This paper reviews the mechanical properties of graphene with particular attention to what is established and what is still uncertain. It clarifies the thickness and the elastic constants, and by also considering also phonon frequencies, it argues that “best values” come from graphite, when available. Properties not available from graphite include bending stiffness; this can be determined from studies of carbon nanotubes as well as graphene. In many ways, nanotubes provide access to fundamental properties of graphene, not least because they are the only form of graphene that can be unsupported (unstrained) in vacuum. Environmental effects are considered, including both interactions with substrates and with other solid and liquid media, which may affect the geometrical parameters defining graphene and associated elastic constants. Major uncertainties persist whether slipping or sticking dominates experimental observation, both between graphene and solid media, and between the layers of bilayer and multilayer graphene. The paper concludes with a short discussion of continuum and atomistic models of graphene.

The reason the InGaN/GaN quantum well system emits intense light even though the dislocation density is high is assessed. First, the evidence from electron microscopy for nanometre-scale In-rich clusters in InGaN quantum wells is presented. Such clusters would localize the excitons away from the dislocations and hence the dislocations would not quench the light emission, consistent with observations. However, it is then shown that InGaN damages extremely rapidly under an electron beam, and that the damage causes In-rich clusters to form. No evidence is found of gross indium clustering at low beam currents and short exposure times in the electron microscope. However, at such low electron doses the image is noisy, and low-level indium clustering in InGaN quantum wells could possibly exist, but be masked by the noise. A different technique, 3-dimensional atom probe field ion microscopy, has therefore been used to image the InGaN quantum wells. This reveals that InGaN is a random alloy, with the local statistical fluctuations in indium content expected in a random alloy, but with no indium clustering. Since In-rich clusters are clearly not necessary for bright light emission from InGaN quantum wells, another mechanism must be responsible for the exciton localization observed. It is shown that thickness fluctuations in the InGaN quantum wells of only one monolayer, observed in electron microscopy, result in an exciton confinement energy of 58 meV, sufficient to localize the carriers at room temperature. An alternative localization mechanism due to randomly formed In-N-In chains proposed by others is discussed. It is concluded that In-rich clusters in InGaN quantum wells do not exist in the specimens we have studied, and in any case they are not necessary to localize the excitons and for bright light emission.

In this paper, we compare and contrast the experimental data and the theoretical predictions of the low temperature optical properties of polar and nonpolar InGaN/GaN quantum well structures. In both types of structure, the optical properties at low temperatures are governed by the effects of carrier localisation. In polar structures, the effect of the in-built electric field leads to electrons being mainly localised at well width fluctuations, whereas holes are localised at regions within the quantum wells, where the random In distribution leads to local minima in potential energy. This leads to a system of independently localised electrons and holes. In nonpolar quantum wells, the nature of the hole localisation is essentially the same as the polar case but the electrons are now coulombically bound to the holes forming localised excitons. These localisation mechanisms are compatible with the large photoluminescence linewidths of the polar and nonpolar quantum wells as well as the different time scales and form of the radiative recombination decay curves.

We demonstrate the use of nanofabricated capillaries, integrated as part of a microfluidic structure, to study the electrophoretic behaviour of single, fluorescently-labelled, molecules of DNA as a function of capillary size. The nanocapillaries, fabricated using a focused ion beam, have cross-sections down to 150 × 180 nm. Control of single-molecule direction and velocity was achieved using voltage manipulation. DNA mobility was found to increase with decreasing cross-section, which we interpret in terms of reduced electro-osmotic counter-flow. Such nanofabricated capillaries as part of larger fluidic structures have great potential for biotechnology, particularly single molecule manipulation and analysis.

We report measurements of optical transitions in single III/V (InGaN) quantum dots as a function of time. Temporal fluctuations in microphotoluminescence peak position and linewidth are demonstrated and attributed to spectral diffusion processes. The origin of this temporal variation is ascribed to randomly generated local electric fields inducing a Stark shift in the optical emission peaks of the InGaN quantum dots.

We present a multi-microscopy study of dislocations in InGaN, whereby the same threading dislocation was observed under several microscopes (atomic force microscopy, scanning electron microscopy, cathodoluminescence imaging and spectroscopy, transmission electron microscopy), and its morphological optical and structural properties directly correlated. We achieved this across an ensemble of defects large enough to be statistically significant. Our results provide evidence that carrier localization occurs in the direct vicinity of the dislocation through the enhanced formation of In-N chains and atomic condensates, thus limiting non-radiative recombination of carriers at the dislocation core. We highlight that the localization properties in the vicinity of threading dislocations arise as a consequence of the strain field of the individual dislocation and the additional strain field building between interacting neighboring dislocations. Our study therefore suggests that careful strain and dislocation distribution engineering may further improve the resilience of InGaN-based devices to threading dislocations. Besides providing a new understanding of dislocations in InGaN, this paper presents a proof-of-concept for a methodology which is relevant to many problems in materials science.