Fig. 2 Typical AFM topographic line scan profiles of the nanosquare after
treatment with 1 at 5 mM for 1.5 h under 2-butanol (a) and water (b).
To estimate the extent of transformation of the localised
surface reactions, we measured the volumes of the nanopatterns
before and after each step. These volumes were compared with
the volumes that would be required to accommodate the
additional structures with sizes calculated using van der Waals
radii. These calculations gave yields over approximately 85%
for the addition of p-xylylenediamine, and a similar yield for the
addition of 1 when added for 3 h using a 10 mM solution. These
values are likely to be underestimates because of the lack of
uniformity, and hence rigidity in the grafted feature, which will
dominate and also exacerbate any tip induced artefacts.
This communication describes an approach to generating and
growing nanoscale features on a surface, which is now being
generalised to build more complex features with more diverse
chemistry. The AFM is seen to be a powerful tool for defining
the original feature size and then monitoring the progress and
extent of each subsequent chemical step.
Fig. 1 AFM 3D images of the nanofeature at different stages of the chemical
manipulation. (a) Friction image of the maleimide nanosquare created by
nanografting, (b) topographic image of (a); (c) topographic image after
treatment with p-xylylenediamine; (d) topographic image after further
treatment with 1 at 5 mM for 1.5 h; (e) topographic image after treating with
1 at 10 mM for 3 h; (f) Topographic image of (e) after treatment with 10 mM
decanethiol for 30 min. All images are in the same x, y and z scales, 800 3
800 nm for x and y, and the highest features in (e) have a z value of 5
nm.
We wish to thank the EPSRC and the Leverhulme Trust for
financial support.
Notes and references
a height up to 5 nm. It was assumed that these domains were of
fully extended SAM structures which had reacted completely in
each of the two steps. This conclusion was supported by a
subsequent experiment where a similar surface was reacted for
longer with a higher concentration of 1 (3 h, 10 mM in
2-butanol). This experiment resulted in significantly more
addition of 1 and consequently more extensive taller domains
were seen within the whole pattern, and the average height
increased to 2.8 nm (Fig. 1(e)).
‡ Spectroscopic data for 1: 1H NMR (400 MHz, CDCl3), d 6.69 (4H, s,
maleimide H), 3.50 (4H, t, J 7 Hz, CH2N), 2.67 (4H, t, J 7 Hz, CH2SSCH2),
1.7–1.2 (36H, m, CH2); 13C NMR (100 MHz, CDCl3), d 170.8 (CNO), 133.8
(CNC), 38.9, 37.7, 29.2, 28.9, 28.8, 28.4, 26.6; HRMS: calc. for
C15H25O2NSNa+ (M + Na)+ m/z 306.1504, found 306.1511. Details of the
synthesis are shown in the ESI.†
§ AFM topographic images were collected in contact mode under minimum
loading force (0.5–1 nN) just enough to obtain a stable image at a scan rate
of 2 Hz. Details of the AFM experiment are supplied in the ESI.†
Two further experiments were carried out to demonstrate
how the surface pattern could be manipulated. Taking a surface
modified by treatment with 1 as above (1.5 h, 5 mM in
2-butanol), the surface was imaged first in 2-butanol and then
water. Respective cross section scans of these features are
shown in Fig. 2(a) and (b), respectively. In 2-butanol the
extended hydrophobic tails from the 11,11A-dimaleimidounde-
cyl disulfide are not well packed and spread out laterally. In
water they are driven together by the hydrophobic effect to form
more rigid aggregates that stand more erect. Finally, decanethiol
(10 mM in 2-butanol) was added to the surface for 20 min. This
led to disulfide exchange, cleaving off the terminal 11-mal-
eimidoundecyl thiol. The subsequent AFM topographic image
showed the disappearance of most of the bright (taller) domains
(Fig. 1(f)). Consistent with this interpretation, the average
height of the pattern decreased to 1.4 nm.
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