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
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 V D - V S = 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
Status one week ago Plot for one of the G-FETs of cell 7. The other structures showed a completely analogous result. Current through graphene vs V back A] µ [ D 32 I 31.5 31 30.5 30 29.5 29 28.5 10 20 30 40 50 60 70 80 90 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 3 / 21
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
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 SiO 2 . D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 5 / 21
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. Graphene resistance vs V − back × 3 10 ] Ω Resistance [M 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 6 / 21
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: V back - V top = 20 V corresponding to the one to assure depletion. Also with this strategy the Dirac point was observed only at a slightly different V back . 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
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
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. V D - V S = 5 mV. Current through graphene vs V back A] µ [ D 11 I 10 9 8 7 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 9 / 21
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: N sq R graphene = R C + (1) n 2 + ( c ox / e ) 2 ( V G − V D ) 2 � µ e where e is the charge of an electron, µ the mobility, c ox the capacitance of the SiO 2 , N sq the number of squares ( L/W ), n the residual charge in graphene, R C the contact resistance, V G the back gate voltage, and V D the Dirac point voltage. D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 10 / 21
Results on G-FET 7.1 Graphene resistance vs V back ] Ω χ χ 2 2 800 / ndf / ndf 157.2 / 112 157.2 / 112 Graphene resistance [ ± ± R R 313.9 313.9 2.766 2.766 C C µ µ ± ± 9782 9782 161.6 161.6 750 ± ± n n 1.278e+12 1.278e+12 1.511e+10 1.511e+10 ± ± V V 92.88 92.88 0.1146 0.1146 700 D D 650 600 550 500 450 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 11 / 21
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. V D - V S = 5 mV. Current through graphene vs V back A] µ [ D 7 I 6.5 6 5.5 5 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 12 / 21
Results on G-FET 7.2 Graphene resistance vs V back ] Ω χ χ 2 2 / ndf / ndf Graphene resistance [ 103.9 / 112 103.9 / 112 1050 ± ± R R 589.6 589.6 3.396 3.396 C C µ µ ± ± 1.117e+04 1.117e+04 246.9 246.9 1000 ± ± n n 1.146e+12 1.146e+12 1.86e+10 1.86e+10 ± ± V V 93.96 93.96 0.1575 0.1575 D D 950 900 850 800 750 700 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 13 / 21
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. V D - V S = 5 mV. Current through graphene vs V back A] 5.8 µ [ D I 5.6 5.4 5.2 5 4.8 4.6 4.4 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 14 / 21
Results on G-FET 7.3 Graphene resistance vs V back 1150 ] Ω Graphene resistance [ χ χ 2 2 / ndf / ndf 150.4 / 196 150.4 / 196 R R ± ± 748.3 748.3 2.829 2.829 C C µ µ 1100 ± ± 8245 8245 199 199 ± ± n n 1.94e+12 1.94e+12 3.396e+10 3.396e+10 ± ± V V 92.05 92.05 0.3306 0.3306 D D 1050 1000 950 900 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 15 / 21
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. V D - V S = 5 mV. Current through graphene vs V back A] µ [ 9 D I 8 7 6 5 4 3 10 20 30 40 50 60 70 80 90 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 16 / 21
Results on G-FET 8.3 Graphene resistance vs V back ] Ω Graphene resistance [ χ χ 2 2 / ndf / ndf 193.9 / 102 193.9 / 102 1800 ± ± R R 186.5 186.5 5.208 5.208 C C µ µ ± ± 3777 3777 31.86 31.86 1600 ± ± n n 1.024e+12 1.024e+12 6.44e+09 6.44e+09 V V ± ± 85.66 85.66 0.0309 0.0309 D D 1400 1200 1000 800 600 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 17 / 21
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. V D - V S = 5 mV. Current through graphene vs V back A] 11 µ [ D I 10 9 8 7 6 5 10 20 30 40 50 60 70 80 90 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 18 / 21
Results on G-FET 8.4 Graphene resistance vs V back ] Ω χ χ 2 2 / ndf / ndf 730.2 / 123 730.2 / 123 Graphene resistance [ 1000 ± ± R R 167.3 167.3 6.243 6.243 C C µ µ ± ± 4924 4924 77.6 77.6 ± ± n n 1.536e+12 1.536e+12 1.405e+10 1.405e+10 900 ± ± V V 75.84 75.84 0.03621 0.03621 D D 800 700 600 500 10 20 30 40 50 60 70 80 90 100 V [V] back D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 19 / 21
Results D. Goretti J. Scherzinger (Unipi) Update on graphene activity: Dirac points observed 06/04/2018 20 / 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
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