolution transmission electron microscopy showed that epitaxial growth occurred along the horizontal plane. The semiconducting temperature-resistance curve and crossjunction rectification were observed, which reveal a staggered-gap lateral heterojunction with a small junction voltage. Quantum correction from the weak antilocalization reveals the well-maintained transport of the topological surface state. This is appealing for a platform for spin filters and one-dimensional topological interface states.

Polystyrene(PS)/ZnO micronano hierarchical structures were fabricated on a flat surface by depositing ZnO nanoparticles from a cluster beam at oblique incidence on the surface predeposited with PS microspheres. The hierarchical structure was composed of submicron-sized PS particle layers covered with dense films of columnar ZnO nanoparticle piles separated with nanoscale pores. It was demonstrated that the cooperative effect that combines the microlens function of the PS microspheres and the enhanced Rayleigh scattering of the ZnO nanoparticle porous layers can be used to greatly reduce the total internal reflection at the medium-air interface. The PS/ZnO hierarchical structures were fabricated on the surface of GaN-based light-emitting diode (LED) chips to enhance the light-extraction efficiency. A 77.7% improvement on the light-output power was realized, which was much greater than that obtained with the PS microstructures alone.

High-mobility (Smx Bi1-x )2 Se3 topological insulators (with x = 0.05) show a Curie temperature of about 52 K, and the carrier concentration and Fermi wave vector can be manipulated by intentional Te introduction with no significant influence on the Curie temperature. The origin of the ferromagnetism is attributed to the trivalent Sm dopant, as confirmed by X-ray magnetic circular dichroism and first-principles calculations. The carrier concentration is on the order of 10(19) cm(-3) and the mobility can reach about 7200 cm(2) V(-1) s(-1) with pronounced Shubnikov-de Haas oscillations.

Coating a polymeric membrane for gas separation is a feasible approach to fabricate gas sensors with selectivity. In this study, poly(methyl methacrylate)-(PMMA-)membrane-coated palladium (Pd) nanoparticle (NP) films were fabricated for high-performance hydrogen (H2) gas sensing by carrying out gas-phase cluster deposition and PMMA spin coating. No changes were induced by the PMMA spin coating in the electrical transport and H2-sensing mechanisms of the Pd NP films. Measurements of H2 sensing demonstrated that the devices were capable of detecting H2 gas within the concentration range 0–10% at room temperature and showed high selectivity to H2 due to the filtration effect of the PMMA membrane layer. Despite the presence of the PMMA matrix, the lower detection limit of the sensor is less than 50 ppm. A series of PMMA membrane layers with different thicknesses were spin coated onto the surface of Pd NP films for the selective filtration of H2. It was found that the device sensing kinetics were strongly affe...

Unsaturated magnetoresistance (MR) has been reported in WTe2, and remains irrepressible up to very high field. Intense optimization of the crystalline quality causes a squarely-increasing MR, as interpreted by perfect compensation of opposite carriers. Herein we report our observation of linear MR (LMR) in WTe2 crystals, the onset of which is first identified by constructing the mobility spectra of the MR at low fields. The LMR further intensifies and predominates at fields higher than 20 Tesla while the parabolic MR gradually decays. The LMR remains unsaturated up to a high field of 60 Tesla and persists, even at a high pressure of 6.2 GPa. Assisted by density functional theory calculations and detailed mobility spectra, we find the LMR to be robust against the applications of high field, broken carrier balance, and mobility suppression. Angle-resolved photoemission spectroscopy reveals a unique quasilinear energy dispersion near the Fermi level. Our results suggest that the robust LMR is the low bound of the unsaturated MR in WTe2.

TiO₂ nanoparticle layers composed of columnar TiO₂ nanoparticle piles separated with nanoscale pores were fabricated on the bottom surface of the hemispherical glass prism by performing gas phase cluster beam deposition at glancing incidence. The porosity as well as the refractive index of the nanoparticle layer was precisely tuned by the incident angle. Effective extraction of the light trapped in the substrate due to total internal reflection with the TiO₂ nanoparticle layers was demonstrated and the extraction efficiency was found to increase with the porosity. An enhanced Rayleigh scattering mechanism, which results from the columnar aggregation of the nanoparticles as well as the strong contrast in the refractive index between pores and TiO₂ nanoparticles in the nanoporous structures, was proposed. The porous TiO₂ nanoparticle coatings were fabricated on the surface of GaN LEDs to enhance their light output. A nearly 92% PL enhancement as well as a 30% EL enhancement was observed. For LED applications, the enhanced light extraction with the TiO₂ nanoparticle porous layers can be a supplement to the microscale texturing process for light extraction enhancement.

