奈米加工與奈米壓痕術之應用研究

方 得 華 博士

Te-Hua Fang, Ph. D

國立虎尾科技大學 機電所/光電所 奈米科技實驗室

National Formosa University

奈米加工與奈米壓痕術之應用研究

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

-3-Introduction

¾

¾

Length scale :

Length scale :

0.1-100

nm

nm

¾

¾

Metrology :

Metrology :

SEM, TEM,

SPM

SPM

(STM, AFM,

(STM, AFM,

FFM,SNOM, MFM,

FFM,SNOM, MFM,

…

…

)

)

¾

¾

Applications:

Applications:

Nanomaterial

Nanomaterial

Nanobiology

_{Nanoelectric and Optic}

Nanoelectric and Optic

Nanotribology and

Mechanics

Nanotechnology

Nanotechnology

Basics of Nanotechnology

• Electron-microscope image of the world's smallest guitar, based roughly on the design for the Fender Stratocaster, a popular electric guitar.

• Its length is 10 millionths of a meter-- approximately the size of a red blood cell and about 1/20th the width of a single human hair. Its strings have a width of about 50 billionths of a meter (the size of approximately 100 atoms).

• Plucking the tiny strings would produce a high-pitched sound at the inaudible frequency of approximately 10 megahertz.

• Made by Cornell researchers with a single silicon crystal, this tiny guitar is a playful example of

nanotechnology, in which scientists are building machines and structures on the scale of billionths of a meter to perform useful technological functions and study processes at the submicroscopic level.

Figure cited from http://www.news.cornell.edu/science/July97/guitar.ltb.html, Dustin W. Carr and Harold G. Craighead, Cornell.

“Nanostructure”

Introduction

Nanostructured Materials

Carbon Nanotube

Au Nanoparticles

Teeth

Nanoporous Alumina

Membrane

Sliding

Self-Assembling Monolayer

GaN nanotube

Butterfly wings

AFM Apparatus

Atomic manipulation

Xe/Ni (111)

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

Thermal probe lithography

The rate of heat flow from the tip to the sample surface Q can be expressed as

Thermal probe lithography

Contact mode

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

Mechanical Lithography

Mechanical Lithography

•The groove depth increased as the applied load increased and the groove depth for Au was larger than that of Pt under the same load.

•The volume of the removed material can be used to evaluate the hardness of the materials.

•On inspection of the volume removed at different loads, the volume was about

10,000 nm3 at a load of 1uN for Au and was approximately equal to that of a load of 2 uN for Pt. This result showed that the scratching hardness of the Pt film is higher than that of Au film.

Mechanical Lithography

•The wear depth of Au and Pt films measured as a function of feed at an applied force of 2.5uN and a speed of 2 um/s.

•When the nanomachining lateral feed was increased, the wear depth for both films decreased. The decreasing ratio of wear depth gradually became smaller as the feed rate was increased.

Mechanical Lithography

Computer aided nanomachining could be for the development of the next generation of

computer numerical control

(CNC) nano-scale machine tools

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

Electrochemical lithography

Si+2OH-ÆSi₂O+2H+

(a)

Water bridge

Water bridge picture from Kelvin model

Molecular Simulation

30

(

) (

)

r

-r

+

z

−

z

=

z

(

)

2

(

)

0

2

⋅

−

+

⋅

−

⋅

=

zr

dz

z

z

r

r

(

) (

)

R

z

z

R

D

r

+

+

−

=

+

z

-R

D

r

tan

+

=

α

α

cos

⋅

−

+

=

D

R

R

h

α

sin

⋅

= R

r

Electrochemical lithography

Electrochemical lithography

Effect of applied voltage

RH= 60% , Time of 5s

Time of 10s

Water bridge :(a) Higher Relative humidity (RH) (b) Lower RH

7

Effect of Humidity

Electrochemical lithography

Applied voltage of 10 V RH of 60% Time of 0.5, 1, 2,5 and 10s

⎟

⎠

⎞

⎜

⎝

⎛

⋅

=

h

h

u

exp

1

dt

dh

Effect of reaction time

GaAs, 10V, 70% and 10s GaAs, 10V, 70% and 150s

Ionic diffusion

Aspect ratio (h/W) of nanodots at different voltages

Contribution of nanodots at relative humidity

Ionic diffusion mechanism

Effect of pulse voltage

GaAs,RH of 65%, Time of 20s

Electrical field and growth rate

E

V

h

=

Electrochemical lithography

Effect of surface roughness

Applied voltage of 10V, RH of 60% and Time of10s

Effect of writing rate on producing nanowires

GaAs: 10, 9, 8 and 7 V

RH：60% ; Writing rate：60nm/s

Growth characteristics of different nanostructures

(a) GaAs

(b) Si

(c) TiN

Activation energies of SiO₂, TiON_xGa₂O₃and As₂O₃are 5eV, 1eV, 2eV and 3.6 eV, respectively

