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Nanomanufacturing Automation 53.2 AFM-Based Nanomanufacturing 935

When the alternating pushing forces at two points

on the nanowire are applied, a nanowire rotates around

two pivots P

and Q

. The distance L

between P

and

can be calculated if the pushing points are deter-

mined. The two pivots P

and P

are connected to form

a straightline, and thedistance d between thetwo points

is calculated. d is then divided into N small segments

(the numberof manipulations). Then L

in Fig.53.9 can

be obtained

, 0 < L

< 2L

. (53.24)

During manipulation, the pivot P

is always on the line

generated by the two points P

and P

. Then the rotation

angle for each step can be obtained

θ =2acos





(53.25)

The rotation angle θ stays the same during manipu-

lation. The initial pushing angle θ

and the ﬁnal pushing

angle θ

in Fig.53.9 can be calculated by ﬁnding the

starting position and the ending position. After θ is de-

termined, the pivots P

and Q

(i = 1,...,N) can be

calculated. The pushing points can then be determined.

Here we show how to determine the pushing points

when a nanowire rotates around the pivot P

as an ex-

ample. Figure53.10 shows the frames used to determine

the tip position.

The following transformation matrix can be easily

calculated. The transformation matrix of the frame orig-

inated at P

relative to the original frame is T

. The

transformation matrix of the frame originated at P

rel-

ative to the frame originated at P

is T

. Supposing the

rotation angle is β(0 <β≤θ), the transformation ma-

trix relative to the frame originated at P

is T

βi

. β can

be obtained by setting a manipulation step size. The

coordinates of the pushing point can then be calculated

⎛

⎜

⎝

⎞

⎟

⎠

βi

⎛

⎜

⎝

L −2s

⎞

⎟

⎠

(53.26)

Similar steps can be followed to determine the pushing

position for a nanowire rotating around the pivot Q

, i ∈

[1, N]. After the coordinates of the pushing point are

obtained, the manipulation path for a nanowire can be

generated.

53.2.3 Automated Local Scanning Method

for Nanomanipulation Automation

The random drift due to thermal extension or contrac-

tion causes a major problem during nanomanipulation,

θ/2

i+1

Fig. 53.10 The coordinates used to compute the AFM tip pushing

position at each step

because the object may be easily lost or manipulated

to wrong destinations. Before the manipulation, the ob-

jects on the surface are identiﬁed and their positions are

labeled. However, the labeled positions of the nanoob-

jects have errors due to random drift. To compensate for

the random drift, the actual position of each nanoob-

ject must be identiﬁed before each operation. Because

the time to scan a big area is quite long, a quick local

scanning mechanism is developed to obtain the actual

position of each nanoobject in a short time. Nanoma-

nipulation is then performed immediately after the local

scan. Figure 53.11 shows the local scanning method.

From the path data, the original position of

a nanoobject is obtained. Also, the nanoobject is cate-

gorized into two groups: the nanoparticle and nanowire.

A scanning pattern is generated for the nanoobject ac-

cording to its group. The scanning pattern is fed to the

imaging interface to scan the surface. If the nanoob-

Original object position

and categorization

Scanning pattern generation

Imaging interface

Line scan

Perpendicular line scan

Actual position computation

Path adjustment

Object found?

New path

Path

YesNo

Fig. 53.11 The local scanning strategy to obtain the actual positions

of nanoobjects

Part F 53.2

936 Part F Industrial Automation

Fig. 53.12 Local scan pattern to search the actual position

of a nanoparticle. O is the original center of the particle,

R is the radius of the particle, O

is the actual center of

the particle, L

,andL

are the horizontal scan lines,

V is the vertical scan line. P

and P

are the interactions

between the particle edge and a horizontal scan line, Q

and Q

are the intersections between the particle edge and

the vertical scan line

ject is not found, a new scanning pattern is generated.

The process continues until the nanoobject is discov-

ered. The actual position of the nanoobject can then be

computed. Themanipulation pathis then adjusted based

on the actual position. For nanoparticles and nanoob-

jects, different scanning patterns must be used in order

to obtain their actual position.

