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The in situ characterization on the individuals offers an effective way to explore the dynamic behaviors and underlying physics of materials at the nanoscale, and this is of benefit for actual applications. In the field of vacuum micro-nano electronics, the existing in situ techniques can obtain the material information such as structure, morphology and composition in the process of electron emission driven by a single source of excitation. However, the relevant process and mechanism become more complicated when two or more excitation sources are commonly acted on the emitters. In this paper, we present an in situ nano characterization technique to trigger and record the electron emission behavior under the photo-electric-common-excitation multiple physical fields. Specifically, we probed into the in situ electron emission from an individual vertical few-layer graphene (vFLG) emitter under a laser-plus-electrostatic driving field. Electrons were driven out from the vFLG’s emission edge, operated in situ under an external electrostatic field coupled with a 785 nm continuous-wave laser-triggered optical field. The incident light has been demonstrated to significantly improve the electron emission properties of graphene, which were recorded as an obvious decrease of the turn-on voltage, a higher emission current by factor of 35, as well as a photo-response on-off ratio as high as 5. More importantly, during their actual electron emission process, a series of in situ characterizations such as SEM observation and Raman spectra were used to study the structure, composition and even real-time Raman frequency changes of the emitters. These information can further reveal the key factors for the electron emission properties, such as field enhancement, work function and real-time surface temperature. Thereafter, the emission mechanism of vFLG in this study has been semi-quantitatively demonstrated to be the two concurrent processes of photon-assisted thermal enhanced field emission and photo field emission.

Vertically aligned Si nanoconstrictions have potential for applications of electronic, photonic and phononic nanodevices. Herein, we report a featured method by utilizing the non-uniaxial tangential tension stress (σ T ) at the Si surface of a vertical hyperbolic Si/SiO2 core-shell nanostructure during thermal oxidation to achieve well defined Si nanoconstrictions. A thermal oxidation model was proposed to describe the correlations between σ T and the structural parameters of the hyperbolic nanostructure, i.e. oxide thickness (t ox ), sidewall curvature radius (R 0) and neck diameter (2r A0). Numerical simulations indicated that the Si surface at the position with the narrowest diameter (neck position) has the highest σ T (∼GPa) and presents a gradient distribution at both ends. By means of stress regulation, an array of well defined Si nanoconstrictions about 10 nm in diameter and about 34 nm in length was obtained. The experimental findings demonstrated that the high σ T would induce a nanofracture and thus a local oxidation to form a nanoconstriction, self-aligned at the neck position. The finding notably extends the capability of stress-assisted 'nanofabrication' of Si via thermal oxidation.

Decorating with metal nanoparticles (NPs) is an effective way to tune the photoluminescence (PL) properties of ZnO nanowires (NWs), but the mechanism for this is insufficiently understood. In this study, ZnO NWs with lower work function were synthesized on Si substrates using thermal oxidation. Au NPs were incorporated onto the surface of the ZnO NWs. The PL properties of ZnO NWs decorated with Au NPs of different sizes were systematically investigated. Quenching rather than enhancement of both the near-band-edge and visible emission of ZnO NWs was observed after decoration with Au NPs. Introducing an approximately 2-nm-thick Al2O3 insulating layer between the ZnO NWs and Au NPs caused the quenching phenomenon to disappear. These results suggest that the quenching was caused by electron transfer from ZnO to the Au NPs under UV irradiation and the PL properties of ZnO NWs decorated with Au NPs are also related to the band structure of ZnO.

All-solid-state strong coupling systems with large vacuum Rabi splitting energy have great potential applications in future quantum information technologies, such as quantum manipulations, quantum information storage and processing, and ultrafast optical switches. Monolayer transition metal dichalcogenides (TMDs) have recently been explored as excellent candidates for the observation of solid-state strong coupling phenomena. In this work, from both experimental and theoretical aspects, we explored the strong coupling effect by integrating an individual plasmonic gold nanorod into the monolayer tungsten diselenide (WSe2). Evident anti-crossing behavior was observed from the coupled energy diagram at room temperature; a Rabi splitting energy of 98 meV was extracted.

