Supplementary Figures
Supplementary Figure 1:
Mask effect of the
nanowire motors
.
A SEM image of a short
nano ridge obtained by using a static 200 nm
-
diameter nanowire as a stationary mask.
Scale
bar, 200 nm
Supplementary Figure 2:
Near
-
field light focusing of Janus spherical motors.
A SEM
image of a nano hole obtained by using a static
2.16
-
μ
m Janus sphere as a near
-
field lens.
The
asymmetric shape of the nano
hole resulted from the asymmetric optical properties of the
Janus sphere.
Scale bar, 500 nm.
Supplementary Figure 3: Crossing feature patterned by nanowire motors
.
a) Schematic
illustration of the moving trajectories of the two magnetically
-
guided nanowire motors used
for patterning crossing features. b) A corresponding AFM image of the crossing feature
patterned by
these nanowire motors.
Cross
a
b
0
80(nm)
0.0
60.0
μm
Supplementary Figure 4:
Patterned feature by a Janus sphere motor.
A trench line
pattern created by a
2.16
-
μ
m Janus sphere motor.
Supplementary Figure 5:
Schematic of nanowire
-
surface
spacing and interaction
energy.
a)
Self
-
positioning of a nanowire motor. b) Total interaction energy (van der Waals
attraction plus electrostatic repulsion) between a nanowire and the photoresist surface.
0
10
0(nm
)
0.0
30.0
μm
r
d
80 100 120 140 160 180 200
Spacing
d
(nm
)
Energy/r
1/2
(10
-
11
)
-
1.0
-
2.0
-
0.8
-
0.6
-
1.2
-
1.4
-
1.6
-
1.8
-
2.2
a
b
Supplementary Figure 6: Schematic of Janus sphere motor
-
surface spacing and
interaction energy.
a)
Self
-
positioning of Janus sphere motor. b) Total interaction energy
(van der Waals attraction plus electrostatic repulsion) between a microsphere and the
photoresist surface.
80 100 120 140 160 180 200
Spacing
D
(nm
)
Energy/R (10
-
14
)
-
1.0
-
2.0
-
0.8
-
1.2
-
1.4
-
1.6
-
1.8
-
2.2
a
b
R
D
-
2.4
Supplementary
Note
s
Supplementary Note 1: Discussion of nanomotor
-
surface spacing: nanowire motors
.
In the first case of nanowire motors, the balance between these forces controls the spacing
d
. For the sake of simplicity, we assume the nanowire motor as a cylindrical structure here, as
displayed in
Supplementary Figure 5a
. The van der Waals inte
raction energy
, between a
cylindrical structure and a surface
,
is given by
1
:
=
−
√
√
(1)
Where
A
is the Hamaker constant,
r
is the radius of the nanowire motor and
d
is the
nanomotor
-
surface spacing.
The electrostatic double
-
layer interaction energy between a cylindrical structure and the
surface is described by
1
:
=
64
휋휀
휀
tan
tanh
푘
푒
(2)
Where
휀
is the dielectric constant of water,
휀
is the free
-
space permittivity,
푘
−
is the
Debye length,
k
is the Boltzmann constant,
T
is the thermodynamic temperature,
q
is the
elementary charge,
and
are the surface potential for the nanomotor and the photoresist
surface, respectively.
The total interaction energy (van der Waals attraction plus electrostatic repulsion) between
the nanowire and the surface can
be written as
=
+
(3)
The mean surface spacing can
be determined by
finding the minimal total interaction
energy
.
While the specific values of
A
,
푘
,
and
were not measured for our systems,
we can estimate the approximate nanomotor
-
surface spacings
by using the reasonable tested
or calculated parameters
.
Here we use
=
J and
=
4
0 mV
by assuming the
metallic nanowire as
a
colloidal metallic nanoparticle
2,3
.
We also use the
Debye length
푘
=
1
0 nm
for the hydrogen peroxide solution and
=
5
0 mV
for a smooth surface
4
.
Supplementary Figure 5b
displays the dependence of the total interaction energy of the
nanowire upon the surface spacing. Our estimated results show the balanced nanowire
-
surface spacing to be 105 nm.
Supplementary Note 2: Discussion of nanomotor
-
surface spacing: Janus sphere motors.
In the second case of Janus sphere motors, the balance between van der Waals force and
the repulsive electrostatic double
-
layer force controls the spacing
D
. To simplify the
discussion, we assume here the Janus sphere motor as a microsphere, as displayed i
n
Supplementary Figure 6a
.
The van der Waals force between a sphere particle and a surface is
well
-
known as
1
:
=
−
(4)
Where
R
is the radius of the microsphere and
D
is the sphere
-
surface spacing.
The electrostatic double
-
layer interaction forces between the microsphere and the surface
can be written as
1
:
=
64
휋휀
휀
tan
tanh
푅
푒
(5)
Total interaction energy (van der Waals attraction plus electrostatic repulsion) between the
nanowire and the surface can be written as
=
+
(
6
)
Similar to the cylindrical wires, the mean surface spacing can
be determined by
calculating the minimal total interaction energy
.
Here we use
=
J
,
Debye
length
푘
=
1
0 nm
, and
=
=
5
0 mV
for the colloidal sphere
-
smooth surface system
4
.
Supplementary Figure 6b
displays the dependence of the total interaction energy of the
microsphere upon the surface spacing. Our estimated results show the balanced sphere
-
surface spacing to be
90
nm.
Supplementary References:
1.
Israelachvili, J. N.
Intermolecular and surface forces,
3rd
Edition, Academic Press, Burlington, MA,
(2011).
2.
Enustun,
D. B. V. &
Turkevich
, J.
Stability of Colloidal Gold and Determination of the Hamaker
Constant
,
J. Phys. Chem
.
82
, 2710
-
2711 (1978).
3.
Dougherty
, G. M.
et al
.
The zeta potential of surface
-
functionalized metallic nanorod
particles in
aqueous solution
.
Electrophoresis
29
, 1131
–
1139
(2008).
4.
Suresh, L. & Walz, J. Y.
Effect of
s
urface
r
oughness on the
i
nteraction
e
nergy between a
c
olloidal
s
phere and a
f
lat
p
late
.
J. Colloid Interface Sci.
183
,
199
–
213
(1996).