Cross-sectional Transmission Electron Microscopy Specimens Research Articles

Progress in the Preparation of Cross-Sectional TEM Specimens by Ion-Beam Thinning

Abstract In transmission electron microscopy (TEM), often the preparation of samples is the most critical part. Specimens have to have disk geometries of 3 mm diameter laterally, and they have to be transparent for the electron beam vertically. Therefore, a specimen thickness in the range of some 1–10 nm has to be achieved by the preparation process. While shrinking the specimen dimensions, care has to be taken to recover the materials properties in the nm-regime. We report and shortly discuss some TEM specimen preparation techniques mainly used in the Stuttgart TEM specimen preparation laboratory. Furthermore, we demonstrate how more advanced techniques lead to a more reliable preparation of weakly-bonded metal/SrTiO3 interfaces. In addition, the advantage of low-voltage ion-milling is demonstrated by a case study for bulk SrTiO3. As a result, low-voltage ion polishing as a final step in the TEM specimen preparation by conventional ion-thinning turns out to significantly increase the specimen quality. In...

Characterisation of PI 3 and RF plasma nitrided austenitic stainless steels using plan and cross-sectional TEM techniques

Type 304 and 316 austenitic stainless steels treated with plasma immersion ion implantation (PI 3™) and RF plasma nitriding have been studied with transmission electron microscopy (TEM). A range of TEM specimen preparation techniques have been used to enable characterisation of the nature of the treated surface layers. Plan view TEM specimens, prepared by thinning from the back, highlighted the removal by sputtering of original surface features in steels during PI 3 processing, while the less energetic RF plasma nitriding retained the original surface features. All treatments resulted in the formation of an austenite phase heavily expanded by the high levels of interstitial nitrogen. Decomposition of this expanded austenite into CrN and α Fe occurred at higher treatment temperatures, and was found to nucleate at the grain boundaries preferentially. Conventional cross-sectional TEM specimens also showed the importance of the surface as a nucleation site for this transformation. The transformation process and the products of expanded austenite decomposition were the same regardless of the treatment process used. The expanded austenite layer was aligned with the underlying steel, with no orientational difference across the interface observed. Focused ion beam milling has the ability to consistently section treatment depths of several micrometers, although further work is necessary to produce through-section specimens thin enough for EELS and EFTEM analysis.

The use of the focused ion beam technique to prepare cross-sectional transmission electron microscopy specimen of polymer solar cells deposited on glass

The use of the focused ion beam (FIB) technique for cross-sectional transmission electron microscopy (TEM) specimen preparation of polymer solar cells deposited on glass substrates is described. Ultra-thin sections were prepared using the ‘lift-out’ technique. Electron microscopy investigations of these specimen resulted in detailed morphological information of the devices (e.g. thickness and interface roughness of the layers). In comparison with standard sample preparation routes for TEM investigations the used technique is well suited for precise sectioning of hybrid structures.

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.

Redeposition Effects During the FIB Milling of Silicon

The technique for the preparation of specimens for transmission electron microscopy (TEM) using the focused ion beam (FIB) miller typically consists of a series of milling steps performed over both sides of an area of interest until an electron transparent membrane is achieved [1]. This process is often accompanied by the formation of damage layers on the surfaces of the specimen. The origins of any damage layer are still not clear. On one hand the process of amorphisation of the target material by the highly energetic ion beam is well known. Alternatively, other workers have reported that this damage layer can be connected with redeposition of milled material. [2,3]. in this paper we have studied redeposition effects during FIB milling of silicon TEM specimens.A FEI xP200 FIB system with a Ga+ ion source operating at 30 kV was used in this work. to study redeposition effects a row of trenches on a silicon specimen was milled under different beam currents ranging from 1000 to 6600 pA. The size of such trenches was 15x10 μm wide and 1 μm deep. The specimen was then removed from the FIB and sputter coated with a ∼50-100 nm thick Au film to preserve the trench surfaces from further damage during subsequent milling. The specimen was then placed back in the FIB system and a second set of trenches 5×8 μm wide and 0.6 μm deep was milled on the bottom of first set of trenches (Fig. 1a). The specimens were sputter coated with Au again and were placed back in the FIB system and the trenches were then covered with 1 μ thick Pt strips using the metal deposition facility of the FIB. The presence of these protection layers (Au and Pt) ensures that the final TEM specimen have unmodified original damage layers resulting from the initial milling steps. Cross-sectional TEM specimens of the trench walls were then prepared using normal FIB procedures (Fig. 1b) [2].