New position

Actual position

Original position

Drift direction

First point

New destination

Original destination

Original position

a) b)

New path

Original path

Fig. 53.13 (a) The updated path after drift compensation. (b) The local scan after the drift direction and size are

determined from the previous local scan

For example, the location of a nanoparticle can be

represented by its center and radius. The radius of each

particle R has been identiﬁed before the manipulation

starts. The actual center of a nanoparticle can be relo-

cated by two lines, a lateral and a cross line as shown

in Fig.53.12. First, the nanoparticle is scanned using

line L

, which passes the original center of the par-

ticle in the image. If the particle is not found, then

the scanning line moves up and down alternatively by

a distance of 3/2R. Once the particle has been found,

two intersection points, P

and P

between the particle

edge and the lateral line are located. A cross line scan

V, which goes through the middle point between P

and P

, is used to locate the center of the particle. The

cross scan line has two intersection points, Q

and Q

with the particle edge. The middle point between Q

and Q

is the actual center of the nanoparticle. The lo-

cal scanning range (the length of the scanning line) l

can be determine by the maximum random drift such

that l > R+r

max

, wherer

max

is the estimated maximum

random drift distance.

After the center of a nanoobject has been identiﬁed,

the drifts in the XY directions are calculated. The drifts

in the XY directions are then used to update the desti-

nation position as shown in Fig.53.13a. Finally a new

path is generated to manipulate the nanoparticle.

After the local scan of the ﬁrst nanoparticle, the

direction and size of the drift can be estimated. The in-

formation can be used to generate the scanning pattern

for the next nanoobject as shown in Fig.53.13b.

Part F 53.2

Nanomanufacturing Automation 53.3 Nanomanufacturing Processes 937

53.2.4 CAD Guided Automated

Nanoassembly

In order to increase the efﬁciency and accuracy of

AFM-based nanoassembly, automated CAD guided

nanoassembly is desirable. A general framework for

automated nanoassembly is developed to manufac-

ture nanostructures and nanodevices, as illustrated

in Fig.53.14. Based on the CAD model of a nanostruc-

ture and the distribution of nanoobjects on a surface

from an AFM image, the tip path planner generates

manipulation paths to manipulate the nanoobjects. The

paths arefed to a user interface to simulate the manufac-

turing process and then to the AFM system to perform

the nanoassembly process.

The AFM tip path planner is the core of the gen-

eral framework. Figure 53.15 shows the architecture of

the tip path planner. Nanoobjects on a surface are ﬁrst

identiﬁed based on the AFM image. A nanostructure

is then designed using the available nanoobjects. Ini-

tial collision-free manipulation paths are then generated

based on the CAD model of a designed nanostruc-

ture. In order to overcome the random drift, a local

scanning method is applied to identify the actual po-

Automated

manipulation

Actual positionLocal scanAFM image

CAD model

Automated

path

generation

Updated path

Fig. 53.15 Automated tip path planner. Initial paths are generated based on the CAD model of a designed nanostructure

and the randomly distributed nanoobjects on a surface. The manipulation path of each nanoobject is adjusted accordingly

based on the local scanning result

Automated tip

path planner

Simulation

and

real-time

operation

General paths

Real-time

display

Interface

CAD model

AFM image

AFM

Commands

Force

Control

Fig. 53.14 The general framework for automated path generation

system. The bottom left is the AFM system and the bottom right

is the augmented reality interface used for simulation and real-time

operation

sition of a nanoobject before its manipulation. Each

manipulation path of the nanoobject is adjusted ac-

cordingly based on its actual position. The regenerated

path is then sent to the AFM system to manipu-

late the nanoobject. The process continues until all

nanoobjects are processed. A nanostructure is ﬁnally

fabricated.

