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A hybrid structure of a graphene nanomesh with the gold nanodisks is studied to enhance the light absorption by the localized surface plasmon resonance. From the reflection spectra of the visible range for graphene nanomesh samples without and with nanodisks, it is found that the absorption of graphene nanomesh structures is greatly enhanced in the presence of gold nanodisks around the resonance wavelength. Simulation results based on the finite-difference time-domain method support the experimental observations. This study demonstrates the potential of constructing graphene based photodetectors with a high light absorption efficiency and wavelength selectivity.

A thin 3-nm-thick parylene layer is deposited by chemical vapor deposition at room temperature on the indium tin oxide (ITO) coated glass substrate to form a bilayer anode of an organic light emitting diode. The parylene layer forms a conformal film to cover the spikes present in the ITO film. This parylene film presents a smoother surface to the subsequent organic layers. The parylene film not only reduces the occurrence of dark spots, acting as a barrier for oxygen diffusion from either the ITO or from the atmosphere and stabilizing the migration of the electrodes during electrical stress, but also improves the injection of holes from the anode. By inserting another parylene layer in between the organic and cathode layers, the probability of formation of nonemissive areas is further reduced.

The degradation and failure of organic light-emitting device are observed via optical microscopy. The “degraded area” has been identified to be made up of three regions: (1) a dark spot at the center, (2) a nonemitting area forming the core, and (3) a weakly emitting area surrounding the core. It is found that due to metal migration, as evidenced from the secondary ion mass spectrometry profiles, the indium tin oxide/polymer interface roughens during operation. The intense local current at sharp points degrades the polymer causing the formation of the dark center. Further current stress caused the central core to carbonize which may lead to short and/or open circuits accompanied by fluctuations in the device current.

Polymer degradation under electrical stress was studied using the device structure indium tin oxide/poly(p-phenylene vinylene)/Ca/Ag. The devices that were used in this study do not show any significant decrease in electroluminescent intensity for up to several thousand hours of operation. However for devices that were electrically stressed and then exposed to normal ambient, there was a significant decrease in the photoluminescence. Those that were not electrically stressed but exposed to normal ambient or were electrically stressed but not exposed to normal ambient, there was no significant degradation in the photoluminescence. These results showed that both conditions of electrical stress and photo-oxidation are necessary for a significant decrease of the photoluminescence intensity. Degradation is accompanied by an increase in the x-ray crystallization peak. We interpret that the photoluminescence intensity degradation is due to the change in polymer crystallinity caused by electrical stress followed by photo-oxidation.

The degradation in electroluminescence of poly(p-phenylene vinylene)-based organic light-emitting devices is studied using optical microscopy, scanning electron microscopy, and secondary ion mass spectroscopy. “Bubbles” are formed at the polymer and indium tin oxide interface or in the polymer layer within the nonemissive area. This formation, which occurs during device electrical stress, is accompanied by a fluctuation of the device current. The bubbles are formed by the degraded polymer and/or the gas released from disintegration of the polymer. High local current density flowing near the dark spot center and the resultant heating, decomposes the polymer layer. The resultant carbonized area causes either local short circuit and/or open circuit leading to the final light-emitting device failure.

Our in situ experimental observations of dark spot growth in organic light-emitting diodes using optical microscopy show a linear rate of growth for the area of all the dark spots. We used uniformly sized silica micro particles to intentionally create size-controllable pinholes on the cathode protective layer. Subsequently, we observed initial formation of dark spots as a result of these pinholes and then monitored their growth. Due to usage of particles of various diameters, we were able to linearly correlate the growth rate with pinhole size. This allows us to estimate the original pinhole sizes that gave rise to the dark spots, which we believe were initiated by “dust” particles. Our studies verify that dark spot formation is due to pinholes on the protective layer that creates pathways for water or oxygen permeation, and that dark spot growth is dependent on the pinhole sizes.

Bottom-contact organic field-effect transistors (FETs) based on regioregular poly(3-hexylthiophene) were fabricated with different surface treatments and were evaluated using a low frequency noise (LFN) spectroscopy. The oxygen-plasma (OP) treated device shows the highest mobility with the lowest current fluctuation. Octadecyltrichlorosilane and perfluorodecyldimetylchlorosilane treated device gives a higher noise compared with the OP treated device. Hexamethyldisilazane treated devices show the highest noise but the lowest mobility. The LFN results are correlated with organic FET device mobility and stability, proved by channel material crystallinity and degree of dislocations analysis. LFN measurement provides a nondisruptive and direct methodology to characterize device performance.

Polarity void formation has been observed at the Cu3Sn∕Cu interfaces in current-stressed Cu∕Sn∕Cu flip-chip joints. Electromigration voids were observed at the Cu3Sn∕Cu anode interface, but no voids were found at the Cu3Sn∕Cu cathode interface. The backstress in the anode’s Cu trace line caused a vacancy backflow toward the Cu3Sn∕Cu anode interface, which led to serious void formation. In the opposite Cu3Sn∕Cu cathode interface, Cu atoms in the cathode’s Cu trace line electromigrated toward the Cu3Sn∕Cu cathode interface, which alleviated or healed possible Kirkendall void formation due to the normal annealing process.

Poly(p-phenylene vinylene)-based polymer light-emitting devices using different thicknesses of tetrahedral amorphous carbon ultrathin films between indium tin oxide and polyethylenedioxythiophene hole transporting layer have been fabricated. The device with a 0.5nm tetrahedral amorphous carbon (ta-C) layer has the highest luminance and current efficiency compared to that of other devices. The current efficiency of a standard device without a ta-C layer is 1.1cd∕A at 5V, however, the current efficiency of a device with a ta-C layer thickness of 0.5nm is 2.7cd∕A; the current efficiency is improved about 2.5 times compared to the standard device. The improvement of the efficiency is due to blocking the hole injection from anode and balancing the hole and electron current. The lifetime of a device with a ta-C layer is significantly much longer than the standard device, and the device with a 0.5nm ta-C layer has the longest lifetime.