Effects of shadowing and steering in oblique-incidence metal (100) epitaxial growth

Shim, Yunsic; Borovikov, V. A.; Amar, Jacques G.

doi:10.1103/physrevb.77.235423

Cited by 26 publications

(16 citation statements)

References 36 publications

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“…Both film properties are intimately related to the molecular beam epitaxy (MBE) deposition process. Oblique incidence deposition results via a self-shadowing effect [2,3] in the formation of grains in the plane of the film that are elongated perpendicular to the incident flux direction and with aspect ratio increasing at larger deposition angle with respect to the surface normal [4]. Consequently, an in-plane uniaxial magnetic anisotropy (UMA) with easy axis perpendicular to the incident flux direction is induced during growth of the magnetic films [4,5,6].…”

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Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence

Zhan

Haesendonck

Vandezande

et al. 2009

Applied Physics Letters

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We have studied surface morphology and magnetic properties of Fe/MgO(001) films deposited at an angle varying between 0 o and 60 o with respect to the surface normal and with azimuth along the Fe [010] or the Fe[110] direction. Due to shadowing, elongated grains appear on the film surface for deposition at sufficiently large angle. X-ray reflectivity reveals that, depending on the azimuthal direction, films become either rougher or smoother for oblique deposition. For deposition along Fe[010] the pronounced uniaxial magnetic anisotropy (UMA) results in the occurrence of "reversed" two-step and of three-step hysteresis loops. For deposition along Fe[110] the growth-induced UMA is much weaker, causing a small rotation of the easy axes.Magnetic anisotropy of epitaxial films and its relationship to surface morphology have attracted much attention in recent years [1]. Both film properties are intimately related to the molecular beam epitaxy (MBE) deposition process. Oblique incidence deposition results via a self-shadowing effect [2,3] in the formation of grains in the plane of the film that are elongated perpendicular to the incident flux direction and with aspect ratio increasing at larger deposition angle with respect to the surface normal [4]. Consequently, an in-plane uniaxial magnetic anisotropy (UMA) with easy axis perpendicular to the incident flux direction is induced during growth of the magnetic films [4,5,6]. UMA was found to play an important role in determining the magnetization reversal in thin films of cubic systems [7,8]. Depending on the strength and orientation of the UMA, hysteresis curves with one, two and three steps are observed in various films at different field orientation. The appearance of the steps can be explained in terms of nucleation and propagation of domain walls (DWs) [8,9]. Consequently, understanding the influence of oblique incidence growth is very important because of its ability to control both magnetic anisotropy and surface morphology [10,11,12].Although shadowing effects have been studied in many magnetic systems, including Fe on MgO(001) [13] and Co on Cu(001) [14], the plane of oblique incidence was always kept parallel to the in-plane cubic easy axes of the magnetic layers. Here, we report on the influence of oblique deposition on the surface morphology and magnetic properties of Fe/MgO(001) films for deposition azimuth both along the Fe Fig. 1(c)). The elongated grains are believed to result from a redistribution of the incident flux due long-range attractive forces [15,16]. During evaporation the incident Fe atoms arrive preferentially on top of already formed grains rather than behind these grains. This shadowing effect is also observed for film deposition at 60 o with azimuth along [110]. The Fe grains on the surface are rhombic in shape with typical length of 15 nm and typical width of 6 nm (see Fig. 1(d)). Based on the STM images we conclude that the self-shadowing effect can be neglected for a deposition angle below 30 o . Moreover, the self-shadowing effect is...