53.3 Nanomanufacturing Processes

The nanomanufacturing process for nanodevices is not

straightforward, especially in nanomaterial preparation,

selection, and deposition processes. To prepare the

nanomaterial, nanoobjects are usually dissolved into

solution, then the nanoobject suspension is put in an

ultrasonicator or a centrifuge for dispersing the nanoob-

jects. Afterwards, speciﬁc properties of the nanoobjects

should be selected. Finally, they are delivered to as-

Part F 53.3

938 Part F Industrial Automation

semble the nanodevices. However, the nanoobjects are

too small to be manipulated by traditional robotic sys-

tems, novel devices and systems must be developed for

this. Since the nanoobjects are dissolved into ﬂuids,

dielectrophoresis and microﬂuidic technology can be

considered to perform the tasks. The material prepara-

tion can be done by micromixers; the selection process

can be done by microﬁlters; and the deposition process

can be done by integrating the microchannel and mi-

croactive nozzle to deposit the nanoobject suspension.

CNT is one of the most common nanoobjects and it

has some promising properties that are useful for gen-

eration nanodevices. In this chapter, the development

of a novel automated CNT separation system to clas-

sify the electronic types of CNTs will be described,

which involves the analysis for DEP force on CNTs

and fabrication of a DEP microchamber. Moreover,

this DEP microchamber was successfully integrated

into an automated deposition workstation to manipulate

a single CNT to multiple pairs of microelectrodes re-

peatedly. The automated deposition processes for both

SWCNTsandMWCNTs will be presented. As a result,

CNT-based nanodevices with speciﬁc and consistent

electronic properties can be manufactured automati-

cally. The resulting devices can potentially be used in

commercial applications.

53.3.1 Dielectrophoretic Force

on Nanoobjects

Dielectrophoresis has been used to manipulate and sep-

arate different types of biological cells. DEP forces

can be combined with ﬁeld-ﬂow fractionation for si-

multaneous separation and measurement [53.46]. DEP

force induces movement of a particle or a nanoobject

under non-uniform electric ﬁelds in liquid medium as

shown in Fig.53.16. The nanoobject is polarized when

it is subjected to an electric ﬁeld. The movement of

the nanoobject depends on its polarization with respect

to the surrounding medium [53.47]. When the nanoob-

ject is more polarizable than the medium, a net dipole

is induced parallel to the electric ﬁeld in the nanoob-

ject and, therefore, the nanoobject is attracted to the

high electric ﬁeld region. On the contrary, an oppo-

site net dipole is induced when the nanoobject is less

polarizable than the medium, and the nanoobject is

repelled by the high electric ﬁeld region. The direc-

tion of the DEP force on the particle is given by the

Clausius–Mossotti factor (CM factor, K). It is deﬁned

as a complex factor, describing a relaxation in the effec-

tive permittivity of the particle with a relaxation time

Microelectrodes

Particle

DEP

Liquid medium

AC voltage

Nonuniform

electric field

Fig. 53.16 Illustration of the dielectrophoretic manipula-

tion

described by [53.47,48]

K(ε

∗

,ε

∗

) =

∗

−ε

∗

+2ε

∗

. (53.27)

Complex permittivities of the nanoobject (ε

∗

)and

medium (ε

∗

) are deﬁned and given by [53.47,48]

∗

=ε

−i

(53.28)

∗

=ε

−i

(53.29)

where ε

and ε

are the real permittivities of the

nanoobject and the medium, respectively, σ

and σ

are

the conductivities of the nanoobject and the medium, re-

spectively, and ω is the angular frequency of the applied

electric ﬁeld; the CM factor is frequency-dependent.

The time-averaged DEP force acting on the particle is

given by [53.47,48]

DEP

Vε

Re(K)∇|E |

, (53.30)

where V is the volume of the nanoobject and ∇|E |

the root-mean-square of the applied electric ﬁeld. Based

on this equation, the direction of the DEP force is de-

termined by the real part of the CM factor K.When

Re[K]> 0, the DEP force is positive, and therefore the

CNT is moved toward the microelectrode in the high

electric ﬁeld region. When Re[K]< 0, the DEP force

Part F 53.3

Nanomanufacturing Automation 53.3 Nanomanufacturing Processes 939

is negative, the particle is repelled away from the mi-

croelectrode. Moreover, we know that the magnitude

and direction of DEP forces depends on the size and

material properties of the nanoobjects, so separation of

nanoobjects can be done.

