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- 저자 : Liao Kung-Ching (검색결과 3 건)
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Fluorination, and Tunneling across Molecular Junctions
Liao, Kung-Ching,Bowers, Carleen M.,Yoon, Hyo Jae,Whitesides, George M. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.11
<P>This paper describes the influence of the substitution of fluorine for hydrogen on the rate of charge transport by hole tunneling through junctions of the form Ag<SUP>TS</SUP>O<SUB>2</SUB>C(CH<SUB>2</SUB>)<SUB><I>n</I></SUB>(CF<SUB>2</SUB>)<SUB><I>m</I></SUB>T//Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn, where T is methyl (CH<SUB>3</SUB>) or trifluoromethyl (CF<SUB>3</SUB>). Alkanoate-based self-assembled monolayers (SAMs) having perfluorinated groups (R<SUP>F</SUP>) show current densities that are lower (by factors of 20–30) than those of the homologous hydrocarbons (R<SUP>H</SUP>), while the attenuation factors of the simplified Simmons equation for methylene (β = (1.05?±?0.02)<I>n</I><SUB>CH<SUB>2</SUB></SUB><SUP>–1</SUP>) and difluoromethylene (β = (1.15?±?0.02)<I>n</I><SUB>CF<SUB>2</SUB></SUB><SUP>–1</SUP>) are similar (although the value for (CF<SUB>2</SUB>)<SUB><I>n</I></SUB> is statistically significantly larger). A comparative study focusing on the terminal fluorine substituents in SAMs of ω-tolyl- and -phenyl-alkanoates suggests that the C–F//Ga<SUB>2</SUB>O<SUB>3</SUB> interface is responsible for the lower tunneling currents for CF<SUB>3</SUB>. The decrease in the rate of charge transport in SAMs with R<SUP>F</SUP> groups (relative to homologous R<SUP>H</SUP> groups) is plausibly due to an increase in the height of the tunneling barrier at the T//Ga<SUB>2</SUB>O<SUB>3</SUB> interface, and/or to weak van der Waals interactions at that interface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-11/jacs.5b00137/production/images/medium/ja-2015-001374_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b00137'>ACS Electronic Supporting Info</A></P>
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Rectification in Tunneling Junctions: 2,2′-Bipyridyl-Terminated <i>n</i>-Alkanethiolates
Yoon, Hyo Jae,Liao, Kung-Ching,Lockett, Matthew R.,Kwok, Sen Wai,Baghbanzadeh, Mostafa,Whitesides, George M. American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.49
<P>Molecular rectification is a particularly attractive phenomenon to examine in studying structure–property relationships in charge transport across molecular junctions, since the tunneling currents across the same molecular junction are measured, with only a change in the sign of the bias, with the same electrodes, molecule(s), and contacts. This type of experiment minimizes the complexities arising from measurements of current densities at one polarity using replicate junctions. This paper describes a new organic molecular rectifier: a junction having the structure Ag<SUP>TS</SUP>/S(CH<SUB>2</SUB>)<SUB>11</SUB>-4-methyl-2,2′-bipyridyl//Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn (Ag<SUP>TS</SUP>: template-stripped silver substrate; EGaIn: eutectic gallium–indium alloy) which shows reproducible rectification with a mean <I>r</I><SUP>+</SUP> = |<I>J</I>(+1.0 V)|/|<I>J</I>(−1.0 V)| = 85 ± 2. This system is important because rectification occurs at a polarity opposite to that of the analogous but much more extensively studied systems based on ferrocene. It establishes (again) that rectification is due to the SAM, and not to redox reactions involving the Ga<SUB>2</SUB>O<SUB>3</SUB> film, and confirms that rectification is not related to the polarity in the junction. Comparisons among SAM-based junctions incorporating the Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn top electrode and a variety of heterocyclic terminal groups indicate that the metal-free bipyridyl group, not other features of the junction, is responsible for the rectification. The paper also describes a structural and mechanistic hypothesis that suggests a partial rationalization of values of rectification available in the literature.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-49/ja509110a/production/images/medium/ja-2014-09110a_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja509110a'>ACS Electronic Supporting Info</A></P>
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Kong, Gyu Don,Kim, Miso,Jang, Hyeon-Jae,Liao, Kung-Ching,Yoon, Hyo Jae The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.21
<P>This paper examines the ability of structural modifications using halogen atoms (F, Cl, Br, and I) to influence tunneling rates across self-assembled monolayer (SAM)-based junctions having the structure Ag<SUP>TS</SUP>/S(CH<SUB>2</SUB>)<SUB><I>n</I></SUB>(<I>p</I>-C<SUB>6</SUB>H<SUB>4</SUB>X)//Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn, where S(CH<SUB>2</SUB>)<SUB><I>n</I></SUB>(<I>p</I>-C<SUB>6</SUB>H<SUB>4</SUB>X) is a SAM of benzenethiol (<I>n</I> = 0) or benzyl mercaptan (<I>n</I> = 1) terminated in a hydrogen (X = H) or a halogen (X = F, Cl, Br, or I) at the <I>para</I>-position. The measured tunneling current densities (<I>J</I>(<I>V</I>); A cm<SUP>−2</SUP>) indicate that replacing a terminal hydrogen with a halogen atom at the X//Ga<SUB>2</SUB>O<SUB>3</SUB> interface leads to a decrease in <I>J</I>(<I>V</I>) by ∼×13 for S(<I>p</I>-C<SUB>6</SUB>H<SUB>4</SUB>X) and by ∼×50 for SCH<SUB>2</SUB>(<I>p</I>-C<SUB>6</SUB>H<SUB>4</SUB>X). Values of <I>J</I>(<I>V</I>) for the series of halogenated SAMs were indistinguishable, indicating that changes in dipole moment and polarizability caused by introducing different halogen atoms at the interface between the SAM and the Ga<SUB>2</SUB>O<SUB>3</SUB>/EGaIn electrode do not significantly influence the rates of charge tunneling across the junctions.</P> <P>Graphic Abstract</P><P>The role of halogenation in charge transport across molecular junctions was investigated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp00145e'> </P>
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