4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 295 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 295 K

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 295 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 295 K

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 373 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 373 K

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 373 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 373 K

max

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 473 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 473 K

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 473 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 473 K

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 573 K

Plastic strain range

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

, GP

a

w1 = 300 nmT = 573 K

Plastic strain range

max

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 300 nmT = 573 K

Plastic strain range

4 6 8 10 120

10

20

Maximum strain , %

Max

imum

, GP

a

w1 = 300 nmT = 573 K

Plastic strain range

max

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 295 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 295 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 373 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 373 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 473 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 800 nmT = 473 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

Plastic strain range

w1 = 800 nmT = 573 K

2 4 6 8 100

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

Plastic strain range

w1 = 800 nmT = 573 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 295 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 295 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 373 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 373 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 473 K

4 6 8 10 120

10

20

Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

w1 = 200 nmT = 473 K

4 6 8 10 12Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

Plastic strain range

w1 = 200 nmT = 573 K

Maximum strain max, %

Max

imum ,

0

10

20

Maximum strain max, %

Max

imum ,

Plastic strain range

w1 = 200 nmT = 573 K

4 6 8 10 12Maximum strain max, %

Max

imum

bend

ing

stre

ss

, GP

a

Plastic strain range

w1 = 200 nmT = 573 K

Maximum strain max, %

Max

imum ,

0

10

20

Maximum strain max, %

Max

imum ,

Plastic strain range

w1 = 200 nmT = 573 K

Y. Isono, T. Namazu and T. Tanaka, IEEE International Conference on Microelectromechanical Systems 2001, Interlaken, Switzerland 2001.

0 4 8 12 16 200

2

4

6

8

Bias voltage, V

Thi

ckne

ss o

fSiO

2fi

lm, n

m

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0 4 8 12 16 200

2

4

6

8

Bias voltage, V

Thi

ckne

ss o

fSiO

2fi

lm, n

m

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0 4 8 12 16 200

2

4

6

8

Bias voltage, V

Thi

ckne

ss o

fSiO

2fi

lm, n

m

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0 4 8 12 16 200

2

4

6

8

Bias voltage, V

Thi

ckne

ss o

fSiO

2fi

lm, n

m

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

0.02μm/s0.1μm/s0.4μm/s0.8μm/s1.6μm/s6.4μm/s12.8μm/s

400

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

Temperature T, K

You

ng’s

mod

ulus

E, G

Pa

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

Temperature T, K

You

ng’s

mod

ulus

E, G

Pa

E0<110> = 169 GPa in Si bulk

E = E0 - 0.04063(T - 295)

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

’,

300 500 600140

150

160

170

180

190

200○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

’,

E0<110> = 169 GPa in Si bulk

E = E0 - 0.04063(T - 295)

400

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

Temperature T, K

You

ng’s

mod

ulus

E, G

Pa

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

Temperature T, K

You

ng’s

mod

ulus

E, G

Pa

E0<110> = 169 GPa in Si bulk

E = E0 - 0.04063(T - 295)

○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

’,

300 500 600140

150

160

170

180

190

200○ w1 = 200 nm, □ w1 = 300 nm△ w1 = 550 nm, ◇ w1 = 800 nm

’,

E0<110> = 169 GPa in Si bulk

E = E0 - 0.04063(T - 295)

AFM Bending Testing of Nanometric Single Crystal Silicon Wire at Intermediate Temperatures for MEMS

Yoshitada Isono, Takahiro Namazu and Takeshi TanakaKobe University and Ritsumeikan University, JAPAN

Objective : To reveal the specimen size and temperature effects on elastic/plastic deformation behavior of nanometric Si at the temperature range from 295 to 573 K

The evaluation of mechanical properties of nanometric single crystal silicon wires at intermediate temperatures is very important for the design of high-density MEMS andelectronic devices, since the devices are serviced at 300 to 500 K which may induce thermal stress. However, mechanical properties of MEMS materials have just been estimated atroom temperature because of difficulties in problems associated with measuring ultra-small physical phenomena in an experiment at elevated temperatures. For safe and reliabledesigns of high-density electronic components, nano-scale material tests of Si at intermediate temperatures are essential.

