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Fabrication and characterization of nanowire devices


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We fabricated Nanowires of Copper (Cu), CuO, Cu-Se etc. and studied I-V Characteristics

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Fabrication and characterization of nanowire devices

  1. 1. Fabrication and Characterization of Nanowire Devices Hardev Singh Virk Professor Emeritus, Eternal University, Baru Sahib (HP), India
  2. 2. Birth of Nanotechnology “There's Plenty of Room at the Bottom” • On December 29, 1959, Richard P. Feynman gave the seminal talk at a meeting at Caltech of the American Physical Society. He presented a vision of the precise manipulation of atoms and molecules so as to achieve amazing advances in information technology, mechanical devices, medical devices, and other areas.
  3. 3. Changing Idea into Reality Eric Drexler of MIT, the Chemist, established the modern field of nanotechnology, with a draft of his seminal Ph.D. thesis in the mid 1980s. His 1991 doctoral thesis at MIT was revised and published as the book "Nanosystems, Molecular Machinery Manufacturing and Computation" (1992), which received the Association of American Publishers award for Best Computer Science Book of 1992.
  4. 4. The Incredible Tininess of Nano Billions of nanometers A two meter tall male is two billion nanometers. The pinhead sized dot is a million nm Biological cells size is Thousands of nm DNA Molecules are about 2.5 nm in width Hydrogen atom spans 0.1 nm 2 Uranium atoms span 1 nm
  5. 5. • AFM Imaging of ATOMS of GOLD (Au 111)
  6. 6. Atomic Lattice Structure of HOPG in 3D Topography using Atomic Force Microscope
  7. 7. Introduction to Nanowires Nanowires of metallic and semi-conducting materials have drawn a lot of research interest because of their potential applications in fields like nanoelectronics, opto-electronics and sensors. Nanowires exhibit unique electrical, magnetic, optical, thermoelectric and chemical properties compared to their bulk counterpart. Electronic conduction takes place both by bulk conduction and through tunneling mechanism.
  8. 8. Special Characteristics • Nanowires exhibit high density of electronic state. • They have diameter-dependant band gap. • They show enhanced surface scattering of electrons and phonons. • They have increased excitation energy, high surface to volume ratio and large aspect ratio.
  9. 9. Fundamental Features • One-dimensionality • – Wire diameter: several nm ~ hundreds of nm’s • – Aspect ratio: L:D >10:1 • Material integrity • – Single crystalline nanostructure • Availability of numerous materials • – Superconductor, metal, semiconductor, insulator • Unique physical properties • – Large surface-to-volume ratio • – High transport/carrier mobility • – Quantum confinement/tunable band structure
  10. 10. Quantum Confinement Effects – Quantum dots (0-D): confined states, and no freely moving ones – Nanowires (1-D): particles travel only along the wire direction – Quantum wells (2-D): confines particles within a thin layer There is no confinement effect in Bulk materials. Refer to energy distribution.
  11. 11. Chemical Routes of Synthesis • Solution-Based Synthesis • – Solution-Liquid-Solid (SLS) Method • – Solvothermal Chemical Synthesis • – Template-Based Synthesis • Gas-Phase Synthesis • – Vapor-Liquid-Solid (VLS) Method • -- Laser abrasion • -- PVD • -- CVD (LPCVD, MOCVD) • – Vapor-Solid (VS) Method • – Oxide-Assisted Growth (OAG)
  12. 12. Growth of Semiconductor Nanowires by VLS method Laser ablation overcomes thermodynamic equilibrium constraints and enables liquid nanocluster formation.
  13. 13. GaN Nanowires Grown by VLS method SEM image of GaN nanowires of diameters 10nm and lengths on the order of 10m (Huang et al., 2002).
  14. 14. ZnO Nanowires on Sapphire by VLS method SEM images of ZnO nanowire arrays grown on a sapphire substrate, (a) shows patterned growth, (b) shows a higher resolution image of the parallel alignment of the nanowires, and (c) shows the hexagonal cross- section of the nanowires (Huang et al., 2001).
  15. 15. Nano-Lasers using ZnO Nanowires ZnO nanowires grown by VLS method.Emission spectrum from ZnO nanowires.