53.3.2 Separating CNTs

by an Electronic Property

Using the Dielectrophoretic Effect

A theoretical analysis of DEP manipulation on a CNT

was performed, and CM factors were calculated for

a metallic SWCNT (m-SWCNT) and a semiconducting

MWCNTs(s-SWCNT), respectively. In the analy-

sis, semiconducting and metallic CNT mixtures are

dispersed in the alcohol medium assuming the permit-

tivities of a s-SWCNT and a m-SWCNT are 5ε

[53.32]

and 10

[53.37], respectively, where ε

is the per-

mittivity of free space (ε

= 8.854188×10

−12

F/m).

The conductivities of a s-SWCNT and a m-SWCNT

are 10

S/m and 10

S/m [53.37], respectively. The

permittivity and conductivity of the alcohol are 20ε

and 0.13μS/m, respectively. Based on these parame-

ters and (53.27), plots of Re[K] for different CNTs

are obtained and shown in Fig. 53.17. The result in-

dicated that s-SWCNTs undergo a positive DEP force

at low frequencies (< 1MHz) while the DEP force

is negative when the applied frequency is larger than

10MHz. However, m-SWCNTs always undergo a pos-

itive DEP force at the applied frequency from 10 to

Hz. The result also matched the experimental re-

sult from [53.33], which showed that the positive DEP

effect on SWCNTs reduced as the frequency of ap-

plied electric ﬁeld increased. In addition, the theoretical

result provides a better understanding of DEP manip-

ulation on different types of CNTs. DEP force can be

used to separate and identify different electronic types

of CNTs (metallic and semiconducting). Based on the

result shown in Fig.53.17, metallic CNTs can be se-

Apply AC voltage to

microelectrodes

CNT dilution

out (semiconducting

CNTs)

Micro-

electrodes

CNTs

CNT dilution in

(with metallic and

semiconducting CNTs)

a) b)

Semiconducting CNTs

Metallic

CNTs

Fig. 53.18a,b DEP microchamber to ﬁlter metallic CNT. Metallic CNTs are attracted on microelectrodes. Only semiconducting

CNTs ﬂow to the outlet.

(a) Side view; (b) top view

Negative

DEP force

Positive

DEP force

K(ω)

K(ω) =

Re [K(ω)] for s-SWCNT in alcohol

Re [K(ω)] for m-SWCNT in alcohol

– ε

+ 2ε

Frequency (Hz)

0.8

0.6

0.4

0.2

–0.2

–0.4

–0.6

Fig. 53.17 Plots of Re[K(ω)] that indicated positive and negative

DEP forces on different CNTs

lectively attracted to the microelectrodes by applying

AC voltage in the high frequency range (> 10MHz).

However, semiconducting CNTs cannot be attracted by

using the same frequency range; this makes the selec-

tion of semiconducting CNTs difﬁcult. In order to select

semiconducting CNTs to make nanodevices, we fabri-

cated a microchamber (DEP chamber) with arrays of

microelectrodes to ﬁlter metallic CNTs in the medium.

Design and fabrication of the DEP chamber will be

discussed in the next section.

53.3.3 DEP Microchamber

for Separating CNTs

A DEP microchamber was designed and fabricated

to ﬁlter metallic CNTsinCNT suspension as shown

in Fig.53.18. Many ﬁnger-like gold microelectrodes

were ﬁrst fabricated inside the chamber. The perfor-

mance of the ﬁltering process was affected by the design

of these ﬁnger-like microelectrodes; the microelectrode

Part F 53.3

940 Part F Industrial Automation

structure with higher density induced a stronger DEP

force such that more CNTs could be attracted to the

microelectrodes. The gap distance between these mi-

croelectrodes is 5–10μm. The micropump pumped the

CNT suspension to the DEP chamber; a high frequency

AC voltage was applied to the ﬁnger-like microelec-

trodes so that metallic CNTs were attracted to them and

stayedintheDEP chamber. Semiconducting CNTs re-

mained in thesuspension and ﬂowed out ofthe chamber.

Finally, the ﬁltered suspension (with semiconducting

CNTs only) was transferred to an active nozzle for the

CNT deposition process. This will be described in the

next section.

