V. Repain

Self-ordering of Au(111) vicinal surfaces and application to nanostructure organized growth

This paper reports on Au(111) vicinal surfaces, either regularly stepped surfaces, reconstructed or not, or periodically faceted surfaces, which are well suited to be used as templates for organized growth of clusters. Angles of misorientation with respect to the (111) plane lie between 1° and 12° and two opposite azimuths are considered: (i) [211], that leads to steps with {100} microfacets, and (ii) [211], that leads to steps with {111} microfacets. The behaviour of the Au( 111) reconstruction in the vicinity of steps depends drastically on the step microstructure, and this is a key point for understanding the various periodic morphologies existing on Au(111) vicinal surfaces. The interaction between the reconstruction and the close-packed steps of the Au( 111) surface is interpreted in terms of the relative stability of both types of step. Self-organized morphologies between 10 and 100 nm are interpreted within the framework of elastic theory and by pointing out the crucial role played by the atomic boundary energy term. The microscopic origin of faceting is discussed, proposing two different models depending on each azimuth. Then, we illustrate the use of Au( 111) vicinal surfaces as templates for growing long range ordered nanostructures. Examples are given in the case of cobalt growth.

Growth of self-organized cobalt nanostructures on Au(111) vicinal surfaces

We studied the growth of cobalt on Au(111) vicinal surfaces in the submonolayer range. We found that the presence of a surface reconstruction leads to interesting self-organized nanostructures, such as very regular arrays of clusters or nanowires. We show that the use of a vicinal substrate strongly improves their long-range order properties. These results, together with the periodic faceting behaviour of gold vicinal surfaces, open the way to fabricate cobalt nanostructures or ultrathin films with original magnetic properties.

Self-ordering in two dimensions : nitrogen adsorption on copper (100) followed by STM at elevated temperature

Abstract We have followed the adsorption and the desorption of nitrogen on the copper (1xa00xa00) surface in real time using scanning tunneling microscopy at elevated temperatures. This gives an unprecedented view, especially of the adsorption behavior at very low coverage. Growth proceeds by splitting of square-shaped islands of critical size without loss of C4 symmetry. The equilibrium structures are analyzed in terms of their dimensionality and shape showing that the phase diagram comprises two periodic domain morphologies as a function of nitrogen coverage: two-dimensional (2D) array of compact nitrogen islands at low and high coverage and a quasi 1D arrangement of striped domains (rows of squares) at intermediate coverages. Furthermore, we investigated the sensitivity of the system to small changes in the elastic properties of the substrate by pre-deposition of gold on the bare copper surface. Finally, the comparison all our observations in the light of existing model predictions for long-range interactions in 2D systems reveals crucial differences and, therefore, these models have to be extended to include short range relaxation and interactions in order to reproduce the fundamental aspects of this system.

Self-ordering on crystal surfaces: fundamentals and applications

Self-ordering on crystal surfaces has been the subject of intense efforts during the last ten years. It has been recognized as a promising way for growing uniform nanostructures with regular sizes and spacings. Continuum models have been proposed where long-range elastic repulsive interactions are responsible for the periodic domain spontaneous formation. Vicinal surfaces unstable towards faceting lead to a one dimensional (1D) periodic morphology. Au(111) vicinals self-ordering provides a unique opportunity to point out the interplay between atomic and mesoscopic order. 2D ordering has been investigated in the complex case of atomic nitrogen adsorbed on Cu(100). Using scanning tunneling microscopy (STM) at elevated temperature, we have followed the ordered arrays of N square-shaped domains spontaneous formation. Observations are discussed in the light of previous continuum models for self-ordering. The question of understanding self-ordering is not only of fundamental but also of technological interest since it is a fruitful way of growing regularly spaced nanostructures in the 1/100 nm range. This will be illustrated by two examples: (i) selfordered substrates can serve as templates for growing 2D square lattice of regular nanostructures; (ii) magnetic domains of an ultrathin film can be tailored by using self-ordered substrates. # 2002 Elsevier Science B.V. All rights reserved.

