kV Field Emission Research Articles

100 keV vacuum sealed field emission gun for high resolution electron microscopy

A standalone 100 kV field emission gun (FEG) has been developed that can be installed and operated on a standard transmission electron microscopy electron optical column or custom designed high voltage electron optical columns. The FEG comprises a thermally assisted field emission cathode and an asymmetric electrostatic lens that can operate from 20 to 100 kV in an ultrahigh vacuum (UHV) chamber. In its current configuration, the FEG has spherical and chromatic aberration coefficients (Cs and Cc, respectively) in the range of Cs = 607–670 mm and Cc = 60–87 mm at 100 keV over a range of working distances of 50–206 mm from the exit plane of the FEG unit. A dedicated high voltage supply unit with voltage ripples of less than 1 ppm at 100 kV has also been developed. The FEG is transported under UHV and does not require the use of SF6 gas during operation, as is customary in high voltage FEG TEMs. Preliminary results of operating the FEG on a Philips Tecnai 12 and a JEOL JEM-1400HR TEM show the resolution of gold (111) crystal planes at 0.235 nm and (200) planes at 0.202 nm.

CryoEM at 100 keV: a demonstration and prospects.

100 kV is investigated as the operating voltage for single-particle electron cryomicroscopy (cryoEM). Reducing the electron energy from the current standard of 300 or 200 keV offers both cost savings and potentially improved imaging. The latter follows from recent measurements of radiation damage to biological specimens by high-energy electrons, which show that at lower energies there is an increased amount of information available per unit damage. For frozen hydrated specimens around 300 Å in thickness, the predicted optimal electron energy for imaging is 100 keV. Currently available electron cryomicroscopes in the 100-120 keV range are not optimized for cryoEM as they lack both the spatially coherent illumination needed for the high defocus used in cryoEM and imaging detectors optimized for 100 keV electrons. To demonstrate the potential of imaging at 100 kV, the voltage of a standard, commercial 200 kV field-emission gun (FEG) microscope was reduced to 100 kV and a side-entry cryoholder was used. As high-efficiency, large-area cameras are not currently available for 100 keV electrons, a commercial hybrid pixel camera designed for X-ray detection was attached to the camera chamber and was used for low-dose data collection. Using this configuration, five single-particle specimens were imaged: hepatitis B virus capsid, bacterial 70S ribosome, catalase, DNA protection during starvation protein and haemoglobin, ranging in size from 4.5 MDa to 64 kDa with corresponding diameters from 320 to 72 Å. These five data sets were used to reconstruct 3D structures with resolutions between 8.4 and 3.4 Å. Based on this work, the practical advantages and current technological limitations to single-particle cryoEM at 100 keV are considered. These results are also discussed in the context of future microscope development towards the goal of rapid, simple and widely available structure determination of any purified biological specimen.

Measurements of synthesized graphene oxides electrophoresed deposition for ultrasensitive humidity detection

Two types of synthesized graphene oxide (GO) were electrophoresed using various reductants and temperature controls on the Au electrode of a quartz crystal microbalance (QCM) device for humidity detection. Characteristics of the synthesized GO, its surface morphology, and its functional groups were investigated by SEM images based on EDS and Fourier transform infrared spectra (FTIR). Structure and lattice were clear resolved using 80 kV field emission gun TEM (FEG-TEM) and electron diffraction (SAED), respectively. The resonant frequency and impedance were complementary utility to illustrate the sensitivity of various GO loaded QCM sensors. The kinetic parameters of the adsorption-desorption at a related humidity of 23–95% were extracted using the Langmuir isotherm model. In this experiment, the GOTC synthesized by a strong reductant NaNO3 and temperature control was demonstrated to exhibit excellent humidity sensing sensitivity with a fast absorption-desorption rate, making it a potential candidate for moisture detection.

