Moisture-harvesting lizards such as the Texas horned lizard (Iguanidae: Phrynosoma cornutum) live in arid regions. Special skin adaptations enable them to access water sources such as moist sand and dew: their skin is capable of collecting and transporting water directionally by means of a capillary system between the scales. This fluid transport is passive, i.e. requires no external energy, and directs water preferentially towards the lizard's snout. We show that this phenomenon is based on geometric principles, namely on a periodic pattern of interconnected half-open capillary channels that narrow and widen. Following a biomimetic approach, we used these principles to develop a technical prototype design. Building upon the Young-Laplace equation, we derived a theoretical model for the local behaviour of the liquid in such capillaries. We present a global model for the penetration velocity validated by experimental data. Artificial surfaces designed in accordance with this model prevent liquid flow in one direction while sustaining it in the other. Such passive directional liquid transport could lead to process improvements and reduction of resources in many technical applications.

We have determined the structure of the ultrathin (sqrt[67] x sqrt[67])R12.2 degrees aluminum oxide on Ni3Al(111) by a combination of scanning tunneling microscopy and density functional theory. In addition to other local defects, the main structural feature of the unit cell is a 0.4-nm-diameter hole reaching down to the metal substrate. Understanding the structure and metal growth on this oxide allows us to use it as a template for growing highly regular arrays of nanoparticles.

Cobalt surface oxides where grown on Pt(111) by depositing Co and dosing with molecular oxygen at temperatures ranging between 300 K and 740 K. Oxidation of 1 monolayer (ML) Co results in a two-dimensional (2D) moiré structure, observed both using low energy electron diffraction and scanning tunneling microscopy, and interpreted as a polar (oxygen terminated) CoO(111) atomic bilayer. With respect to bulk CoO, it is expanded by 2.7±0.5% in the surface plane. An almost flawless moiré pattern is obtained after a final step of annealing at 740 K in oxygen. Insufficient oxidation leads to defects in the moiré pattern, consisting of triangular dislocation loops of different sizes; the smaller ones occupying one half of the moiré cell. Low-temperature annealing (450 K) can be used to create a zigzag phase, which is mainly observed in 1-ML thick areas after several cycles of Co deposition (1 ML each) and oxidation at 10 -7 mbar. The CoO films obtained by deposition/oxidation cycles exhibit Stranski-Krastanov growth; the structure of the 2D layer in between the islands depending on the thermal treatment. After annealing at 740 K it exhibits the moiré pattern, while the zigzag phase was observed after low-temperature annealing. The second monolayer consists of a moiré pattern different from that of the 1st layer, presumably a wurtzite-like structure. Above the 3rd layer, we observe only small 3D islands, which exhibit a band gap. We have also studied oxidation of surface alloys obtained by depositing Co and annealing. On these surfaces, we found a quasi-(3×3) reconstruction. Structure models are presented for all phases observed, and we argue that some of the moiré-like structures might be useful as templates for metal cluster growth.

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Abstract. We present multimodal noncontact photoacoustic (PA) and optical coherence tomography (OCT) imaging. PA signals are acquired remotely on the surface of a specimen with a Mach-Zehnder interferometer. The interferometer is realized in a fiber-optic network using a fiber laser at 1550 nm as the source. In the same fiber-optic network, a spectral-domain OCT system is implemented. The OCT system utilizes a supercontinuum light source at 1310 nm and a spectrometer with an InGaAs line array detector. Light from the fiber laser and the OCT source is multiplexed into one fiber using a wavelength-division multiplexer; the same objective is used for both imaging modalities. Reflected light is spectrally demultiplexed and guided to the respective imaging systems. We demonstrate two-dimensional and three-dimensional imaging on a tissue-mimicking sample and a chicken skin phantom. The same fiber network and same optical components are used for PA and OCT imaging, and the obtained images are intrinsically coregistered.