We demonstrate a promising method to fabricate highly adhesive silver nanoparticle coating on glass carbon electrode with good dispersity by using gas phase cluster beam deposition. The fabricated nanoparticles have clean surface and show enhanced electrocatalytic activity toward the reduction of H 2 O 2 with a considerably decreased overpotential. A nonenzyme sensing platform for stable detection of H 2 O 2 with a very rapid response time (less than 1 s), high sensitivity (63 μA/mM) as well as a low detection limit (1.3 μM) is realized from the silver nanoparticle based electrode with a optimized nanoparticle coverage.

The CoFe2O4/Pb(Zr0.52Ti0.48)O3 bilayer films were prepared by a sol–gel process, and the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films was studied. The ferroelectric polarization hysteresis loops under various choices of magnetic bias were measured by an integrating current method. The results showed that after undergoing cycling electric polarization the ferroelectric polarization of the bilayer films enhanced and the suppression of ferroelectric polarization by external magnetic bias remarkably weakened. Based on the measurements of activation energy and leakage current, we confirmed that the oxygen vacancy migration in the bilayer films occurred during cycling electric polarization. Furthermore, we analyzed the mechanism of the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films and attributed it to the oxygen vacancy migration, which could cause a part of ferroelectric domains to be unpinned from the oxygen vacancies and become more active under electric field and magnetic bias.

Multiferroic La-doped BiFeO3 thin films have been prepared by a sol-gel plus spin-coating process, and the local magnetoelectric coupling effect has been investigated by the magnetic-field-assisted scanning probe microscopy connected with a ferroelectric analyzer. The local ferroelectric polarization response to external magnetic fields is observed and a so-called optimized magnetic field of ~40 Oe is obtained, at which the ferroelectric polarization reaches the maximum. Moreover, we carry out the magnetic-field-dependent surface conductivity measurements and illustrate the origin of local magnetoresistance in the La-doped BiFeO3 thin films, which is closely related to the local ferroelectric polarization response to external magnetic fields. This work not only provides a useful technique to characterize the local magnetoelectric coupling for a wide range of multiferroic materials but also is significant for deeply understanding the local multiferroic behaviors in the BiFeO3-based systems.

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

Atomic defects are easily created in the single-layer electronic devices of current interest and cause even more severe influence than in the bulk devices since the electronic quantum paths are obviously suppressed in the two-dimensional transport. Here we find a drop of chemical solution can repair the defects in the single-layer MoSe2 field-effect transistors. The devices’ room-temperature electronic mobility increases from 0.1 cm2/Vs to around 30 cm2/Vs and hole mobility over 10 cm2/Vs after the solution processing. The defect dynamics is interpreted by the combined study of the first-principles calculations, aberration-corrected transmission electron microscopy, and Raman spectroscopy. Rich single/double Selenium vacancies are identified by the high-resolution microscopy, which cause some mid-gap impurity states and localize the device carriers. They are found to be repaired by the processing with the result of extended electronic states. Such a picture is confirmed by a 1.5 cm−1 red shift in the Raman spectra. Defects can heavily influence the electrical transport properties of three-dimensional materials. But their impact becomes even more pronounced in low-dimensional systems. Fengqi Song and colleagues use a combination of calculations and experiments to show that a simple drop of a chemical solution can repair the selenium vacancies in field-effect transistors made from single layer molybdenum diselenide. By reducing the number of vacancies, which localize the electronic transport, the authors increased the carrier mobilities to nearly the intrinsic value by 2–3 orders of magnitude. The defect dynamics is visualized by the high resolution electron microscopy and multislice simulations. Such an approach could provide a route for enabling practical devices to be made from these relatively fragile materials.

A novel growth process of silver nanowires was revealed by tracing the morphology evolution of Ag nanostructures fabricated by an improved polyol process. A mixture of Ag nanowires and nanoparticles was obtained with the usage of PVP-K25 (MW = 38,000). The products sampled at different reaction time were studied in detail using UV-visible absorption spectra and transmission electron microscopy (TEM). An interesting phenomenon unknown in the past was observed where Ag nanoparticles undergo an important dissolution-recrystallization process and Ag nanowires are formed at the expense of the preformed Ag nanoparticles. A plausible novel growth mechanism for the silver nanowires was proposed.

