Electronic Current Transport through Molecular Monolayers: Comparison between Hg/Alkoxy and Alkyl Monolayer/Si(100) Junctions

Abstract

Electronic current transport through alkoxy and alkyl monolayer‐based junctions is presented. Monolayers are prepared on n‐Si(100) with sufficiently high quality to reliably investigate the actual molecular effect of each monolayer on their current–voltage characteristics. The results show that extending the Si‐binding chemistry from alkene to alcohol is feasible, which should significantly facilitate preparation of monolayers with modified molecules.

Molecules on Si: Electronics with Chemistry

“…Only at higher forward bias do the currents vary according to the thickness of the insulator, i.e., the molecular layer width here. Such length-independence of current at low forward bias was observed for several moderately-doped n-type MOMS junctions with n-Si [29,56,88,134,135,138,139] and n-GaAs, [35,36,140] contacted with medium-high work-function metals such as Hg.…”

“…[33,43,83] Furthermore, the observed inversion [20] in n-SiÀalkyl/Hg (Fig. 3) and n-SiÀOÀalkyl/Hg junctions [88] (see Section 4.2) implies that the Si surface is not pinned, supporting the idea that CÀSi and CÀOÀSi surface terminations effectively passivate the Si surface both chemically (preventing oxidation) and electronically (small density of surface states). The analysis of interface states of complete junctions can be done with frequency-noise analysis [73] or forward bias capacitance.…”

“…[21,23] In how far can we carry these understandings over to MOMS? Changing molecule-substrate binding from SiÀCÀ to SiÀOÀCÀ [88] and from (Ga(As)ÀO) 2 ÀP(O) to (Ga)AsÀS [140] or the top contact from a physi (ÀCH 3 /Hg) to a chemisorbed (ÀSÀHg) [134] one, showed clear effects on the semiconductorlimited J-V characteristics, which can be rationalized as a dipole effect on the SBH.…”

“…Many functionalized groups, apart from alkenes (C¼ À C), [31,69,80,86] can adsorb on H-terminated Si, such as alkynes (C¼C), [87] alcohols, [69,88] aldehydes, [69] thiols (SH) [72,89] or Grignard reagents. [42,83,90] Aromatic molecules are mostly electrochemically adsorbed as diazonium salts [43,62,91] or by photochemical binding of ethynylbenzene.…”

“…Still, the TE model is commonly assumed as a simple means for comparing samples/ data, using an ''effective barrier height'' that is deduced from J-V measurements, SBH(J 0 ). [19,56,63,64,88,90,135] Alternatively, the barrier height can be extracted from reverse bias C-V data with the MottÀSchottky relation (see Eq. (4), SBH(C 0 ) ¼ C SC þ j).…”