Oxidation Behavior of Ti Added Alumina Dispersion Strengthening Copper Alloy

【Alumina dispersion strengthening copper(ADSC) alloy has great potential for use in many industrial applications such as contact supports, frictional break parts, electrode materials for lead wires, and spot welding with relatively high strength and good conductivity. In this study, we investigated the oxidation behavior of ADSC alloys. These alloys were fabricated in forms of plate and round type samples by surface oxidation reaction using Cu-0.8Al, Cu-0.4Al-0.4Ti, and Cu-0.6Al-0.4Ti(wt%) alloys. The alloys were oxidized at $980^{\circ}C$ for 1 h, 2 h, and 4 h in ambient atmosphere. The microstructure was observed with an optical microscope(OM) and a scanning electron microscope(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS). Characterization of alumina was carried out using a 200 kV field-emission transmission electron microscope(TEM). As a result, various oxides including Ti were formed in the oxidation layer, in addition to ${\gamma}$ -alumina. The thickness of the oxidation layer increased with Ti addition to the Cu-Al alloy and with the oxidation time. The corrected diffusion equation for the plate and round type samples showed different oxidation layer thickness under the same conditions. Diffusion length of the round type specimen had a value higher than that of its plate counterpart because the oxygen concentration per unit area of the round type specimen was higher than that of the plate type specimen at the same diffusion depth.】

Nanoscale characterisation of crystal zoning

Advances in analytical techniques are fundamental to the enhanced understandings of many geological processes. Zoned volcanic crystals have been analysed by low (5) kV field emission gun electron probe micro-analyser (FEG-EPMA) and NanoSIMS to obtain sub-micrometre chemical profiles and compared to time-of-flight SIMS (TOF-SIMS) and high (15–20) kV EPMA profiles. Plagioclase and orthopyroxene crystals have been analysed by FEG-EPMA, at accelerating voltages of 5kV providing a spatial resolution (step size) of ≤350nm (the resolution of the lowest energy X-ray) for orthopyroxene crystals using a 30nm beam and ca. 750nm for plagioclase crystals which at low voltages are unstable and require a 500nm defocused beam. Step sizes are comparable in size to interaction volumes. Analytical protocols are detailed that permit quantitative major and minor element compositions to be acquired at similar precision and accuracy as traditional EPMA analyses at 15–20kV. NanoSIMS analysis of the same crystals provides a greater spatial resolution of up to 200nm and allows the measurement of Li also. The NanoSIMS profiles, however, cannot currently be quantified. The ability to analyse crystals at sub-micrometre scales is demonstrated by the good agreement between NanoSIMS, FEG-EPMA, conventional EPMA and TOF-SIMS data. FEG-EPMA, NanoSIMS and TOF-SIMS techniques have broad applications within the earth sciences. In petrologic studies for example, these methods have the ability to analyse small crystals in experimental charges and provide chemical profiles of crystal zoning at a spatial resolution of ca. 200–300nm. Such profiles are important in crystal forensics and diffusion chronometry studies. The implications for the latter application are that timescales of volcanic processes that occur in the days–years immediately prior to the eruption can now be studied.

Characterization of the Molecular Architecture of Human Caveolin-3 and Interaction with the Skeletal Muscle Ryanodine Receptor

Caveolin-3 facilitates both caveolae formation and a range of cell signaling pathways, including Ca(2+) homeostasis. Caveolin-3 forms a disc-shaped nonamer that binds the Ca(2+)-release channel, RyR1. Multiple caveolin-3 nonamers bind to a single RyR1 homotetramer. First three-dimensional structural insights into caveolin-3 assembly, interactions with RyR1 suggest a novel role in muscle contraction and/or for channel localization within the membrane. Caveolin-3 (cav-3), an integral membrane protein, is a building block of caveolae as well as a regulator of a number of physiological processes by facilitating the formation of multiprotein signaling complexes. We report that the expression of cav-3 in insect (Sf9) cells induces caveola formation, comparable in size with those observed in native tissue. We have also purified the recombinant cav-3 determining that it forms an oligomer of ∼220 kDa. We present the first three-dimensional structure for cav-3 (using transmission electron microscopy and single particle analysis methods) and show that nine cav-3 monomers assemble to form a complex that is toroidal in shape, ~16.5 nm in diameter and ~ 5.5 nm in height. Labeling experiments and reconstitution of the purified cav-3 into liposomes have allowed a proposal for the orientation of the protein with respect to the membrane. We have identified multiple caveolin-binding motifs within the ryanodine receptor (RyR1) sequence employing a bioinformatic analysis. We have then shown experimentally that there is a direct interaction between recombinant cav-3 nonamers and purified RyR1 homotetramers that would imply that at least one of the predicted cav-3-binding sites is exposed within the fully assembled RyR1 structure. The cav-3 three-dimensional model provides new insights as to how a cav-3 oligomer can bind multiple partners in close proximity to form signaling complexes. Furthermore, a direct interaction with RyR1 suggests a possible role for cav-3 as a modifier of muscle excitation-contraction coupling and/or for localization of the receptor to regions of the sarcoplasmic reticulum.

