Electrochemical Atomic Layer Epitaxy Se on Au100

In the formation of the compound semiconductor CdSe on Au(100) by EC ALE [6] the chalcogenide is the choice for the first atomic layer due to its increased stability after loss of potential control. If Cd is deposited first, it undergoes partial but spontaneous oxidation by residual oxygen gas; in the presence of an Se adlayer, no such Cd oxidation occurs as it is now stabilized by compound formation with Se.

On Au(100), Se is cathodically deposited, from a HSe03" solution in, different atomic layer structures depending upon the duration and potential of electrodeposition. The structures formed were: Au(100)-p(2x2)-Se at a coverage 0 (= Se atoms/Au atoms) of 0.2, Au(100)-(2 x Vl0)-Se at 0 = 0.3, Au(100)-c(2 x 2)-Se at © = 0.5, and Au(100)-(3 x VlO)Se at © = 0.9 [61. The LEED patterns for the Au(100)-c(2 x 2)-Se and Au(100)-(2xVl0)-Se and adlattices are shown in Figs. 4(A) and 4(B), respectively.

Fig. 4. Low-energy electron diffraction (LEED) patterns. Top, Au(100)-c(2 x 2 )-Se at ® = 0.5; bottom, Au(100)-(3 x Vl0)-Se at © = 0.9. Beam energy = 62 eV; beam current = 2 pA.

Although the two-dimensional adlayer symmetries can quite readily be deduced from the LEED patterns, no information can be obtained on the chemical nature of the

Fig. 5. Scanning tunneling microscope images. Top, Au(100)-c(2x2)-Se at 0 = 0.5; bottom, Au(100)-(3xVl0)-Se at 0 = 0.9.

adlayer unless dynamical LEED simulations are performed [11], The inclusion of STM in the arsenal of surface structural tools often negates the requirement of such LEED simulations. This is clearly illustrated in Figs. 5(A) and 5(B) which, respectively, show the evolution of Ses rings as the coverage is increased from just above 0.5 to 0.9. Coincident with the development of the Seg rings was the formation on the surface of pits, a random occurrence that can be revealed only by STM experiments. Quantitative analysis of the STM images suggested that the pits (i) were monatomic in depth and, (ii) contained the same Ses ring structure at the bottom. The coverage of the pits accounts for about 10% of the total surface area at high Se coverages. Pit formation is discussed in greater detail elsewhere [6].

0 0

Post a comment