2GaAs + 12h++ 6H₂O → Ga₂O₃ + As₂O₃+12H+ Si+2OH-ÆSiO2+2H + 2TiN+2O2Æ2TiO2+N2

Electrochemical lithography

Lithography with CNT probe

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

Introduction to Nanoindentation

• Materials and Optoelectronic engineering :

Optimizing material

composition, structure, processing for particular applications (bulk and thin films)

•

Mechanics of small volumes:

Understanding whether thin films, lines, dots

have different mechanical properties than bulk counterparts

•

Material physics:

Measuring deformation processes such as dislocation

nucleation, crack growth, etc.

•

Indentation tests are the most commonly applied

means of testing the nanomechanical properties of

materials. The area of the residual indentation in the

sample is measured and the hardness, H, is defined

as H = P/A

•

Nanoindentation refers to depth-sensing

indentation testing in the nanometer range and has

been made possible by the development of machines

and analysis models

•

Indentation tests are the most commonly applied

means of testing the nanomechanical properties of

materials. The area of the residual indentation in the

sample is measured and the

hardness

, H, is defined

as H = P/A

•

Nanoindentation refers to depth-sensing

indentation testing in the nanometer range and has

been made possible by the

development of machines

Nanoindentation

Unique mechanics of small volumes in Materials

and Optoelectronic engineering

•Are mechanical properties affected by constraint?

•Are E, s

, n f(size)?

•When structure dimensions approach atomic dimensions, is

mechanical behavior quantized?

•Are mechanical properties affected by constraint?

•Are E, s

, n f(size)?

•When structure dimensions approach atomic dimensions, is

mechanical behavior quantized?

Elastic Contact Analysis

(

ν

)

π

A

E

S

1

2

−

=

E

E

E

)

1

(

)

1

(

1

₌

−

ν

₊

−

ν

C

dP/dh

W

W

Show variables in response:

C = loading curvature

dP/dh = unloading stiffness

P

, h

W

= plastic work of indentation

W

= total work of indentation

Experimental nanoindentation results

•The relative amount of pile-up is significantly smaller because a greater portion of the deformed volume is in the sample.

InGaN

XRD spectra (left) and AFM images (right) of InGaN films deposited at growth

temperatures of 790, 760 and 730 0C for In-content of (a)

InGaN

XRD spectra (left) and AFM images (right) of InGaN films deposited at growth

temperatures of 790, 760 and 730 0C for In-content of (a)

Nanoindentation of nanostructures

• Buckling characterization of vertical ZnO

nanowires using nanoindentation

Glass substrate 2 μm diameter circular flat diamond punch 300 350 400 450 500 550 600 3.26 eV (380 nm) PL Intensity (a.u.) Sample A Sample B Wavelength (nm) 20 30 40 50 60 70 80 ZnO (004) ZnO (002) Incident Angle (2θ) XRD Intensity (a.u) Sample B Sample A

200 400 600 800 1000 0 1k 2k 3k 4k 5k Unloading Loading

Sample A

Load

(

N

)

Displacement (nm)

Sample B

Load

(

N

)

Displacement (nm)

Sample description σ_cr(MPa) K ε_cr(%) E (GPa) 0.5 0.62 117 0.7 0.32 229 0.5 0.35 232 0.7 0.18 454 B length: 800 nm diameter: 30 nm 806 A length: 2000 nm diameter: 100 nm 723

• Buckling characterization of vertical ZnO

nanowires using nanoindentation

Buckling

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

zConclusion

Electrochemical lithography

combined with wet etching

(a)

(c)

(d)

