Fe nanoclusters on the Ge(001) surface studied by scanning tunneling microscopy, density functional theory calculations and X-ray magnetic circular dichroism

Abstract

The growth of Fe nanoclusters on the Ge(001) surface has been studied using lowtemperature scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations. STM results indicate that Fe nucleates on the Ge(001) surface, forming wellordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge(001) surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism. IntroductionThe self-assembly of atoms or molecules into ordered surface-supported nanostructures is one of the key topics in solid state physics and surface science [1-9]. One major reason for this attention is the prospect of controlling atomic scale structures on surfaces, which can lead to mass fabrication of usable systems and novel devices. A promising approach towards the control of self-assembly is the use of preformed surface templates onto which particular nanostructures can be arranged in a well-ordered fashion [10][11][12]. Semiconductor surfaces such as the Ge(001)-(2×1) reconstructed surface are suitable templates for the growth of wellordered, uniformly-sized metal nanoclusters [13,14]. Their size, shape, and the spacing between clusters are dictated by the substrate. Such metal-nanocluster -semiconductor systems can be considered to be examples of low-dimensional dilute magnetic semiconductors (DMS), as the interaction between transition metal clusters takes place via the semiconducting substrate [15]. Furthermore, the layout of clusters on the surface into a regular exposed system allows for good control of the separation between clusters, which cannot be achieved in most DMS three-dimensional systems.DMS are promising materials for use in many technological applications and their study is important for future developments in nanotechnology as well as from the fundamental point of view. Such systems have attracted much attention recently since they can be utilized as essential building blocks in the field of spin-dependent electronic (spintronic) devices, providing a link between magnetism and semiconductor technologies [16][17][18][19]. The incorporation of ferromagnetic elements into semiconductor devices may lead

Self-assembly of Fe nanocluster arrays on templated surfaces

“…150 K. This indicates a superparamagnetic behavior of the Fe nanocluster arrays on Ge(001) similar to the one observed for the separated nanoclusters. 11 Furthermore, no magnetic hysteresis loop with remanence was observed at 150 K, in comparison to the ferromagnetic response of larger clusters and nanorods. 3,[15][16][17] This suggests that the nanocluster array size is still too small to provide a ferromagnetic response.…”

“…1(a)). Each individual nanocluster consists of 16 Fe atoms 11 and its size is equal to 9 Å Â 9 Å . They have an apparent corrugation height of (1.1 6 0.1) Å , which does not depend on the bias voltage.…”

“…8,9 Such surfaces are suitable templates for the growth of well-ordered, uniformly sized metal nanoclusters. 10,11 In the present work we use the Ge(001)-(2 Â 1) reconstructed surface and the MoO 2 /Mo(110) surface as templates for the growth of ordered arrays of Fe nanoclusters. We employ scanning tunneling microscopy (STM) and X-ray magnetic circular dichroism (XMCD) to study the nucleation, structure, and magnetic properties of the Fe nanoclusters.…”

Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

“…The self-assembly of atoms or molecules into one-and two-dimensional surface-supported nanostructures is one of the key topics in surface science and nanotechnology [1][2][3][4][5][6]. This bottom-up approach has been widely employed over the past decade for the controlled formation of ordered molecular structures on surfaces, which can lead to mass fabrication of useable systems and novel molecule-based devices with different functionalities [6][7][8][9][10].…”