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Strong water-mediated friction asymmetry and surface dynamics of zwitterionic solids at ambient conditions: L-alanine as a case study
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10.1063/1.3571453
/content/aip/journal/jcp/134/12/10.1063/1.3571453
http://aip.metastore.ingenta.com/content/aip/journal/jcp/134/12/10.1063/1.3571453
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Figures

Image of FIG. 1.
FIG. 1.

(a) Top and (b) side views of the (011) crystal face of L-alanine projected across and along the a-axis, respectively. The room temperature crystal structure is orthorhombic, space group P212121, with four molecules per unit cell and cell parameters a = 0.6032, b = 1.2343, and c = 0.5784 nm. Crystallographic data taken from Lehmann et al. (Ref. 50). Carbon, oxygen, nitrogen, and hydrogen atoms are represented by black, red, blue, and white spheres, respectively. The surface unit cell, in blue in (a), is 0.60 × 1.36 nm2.

Image of FIG. 2.
FIG. 2.

Topographic SFM images of a (011) surface of a L-alanine single crystal. The images were acquired on freshly cleaved surfaces in the acoustic (tapping) operation mode in a glovebox at room temperature and at the RHs: (a) 10%, (b) 30%, (c) 50%, and (d) 70%. Cleavage was performed at RH ∼ 5%. Scale is .

Image of FIG. 3.
FIG. 3.

(a) Topographic SFM images of a (011) surface of a L-alanine single crystal. The images were acquired on freshly cleaved surfaces in the acoustic (tapping) operation mode in a glovebox at room temperature and at RHs: (left) ∼ 25% and (right) ∼ 40%. Cleavage was performed at RH ∼ 5%. (b) Time evolution of SFM images evidencing Ostwald ripening taken at RH ∼ 40%. (c) Time evolution of the area fraction (in %, red squares), the area to perimeter ratio (black triangles), and RH (blue continuous line). The time where the images from (b) were taken is indicated by blue arrows.

Image of FIG. 4.
FIG. 4.

Topographic SFM images of a (011) surface of a L-alanine single crystal. The images were acquired on freshly cleaved surfaces in the acoustic (tapping) operation mode in a glovebox at room temperature and at RHs: (a) 50%, (b) 60%, (c) 70%, and (d) 80%. Cleavage was performed at RH ∼ 5%.

Image of FIG. 5.
FIG. 5.

(a) Topography (left) and lateral force (right) images taken in contact mode at room temperature and 40% RH. Scale is 11 μm × 11 μm. (b) Topography (top left), forward scan lateral force (middle left), and backward scan lateral force (bottom left) images taken at room temperature and 40% RH. The corresponding cross section profiles are shown to the right. A stands for the friction asymmetry while F lf and F lb represent the lateral force signals along the forward and backward scan directions, respectively. The total friction is calculated as 1/2(F lfF lb).

Image of FIG. 6.
FIG. 6.

(a) Topography (left) and lateral force (right) contact mode images and (b) SPFM (left) and KPFM (right) images of (011) surfaces of L-alanine taken at 50% RH.

Image of FIG. 7.
FIG. 7.

(a) Scheme showing the cantilever scanning direction and sample orientation (θ) with regard to the torsional and deflection responses in the four-sectors detector. (b) Friction asymmetry as a function of θ with respect to the forward scan direction. (c) Friction asymmetry as a function of RH. Selected lateral force images corresponding to ∼ 20 and 40% RH are displayed. The lines in (b) and (c) are guides to the eye.

Image of FIG. 8.
FIG. 8.

High resolution topographic image (100 nm × 100 nm) of a terrace and an island, taken in contact mode after exposure to the sample to 40% RH.

Image of FIG. 9.
FIG. 9.

(a) Top and (b) side views of the (040) crystal face of L-alanine projected along the b- and c-axis, respectively. Carbon, oxygen, nitrogen, and hydrogen atoms are represented by black, red, blue, and white spheres, respectively. The surface unit cell, a × 2c = 0.60 × 1.16 nm2 (red), is compared to that from (011) shown in Fig. 1(a), 0.60 × 1.36 nm2 (blue).

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/content/aip/journal/jcp/134/12/10.1063/1.3571453
2011-03-28
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Strong water-mediated friction asymmetry and surface dynamics of zwitterionic solids at ambient conditions: L-alanine as a case study
http://aip.metastore.ingenta.com/content/aip/journal/jcp/134/12/10.1063/1.3571453
10.1063/1.3571453
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