Direct Imaging of Space‐Charge Accumulation and Work Function Characteristics of Functional Organic Interfaces

Abstract

The tailoring of organic systems is crucial to further extend the efficiency of charge transfer mechanisms and represents a cornerstone for molecular device technologies. However, this demands control of electrical properties and understanding of the physics behind organic interfaces. Here, a quantitative spatial overview of work function characteristics for phthalocyanine architectures on Au substrates is provided via kelvin probe microscopy. While macroscopic investigations are very informative, the current approach offers a nanoscale spatial rendering of electrical characteristics which is not possible to attain via conventional techniques. Interface dipole is observed due to the formation of charge accumulation layers in thin F CuPc, F CoPc, and MnPc films, displaying work functions of 5.7, 6.1, and 5.0 eV, respectively. The imaging and quantification of interface locations with significant surface potential and work function response (<0.33 eV for material thickness <1 nm) show also a dependency on the crystalline state of the organic systems. The work function mapping suggests space-charge carrier regions of about 4 nm at the organic interface. This reveals rich spatial electric parameters and ambipolar characteristics that may drive electrical performance at device scales, opening a realm of possibilities toward the development of functional organic architectures and its applications.

Reorganization Energy upon Controlled Intermolecular Charge‐Transfer Reactions in Monolithically Integrated Nanodevices

“…Our measured CuPc work function is ≈5 eV, which is compatible with the value obtained for metal-phthalocyanine thin films. [51] This agreement suggests that the Au/CuPc heterostructure should exhibit Ohmic charge carrier injection since holes play a major role in charge transport, [37] and no Schottky barrier for holes is expected.…”

High‐Performance Ultrathin Molecular Rectifying Diodes Based on Organic/Inorganic Interface Engineering

“…[1][2][3] The use of organic materials to incorporate novel functions to the temperatures has enabled better control of molecular orientation, which can profoundly impact both charge injection and transport. [20][21][22][23][24] Another example is the electronic tunability displayed by metal/molecule heterostructures when surrounded by different atmospheres or submitted to different temperatures. [25][26][27] In most cases an appropriate (quantitative) evaluation of the electrostatic energy at the surface of molecular layers deposited on different work-function substrates can provide a realistic picture of the organic/inorganic hybrid system's inherent ability to transport charges.…”

“…[29,30] In addition, the AFM-KPFM combined analysis may offer valuable insights on the space-charge density, interfacestate relaxation, and energetic level evolution as a function of the organic film thickness. [24,31,32] Such figures of merit can be used to elucidate important properties of hybrid devices, such as the injection barrier, materials bandgap, work function (φ), and interface dipole (Δ). [20,21,33] Here, we design and fabricate hybrid interface-based molecular diodes, and further apply them as active components in practical circuitry half-wave rectifiers (HWRs), thus exploiting their ability to convert AC signals into DC outputs.…”

Interface Charge Characteristics in Polymer Dielectric Contacts: Analysis of Acoustic Approach and Probe Microscopy

“…[79,80] KPFM measures the work function between the tip and the surface as a function of potential difference. [81,82] This technique is beneficial for studying electronic properties near the surface in nanotechnology and semiconductor fields. [83] In addition, the probe microscopy technique is effective in detecting interface charge on a microscopic scale.…”