Wavelength tunability of ion-bombardment-induced ripples on sapphire

Zhou, Hua; Wang, Yiping; Zhou, Lan; Headrick, Randall L.; Özcan, Ahmet; Wang, Yiyi; Özaydin, Gözde; Ludwig, Karl; Siddons, D. P.

doi:10.1103/physrevb.75.155416

Cited by 44 publications

(36 citation statements)

References 36 publications

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“…16 Divergence of the ripple wavelength is observed near the transition, which is consistent with the CV mechanism. In this paper we test additional features of Carter's model through direct comparison to careful experiments.…”

Section: Introductionsupporting

confidence: 84%

“…First, a ripple pattern is produced by 45°off-normal incidence Ar + ions at 600 eV, where the off-normal incidence is in the x-z plane, as detailed in our previous study. 16 An atomic force microscope ͑AFM͒ image of the patterned starting surface of Al 2 O 3 is shown in Fig. 1͑b͒, which reveals a wavy ripple morphology across the entire image.…”

Section: Resultsmentioning

confidence: 98%

“…7,16 This smoothening, in combination with the q 2 -dependent surface instability induced by curvaturedependent erosion ͑CDE͒ from classic sputtering theory, always produces pattern formation regardless of the strength of q 4 -dependent smoothening mechanism. 4,10, 18 We emphasize that there is no way to produce smoothening ͓i.e., b͑q͒ Ͼ 0͔ over the entire spectrum with only the IVF smoothening mechanism in the presence of the CDE instability ͑i.e., when CDE Ͻ 0͒.…”

Section: Langevin Equation That Models the Operative Ion-induced Effementioning

confidence: 95%

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Mechanisms of pattern formation and smoothing induced by ion-beam erosion

Zhou

Özaydin

et al. 2008

Phys. Rev. B

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We have investigated bombardment-induced pattern formation and smoothening during Ar + ion erosion of Al 2 O 3 surfaces. The experiments show that ion smoothening of a patterned surface is explained by a mechanism where collisions with near-surface atoms produce an effective downhill current. Quantitative agreement is obtained using ion-collision simulations to compute the magnitude of the surface current. The results lead to predictions for the surface morphology phase diagram as a function of ion energy and incidence angle that substantially agree with experimental results.

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Section: Introductionsupporting

confidence: 84%

Section: Resultsmentioning

confidence: 98%

Section: Langevin Equation That Models the Operative Ion-induced Effementioning

confidence: 95%

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Mechanisms of pattern formation and smoothing induced by ion-beam erosion

Zhou

Özaydin

et al. 2008

Phys. Rev. B

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“…In case of smoothening by surface diffusion mechanism, the wavelength should decrease with increasing ion energy [23]. The opposite is expected in case of smoothening by surface confined viscous flow [24]. Here we have observed the increase of wavelength with increasing ion energy.…”

Section: Resultsmentioning

confidence: 48%

High energy ion irradiation induced surface patterning on a SiO 2 glass substrate

Srivastava

Ganesan

Gangopadhyay

et al. 2014

Nuclear Instruments and Methods in Physics Research Section B:

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“…Some studies were already performed aiming to gain the full control on ripple formation process on various substrates: sapphire [4], silicon [5,6], ZnO [7], or to investigate the influence of ripples on various physical properties, most notably the magnetic anisotropy, exchange bias [8], or morphology of magnetic domains. Recently many papers are devoted to rippled surfaces of diluted magnetic semiconductors (DMSs), with (Ga, Mn) As being probably the most frequently studied substance in this class [9,10].…”

Section: Discussionmentioning

confidence: 99%

Magnetic Anisotropy at Nanoscale

Gutowski

2011

Journal of Nanotechnology

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Nanoscale objects often behave differently than their "normal-sized" counterparts. Sometimes it is enough to be small in just one direction to exhibit unusual features. One example of such a phenomenon is a very specific in-plane magnetic anisotropy observed sometimes in very thin layers of various materials. Here we recall a peculiar form of the free energy functional nicely describing the experimental findings but completely irrelevant and thus never observed in larger objects. Intriguing Experimental ObservationsIn [1] we find the experimentally observed in-plane magnetic anisotropy energy (MAE) diagrams for multilayer structure Cr(4)/Fe(2)/Cr(d Cr )/Fe(4)/Cr(2), where numbers are thicknesses of components, expressed in nm. The thickness of the middle Cr layer, d Cr , was varied in few nm range, and the complete structures were deposited on Si(100) substrate, covered with natural SiO 2 layer 1.5-2.0 nm thick. The substrate was not perfectly flat-as a result of ion beam erosion it was covered with quite well-ordered ripples (see atomic force microscopy (AFM) images of the substrates, Figure 1 in [1]). The metallic layers were deposited using molecular beam epitaxy (MBE) technique. Their transmission electron microscopy (TEM) cross-sections revealed mostly amorphous structure with small inclusions of polycrystalline character. The values of MAE were derived from hysteresis loop area observed while exciting field was oriented along successive in-plane directions.In principle, samples of this kind should not exhibit any in-plane magnetic anisotropy. This is indeed the case when the substrate is flat (see Figure 4(a) in [1]). On the rippled substrate, however, this is no longer true and the sample exhibits peculiar twofold in-plane anisotropy (coercive field, Figure 4(b) in [1], MAE-in Figure 4(c)). It is peculiar since it is not the uniaxial anisotropy: four maxima are visible instead of just two. The Surface Magnetic Anisotropy of a CylinderConsider the static configuration of individual spins located on a surface of a long (ideally: infinitely long), hollow ferromagnetic cylinder. In absence of any external field, one may expect that individual spins may adopt one of the two stable configurations:(i) they all may be aligned with C ∞ symmetry axis of a cylinder. This is the lowest exchange energy configuration; (ii) they all may be oriented perpendicularly to the above symmetry axis. Now the exchange energy is no longer at its global minimum. Nevertheless, such a configuration is stable since it realizes a local minimum of exchange energy.In the second case we may again distinguish two cases: either individual spins are aligned with local C 2 symmetry axis (there are infinitely many of them, each perpendicular to C ∞ ) thus pointing inwards or outwards of a cylinder and being perpendicular to the cylinder's surface, or they can be perpendicular to the local C 2 axis (laying on the cylinder's circumference), making a ring-shaped configuration and producing no net magnetization. It is easy to see that both of thos...

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Wavelength tunability of ion-bombardment-induced ripples on sapphire

Cited by 44 publications

References 36 publications

Mechanisms of pattern formation and smoothing induced by ion-beam erosion

Mechanisms of pattern formation and smoothing induced by ion-beam erosion

High energy ion irradiation induced surface patterning on a SiO 2 glass substrate

Magnetic Anisotropy at Nanoscale

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