Preparation of cross-sectional transmission electron microscopy specimens of obliquely deposited magnetic thin films on a flexible tape

In this article a method is described for preparing cross sections of obliquely deposited metal thin films on polymer substrates for transmission electron microscopy (TEM) observation. The layers of interest are brittle in nature and therefore it is difficult to obtain suitable TEM samples with conventional methods. Apart from the sample preparation method some details of the deposition technique will be elucidated.

In situ transmission electron microscopy study of thermal-stress-induced dislocations in a thin Cu film constrained by a Si substrate

Thermal-stress-induced dislocation motion in a Cu film on an amorphous SiN x (a-SiN x ) passivated Si substrate was investigated by in situ transmission electron microscopy (TEM). Plan-view, in situ TEM experiments revealed a relatively constant dislocation density of 3.4×10 9–5.9×10 9 cm −2 throughout thermal cycling. However, dislocation motion was strongly temperature dependent. At elevated temperatures dislocation moved continuously, while at temperatures below ∼220°C dislocation motion became jerky with a projected mean free path of ∼70 nm. Furthermore, cross-sectional TEM specimens revealed that dislocations were attracted and pulled into the Cu/a-SiN x interface, where upon dislocation contrast disappeared. The limited dislocation mobility observed at low homologous temperatures may contribute to the high yield stress of the Cu films.

TEM Specimen Preparation of Oxidized Ni-Base Alloys using the Focused Ion Beam (FIB) Technique

Abstract Microstructural characterization of thin alumina scales formed on oxidized Ni-base alloys using transmission electron microscopy (TEM) has long been a challenge as a result of the many problems encountered during the preparation of thin specimens. Successful and reproducible preparation of uniformly thin, cross-section TEM specimens from these multicomponent “layered” structures (alumina scale on a metallic substrate) is extremely difficult using standard ion beam thinning procedures for several reasons: (1) differential thinning of the various constituents in the system can occur, (2) a weak ceramic-metal interface may lead to separation during the harsh mechanical grinding and thinning procedure, (3) fully intact scales are rarely achieved since native surface structures are usually lost during ion milling, and (4) extensive damage can be created in the scale and alloy during rough grinding and polishing steps as well as during final ion beam thinning.

Method for Cross-sectional Transmission Electron Microscopy Specimen Preparation of Composite Materials Using a Dedicated Focused Ion Beam System.

: A new method for transmission electron microscope (TEM) specimen preparation using a focused ion beam (FIB) system that results in a lower rate of gallium (Ga) implantation has been developed. The method was applied to structural and analytical studies of composite materials such as silicon (Si)-devices and magneto-optical disk. To protect the specimens against Ga ion irradiation, amorphous tungsten (W) was deposited on the surface of the specimen prior to FIB milling. The deposition was quite effective in reducing the Ga implantation rate, and energy-dispersive X-ray (EDX) analysis of these specimens detected 0.3-1.5% Ga incorporated in the thinned area. FIB milling times for these specimens were 1.5-2 hr, with a starting thickness of about 50 µm. Although the milling rate was high, all the materials were properly prepared for TEM study, and clear crystal lattice images were observed on all specimens.

Applications of focused ion beam microscopy to materials science specimens

Focused ion beam (FIB) systems based on high-brightness gallium liquid-metal ion sources became commercially available in the late 1980s, although even today such instruments are relatively rare outside the somewhat enclosed world of semiconductor manufacturing. The use of FIB systems as precision sectioning tools down to a submicron scale and their ability to deposit metals and insulators on a micron scale is well documented. Recently, FIB systems have achieved spatial resolution rivaling that of the standard scanning electron microscope, giving them respectable capability as an imaging tool in addition to their sectioning and deposition capabilities. This improved resolution and novel FIB contrast mechanisms combined with the capability of FIB to produce in-situ stress-free bulk cross-sections and precision cross-sectional transmission electron microscopy specimens has recently attracted great interest among materials scientists. Examples of the use of FIB in materials science, both as a specimen preparation tool and as a microscope in its own right, are illustrated.

