FIELD EMISSION IMAGING AND TRANSPORT CHARACTERISTICS OF NANO-COMPOSITE FILMS

Final Evaluation (B.Tech Project-part 1)

November 29, 2013(Department of Physics, IIT Delhi)

Under the supervision of

Prof. Pankaj Srivastava and Dr. Santanu Ghosh

Presented by,

Sumit Kumar(2010PH10873)

Palash Biswas(2010PH10859)

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OVERVIEW

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1. INTRODUCTION (Slide No. 3)(Regarding Field Emission, F-N equation, CNT’s and problems associated with it)

2. OBJECTIVES (Slide No. 4)

3. EXPERIMENTAL TECHNIQUES (Slide No. 5- 7)(CNT preparation, Indium Deposition, Field Emission Set up)

4. RESULTS (Slide No. 8- 13)

5. CONCLUSIONS (Slide No. 14)

6. REFERENCES (Slide No. 15)

7. ACKNOWLEDGEMENTS (Slide No. 16)

INTRODUCTION

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Field Emission:1) Emission of electrons from surface of amaterial in presence of high electric fields2) Also known as Fowler-Nordheim tunneling(High electric field narrows the potentialbarrier; electron have finite tunnelingprobability)

e is the electron chargeh is the Planck constantμ is the Fermi level relative to the bottom of the conduction bandφ is the work function (energy to move an electron from fermi level to vacuum)m is the electron massF is the electric field (volts/meter)j is the current density (amps/sq meter)

F-N EQUATION :

Carbon Nanotubes:1) It shows high current density under lowfields attributed to its shape (high aspectratio), robustness, mechanical strength,conductivity, ease in manufacture andprocessing2) The stability of current density with timeattributed to CNT is low.3) coating CNT with oxides and hexaborides ofmetal increases the temporal stability of fieldemission compromising drastically with thecurrent density.

Assumptions in F-N Theory1) Emitting surface is a metal that obeys thefree electron model with Fermi-Dirac statistics2) Surface is planar3) Temperature = 0 K (all electrons below Fermilevel)4) The potential in the metal is constant and itselectron states are unaffected by applied field

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OBJECTIVES

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1) To grow Carbon Nanotube using Catalytic Chemical vapour Deposition2) To Deposit Indium Layer over CNT using Thermal vapour Deposition3) To analyze the field emission from CNT , Indium coated CNT4) To observe the temporal stability of current density at constant voltage applied for

Indium coated CNT5) To oxidise Indium coated CNT by annealing it in a tubular furnace6) To analyze the field emission and it’s temporal stability of Indium oxide coated CNT

and compare it with the Indium coated CNT and pristine CNT7) To observe the field emission of other oxides over CNT8) To utilize the oxide coated CNT for display devices

PROGRESS1) Growth of CNT2) Deposition of Indium over CNT ( Thickness : 10 nm and 20 nm)3) Field emission of CNT and Indium coated CNT4) Temporal stability of Indium coated CNT5) SEM of pristine CNT6) X-Ray diffraction of Indium coated CNT

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EXPERIMENTAL TECHNIQUES

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1) Catalytic Chemical Vapour Deposition• A solution of 10 ml xylene with 2 g of ferrocene was prepared and kept in ultrasonic

bath for 20 min.• Fe(C5H5)2 was used as catalyst during CVD along with xylene, C8H10, which acts

carbon source• A solution of 10 ml xylene with 2 g of ferrocene was prepared and kept in ultrasonic

bath for 20 min and then put into a quartz tube • Maximum temperature of 750oCelsius was set on the double zoned tubular furnace

Fig 1: Double zone furnace and tube arrangement for catalytic CVD to produce CNTs

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EXPERIMENTAL TECHNIQUES

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2) Thermal Vapour Deposition

Material deposited Thickness Pressure

In coated CNT (1) 10 nm 8.0 × 10-5 torr

In coated CNT (2) 20 nm 7.5 × 10-5 torr

Fig 2. Thermal deposition chamber used todeposit indium over CNT substrate

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EXPERIMENTAL TECHNIQUES

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3) Field Emission set-up

Fig 3. Field emission set up for CNT composites on Si substrates

EXPERIMENTAL TECHNIQUES

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S.No Sample Thickness of sample

(nm)

Distance between anode and sample

(µm)

Variation of applied voltage

(V)

1 CNT - 200 100-3000

2 In coated CNT 10 200 100-3000

3 In coated CNT 20 200 100-3000

Table : Field emission parameters with pressure of 10-6 torrs.

4) Temporal Stability of current density of the In coated CNT sample was observed at constant applied voltage of 3000 Volts

5) Morphology: SEM (Scanning Electron Microscopy) of pristine CNT was carried out which gives information about the surface’s topography and confirms the presence of carbon nanotubes. The presence of indium with C in other two samples was confirmed by XRD (X-Ray Diffraction) studies.

