Scanning Tunneling Luminescence of Pentacene Nanocrystals

摘要: Organic semiconductors are promising materials for future electronic and electroluminescence applications. A detailed understanding of organic layers nano-sized crystals down to single molecules can address fundamental questions contacting at the nanometer limit obtaining luminescence from them. In this thesis, spectra pentacene, a policyclic hydrocarbon (acene), discussed. The is induced by current tip scanning tunneling microscope (STM). Pentacene an semiconductor which gained lot attention in technology because its properties suitable applications thin film devices. Moreover, recent studies employed pentacene as standard demonstrate sub-molecular resolution probe techniques. This work reports first observation light emission nanometer-sized grown on ultrathin insulating layer noble metal surfaces. Different STM-techniques combined characterize individual systems studied with respect topography, crystal structure, function changes. initial step project was implementation optical system collection tunnel-junction low-temperature STM. set-up, novel approach based use situ adjustable lenses has been realized. Three placed vicinity tip-apex allow into three independent channels be used versatile analysis. An important part characterization clarify interaction between adsorbed substrates. We investigated different insulator-metal systems. With STM tunnel contact, situated double barrier junction formed one side vacuum gap other side. surface STM-tip form electrodes. configuration have characterized. Insulator-metal-systems, provide good decoupling metal, chosen substrates growth nanocrystals. Using we resolved structure top-layer nanocrystals found that phase agrees bulk structure. comparison charge injection barriers indicates significant change after formation ordered building blocks. Optical spectroscopy emitted reveals excitonic nanocrystals, very agreement photoemission macroscopic crystals. Although highly localized current-injection excitation, it concluded source delocalized. contrast measurements reported STM, excitation not molecule, injected STM-tip. Our study importance inter-molecular coupling leading high mobility excited state considered framework STM-induced luminescence. further result Stark shift luminescence, so far measured large electric fields order 1V/nm. evaluation provides information dipole polarizability during decay exciton. lowest singlet exciton mixing Frenkel (FE) small contribution charge-transfer (CT). Finally, developed set-up photon correlation statistics means unambiguously prove due single-photon source, i.e. emits no more than time. typical example such molecule. performed correlations C60 While expected represent emitter, also did observe anticorrelations case indicating local environment STM-junction, e.g. short distance