Interfacial Interaction of Absorbate Copper Phthalocyanine with PVDF Based Ferroelectric Polymer Substrates: A Spectroscopic Study

Abstract

Studies of CuPc thin films on underlying ferroelectric copolymeric and terpolymeric substrates have been performed by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Work function (WF) and highest occupied molecular orbital (HOMO) energy level shift observed from UPS spectroscopy for successive deposition of CuPc molecules on ferroelectric polymer surfaces confirm the formation of interface dipole at the CuPc−ferroelectric polymer interface owing to charge transfer from the tailing region of the CuPc HOMO density of states (DOS) to the ferroelectric polymer layer. According to our thickness dependent XPS data, CuPc molecules are coupled to the organic ferroelectric surfaces through the central metal atom of the CuPc molecules, i.e., copper atom, and the halogens of underlying ferroelectric polymer surfaces, and hence support the charge transfer phenomenon from CuPc molecules to the ferroelectric polymer substrate. Polarization dependent NEXAFS results reveal that CuPc molecules retain their tilted geometrical configuration even at submonolayer thickness of the molecular films on both ferroelectric surfaces and confirms the electronic structural disturbance associated with structural modification of CuPc molecules due to interfacial charge transfer. Therefore, the energy level alignment with increment in the thickness of CuPc films at both the organic semiconductor−ferroelectric polymer interface is controlled by the charge transfer phenomenon from deposited CuPc molecules to the organic ferroelectric substrates. Our results provide a clear understanding about chemical interactions, molecular configurations, energy level alignment, and their correlation at CuPc/polymeric ferroelectric interfaces that can be important for organic nonvolatile memory and synaptic based thin-film transistor devices.

Dipolar Alignment in a Ferroelectric Dielectric Layer of FeFETs to Boost Charge Mobility and Nonvolatile Memory

“…We have four peaks of CuPc, which are benzene carbon (C C ), pyrrole carbon (C N ), and their corresponding shake-up satellites (S C and S N ). The relative intensity of C C , which is supposed to be three times to that of C N , as obtained in the case of CuPc on the SiO 2 surface, is reduced to 0.7 (Table ) in the case of CuPc on the ferroelectric surface at monolayer thickness. − The deviation of the result from the expected ratio validates the appearance of reasonable interaction of the ferroelectric polymer with the CuPc semiconductor at the semiconductor–dielectric interface of the FeFET.…”

“…Therefore, the deposition of CuPc on the ferroelectric polymer surface resulted in a decrease in CuPc work function and shift of the HOMO peak of CuPc to higher binding energy compared to the SiO 2 surface. The data indicate the formation of the interfacial dipole between CuPc and P­(VDF-TrFE), derived from the charge transfer from CuPc to the P­(VDF-TrFE) ferroelectric polymer surface. , Schematic band alignment of CuPc at SiO 2 and ferroelectric polymer substrates (semiconductor–dielectric interface) before and after the formation of the interface with respective surfaces has been depicted in Figure S5 (Supporting Information). Thus, enhancement of transport channel mobility happens because of the increase in hole carrier concentration in the CuPc near the semiconductor–dielectric interface.…”

Evolution of Electronic Structures of Polar Phthalocyanine–Substrate Interfaces

“…The UPS and XPS measurements of the substrates and the deposited ClGaPc films were carried out in an ultrahigh vacuum (UHV) multiprobe setup (Omicron Nanotechnology) at a base pressure of ∼2.0 × 10 –9 mbar, which was equipped with an EA125 hemispherical energy analyzer and two light sources. − For the UPS measurements, a He gas discharge lamp of 21.2 eV photon energy was used as the source and the corresponding spectrometer energy resolution was ∼0.1 eV. The UPS measurements were carried out by applying a sample bias of −6.0 V to determine the high binding energy cutoff (HBEC) with respect to the substrate FL of a spectrum.…”

Functionality Tuning in Hierarchically Engineered Magnetoelectric Nanocomposites for Energy-Harvesting Applications

“…49,50 The larger difference in the electrical conductivity and the Fermi level of Fe 3 O 4 nanoparticles (ϕ ∼5.7 eV) and the P(VDF− TrFE) matrix (ϕ ∼5.1 eV) results in the space charge accumulation at the interfacial region. 28,51 Therefore, increasing interfacial polarization resulted in the increased dielectric constant up to 5 wt % concentration of the filler, but it decreased further for MFPT10 and MFPT15 films. The decreased ε r at lower frequencies can be explained using percolation theory, which suggests that nanocomposites consisting of conducting fillers experience a transition from being an insulator to a metal-like electrical behavior when the concentration of the filler goes beyond a threshold value.…”

“…The composite with only Fe 3 O 4 nanoparticles as the filler showed the highest leakage current, and the ferroelectric property of the composite was also lost. The schematic in 28,51 The double layer consists of the Stern and diffused (Gouy−Chapman) layers. The Stern layer is formed of opposite polarity charges and firmly bonded to the nanoparticle.…”