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3D lattice distortions and defect structures in ion-implanted nano-crystals

View Article: PubMed Central - PubMed

ABSTRACT

Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.

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Displacements, strains and stresses after FIB milling (crystal C).(A) 3D rendering of crystal C reconstruction coloured by lattice displacement magnitude. q vectors of the six measured reflections are superimposed. (B) Crystal coordinates and section on which the lattice strains are plotted. The x, y and z axes correspond to [-12-1], [111] and [10-1] crystal directions respectively. (C) Maps of the six independent lattice strain tensor components plotted on the xy section shown in (B). (D) Magnified view of amplitudes and phases of the complex electron density reconstructed from {200} reflections. The region corresponds to that marked by a black box in (C) and is centred on a defect. Areas of reduced amplitude (white arrows) and phase jumps (in radians, circular arrows) are visible in the (020) and (002) reflections. (E) Semi-transparent rendering of the outer crystal shape. Superimposed are iso-surfaces of von Mises stress (300 MPa (blue), 400 MPa (green), 500 MPa (red)). Three different viewpoints are shown. In the middle view dashed black lines have been superimposed as a guide to the eye to illustrate the arrangement of defects in lines. Scale bars correspond to 300 nm in (A–C) and (E), and 100 nm in (D).
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f3: Displacements, strains and stresses after FIB milling (crystal C).(A) 3D rendering of crystal C reconstruction coloured by lattice displacement magnitude. q vectors of the six measured reflections are superimposed. (B) Crystal coordinates and section on which the lattice strains are plotted. The x, y and z axes correspond to [-12-1], [111] and [10-1] crystal directions respectively. (C) Maps of the six independent lattice strain tensor components plotted on the xy section shown in (B). (D) Magnified view of amplitudes and phases of the complex electron density reconstructed from {200} reflections. The region corresponds to that marked by a black box in (C) and is centred on a defect. Areas of reduced amplitude (white arrows) and phase jumps (in radians, circular arrows) are visible in the (020) and (002) reflections. (E) Semi-transparent rendering of the outer crystal shape. Superimposed are iso-surfaces of von Mises stress (300 MPa (blue), 400 MPa (green), 500 MPa (red)). Three different viewpoints are shown. In the middle view dashed black lines have been superimposed as a guide to the eye to illustrate the arrangement of defects in lines. Scale bars correspond to 300 nm in (A–C) and (E), and 100 nm in (D).

Mentions: At higher Ga doses a distinctly different behaviour is observed. Nano-crystals B and C were exposed to fluences of 1.3 × 107 ions/μm2 and 1.5 × 108 ions/μm2 respectively, causing the removal of ~3 nm and ~40 nm thick surface layers by sputtering, as predicted by SRIM. Lattice displacements and strains in both crystals were reconstructed using six crystal reflections (SIFig. S5 and Fig. 3 respectively). The spatial resolutions of these reconstructions are ~45 nm and ~47 nm respectively. Even for these highly damaged crystals agreement of the reconstructed morphology and SEM micrographs is excellent (SIFig. S1).


3D lattice distortions and defect structures in ion-implanted nano-crystals
Displacements, strains and stresses after FIB milling (crystal C).(A) 3D rendering of crystal C reconstruction coloured by lattice displacement magnitude. q vectors of the six measured reflections are superimposed. (B) Crystal coordinates and section on which the lattice strains are plotted. The x, y and z axes correspond to [-12-1], [111] and [10-1] crystal directions respectively. (C) Maps of the six independent lattice strain tensor components plotted on the xy section shown in (B). (D) Magnified view of amplitudes and phases of the complex electron density reconstructed from {200} reflections. The region corresponds to that marked by a black box in (C) and is centred on a defect. Areas of reduced amplitude (white arrows) and phase jumps (in radians, circular arrows) are visible in the (020) and (002) reflections. (E) Semi-transparent rendering of the outer crystal shape. Superimposed are iso-surfaces of von Mises stress (300 MPa (blue), 400 MPa (green), 500 MPa (red)). Three different viewpoints are shown. In the middle view dashed black lines have been superimposed as a guide to the eye to illustrate the arrangement of defects in lines. Scale bars correspond to 300 nm in (A–C) and (E), and 100 nm in (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5382701&req=5

f3: Displacements, strains and stresses after FIB milling (crystal C).(A) 3D rendering of crystal C reconstruction coloured by lattice displacement magnitude. q vectors of the six measured reflections are superimposed. (B) Crystal coordinates and section on which the lattice strains are plotted. The x, y and z axes correspond to [-12-1], [111] and [10-1] crystal directions respectively. (C) Maps of the six independent lattice strain tensor components plotted on the xy section shown in (B). (D) Magnified view of amplitudes and phases of the complex electron density reconstructed from {200} reflections. The region corresponds to that marked by a black box in (C) and is centred on a defect. Areas of reduced amplitude (white arrows) and phase jumps (in radians, circular arrows) are visible in the (020) and (002) reflections. (E) Semi-transparent rendering of the outer crystal shape. Superimposed are iso-surfaces of von Mises stress (300 MPa (blue), 400 MPa (green), 500 MPa (red)). Three different viewpoints are shown. In the middle view dashed black lines have been superimposed as a guide to the eye to illustrate the arrangement of defects in lines. Scale bars correspond to 300 nm in (A–C) and (E), and 100 nm in (D).
Mentions: At higher Ga doses a distinctly different behaviour is observed. Nano-crystals B and C were exposed to fluences of 1.3 × 107 ions/μm2 and 1.5 × 108 ions/μm2 respectively, causing the removal of ~3 nm and ~40 nm thick surface layers by sputtering, as predicted by SRIM. Lattice displacements and strains in both crystals were reconstructed using six crystal reflections (SIFig. S5 and Fig. 3 respectively). The spatial resolutions of these reconstructions are ~45 nm and ~47 nm respectively. Even for these highly damaged crystals agreement of the reconstructed morphology and SEM micrographs is excellent (SIFig. S1).

View Article: PubMed Central - PubMed

ABSTRACT

Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology.

No MeSH data available.


Related in: MedlinePlus