Highly Ordered Organic Alq₃ Chiral Luminescent Thin Films Fabricated by Glancing‐Angle Deposition

Abstract

We have fabricated 3D photonic crystals based on the woodpile structure by means of the two-photon polymerization technique. The crystals have a photonic bandgap at a wavelength of 1.2 lm and show superprism effects at wavelengths slightly below their PBG. We have demonstrated these wavelength-dependent dispersion properties experimentally, and they are in good agreement with our theoretical calculations. We were able to observe a change in the propagating angle of more than 10°for a wavelength tuning range of 20 nm. This effect is two orders of magnitude larger than in conventional prisms. The results show the great potential of low-refractive-index 3D PCs, fabricated in a very fast and single-step process, to serve directly as functional micro-optical devices in the NIR wavelength regime. ExperimentalFor the fabrication of the woodpile structures, organic/inorganic hybrid polymers of high optical quality, called Ormocers, were used. After laser irradiation, the samples were developed in a mixture of 4-methyl-2-pentanone and isopropyl alcohol (volume ratio of 1:2) for approx. 1 min and subsequently rinsed in isopropyl alcohol. To fabricate the structures by means of 2PP, we used an optical parametric oscillator (Coherent Mira OPO) at a wavelength of 580 nm, a repetition rate of 90 MHz, and pulse duration of 100 fs. The pulses were focused into a thin Ormocer film with an immersion oil objective lens (Olympus; numerical aperture, NA= 1.4, 100×). In order to move the laser focus three-dimensionally through the resin, the sample was mounted on a computer-controlled piezo-driven nanoscanner (PI). The transmission spectra were measured with a FTIR spectrometer (Thermo Nicolet) in combination with an IR microscope. The IR light was focused onto the sample using a 32× reflective microscope objective. The superprism characterization was performed with a tunable Ti:sapphire laser operated in continuous-wave mode (Spectra Tsunami), allowing for a maximum wavelength of approx. 1020 nm. The light was focused onto the crystals with a 6.3× objective lens (NA= 0.2), leading to a focal size of approx. 10 lm. The angles of propagation were derived quantitatively by computational analysis of the CCD images of the propagating light (a Gaussian function was fitted to the recorded light distribution at different positions inside the crystal. The accuracy of the fitting determined the size of the error bars). All of the band structures shown were calculated using the freely available MIT Photonic Bands software package [23]. Calculations of the transmittance and reflectance of the woodpile structures were not performed.

Organic Electronic Devices and Their Functional Interfaces

“…In GLAD, a large angle a between the substrate surface normal and the direction of the molecular evaporation source is chosen, while the substrate is rotated about its surface normal during deposition. [158] Due to shadowing effects on lower surface areas during island growth, highaspect-ratio nanocolumns of organic semiconductor materials can be grown, [159,160] as shown, for instance, in Figure 12 for pentacene on ITO. It can be anticipated that by combination with a second organic layer (e.g.…”

Porous Nanostructured Optical Filters Rendered Insensitive to Humidity by Vapor-Phase Functionalization

“…The GLAD technique is versatile and has been successfully applied to a host of materials, including dielectrics, metals, semiconductors, and organics, the details of which are described in the literature. [27][28][29][30] Gradient-index optical filters can be fabricated by GLAD through variation of the deposition angle. Highly oblique deposition angles create thin-film layers that exhibit a low refractive index because the effective medium is predominately composed of air-filled pores.…”

Cadmium(II) (8‐Hydroxyquinoline) Chloride Nanowires: Synthesis, Characterization and Glucose‐Sensing Application

“…[2,3] Brett and co-workers fabricated chiral thin films, consisting of submicrometer scaled helical Alq 3 structures that generate circularly polarized photoluminescence. [4] As electroluminescent materials, Mq n and its derivatives have been widely used in organic light-emitting devices (OLEDs). [5][6][7][8][9][10] Alq 3 has been used frequently because of its good electronic conductivity and strong electroluminescence emission.…”