Well-shaped micro/nano-structured suspended graphene is a versatile building block for micro/nano-electromechanical (MEMS/NEMS) devices. Directly 'sculpting' the suspended graphene membrane using an accelerated energetic electron/ion beam to form micro/nano-structured graphene possesses the merits of high resolution and well-processed flexibility. However, both the residual and process-induced stress in the membrane still challenge the obtaining of non-distorted freestanding graphene patterns. We report a featured double-sided masking and stress-release etching method to fabricate well-defined suspended graphene micro-ribbon. We demonstrated that the one-step low-energy (10 keV) electron beam induced the deposition of amorphous carbon (a-C) on both sides of the suspended graphene. The a-C layers were precisely self-aligned, not only allowing its use as reliable masks for the following plasma etch of suspended graphene, but showing potential for future applications of effectively 'writing' circuits/devices directly on both sides of a suspended 2D atomic-layered platform. A stress-release plasma etching process and its 'self-crumpling' mechanism were demonstrated. High-aspect-ratio micro-structured graphene (bridge and cantilever) with a good shape was obtained. This provides a promising and universal processing method for making suspended structures of 2D materials with in-plane flatness for potential MEMS/NEMS applications.

α-Fe2O3 nanomaterials were synthesized by thermal oxidation of pure iron foil and the effects of current aging treatment and morphology on their field emission properties were systematically investigated. The current aging treatment was found to be an efficient method to improve the field emission properties of α-Fe2O3 nanoflakes. The emission current density was largely enhanced from 0.05-5.70 mA cm-2 under an applied electrical field of 7.8 MV m-1, and their threshold field decreased from than 11.0-6.6 MV m-1 after the current aging treatment. The mechanism of the improvement in the field emission performance of α-Fe2O3 nanoflakes induced by the current aging treatment is discussed. α-Fe2O3 nanostructures with various morphologies were synthesized by adjusting the growth temperatures between 300 °C-450 °C to optimize their morphologies. α-Fe2O3 nanoflakes synthesized at 350 °C were superior field emitters with a low threshold field of 5.1 MV m-1, high current density of 63.4 mA cm-2, and stable emission, which demonstrated that α-Fe2O3 nanoflakes could be a promising material for application as field emitters.

The electron emission from single-wall carbon nanotubes (SWCN) is investigated theoretically by using the tunnelling theory with the tight-binding approach. We compare the electron emission from SWCN in different temperatures and electric fields. In the normal condition, T 6 V nm−1. A minimum of the fractional TEE current occurs at the electric field, 5–6 V nm−1 minimum. This is because the strong electric field suppresses both the width and the height of the vacuum potential barrier, which leads to a competition between the FEE and the TEE current.

Various types of tungsten oxide nanostructures, including nanowires, nanobundles, and three-dimensional nanowire networks, have been synthesized on large-area silicon substrates by simply heating an array of tungsten filaments in a vacuum chamber. The fine structure and components of as-prepared products can been controlled by changing the tungsten filament temperature. This approach is free of catalysts and templates, and provides an economical method for large-scale preparation of various types of tungsten oxide nanostructures for applications.

A convenient fabrication technique for samarium hexaboride (SmB6) nanostructures (nanowires and nanopencils) is developed, combining magnetron-sputtering and chemical vapor deposition. Both nanostructures are proven to be single crystals with cubic structure, and they both grow along the [001] direction. Formation of both nanostructures is attributed to the vapor-liquid-solid (VLS) mechanism, and the content of boron vapor is proposed to be the reason for their different morphologies at various evaporation distances. Field emission (FE) measurements show that the maximum current density of both the as-grown nanowires and nanopencils can be several hundred μA/cm2, and their FN plots deviate only slightly from a straight line. Moreover, we prefer the generalized Schottky–Nordheim (SN) model to comprehend the difference in FE properties between the nanowires and nanopencils. The results reveal that the nonlinearity of FN plots is attributable to the effect of image potential on the FE process, which is almost independent of the morphology of the nanostructures. All the research results suggest that the SmB6 nanostructures would have a more promising future in the FE area if their surface oxide layer was eliminated in advance.