A review of focused ion beam milling techniques for TEM specimen preparation

The use of focused ion beam (FIB) milling for the preparation of transmission electron microscopy (TEM) specimens is described. The operation of the FIB instrument is discussed and the conventional and lift-out techniques for TEM specimen preparation and the advantages and disadvantages of each technique are detailed. The FIB instrument may be used for rapid site-specific preparation of both cross-section and plan view TEM specimens.

Transmission electron microscopy study ofInxGa1−xAsquantum dots on a GaAs(001) substrate

A transmission electron microscopy (TEM) investigation of the morphology of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum dots grown on a GaAs(001) substrate has been carried out. The size and the shape of the quantum dots have been determined using bright-field images of cross-section TEM specimens and [001] on-zone bright-field images with imaging simulation from plan-view TEM specimens. The results suggest that the coherent quantum dots are lens shaped with base diameters of $25--40 \mathrm{nm}$ and aspect ratios of height to diameter of $1:6--1:4$.

Spontaneous twin formation in ZnSe films grown by molecular beam epitaxy

Abstract Defects present in molecular-beam-epitaxy (MBE}-grown ZnSe films on GaAs(100), Ge(100) and Si(100) substrates were studied using transmission electron microscopy and X-ray pole figures. Growth twins, lying preferentially on two of the four possible {111} planes, were the primary defects. A mechanism for spontaneous twin formation, based on the orientation of initial nuclei for three-dimensional island nucleation and growth, is postulated. The anisotropic distribution of twins and their visibility in cross-sectional transmission electron microscopy specimens has been explained using the model.

Spontaneous twin formation in ZnSe films grown by molecular beam epitaxy

Abstract Defects present in molecular-beam-epitaxy (MBE}-grown ZnSe films on GaAs(100), Ge(100) and Si(100) substrates were studied using transmission electron microscopy and X-ray pole figures. Growth twins, lying preferentially on two of the four possible {111} planes, were the primary defects. A mechanism for spontaneous twin formation, based on the orientation of initial nuclei for three-dimensional island nucleation and growth, is postulated. The anisotropic distribution of twins and their visibility in cross-sectional transmission electron microscopy specimens has been explained using the model.

Microstructure of PbTi03/SrTi03 Superlattice Grown by MBE

Abstract Ferroelectric superlattices have been actively and intensively studied in recent years for their great scientific and technological interest. Superlattice containing Pb-based ferroelectric layers are important among ferroelectric superlattice systems, however, it is difficult to grow such superlattice due to the high volatility of Pb. Recently, great progress has been made in fabricating superlattice structure of PbZrO3/PbTiO3 by multi-ion-beam sputtering’ and molecular beam epitaxy (MBE). In this paper, we report the microstructural investigations of PbTiO3/SrTiO3 superlattice films, which were epitaxially grown on the SrTi03 substrate by MBE, using transmission electron microscopy (TEM). [(PbTiO3)l0/(SrTiO3)l0]15 superlattice films were stacked on (100) SrTiO3 substrate alternately by MBE. Before growing the superlattice structure, a baffle layer including the 1000Å La-doped SrTi03 and the subsequent 500 Å PbTiO3 thin films was grown on the substrate. Above the PbTi03/SrTi03 superlattices, another PbTi03 thin film (1000 Å) was grown. Cross-section TEM specimens were prepared by standard methods.

Microstructure and Strain Relaxation of Epitaxial SrRuO3 Films

Abstract It is widely believed that the stress in the epitaxial thin films, caused by the lattice mismatch between the thin film and substrate, has a strong influence on the properties. For example, lattice strained epitaxial thin films of SrRu03 grown on (001) SrTiO3 demonstrated magnetic and electrical properties different from those in bulk materials.1 In this paper, we report the effect of strain relaxation of the thin film on microstructure by means of transmission electron microscopy (TEM). SrRuO3 thin film on a vicinal (001) SrTiO3, with a miscut angle 0.9° and miscut direction 5.7° away from the in-plane [100] axis, was grown by 90° off-axis sputtering. Cross-section and plan-view TEM specimens were prepared following the procedure described in Ref. 2. TEM investigations were conducted in a Philips CM 12 microscope in the EMAL at the University of Michigan. X-ray diffraction studies of the as-grown SrRu03 thin film using a four-circle diffractometer showed that the film consists of a single [ 110]-type domain structure.