  16. 16. Nanowire Fabrication  Template synthesis using polymer and anodic alumina membranes  Electrochemical deposition Ensures fabrication of electrically continuous wires since only takes place on conductive surfaces Applicable to a wide range of materials  High pressure injection Limited to elements and heterogeneously-melting compounds with low melting points Does not ensure continuous wires Does not work well for diameters < 30-40 nm  Chemical Vapor Deposition (CVD) or VLS technique  Laser assisted techniques
  17. 17. Polymer Template Synthesis of Nanowires
  18. 18. Large Etched Ion TracksLarge Etched Ion Tracks
  19. 19.  Anodization of aluminum  Start with uniform layer of ~1µm Al  Al serves as the anode, Pt may serve as the cathode, and 0.3M oxalic acid is the electrolytic solution  Low temperature process (2-50 C)  40V is applied  Anodization time is a function of sample size and distance between anode and cathode  Key Attributes of the process (per M. Sander)  Pore ordering increases with template thickness – pores are more ordered on bottom of template  Process always results in nearly uniform diameter pore, but not always ordered pore arrangement  Aspect ratios are reduced when process is performed when in contact with substrate Anodic Alumina Template Preparation
  20. 20. Electrochemical mechanism • The overall reaction that takes place during anodization is: 2Al + 3H2 O => Al2 O3 + 3H2 At the anode: 2Al + 3O2- => Al2 O3 + 6e- At the cathode: 6H+ + 6e- ==> 3H2 • The Al is oxidized at the metal/oxide interface • The oxide is etched away by the acid with the applied potential • The pores are induced by the roughness of the top surface TEM micrographs
  21. 21. (T. Sands/ HEMI group Anodic alumina (Al2O3) Template 100nmSi substrate alumina template (M. Sander)
  22. 22. Electrolytic CellElectrolytic Cell
  23. 23. Replica of Nanowires
  24. 24. Microtubule Fabrication
  25. 25. Electrochemical Synthesis • Electrochemistry has been used to fabricate nanowires of Cu and heterojunctions of Cu-Se and Cd-S. The results of our investigations can be exploited for fabrication of nanodevices for application in opto-electronics and nano- electronics. During failure of our Experiments, exotic patterns ( nanoflowers, nanocrystals, nanobuds) were produced under nature’s self assembly.
  26. 26. Template Synthesis of CopperTemplate Synthesis of Copper NanowiresNanowires The electro-deposition of metals is identical toThe electro-deposition of metals is identical to an electroplating process. Polymer ITFs and anodicand anodic alumina can be used as a template. The electrolytealumina can be used as a template. The electrolyte used here is CuSO4.5H2O acidic solution. The rate ofused here is CuSO4.5H2O acidic solution. The rate of deposition of metallic film depends upon: currentdeposition of metallic film depends upon: current density, inter-electrode distance, cell voltage,density, inter-electrode distance, cell voltage, electrolyte concentration, pH value and temperatureelectrolyte concentration, pH value and temperature etc. In our case, electrode distance was kept 0.5 cmetc. In our case, electrode distance was kept 0.5 cm and a current of 2mA was applied for 1 hour. Theand a current of 2mA was applied for 1 hour. The developed nanostructures were scanned under SEMdeveloped nanostructures were scanned under SEM for morphological and structural studies.for morphological and structural studies.
  27. 27. Atomic Force Microscope(NT-MDT)
  28. 28. AFM image of hexagonal pores ofAFM image of hexagonal pores of Anodic Alumina Membrane (AAM)Anodic Alumina Membrane (AAM)
  29. 29. SEM Images of Cu Nanowires usingSEM Images of Cu Nanowires using Electrodeposition TechniqueElectrodeposition Technique
  30. 30. Copper Nanowire Bundles in AAMCopper Nanowire Bundles in AAM
  31. 31. Cu Nanowires under Constant CurrentCu Nanowires under Constant Current
  32. 32. Capping Effect of Current VariationCapping Effect of Current Variation
  33. 33. I-V Characteristics of CopperI-V Characteristics of Copper Nanowires grown in-situ in AAMNanowires grown in-situ in AAM
  34. 34. Copper Lillies grown due to over-Copper Lillies grown due to over- deposition of Copper in AAMdeposition of Copper in AAM
  35. 35. A Garden of Copper NanoflowersA Garden of Copper NanoflowersA Garden of Copper NanoflowersA Garden of Copper Nanoflowers
  36. 36. Copper Nanoflowers grown in Polymer Template (100nm pores)
  37. 37. Copper Marigold Flower
  38. 38. SiC Crystalline Nanowire Flowers G. W. Ho (Nanotechnology, 2004)