BOE( Buffered Oxide Etch)-HF, NH4F and H2O

Application for Nanodevices

Electrochemical lithography

combined with wet etching

Current-voltages of nanodots

(a) I-V curve

(b) Fowler-Nordheim curve (ln(I/V

_{) vs 1/V)}

Fowler-Nordheim (FN)

Current density J：

⎟

⎠

⎞

⎜

⎝

⎛ −

=

E

E

C

J

exp

β

C

q

/

8

π

h

φ

=

hq

m

/

3

2

8

π

φ

β

=

Current-voltages of nanodots

Nanoindentation of nanowires and

nanodots

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulation

Molecular dynamics (MD)

• Simulation that shows how the atoms in the

system move with time

• Model phenomena that cannot be observed

experimentally

• Typically on the nanosecond timescale

• Solve the Newtonian equations of motion

Cons:

limited run time

Pros:

Nanomechanics

-a subset of the field of

nanotechnology, also sometimes called “Molecular

Mechanics” or “ Atomistic Simulation”

Quantum Mechanics Nano Mechanics Continuum Mechanics Microstructure Mechanics

nm

μm

mm

psec

nsec

msec

sec

Length

Time

fsec

Interaction

distance (nm)

Get initial configuration

From crystallography or physical model

Assign initial velocities

At thermal equilibrium, the expected value of the kinetic

energy of the system at temperature T is:

This can be obtained by assigning the velocity

components v

from a random Gaussian distribution with

mean 0 and standard deviation (k

_B

T/m

_i

):

How do we run a MD simulation?

T

k

N

v

m

E

_B

N

i

i

i

kin

(

3

)

2

1

2

1

3

1

2

=

=

∑

=

For each time step:

Compute the force on each atom:

U is potential energy function

Solve Newton’s 2

_{law of motion for each atoms, to get new}

coordinates and velocities

Store coordinates

Stop

X

U

X

U

X

F

∂

∂

−

=

−∇

=

(

)

)

(

)

( X

F

X

M

=

X: Cartesian vector of the system

M diagonal mass matrix

..

means second order

differentiation with

respect to time

How do we run a MD simulation?

Empirical Force Fields :

How do we run a MD simulation?

(

)

(

)

( )

[

]

∑

∑

∑

∑

∑

+

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+

−

+

−

+

−

=

r

q

q

r

R

r

R

n

K

K

b

b

K

U

4

2

cos

1

2

1

2

1

ε

πε

ε

φ

θ

θ

U

U

How do we run a MD simulation?

Many-body potential of the tight-binding second-moment approximation

(

TB-SMA

) model for Metals-Metals

)]

1

(

2

exp[

]

[

)]

1

(

exp[

−

−

+

−

−

−

=

r

r

q

r

q

r

r

p

r

Ap

F

ξ

φ

φ

∑

⎥

⎦

⎤

⎢

⎣

⎡

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

−

=

r

r

q

1

2

exp

φ

)}}

(

exp{

2

)}

(

2

{exp{

)

(

r

D

r

r

r

r

U

=

−

α

−

−

−

α

−

Morse

potential function for Metals-Diamond

Simulated nanoscratch

Process- constant depth

Simulated nanoscratch

Different tip shapes

Simulated nanoscratch

40x40x15a

Simulated nanoscratch

•The relationship of the wear depth and the temperature at an applied force of Fz = 570×10−10 N and Fy = 200×10−10 N and a simulated velocity of 250 m/s after being scratched is shown in above Figure.

• The wear depth increased while increasing the simulated temperature under the constant force due to increasing the kinetic

energy.

Simulated nanoscratch

•Figure illustrates the relationship of the wear depth and the velocity at an applied force of Fz = 570×10−10 N and Fy = 200×10−10 N and a temperature of 300K after being nanoscratched.

•The wear depth decreased while increasing the nanoscratching velocity. This is because the dislocations propagation in the material is difficult to make slip when the velocity was too fast and the diffusion time of the dislocations became shorter.

