利用STM和CV方法测定有机发光材料的能带参数

利用扫描隧道显微镜/扫描隧道谱(STM/STS)的技术,研究了有机发光材料Alq₃、DPN-2CN和DNP-2CN的表面电子结构。将材料DPN-2CN和DNP-2CN的表面电子结构与Alq₃的表面电子结构进行对比,判定了DPN-2CN和DNP-2CN的最低空轨道(LUMO)能级。通过电化学循环伏安(CV)法,对DPN-2CN和DNP-2CN的LUMO能级和最高占有轨道(HOMO)能级进行了表征。两种测试方法所得到的LUMO能级参数基本一致。

Energy-band Structures of Organic Light-emitting Materials by STM and Cyclic Voltammetry

Scanning probe microscopy offers the possibility of probing physical properties with high spatial(resolution).In particular,scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS) can be used to combine structural characterization with probing the electronic signature of the organic compounds on a molecular scale.A number of STS investigations on organic materials have been published in(recent) years.And most of the authors observed electron transport through the frontier orbitals of the organic molecules(i.e.,through the highest occupied molecular orbital(HOMO) and the lowest unoccupied mole-(cular) orbital(LUMO).The measurements of the contributions of the second filled and second unfilled molecular orbitals to the tunneling current have also been studied in a few researches.Compared with other methods of molecular energy structure characterization,such as Ultraviolet-Visible Spectrophotometry(UV-Vis),(Cyclic) Voltammetry(CV) and Ultraviolet Photoelectron Spectroscopy(UPS),STM/STS can show the nano-sized surface microscopy of the molecule in real time and the detailed information of surface roughness and graininess of the thin solid film can be obtained.The STM/STS measurement has become a powerful tool for the study of nanostructures in numerous areas of science and technology.The application of STM/STS in the field of(organic) light-emitting diodes(OLEDs) is promising.We present here a study of vapor deposition thin film(layers) of tris(8-hydroxyquinolino) aluminum(Alq_3), 4-(2-(3,3-dicyano-methylene-5,5-dimethyl-1-(cyclo)-hexylidene)vinyl)phenyl(1-naphthyl)phenyl-amine(DPN-2CN),and 4-(2-(3,3-dicyano-methylene-5,5-dimethyl-1-cyclohexyl-idene)vinyl)phenyldi(1-naphthyl)-amine(DNP2CN) on the substrate of ITO.The surface electronic structures of organic light-emitting materials Alq_3,DPN-2CN and DNP-2CN were studied by STM/STS.The obtained E_(LUMO) of compound DPN-2CN were 3.50 eV and 3.51 eV respectively.And the(energy)-band parameters of DPN-2CN and DNP-2CN were determined by comparing their surface electronic structures with Alq_3.The energy-band parameters of DPN-2CN and DNP-2CN obtained from the above method was compared with the result of CV experiments.The E_(LUMO) obtained from CV experiment is 3.68 eV for compound DPN-2CN,and 3.69 eV for compound DNP-2CN respectively.The result of STM/STS was basically in accordance with that of CV.