The fabrication process of the DEP microcham-

ber is shown in Fig. 53.19. It was composed of two

different substrates. Polymethylmethacrylate (PMMA)

was used as the top substrate because it is electrically

and thermally insulating, optically transparent, and bio-

compatible. By using a hot embossing technique, the

PMMA substrate was patterned with a microchan-

nel (5mmL×1mmW×500 μm H) and a microcham-

ber (1cmL×5 mm W×500μm H) by replicating from

a fabricated metal mold. In order to protect the PMMA

Metal

mold

PMMA

Top substrate

Coat parylene C

UV glue bonding

Hot embossing of PMMA

substrate on metal mold

Bottom substrate

Spin on photoresist

on quartz substrate

Pattern and

develop PR

Deposit Ti and Au

Remove PR

Microchamber

PMMA Parylene C

Quartz Photoresist Titanium Gold

Fig. 53.19 The fabrication process of a DEP microchamber

substrate from the CNTs-alcoholsuspension, a parylene

C thin ﬁlm layer was coated on the substrate, because

parylene resists chemical attack and is insoluble in all

organic solvents. Alternatively, quartz was used as the

bottom substrate,and arraysof the gold microelectrodes

were fabricated on the substrate by using a standard

photolithography process. A layer of AZ5214E pho-

toresist with thickness of 1.5μm was ﬁrst spun onto

the 2



×1



quartz substrate. It was then patterned by

AB-M mask aligner and developed in an AZ300 de-

veloper. A layer of titanium with a thickness of 3nm

was deposited by thermal evaporator followed by de-

positing a layer of gold with thickness of 30nm. The

titanium provided a better adhesion between gold and

quartz. Afterwards, photoresist was removed in acetone

solution, and arrays of microelectrodes were formed on

the substrate. Finally, PMMA and quartz substrate were

bonded together by UV-glue to form a close cham-

ber. The ﬁttings were connected at the ends of the

channel to form an inlet and an outlet for the DEP

chamber.

The separation performance of the DEP chamber

should be optimized for different nanoobjects. Several

parameters shouldbe considered in theprocess: thecon-

centration of nanoobjects in the suspension, the strength

of the DEP force, the ﬂow rate of the suspension in

the DEP chamber, the structure of the channel, and the

microelectrodes of the DEP chamber.

53.3.4 Automated Robotic CNT Deposition

Workstation

In order to manipulate a speciﬁc type of CNTs precisely

and fabricate the CNT-based nanodevices effectively,

anewCNT deposition workstation has been devel-

oped as shown in Fig. 53.20. The system consists of

a microactive nozzle, a DEP microchamber, a DC mi-

crodiaphragm pump, and three micromanipulators. By

integrating these components into the deposition work-

station, a speciﬁc type of CNT can be deposited to

the desired position of the microelectrodes precisely

and automatically. The micron-sized active nozzle with

adiameterof10μm was fabricated from a micropipette

using a mechanical puller and is shown in Fig. 53.21.

It transferred the CNT suspension to the microelec-

trodes on a microchip, and a small droplet of the CNT

suspension (about 400 μm) was deposited on the mi-

crochip due to the small diameter of the active nozzle.

The volume of the droplet is critical because exces-

sive CNT suspension easily causes the formation of

multiple CNTs. The microactive nozzle was then con-

Part F 53.3

Nanomanufacturing Automation 53.3 Nanomanufacturing Processes 941

CNT suspension

Electrical circuit of

AC voltage for

DEP manipulation

Another electrical

circuit of AC

voltage for filtering

Micropump for

delivering CNT

suspension

DEP chamber for

filtering

Micromanipulator

for positioning

active nozzle

Microelectrodes

on microchip

Active nozzle

Fig. 53.20 Illustration of the CNT deposition workstation

nected to the DEP chamber, which was designed to

ﬁlter metallic CNTs and select semiconducting CNTs

in the CNT suspension. The raw CNT suspension was

ﬁrstly pumped to the DEP chamber through a DC

microdiaphragm pump (NF10, KNF Neuberger, Inc.).

