Heterostructures in the form of thin layers of one material grown on a substrate have been the subject of intense study for several years. In the case of semiconductor systems the aim is to grow epitaxial layers of, for example, Si_1-xGe_x on Si, and devices based on such structures are already in use. Much is known, as is summarized in this review, about the stability of such systems against the insertion of dislocations, and about the critical thicknesses up to which strained layer structures are stable. The effects of dislocation nucleation and the dynamics of dislocation motion which lead to strain relaxation in metastable systems are also reviewed. The present state of theoretical understanding is compared with what is known experimentally. For metallic systems, which often exhibit magnetic properties, the underlying problems of lattice mismatch and strain relief are similar, but much of the interest has been concentrated on the commensurate-incommensurate transition in both structurally and magnetically modulated materials. The theory of this transition is reviewed, both for metallic systems and for epitaxial layers on graphite. In bringing together these different classes of systems within one review, it has been possible to demonstrate the parallels between them. It is hoped that, as a result, transfers of ideas between the fields will be promoted.

Finite element calculations of stresses and strains in substrates and stripe films of thickness h and width 2l are reported. Both variation of the stress in the vertical direction (away from the interface) in the film and distortion of the substrate are taken into account. The calculations show that both the horizontal and vertical lattice planes are curved in the film as well as in the substrate. If the thickness of the substrate is infinite, the curvature in the substrate is maximum near the interface and decays rapidly with depth. Furthermore, the edges near the top are over‐relaxed, i.e., if the film is originally under compression, the stress becomes tensile because the free edge surfaces affect the relaxation. For a film with h/l=1 or greater, the stress is reversed throughout the top layer. The change from compression to tension takes place partly because of the Poisson effect and partly due to the bending of the lattice planes. The approximations made in the existing analytical models were examined and the conditions under which the models describe the stresses in the film or in the substrate were determined to a good approximation. Our finite element calculations agree with the available experimental data. Ours are the only theoretical results with which measured substrate stresses agree qualitatively.

Radiation damage in KCl can be produced by the decay of a self-trapped exciton into an F centre and an H centre. The authors present calculations of the energies of the states involved for various stages in the evolution of the damage. These lead to important conclusions about the very rapid damage process, and support strongly Itoh and Saidoh's suggestion (1973) that damage proceeds through an excited hole state. The results also help in understanding the prompt decay of F and H pairs at low temperatures, the thermal annihilation of F and H centres, the effects of optical excitation of the self-trapped exciton, and some of the trends within the alkali halides. The calculations use a self-consistent semi-empirical molecular-orbital method. A large cluster of ions is used (either 42 or 57 ions) plus long-range Madelung terms. The ion positions were obtained from separate lattice-relaxation calculations with the HADES code. The choice of CNDO parameters and the adequacy of the method were checked by a number of separate predictions.

Targeted delivery of potent, toxic chemotherapy drugs, such as cisplatin, is a significant area of research in cancer treatment. In this study, cisplatin was successfully encapsulated with high efficiency (>70%) in poly (lactic-co-glycolic acid) polymeric nanoparticles by using electrohydrodynamic atomization (EHDA) where applied voltage and solution flow rate as well as the concentration of cisplatin and polymer were varied to control the size of the particles. Thus, nanoparticles were produced with three different drug:polymer ratios (2.5, 5 and 10wt% cisplatin). It was shown that smaller nanoparticles were produced with 10wt% cisplatin. Furthermore, these demonstrated the best sustained release (smallest burst release). By fitting the experimental data with various kinetic models it was concluded that the release is dependent upon the particle morphology and the drug concentration. Thus, these particles have significant potential for cisplatin delivery with controlled dosage and release period that are crucial chemotherapy parameters.