Experimental Procedure

Background

SEM photographs of nanometric Si wires with the width of 200 nm

w1 = 200 nm

Upper widthw1 [nm]

Lower widthw2 [nm]

Thicknesst [nm]

Lengthl [mm]

200 370 255 6300 470 255 6550 720 255 6800 980 255 6

Upper widthw1 [nm]

Lower widthw2 [nm]

Thicknesst [nm]

Lengthl [mm]

200 370 255 6300 470 255 6550 720 255 6800 980 255 6

Upper widthw1 [nm]

Lower widthw2 [nm]

Thicknesst [nm]

Lengthl [mm]

200 370 255 6300 470 255 6550 720 255 6800 980 255 6

Nominal dimensions of nanometric Si wires

Fabrication of nanometric Si wire AFM bending test

w1 = 200 nm

t

lw1

w2

e1e2

t

lw1

w2

e1e2

0

6

[n

m]

01

23

45

01

23

45

67

8[m] Bias voltage : 20V

0.1m/s0.4m/s0.8m/s1.6m/s6.4m/s12.8m/s

SiO2

Si

0.02m/s

0

6

[n

m]

01

23

45

01

23

45

67

8[m] Bias voltage : 20V

0.1m/s0.4m/s0.8m/s1.6m/s6.4m/s12.8m/s

SiO2

Si

0.02m/s

Schematic diagram of bending test procedure

AFM tip for bending test

Variation of the SiO2 film thickness with the bias voltage applied in the field-enhanced anodization process

AFM image of SiO2 lines deposited on the SIMOXwafer at the bias voltage of 20 V

Fabrication process of nanometric Si wires using field-enhanced anodization technique

Results and discussions

Maximum stress-strain curves during bending test

Variation of Young’s modulus with increasing temperature

Bending analysis of fixed wire using FEM

Results of AFM bending test

Young’s modulus decreases with an increaseof the test temperature, but has no size effect.

mI

lE

192

3

Bending force Fn ;

Sensitivity)×kDIFDIFF exinitn /)((Maximum displacement in the z-direction of the wire D ;

ySensitivitDIFZPZTD ex /)( Young’s modulus E ;

Bending stress B ;

Stainless steel cantilever

Diamond tip (r = 100 nm)

Nanometric Si wires fracture in a brittle manner at room temperature, whereas Si wires deform plastically at intermediate temperatures.

<001>

<110> <110>

<001>

<110> <110><110>

I

elFnB

8

)( 1max ・・

I

elFnB

8

)( 1max ・・

Equivalent Von Mises Stress

Si+2OH- SiO2+H2+2e- (Anode)

2H++2e- H2 (Cathode)

Si+2H2O SiO2+2H2

2H2O 2H++2OH-

ⅰ）SIMOX wafer

ⅱ）Si etching

ⅲ）SiO2 etching

ⅳ）Anodization

ⅴ）Si etching

ⅵ）SiO2 etching

Si cantilever coated with Au

Si

SiO2

Si

SiO2

Si+2OH- SiO2+H2+2e- (Anode)

2H++2e- H2 (Cathode)