After the ﬁltering process, the CNT suspension from

the DEP chamber was delivered to the active nozzle

for CNT deposition. By mounting the active nozzle

to one of the computer controllable micromanipulators

(CAP945, Signatone Corp.), the active nozzle could be

moved to the desired position of the microelectrodes

automatically. In order to apply the electric ﬁeld to

the microelectrodes during the deposition process, the

other pair of micromanipulators was connected to an

electrical circuit and moved to the desired location of

the microelectrodes; therefore, AC voltage with dif-

ferent magnitudes and frequencies could be applied.

15 kV 12.3 mm ×50 SE(U) 9/4/2006 18:32 1 mm

Fig. 53.21 SEM image of the micro active nozzle with

10μm tip diameter

The micromanipulators, DC microdiaphragm pump,

and electrical circuit were connected to the computer

and controlled simultaneously during the deposition

process. By controlling the position of the micromanip-

ulators, the magnitude and frequency of the applied AC

voltage, and the ﬂow rate of the micropump, the CNT

suspension can be handled automatically and deposited

to the desired position.

In the depositionprocess, AC voltage of 1.5V peak-

to-peak with frequency of 1kHz was applied; a positive

DEP force was induced to attract CNTstothemi-

croelectrodes. CNT deposition on multiple pairs of

microelectrodes was implemented by controlling the

movement of the micromanipulator, which was con-

nected with the active nozzle. Since the position of

each pair of the microelectrodes was known from the

design CAD ﬁle, distances (along x and y axes) be-

tween each pair of microelectrodes were then calculated

and recorded in the deposition system. At the start, the

active nozzle was aligned to the ﬁrst pair of the micro-

electrodes as shown in Fig. 53.22a. The position of the

active nozzle tip was 2mm above the microchip. When

the deposition process started, the active nozzle moved

down 2mm and a droplet of CNT suspension was de-

posited on the ﬁrst pair of microelectrodes as shown

in Fig.53.22b. Afterwards, the active nozzle moved up

2mm and traveled to the next pair of microelectrodes

as shown in Fig. 53.22c. The micromanipulator moved

down again to deposit the CNT suspension on the sec-

ond pair of microelectrodes as shown in Fig.53.22d.

This process repeated continuously until CNT suspen-

sion was deposited on each pair of microelectrodes on

the microchip. By activating the AC voltage simultane-

ously, a CNT was attracted and connected between each

pair of microelectrodes. The activation time was short

Part F 53.3

942 Part F Industrial Automation

Active nozzle

2nd

Electrodes

2nd

Electrodes

3rd

Electrodes

2nd

Electrodes

CNT suspension

1st

Electrodes

a) b) c) d)

Fig. 53.22a–d CNT deposition process ﬂow observed under the optical microscope. (a) The active nozzle tip aligned

to the initial electrodes,

(b) CNT suspension deposited, (c) the nozzle was moving to next electrodes, and (d) CNT

suspension deposited on the second electrodes

(≈ 2s) to avoid the formation of bundled CNTsonthe

microelectrodes.

After the deposition process, AFM was used to

check theCNT formation as shown inFig.53.23.Some-

times, there are some impurities or more than one

CNT trapped between the microelectrodes as shown

in Fig.53.23f. Therefore, it is necessary to take another

step to clean up the microelectrodes gap area and adjust

the position of the CNT to make the connection. This ﬁ-

nal step is very critical and is termed CNT assembly; it

can be done by our AFM-based nanomanipulation sys-

tem. I–V characteristicsof theCNT-based devices were

also obtained as shown inthe inset images of Fig.53.23.

Based on the results, this indicates that both SWCNTs

and MWCNTs could be repeatedly and automatically

manipulated between the microelectrodes by using the

deposition system. This CNT deposition workstation

integrates all essential components to manipulate the

speciﬁc type of CNTs to desired positions precisely

a) b) c)

d) e) f)

Fig. 53.23a–f AFM images showing the individual CNTswas

deposited on the microelectrodes.

Panels (a–c) are SWCNTs,

panels (d–f) are MWCNTs.The inset images are the corresponding

I–V curves of each CNT

by DEP force. The development of this system pro-

duces beneﬁts to the assembling and manufacturing of

CNT-based devices. The yield of depositing CNTson

the microelectrodes is very high after optimizing the

following factors: the concentration of the CNT suspen-

sion, the volume of theCNT suspension droplet, and the

activation time, magnitude and frequency of the applied

electric ﬁeld.

