**2.5 Characterization**

56 Recent Advances in Nanofabrication Techniques and Applications

Sheme 3. Shematic setup of the sample exposure to MAB for atom lithography.

a good repetition of the lithographic patterns in different runs.

During exposure He\*-MAB impacted the surface of SAM formed on silicon substrate after the beam was patterned in transverse direction by the TEM grids. Atoms with kinetic energy smaller than 1eV do not pass freely through materials. So, the physical mask (i.e., TEM grids) with thickness in the order of sub-micrometers was enough to pattern the He\*- MAB. Our experimental results showed good reproducibility with a high fidelity of the patterns of the TEM copper grids and TEM holey carbon grids (shown in figure 1), as well as

Fig. 1. (a) SEM image of TEM Cu grid used as a mask (Note: the pitch size of patterns is 12.5 um, 5.5 um for wires, and 7.0 um for spaces) and (b) SEM image of TEM holey carbon grid used as a mask (Note: The diameters of the circular holes are about 1, 1.4, and 2µm, the bar widths range from 0.5 to 4µm, the oval holes with a dimension of 8х2µm and 4х1 µm).

Two kinds of physical masks (i.e., TEM Cu grids and TEM holey carbon grids) were used in our experiments. The SEM images and parameters of the TEM grids were shown in figure 1. AFM images of the samples were taken by a multimode Nanoscope IV atomic force microscope (Veeco Metrology Group, Santa Barbara, CA), operated at ambient conditions. For all images we recorded the retrace direction of the tip using a scan angle of 0º or 90º. Substrates decorated with organosilanes SAMs were imaged in tapping mode using silicon cantilevers (NanoWorld, Neuchâtel, Switzerland) with a spring constant of 42 N m-1. All images were recorded at a rate of 1.0 Hz, and with a pixel resolution of 512. SEM inspection of patterned Si substrates and the masks were carried out with a JSM-6500/SG scanning electron microscope operated at 30 keV.
