Thin-film specimen preparation

THIN FILM SPECIMEN PREPARATION. Iodinated polystyrene (IPS) and polystyrene (PS) were dissolved separately in toluene at 0.5w% concentration. These two solutions were mixed to obtain a ratio of IPS to PS ranging from 1 1 to 1 100. For ratios below 1 100 the solution of IPS was further diluted by a factor of ten before mixing with the PS solution. The final solutions were stirred overnight before preparing the films. 

Film and sheeting materials test methods have been standardized by ASTM, DIN, and others. As with all materials, the test specimens must be carefiiUy prepared and conditioned. Thin-film specimens are vulnerable to nicks and tears which mar the results. Moisture and temperature can affect some materials. Common test methods are Hsted in Table 1. 

The most convenient and effective method for preparing a tip specimen is by electrochemical polishing of a piece of thin wire of 0.05-0.2 mm diameter. Usually the methods developed for electropolishing thin film specimens in transmission electron microscopes are also applicable for polishing field ion microscope tips.7 In Table 3.1 some of the commonly used emitter polishing solutions and conditions for the polishing are listed for various materials.8... 

Sample preparation In order to measure the interfacial thickness, always bilayer specimens were prepared containing a thick substrate (about 1mm) and a thin film on top (in the range from 15 to 100 nm). The substrates were melt-pressed between two silicon wafers at 200 °C. The thin films were prepared by spin-casting of the polymer solutions onto a silicon wafer and the resulting films were floated off onto a water surface. The floating films were then picked up with the substrate and dried at elevated temperatures in a vacuum oven. 

A thin film specimen must be prepared that is representative of the bulk and has a reasonably uniform thickness. 

The blend sample was compression molded into a thin film with 25-pm thickness at 300°C mold temperature and then was quickly quenched in ice water. The film specimen prepared in this procedure is amorphous. 

The primary consideration for all AEM analysis is that the specimen be thin (generally carbon coated electron microscope grid either dry or in a suitable liquid. If a liquid suspension is used in preparing the specimen, it is important that all elements of interest are insoluble in that liquid. Only particles thin enough to meet AEM thin-film criteria (15) should be analyzed quantitatively. Scraping surface particles from a catalyst pellet for specimen preparation may be more useful than grinding the entire pellet. 

The major disadvantages in application of the AEM method relative to AAS is the time required for specimen preparation and analysis. Care must be taken that the particles analyzed are characteristic of the bulk material, that they are thin enough to meet the "thin-film criteria" of Equations (2) and (3), and that enough particles are analyzed to reduce the random error to acceptable levels. The AEM analyses shown in Figure 6 took several days to collect and involved considerble operator attention. 

Fig. 11 Craze in commercial polystyrene showing the characteristic steps nucleation through void formation in a pre-craze zone, growth of the fibrillar structure of the widening craze by drawing-in of new matrix material in the process zone, and final breakdown of the fibrillar matter transforming a craze into a crack (the crack front is more advanced in the center of the specimen, shielded by a curtain of unbroken fibrils marked by the arrow). The fibril thickness depends—of course—on the molecular variables, the strain rate-stress-temperature regime of the crazing sample and on its treatment (preparation, annealing) and geometry (solid, thin film) for PS typical values of between 2.5 and 30 nm are found [1,60,61]...

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... 

A consistent protocol for the collection and analysis of thin-film EDS data requires an assessment of both instrument and specimen dependent parameters. Major parameters which should be considered for thin-film analyses include spurious X-rays, spectral artifacts, detector geometry, probe diameter, beam broadening, contamination, sample preparation artifacts, sample orientation and temperature and X-ray absorption. Many of these parameters are interdependant during an analysis and the prudent operator will evaluate as many as possible before routine use of an AEM. Further explanations of these parameters can be found in a number of publications [4,6.,9.,7] Only selected parameters are discussed below. 

The surface areas of dust samples as determined by optical and electron microscope have also been compared [167]. Pore size distributions of thin films of AI2O3, as measured by TEM, have also been compared with those determined by gas adsorption/desorption [168]. It has also been suggested that electron microscope gives a truer estimate of surface area than gas adsorption techniques [169]. Further information can be obtained in a recent review of specimen preparation for TEM [170]. 

Specimen preparation. Most HRTEM investigations have used specimens in the form of crushed fracture fragments supported on a holey carbon film attached to a standard copper grid. Specimens thinned by ion (or atom) bombardment are also used, but the amorphous film which tends to form on the surfaces of foils prepared in this way is sometimes too thick for successful high-resolution imaging. See also Section 2.7. 

---