In order to validate the separation performance of

different CNTsbytheDEP chamber, experiments for

both raw CNT suspension (before passing through the

DEP chamber) and ﬁltered CNT suspension were con-

ducted, respectively. The procedure for preparing the

CNT suspension was the same as the process presented

in the previous section. SWCNT powder (BU-203,

Bucky USA, Nanotex Corp.) was dispersed in an al-

cohol liquid medium, and the CNT suspension was

put in the ultrasonicator for 15 min. The length of the

SWCNT is 0.5–4μm. Finally, the raw SWCNT sus-

pension was prepared and the concentration was about

1.1μg/ml. Afterwards, the separation process was per-

formed on the raw SWCNT suspension as illustrated

in Fig.53.24. During the process, the raw SWCNT

suspension was pumped to the DEP chamber through

the micropump. The ﬂow rate was about 0.03l/min.

A high frequency AC voltage (1.5Vpp, 40MHz) was

applied to the microelectrodes in the DEP chamber; it

induced a positive DEP force on metallic SWCNTsin

the suspension but a negative DEP force on semicon-

ducting SWCNTs. Since the metallic SWCNTs were

attracted to the microelectrodes and stayed in the DEP

chamber, it was predicted that only semiconducting

SWCNTs remained in the ﬁltered SWCNT suspension.

The ﬁltered SWCNT suspension was then collected at

the outlet of the chamber for later CNT disposition

process.

After preparing the raw and ﬁltered SWCNT

sus-

pension, the deposition process was performed by using

our CNT deposition workstation, which was intro-

Part F 53.3

Nanomanufacturing Automation 53.3 Nanomanufacturing Processes 943

Micropump

Raw CNT

suspension

Filtered CNT

suspension

Selection chamber

Fig. 53.24 The CNT ﬁltering process

duced in the previous section. In the experiment, the

raw SWCNT suspension and the ﬁltered SWCNT sus-

pension were deposited on the microchip 20 times,

respectively. The electronic properties of CNTs in both

suspensions were then studied by measuring the I–V

curves. The yields to obtainsemiconducting CNTs from

the raw CNT suspension and ﬁltered CNT suspension

were also compared. Based on the preliminary results,

the yield of depositing semiconducting SWCNTs (from

the raw SWCNT suspension) was about 33% as shown

in Fig.53.25; the yield of depositing semiconducting

SWCNTs (from the ﬁltered SWCNT suspension) was

about 65% as shown in Fig.53.25. The yield to form

semiconducting CNTs is very important because many

devices require materials with semiconducting prop-

erties. The results indicated that there was signiﬁcant

improvement in forming semiconducting CNTsonthe

microelectrodes by using our DEP chamber. The yield

0.01 0.1 1 10

Log voltage (V)

–3

–4

–5

–6

–7

–8

–9

1– Metallic

4– Metallic

7– Semiconducting

10– Metallic

13– Semiconducting

16– Metallic

19– Metallic

2– Semiconducting

5– Metallic

8– Semiconducting

11– Metallic

14– Semiconducting

17– Metallic

20– Semiconducting

3– Semiconducting

6– Metallic

9– Metallic

12– Metallic

15– Metallic

18– Metallic

a) Log current (A)

0.01 0.1 1 10

Log voltage (V)

–4

–5

–6

–7

–8

–9

–10

–11

1– Semiconducting

4– Semiconducting

7– Metallic

10– Metallic

13– Semiconducting

16– Semiconducting

19– Semiconducting

2– Metallic

5– Semiconducting

8– Semiconducting

11– Semiconducting

14– Semiconducting

17– Semiconducting

20– Metallic

3– Metallic

6– Metallic

9– Semiconducting

12– Semiconducting

15– Semiconducting

18– Metallic

b) Log current (A)

Fig. 53.25a,b I–V characteristics of SWCNTs. (a) For the raw SWCNT suspension, (b) for the ﬁltered SWCNT suspension

in forming semiconducting CNTs changed from 33%

(before the ﬁltering process) to 65% (after the ﬁltering

process). The yield should be improved by optimizing

the concentration of CNT suspension, the strength of

the DEP force, the ﬂow rate of the suspension in the

DEP chamber, the structure of the channel, and the mi-

croelectrodes of the DEP chamber.

