Self-Organized Patterning: Regular and Spatially Tunable Luminescent Submicrometer Stripes Over Large Areas
✍ Scribed by X. Chen; M. Hirtz; H. Fuchs; L. Chi
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 315 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0935-9648
No coin nor oath required. For personal study only.
✦ Synopsis
The reaction mixture was heated under alternate vacuum and argon atmospheres for 30 min at 155 °C, when TOP-Se (selenium dissolved in TOP; 10 mL, 1 M) was rapidly injected into the reaction flask leading to very fast nucleation and growth of the PbSe NCs. The resulting NCs, withdrawn in several aliquots from the flask, were quenched with toluene (approximately ten times the volume of an aliquot), precipitated with ethanol (twice the volume of toluene) several times, and redispersed in a variety of solvents without any post-synthesis size-selection procedure.
Device Processing: A composite solution of PVK/ECZ/DEANST and PbSe NCs was produced by dissolving all the components in known proportions in toluene. Devices were fabricated by spin-coating (for photoconductive samples) or drop-casting (for PR samples) a film from this composite solution onto an ITO-coated glass substrate with an etched pattern. The film was dried in vacuum overnight (10 -2 atm pressure; 1 atm = 101.325 kPa), followed by drying in a vacuum oven at 80 °C for several hours to ensure complete solvent removal. For photoconductive samples of thickness ∼ 200 nm, upper contact electrodes (∼ 4 mm × 4 mm) of aluminum were deposited by vacuum evaporation. For PR samples, the dried film was softened by placing it on a hotplate (∼ 90-100 °C) for 30 s, and subsequently pressing it with another ITO-coated glass substrate to yield the sandwich structure of samples with thickness ∼ 50-60 lm. Both the colloidal NC solution and the composite films are stable over several weeks.
Sample Characterization: The morphology of the nanocrystal assembly was studied by TEM images acquired with a JEOL model JEM-100CX microscope operating at an acceleration voltage of 80 kV. All absorption spectra were obtained with a Shimazdu 3101 spectrophotometer. The photoconductivity measurements were performed using a Keithley 2400 SourceMeter interfaced with LabView software for data acquisition. The optical excitation was provided by 15 ms pulses from a 1550 nm continuous-wave semiconductor laser. Holographic gratings were written in a standard tilted geometry (1, 2, 8, 16) through the intersection of two coherent laser beams from the same laser that was used in the photoconductivity experiment. Writing beams were incident at angles of 35°and 55°(in air) with the sample normal. Asymmetric energy transfer was observed by monitoring the intensity of the two p-polarized writing beams with photodiodes after they crossed the sample. Diffraction efficiency was measured by degenerate four-wave mixing experiments in the same setup. The equal-intensity writing beams (50 mW cm -2 ), in this case, were s-polarized. A p-polarized reading beam of much weaker power density was counter-propagated with respect to the writing beam closer to the sample normal. The diffracted component of the reading beam was monitored with a photodiode as a function of applied device bias and time.