Microscopy Characterization of Organic Pigments and Polymer Composite Materials for Xerography Applications.,

Abstract

We discuss the characterization of radiation sensitive organic pigment particles by TEM, as well as retrieval of internal microstructure of polymer composite particles used in xerographic toners by electron tomography and by slice-and-view in dual beam (FIB/SEM) instrument.Printing is a multibillion dollar industry that relies on high-quality marking materials to deliver excellent print quality, speed and value to consumers. New innovations in marking materials require an understanding of the attributes and microstructure of dye or pigments used as colorant. Since the color properties of organic pigments are mainly determined by the choice of chromogen molecule as well as pigment size and morphology [1], then electron microscopy provides a suitable means to investigate the physical structure and microstructure of pigments and other components that are located within toner particles. As both toners and pigment particles are 'soft' organic materials that are highly sensitive to electron beam irradiation, it is necessary to optimize microscopy to maximize information per unit irradiation dose.We studied commercially available quinacridone-type pigments, such as 2,9-dimethylquinacridone pigment known as Pigment Red 122 (PR 122). We estimated the loss of long range order from loss of intensity in diffraction ring corresponding to 0.3 nm lattice spacings in the pigment crystallites. At room temperature we have obtained characteristic dose D C = (0.35±0.05) C/cm 2 . All imaging experiments were performed at less than ½ D C . The dose D C corresponds to the cross section for carbon 1s carbon excitation within a factor of two, suggesting that the primary damage mechanism is due to core loss excitation of carbon [2]. When the samples were observed at T = 90 K, the characteristic dose increased by about factor of 2.4. At T = 90 K, lattice fringes with spacings down to 0.32 nm were observed in the sample. All experiments were conducted at 200 keV incident electron energy. Fig. 1 shows a typical thickness map obtained at a magnification sufficient to observe 1.6 nm lattice fringes (the presence and spacing of lattice fringes was confirmed in zero-loss filtered images). Fig. 2 depicts the relationship between the pigment particle external morphology and the crystal lattice planes. Fig. 3 shows a diffraction pattern of the PR 122. The spacings correspond to alpha, beta or gamma structure of 2,9-dimethylquinacridone. The pigment particle shape in 3D was determined from the thickness maps. The distribution of particle sized for PR122 was obtained by examining dimensions of individual particles in the plane perpendicular to the incident electron beam, while the third size dimension of the particle was obtained from thickness mapping by energy-filtering TEM. We have found that the PR122 particles were tetragonal with a long axis L = (190 ± 30) nm while the other two dimensions were found to be W =T = (28 ± 8) nm, an aspect ratio of approximately 7. HRTEM images similar to Fig. 1 revealed that the 1.6 nm spacing of the molecules is...

The double Gaussian distribution of inhomogeneous barrier heights in the organic‐on‐inorganic Schottky devices

“…Nowadays, organic thin films and organic‐based hybrid structures have gradually rising application areas in various electronic devices, such as diodes 1–3, dye sensitized solar cells (DSSCs) 4, organic light emitting diodes (OLEDs) 5, 6, RFID tags 7 and xerography 8. Therefore, it would be quite important a better understanding of the metal–organic interface in the further development and improvement of organic and molecular electronics.…”

“…The most important feature characterizing a Schottky barrier is its barrier height Φ B . Recently, considerable attention has been focused on the barrier height inhomogeneity in the Schottky devices 1–28. Several methods and approximations have been proposed to explain the formation of barrier from different materials including inorganic and/or organic interfaces and also to specify the behaviour of barriers at different bias and environmental conditions.…”