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Volumn 22, Issue 16, 2006, Pages 6915-6922

Importance of monolayer quality for interpreting current transport through organic molecules: Alkyls on oxide-free Si

Author keywords

[No Author keywords available]

Indexed keywords

CONTACT ANGLE; ELECTRIC CURRENTS; ELLIPSOMETRY; SCHOTTKY BARRIER DIODES; THERMIONIC EMISSION; TRANSPORT PROPERTIES; TUNNEL DIODES; X RAY PHOTOELECTRON SPECTROSCOPY;

EID: 33747172298     PISSN: 07437463     EISSN: None     Source Type: Journal    
DOI: 10.1021/la060718d     Document Type: Article
Times cited : (136)

References (38)
  • 14
    • 24644510823 scopus 로고    scopus 로고
    • We note that high quality alkyl SAMs are also of interest for their potential use as insulators in semiconductor devices. In principle, SAMs formed on oxide-free H-terminated silicon offer a potentially homogeneous insulating material because there is no oxide. See: Shirahata, N.; Hozumi, A.; Yonezawa, T. Chem. Rec. 2005, 5, 145-159.
    • (2005) Chem. Rec. , vol.5 , pp. 145-159
    • Shirahata, N.1    Hozumi, A.2    Yonezawa, T.3
  • 19
    • 33747199474 scopus 로고    scopus 로고
    • note
    • The electron transport data in refs 15 and 17 were analyzed using the Schottky thermionic emission model, including an empirical correction for the organic monolayer. We find, though, that data in the low bias regime can be characterized by a single mechanism, thermionic emission, without the need to include a term for the monolayer.
  • 23
    • 33747152404 scopus 로고    scopus 로고
    • note
    • +-Si was due to the formation of metallic filamentary pathways formed during evaporation of metal onto the SAM. Indeed, we encountered this problem of shorting in (unpublished) experiments with indirectly evaporated Au contacts on alkyl monolayers. However, we never saw evidence for it with our Hg/alkylC-Si junctions. This is not surprising because formation of filamentary shorts with the high surface tension Hg contact and the very smooth substrates that we use is rather improbable, unless large pinholes are present. Simple wetting calculations, using a 150° Hg/alkyl monolayer contact angle and a 2 nm thick monolayer, show that only if the (circular) pinhole is well over 5 nm in diameter, can we get direct Hg-substrate contact. Naturally, at some distance between Hg and substrate, before direct Hg/substrate contact is reached, tunneling through vacuum (between the Hg surface and the pinhole bottom) can become favored over transport through the molecules. The distance where this will occur will depend on the mechanism of tunneling through the molecular monolayer.
  • 30
    • 33747203649 scopus 로고    scopus 로고
    • note
    • Assuming a densely packed monolayer with fully extended (all trans bonds) chains, the thickness, d, of the monolayer as deduced from ellipsometry, is given by d = 1.86 Å + L cos α, where L is the length of the alkyl chain and a is the tilt angle of the chain from surface normal. 1.86 Å is the length of the Si-C bond, which is normal to the surface for Si(111). The length L of the alkyl chain was calculated based on standard bond lengths (C-C, 1.53 Å; C-H 1.11 A) and angles (111°), using the formula L = 1.26(n-1) + 0.9, where n is the number of carbons in the alkyl chain.
  • 31
    • 19744366928 scopus 로고    scopus 로고
    • 2 or water). We can then subtract the contribution of the oxygen (% O1s) in the thickness calculation. We note, though, that even considering the 0 in the calculation gives less than 0.1 nm extra thickness for the organic monolayer.
    • (2005) J. Am. Chem. Soc. , vol.127 , pp. 7871
    • Wallart, X.1    De Villeneuve, C.H.2    Allongue, P.3
  • 36
    • 0345979435 scopus 로고    scopus 로고
    • Ulman, A. Chem. Rev. 1996, 96, 1533-1554.
    • (1996) Chem. Rev. , vol.96 , pp. 1533-1554
    • Ulman, A.1
  • 38
    • 33747189929 scopus 로고    scopus 로고
    • note
    • The barrier height of GaAs semiconductors can be controlled by incomplete monolayers. See the Supporting Information for a more detailed discussion and references.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.