In the Poisson-spot experiment, waves emanating from a source are blocked by a circular obstacle. Due to their positive on-axis interference an image of the source ͑the Poisson spot͒ is observed within the geometrical shadow of the obstacle. In this paper we report the observation of Poisson's spot using a beam of neutral deuterium molecules. The wavelength independence and the weak constraints on angular alignment and position of the circular obstacle make Poisson's spot a promising candidate for applications ranging from the study of large molecule diffraction to patterning with molecules. DOI: 10.1103/PhysRevA.79.053823 PACS number͑s͒: 37.20.ϩj, 03.75.Ϫb, 37.25.ϩk Diffraction experiments played a crucial role in establishing the existence of de Broglie matter waves ͓1-3͔. Today, matter-wave diffraction is used, among other applications, to investigate quantum interference of large molecules ͓4͔, enabling the study of quantum decoherence ͓5͔ and its role in the quantum-to-macroscopic-world transition. These experiments have mostly been carried out with free-standing material gratings ͓6,7͔ or light wave gratings ͓8͔. The largest molecules so far ͑Ͼ3 nm͒ for which quantum interference was successfully demonstrated were perfluoroalkylfunctionalized azobenzenes in a Kapitza-Dirac-Talbot-Lau interferometer ͓9͔. Scaling such experiments to even larger objects, such as macromolecules or perhaps even viruses, is a tantalizing prospect. In principle, this should be possible to some degree with a Kapitza-Dirac-Talbot-Lau interferometer. However, as the size of the molecule and/or object approaches the distance between grating bars difficulties arise. In the case of material gratings, van der Waals ͑vdW͒ forces increasingly limit interference contrast by adding a locally varying coherent phase shift. In fact, even blocking may occur. In the case of light gratings spontaneous emission and photon absorption are likely to perturb coherence. Furthermore, for the Talbot-Lau configuration the distance between the three gratings is a function of wavelength, and thus requires wavelength selection. This limits effective intensity of the commonly used thermal sources because only a fraction of the emitted molecules can be used in the experiment. In the case of clusters, the necessity of mass selection constrains effective source intensity additionally. Finally, alignment of the gratings, both with respect to each other and the vertical, is challenging, and misalignment can cause classical Moiré fringes which differ from expected interference patterns only in visibility and wavelength dependence.In this paper we make use of the Poisson-spot configuration to demonstrate quantum interference in a beam of molecules. The Poisson spot refers to a classical-optics experiment, in which a point light-source is blocked by a circular obstacle. Wave theory predicts that the intensity on the optical axis within the geometrical shadow is the same as without the blocking obstacle due to the cylindrical symmetry ͓11͔, resulting in a bright i...

Porous, polymer-based materials are increasingly used as stationary phases in separation science and catalysis, yet their morphology remains largely unknown. The main difficulty lies in reconciling their soft matter nature with the demands of microscopic imaging techniques. We analyze the morphology of a hyper-cross-linked poly(styrene-divinylbenzene) monolith in capillary column format from a sample volume of 60.5 × 60.5 × 19.9 μm(3) reconstructed by serial block-face scanning electron microscopy. To obtain a suitable specimen, the polymer skeleton was stained with tetraphenyllead and the void space filled with resin before the whole monolith was resin-embedded after removing the fused-silica capillary. Chord length distribution analysis revealed characteristic lengths of 7.32 and 0.73 μm, corresponding to two distinct macropore types. The macroporosity (77% on average) was found to increase systematically from the wall to the center. Our results provide valuable insights into the formation process of the monolith and its stationary-phase properties.

Polymethacrylate-based monoliths have excellent flow properties. Flow in the wide channel interconnected with narrow channels is theoretically assumed to account for favorable permeability. Monoliths were cut into 898 slices in 50nm distances and visualized by serial block face scanning electron microscopy (SBEM). A 3D structure was reconstructed and used for the calculation of flow profiles within the monolith and for calculation of pressure drop and permeability by computational fluid dynamics (CFD). The calculated and measured permeabilities showed good agreement. Small channels clearly flowed into wide and wide into small channels in a repetitive manner which supported the hypothesis describing the favorable flow properties of these materials. This alternating property is also reflected in the streamline velocity which fluctuated. These findings were corroborated by artificial monoliths which were composed of regular (interconnected) cells where narrow cells followed wide cells. In the real monolith and the artificial monoliths with interconnected flow channels similar velocity fluctuations could be observed. A two phase flow simulation showed a lateral velocity component, which may contribute to the transport of molecules to the monolith wall. Our study showed that the interconnection of small and wide pores is responsible for the excellent pressure flow properties. This study is also a guide for further design of continuous porous materials to achieve good flow properties.