Growth modes of Fe(110) revisited: a contribution of self-assembly to magnetic materials

We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and propose an overview or our contribution to the field. We show that the Stranski-Krastanov growth mode, recognized for a long time in these systems, is in fact characterized by a bimodal distribution of islands for growth temperature in the range 250-700°C. We observe firstly compact islands whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat islands that display a preferred height, ie independant from nominal thickness and deposition procedure (1.4nm for Mo, and 5.5nm for W on the average). We used this effect to fabricate self-organized arrays of nanometers-thick stripes by step decoration. Self-assembled nano-ties are also obtained for nucleation of the flat islands on Mo at fairly high temperature, ie 800°C. Finally, using interfacial layers and solid solutions we separate two effects on the preferred height, first that of the interfacial energy, second that of the continuously-varying lattice parameter of the growth surface.Comment: 49 pages. Invited topical review for J. Phys.: Condens. Matte

Large Nc QCD and Harmonic Sums

In the Large-Nc limit of QCD, two--point functions of local operators become Harmonic Sums. I review some properties which follow from this fact and which are relevant for phenomenological applications. This has led us to consider a class of Analytic Number Theory Functions as toy models of Large-Nc QCD which I also discuss.Comment: Based on my talk at "Raymond Stora's 80th Birthday Party", LAPP, July 11th 201

Evidence of bcc Mn epitaxial growth in Mn/M

This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of bcc Mn near room temperature. For this purpose, Mn is deposited on bcc MxV$_{1-x}$(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the MxV$_{1-x}$ alloy's buffer layers can be adjusted from 2.95 Å to 3.3 Ådepending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing of the initial MxV$_{1-x}$ lattice. Thick Mn films are always found to grow epitaxially in the Mnα structure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), FexV$_{1-x}$(001) and NbxV$_{1-x}$(001) for $x\leq 25\%$. This tetragonal structure is shown to be a distorsion of a Mn bcc structure with $a=2.92 { \AA}$. Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples. These results are compared to theoretical predictions