Si+2H2O SiO2+2H2

2H2O 2H++2OH-

ⅰ）SIMOX wafer

ⅱ）Si etching

ⅲ）SiO2 etching

ⅳ）Anodization

ⅴ）Si etching

ⅵ）SiO2 etching

Si cantilever coated with Au

Si

SiO2

Si

SiO2

< Step 2 >Calibration of the sensitivity of cantilever

< Step 3 >Bending test with AFM

< Step 4 >Calculation of Young's modulus and bending stress

< Step 1 >Measurement of beam size using AFM

① ② ③ ④

⑤

Visible laserDetector

Diamond plate

Visible laserDetector

Diamond plate

DIF voltage

FFM voltage

Wire’s deflection

Cantilever

Heater

Cantilever’s deflection

10-510-410-30

1

2

3

10-210-10

1

2

3

◇ 295 K, △△ 373 K■ 473 K, ● 573 K

◇ 295 K, △△ 373 K■ 473 K, ● 573 K

Effective surface area SE, m2

Effective volume VE, m3

nanometermicrometer

nanometermicrometer

Plas

tic

stra

in r

ange

⊿ p

, %

10-510-410-30

1

2

3

10-210-10

1

2

3

◇ 295 K, 373 K■ 473 K, ● 573 K

◇ 295 K, 373 K■ 473 K, ● 573 K

10-510-410-30

1

2

3

10-210-10

1

2

3

10-510-410-30

1

2

3

10-210-10

1

2

3

10-510-410-3

10-210-1

◇ 295 K, 373 K■ 473 K, ● 573 K◇ 295 K, 373 K■ 473 K, ● 573 K

◇ 295 K, 373 K■ 473 K, ● 573 K◇ 295 K, 373 K■ 473 K, ● 573 K

Effective surface area SE, m2

Effective volume VE, m3

nanometermicrometer

nanometermicrometer

10-510-410-30

1

2

3

10-210-10

1

2

3

◇ 295 K, △△ 373 K■ 473 K, ● 573 K

◇ 295 K, △△ 373 K■ 473 K, ● 573 K

Effective surface area SE, m2

Effective volume VE, m3

nanometermicrometer

nanometermicrometer

Plas

tic

stra

in r

ange

⊿ p

, %

10-510-410-30

1

2

3

10-210-10

1

2

3

◇ 295 K, 373 K■ 473 K, ● 573 K

◇ 295 K, 373 K■ 473 K, ● 573 K

10-510-410-30

1

2

3

10-210-10

1

2

3

10-510-410-30

1

2

3

10-210-10

1

2

3

10-510-410-3

10-210-1

◇ 295 K, 373 K■ 473 K, ● 573 K◇ 295 K, 373 K■ 473 K, ● 573 K

◇ 295 K, 373 K■ 473 K, ● 573 K◇ 295 K, 373 K■ 473 K, ● 573 K

Effective surface area SE, m2

Effective volume VE, m3

nanometermicrometer

nanometermicrometer

△△

△△

△△

10-510-410-3

3

10-210-1

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

nanometermicrometer

nanometermicrometer

△△■ 473 K

△△■ 473 K

10-50

1

2

0

1

2

3

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

10-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K

■ 473 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

△△

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

△△■ 473 K

■ 473 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K

■ 473 K

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

473 K573 K

△△

△△

△△

10-510-410-3

3

10-210-1

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

nanometermicrometer

nanometermicrometer

△△■ 473 K

△△■ 473 K

10-50

1

2

0

1

2

3

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

10-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K

■ 473 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

△△

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

△△■ 473 K

■ 473 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

■ 473 K● 573 K

-5

Effective volume VE, m3

Effective surface area SE, m2

[×109]

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K

■ 473 K

Effective volume VE, m3

Effective surface area SE, m2

[×109

[×109]

Slip

line

den

sity

,cm

-2Sl

ip li

ne d

ensi

ty,

cm-2

■ 473 K373 K

■ 473 K● 573 K

■ 473 K373 K

473 K573 K

200 400 600 800 1000 120010-3

10-2

10-1

100

101

300 400 500 600345678

○○● w1 = 200 nm□□■ w1 = 300 nm△△▲ w1 = 550 nm◇ ◆ w1 = 800 nm▼ Millimeter size

specimen

Temperature T, K

Cri

tica

l res

olve

d sh

ear

stre

ss

c, G

Pa

200 400 600 800 1000 120010-3

10-2

10-1

100

101

300 400 500 600345678

○○● w1 = 200 nm□□■ w1 = 300 nm△△▲ w1 = 550 nm◇ ◆ w1 = 800 nm▼ Millimeter size

specimen

200 400 600 800 1000 120010-3

10-2

10-1

100

101

300 400 500 600345678

○○● w1 = 200 nm□□■ w1 = 300 nm△△▲ w1 = 550 nm◇ ◆ w1 = 800 nm▼ Millimeter size

specimen

200 400 600 800 1000 120010-3

10-2

10-1

100

101

300 400 500 600345678

○○● w1 = 200 nm□□■ w1 = 300 nm△△▲ w1 = 550 nm◇ ◆ w1 = 800 nm▼ Millimeter size

specimen

Temperature T, K

Cri

tica

l res

olve

d sh

ear

stre

ss

c, G

Pa

Results and discussions

Weibull plots of bending strength for nanometric Si wires Wire size dependency of Weibull plots

Weibull plot of bending strength

Y. Isono, T. Namazu and T. Tanaka, IEEE International Conference on Microelectromechanical Systems 2001, Interlaken, Switzerland 2001.

Plastic deformation behavior

Correlation of critical resolved shear stress with temperature

Wire size effect on plastic strain range

Critical resolved shear stress is inversely proportional to wire size and temperature.

It is possible to induce plastic deformation in ananometer-scale specimen at even 373 K, which is closeto room temperature.

