Electron affinity states of metal supported phthalocyanines measured by tunneling spectroscopy

2012 ◽  
Vol 16 (03) ◽  
pp. 273-281 ◽  
Author(s):  
K.W. Hipps ◽  
Ursula Mazur
Keyword(s):  
Gas Phase ◽  
Electron Affinity ◽  
Electron Tunneling ◽  
Tunneling Spectroscopy ◽  
Film Deposition ◽  
Solution Phase ◽  
Minor Role ◽  
Electron Affinities ◽  
Langmuir Blodgett ◽  
Metal Insulator Metal

Orbital Mediated Tunneling Spectroscopy OMTS (elastic electron tunneling) was employed in measuring electron affinity levels (EA) of unsubstituted, alkylated, sulfonated, and metalated phthalocyanines (Pc) adsorbed as single molecules or aggregates on metal substrates and imbedded in metal-insulator-metal (M-I-M) devices. MPc complexes were vapor deposited, solution phase doped, or transferred as Langmuir–Blodgett films. It was determined that while the nature of the substituents has a large effect on the gas phase electron affinities, they play a minimal role on the electron affinities of metal supported phthalocyanines. Moreover, the orientation of monolayer films and the method of film deposition (vapor, solution, Langmuir–Blodgett) also appear to play only a minor role in determining the electron affinities. Electrochemical reduction potentials obtained for the solution phase molecular systems are compared to the OMTS data and a strong correlation is observed. In contrast, the predicted EA values for the gas phase molecules show little correspondence with their OMTS equivalents for adsorbed phthalocyanines. Inelastic scattering from phthalocyanine π→π* transitions and metal centered d–d transitions are observed for chromophores imbedded in tunnel diodes. Both the observed lowest spin forbidden transitions and the calculated gas phase HOMO–LUMO gaps are only weakly affected by Pc substitution and surface orientation.

The acidity of polyhalogenated silanes and silyl radicals

1992 ◽  
Vol 70 (8) ◽  
pp. 2234-2240 ◽  
Author(s):  
C. F. Rodriquez ◽  
A. C. Hopkinson
Keyword(s):  
Gas Phase ◽  
Molecular Orbital ◽  
Electron Affinity ◽  
Substituent Effects ◽  
Linear Interpolation ◽  
Molecular Orbital Calculations ◽  
Electron Affinities ◽  
Silyl Radicals ◽  
Experimental Values ◽  
Cl Atom

The results of abinitio molecular orbital calculations at the MP4SDTQ/6-31++G(d,p)//HF/6-31++G(d,p) level have been used to calculate acidities of fluoro- and chloro-substituted silanes and silyl radicals. The radicals are more acidic than the silanes and substituent effects are also slightly larger in the radicals. For the gas phase deprotonation of fluorosilanes at 298 K, ΔHr (kcal/mol) values are SiH4, 378.5; SiH3F, 374.5; SiH2F, 366.7, and SiHF3, 351.0, i.e., interaction between fluorine atoms leads to increased enhancement of acidity. For chlorosilanes substituent effects are larger but strictly additive (13 kcal/mol for each Cl atom) with ΔHr values SiH3Cl, 365.4; SiH2Cl2 352.5, and SiHCl3 339.4. The electron affinities of silyl radicals calculated using isogyric reactions at the MP4SDTQ/6-31++G(d,p) level are too low by ~0.3 eV, but at the MP4SDTQ/6-311++G(2df,p) level the calculated electron affinity of SiH3 is 1.39 eV, compared with an experimental value of 1.44 ± 0.03 eV. This higher level of theory gives calculated electron affinities of 1.53 eV for SiH2F and 1.92 eV for SiH2Cl. Heats of formation obtained by using isogyric reactions to calculate atomization energies at the MP4SDTQ/6-311++G(2df,p) level are within 3 kcal/mol of experimental values except for SiH2F (where the "experimental" value was obtained from linear interpolation between SiH3 and SiF3). [Formula: see text] (kcal/mol) calculated for the anions are SiH3−, 14.4; SiH2F−, −78.0; and SiH2Cl−, −37.6.

Licvd of Cr(C,O) Films from Cr(CO)6 at 248 NM: Gas-Phase and Surface Processes

1988 ◽  
Vol 129 ◽  
Author(s):  
R. Nowak ◽  
L. Konstantinov ◽  
P. Hess
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Laser Fluence ◽  
Film Deposition ◽  
Surface Processes ◽  
Minor Role ◽  
Relative Importance ◽  
Experimental Conditions ◽  
Krf Excimer Laser ◽  
A Minor

ABSTRACTThe influence of laser fluence and carbon monoxide partial pressure on the deposition rate of thin Cr(C,O) films was investigated. The films were deposited from Cr(CO)6 mixtures with CO and Ar using a KrF excimer laser. The observed results are discussed with respect to the relative importance of gasphase and surface processes. The results reveal that under the present experimental conditions chromium atoms produced in the gas phase play only a minor role as direct film precursors in KrF laser-induced film deposition.

Electron Affinities from Thermal Proton-Transfer Reactions: C6H5 and C6H5CH2

1971 ◽  
Vol 49 (17) ◽  
pp. 2918-2920 ◽  
Author(s):  
D. K. Bohme ◽  
L. Brewster Young
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Electron Affinity ◽  
Transfer Reactions ◽  
Electron Affinities ◽  
Bond Energies ◽  
Preferred Direction ◽  
Proton Transfer Reactions

The observation of the preferred direction of proton transfer reactions in the gas phase at 300 °K has been employed to bracket the electron affinity, e.a., of the radicals C6H5 and C6H5CH2 using well-established values for electron affinities and bond energies. The results indicate that 1.2 eV ≤ e.a.(C6H5) ≤ 1.6 eV and that 0.4 eV ≤ e.a.(C6H5CH2) ≤ 0.9 eV.

scholarly journals Characterization of 10,12-pentacosadiynoic acid Langmuir–Blodgett monolayers and their use in metal–insulator–metal tunnel devices

2014 ◽  
Vol 5 ◽  
pp. 2240-2247 ◽  
Author(s):  
Saumya Sharma ◽  
Mohamad Khawaja ◽  
Manoj K Ram ◽  
D Yogi Goswami ◽  
Elias Stefanakos
Keyword(s):  
Electron Tunneling ◽  
Metal Insulator ◽  
Precise Control ◽  
Force Microscopy ◽  
Langmuir Blodgett ◽  
Current Voltage ◽  
Metal Insulator Metal ◽  
Current Voltage Characteristics ◽  
Monolayer Assembly

The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA) and their use in metal–insulator–metal (MIM) devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition) and Langmuir–Schaefer (LS, horizontal deposition) techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass). The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V), and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

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