The epitaxial growth of carbon nanotubes (CNTs) is an important subject of research. Recent attention has been paid to finding new strategies for the controlled growth of single-wall CNTs with a defined chirality. In addition, many potential applications require multiwall CNTs (MWCNTs) to grow vertically from the substrate and the interface property is crucial. Here, we report for the first time that MWCNTs can grow directly from the surface of a substrate by epitaxy, based on the experimental study of individual multiwall carbon nanotubes on a large-area stainless steel substrate, which is a very useful system for electrical and mechanical applications. In particular, evidence is given of the lattice matching between the MWCNT and the lattice of a hexagonal Cr2O3: (Fe, Mn) film formed on the surface of the substrate. Furthermore, a method is developed to increase the density of the MWCNTs; a mechanism of simultaneous top and bottom growth is proposed. The resultant significantly improved electrical transport and field emission properties are also presented, showing the Ohmic contact for electrical conduction and high performance in resisting the catastrophic cold-cathode vacuum breakdown of the CNTs.

Field electron emission properties of aligned multi-walled carbon nanotube films were studied with variation of the vacuum gap d between anode and cathode. With d varying in the range of 0.4-2 mm, the emission current-gap voltage characteristics and the corresponding Fowler-Nordheim (FN) plots show distinct nonlinearity and regular changes with electrode separation. Three field enhancement factors may be derived from the three linear sections of a FN plot. Their variation with gap d results in different behaviours; significantly a drop of five times in the field enhancement factor is observed. The physical process responsible for our findings is suggested to be the space charge effect and both theoretical and experimental evidence is provided to support our arguments. The implication of our findings in technical applications is also discussed.

Stable electron emission from amorphous diamond film at a low threshold field of 6-7 mV m-1 has been observed using a transparent anode technique. The electron emission characteristics are discussed in terms of the structural properties of films. Using scanning electron microscopy and Raman spectra, the emitting and the non-emitting regions of the amorphous diamond film are analysed. The emitting regions exhibit rougher microstructure in morphology and a stronger Raman peak at 1360 cm-1 than the non-emitting regions, a signature of having more micro-sp2 components. It is suggested that field emission is prone to take place at the regions containing more sp2 nanoclusters or nanocrystalline graphite.

Nitrogen containing nanocrystalline diamond films have been synthesized by microwave plasma enhanced chemical vapour deposition using N-2/CH4 as the reactant gas. The films prepared under different N-2/CH4 flow ratios were studied by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and secondary ion mass spectroscopy. Their field emission characteristics, i.e. both the distribution of the emission sites and current-voltage characteristics, were recorded using a transparent anode technique. It was found that the grain size of films prepared under different conditions varies and has a relationship with their turn-on fields. A possible explanation is given, which proposes that nanocrystalline boundary induced defect states might affect the field emission characteristics.

Large-area patterned films of boron nanowires (BNWs) are fabricated at various densities by chemical vapor deposition (CVD). Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are 100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.

Large-area boron nanowire (BNW) films were fabricated on the Si(111) substrate by chemical vapor deposition (CVD). The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires (GC-BNWs) were obtained by microwave plasma chemical vapor deposition (MPCVD). Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.

The structural feature of molybdenum (Mo) nano emitters has a significant effect on their field emission reliability in the oxidizing environment. Mo nanowalls have been studied to exhibit high oxygen damage immunity. The two-dimensional (2D) nanostructure has shown stable and recoverable field emission performance during oxygen exposure in the order of magnitude of 10−4 Pa. By contrast, quasi 1D nanoscrews have more easily suffered irreversible emission degradation due to more serious oxygen molecule and ion erosion at a higher local electric field around the emitter surface. The 2D wall-like structure with a large emission edge has been proven to contribute to such strong immunity. The results indicate that the Mo nanowall emitter apparently could work properly in the vacuum environment with a certain amount of oxygen.

The threshold voltage shift (ΔV th) under positive gate bias stress (PGBS), generally found in amorphous InGaZnO thin-film transistors (a-IGZO TFTs), has usually been suppressed by external passivation layers. We report it can also be alleviated by the self-passivation effect of the active layer, where moderately increasing the active layer thickness (d s) reduces ΔV th by 82% in SiO x -passivated a-IGZO TFTs. Our experiments in conjunction with simulations show that the instability of V th comes from ambient factors at the back channel. Larger d s results in lower carrier concentrations at the back channel (N back), fewer diffusive ions affecting the front channel, and much more stable operations under PGBS. The optimal thickness of an IGZO film simultaneously obtaining a small ΔV th, near-zero V th, and sharp sub-threshold swing is about 80–90 nm, thicker than those usually adopted. The self-passivation effect combined with the externally deposited passivation layer can improve the overall device reliability.