Ordered growth of cobalt nanostructures on a Au(111) vicinal surface: nucleation mechanisms and temperature behavior

We study the growth of submonolayer coverage of cobalt on the Au(788) vicinal surface. Due to a large unit cell reconstruction, this surface is spontaneously patterned in two dimensions at a nanometer scale. We show that the cobalt growth on this substrate displays a long-range ordered nanodots array in a wide temperature range. The atomic processes responsible for such an organized growth are discussed using STM images with atomic resolution and chemical contrast.

Reconstruction, step edges and self-organization on the Au(111) surface

Abstract It has been shown recently that vicinal surfaces of Au(111) are unstable towards faceting. The period of the faceted morphology is very sensitive to the step edge atomic structure and can vary from about 10 up to 200 nm. We report a scanning tunneling microscopy (STM) study demonstrating that the famous 22×√3 reconstruction of the Au(111) surface interacts differently with both types of close-packed step edges that can be found on a (111) surface: the lines of discommensuration cross {111} step edges and are stopped by {100} ones. This observation could be essential in order to explain the drastic change in the faceted morphology of Au(111) vicinal surfaces with different step edges. Furthermore, it is promising in the way of realizing original nanostructures on these vicinal surfaces. Preliminary results are shown.

Pre-structured metallic template for the growth of ordered, square-based nanodots

Abstract We present new features of the self-ordered N/Cu(1xa00xa00) surface: this pre-patterned template offers the possibility of growing ordered square-based nanodots regular in sizes and spacings on the bare copper areas in-between the octagonal-shaped nitrogen domains at high N coverage. Furthermore, we applied another method of nitrogen adsorption on the copper (1xa00xa00) surface leading to a higher quality template, namely adsorption at a sample temperature of 630 K and the sample surface being not directly seen by the filament activating the nitrogen. As example, we deposited gold onto this pre-structured template N/Cu(1xa00xa00) surface resulting in a perfect arrangement of regular and ordered square-based two atomic layers high gold nanodots.

Thermal faceting behavior of Au(4,5,5)

Abstract The reversible Au(4,5,5) surface structure transformation has been followed by grazing incidence X-ray diffraction between 300 and 1000xa0K. At 300xa0K, the hill-and-valley morphology obtained after sputtering and annealing at a temperature above 800xa0K has been found to be in remarkable agreement with low energy electron diffraction and scanning tunneling microscopy studies. It consists of two orientational phases which are both Au(1,1,1) vicinal surfaces: the 4°-phase which is reconstructed and the non-reconstructed 10°-phase. The 4°-phase presents a periodicity of 79xa0A, and the lines of discommensurations are perpendicular to the step edges. This result is consistent with the known interaction on the close-packed Au(111) surface between the reconstruction and the step edge atomic structures. The temperature dependence of the faceted morphology is found to be reversible and independent of the cooling rate. Between 550 and 1000xa0K, the 4°-phase continuously increases its angle of misorientation and it is still reconstructed. On the other hand, the 10° phase structure does not change its angle of misorientation within the temperature range, but decreases in intensity.

Temperature dependence of ordered cobalt nanodots growth on Au(7 8 8)

A complete study of the link between growth conditions and cobalt nanodots morphology is performed on a Au(7 8 8) vicinal template using STM images at different temperatures. Once a good long-range order is established for the nanostructure superlattice, we elucidate how the substrate temperature during deposition influence the local order of the dots array. This work allows a full control of the local order of the nanostructure assembly and thus is an important step for the one who wants to perform physical properties measurements of nano-objects.

Symmetry-selected spin-split hybrid states in C-60/ferromagnetic interfaces

The understanding of orbital hybridization and spin-polarization at the organic-ferromagnetic interface is essential in the search for efficient hybrid spintronic devices. Here, using first-principles calculations, we report a systematic study of spin-split hybrid states of C