AFM observations of slip line

AFM images of slip lines at the top surface of Si wires with widths of 200, 300 and 800 nm

w1 = 200 nmT = 373 K

w1 = 200 nmT = 473 K

w1 = 200 nmT = 573 K

w1 = 200 nmT = 573 K

Building up slip lines on an atomic scale,nanometric Si wires can deform plasticallyat intermediate temperatures.

Magnified image

Bending strength , GPa8 10 12 14 16 18 20

0.1

0.51.0

3.05.0

10.020.0

50.070.090.099.099.9

Cum

ulat

ive

prob

abil

ity

Pi,

%

Bending strength , GPaBending strength , GPa8 10 12 14 16 18 20

0.1

0.51.0

3.05.0

10.020.0

50.070.090.099.099.9

Cum

ulat

ive

prob

abil

ity

Pi,

% 295 373 473 573200nm300nm550nm800nm

T[K]w1 295 373 473 573200nm300nm550nm800nm

T[K]w1

Bending strength , GPa8 10 12 14 16 18 20

0.1

0.51.0

3.05.0

10.020.0

50.070.090.099.099.9

Cum

ulat

ive

prob

abil

ity

Pi,

%

Bending strength , GPaBending strength , GPa8 10 12 14 16 18 20

0.1

0.51.0

3.05.0

10.020.0

50.070.090.099.099.9

Cum

ulat

ive

prob

abil

ity

Pi,

% 295 373 473 573200nm300nm550nm800nm

T[K]w1 295 373 473 573200nm300nm550nm800nm

T[K]w1

10-510-410-3

10

15

20

10-210-1

10

15

20

Effective volume VE, m3

Effective surface area SE, m2

Sca

le p

aram

eter

b, G

Pa

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

nanometermicrometer

nanometermicrometer

10-510-410-3

10

15

20

10-210-1

10

15

20

Effective volume VE, m3

Effective surface area SE, m2

Sca

le p

aram

eter

b, G

Pa

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

nanometermicrometer

nanometermicrometer

10-210-1

10

15

20

Effective volume VE, m3

Effective surface area SE, m2

Sca

le p

aram

eter

b, G

Pa

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

nanometermicrometer

nanometermicrometer

10-210-1101

102

10-510-410-3101

102

Effective volume VE, m3

Effective surface area SE, m2

Sha

pe p

aram

eter

m

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

nanometermicrometer

nanometermicrometer

10-210-1101

102

10-510-410-3101

102

Effective volume VE, m3

Effective surface area SE, m2

Sha

pe p

aram

eter

m

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

◇ 295 K, △ 373 K□ 473 K, ○ 573 K

nanometermicrometer

nanometermicrometer

Variation of slip line density with decreasing wire size

Future work

w1 = 300 nmT = 373 K

w1 = 300 nmT = 473 K

w1 = 300 nmT = 573 K

w1 = 300 nmT = 573 K

Magnified imagew1 = 800 nmT = 373 K

w1 = 800 nmT = 473 K

w1 = 800 nmT = 573 K

w1 = 800 nmT = 573 K

Magnified image

Bending strength of nanometric Si wires shows a gradualreduction with increasing the test temperature. This is caused bya reduction of the yield stress at higher temperature.

The bending strength of the 200 nm-wide wires ranges from 17.76to 15.87GPa, which is about 1.5 times larger than the strength ofthe 800 nm-wide wires.

Plastic flow is obtained at the temperature from 373 to573 K in the nanometric wires.

Several slip lines appear in the 200 nm-widewires at higher temperature. The extent ofthe thermal activation of dislocation causesan increase of the number of slip lines in thewires. However, a few slip lines are observedin the 800 nm-wide wires at the temperaturesapplied in tests.

The slip line density increases with adecrease of the wire size at each temperature,which is likely to determine the plastic strainrange during the deformation.

Arrhenius formula ;

kT

TG0

),(exp

<110

><001>

<110>

<110

><001>

<110><110>

Plastic strain range increases with decreasing the wiresize, whereas it is proportional to temperature.

Cause of specimen size effecton plastic deformation behavior

Contribution of the surface energy to an increase of the activation energy of dislocations ?

Stress dependency of the activation energy ?Stress relaxation test

Size effect on b ○Temperature effect on b ○

Size effect on m ○Temperature effect on m ×

Weibull parameters b and m of nanometric Si wires can be predicted by a function as the following,

and .m = exp(1.78)

SE0.506 b = exp(-3.07T×10-4+2.29)・SE

5.03T×10-5-0.167