Sample Preparation for TEM Analysis

TEM has been applied to the analysis of dry powder pigments, flushes, pastes, and dispersions. In most cases the sample preparation is quite simple. 

For dry colors, 5-10 mg of the sample is dispersed in 5-10 mL of ethanol in a small vial (15 mL size) by sonication for approximately 1 min. One drop of the dispersed sample is then transferred onto a grid on a piece of filter paper floating in the ultrasonic bath. The sonication is continued for another minute. If necessary, additional drops of sample are added to obtain enough samples for analysis. For flush, dispersion or ink samples approximately 1-2 mg is placed in 7 mL of toluene and sonicated to disperse the particles. If the sample bleeds in toluene a weaker solvent such as ether may be used. Small portions of the dispersed sample are added to the grid while continuing to sonicate until adequate amount is collected on the grid for analysis. 

The primary particle size of HPOP is usually in the range of 10 to 500 nm. More opaque pigments may have intentionally grown larger particles. Aggregates and agglomerates can be several micrometers in size. 

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Sample preparation for TEM analysis of colloidal metals is usually a simple procedure, involving the evaporation of a drop of suitably diluted colloid suspension onto a microscope grid. For polymer stabilized colloids, the polymer forms a thin transparent film by this procedure. Thin films can be alternatively prepared by ultramicrotomography of thick polymer/metal samples produced by evaporation of the liquid suspension. 

High-resolution TEM only probes a very small volume, which may or may not be representative of the total composite. Moreover sample preparation for TEM analysis is difficult and time-consuming. Therefore, the method is too costly for routine characterization of nanoeomposites. As a result researchers are now using melt rheology as a complementary method to analyse the dis-persion/exfoliation in polymer lay nanoeomposites. Several authors found that the shear thinning index, n, gives a semi-quantitative measure of the degree of exfoliation. 

What techniques are used to prepare thin sample sections for TEM analysis ... 

Sample preparation for SEM analysis is trivial relative to TEM, with the sample simply deposited onto the top of an adhesive fastened to an aluminum stub/holder. Most often, conductive carbon tape is used to sequester the sample for FESEM,... 

To develop a feeling for the sensitivity of the allocation scheme to values of ol and ag, we have prepared examples that reflect passive sampling, followed by TEM analysis. Me use values of Cl = 20 and C2 = 500 and evaluate the solution for total budgets of 5,000 and 15,000. These figures are based on typical costs for TEM analysis. Costs will vary among laboratories and depend on the analytical method (TEM, SEM, or PCM) chosen. Mote that Ol and Og... 

To prepare the sample for TEM analysis, put a drop of the chloroform suspension on a TEM grid and allow the solvent to evaporate. Alternatively, you may spray the solvent suspension onto a grid using an aerosol delivery device. 

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.

Transmission electron microscopy (TEM) is probably the most powerful technique for obtaining structural information of supported nanoparticles [115-118], Complementary methods are STM, AFM, and SEM. Both the latter and TEM analysis provide more or less detailed size, shape, and morphology information, i.e., imaging in real space. TEM has the great additional advantage to provide information in Fourier transform space, i.e., diffraction information, which can be transformed to crystal structure information. From a practical point of view, considering the kinds of planar model catalysts discussed above, STM, AFM, and SEM are more easily applied for analysis than TEM, since the former three can be applied without additional sample preparation, once the model catalyst is made. In contrast, TEM usually requires one or more additional preparation steps. In this section, we concentrate on recent developments of microfabrication methods to prepare flat TEM membrane supports, or windows, by lithographic methods, which eliminate the requirement of postfabrication preparation of model catalysts for TEM analysis. For a more comprehensive treatment of other, more conventional, procedures to make flat TEM supports, and also similar microfabrication procedures as described here, we refer to previous reviews [118-120]. 

Electron microscopic studies of fresh and used samples were provided with units EM-125K, Ukraine and JEM-IOOCX, Japan with a resolution of about 0.5 ran. Specimens for TEM-analysis were prepared by conventional methods with use both of dried suspension and extraction carbon replica. The identification of phases was performed with the help of ASTM (American Society for Testing and Materials, 1986). 

A JEOL lOOCX-II TEM, operating at 100 kV, was used to investigate the samples. The samples for TEM analysis were preparated through freeze-drying as above. 

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