A distinct odd-even effect on the electrical properties, induced by monolayers of alkyl-phenyl molecules directly bound to Si(111), is reported. Monomers of H2C═CH-(CH2)n-phenyl, with n = 2-5, were adsorbed onto Si-H and formed high-quality monolayers with a binding density of 50-60% Si(111) surface atoms. Molecular dynamics simulations suggest that the binding proximity is close enough to allow efficient π-π interactions and therefore distinctly different packing and ring orientations for monomers with odd or even numbers of methylenes in their alkyl spacers. The odd-even alternation in molecular tilt was experimentally confirmed by contact angle, ellipsometry, FT-IR, and XPS with a close quantitative match to the simulation results. The orientations of both the ring plane and the long axis of the alkyl spacer are more perpendicular to the substrate plane for molecules with an even number of methylenes than for those with an odd number of methylenes. Interestingly, those with an even number conduct better than the effectively thinner monolayers of the molecules with the odd number of methylenes. We attribute this to a change in the orientation of the electron density on the aromatic rings with respect to the shortest tunneling path, which increases the barrier for electron transport through the odd monolayers. The high sensitivity of molecular charge transport to the orientation of an aromatic moiety might be relevant to better control over the electronic properties of interfaces in organic electronics.

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Acoustic manipulation is an emerging non-invasive method enabling precise spatial control of cells in their native environment. Applying this method for organizing neurons is invaluable for neural tissue engineering applications. Here, we used surface and bulk standing acoustic waves for large-scale patterning of Dorsal Root Ganglia neurons and PC12 cells forming neuronal cluster networks, organized biomimetically. We showed that by changing parameters such as voltage intensity or cell concentration we were able to affect cluster properties. We examined the effects of acoustic arrangement on cells atop 3D hydrogels for up to 6 days and showed that assembled cells spontaneously grew branches in a directed manner towards adjacent clusters, infiltrating the matrix. These findings have great relevance for tissue engineering applications as well as for mimicking architectures and properties of native tissues. The architecture of the brain and the nervous system is very complex, yet it is well organized 1,2. High-level architectures can be found in the spinal cord 3,4 , retina 5,6 , six-layered cortex 7 , hippocampus 8,9 , cerebellum 10 , and many other neuronal sub-regions. Between these organized sub-regions, specific neuronal networks, consisting of myriad neurons, work together to transfer and process information efficiently and to perform specific tasks that later are translated into various behaviors 2,11,12. Hence, the ability to artificially organize and pattern neurons at specific spatial positions in order to mimic different architectures and properties of neural networks is of great importance. In various fields in neuroscience research such as neural tissue engineering and regenerative medicine 13-16 , brain-machine interface 17-19 , developmental neuroscience 20 , and neuropharmacology 21,22 such controlling ability may be crucial. Indeed, in neural tissue engineering, much effort has been devoted to artificially mimic the highly organized architectures and properties of native tissues. Tang-Schomer and colleagues engineered functional brain-like cortical tissue by assembling donut-shaped layers. Their work offers a model with physiologically relevant features for assessing different brain disorders 23. Qian and colleagues have generated forebrain-, midbrain-, and hypothalamic-specific organoids from human-induced pluripotent stem cells, which were able to recapitulate the key features of these brain regions 24. Current methods for arranging specific cells include selective surface modifications 25,26 , direct bioprinting 27,28 , specific micromolding 29,30 , and the use of different forces such as optical 31 , magnetic 32 , and fluidic forces 33. Although these methods allow successful cell patterning, each technique has its own limitations. For example, bioprinting is costly and time consuming because it is applied sequentially, and its implementation in vivo is limited. In addition, parameters such as shear stress on cells, the material's viscosity, and different droplet sizes can dramatically affect th...

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