-
Nature Material 02/2008; 7(3):168-168. · 32.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The interplay between ionic and electronic charge carriers in mixed conductors offers rich physics and unique device potential. In light-emitting electrochemical cells (LEECs), for example, the redistribution of ions assists the injection of electronic carriers and leads to efficient light emission. The mechanism of operation of LEECs has been controversial, as there is no consensus regarding the distribution of electric field in these devices. Here, we probe the operation of LEECs using electric force microscopy on planar devices. We show that obtaining the appropriate boundary conditions is essential for capturing the underlying device physics. A patterning scheme that avoids overlap between the mixed-conductor layer and the metal electrodes enabled the accurate in situ measurement of the electric-field distribution. The results show that accumulation and depletion of mobile ions near the electrodes create high interfacial electric fields that enhance the injection of electronic carriers.
Nature Material 12/2007; 6(11):894-9. · 32.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In order to determine energetic disorder's role in facilitating charge injection from gold into a molecularly doped polymer, we have examined the dependence of current on the local electric field, measured using electric force microscopy, at temperatures ranging from 250 to 330 K. From these data we infer, in a single experiment, the temperature dependence of the main factors governing the injection current: the electric-field induced lowering of the image-potential barrier, the interfacial charge density, and the mobility. In this system, the Schottky effect is anomolously large, and the interfacial charge density is larger than expected and strikingly non-Arhennius. Our analysis indicates that these effects are all a consequence of the Gaussian density of states in the organic.
Physical Review Letters 03/2007; 98(6):066101. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have measured the chemical potential and capacitance in a disordered organic semiconductor by electric force microscopy, following the electric field and interfacial charge density microscopically as the semiconductor undergoes a transition from Ohmic to space-charge limited conduction. Electric field and charge density at the metal-organic interface are inferred from the chemical potential and current. The charge density at this interface increases with electric field much faster than is predicted by the standard diffusion-limited thermionic emission theories.
Physical Review Letters 10/2004; 93(11):116104. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have developed a variable temperature inertial coarse approach mechanism for use in scanned probe microscopy. This reliable micropositioner has a coarse range of 2.5 mm and can take individual steps of less than 10 nm from 4 to 300 K. This simple, compact device is both nonmagnetic and glueless. It is operational in both horizontal and vertical geometries and is driven by a low voltage sawtooth waveform. We report on the design and performance of the device. © 2003 American Institute of Physics.
Review of Scientific Instruments 12/2002; 74(1):267-269. · 1.37 Impact Factor
