TEM samples

In the early days of TEM, sample preparation was divided into two categories, one for thin films and one for bulk materials. Thin-films, particularly metal layers, were often deposited on substrates and later removed by some sort of technique involving dissolution of the substrate. Bulk materials were cut and polished into thin slabs, which were then either electropolished (metals) or ion-milled (ceramics). The latter technique uses a focused ion beam (typically Ar+) of high-energy, which sputters the surface of the thinned slab. These techniques produce so-called plan-view thin foils. 

These authors produced TEM samples of Bi-doped, Sb-doped and Ag-doped copper foils, thinned to electron transparency using conventional preparation procedures. In all cases the presence of impurity segregation was confirmed using conventional X-ray energy-dispersive spectrometry. The EELS measurements were carried out with a STEM operating at 100 keV, with a nominal probe size of 1 nm (full width at half maximum) with a current of about 0.5 nA. The conditions required to optimize detection sensitivity for interface analysis require the highest current density and are not consistent with achieving the smallest probes. 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

The OLED is composed of hard and soft layers so that the conventional cross-sectional TEM sample preparation techniques cannot be applied. Figure 10.3 is a first DB microscopy-prepared TEM image of an OLED in cross-sectional view [37], The glass substrate, ITO, organic layers, and A1 cathode are indicated in the image. The microstructure and interfaces of all these layers can be well studied now. The nanometer-sized spots in organic layers are indium-rich particles. We believe the combination of DB microscopy and TEM will greatly advance the OLED research and development in the near future. 

The thin film approximation assumes that absorption of X-rays within the sample (and any second order efifeet ensuing from absorption) is negligible. It is a good approximation for many of the TEM samples. Within this approximation the detected intensity (Iac) for the analytical line (a) of element A is proportional to the number of generated X-rays (Gao) and the detection efficiency (Pao) for this line. 

In terms of the common features of colloids just listed, nanoparticles with a clean surface have tendency to amalgamate when placed on a TEM sample mesh that is evident in Figures 9.4.16 and 9.4.17. Furthermore, the particles often grow by collision (not by Ostwald ripening because metal ions are hard to dissolve in organic liquids) in the suspension state when the number density of particles in... 

Bulk spectroscopic techniques such as x-ray fluorescence and optical and infrared spectroscopies involve minimal sample preparation beyond cutting and mounting the sample. These are discussed in Section 9.2.1. Spectroscopic techniques such as wavelength dispersive spectroscopy (WDS) and energy dispersive spectroscopy (EDS) are performed inside the SEM and TEM during microscopic analysis. Therefore, the sample preparation concerns there are identical to those for SEM and TEM sample preparation as covered in Section 9.3. Some special requirements are to be met for surface spectroscopic techniques because of the vulnerability of this region. These are outlined in Section 9.5. 

As mentioned earlier, once a TEM sample is cut into a thin roughly uniform slice, it needs to be thinned extensively in regions where it will be electron transparent. In extremely rare cases of synthetic materials, the specimen itself can be prepared as a thin film. This is often the technique used to make... 

Focused Ion Beam (FIB) Selective choice of the interface of interest to prepare TEM samples from... 

The metallic layers were examined either by conventional or cross-section TEM in a Jeol 200 Cx microscope. For the cross section preparation a sandwich of two laminates is made, glued face to face with an epoxy, cut in small pieces, mechanically polished, and then ion milled to a final TEM observation thickness. The plane section TEM sample are prepared by dissolving the PET in trifluoroacetic acid for 5 to 10 mn. The area observed, on plane section TEM, for the grain size calculation is close to 0.2 urn. For the adhesion measurements, test pieces consist of aluminum support (1 mm thick) double sided tape (Permacel P-94) PET (12pm) / evaporated aluminum/ ethylene acrylic acid (EAA) copolymer film. These laminates are prepared for the peel test by compression under 1.3 105 N.m2 at 120°C for 10 seconds. The peel test is performed by peeling the EAA copolymer sheet from the laminate in an INSTRON tensile tester at 180° peel angle and 5 cm min peel rate. 

Cmcial to the success of ab initio stmcture determinations is the collection of 3-D diffraction data. The conventional TEM sample holders can handle limited rotation... 

Figure 7.10. Sectioning of a TEM sample using an ultramicrotome instrument. Shown is an ultramicrotome instrument with a built-in nitrogen cryogenic system, used to section samples with a thickness of 25 nm-5 mm.h7l Also shown is a TEM image of polymer capsules that have been sectioned using an ultramicrotome instrument. Image reproduced with permission from Dai, Z. Mohwald, H. Langmuir 2002,18, 9533. Copyright 2002 American Chemical Society.

The morphology of the BT powders was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A small amount of the BT powders were pressed on a carbon tape, which attached to the brass sample stub for SEM. To prepare TEM samples, a tiny amount of the BT particles was dispersed in isopropanol by grinding in an agate mortar before placing it on a copper grid. 

Figure 1. Example of a TEM sample prepared for in-depth EELS analysis of a breakdown spot in ultrathin gate dielectrics. The width, W, of the nanosize transistor has to be kept below 0.4 pm so that the probability of capturing a breakdown defect is relatively high while the length, L, can be ranged from sub-micrometer to a few micrometers. The shaded aea is the te dielectric beneath the gate electrode, typically polysilicion.

Prior to the physical analysis by the TEM, the electrical behavior of the dielectric layer is routinely characterized and then stressed to induce a breakdown using the standard constant voltage stress methodology [9]. However, in order to ensure that the dielectric breakdown spot has a high probability of being captured in the TEM samples, the width, i.e., W, of about 0.4 pm or less of the transistor shown in Fig. 1 has to be selected [10-14]. 

As a result of shell-crosslinking, the one-dimensional micellar structures were locked-in and preserved even if transferred from hexane to a common solvent for both blocks.26,49 Figure 3.6 illustrates a TEM image for PI32o- -PFS53 shell-cross-linked micelles. The TEM sample was prepared from a micellar solution in THF, a common solvent for both PFS and PI blocks. 

In the TEM samples, the rubber domains are uniformly distributed and on the order of a few hundred angstroms in size. The micrographs also show the presence of domains that have no rubber in them. The rubber-free domains probably contain polyester and epoxy that have reacted, but it is not possible to confirm this possibility. Styrene-cross-linked polyester has a Tg of 185 °C. When the epoxy is introduced in a 1 2 ratio (epoxy-.polyester), Tg de-... 

---