Molecular dynamics of nanoindentation

Molecular dynamics of nanoindentation

constant depth mode

Berkovich Recovery ratio~28.6% 209 adhesion atoms Vickers Recovery ratio~14.3% 74 adhesion atoms Sphere Recovery ratio~28% 418 adhesion atoms Cone Recovery ratio~14% 289 adhesion atoms

Molecular dynamics of nanoindentation

Simulated nanoindentation

•The plastic indentation depth, hp, is the depth of the permanent impression in the specimen after the removal of applied force and the plastic energy represents the area between the loading and unloading curves

• The plastic energy, Ur, depends on the indenter’s geometry, the operating

conditions, the material’s hardness, and the maximum of applied load, Pmax. The plastic energy is proportional to a function of the maximum applied load

•Load–displacement data for GaAs obtained during nanoindentation with a Berkovich

indenter showing pop-in behavior during loading

•The cross sectional view of the (0 1 0) plane corresponds to II–V steps

•3D MD simulation views of the dissociated dislocation loops,

•the cross-sectional view of dislocation loops surrounded the indenter tip and rotating 308 along the [1 1 1] plane (corresponding to the IV step), and

• top view of the MD simulation surface

showing the dislocation loops formed on and under the {1 1 1} plane. Red, green and blue represent the C, Ga and As atoms, respectively.

Outline

zIntroduction

zThermal probe lithography

zMechanical lithography

zElectrochemical lithography

zNanoindentation

zNanodevices and characterization

zMolecular dynamics simulations

Conclusion

•

Nanomachining Characterization

To achieve nanoscale fabrication

•

Mechanical and Thermal Lithography

•

Nanoelectrochemical Lithography

Acknowledgments

Thank NSC plans, STUT, NCKU, my students and coworkers~ L.W

Ji., S. L. Tasi, Y.H. Lin, S. R. Jian, J.D. Wu, W.I. Weng and W. J.

Chang etc

Literature

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atomic force microscopy, NanotechnologyVol. 11. pp. 181-187, 2000.

• T. H. Fang, C I Weng, J G Chang, C C Hwang, Nanotribology of amorphous hydrogenated carbon

films by using a scanning probe microscopy,Thin Solid Films, Vol. 396, pp.166-172, 2001.

• T. H. Fang, C. I Weng, M. J. Chiang, Effect of substrate bias on nanotribology of a-C:H films

deposited by ECR-MPCVD,Diamond and Related Materials ,Vol. 11, pp.1653-1659, 2002.

• T. H. Fang, W. J. Chang, Effects of AFM-based nanomachining process on aluminum surface,

Journal of Physics and Chemistry of Solids, Vol. 64, pp.914-918, 2003.

• T. H. Fang, W. J. Chang, Microthermal machining using scanning thermal microscopy, Applied

Surface Science, Vol. 240, pp. 312-317, 2005.

• T. H. Fang, S. R. Jian, D. S. Chuu, Nanotribology and fractal analysis of ZnO thin films by using

scanning probe microscopy, Journal of Physics D: Applied Physics, Vol.36, pp.878-883, 2003.

• T. H. Fang, W. J. Chang, Nanoindentation characteristics on polycarbonate polymer film,

Microelectronics Journal, Vol. 35, pp. 595-599,2004.

• T. H. Fang, Mechanisms of nanooxidation of Si(100) from atomic force microscopy,

Microelectronics Journal, Vol. 35/9, pp 701-707, 2004.

• T. H. Fang, W. J. Chang, Nanolithography and nanoindentation of tantalum-oxide nanowires and

nanodots using scanning probe microscopy,Physica B: Condensed Matter, Vol. 352, pp. 190-199, 2004.

• T. H. Fang, W. J. Chang, C. M. Lin, Nanoindentation and nanoscratch characteristics of Si and GaAs,

Microelectronic Engineering, Vol. 77, 389-398, 2005.

• T. H. Fang , Oxidation characteristics of nanodot and nanobump on TiN thin films by atomic force

microscopy,Electrochimica ActaVol. 50/14 pp 2793-2797,2005.

• T. H. Fang, W. J. Chang, C. I. Weng, Surface analysis of nanomachined surface using atomic force

microscopy,Materials Chemistry and Physics, Vol.32, pp. 141-146, 2005.

• T. H. Fang, W. J. Chang, C. I. Weng, Nanoindentation and nanomachining characteristics of gold

and platinum thin films, Materials Science & Engineering A, Vol. 430, pp.332-340, 2006.

• T. H. Fang, K. T. Wu, Local oxidation characteristics on titanium nitride film by electrochemical

nanolithography with carbon nanotube tip, Electrochemistry Communications, vol. 8, pp.173-178, 2006.