The World’s Smallest Galvanic Cell
In recent years chemists have become increasingly interested in “nanotechnology”, that is, the manipulation of chemical systems on the atomic and molecular scale. (A typical atomic radius is 0.1 nm). This approach helps chemists to better understand the mechanisms of various processes and opens the way for fabricating materials in a controlled way, by adding atoms one at a time.
One product of this research is a nanometer – scale galvanic cell. In 1992 chemists at the University of California Irvine used the scanning tunneling microscope to deposit minuscule dots of metals close to each other on a surface. The galvanic cell they made consists of four electrodes – two copper and two silver–in the shape of mounds on a crystalline graphite surface. The mounds measure 15 to 20 nm in diameter and 2 to 5 nm in height, the overall dimension of the cell is 70 nm, which is about a hundredth the size of a red blood cell. When the cell is immersed in a dilute copper sulfate solution, the copper mounds begin to dissolve and copper atoms start to plate on the silver mound. The half – reactions are
Copper anode: Cu (s) -> Cu2+ (aq) + 2e-
Silver cathode: Cu2+ (aq) + 2e- -> Cu (s)
Note that this is a net transfer of copper from the anode to the cathode via the Cu2+ ions in solution. Externally, electrons flow from the anode to the cathode through the graphite. Such a cell generates about 20 mV and a tiny current (1x10-18 ampere).
Understanding electrochemical processes at the atomic level has great significance in solid – state electronics, particularly in the semiconductor field. The fact that chemists can now investigate redox processes on a microscopic scale will also enable them to better understand metal corrosion and find ways to prevent it. Sometimes thinking small can be as important as studying reactions in a beaker
manipulation: sự vận dụng
fabricating: chế tạo, sản xuất
minuscule: nhỏ xíu, rất nhỏ
dot: điểm, chấm nhỏ
dimension: kích thước
externally: bên ngoài