Measurement of effective source distribution and its importance for quantitative interpretation of STEM images

We review the manner in which lens aberrations, partial spatial coherence, and partial temporal coherence affect the formation of a sub-Å electron probe in an aberration-corrected transmission electron microscope. Simulations are used to examine the effect of each of these factors on a STEM image. It is found that the effects of partial spatial coherence (resulting from finite effective source size) are dominant, while the effects of residual lens aberrations and partial temporal coherence produce only subtle changes from an ideal image. We also review the way in which partial spatial and temporal coherence effects are manifest in a Ronchigram. Finally, we provide a demonstration of the Ronchigram method for measuring the effective source distribution in a probe aberration-corrected 300 kV field-emission gun transmission electron microscope.

In situ dynamic HR-TEM and EELS study on phase transitions of Ge 2Sb 2Te 5 chalcogenides

The phase transition phenomena of Ge 2Sb 2Te 5 chalcogenides were investigated by in situ dynamic high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS). A 300 kV field emission TEM and a 1250 kV high voltage TEM were employed for the in situ heating experiments from 20 to 500 °C for undoped and 3 wt% nitrogen-doped Ge 2Sb 2Te 5 thin films deposited by DC sputtering. Crystallization of amorphous Ge 2Sb 2Te 5 to its cubic structure phase started at 130 °C and then rapid crystal growth developed from cubic to hexagonal phase in the range of 130–350 °C; finally, the hexagonal crystals started to melt at 500 °C. For nitrogen-doped Ge 2Sb 2Te 5, its crystallization from amorphous film occurred at higher temperature of ca. 200 °C, and the cubic and hexagonal phases were usually formed simultaneously without significant growth of crystals at further heating to 400 °C. EELS measurements showed that the electronic structures of Ge, Sb and Te stayed almost the same regardless of the amorphous, FCC and hexagonal phases. The nitrogen doped in Ge 2Sb 2Te 5 was confirmed to exist as a nitride. Also, the doped nitrogen distributed homogeneously in both amorphous and crystalline phases. Localization of doped nitrogen was not found in the grain boundary of crystallized phases. The dynamic process of phase transition was enhanced by high-energy electron irradiation. Peeling of atomic layers in nitrogen-doped Ge 2Sb 2Te 5 film was detected during heating assisted with electron beam irradiation.

TEM and impedance spectroscopy of doped ceria electrolytes

Preliminary investigations are presented into the grain boundary structure of gadolinia doped ceria by high-resolution transmission electron microscopy (HR-TEM) imaging using a 300 kV field emission FEI TITAN 80/300 monochromated transmission electron microscope, with a spatial resolution of < 0.2 nm. Impedance spectroscopy over the temperature range 150–350 °C and frequency range 0.1 Hz–10 MHz has been used to separate the contribution to the total conductivity of the grain interior and grain boundary for ceramic samples. The samples were fabricated from powder of composition Ce 1 − x Gd x O 2 − δ , x = 0.1 (CGO10) and x = 0.2 (CGO20) which were obtained from three different commercial suppliers. These impedance measurements have been correlated with scanning electron microscopy (SEM) images of the material microstructure in order to estimate the specific grain boundary conductivity. The bricklayer model has been used to interpret the impedance data, which show wide variation in specific grain boundary conductivity between samples of the same nominal composition. No grain boundary second phases have been observed at any boundaries and the grain boundary blocking effect has been attributed to the presence of space charge layers. HR-TEM studies at these interfaces reveal defect structures, which may play a significant role in the grain boundary conductivity behaviour of these materials.