  39. 39. Crystalline Nano-comb of ZnO NW H. Yan (JACS 2003)
  40. 40. SEM micrograph of Copper Buds
  41. 41. SEM micrograph of Nanocrystals ofSEM micrograph of Nanocrystals of Polycrystalline CopperPolycrystalline Copper
  42. 42. XRD Spectrum of polycrystallineXRD Spectrum of polycrystalline Copper nanocrystalsCopper nanocrystals Position [°2Theta] (Copper (Cu)) 10 20 30 40 50 60 70 Counts 0 20000 40000 60000 36.637[°] 38.283[°] 43.461[°] 45.448[°] 48.920[°] 50.580[°] 54.304[°] 54.956[°] 64.809[°] 74.299[°] KK1
  43. 43. XRD spectrum of Cu nanowiresXRD spectrum of Cu nanowires Position [°2Theta] (Copper (Cu)) 30 40 50 60 70 80 90 Counts 0 400 1600 Cu polycrystalline
  44. 44. SEM Image of CdS NanowiresSEM Image of CdS Nanowires
  45. 45. HRTEM image showing CdS NanowireHRTEM image showing CdS Nanowire & Heterojunctions& Heterojunctions
  46. 46. I-V plot of CdS Nanowire arraysI-V plot of CdS Nanowire arrays showing RTD characteristicsshowing RTD characteristics
  47. 47. SEM image of Cu-Se NanowiresSEM image of Cu-Se Nanowires
  48. 48. Cu-Se nanowires exhibit p-n junctionCu-Se nanowires exhibit p-n junction diode characteristicsdiode characteristics
  49. 49. A Billion Dollar Question … • What can nanowires offer for semiconductor nanoelectronics? • Nonlithographic & extremely cost-effective • Reduced phonon scattering: High carrier mobility but reduced thermal conductance(?) • Tunable electrical/optical properties • Large surface-to-volume ratio: Sensor sensitivity & memory programming efficiency
  50. 50. Advantages of 1-D Nanowires • High-quality single-crystal wires with nearly perfect surface • Scalable nanostructure with precisely controlled critical dimensions • Best cross-section for surround-gate CMOS • Very cost-effective materials synthesis • High transport low-dimensionality structure • May use as both device and interconnect for ultra-compact logic (e.g., SRAM)
  51. 51. Nanowire Field-Effect Transistor • Ambipolar transport • Carrier mobility study • Quantum effect A single device for numerous applications Device physics study
  52. 52. Quantum-Wire Device M. Bjork (Nano Letters, Sept. 2004) 1. In-situ control of nanowire synthesis allows design of strongly confined quantum mechanical systems inside nanowires, possibly useful for SET . 2. Next-generation nanoelectronic devices with extremely-low power, high performance, and radiation tolerance.
  53. 53. 3-D Nanowire Logic Chip H. Ng (Nano Letters, July 2004)
  54. 54. Si NW Thermal Conductance D. Li (APL Oct. 2003)
  55. 55. Thermoelectric (TE) Conversion E.J. Menke (Nano Letters, Oct. 2004) Bismuth Telluride (Bi2Te3) nanowires
  56. 56. Role of Nanowires for Next- Generation Electronics • The chemical and physical characteristics of nanowires, including composition, size, electronic and optical properties, can be rationally controlled during synthesis in a predictable manner, thus making these materials attractive building blocks for assembling electronic and optoelectronics nanosystems.
  57. 57. Some Observations & Remarks • Nanotechnology will be the driving force for next technology revolution. • Nanowires open door to a wonderland where the next generation electronics would emerge. • Scope for innovating new synthesis method and complex functional nanostructures. • New device and interconnect concepts will emerge from horizon, driven by materials synthesis.
  58. 58. Our Publications • My website: http:// for list of our published research papers. Go to for purchase of reprints. Free download of Review Paper on Nanowires: visit: ttp:// • Chapter 20 of Book “Nanowires - Implementations and Applications”, InTech Open, Abbass Hashim (Ed).
  59. 59. AcknowledgementsAcknowledgements • Reimer Spohr & Christina Trautman (GSI, Darmstadt)Reimer Spohr & Christina Trautman (GSI, Darmstadt) • Sanjit Amrita Kaur (GND University, Amritsar)Sanjit Amrita Kaur (GND University, Amritsar) • Vishal, Gurmit, Sehdev & KK (DAVIET, Jalandhar)Vishal, Gurmit, Sehdev & KK (DAVIET, Jalandhar) • Dr SK Mehta, Chemistry Deptt. (PU, Chandigarh)Dr SK Mehta, Chemistry Deptt. (PU, Chandigarh) • CSIO Chandigarh & IIT Roorkee for FESEM & TEM facility.CSIO Chandigarh & IIT Roorkee for FESEM & TEM facility. • SEM & TEM facility (SAIF, PU, Chandigarh)SEM & TEM facility (SAIF, PU, Chandigarh) • Rajeev Patnaik (Geology Deptt., PU, Chandigarh)Rajeev Patnaik (Geology Deptt., PU, Chandigarh) • DAV MC, New Delhi for Research Grants.DAV MC, New Delhi for Research Grants. • Dr. MS Atwal, VC, Eternal University, Baru Sahib.Dr. MS Atwal, VC, Eternal University, Baru Sahib.
  60. 60. Thank You !!!