Interfacial Properties of Organic Semiconductor–Inorganic Magnetic Oxide Hybrid Spintronic Systems Fabricated Using Pulsed Laser Deposition

Abstract

We report fabrication of a hybrid organic semiconductor-inorganic complex oxide interface of rubrene and La0.67Sr0.33MnO3 (LSMO) for spintronic devices using pulsed laser deposition (PLD) and investigate the interface structure and chemical bonding-dependent magnetic properties. Our results demonstrate that with proper control of growth parameters, thin films of organic semiconductor rubrene can be deposited without any damage to the molecular structure. Rubrene, a widely used organic semiconductor with high charge-carrier mobility and spin diffusion length, when grown as thin films on amorphous and crystalline substrates such as SiO2-glass, indium-tin oxide (ITO), and LSMO by PLD at room temperature and a laser fluence of 0.19 J/cm2, reveals amorphous structure. The Raman spectra verify the signatures of both Ag and Bg Raman active modes of rubrene molecules. X-ray reflectivity measurements indicate a well-defined interface formation between surface-treated LSMO and rubrene, whereas X-ray photoelectron spectra indicate the signature of hybridization of the electronic states at this interface. Magnetic measurements show that the ferromagnetic property of the rubrene-LSMO interface improves by >230% compared to the pristine LSMO surface due to this proposed hybridization. Intentional disruption of the direct contact between LSMO and rubrene by insertion of a dielectric AlOx layer results in an observably decreased ferromagnetism. These experimental results demonstrate that by controlling the interface formation between organic semiconductor and half-metallic oxide thin films, it is possible to engineer the interface spin polarization properties. Results also confirm that by using PLD for consecutive growth of different layers, contamination-free interfaces can be obtained, and this finding is significant for the well-controlled and reproducible design of spin-polarized interfaces for future hybrid spintronics devices.

Rubrene Thin Films with Viably Enhanced Charge Transport Fabricated by Cryo-Matrix-Assisted Laser Evaporation

“…Pentacene films PLD-deposited on preheated substrates (403 K) and thermally evaporated films have demonstrated improved morphology and decreased surface roughness, compared to films prepared on room temperature substrates, corresponding to μ values obtained for OFET devices of 10 −4 and 3 × 10 −2 cm 2 V −1 s −1 , respectively. In PLD-deposited RB films on SiO 2 and La 0.67 Sr 0.33 MnO 3 (LSMO), the X-ray diffraction (XRD) patterns revealed the presence of crystalline orthorhombic RB and a dominating amorphous phase [ 4 , 36 ], in agreement with carrier mobility values of ~10 − 6 cm 2 V − 1 ∙s − 1 , that corresponds to previous reports [ 37 ].…”

“…The majority of μ values in Table S1 are between10 −2 and 10 −1 cm 2 V −1 s −1 ; these values for RB films deposited by MAPLE are several orders of magnitude higher than those reported for the amorphous material (~10 −6 cm 2 V −1 s −1 ) [ 37 ] and the PLD-deposited RB films [ 4 , 36 ], approaching the technologically accepted level of 1 cm 2 V −1 s −1 ( Figure 6 c). This improvement in mobility can be attributed to the higher amount of orthorhombic crystalline phase of the MAPLE deposited RB films and better connectivity between the crystallites of rubrene compared to films deposited by other evaporation techniques.…”

“…These properties, and the rapidly growing interest in the application of organic materials, have stimulated research on OS processing methods for fabricating thin films for multilayer structures. These are the basic components of functional devices, e.g., organic light emitting diodes (OLEDs), field-effect transistors (OFETs), lasers, sensors, spin valves, and memory blocks [ 4 ]. The key requirement of their design is the controlled fabrication of chemically clean OS layers.…”

“…Recently, MAPLE has been used for the growth of RB nanocrystals [ 41 ] and in the fabrication of RB layers [ 42 ]. The slight increase in crystallinity, compared to films fabricated by PLD [ 4 ], is accompanied by RB thermal and photochemical decomposition, and a dependence on deposition parameters was observed. However, the parameters that determine the application capacity of films fabricated by this method, such as film structure and crystallinity, and their relation to charge transport properties, have not been reported.…”

Synthesis and Nonlinear Optical Studies on Organic Compounds in Laser-Deposited Films

“…For each type, there are several techniques applied. Physical deposition techniques for thin organic films include physical vapor deposition (PVD) [38][39][40][41][42], organic vapor phase deposition (OVPD) [43][44][45], organic molecular beam deposition (OMBD) [46][47][48][49][50][51], solvent vapor annealing (SVA) [52][53][54][55][56], self-assembled monolayers (SAMs) [57,58], inkjet printing [59,60], pulsed laser deposition (PDL) [61][62][63][64], and laser evaporation [65][66][67] techniques. The chemical methods include solution techniques and gas-phase deposition methods.…”