TY - JOUR
T1 - Energy Level Alignment of Organic Molecules with Chemically Modified Alkanethiolate Self-Assembled Monolayers
AU - Shibuta, Masahiro
AU - Ogura, Munehisa
AU - Eguchi, Toyoaki
AU - Nakajima, Atsushi
N1 - Funding Information:
This work is partly supported by the program of Exploratory Research for Advanced Technology (ERATO) in Japan Science and Technology Agency (JST) entitled "Nakajima Designer Nanocluster Assembly Project", by JSPS KAKENHI of Grant-in-Aids for Young Scientists (B) Grant Number 25810010 and for Scientific Research (A) Grant Number 15H02002 and by JSPS KAKENHI of Challenging Research (Pioneering) grant no. 17H06226.
Funding Information:
This work is partly supported by the program of Exploratory Research for Advanced Technology (ERATO) in Japan Science and Technology Agency (JST) entitled “Nakajima Designer Nanocluster Assembly Project”, by JSPS KAKENHI of Grant-in-Aids for Young Scientists (B) Grant Number 25810010 and for Scientific Research (A) Grant Number 15H02002 and by JSPS KAKENHI of Challenging Research (Pioneering) grant no. 17H06226.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/12/14
Y1 - 2017/12/14
N2 - We have employed two-photon photoemission spectroscopy to nondestructively resolve the unoccupied energy levels of fullerene C60 molecules deposited on alkanethiolate self-assembled monolayers (SAMs). By fluorine substitution of the hydrogen atoms in the alkyl chain, the work function (WF) increased from 4.3 eV for the alkanethiolate-SAM (H-SAM) to 5.7 eV for the fluorine-substituted SAM (F-SAM), owing to the formation of surface dipole layers. When C60 is deposited on the H-SAM and F-SAM, the energy positions of the unoccupied/occupied levels of C60 are pinned to the vacuum level (Fermi level (EF) + WF). As a result of the energy level alignment, on the F-SAM, the relative energy from EF of the highest occupied molecular orbital of C60 almost equals that of the lowest unoccupied molecular orbital, implying that the C60 film on the F-SAM exhibits both p- and n-type (ambipolar) charge transport properties, while C60 is known as a typical n-type semiconductor. The energetics are preserved even with multilayered C60 films at least up to ∼5 nm in thickness, showing that the dipole layers induced by SAMs are robust against molecular overlayers. Such a spectroscopic study on the energy levels for organic films will be of importance for further development of organic thin film devices.
AB - We have employed two-photon photoemission spectroscopy to nondestructively resolve the unoccupied energy levels of fullerene C60 molecules deposited on alkanethiolate self-assembled monolayers (SAMs). By fluorine substitution of the hydrogen atoms in the alkyl chain, the work function (WF) increased from 4.3 eV for the alkanethiolate-SAM (H-SAM) to 5.7 eV for the fluorine-substituted SAM (F-SAM), owing to the formation of surface dipole layers. When C60 is deposited on the H-SAM and F-SAM, the energy positions of the unoccupied/occupied levels of C60 are pinned to the vacuum level (Fermi level (EF) + WF). As a result of the energy level alignment, on the F-SAM, the relative energy from EF of the highest occupied molecular orbital of C60 almost equals that of the lowest unoccupied molecular orbital, implying that the C60 film on the F-SAM exhibits both p- and n-type (ambipolar) charge transport properties, while C60 is known as a typical n-type semiconductor. The energetics are preserved even with multilayered C60 films at least up to ∼5 nm in thickness, showing that the dipole layers induced by SAMs are robust against molecular overlayers. Such a spectroscopic study on the energy levels for organic films will be of importance for further development of organic thin film devices.
UR - http://www.scopus.com/inward/record.url?scp=85038368909&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85038368909&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.7b07955
DO - 10.1021/acs.jpcc.7b07955
M3 - Article
AN - SCOPUS:85038368909
SN - 1932-7447
VL - 121
SP - 27399
EP - 27405
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 49
ER -