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Update on graphene activity: Dirac points observed D. Goretti J. - - PowerPoint PPT Presentation

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Update on graphene activity: Dirac points observed D. Goretti J. Scherzinger Universit di Pisa 06/04/2018 D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 1 / 21 Status one week ago We

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SLIDE 1

Update on graphene activity: Dirac points observed

  • D. Goretti
  • J. Scherzinger

Università di Pisa

06/04/2018

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 1 / 21

slide-2
SLIDE 2

Status one week ago

We received a new structure from NEST with around 10/25 cells with graphene implants; Unfortunately the firsts results on them, were not completely satisfying: sweeping the back contact while maintaining the top contact at 0 V and VD - VS = 10 mV showed a modulation of the current through graphene but no Dirac point have been seen with this procedure.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 2 / 21

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SLIDE 3

Status one week ago

Plot for one of the G-FETs of cell 7. The other structures showed a completely analogous result.

10 20 30 40 50 60 70 80 90 [V]

back

V 28.5 29 29.5 30 30.5 31 31.5 32 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 3 / 21

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SLIDE 4

Status now

Using a different approach (sweeping both the top and the back contacts) we found 5 G-FETs that showed a clear Dirac point on the chip given in two interesting cells (cell 7 and cell 8). Not all G-FETs of the sample given have been connected since two cells with graphene are under the clamp or so near to it to make them unreachable with the needles of the probes.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 4 / 21

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SLIDE 5

First Dirac point observed

The first Dirac point was observed on one of the structure of the cell 7 of the structure with 300nm thick SiO2.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 5 / 21

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SLIDE 6

First Dirac point obtained

The Dirac point was obtained maintaining at the same value the voltage at the top and back contact while sweeping them from 0 V to 100 V.

10 20 30 40 50 60 70 80 90 100 [V]

back

V 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8

3 −

10 × ] Ω Resistance [M

back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 6 / 21

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SLIDE 7

Different strategy to obtain the Dirac point

Since we would like to deplete the silicon below graphene we tried to obtain the Dirac point sweeping the top contact and the back together, while maintaining an offset between the two of: Vback-Vtop = 20 V corresponding to the one to assure depletion. Also with this strategy the Dirac point was observed only at a slightly different Vback. We measured the Dirac points for 5 different G-FETs belonging to cell 7 and cell 8 of the structure given.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 7 / 21

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SLIDE 8

Cell 7 Dirac point

We connected the cell 7 with this nomenclature for the G-FETs present on

  • it. For the cell 8 was used an identical nomenclature.
  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 8 / 21

slide-9
SLIDE 9

Results on G-FET 7.1

The measure was performed with the top contact swept from -20 V to 80

  • V. The back voltage was swept from 0 to 100 V. VD-VS = 5 mV.

10 20 30 40 50 60 70 80 90 100 [V]

back

V 7 8 9 10 11 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 9 / 21

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SLIDE 10

Results on G-FET 7.1

We translated the information on the current through graphene in an information in the resistance and we fitted the plot obtained with the known formula: Rgraphene = RC + Nsq µe

  • n2 + (cox/e)2(VG − VD)2

(1) where e is the charge of an electron, µ the mobility, cox the capacitance of the SiO2, Nsq the number of squares (L/W ), n the residual charge in graphene, RC the contact resistance, VG the back gate voltage, and VD the Dirac point voltage.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 10 / 21

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SLIDE 11

Results on G-FET 7.1

10 20 30 40 50 60 70 80 90 100 [V]

back

V 450 500 550 600 650 700 750 800 ] Ω Graphene resistance [

/ ndf

2

χ 157.2 / 112

C

R 2.766 ± 313.9 µ 161.6 ± 9782 n 1.511e+10 ± 1.278e+12

D

V 0.1146 ± 92.88 / ndf

2

χ 157.2 / 112

C

R 2.766 ± 313.9 µ 161.6 ± 9782 n 1.511e+10 ± 1.278e+12

D

V 0.1146 ± 92.88

back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 11 / 21

slide-12
SLIDE 12

Results on G-FET 7.2

The measure was performed with the top contact swept from -20 V to 80

  • V. The back voltage was swept from 0 to 100 V. VD-VS = 5 mV.

