Al

SOj/Si Substrate

Figure 13.21. Cross section of a molecular switch prepared lithographically, incorporating roxatane molecules that have the structure sketched in Fig. 13.20, sandwiched between aluminum electrodes, and mounted on a substrate. The upper electrode has a layer of titanium, and the lower one is coated with aluminum oxide. [Adapted from C. P. Collier et al., Science 285, 391 (1999).]

opened by applying 0.7 V The difference in the current between the open and closed switch was a factor of60-80. A number of these switches were wired together in arrays to form logic gates, essential elements of a computer. Two switches (A and B) connected as shown in die top of Fig. 13.23 can function as an AND gate. In an AND gate both switches have to be on for an output voltage to exist. There should be littie or no response when both switches are off, or only one switch is on. Figure 13.23 shows the response of the gate for the different switch positions, A and B (called address levels). There is no current flow for both switches off (A = B=0), and very little current for only one switch on (A = 0 and 5= 1, or A = 1 and B = 0). Only the combination A = 1 and B = 1 for both switches on provides an appreciable output current, showing that the

Figure 13.22. Current-voltage characteristics of the molecular switch shown in Fig. 13.21. [Adapted from C. P. Collier et al., Science 285, 391 (1999).]
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