The yield to form semiconducting CNTs is very im-

portant because it affects the successful rate to fabricate

nanodevices. The yield to form semiconducting CNTs

was increased by using our system. Although there is

a synthesis that produces nearly90% of semiconducting

CNTsbyPECVD [53.49], both CNT synthesis methods

and post-processing separation methods are important

and can be combined for differentapplications. Oursep-

aration system is a post-processing method, which can

be used together with different CNT synthesis methods.

Since our system used electrical signal to control the

Part F 53.3

944 Part F Industrial Automation

0 5 10 15

IR laser is ON

IR laser is OFF

20 25 30

Current (nA)

Time (s)

–0.2

–0.4

–0.6

–0.8

–1

–1.2

–1.4

–1.6

–1.8

Fig. 53.26 Temporal photoresponses of a CNT-based IR detector

DEP manipulation and separation, it can be integrated

with current robotic manufacturing systems easily, and

eventually the process can be operated automatically

and precisely. As a result, batch nanomanufacturing of

nanodevices can be achieved by this system.

53.3.5 CNT-Based Infrared Detector

When semiconducting CNTs are deposited on the mi-

croelectrodes, the photonic effects of the CNT-based

nanodevice can be studied. For example, a CNT device

was put under the infrared (IR) laser source (UH5-

30G-830-PV, World Star Tech, optical power: 30mW;

wavelength: 830 nm), and the photocurrent from the

CNT-based nanodevice was measured. The laser source

was conﬁgured to switch on and off in several cycles;

the temporal photoresponses of the device are shown

in Fig.53.26. The experimental result showed the CNT-

based device was sensitive to the IR laser, so CNTs can

be used to make novel IR detectors. More detail design

and fabrication of CNT-based IR detectors are given

in [53.50–52]

53.4 Conclusions

Automated nanomanipulation is desirable to increase

the efﬁciency and accuracy of nanoassembly. Auto-

mated nanoassembly of nanostructures isvery challeng-

ing because of the manipulation path generation for

different nanoobjects, position errors due to random

drift, and cantilever deformation during nanomanip-

ulation. This chapter discussed automated nanoma-

nipulation technology for nanoassembly. Automated

nanomanipulation methods of nanoobjects were devel-

oped, and an automated local scanning method was

presented to compensate for the random drift. A CAD

guided automated nanoassembly method was devel-

oped. CAD guided automated nanoassembly was able

to open a door to assembly of complex nanostructures

and nanodevices. The effectiveness of the system has

also been veriﬁed by inscribing nano features on soft

surface, manipulating nanoparticles DNA molecules

and characterization of biological samples [53.53–56].

Moreover, CNT separation by a DEP chamber and the

development of an automated CNT deposition work-

station that applies DEP manipulation on CNTs were

presented. The system assembles semiconductingCNTs

to the microelectrodes effectively and, therefore, it is

possible to improve the success rate to fabricate nano-

devices. The separation method developed in this paper

is a post-processing method, which can be used together

with different CNT synthesis methods. Since our sys-

tem used electrical signals to control CNT separation

and DEP manipulation, it can be integrated into current

robotic manufacturing systems easily, and eventually it

will be possibleto operatethe process automatically and

precisely. It opens the possibility of batch fabricating

CNT-based devices. Furthermore, the nanomanufac-

turing process is not limited to CNTs, but it can be

used on other nano materials such as ZnO and InSb

nanowires etc. The development of the nanomanufac-

turing process will achieve different novel nano devices

effectively.

References

53.1 G. Binning, C.F. Quate, C. Gerber: Atomic force

microscope, Phys. Rev. Lett. 56(9), 930–933 (1986)

53.2 D. Wang, L. Tsau, K.L. Wang, P. Chow: Nanofabri-

cation of thin chromium ﬁlm deposited on Si(100)

Part F 53