Effect of dynamic precursor gas pressure on growth behavior of amorphous Si–C–O nanorods by electron beam-induced deposition

Electron beam-induced deposition (EBID) is a versatile maskless technology [1] to fabricate submicronor nanometerscale structures from various elements in scanning electron microscope [2] as well as transmission electron microscope [3] and scanning transmission electron microscope [4]. During EBID, adsorbed precursor gas molecules on a substrate surface are irradiated and dissociated by an electron beam. This induces a chemical reaction that results in the deposition of non-volatile materials. If the electron beam is not moved relative to the substrate, a nanodot can be formed; electron beam scanning can produce nanorod within a suitable precursor gas pressure. Nanofabrication by using EBID is hence exceeding in terms of controlling the position and morphology of low dimensional functional nanostructures, e.g., carbon nanotube and ferromagnetic FePt alloy nanorods [5, 6]. It is very necessary to probe the effects of various deposition parameters on the target deposits, e.g., electron beam scan speed, precursor gas pressure, and deposition time, in order to fully develop and improve EBID serving as nanotechnology. No much importance, however, has been attached to dynamic precursor gas pressure in EBID, although it is generally known that the higher the precursor gas pressure is, the more the decomposed gas molecules are, and the larger the size of the deposits should be during EBID [7–9]. Undoubtedly, it will be the most direct route to know about the transport of precursor gas molecules by real-time monitoring (dynamic) precursor gas pressure, which helps to unravel the microscopic effect of gas pressure on the successive nanofabrication. In this paper, we will investigate the effects of dynamic precursor gas pressure and electron beam scan speed on the EBID process. Electron beam-induced deposition experiment was carried out in a 30 kV field emission gun scanning electron microscope (JEOL JSM-7800UHV). The electron beam current was about 0.8 nA with a beam diameter of 4 nm. The irradiation position and time of electron beam were controlled by an external voltage input to the beam deflectors using a computer with digital–analog converters. Tetraethoxy-silane SiOC2H5 was used as a precursor. A gas introduction system consists of a nozzle (its tip was about 1 mm away from the electron beam position, as shown in Fig. 1), gas pipeline, variable leak valve, and gas source reservoirs. The base gas pressure in the specimen chamber was 2 9 10 Pa and the maximum allowable gas pressure is 2 9 10 Pa. A holey carbon film was used as substrates. A 300 kV JEM-3000F field-emission gun transmission electron microscope, attached with a post-column Gatan imaging filter and a 1 k 9 1 k Ultrascan CCD camera, was employed to characterize the deposits by a high-resolution transmission electron microscopy (HRTEM) and energyfiltered transmission electron microscopy (EFTEM). To obtain elemental maps, the 3-window method [10] was applied, where the intensities from the first two windows (pre-edges 1 and 2) and third window (post-edge) are used for the background subtraction and the map, respectively. The sample was stabilized for 60 min before recording, in order to minimize the possible mechanical drift of the sample stage. When the focused electron beam position was moved into space at a certain speed (here 1.2–3 nm/s) along the edge of holey carbon film, freestanding rod-like nanostructures W. Zhang (&) K. Furuya National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0003, Japan e-mail: phdweizhang@gmail.com

Dodecameric Structure of the Small Heat Shock Protein Acr1 from Mycobacterium tuberculosis

Small heat shock proteins are a ubiquitous and diverse family of stress proteins that have in common an alpha-crystallin domain. Mycobacterium tuberculosis has two small heat shock proteins, Acr1 (alpha-crystallin-related protein 1, or Hsp16.3/16-kDa antigen) and Acr2 (HrpA), both of which are highly expressed under different stress conditions. Small heat shock proteins form large oligomeric assemblies and are commonly polydisperse. Nanoelectrospray mass spectrometry showed that Acr2 formed a range of oligomers composed of dimers and tetramers, whereas Acr1 was a dodecamer. Electron microscopy of Acr2 showed a variety of particle sizes. Using three-dimensional analysis of negative stain electron microscope images, we have shown that Acr1 forms a tetrahedral assembly with 12 polypeptide chains. The atomic structure of a related alpha-crystallin domain dimer was docked into the density to build a molecular structure of the dodecameric Acr1 complex. Along with the differential regulation of these two proteins, the differences in their quaternary structures demonstrated here supports their distinct functional roles.

