Since its inception, the nanotechnology working group at the European Patent Office has been constantly updating the content of its different nanotechnology classification tags which it applies to patent publications worldwide. The main technologies in the nanophotonics area are photonic crystals, surface plasmon devices, semiconductor superlattices and scanning near-field microscopy. Some patent statistics are shown and a brief summary of legal issues is given.

We report the dynamics of amplified spontaneous emission (ASE) in thin organic films of tris-(8-hydroxyquinoline)-aluminum (Alq3) doped with small amounts of the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The energy transfer from the initially photoexcited Alq3 to the DCM molecules affects the high excitation density dynamics significantly. The time delay between pulsed photoexcitation and the ASE burst depends on the pumping level. For higher pumping levels the competition between depopulation by ASE and refilling of the DCM states via energy transfer leads to an oscillatory emission with a fundamental frequency of up to 0.2 THz.

We have fabricated a mechanically flexible conjugated polymer laser utilizing distributed feedback due to a two-dimensional photonic band structure. An ultraviolet-embossing process is used for nanopatterning a plastic substrate. On top we spin-coat a ladder-type poly(p-phenylene) as the active laser medium. Upon optical pumping, we observe a low threshold and nearly diffraction limited monomode laser emission perpendicular to the surface. Our results are explained within a Laue formulation for the feedback mechanism in the two-dimensional organic photonic crystal.

Summary form only given. Recent approaches towards low threshold solid state lasers are based on two-dimensional photonic bandstructures (2D-PBS). Stimulated emission and optically pumped lasing action has been observed for a variety of organic electroluminescent materials like e.g. conjugated polymers. Due to their high optical gain and the ease of fabrication organic solid state laser materials are well suited as active media in photonic crystal lasers. We have fabricated a surface emitting 2D-PBS laser utilizing a substrate which is nanopatterned through a UV-embossing process.

We report on the fabrication and characterization of ultrathin self-assembled fullerene films. Using a carboxy-functionalized fullerene and poly(ethylene imine), we prepare fullerene films by the layer-by-layer adsorption technique. Our structures exhibit a modulated electron density as evidenced by the observation of a quasi-Bragg reflection in X-ray reflectivity studies. This relatively high degree of order is attributed to the formation of hydrogen bonds.

We investigate the exciton dynamics in composite systems of conjugated polymers and fullerene molecules by photoluminescence (PL) and femtosecond transient absorption experiments. In solid mixtures (blends) we find a strong concentration-dependent quenching of the polymer FL. This is attributed to an efficient electron transfer (ET) from the photoexcited conjugated polymer to the fullerene. The ET dynamics is directly monitored by measuring the transient stimulated emission of the conjugated polymer. The transfer rate depends linearly on the C-60 concentration and ranges between (66 ps)(-1) and (5 ps)(-1) for concentrations from 0.5% to 5%. This dependence is in accordance with an exciton diffusion process occurring prior to the ET. The exciton diffusion length in the conjugated polymer is directly determined by measuring the PL quenching in well-defined heterostructures comprising a self-assembled fullerene monolayer and a thin spin-coated polymer layer of variable thickness. From these measurements we infer a value of 14 nm for the exciton diffusion length in ladder-type poly (p-phenylene). Our results are of direct relevance for further optimization of polymer photovoltaic devices. [S0163-1829(99)07923-0].

The emission dynamics in photoexcited planar conjugated polymer waveguides is investigated at high excitation densities. Using femtosecond pump/probe experiments and photoluminescence spectroscopy we investigate the interplay of nonlinear radiative and nonradiative recombination processes. Amplified spontaneous emission (ASE) leads to an ultrafast depletion of the excited state at excitation densities above 1018 cm−3 in an ladder-type poly(p-phenylene) film deposited on a glass substrate. Owing to the different waveguide structure ASE is not observed for the same polymer deposited on an indium–tin–oxide (ITO)-coated substrate. Instead, we observe nonradiative bimolecular annihilation with a coefficient γ=4.2×10−9 cm3 s−1. Our results demonstrate that even in the absence of a resonator collective stimulated emission can be much more efficient than nonradiative recombination. A mandatory prerequisite, however, is a suitable waveguide design. The use of ITO as a hole-injecting contact is problematic due to its high refractive index and its relatively high losses.

Summary form only given. The discovery of stimulated emission in semiconducting polymers has triggered intense research towards the realization of an organic injection laser. One of the most promising approaches towards novel organic thin film lasers is the use of distributed feedback resonators realized with flexible substrates. Such a strategy might lead to novel large area lasing devices of virtually any shape not possible with inorganic semiconductor materials. In order to achieve a low lasing threshold and to control the emission properties, it is crucial to reduce the number of modes participating in the lasing operation. A particularly interesting way to fulfill these requirements is the use of two-dimensional photonic bandstructure (PBS) materials. We present experiments on optically pumped flexible polymer lasers using a two-dimensional PBS based distributed feedback.

We report a detailed investigation of optical gain narrowing processes in thin films of a conjugated ladder-type poly(p-phenylene) polymer. The intensity-dependent optical emission spectra of samples of varying thickness are compared. For thin high-quality spin-coated samples spectral narrowing of the emission is observed for pump pulse energies as low as 10 nJ. Picosecond time-resolved measurements show that the spectral narrowing is accompanied by an accelerated emission for high pump energies. Our experimental findings are in full agreement with the assumption that amplified spontaneous emission in a lateral direction is the underlying physical mechanism.

Lasing in conjugated polymers A. Haugeoederl. C. Ki lhgerl, M. Nigcs1.41 Hilmerl, U I.cmme:I, W'. Sptrkl', I. F c l d m m ' , 1;. Scherfz, A. Goinbcn3. .md V. W~ttuer' cnd Opioelrkiii?nrk. Luiiuig~!~f~ronr!ior!s-C",ir e wit . German),. f'el.. +49~89~2180-3412. FAX 40-89-218 ~ M ~ i P l ~ , i c * ; l n s i i r u ! , ~ ~ .J'o!oiymerjorschurzg, AckemnrmWcg 10, f5118 ,Wm 'Fraunhojhr LYE, 0lrmannscr.f. 79100 Frehurg, Gemron)

Folded graphitic sheets have been produced and studied using a scanning tunnelling microscope. Folds of one and two layers are observed at steps on highly oriented pyrolytic graphite. Images at atomic resolution show that the folding axes lay along the [210] or [100] directions resulting in AB- or AA-stacking of the folding sheets on the graphite surface, respectively. The stability of the observed structures is studied and the attractive inter-plane energy is found to be larger than the repulsive folding energy.

Collective stimulated emission processes in conjugated polymers makes these materials potential candidates for laser applications. The fabrication of a low-cost flexible distributed feedback laser (see Figure and also the cover) by spin-coating a conjugated polymer onto a specially structured, flexible plastic substrate is reported. Single-mode laser emission in the blue-green spectral region has been achieved.

Folding and unfolding of atomic layers has been performed at step edges of graphite using a scanning tunneling microscope. The technique consists of modulating the distance or bias voltage between the microscope tip and the sample when scanning selected areas. Calculation of the energies involved in the manipulations shows that tip-sample vibration can account for tearing and folding of graphitic layers.

We investigate electron transfer in conjugated polymer/fullerene heterostructures prepared by a combination of spin-coating and self-assembly methods. Via insertion of ultrathin (<10nm) spacer layers of varying thickness between the conjugated polymer layer and a self-assembled monolayer of a functionalized fullerene, it is possible to control the electron transfer between the photoexcited conjugated polymer acting as a donor and the electron accepting fullerene.