http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10−4 s for the stabilized blue phases at room temperature.

Polymer-stabilized liquid crystal blue phases

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Within the different organic photovoltaic devices the conjugated polymer/fullerene bulk heterojunction approach is one of the foci of today's research interest. These devices are highly dependent on the solid state nanoscale morphology of the two components (donor/acceptor) in the photoactive layer. The need for finely phase separated polymer–fullerene blends is expressed by the limited exciton diffusion length present in organic semiconductors. Typical distances that these photo-excitations can travel within a pristine material are around 10–20 nm. In an efficient bulk heterojunction the scale of phase separation is therefore closely related to the respective exciton diffusion lengths of the two materials involved. Once the excitons reach the donor/acceptor interface, the photoinduced charge transfer results in the charge separation. After the charges have been separated they require percolated pathways to the respective charge extracting electrodes in order to supply an external direct current. Thus also an effective charge transport relies on the development of a suitable nanomorphology i.e. bicontinuous interpenetrating phase structures within these blend films. The present feature article combines and summarizes the experimental findings on this nanomorphology–efficiency relationship.

Morphology of polymer/fullerene bulk heterojunction solar cells

We report the first observation of cholesteric blue phases in chiral anisotropic polymer networks. In two-component mixtures of a chiral and a non-chiral diacrylate, we observed typical textures of BPI, BPII and BPIII phases. By photopolymerization of these materials at constant temperature we obtained blue phase networks. After polymerization, the blue phases were stored, which enabled us to further study them without any temperature control.

Observation of blue phases in chiral networks

Polymer-dispersed liquid crystals (PDLC) are widely used for electro-optic applications such as flexible displays, privacy windows or projection displays. Besides these applications, the confinement of a liquid crystal to small cavities is of fundamental interest. The present paper contains a review of the work on nematic and cholesteric PDLCs. Moreover, some very recent developments are summarized such as the use of ferroelectric liquid crystals for PDLC applications.

/pdf/polymer-dispersed-liquid-crystals-from-the-nematic-3g8vfyy6xv.pdf

Polymer-dispersed liquid crystals From the nematic curvilinear aligned phase to ferroelectric films

An experimental review on electric field effects in blue phases is presented. Electric fields have a profound effect on these phases which appear in chiral liquid crystals. In addition to producing elec-trostrictive effects on blue phase lattices, they also cause new field induced phases—tetragonal BPX, hexagonal BPH3D and BPH2D, and possible other phases yet to be identified. In recent experiments on BPIII for materials with negative dielectric anisotropy, it was found that electric fields cause a dramatic increase in the otherwise weak BPIII selective reflection. These experimental results were discussed with respect to possible models for the unknown structure of BPIII. Recently, efforts were also made to investigate the dynamics of different electrooptic effects more precisely.

/pdf/the-effect-of-electric-fields-on-blue-phases-20kpigfzva.pdf

The effect of electric fields on blue phases

We demonstrate that ferroelectric liquid crystals are suitable for application in polymer‐dispersed liquid crystal (PDLC) displays. The alignment of the liquid crystal can be controlled by mechanical shear during the polymerization‐induced phase separation between the liquid crystal and the UV‐curable adhesive which forms the polymer matrix. Helical unwinding in the smectic SmC phase and the electroclinic effect in the smectic SmA phase have been found in these samples. Both effects lead to a rotation of the optical axis in the plane perpendicular to the electric field. Switching times are of the order 100 μs.

Linear electro‐optic effects in polymer‐dispersed ferroelectric liquid crystals

We here report on the optical, alignment and electro-optic properties of a nematic liquid crystal affected by the presence of semiconductor CdSe magic-sized nanocrystals (MSNCs). Three single-sized CdSe samples were tested, exhibiting bright bandgap photoluminescence (PL) with λmax ≈ 463 nm and ∼10 nm full width at half-maximum (fwhm). The three quantum dot (QD) samples were passivated with a monolayer of myristic acid. Two of them (QD1 and QD2) only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample (QD3) is compositionally different, doped with Zn. These MSNCs with almost identical sizes were doped at different concentrations (1–5 wt%) into the nematic phase of 5-n-heptyl-2-(4-n-octyloxyphenyl)-pyrimidine (LC1). Only QD3 showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticle-doped nematic liquid crystals reported earlier by our group. In polyimide-coated glass slides favouring planar orientation of the nematic director, planar alignment was observed. Surprisingly, only the Zn-doped magic-sized QD3quantum dots (CdSe@Zn) significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality, which highlights the tremendous effect of the nanocrystal core composition on the electro-optic properties of the nematic host. In addition, fluorescence confocal (polarizing) microscopy studies show the director field within and around the birefringent stripes and confirm locally elevated concentrations or aggregates of the MCNC that are otherwise randomly distributed in the nematic host.

/pdf/nanocomposites-of-a-nematic-liquid-crystal-doped-with-magic-45qu5z9d4z.pdf

Heinz-S. Kitzerow

Papers

Observation of blue phases in chiral networks

Polymer-dispersed liquid crystals From the nematic curvilinear aligned phase to ferroelectric films

The effect of electric fields on blue phases

Linear electro‐optic effects in polymer‐dispersed ferroelectric liquid crystals

Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots