Study Of Electronic Structure,Spin Transport And Quantum Magnetism In Several Organic Semiconductors

Organic semiconductors?OSCs?have excellent photoelectric properties,as well as other advantages such as lightness,softness,low cost,easy processing and so on,which make them have broad application prospects in electronic devices including organic light-emitting diode?OLED?,organic field effect transistor?OFET?and organic photovoltaic solar cell?OPVC?.In addition,since their weak spin orbit coupling and hyperfine interaction,OSCs also have long spin relaxation time,which indicated that they have hold promise for quantun information processing by manipulating and propagating the spin degree of freedom of electrons.Therefore,it is of great significance to study their underluying charge and spin characteristics and for improving the performance of electronics and spintronics devices.In this paper,three typical organic semiconductors,i.e.,3,4,9,10-perylene-tetracarboxylic-dianhydride?PTCDA?,rubrene,iron phthalocyanine?FePc?,are selected to study their electronic structure,spin transport and quantum magnetism,respectively.Firstly,the electronic structure of a 3,4,9,10-perylene-tetracarboxylic-dianhydride?PTCDA?thin film is investigated in situ using synchrotron-based near edge X-ray absorption fine structure?NEXAFS?spectroscopy and resonant photoemission spectroscopy?RPES?.According to the dependence of kinetic energy of the emitted photoelectrons upon the change of incident photons energy,three typical features of the C 1s signals excited by second-order harmonic X-ray,resonant photoemission and resonant Auger features are observed in RPES spectra,and are identified.It is found that the resonant enhancement of molecular orbitals dependent on photon energy,which due to the difference distribution of molecular orbitals of PTCDA.Moreover,the high binding energy molecular orbitals?>4.1eV?participate in the resonant Auger deexcitation process.Clarifying each resonant feature in RPES spectra and their origin will pave the way for accurately determining the ultrafast charge transfer time at organic/electrode interfaces using synchrotron-based core hole clock technique implementation of RPES.In order to investigate the spin transport property of rubrene,we fabricate a series of Ni₈₀Fe₂₀/Rubrene/Pt devices with various rubrene thickness.By utilizing the spin pumping technology,we pure spin current is injected into rubrene film and finally detected by inverse spin Hall effect.According to the exponential relationship between rubrene thickness and inverse spin Hall voltage,the spin diffusion length?=132±9 nm is obtained.Futhermore,the spin relaxation time?=3.8±0.5 ms was estimated by using carrier mobility?of rubrene of 1.76?10^-6 cm²/V and formular?₌?²/D.These results is closer to the spin relaxation characteristics compared to that of spin valves because the former overcomes the conductance mismatch and spinterface problems,which suggest that the charge relaxation at OSCs/Ferromagnetic electrode interface could intensified the spin relaxation process.Thus,tuning both the interfacial energetics and interfacial spin polarized electronic states are valuable strategies available to enhance the performance of spintromic devices.Last but not least,we introduced the results of low-dimensional magnetism of?-FePc single crysal,in which the Fe atoms with S=1 could form a one-dimensional?1-D?axis.The angular dependent synchrotron-based near edge X-ray absorption fine structure?NEXAFS?spectroscopy demonstrate that the?-FePc molecule oritation is almost upright to the bc crystal plane.The magnetic susceptibility and magnetization show a clear anisotropy between H//b and H^b.The magnetic susceptibility is explained well by the Large-D phase theory,and the anisotropic D/k_B is obtained,which is 67.6 K for H//b and116.3 K for H^b.The susceptibility?_AFM^?14??14?obtained by subtracting paramagnetism and diamagnetism demonstrates a flat region drawing near to zero below 8 K,which indicated that a singlet?S=0?gournd state of FePc 1-D chains.