Graphene — a recently isolated one-atom-thick layered form of graphite — is a hot topic in the materials science and condensed matter physics communities, where it is proving to be a popular model system for investigation. An experiment involving individual graphene sheets suspended over a microscale scaffold has allowed structure determination using transmission electron microscopy and diffraction, perhaps paving the way towards an answer to the question of why graphene can exist at all. The 'two-dimensional' sheets, it seems, are not flat, but wavy. The undulations are less pronounced in a two-layer system, and disappear in multilayer samples. Learning more about this 'waviness' may reveal what makes these extremely thin carbon membranes so stable. Investigations of individual graphene sheets freely suspended on a microfabricated scaffold in vacuum or in air reveal that the membranes are not perfectly flat, but exhibit an intrinsic waviness, such that the surface normal varies by several degrees, and out-of-plane deformations reach 1 nm. The recent discovery of graphene has sparked much interest, thus far focused on the peculiar electronic structure of this material, in which charge carriers mimic massless relativistic particles1,2,3. However, the physical structure of graphene—a single layer of carbon atoms densely packed in a honeycomb crystal lattice—is also puzzling. On the one hand, graphene appears to be a strictly two-dimensional material, exhibiting such a high crystal quality that electrons can travel submicrometre distances without scattering. On the other hand, perfect two-dimensional crystals cannot exist in the free state, according to both theory and experiment4,5,6,7,8,9. This incompatibility can be avoided by arguing that all the graphene structures studied so far were an integral part of larger three-dimensional structures, either supported by a bulk substrate or embedded in a three-dimensional matrix1,2,3,9,10,11,12. Here we report on individual graphene sheets freely suspended on a microfabricated scaffold in vacuum or air. These membranes are only one atom thick, yet they still display long-range crystalline order. However, our studies by transmission electron microscopy also reveal that these suspended graphene sheets are not perfectly flat: they exhibit intrinsic microscopic roughening such that the surface normal varies by several degrees and out-of-plane deformations reach 1 nm. The atomically thin single-crystal membranes offer ample scope for fundamental research and new technologies, whereas the observed corrugations in the third dimension may provide subtle reasons for the stability of two-dimensional crystals13,14,15.

/pdf/the-structure-of-suspended-graphene-sheets-1hs19mwg5z.pdf

The structure of suspended graphene sheets

The 2D–3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum‐sized dot structures. Transmission electron micrographs reveal that when the growth of In0.5Ga0.5As is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of the InGaAs result. Size distributions indicate that these dots are ∼300 A in diameter and remarkably uniform to within 10% of this average size. The areal dot densities can be varied between 109 and 1011 cm−2. The uniformity of the dot sizes is explained by a mechanism based on reduction in adatom attachment probabilities due to strain. We unambiguously demonstrate photoluminescence at ∼1.2 eV from these islands by comparing samples with and without dots. The luminescent intensities of the dots are greater than or equal to those of the underlying reference quantum wells.

Direct formation of quantum‐sized dots from uniform coherent islands of InGaAs on GaAs surfaces

We describe the synthesis of very thin sheets (between a few and ten atomic layers) of hexagonal boron nitride (h-BN), prepared either on a SiO2 substrate or freely suspended. Optical microscopy, atomic force microscopy, and transmission electron microscopy have been used to characterize the morphology of the samples and to distinguish between regions of different thicknesses. Comparison is made to previous studies on single- and few-layer graphene. This synthesis opens the door to experimentally accessing the two-dimensional phase of boron nitride.

/pdf/the-two-dimensional-phase-of-boron-nitride-few-atomic-layer-9s12kw5nnu.pdf

The two-dimensional phase of boron nitride: Few-atomic-layer sheets and suspended membranes

http://w0.rz-berlin.mpg.de/hjfdb/pdf/260e.pdf

Metal deposits on well-ordered oxide films

Nanocrystalline cellulose (NCC) is an emerging renewable nanomaterial that holds promise in many different applications, such as in personal care, chemicals, foods, pharmaceuticals, etc. By appropriate modification of NCC, various functional nanomaterials with outstanding properties, or significantly improved physical, chemical, biological, as well as electronic properties can be developed. The nanoparticles are stabilised in aqueous suspension by negative charges on the surface, which are produced during the acid hydrolysis process. NCC suspensions can form a chiral nematic ordered phase beyond a critical concentration, i.e. NCC suspensions transform from an isotropic to an anisotropic chiral nematic liquid crystalline phase. Due to its nanoscale dimension and intrinsic physicochemical properties, NCC is a promising renewable biomaterial that can be used as a reinforcing component in high performance nanocomposites. Many new nanocomposite materials with attractive properties were obtained by the physical incorporation of NCC into a natural or synthetic polymeric matrix. Simple chemical modification on NCC surface can improve its dispersability in different solvents and expand its utilisation in nano-related applications, such as drug delivery, protein immobilisation, and inorganic reaction template. This review paper provides an overview on this emerging nanomaterial, focusing on the surface modification, properties and applications of NCC.

Chemistry and Applications of Nanocrystalline Cellulose and its Derivatives: a Nanotechnology Perspective

Clustering on surfaces

Phase separation on solid surfaces: nucleation, coarsening and coalescence kinetics

The time-dependent topology of domains in supported phospholipid bilayers of a binary mixture of dioleoylphosphatidylcholine and dipalmitoylphosphatidylcholine under a buffer solution has been studied by atomic force microscopy. We observe a transient regime of the phase separation until 45 min after a temperature quench from a miscible state of the system into the gel−liquid crystal coexistence region with the earliest observation after 20 min showing large gel-phase domains (containing ∼104−106 molecules) of irregular shapes. The transient regime is characterized by a power law for the growth rate of the domain size (A) with n = 3.0 ± 0.4 in A ∝ t2/n. After 45 min, an asymptotic power law with n = 20 ± 10 is observed and is linked to an inhibited domain growth. The evolution of individual domains suggests that domain growth in the transient regime is governed by a ripening mechanism. The growth inhibition is linked to the observation that the gel domains in each leaflet of the bilayer must grow simultan...

Phase Topology and Growth of Single Domains in Lipid Bilayers

The effect of carbon nanotube aspect ratio and loading on the elastic modulus of electrospun poly(vinyl alcohol)-carbon nanotube hybrid fibers

The clustering behavior of Ge thin films deposited on Si has been investigated by ion scattering and electron microscopy. Post-deposit-annealed Ge is shown to cluster according to an Ostwald ripening mechanism. The cluster-volume growth is linear in time, and the cluster-size distribution is in agreement with the theoretical prediction. Cluster formation during low deposition rates is also studied. This permits an estimate of the limit for the application of the Ostwald-ripening approach to the nonzero deposition-rate regime.

Martin Zinke-Allmang

Papers

Clustering on surfaces

Phase separation on solid surfaces: nucleation, coarsening and coalescence kinetics

Phase Topology and Growth of Single Domains in Lipid Bilayers

The effect of carbon nanotube aspect ratio and loading on the elastic modulus of electrospun poly(vinyl alcohol)-carbon nanotube hybrid fibers

Growth mechanism and clustering phenomena: The Ge-on-Si system.