We present a systemic study on the tailoring of light emission properties of the InGaN/GaN quantum wells (QWs) with nanoparticle-assembled on-top layers. A layer of silver nanoparticles was deposited on the top of the quantum wells in gas-phase with a dielectric spacer layer of 15nm thickness grown between them. Time-resolved photoluminescence (PL) spectroscopy was used to study the radioactive recombination of electrons and holes in the QWs from 15 K to room temperature. A significant increasing of the internal quantum efficiency of the QWs is achieved at room temperature with a suitable nanoparticle coverage. The coupling of the spontaneous emission from InGaN QWs into the surface plasmon modes of the silver nanoparticle layers was demonstrated. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Following our recent work which revealed the lowest-energy structures of Cd n Te n ( n = 1–14) clusters follow the hollow cage and the endohedral cage structural growth patterns, we extend the search for the most stable structures to some larger clusters, i.e., Cd n Te n ( n = 15, 16, 20, 24 and 28). Within the size range studied, the endohedral cages are more stable than the hollow cages. The endohedral atoms increase as the cluster size increases. The computed dipole moments and polarizabilities show a clear dependence on the cluster geometry and symmetry. The hollow cage isomers possess smaller dipole moments and larger polarizabilities than the endohedral ones.

Employing the graphene sheets (GSs), the electron scattering constants are measured in the high-angle annular dark-field (HAADF) imaging by the scanning transmission electron microscopy. Single scattering is found to be dominant until the layer number of 200, complying with a simple relation of I = Io(1 - e(-tau/lambda)). The discrete layer counting of the GSs enables precise determination of incident depths. This work results values of lambda = 48.2, 61.4, 97.9 and 115.6 nm for 80, 120, 160 and 200 keV electrons, respectively. The uncertainties with the mean free paths and the cross sections are confined to 10 percent. The dependences on the electron beam energy and the collection angle are discussed based on a multislice simulation.

Closely spaced palladium nanoparticle arrays were fabricated in between a pair of interdigital electrodes by means of gas phase cluster beam deposition with controlled coverage. The quantum conductance change induced by hydrogen absorption was used for hydrogen sensing. The hydrogen response behavior of a sensor chip was investigated in N2 + H2 mixture gas. The sensor could be calibrated with three linear response hydrogen concentration regimes. A sub-second fast response was shown at 2.2% H2 concentration. The influence of the temperature variation to the quantitative hydrogen concentration measurement with this sensor was discussed.

Anisotropic interactions in self-assembly of nanostructures always result in novel patterns. We demonstrate that, by the aid of high-power sonication, 16 nm e-cobalt ferromagnetic nanoparticles (FMNPs) dispersed in dilute suspensions at room temperature would self-assemble into rings as small as ∼50 nm in diameter. The well-defined size and shape and the uniform surfactant coating layer of the cobalt nanoparticles enable quantitative calculations of particle–particle and particle–interface interactions. The experiments, in conjunction with cluster-moving Monte Carlo simulations mimicking the self-assembly in solution and dynamics during solvent evaporation, have revealed three key factors that influence the ring formation most, i.e., FMNP density, dipolar strength, and surfactant layers. Two very different mechanisms of the FMNP-ring formation are found by changing these factors. The results provide a guide to the fabrication of nanorings as well as diverse patterns assembled by FMNPs.

Thin Bi2Te3 flakes, with as few as 3 quintuple layers, are optically visualized on the SiO2-capped Si substrates. Their optical contrasts vary with the illumination wavelength, flake thickness and capping layers. The maximum contrast appears at the optimized light with the 570 nm wavelength. The contrast turns reversed when the flake is reduced to less than 20 quintuple layers. A calculation based on the Fresnel law describes the above observation with the constructions of the layer number-wave length-contrast three-dimensional (3D) diagram and the cap thickness-wavelength-contrast 3D diagram, applicative in the current studies of topological insulating flakes.

Few-layer graphene sheets were prepared by splitting expanded graphite using high-power sonication. Atomic-level calibrated scanning transmission electron microscopy was used to obtain efficient layer statistics, enabling optimization of the experimental conditions. This resulted in a two-step splitting mechanism in which the mean number of layers was first reduced to less than 20 by heating to 1100 °C and then to a few-layer region by a 5-min 104 W L−1 – power-density sonication. Raman spectroscopic analysis confirms the above mechanism and demonstrates that the sheets are largely free of defects and functional groups.

Polyvinyl pyrrolidone (PVP) with different molecular weights was used as capping agent to synthesize silver nanowires through a polyol process. The results indicated that the yields and aspect ratios of silver nanowires were controlled by the chain length of PVP and increased with increasing the molecular weight (MW) of PVP. When the long-chain PVP-K90 (MW = 800,000) was used, the product was uniform in size and was dominated by nanowires with high aspect ratios. The growth mechanism of the nanowires was studied. It is proposed that the chemical adsorption of Ag+on the PVP chains at the initial stage promotes the growth of Ag nanowires.

