charge limit. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer. Growth modes Frank–van der Merwe growth ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism. Stranski–Krastanov growth ("joint islands" or "layer-plus-island"). In this growth mode the adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions. Volmer–Weber ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away. Epitaxy A subset of thin-film deposition processes and applications is focused on the so-called epitaxial growth of materials, the deposition of crystalline thin films that grow following the crystalline structure of the substrate. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon". The term homoepitaxy refers to the specific case in which a film of the same material is grown on a crystalline substrate. This technology is used, for instance, to grow a film which is more pure than the substrate, has a lower density of defects, and to fabricate layers having different doping levels. Heteroepitaxy refers to the case in which the film being deposited is different from the substrate. Techniques used for epitaxial growth of thin films include molecular beam epitaxy, chemical vapor deposition, and pulsed laser deposition. Stress and strain Thin films may be biaxially loaded via stresses originated from their interface with a substrate. Epitaxial thin films may experience stresses from misfit strains between the coherent lattices of the film and substrate. Thermal stress is common in thin films grown at elevated temperatures due to differences in thermal expansion coefficients with the substrate. Differences in interfacial energy and the growth and coalescence of grains contribute to intrinsic stress in thin films. These intrinsic stresses can be a function of film thickness. These stresses may be tensile or compressive and can cause cracking or buckling among other forms of stress relaxation. In epitaxial films, initially deposited atomic layers may have coherent lattice planes with the substrate. However, past a critical thickness misfit dislocations will form leading to relaxation of stresses in the film. Measuring stress and strain The stresses in Films deposited on flat substrates such as wafers can be measured by measuring the curvature of the wafer