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RESULTS

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1) CNT Sample

Fig 5. SEM images of Pristine CNT

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RESULTS

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Fig 6. F-N plot and J-E plot for pristine CNT

Turn on Field: 1.31 V/μm.Threshold Field: 1.79 V/μm Field Enhancemet Factor: 6218

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RESULTS

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2) In coated CNT

Fig 7. XRD pattern of In coated CNT

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RESULTS

12Fig 9. FN plot and J-E plot for high thickness Indium coated CNT

Fig 8. FN plot and J-E plot for low thickness Indium coated CNT

Field Emission is averaged over 5cycles

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RESULTS

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S.No Sample In Thickness

(nm)

Turn on Field

(V/µ𝒎)

Threshold Field

(V/µ𝒎)

Field Enhancemet

Factor

1 Pristine CNT - 1.31 1.79 6218

2 Indium coated CNT 10 2.02 2.77 3860

3 Indium coated CNT 20 1.11 1.41 4935

Table: Results obtained from Field Emission

Work Function Calculation

From F-N equation one can derive, Where,1 = work function of pristine CNT2 = work function of In-CNTslope1 = slope of FN curve of pristine CNTslope2 = slope of FN curve of In-CNTThe work-function of In-CNT comes out to be 6.2 Volts11/29/2013

RESULTS

Temporal Stability

Fig 10: Emission current versus time at a constant voltage (3000V) for LT In-CNT

Stability is greater for In-CNT at 0.74%

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Fig Reference: Rajkumar Patra, Santanu Ghosh, Himani Sharma and Vasant D. Vankar. “High stability field emission from zinc oxide coated multiwalled carbon nanotube films”, Advanced Materials Letter, DOI

CONCLUSIONS

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1) The addition of In layer over the CNTs decreases the field enhancement factor andhence increasing the turn-on field and the threshold field.

2) This is probably due deposition of In which reduces the aspect ratio of the CNTs3) However, a greater thickness of the In causes a lower threshold and turn-on field

and hence higher current density. The field enhancement factor is also greater.4) It was observed that the stability is greater for In-CNT at 0.74%5) The current density by Indium coated CNT’s (10 nm) meet the industry standards

Future Scope

1) To optimize the current density and temporal stability by varying the thickness of the Indium layer over the CNT sample.

2) To observe field emission imaging where electrons strike thephosphor to produce the colour display as an electronic visual display

3) Coating CNT with different metal oxide and observe its field emission characteristics

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REFERENCES

[1] Fowler, R. H.; Nordheim, L. P. Roy. Soc. Lond. A 1928[2] Huang, C. S.; Yeh, C. Y.; Chang, Y. H.; Hsieh, Y.M.; Ku, C.Y.; Lai, Q.T. Diam. Relat. Mater. 2009, 18,452.[3] deHeer, W. A.; Chatelain, A.; Ugate, D. Science 1995, 270, 1179.[4] Cheng, Y.; Zhou, O. C. R. Physique 2003, 4, 1021.[5] Lysenkov, D.; Müller, G. Int. J. Nanotechnology 2005, 2, 239.[6] Rajkumar Patra, Santanu Ghosh, Himani Sharma and Vasant D. Vankar. “High stability field emission from zinc oxide coated multiwalled carbon nanotube films”, Advanced Materials Letter, DOI 10.5185/amlett.2013.4465[7] Ijima, S. Nature 1991, 354, 56.[8] Handuja, S.; Srivastava, P.; Vankar, V. D. Nanoscale Res. Lett. 2010, 5, 1211.[9] Srivastava, S. K.; Shukla, A. K.; Vankar, V. D.; Kumar, V. Thin Solid Films 2006, 515, 1552.[10] Puretzky, A. A.; Geohegan, D. B.; Fan, X.; Pennycook, S. J. Appl. Phys. Lett. 2000, 76, 182.[11] Meyyappan, M.; Delzeit, L.; Cassell, A.; Hash, D. Plasma Sources Sci. Technol. 2003, 12, 205.[12] Zhu, Y.; Elim, H. I.; Foo, Y. L.; Yu, T.; Liu, Y.; Ji, W.; Lee, J. Y.; Shen, Z.; Wee, A. T. S.; Thong, J. T. L.; Sow, C.H. Adv. Mater. 2006, 18, 587.

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ACKNOWLEDGEMENTS

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On the outset of this report we would like to extend our sincere and heartfelt obligationstowards all the people, without whose cooperation, help, guidance and motivation thisproject could not be completed. We are indebted to Prof. Pankaj Srivastava and Dr.Santanu Ghosh (Physics Department, IIT Delhi) for showing faith in us and theirconstant guidance and support helped us to accomplish the project. We would like toexpress our sincere gratitude to Sreekanth sir (Nanostech Laboratory, PhysicsDepartment, IIT Delhi) whose guidance and invaluable discussions led to the completionof the project.

Thank You!!Questions??

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