13.2. NANOELECTROMECHANICAL SYSTEMS (NEMSs)
337
Imprint
Press Mold
f l mold
Remove Mold
Pattern Transfer
Figure 13.3. Schematics of steps in a nanoimprint lithography process: (a) a mold of a hard
material made by electron beam lithography is pressed into a resist, a softer material, to make an
imprint; (b) the mold is then lifted off; (c) the remaining soft material is removed by etching from
the bottom of the groves. [Adapted from S. Y. Chou et al., Science 272, 85 (1996).]
The scanning tunneling microscope has been used to build nanosized structures
atom by atom on the surface of materials. An adsorbed atom is held on the surface
by chemical bonds with the atoms of the surface. When such an atom is imaged in an
STM, the tip has a trajectory of the type shown in Fig. 13.4a. The separation between
the tip and the adsorbed atom is such that any forces between them are small
compared to the forces binding the atom to the surface, and the adsorbed atom will
not be disturbed by the passage of the tip over it. If the tip is moved closer to the
adsorbed atom (Fig. 13.4b) such that the interaction of the tip and the atom is greater
than that between the atom and the surface, the atom can be dragged along by the tip.
At any point in the scan the atom can be reattached to the surface by increasing the
separation between the tip and the surface. In this way adsorbed atoms can be
rearranged on the surfaces of materials, and structures can be built on the surfaces
atom by atom. The surface of the material has to be cooled to liquid helium
temperatures in order to reduce thermal vibrations, which may cause the atoms to
diffuse thermally, thereby disturbing the arrangement of atoms being assembled.
Thermal diffusion is a problem because this method of construction can be carried
337
Imprint
Press Mold
f l mold
Remove Mold
Pattern Transfer
Figure 13.3. Schematics of steps in a nanoimprint lithography process: (a) a mold of a hard
material made by electron beam lithography is pressed into a resist, a softer material, to make an
imprint; (b) the mold is then lifted off; (c) the remaining soft material is removed by etching from
the bottom of the groves. [Adapted from S. Y. Chou et al., Science 272, 85 (1996).]
The scanning tunneling microscope has been used to build nanosized structures
atom by atom on the surface of materials. An adsorbed atom is held on the surface
by chemical bonds with the atoms of the surface. When such an atom is imaged in an
STM, the tip has a trajectory of the type shown in Fig. 13.4a. The separation between
the tip and the adsorbed atom is such that any forces between them are small
compared to the forces binding the atom to the surface, and the adsorbed atom will
not be disturbed by the passage of the tip over it. If the tip is moved closer to the
adsorbed atom (Fig. 13.4b) such that the interaction of the tip and the atom is greater
than that between the atom and the surface, the atom can be dragged along by the tip.
At any point in the scan the atom can be reattached to the surface by increasing the
separation between the tip and the surface. In this way adsorbed atoms can be
rearranged on the surfaces of materials, and structures can be built on the surfaces
atom by atom. The surface of the material has to be cooled to liquid helium
temperatures in order to reduce thermal vibrations, which may cause the atoms to
diffuse thermally, thereby disturbing the arrangement of atoms being assembled.
Thermal diffusion is a problem because this method of construction can be carried