Jakub Haberko

Ordering domains of spin cast blends of conjugated and dielectric polymers on surfaces patterned by soft- and photo-lithography

Spin casting polymer blends of conjugated and dielectric macromolecules onto chemically patterned metal and oxidized silicon surfaces might provide a simple method to fabricate polymer-based circuitries that can be integrated with conventional electronics. Such solution-processing of the blend components offers simultaneous deposition and pattern-directed alignment of the phase separated polymer domains. The alignment is driven by self-organization guided by preferential surface segregation. Here we demonstrate that the laterally arranged domain structures in spin cast films of the conjugated poly(3-alkylthiophenes) (P3ATs): P3BT, P3DDT and regioregular R-P3HT, blended with dielectric polystyrene (PS), can be ordered by three different surface templates. The templates are formed by a patterned self-assembled monolayer (SAM), micro-contact printed on the surface of interest, i.e. hexadecanethiols on gold (for alignment of P3DDT/PS blend) and octadecyltrichlorosilanes on oxidized silicon (for R-P3HT/PS). Additionally gold lines are micro-patterned on SiO2 with photo-lithography (for P3BT/PS mixture). The forces driving pattern-directed self-organization of the polymers are discussed based on complementary studies of preferential surface segregation, observed for blend films spin cast on homogeneous surfaces that correspond to the different regions of the surface templates.

Protein coverage on silicon surfaces modified with amino-organic films: A study by AFM and angle-resolved XPS

An approach to determine structural features, such as surface fractional coverage F and thickness d of protein layers immobilized on silicon substrates coated with amino-organic films is presented. To demonstrate the proposed approach rabbit gamma globulins (RgG) are adsorbed from a 0.66muM solution onto SiO(2) and Si(3)N(4) modified with (3-aminopropyl)triethoxysilane (APTES). Atomic force microscopy data are analyzed by applying an integral geometry approach to yield average coverage values for silanized Si(3)N(4) and SiO(2) coated with RgG, F=0.99+/-0.01 and 0.76+/-0.08, respectively. To determine the RgG thickness d from angle-resolved X-ray photoelectron spectroscopy (ARXPS), a model of amino-organic bilayer with non-homogeneous top lamellae is introduced. For an APTES layer thickness of 1.0+/-0.1nm, calculated from independent ARXPS measurements, and for fractional surface RgG coverage determined from AFM analysis, this model yields d=1.0+/-0.2nm for the proteins on both silanized substrates. This value, confirmed by an evaluation (1.0+/-0.2nm) from integral geometry analysis of AFM images, is lower than the RgG thickness expected for monomolecular film ( approximately 4nm). Structures visible in phase contrast AFM micrographs support the suggested sparse molecular packing in the studied RgG layers. XPS data, compared for bulk and adsorbed RgG, suggest preferential localization of oxygen- and nitrogen-containing carbon groups at silanized silicon substrates. These results demonstrate the potential of the developed AFM/ARXPS approach as a method for the evaluation of surface-protein coverage homogeneity and estimation of adsorbed proteins conformation on silane-modified silicon substrates used in bioanalytical applications.

Role of Short-Range Order and Hyperuniformity in the Formation of Band Gaps in Disordered Photonic Materials.

We study photonic band gap formation in two-dimensional high-refractive-index disordered materials where the dielectric structure is derived from packing disks in real and reciprocal space. Numerical calculations of the photonic density of states demonstrate the presence of a band gap for all polarizations in both cases. We find that the band gap width is controlled by the increase in positional correlation inducing short-range order and hyperuniformity concurrently. Our findings suggest that the optimization of short-range order, in particular the tailoring of Bragg scattering at the isotropic Brillouin zone, are of key importance for designing disordered PBG materials.

Microstructured gradient-index antireflective coating fabricated on a fiber tip with direct laser writing

We present a simple broadband gradient-index antireflective coating, fabricated directly on a single mode telecom fiber tip. A regular array of hemi-ellipsoidal protrusions significantly reduce the Fresnel reflection from the glass-air interface. The parameters of the structure were optimized with numerical simulation for the best performance at and around 1550 nm and the coating was fabricated with Direct Laser Writing. The measured reflectance decreased by a factor of 30 at 1550 nm and was below 0.28% for the 100 nm spectral band around the central wavelength. Compared to quarter wavelength antireflective coatings the demonstrated approach offers significantly reduced technological challenges, in particular processing of a single optical material with low sensitivity to imperfections in the fabrication process.

Direct laser writing of three-dimensional network structures as templates for disordered photonic materials

In the present article we substantially expand on our recent study about the fabrication of mesoscale polymeric templates of disordered photonic network materials. We present a detailed analysis and discussion of important technical aspects related to the fabrication and characterization of these fascinating materials. Compared to our initial report we were able to reduce the typical structural length scale of the seed pattern from

Fabrication of mesoscale polymeric templates for three-dimensional disordered photonic materials

a=3.3\mu m

Highly asymmetric near infrared light transmission in an all-dielectric grating-on-mirror photonic structure.

to

Conductivity of Thin Polymer Films Containing Polyaniline

a=2\mu m

Electron-Beam Lithographic Grafting of Functional Polymer Structures from Fluoropolymer Substrates

, bringing it closer to the technologically relevant fiber-optic communications wavelength range around

XPS depth profiling of organic photodetectors with the gas cluster ion beam

\lambda \sim 1.5 \mu m