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Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence

Zhan

Haesendonck

Vandezande

et al. 2009

Applied Physics Letters

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“…As shown in Fig. 3, the approximate expression is accurate for glancing angles beyond 80 o and for typical kinetic energies around 0.2 eV [16,[20][21][22]; below 80 o , the deflection becomes unimportantly small. It is important to note that the deflection can be as large as 100 nm, which is comparable to typical diameters and separations of nanorods and is therefore consequential for the growth of nanorods.…”

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confidence: 76%

“…For the system in Fig. 2, the interaction energy is − / - [16][17][18]. For copper-copper interactions, as the prototype in this Letter, a typical value of is 2.1×10 1-eV • nm - [19].…”

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confidence: 81%

“…1 can be determined by including the modification of effective flux given in Eq. (16), which is about 9.4 nm for 87° deposition, 9.6 nm for 88° deposition, and 10.5 nm for 89° deposition. The factor has a value of about 2.2 for 87° deposition, 3.0 for 88° deposition, and 5.4 for 89° deposition.…”

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confidence: 93%

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Generalized theory of smallest diameter of metallic nanorods

Elliott

Huang

2017

Phys. Rev. Materials

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This Letter reports a generalized theory of the smallest diameter of metallic nanorods from physical vapor deposition. The generalization incorporates the effects of nanorod separation and those of van der Waals interactions on geometrical shadowing. In contrast, the previous theory for idealized geometrical shadowing [Phys. Rev. Lett. 110, 136102 (2013)] does not include any dependence on nanorod separation and it predicts the diameter to be about 1/2 to 1/3 of what the generalized theory does. As verification, numerical solutions and the generalized theory in closed-form agree in terms of effective deposition flux. As validation, experiments of physical vapor deposition and the generalized theory agree in terms of the diameter as a function of the separation of nanorods. The diameter of metallic nanorods from physical vapor deposition (PVD) is a critical quantity that defines their functionalities, such as mechanical strength [1][2][3] and sensitivity in surface enhanced Raman spectroscopy [4][5][6]. Conventional PVD processes typically lead to the growth of thin films [7,8]. Under glancing angle deposition (GLAD), PVD processes result in the growth of nanorods [9,10]. As atoms arrive on a substrate with a glancing angle that is close to 90 o , they land at peaks and avoid valleys due to geometrical shadowing effects. As an effect of positive feedback, the peaks grow into nanorods due to geometrical shadowing. In the processes of nanorod growth, multiple-layer surface steps form and impose three-dimensional (3D) Ehrlich-Schwoebel (ES) barriers [11,12] that are larger than the conventional ES barriers from monolayer surface steps [13,14].The diameter of nanorods is the smallest when the 3D ES barriers dominate or equivalently when multiple-layer surface steps bound the top of nanorods [15] under a given geometrical shadowing condition. The geometrical shadowing goes to complete or ideal as the incidence angle approaches 90 o . Under this idealized condition, all atoms will be deposited on the top surface of nanorods with none reaching their side surfaces, independent of nanorod separation. For such idealized geometrical shadowing, we recently reported a closed-form theory of the smallest diameter [15].Going beyond the idealized shadowing condition, we here report a generalized theory, in closed-form, with non-ideal shadowing conditions and with the effects of van der Waals (vdW) interactions. Figure 1 schematically illustrates the generalization of a nanorod growth process. The direct deposition on the top results in a diameter of the core (orange in the figure), which is governed by our previous theory [15]. The deposition on the sides gives the thickness of the shell (tan in Fig. 1), and it depends on the separation of nanorods. Further, due to vdW interactions, the atomic flux on the 1 Author to whom correspondence should be addressed; electronic mail: h.huang@northeastern.edu top is greater than on the side of nanorods, as indicated by the denser flux lines in Fig. 1. FIG. 1. Schematic of nanorod growth,...

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“…As shown in Fig. 1(a), because of the shadowing effect, the oblique deposition of magnetic atoms on suitable substrates can lead to highly elongated grains or ripples on nanometer scale [3][4][5][6][7][8]. These elongated nanograins or ripples can induce a uniaxial MAE.…”

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confidence: 99%

Modulation of magnetic anisotropy in Fe/Si(111) thin films through interface property

Lin

Sung

et al. 2013

Thin Solid Films

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Effects of shadowing and steering in oblique-incidence metal (100) epitaxial growth

Cited by 26 publications

References 36 publications

Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence

Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence

Generalized theory of smallest diameter of metallic nanorods

Modulation of magnetic anisotropy in Fe/Si(111) thin films through interface property

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