 layer of atoms. They create two to five layers of stress-engineered metal by depositing the atoms with varying amounts of energy. They use a high level of energy for the bottom layer, causing the atoms to be packed very tightly. In successive layers, they use progressively less energy, until, at the top layer, the atoms land with very little force, analogous to that of gently falling snow. This technique harnesses both tensile and compressive stress of metal. Pairs of metal atoms act as springs, causing them to push apart (compressive stress) or pull closer (tensile stress) to maintain a consistent distance between them. Tensile stress is caused when the loosely spaced atoms at the top pull more tightly together, as their electron clouds overlap and bond to one another. Compressive stress is caused when the tightly packed atoms on the bottom layer expand and push away from each other. When the metal is freed from the sacrificial layer, the compressive and tensile stresses in each layer bend the metal into the prescribed shapes. 2.13.3 The Nanoguitar Several years ago, Cornell University researchers built the world's smallest guitar-about the size of a red blood cell -to demonstrate the possibility of manufacturing tiny mechanical devices using techniques originally designed for building microelectronic circuits. Now, by "playing" a new, streamlined nanoguitar (Fig. 2-4), Cornell physicists are demonstrating how such devices could substitute for electronic circuit components to make circuits smaller, cheaper, and more energy efficient. The guitar is SO small that it falls into the nano-electro-mechanical system (NEMS) family. NEMS usually refers to devices about two orders of magnitude smaller than MEMS. 2 micron Figure 2-4 Streamlined nanoguitar. NUTS AND BITS-TELECOM HARDWARE, SOFTWARE, AND MORE Lidija Sekaric, now a researcher at IBM's Watson Research Center in Yorktown Heights, New York, worked with Cornell graduate student Keith Aubin and undergraduate researcher Jingqing Huang on the new nanoguitar, which i