Abstract
A tin oxide/copper phthalocyanine (CuPc) layer stack was investigated with two complementary photoemission methods. Non-destructive analysis of the electronic properties at the SnOx/CuPc interface was performed applying angle-dependent measurements with X-ray photoelectron spectroscopy (ADXPS) and energy-resolved photoemission yield spectroscopy (PYS). The different components (related to oxide layer and organic overlayer as well as to contamination features) observed in the spectra were assigned to a particular layer by relative depth plot analysis. ADXPS allowed determination of the chemical and electronic structure of the investigated samples. The addition of the organic ultra-thin film to the oxide layer caused a significant increase of the structure's photoemission yield. The combination of ADXPS and PYS allowed determination of the work function of constituent layers, and charge transfer phenomena at the SnOx/CuPc buried interface. An interface dipole of 0.23 eV was detected, assigned to charge transfer across the interface from the oxide layer towards the organic film. The energy level alignment at the SnOx/CuPc interface was determined, and presented in a band-like diagram, together with depth-dependent changes of the core energy levels of the structure's constituents. Finally the role of the oxide's defect-related energy levels in the charge transfer was discussed. The results obtained exhibit significance ranging from investigation, basic understanding and application of such hybrid films. Application of these results in hybrid electronic devices can help understanding and furthering this technology.
Highlights
In recent times, low-dimensional nanoscale materials have attracted more and more attention owing to a number of technological applications.[1,2,3] Among them hybrid materials and the creation of inorganic–organic heterojunctions are especially under rapid development owing to their vast range of applications, ranging from photovoltaics[4,5] through other optoelectronic and thermoelectronic devices[6,7,8] to inorganic–organic transistors.[9]
The two evident components have been assigned to oxygen bonded to tin and to adsorbed oxygen contamination
Because the method is based on the depth positioning with respect to the samples’ surface and because all calculations (IMFP, attenuation length and others) take into consideration the CuPc-related material constants, the respective energy changes in the oxide layer have to be plotted a as function of TOA
Summary
Low-dimensional nanoscale materials have attracted more and more attention owing to a number of technological applications.[1,2,3] Among them hybrid materials and the creation of inorganic–organic heterojunctions are especially under rapid development owing to their vast range of applications, ranging from photovoltaics[4,5] through other optoelectronic and thermoelectronic devices[6,7,8] to inorganic–organic transistors.[9]. Occurring at the buried heterojunction.[22,23] It is especially important in the case of ultra-thin layers where the Debye screening length is in the order of the layer thickness, as the surface, subsurface and interfacial phenomena can affect the quality and efficiency of component operation.[24] monitoring the processes at the interface, including charge carrier transfer together with interfacial electronic and chemical properties and energy level alignment, becomes crucial for optimal performance of heterostructures. In the case of ultra-thin layered systems, angledependent photoemission measurements are at the center of attention, as these permit non-destructive examination of layered samples with extremely low influence of the probing medium onto the structure being probed Another advantage is the ability to use standard lab-based experimental techniques for post-process quality assessment of the structures. In order to augment the ADXPS with the ability to determine the electronic properties (e.g. work function) at the interface, photoemission yield spectroscopy (PYS) was applied. The uncertainty analysis takes into account possible charging effects[39,40] angular broadening[41] and random errors that could occur during the experiment
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