Atomic Force Electroluminescence Microscopy
INVENTION: Northwestern University scientists have invented a new atomic force microscope tool, AFEM, capable of gathering simultaneous topographical, current, and electroluminescence information through a commercially available conductive AFM tip. Characterization of individual bottom-emitting opto-electronic devices, such as light-emitting diodes and electroluminescent devices at 10 nm resolution potential is offered.ADVANTAGES: The AFEM provides advances in operation, light sensitivity, resolution, current input and emission spectroscopy measurement versus other device characterization techniques. AFEM can concurrently monitor device topography, charge transport, and electroluminescence with nanometer spatial resolution.
SUMMARY:Organic light-emitting diodes (OLEDs) receive increasing attention due to their potential use in inexpensive, large area, high brightness, and flexible color displays. OLED miniaturization for high density displays requires greater knowledge of OLED structure and performance. Spatial mapping and correlation of topology, current, and electroluminescence characteristics of operating OLEDs at the nanometer scale is critical to this end.
Conductive atomic force microscopy can directly stimulate OLED electroluminescence at nanometer scale spatial resolution. Incorporation of collection optics and photon detectors enables the resulting electroluminescence to be spatially correlated with tip position and nanometer scale mapping. The AFEM concurrently monitors topography, charge transport, and electroluminescence with nanometer spatial resolution, suited for probing the characteristics of operating OLEDs. Charge is injected into individual OLED structures with the tip, and the resulting electroluminescence and current are measured with collecting optics and a variable gain photomultiplier tube. Thus, real-time spatial and temporal current-voltage and electroluminescence-voltage properties of 8 μm × 8 μm OLED pixels were analyzed. With the AFEM tip positioned over an individual OLED pixel in contact with the top gold electrode, the applied bias was swept as the current and light emission were recorded (Figure 1). Simultaneous topography, current, and light emission images were also determined on the OLED pixel array at an applied bias of 20 V, illustrating spatial variations in current and electroluminescence from pixel to pixel (Figure 2). AFEM flexibility can also serve to characterize electroluminescence from semiconducting nanowires, nanotubes, and sub-micron optoelectronic devices difficult to address directly with large-scale probes.
Inventor(s): Mark Hersam and Liam Pingree
Type of Offer: Licensing
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