10 20 30 40 50 60 70 80 90 100 [V]

back

V 5 5.5 6 6.5 7 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 12 / 21

slide-13
SLIDE 13

Results on G-FET 7.2

10 20 30 40 50 60 70 80 90 100 [V]

back

V 700 750 800 850 900 950 1000 1050 ] Ω Graphene resistance [

/ ndf

2

χ 103.9 / 112

C

R 3.396 ± 589.6 µ 246.9 ± 1.117e+04 n 1.86e+10 ± 1.146e+12

D

V 0.1575 ± 93.96 / ndf

2

χ 103.9 / 112

C

R 3.396 ± 589.6 µ 246.9 ± 1.117e+04 n 1.86e+10 ± 1.146e+12

D

V 0.1575 ± 93.96 back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 13 / 21

slide-14
SLIDE 14

Results on G-FET 7.3

The measure was performed with the top contact swept from -20 V to 80

  • V. The back voltage was swept from 0 to 100 V. VD-VS = 5 mV.

10 20 30 40 50 60 70 80 90 100 [V]

back

V 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 14 / 21

slide-15
SLIDE 15

Results on G-FET 7.3

10 20 30 40 50 60 70 80 90 100 [V]

back

V 900 950 1000 1050 1100 1150 ] Ω Graphene resistance [

/ ndf

2

χ 150.4 / 196

C

R 2.829 ± 748.3 µ 199 ± 8245 n 3.396e+10 ± 1.94e+12

D

V 0.3306 ± 92.05 / ndf

2

χ 150.4 / 196

C

R 2.829 ± 748.3 µ 199 ± 8245 n 3.396e+10 ± 1.94e+12

D

V 0.3306 ± 92.05 back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 15 / 21

slide-16
SLIDE 16

Results on G-FET 8.3

The measure was performed with the top contact swept from -20 V to 80

  • V. The back voltage was swept from 0 to 100 V. VD-VS = 5 mV.

10 20 30 40 50 60 70 80 90 [V]

back

V 3 4 5 6 7 8 9 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 16 / 21

slide-17
SLIDE 17

Results on G-FET 8.3

10 20 30 40 50 60 70 80 90 100 [V]

back

V 600 800 1000 1200 1400 1600 1800 ] Ω Graphene resistance [

/ ndf

2

χ 193.9 / 102

C

R 5.208 ± 186.5 µ 31.86 ± 3777 n 6.44e+09 ± 1.024e+12

D

V 0.0309 ± 85.66 / ndf

2

χ 193.9 / 102

C

R 5.208 ± 186.5 µ 31.86 ± 3777 n 6.44e+09 ± 1.024e+12

D

V 0.0309 ± 85.66 back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 17 / 21

slide-18
SLIDE 18

Results on G-FET 8.4

The measure was performed with the top contact swept from -20 V to 80

  • V. The back voltage was swept from 0 to 100 V. VD-VS = 5 mV.

10 20 30 40 50 60 70 80 90 [V]

back

V 5 6 7 8 9 10 11 A] µ [

D

I

back

Current through graphene vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 18 / 21

slide-19
SLIDE 19

Results on G-FET 8.4

10 20 30 40 50 60 70 80 90 100 [V]

back

V 500 600 700 800 900 1000 ] Ω Graphene resistance [

/ ndf

2

χ 730.2 / 123

C

R 6.243 ± 167.3 µ 77.6 ± 4924 n 1.405e+10 ± 1.536e+12

D

V 0.03621 ± 75.84 / ndf

2

χ 730.2 / 123

C

R 6.243 ± 167.3 µ 77.6 ± 4924 n 1.405e+10 ± 1.536e+12

D

V 0.03621 ± 75.84

back

Graphene resistance vs V

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 19 / 21

slide-20
SLIDE 20

Results

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 20 / 21

slide-21
SLIDE 21

Prospects

– Next week a new sample with G-FETs to be tested should arrive in our labs; – as a next step we would like to test the device response to a laser in order to understand if it is possible to extract the information on the intensity of the beam hitting the device from the change in resistance induced in graphene.

  • D. Goretti
  • J. Scherzinger (Unipi)

Update on graphene activity: Dirac points observed 06/04/2018 21 / 21