Real-time observation of liquid Indium unusual behavior inside silica nanotubes

Behavior of Indium embedded into amorphous silica nanotubes has been analyzed using a 300 kV field emission TEM. Under electron beam irradiation with a beam current density nearly 10 times that of normal TEM imaging conditions, a variety of unusual phenomena has been recorded: (i) melting, expansion and/or sudden shrinkage of encapsulated In-columns; (ii) liquid In squeezing out of fully sealed tubes, with the tube shape fully retained, accompanied by cyclic growth and ‘explosion’ of liquid In nanoballs on the tube periphery; (iii) ultrafast ‘birth’, ripening, coalescence and boiling of tiny In droplets inside and/or outside of tubular channels in areas where In was originally not present. The results are explained in the framework of electromigration theory.

A combined SNMS and EFTEM/EELS study on focused ion beam prepared vanadium nitride thin films

We investigated the diffusion profiles and core-loss fine-structures (ELNES) of thin vanadium nitride films by electron energy-loss spectroscopy (EELS) and energy filtering transmission electron microscopy (EFTEM). The nitride layers have been produced by rapid thermal processing in a NH 3 or N 2 atmosphere and have then been cross-sectioned with a focused ion beam instrument (FIB) under mild milling conditions to maintain crystallography. For the high-resolution electron energy-loss spectroscopy studies (HREELS), a recently developed TEM gun monochromator, implemented into a 200 kV field emission gun column was used in combination with a new post-column spectrometer. It was found that, dependent on substrate and atmosphere, layers with different vanadium and nitrogen content were formed, showing distinct differences in their ELNES. With an energy resolution at the 0.2 eV level and a TEM beam spot size of approximately 2 nm these layers could be unambiguously identified when compared to theoretical ELNES simulations from the literature.

Profile structure of magnetic flux lines in type-II superconductor from a rectangular electron hologram.

Profile magnetic configuration of a quantized flux line and flux-line lattice penetrating a type-II superconductor thin foil, niobium, was observed by electron holography and Lorentz microscopy using a 300 kV field-emission electron microscope. Each single flux line was distributed periodically as lattice structure in the mixed state just below its critical temperature of 8.5 K, while at low temperature of 5 K the flux lines were weakly bound as bundles. In order to observe the flux-line distribution over a wide area, discrete Fourier transform reconstruction in the holography was extended for a rectangular area without loss of information and data precision.

Blue-emitting ZnS:Ag,Al phosphors with low defect density for high-voltage field-emission displays

In recent years, deterioration of luminescence efficiency of blue-emitting ZnS:Ag,Al powder phosphors has been investigated for high-voltage (e.g., 6–10 kV) field-emission displays (FEDs). It has been found by cross-sectional transmission electron microscopy that the degree of crystallinity of ZnS host crystal within the electron penetration depth is one of the important factors in order to obtain ZnS:Ag,Al phosphors having a longer lifetime of luminescence efficiency. ZnS:Ag,Al phosphors with lower defect density N0 as compared with a P22B ZnS:Ag,Al phosphor for color-TV use have been developed by using a suitable firing method with subsequent annealing and surface treatments. As a result, ZnS:Ag,Al phosphors with lower N0 were successfully prepared, and also FED tubes having a longer lifetime in blue luminescence were made by using ZnS:Ag,Al phosphors with lower N0. In addition, it was revealed that both the initial luminescence efficiency and the thermal quenching point of ZnS:Ag,Al phosphors with lower N0 are considerably higher than those of a P22B ZnS:Ag,Al phosphor.