Significant field emission has been observed from thin (< 1000A) amorphous-carbon-nitride (a-CN) films. X-ray photoelectron spectroscopy, infrared spectrometry, and UV-visible optical absorption spectrometry have been used to characterize the films. The field emission properties of the thin film have been studied by using a transparent anode imaging system. It is proposed that this class of films should be studied as candidates of coating material for cold cathode emitter, in order for one to benefit from their very high thermal conductivity and super hardness.

The changes in the microstructure of ZnO nanowire were studied after exposure to different radiation doses of energetic x-rays. Detailed structural, composition and optical analyses were carried out. It was found that the surface composition changed and defects were formed in the irradiated ZnO nanowires. The structural change of ZnO nanowires after thermal treatment was also studied and similar defects were observed. It is proposed that phonon-induced localized heating is the main reason for the observed changes in microstructure. Finally, the field emission properties of ZnO nanowires before and after x-ray radiation were studied. It was found that the increase of work function and change in morphology induced by the irradiation were the reasons for the observed change in field emission properties.

We have successfully synthesized a new layered pnictide-oxide: BaTi2As2O. It shares similar characteristics with Na2Ti2Sb2O. The crystal has a layered structure with a tetragonal P4/nmm group (a = 4.047(3)??, c = 7.275(4)??). The resistivity shows an anomaly at 200?K, which should be ascribed to an SDW or structural transition. The SDW or structural transition is confirmed by magnetic susceptibility and heat capacity measurements. These behaviors are very similar to those observed in parent compounds of high-Tc iron-based pnictide superconductors, in which the superconductivity shows up when the anomaly due to the SDW or structural transition is suppressed. Therefore, the new layered pnictide-oxide, BaTi2As2O, could be a potential parent compound for superconductivity. It is found that Li + doping significantly suppresses the anomaly, but no superconductivity emerges so far.

Large-area tungsten oxide nanorod arrays were synthesized by the catalyst-free tungsten hot-filament thermal vapor method. The diameter, height, interval and alignment of the nanorods were all found to be sensitive to the distance between hot filament and substrates. And the field emission property of the nanorod arrays prepared at various distances was shown to be significantly different. This demonstrates that optimal conditions can be found for preparing W18O49 nanorod arrays of better field emission property.

Crystalline W20O58 nanowires were grown on silicon substrates by thermal evaporation of tungsten powders in a flow of argon gas without using any catalyst. Scanning electron microscopy shows that typical nanowires vary from 30 to 100?nm in diameter and around 8??m in length. X-ray diffraction and high-resolution transmission electron microscopy with electron diffraction study reveal that the nanostructures are crystalline. The laser power effect on the structure change of W20O58 nanowires has also been studied, which shows that W20O58 can be directly oxidized to WO3 very easily only by laser heating.

A uniform submicron periodic square structure was fabricated on the surface of ZnO by a technique of two linearly polarized femtosecond laser beams with orthogonal polarizations ablating material alternately. The formed two-dimensional ordering submicron structure consists of close-packed submicron squares with a spacial periodicity of 290 nm, which arises from the intercrossing of two orthogonal submicron ripple structures induced by the two beams respectively. The result demonstrates a noninterference effect of two-beam ablation based on the alternate technique, which should come from the polarization-dependent enhancement of the subwavelength ripple structure and the large interval of two alternate pulses. This two-beam alternate ablation technique is expected to open up prospects for the submicron fabrication of wide-bandgap materials.

WO3 nanowire films have been prepared by thermal evaporation on both a silicon substrate and a quartz substrate. The gasochromic effect and the colouration mechanism of the films are investigated in detail by ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy, x-ray diffraction (XRD) spectroscopy, micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and electrical transport measurements. The studies reveal that the gasochromism of WO3 nanowire films is caused by hydrogen injection. Along with the injection, a part of the tungsten ions' valences and the lattice structure change, giving rise to the colouration of the films. Moreover, electrical transport measurements show the lower conductance of the coloured film, which further confirms the hydrogen injection mechanism. Finally, a gasochromic model of the WO3 nanowire films is proposed.