Epitaxial growth of magnetic Au/Co/Au sandwiches studied by TEM

Au/Co(4 ML)/Au sandwiches grown on molybdenite substrates and showing strong perpendicular anisotropy have been studied by transmission electron microscopy (TEM). The growth characteristics and relaxation mechanisms of the ultrathin magnetic layers have been determined by combining information given in plan view and cross-sectional TEM specimens micrographs. In-plane and out-of-plane elastic strains in the Co layer have been deduced from the measurement of moiré fringes spacing and atomic planes spacing obtained by high-resolution imaging followed by image processing. Our results give evidence for an island growth mode of the Co layer and a volume expansion of the cobalt lattice. They are analysed through the comparison with results obtained by other experimental techniques and in particular, in noncovered cobalt layers.

Cross-Section TEM Study On Kr+ Irradiation-Induced Amorphization in Quartz

Abstract Radiation damage in quartz has been of interest to the semiconductor industry, optical fiber industry, and nuclear industry. Cross-section transmission electron microscopy (TEM) is a powerful tool for investigating the irradiation effects since it provides a direct measurement of the ion and the damage distributions, and can also provide detailed microstructural information such as the presence of amorphous regions and the size, density and chemical nature of defect aggregates. The results reported below are from a systematic cross-section TEM study on 1.5 MeV Kr+ ion irradiated quartz. 3-mm discs of quartz (along 010 face) were prepared with 100 μm in thickness. One side for each discs was well polished using a 0.05 μm diamond paste. The well-polished side was irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory. Following irradiation, cross-section TEM specimens were prepared using the so-called T-tool technique, a modified tripot technique

Characterization of Chemically Vapor Deposited GaN on Sic on a Simox Substrate

Abstract GaN has been intensively studied because of its potential applications for the fabrication of blue- or ultraviolet-light emitting devices. Sapphire (α-Al2O3) is generally used as the substrate for growth of GaN film. However, the large lattice mismatch between GaN and Al2O3is a possible cause of the large defect density in the GaN films. Consequently, alternative substrates are being studied with the aim of growing films of lesser defect densities and improved opto-electronic properties. In this paper, we report a transmission electron microscopy (TEM) study of a GaN film grown on cubic SiC which has been obtained by carbonization of the top silicon layer of a SIMOX substrate, i.e. the system GaN/SiC/Si/SiO2/Si. Cross-sectional TEM specimens were prepared by the conventional sandwich technique with the foil surface normal to the Si[l10] direction. The composite sample was ground and dimpled to a thickness of ∼ 10μm, and subsequently ion thinned to electron transparency.

Electron irradiation induced crystallization of amorphous MgAl 2O 4

Using transmission electron microscopy (TEM), an electron beam was used to irradiate cross-sectional TEM specimens of an amorphous MgAl 2O 4 thin film on a single crystal spinel substrate. Amorphous MgAl 2O 4 thin films of 160 nm thickness were initially formed by 400 keV Xe ion irradiation at liquid nitrogen temperatures in single crystal spinel substrates. It was observed that electron irradiation at 300 keV induced a phase transformation from an amorphous to a metastable crystalline structure. Crystallization of amorphous MgAl 2O 4 was observed to occur both at the amorphous/crystalline interface by epitaxial growth and in the amorphous region by nucleation and growth. Under large doses of electron irradiation, a polycrystalline metastable phase was formed over the entire amorphous region. In contrast, thermal annealing at 600 °C for 1 h only produced negligible crystallization at the amorphous/crystalline interface. The major driving force for crystallization is the energy difference between the amorphous phase and the metastable crystalline phase. Electron irradiation provides the necessary defects to kinetically drive the transformation.