Software techniques for EELS to realize about 0.3 eV energy resolution using 300 kV FEG-TEM.

In this short communication we describe some software techniques for electron energy-loss spectrum measurement. We prepared DigitalMicrograph (Gatan) scripts for multiple spectrum acquisitions, quasi-simultaneous acquisition of low-loss and core-loss spectra, energy drift correction, and other operations. Narrow zero-loss spread of 0.27 eV is demonstrated using a 300 kV field-emission transmission electron microscope (TEM) (Hitachi, HF-3000) and a post-column energy filter (Gatan, GIF2002). The core-loss spectrum is acquired with an energy resolution of 0.36 eV with high reproducibility. The present software techniques effectively achieve the intrinsic energy resolution of electron sources. Sample scripts are provided in the Appendix.

Atomic configuration in core structure of Lomer dislocation in Si 0.76Ge 0.24/Si

The core structure of a Lomer dislocation in SiGe/Si system has been revealed at atomic level. This is attained by applying the image deconvolution technique in combination with dynamical diffraction effect correction to the high-resolution image taken with a 200 kV field-emission gun high-resolution electron microscope. The Lomer dislocation has a Hornstra-like core. The contrast of the image simulated on the basis of derived atomic configuration is in agreement with that of the experimental image.

Imaging columns of the light elements carbon, nitrogen and oxygen with sub Ångstrom resolution

It is reported that lattice imaging with a 300 kV field emission microscope in combination with numerical reconstruction procedures can be used to reach an interpretable resolution of about 80 pm for the first time. A retrieval of the electron exit wave from focal series allows for the resolution of single atomic columns of the light elements carbon, nitrogen, and oxygen at a projected nearest neighbor spacing down to 85 pm. Lens aberrations are corrected on-line during the experiment and by hardware such that resulting image distortions are below 80 pm. Consequently, the imaging can be aberration-free to this extent. The resolution enhancement results from increased electrical and mechanical stability of the instrument coupled with a low spherical aberration coefficient of 0.595+0.005 mm.

Quantitative Investigations of Interfaces and Grain Boundaries by Phase Contrast Electron Microscopy with Ultra High Resolution

Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission microscope'"". A reconstruction of the electron exit wave from a focal series of lattice images converts the recorded information into interpretable resolution. The present contribution illustrates some recent applications of this technique to interfaces.Fig. 1 shows a reconstructed electron exit wave of a heterophase interface between GaN and sapphire. The experiment takes advantage of three factors: First, we resolved the GaN lattice inprojection, which requires at least 0.15 nm resolution. Theprojection eliminates the stacking fault contrast that usually obscures lattice images in the commonly recordedprojection. Thus, image interpretation is drastically simplified. Second, all atom columns at the interface and in the sapphire are resolvable with a smallest projected aluminum - oxygen spacing of 85 pm in the sapphire.

Boron Nitride Nanotube, Nanocable and Nanocone

AbstractBoron nitride nanotubes, nanocones and nanocables were prepared and their atomic structures were identified by using a 300 kV field emission transmission electron microscope equipped with an electron energy loss spectrometer and energy dispersion X-ray detector. Multiwalled BN nanotubes and nanocones were synthesized by reacting C nanotube templates and boron oxide under nitrogen atmosphere at 1723-2023 K. Additions of metal oxide promoters, e.g. MoO3, CuO, and PbO, significantly improved BN-rich nanotube yield at the expense of B-C-N nanotubes. It was shown that BN nanotubes had preferential “zigzag” chirality and exhibited either hexagonal or rhombohedral stacking between shells. An efficient synthetic route for bulk quantities of BN tube production was also developed, where a B-N-O precursor was used during a CVD process. Nanocones of BN were mostly found to have 240° disclinations which ensure the presence of B-N bonds only. One case was observed of a cone constituted of 300° disclination implying that structures may contain line defects of non B-N bonds. The first synthesis of insulating BN nanocables was carried out, where BN nanotubes were entirely filled with Invar Fe-Ni nanorods. The filled nanotube diameters ranged between 30 to 300 nm, whereas the length of filling reached several microns.