Introduction to the Molecule–Metal Interface

Ultraviolet Photoelectron Spectroscopy (UPS) III: Direct Study of “Invisible” Band Gap States by Ultrahigh-Sensitivity UPS

“…Thus the intrinsic p-type film, which is defined by majority thermal carrier (hole), can also show n-type conduction in an organic field effect transistor when one uses an electrode with much lower work function (WF) than for example pentacene for electron injection, where the concentration of electrons under the device operation can be much larger than that of thermally created holes. It is true, however, that the intrinsic p-type property of pentacene, where the Fermi level is located closer to HOMO in the gap in air, greatly helps hole This can be due to larger tailing from LUMO into the band gap than tailing from HOMO [10,12]. For n-type films, namely C 60 , the situation is reversed.…”

“…To be more careful the UPS system is installed on a floor separated mechanically from working floor to minimize vibration-induced electrical and magnetic noises. Some of the results obtained with a prototype instrument [4,[7][8][9] were also discussed in [10] and Chap. 5.…”

“…When we introduce excess charges into organic films, various polarization (relaxation) effects appear in the film by changes in electron distribution, positions of atoms in each molecule and positions of molecules [31]. These polarization effects exist near the excess charge, and each excess charge with the polarization behaves as a quasi-particle, namely polaron.…”

“…The time scale (t) of the polarization effects is different for the movement of electrons (t e ), atoms in each molecule (t vib ) and molecules in a molecular crystal (t ph ), and generally t e ( t vib ( t ph for molecular crystals since the time depends on mass of moving body. Accordingly there are various polarons, namely electronic polaron, molecular-vibration related polaron and crystal-phonon related polaron, which can be distinguished by the time required for the relaxation of the system after introducing the charges [31]. measured with a high-energy-resolution radiation-damage-free IPES are used [29].…”

Impact of Film Structure on Ionization Energy of Titanyl-Phthalocyanine in Thin Films

“…IE of frontier MOs of organic thin films, which is an important parameter for the energy level alignment at interfaces in various organic devices, is known to be influenced by molecular orientation and molecular packing structure [1][2][3]. In fact, this concept, which is somewhat similar to the surface plane dependent work function of metal single crystals [4], has been successively adopted for various molecular thin films, such as (perfluorinated-) pentacene, (perfluorinated-) copper Pc, diindenoperylene, (alkyl-) oligothiophene, and even π-conjugated polymers [3,[5][6][7][8]. In fact, this concept, which is somewhat similar to the surface plane dependent work function of metal single crystals [4], has been successively adopted for various molecular thin films, such as (perfluorinated-) pentacene, (perfluorinated-) copper Pc, diindenoperylene, (alkyl-) oligothiophene, and even π-conjugated polymers [3,[5][6][7][8].…”