Ali Bilge Guvenc

Centimeter-scale high resolution metrology of entire CVD grown graphene sheets

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a fluorescence microscope. A large-area fluorescence montage image of the dyed graphene sample is collected and processed to identify the graphene and indicate the graphene layer thickness throughout the entire graphene sample. Using this metrology method, the effect of different transfer techniques on the quality of the graphene sheet is studied. It is shown that small-area characterization is insufficient to truly evaluate the effect of the transfer technique on the graphene sample. The results indicate that introducing a drop of acetone or liquid poly(methyl methacrylate) (PMMA) on top of the transfer PMMA layer before soaking the graphene sample in acetone improves the quality of the graphene dramatically over immediately soaking the graphene in acetone. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates. This metrology technique is well suited for many industrial applications due to its repeatability and flexibility.

Effect of incident light power on Schottky barriers and I-V characteristics of organic bulk heterojunction photodiodes

The space charge region (SCR) width of the Schottky barrier (SB) that forms on the interface between aluminum and organic semiconductor polymer of bulk-heterojunction (BH) organic photodiodes (OPD) based on poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric acid methylester (PCBM) blend, has been investigated according to reverse voltage bias over the OPD. We focused on the effect of incident light power (ILP) on the SCR and the I-V characteristics of the devices. Comparison of the mathematical models and experimental data measured under different ILPs indicate a dependency of SCR to the ILP.

Data transmission performance of CVD grown sub-20 nm indium antimonide nanowires

We investigated the data transmission performance of indium antimonide (InSb) nanowires (NWs) synthesized on InSb (100) substrate using chemical vapor deposition (CVD) having diameters below 20 nm. The data transmission measurement was accomplished over the NW field effect transistors (NWFETs) fabricated on Si/SiO2 substrates. Digital data stream is randomly generated and then uploaded to a waveform generator which generates the stream and transmits it repeatedly with the desired frequency. The signal was applied on the sources of the NWFETs and collected from the drains of the same devices. Collected data was first filtered with a low pass filter (LPF), and then the output of the filter was used to create the eye diagrams of the NWs. Bit error rate (BERs), attenuation , quality factor (Q-factor) and maximum data transmission are extracted from eye diagrams. The results indicate that the data transmission performance of NWs suffer from low mobility values on the order of 10-to-15 cm2V-1s-1 because of their small diameters, crystal defects and oxidation occurs during growth and cooling. 20 nm NWs can sustain data rates up to 10 mega bits per second (Mbps) and the data rate is directly proportional to the diameter of the NWs.