Three-dimensional rendering of a large area image of the standard sample. Five identical convoluted images of the tip profile can be seen on the position of each Si spike. The scale bar indicates the dimension in x – y directions. 

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... all cleaning agents. The results obtained in this second phase allowed a fine tuning of results obtained in the first phase, ultimately enabling the proposal of a simple recycling route for used SPM tips. Table 1 summarizes the final results after all tests over a hundred ! . Only the most efficient cleaning processes are shown, with their respective optimized cleaning agent combinations and duration times. When inorganic material only is contaminating the SPM tip, the present studies have shown that bathing for 10 s in hydrochloric acid solution 1% v / v, or in hydrofluoric acid solution 1% v / v, followed by 30 s sonication in deionized water are the two most efficient cleaning methods. It must be noted that the HF solution is very aggressive to the SPM tip and eventually damages it if long bathing times are employed. On the other hand, it is very efficient in removing large amounts of inorganic material, and, therefore, is considered an excellent cleaning option when only inorganic contamination is present. Figure 1 illustrates a typical application of HF cleaning. In Figure 1a, a convoluted image of the standard sample indicates the profile of a new SPM tip. The scale bar on the right indicates the SPM tip dimensions in x , y , and z directions. The image in Figure 1b shows the physical profile of the same tip after inorganic material ~ calcium carbonate ! has been purposely aggregated. The enlargement of tip lateral dimensions is evident in this image. Such a tip would normally be considered inadequate for further scans and would usually be discarded. However, after the HF treatment described in Table 1, the tip came out completely clean, as shown in the image of Figure 1c. Actually, it is interesting to note that, in a comparison with Figure 1a, the tip appears to be even sharper than it initially was. It is important to stress that the images in Figure 1a, b, and c are not artifacts due to nonhomogeneities in the standard sample, that is, apart from convolution effects, they represent the true morphology of the SPM tip under investigation. Any effects of nonhomogeneities in the standard sample, like a broken Si spike, are prevented by initially imaging a large area of the sample encompassing several Si spikes and thus producing several convoluted images of the SPM tip. Figure 2 illustrates such a procedure showing, at a different view angle, five images of the tip shown in Figure 1b. Since all images look identical, it is assumed that the standard sample is correctly imaging this SPM tip and, thus, an image of a single Si spike was acquired ~ Fig. 1b ! and used to characterize the tip physical profile. The cleaning efficiency of the HF solution for different types of inorganic contaminants may not be associated with a direct attack on the aggregated material. Rather it seems to be associated with the removal of the silicon oxide layer that always covers a silicon-made SPM tip, either new or used. It is well known in the semiconductor community that HF readily dissolves silicon oxide ~ Ghandhi, 1994 ! . Removing such an oxide layer, where the inorganic contaminants are attached, leads to cleaning of the SPM tip. This oxide removal may also explain the observation that the cleaned tip in Figure 1c appears to be actually sharper than the new tip in Figure 1a. However, such a general and, ...