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Scanning tunneling microscopy observations show that (i) the lattice mismatch between Ni and Ru leads to a sequence of increasingly relaxed structures in Ni films grown on Ru(0001), and (ii) the density of Ni islands changes drastically with the thickness of the underlying Ni film. The latter is associated with an increase in Ni mobility; from monolayer to three-layer Ni films a reduction in Ni adatom diffusion barrier of 300 meV is estimated. Such effects are shown to significantly affect film growth and, in this case, to promote smoother growth. New possibilities for obtaining smoother film growth for heteroepitaxial systems, in general, are discussed. PACS numbers: 68.55. -a, 61.16.Ch Epitaxial growth affords the opportunity to make materials with morphologies and chemical compositions which would not ordinarily occur in nature [1 -4]. By varying the experimental parameters of temperature, deposition rate, and, more recently, additive (surfactant) concentrations the characteristics of the growing film can be controlled to a certain extent [5 -12]. For heteroepitaxy further effects come into play, namely, the change in film structure due to the removal of strain, and the change in electronic properties with increasing film thickness. The strain results from the lattice mismatch between the substrate and the growing film. In this Letter we demonstrate that these surface modifications can have a drastic effect on the adatom mobilities, leading to layerdependent island densities. The structure of and adatom mobilities on films of different layer thicknesses were determined by scanning tunneling microscopy (STM). For these experiments we first prepared well-defined Ni films on a Ru (0001) substrate by deposition at 550 K. This temperature is sufficiently high to produce well-ordered surfaces and rather large terraces, but not high enough to create the equilibrium morphology of that system, which consists of 3D crystallites growing on a single Ni layer (Stranski-Krastanov growth) and which is obtained after deposition at or annealing to higher temperatures [13,14].On these thin film substrates we subsequently deposited small amounts of Ni in a second dose at room temperature. From the distribution and density of the Ni islands obtained after the second dose we gain insight into adatom diffusion on and among the various well-defined Ni layers. The results lead us to introduce layer dependent mobilities and island densities as a general concept for heteroepitaxy with substantial implications for growth descriptions and film morphologies.Deposition and STM imaging were carried out at p ( 3 x 10 " Pa, on carefully cleaned Ru(0001) substrates.Further details on the experimental setup and procedures and on the growth behavior of that system will be described elsewhere [14]. STM images were recorded in a pocket-sized STM at tunnel currents around 1 nA and bias voltages of 100 mV. The images are presented in either a top view representation, v .ih darker areas corresponding to lower levels, or in a bird's eye view with illu...

The prospects of two classes of diamond devices are reviewed, namely electronic devices on single-crystal substrates and microsystems devices on Si substrate. The transistor structures on single-crystal diamond represent still proof-of-concept experiments; however, they already allow us to extract their potential. The microsystems actuator and sensor devices already reflect the materials properties in their characteristics. Two of the most complex structures and future trends are discussed.

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