Field Emission Gun Transmission Electron Microscope Research Articles

C 60 encapsulation inside single-walled carbon nanotubes using alkali–fullerene plasma method

It is reported that alkali–fullerene plasmas consisting of positive alkali-metal ions, negative fullerene ions, and residual electrons are effective in encapsulating fullerenes inside single-walled carbon nanotubes (SWNTs). When positive or negative bias-voltages are applied to SWNTs in plasmas, accelerated negative fullerene or positive alkali-metal ions are irradiated to the SWNTs through the plasma sheath, respectively. Field emission gun transmission electron microscopy (FEG-TEM) clearly shows that drastic structural modifications such as severe bending of SWNT bundles, tube dislocation, and tube tip termination take place after the ion irradiation. Energy dispersive X-ray spectrometry (EDS) confirms the existence of the alkali-metal elements in the sample after the alkali-metal irradiation. In addition to this, the SWNTs encapsulating fullerene molecules are directly observed after only 1 h fullerene-ion irradiation. These results suggest that our experimental system could permit us to intercalate not only fullerenes but also other elements inside the SWNTs by the applied-bias control. Raman scattering spectroscopy is also adopted for the purpose of evaluating pure SWNTs and fullerene encapsulated SWNTs.

The Effect of Implanted Gallium on the Recrystallization of Amorphous Layers formed during FIB Milling of Silicon

The focused ion beam (FIB) miller allows preparation of site-specific transmission electron microscopy (TEM) specimens from a wide range of materials in both cross-sectional and planar configurations [1,2]. However, radiation damage during exposure to the high-energy gallium beam may result in the formation of amorphous regions on thin film specimens. The thickness of such damage layers, on both sides of a TEM specimen, is comparable with the thickness required for lattice imaging. For example, the thickness of an amorphous layer in Si after 30 kV Ga+FIB processing has been reported in the range from 15 [3] to 28 nm [4]. This problem limits the capabilities of FIB sample fabrication.The aim of this study was to investigate, in detail, the structure, composition and the thickness of the damage layers in Si specimens after milling with a gallium ion beam. Using a FEI xP200 FIB system, with 30 kV Ga+ions, a row of trenches on a silicon sample was milled under different beam currents ranging from 150 to 6600 pA. The average size of such trenches was 15×10 μm wide and 1 μm deep. The trenches were then removed from the FIB and sputter coated with a thick Au film to preserve the trench surfaces from further damage during subsequent TEM specimen preparation steps. Cross-sectional TEM specimens of the trench walls were then prepared using standard FIB procedures [5]. Observations were made using a Philips CM 200 Field Emission Gun TEM operating at an accelerating voltage of 200 kV.

Electron beam induced in situ clusterisation of 1D ZrCl4 chains within single-walled carbon nanotubes

Cluster formation can be induced in situ in SWNTs filled with ZrCl4 by electron beam irradiation of SWNT/ZrCl4 composites within a field emission gun transmission electron microscope (FEGTEM); the process represents a possible route to the synthesis of 1D-quantum dot arrays formed by related materials.

Age Hardening in Martensitic/Bainitic Matrices in a Copper-Bearing Steel

In order to understand the influence of matrix microstructures on age-hardening behavior in a copper-bearing steel, NAK 80, the phase transformation of austenite (during a variety of continuous cooling treatments) and the consequent precipitation of copper particles (during isothermal aging) were investigated by dilatometry, optical metallography, hardness measurement, transmission electron microscopy, and field-emission-gun transmission electron microscopy (FEG-TEM). It was found that at a wide range of cooling rates (about from 30 to 0.3° C/s) after austenitization at 900°C for 15 min, the steel produces a mixture of martensite and bainite. Three different pre-treated specimens, which had been continuously cooled at 120, 5 and 1°C/s, respectively, were studied in order to determine their response to copper age-hardening. The results show that the general level of peak hardness for the fully martensitic specimen is the lowest when compared with those of the other two specimens, which contained a mixture of nearly equal volume fractions of martensite and bainite. The findings in this work show that tempering martensite during aging drastically hinders the hardening of copper precipitates.

Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN

The microstructure of oxidized Ni/Au films on p-GaN was examined to elucidate the formation of a low resistance ohmic contact to p-GaN with a field-emission gun transmission electron microscope in conjunction with composition analyses. The p-GaN/Ni/Au samples were heat treated at 500 °C in air mainly composed of a mixture of crystalline NiO, Au, and amorphous Ni–Ga–O phases. Small voids adjacent to the p-GaN film were also observed. The as-deposited Au film converted into discontinuous islands containing small amounts of Ni that connect with p-GaN. NiO formed a continuous film at the surface that covers the Au islands and the amorphous Ni–Ga–O phases. Moreover, NiO partially contacts p-GaN as well as Au islands and the amorphous Ni–Ga–O phase. The orientation relationship of the crystalline NiO, Au-rich islands, and p-GaN film was identified as NiO(111)//Au(111̄)//GaN(0002) and NiO[11̄0]//Au[11̄0]//GaN[112̄0]. The results suggested that Ni atoms diffuse through the Au layer onto the surface and react with oxygen to form NiO, whereas Au atoms diffuse towards the inside to form a Au–Ni alloy. The microstructural examination indicated that the crystalline NiO and/or the amorphous Ni–Ga–O phases may significantly affect the low resistance ohmic contact to p-GaN.

Microstructure, magnetic properties and giant magnetoresistance of granular Cu-Co alloy

The microstructure in a granular Cu88Co12 alloy was investigated by means of x-ray diffraction (XRD), a field ion microscope with atom probe (AP-FIM) and a field emission gun-transmission electron microscope (FEG-TEM) with energy dispersive x-ray spectroscopy (EDS). Giant magnetoresistance (GMR) and magnetic properties were studied to clarify the relationship between the GMR, magnetic properties and microstructures. The morphology of nanometre-sized cobalt granules within the grains were directly determined utilizing AP-FIM and FEG-TEM with EDS. Most cobalt granules are spherical and some others are plate-like in shape. GMR was observed in alloys with an average granule size ranging from 1.5 to 6 nm in diameter. TEM investigations showed that larger Co-rich precipitates formed at grain boundaries. The magnetic properties of the granular alloy were interpreted using the microstructure information and the dependence of GMR on magnetization was discussed.

Electron Microscopy Analysis of Grain Boundary Structure and Composition in Superplastically Deformed Al-Mg Alloys

Evaluation of grain boundary composition and structure in superplastically deformed AA5083-based alloys (AI-4.5Mg-1.6Mn-0.2Zr) was carried out in a field-emission gun transmission electron microscope (FEG-TEM). During superplastic deformation at high homologous temperatures materials undergo extensive grain boundary sliding (GBS) which creates a flow of defects in the near-boundary region. Recent literature has shown that the grain-boundary composition in Al-Mg alloys is not necessarily the same as the matrix, and that these differences can have an effect on GBS.Two alloy conditions were tested, with slightly different particulate content and superplastic deformability. Samples were tested at temperatures of 400°C and 450°C and a strain rate of 1x10-−3s−1 to vary the degree of grain boundary sliding, then quenched under load to preserve as much of the high-temperature structure as possible. TEM samples were prepared by carefully punching disks from the gage section of the deformed sample and electropolishing. Additionally, one sample was brought up to temperature and quenched but not deformed.

Analytical Electron Microscopy of nanometer-size precipitates in al alloys with a 200-kV field-emission TEM

Certain trace elements are known to have a pronounced effect on the nucleation kinetics of metastable phases in Al alloys. This provides many opportunities for alloy design. Understanding the role of trace elements in the precipitation process is difficult because they are typically present at levels of less than 0.1 at.% and involve early stages of clustering or segregation to precipitates. This paper presents recent results from the application of a 200 kV thermal field-emission gun (FEG) transmission electron microscope (TEM) to study trace element additions and the early stages of precipitation in Al alloys, using the case of an experimental alloy designated ALMAGEM as an example.An Al-2.41Cu-0.34Mg-0.lSi-0.04Ge alloy was cast into a book mold, homogenized, solution treated at 525°C, water quenched and aged for 12.5 h at 170°C to peak hardness. Disks 3 mm in diameter were electropolished in a HNOs/methanol solution and examined at 200 kV in a JEOL 2010F FEG TEM with a high-tilt (±30°) pole piece.