A surfactant‐free solution methodology, simply using water as a solvent, has been developed for the straightforward synthesis of single‐phase orthorhombic SnSe nanoplates in gram quantities. Individual nanoplates are composed of {100} surfaces with {011} edge facets. Hot‐pressed nanostructured compacts (E g≈0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S 2 σ) at 550 K. S 2 σ values are 8‐fold higher than equivalent materials prepared using citric acid as a structure‐directing agent, and electrical properties are comparable to the best‐performing, extrinsically doped p‐type polycrystalline tin selenides. The method offers an energy‐efficient, rapid route to p‐type SnSe nanostructures.

No abstract

As urfactant-free solution methodology,s imply using water as as olvent, has been developed for the straightforwards ynthesis of single-phase orthorhombic SnSe nanoplates in gram quantities.Individual nanoplates are composed of {100} surfaces with {011} edge facets.H ot-pressed nanostructured compacts (E g % 0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S 2 s)a t5 50 K. S 2 s values are 8-fold higher than equivalent materials prepared using citric acid as as tructure-directing agent, and electrical properties are comparable to the best-performing,extrinsically doped p-type polycrystalline tin selenides.T he method offers an energy-efficient, rapid route to p-type SnSe nanostructures.Growing global energy demands,together with the negative impacts resulting from combustion of fossil fuels,h ave diverted attention to technologies for sustainable energy generation and conversion.[1] Thermoelectrics realize direct inter-conversion between thermal and electrical energy and provide opportunities to harvest useful electricity from waste heat (and conversely to perform refrigeration). Thet hermoelectric conversion efficiencyo famaterial is determined by its dimensionless figure of merit, ZT= S 2 sT/k,where S, s, T, and k represent the Seebeck coefficient, electrical conductivity,a bsolute temperature,a nd thermal conductivity,r espectively.[2] Extensive efforts have been devoted to the improvement of the thermoelectric performance of state-of-the-art materials, [3] and to the discovery of new thermoelectrics [4] with ZT values > 2. Single-crystalline SnSe combines ah ighZTwith arelatively low toxicity and high Earth-abundance of the component elements.[4] SnSe crystals possess very low thermal conductivity owing to lattice anharmocity,y ielding record high ZTvalues of 2.6 and 2.3 at 923 Kalong the b and c crystallographic directions,r espectively.[4] Polycrystalline SnSe materials have been fabricated to improve mechanical properties, [5] but ZT has been limited to 1, owing to both increased electrical resistivity and thermal conductivity. [5] Unfortunately,t he synthesis of SnSe is protracted and energy-intensive,i nvolving heating, melting, and annealing at high temperatures ( % 800-1223 K). [4][5] Before the potential of SnSe can be realized, afast, cost-effective,and large-scale synthesis route to the pure selenide that does not sacrifice performance is essential.Nanostructuring very effectively enhances ZT. Theh igh density of interfaces improves phonon scattering, decreasing the lattice thermal conductivity. [2,3] Bottom-up solution synthesis methods facilitate control of size,m orphology,c rystal structure,and defects.[6] However,the organic surfactants that can control morphology through surface modification are commonly electrically insulating, which can drastically reduce the electrical conductivity of the materials.[7] Ligand replacement methods switch smaller species for long chain surfactant molecules, [7] but sometimes involve using high toxicity chemicals, ...

A system for the back projection of computer-generated visual images onto a screen or screens that cover 240 of the horizontal visual field is described. Its applicability for the study of crab vision is tested by comparing the frequency response of the optokinetic response of the land crab, Cardisoma guanhumi, to sinusoidal oscillation of computer-generated striped patterns and a real striped drum. Significant differences were observed only at the low end of the frequency spectrum. The flexibility of computer-generated visual stimulation and its advantages for the study of optic flow are illustrated by experiments that: (a) demonstrate how well crabs separate the translational and rotational components of optic flow by showing compensatory eye movements to only the latter; (b) show that the ability to compensate for rotation is not impaired by combinations of rotation and translation; (c) show that motion parallax cues are used in addition to previously-described global cues for making the distinction between rotation and translation. Finally, the use of these methods in a successful search for visual interneurones sensitive to optic flow stimuli is demonstrated for the shore crab, Carcinus maenas.

Using a novel suite of computer-generated visual stimuli that mimicked components of optic flow, the visual responses of the tropical land crab, Cardisoma guanhumi, were investigated. We show that crabs are normally successful in distinguishing the rotational and translational components of the optic flow field, showing strong optokinetic responses to the former but not the latter. This ability was not dependent on the orientation of the crab, occurring both in "forwards-walking" and "sideways-walking" configurations. However, under conditions of low overall light intensity and/or low object/background contrast, the separation mechanism shows partial failure causing the crab to generate compensatory eye movements to translation, particularly in response to low-frequency (low-velocity) stimuli. Using this discovery, we then tested the ability of crabs to separate rotational and translational components in a combined rotation/translation flow field under different conditions. We demonstrate that, while crabs can successfully separate such a combined flow field under normal circumstances, showing compensatory eye movements only to the rotational component, they are unable to make this separation under conditions of low overall light intensity and low object/background contrast. Here, the responses to both flow-field components show summation when they are in phase, but, surprisingly, there is little reduction in the amplitude of responses to rotation when the translational component is in antiphase. Our results demonstrate that the crab's visual system finds separation of flow-field components a harder task than detection of movement, since the former shows partial failure at light intensities and/or object/background contrasts at which movement of the world around the crab is still generating high-gain optokinetic responses.