Mn:ZnO/Pb(Zr0.52Ti0.48)O3 (PZT) heterostructured films have been prepared on Pt/Ti/SiO2/Si wafers by a sol-gel process. Nonvolatile and reversible manipulation of the magnetism and resistance by electric fields has been realized. Compared with the saturation magnetic moment (Ms) in the +3.0 V case, the modulation gain of Ms can reach 270% in the −3.0 V case at room temperature. The resistance change is attributed to the interfacial potential barrier height variation and the formation of an accumulation (or depletion) layer at the Mn:ZnO/PZT interface, which can be regulated by the ferroelectric polarization direction. The magnetism of Mn:ZnO originates from bound magnetic polarons. The mobile carrier variation in Mn:ZnO, owing to interfacial polarization coupling and the ferroelectric field effect, enables the electric manipulation of the magnetism in the Mn:ZnO/PZT heterostructured films. This work presents an effective method for modulating the magnetism of magnetic semiconductors and provides a promising avenue for multifunctional devices with both electric and magnetic functionalities.

We studied the structure and electronic properties of Al 7 OH clusters using density functional theory with generalized gradient approximation. OH prefers to the ontop site of Al atoms, and the hollow form is not stable. The Al 7 moieties can keep their structures in ontop form Al 7 OH cluster, while it dramatically changes for bridge form ones. The binding strength between Al 7 and OH are much larger than that of Al 7 I and Al 7 H . The bonding characteristic of Al 7– OH is mainly ionic according to the population analysis. Large binding energy, HOMO–LUMO gap, and high ionization potential imply that Al 7 OH cluster is physically high and chemically stable.

The giant magnetostrictive Tb–Fe films assembled by nanoparticles have been prepared by the low energy cluster beam deposition. The dependence of the magnetostriction on the size of the nanoparticles is examined for the films. It is shown that the nanofilms have obtained higher saturation magnetostriction at the cluster size of 30 nm in average. The dependence of magnetostriction on particle size is ascribed to the degree of magnetic anisotropy which is related to the effective distance of exchange coupling between the adjacent Tb–Fe nanoparticles. This work demonstrates that the magnetostriction can be varied by tuning the particle size, which is important for control over the magnetostrictive properties of the films at nanoscale.

We demonstrate the fabrication of a single electron transistor device based on a single ultra-small silicon quantum dot connected to a gold break junction with a nanometer scale separation. The gold break junction is created through a controllable electromigration process and the individual silicon quantum dot in the junction is determined to be a Si_170 cluster. Differential conductance as a function of the bias and gate voltage clearly shows the Coulomb diamond which confirms that the transport is dominated by a single silicon quantum dot. It is found that the charging energy can be as large as 300meV, which is a result of the large capacitance of a small silicon quantum dot (1.8 nm). This large Coulomb interaction can potentially enable a single electron transistor to work at room temperature. The level spacing of the excited state can be as large as 10 meV, which enables us to manipulate individual spin via an external magnetic field. The resulting Zeeman splitting is measured and the lande factor of 2.3 is obtained, suggesting relatively weak electron-electron interaction in the silicon quantum dot which is beneficial for spin coherence time.

Anisotropic plasmon coupling in closely spaced chains of Ag nanoparticles is visualized using electron energy-loss spectroscopy in a scanning transmission electron microscope. For dimers as the simplest chain, mapping the plasmon excitations with nanometer spatial resolution and an energy resolution of 0.27 eV intuitively identifies two coupling plasmons. The in-phase mode redshifts from the ultraviolet region as the interparticle spacing is reduced, reaching the visible range at 2.7 eV. Calculations based on the discrete-dipole approximation confirm its optical activeness, where the longitudinal direction is constructed as the path for light transportation. Two coupling paths are then observed in an inflexed four-particle chain.

Cobalt doped ZnO film assembled by the nanoparticles was prepared by low energy cluster beam deposition. The microstructure, phase structure and optical properties were investigated for the nanostructured films. The results show that the nanostructured film was assembled by monodisperse spherical nanoparticles with average diameter of about 29.3 nm which are distributed uniformly and compactly. The results of X-ray diffraction (XRD) show that cobalt doped ZnO nanostructured film is indexed to a wurtzite structure of ZnO, and no Co-phase structure and other phases are observed. The UV-visible absorption spectra show that the optical band-gap of the film is broadened after doping.

Structural and electronic properties of single-walled TiO 2 nanotubes were investigated using density-functional theory. The strain energies were computed as a function of tube diameter and the small-sized nanotubes are less stable than the large-diameter ones. All TiO 2 nanotubes are semiconductors with indirect bandgaps independent of the tube chirality. The bandgaps of those nanotubes slightly increase with increase in tube diameter, and they are higher than that of the bulk TiO 2 solid. The hydrogen-storage capacity for a selected TiO 2 nanotube is 3.2 wt% with the binding energy of 0.05 eV per H 2 molecule.