Functional nanostructures

Transcription

1 Functional nanostructures Ionut Enculescu Functional Nanostructures group Multifunctional Materials and Structures Lab National Institute of Materials Physics Magurele, Romania

2 Outline Introduction Fabricating nanowires by template methods Metallic nanowires Semiconductor nanowires Nanowire devices and transport properties Electrospinning process and nanofibers Nanofiber devices Fibers and wires hierarchical structures Conclusions

3 Outline Introduction Fabricating nanowires by template methods Metallic nanowires Semiconductor nanowires Nanowire devices and transport properties Electrospinning process and nanofibers Nanofiber devices Fibers and wires hierarchical structures Conclusions

4 One-dimensional (1D) structures: high aspect ratio Fibers Tubes Wires Rods

5 Spectacular look lots of preparation methods: wet, physical, chemical, top down or bottom up 1-D Nanostructures 5

6 Applications of 1D structures Electronics Biomimetics Optoelectronics Solar cells Sensors Catalysis

7 Outline Introduction Fabricating nanowires by template methods Metallic nanowires Semiconductor nanowires Nanowire devices and transport properties Electrospinning process and nanofibers Nanofiber devices Fibers and wires hierarchical structures Conclusions

8 Ionut Enculescu, National Institute of Materials Physics, Magurele, Romania How to prepare a nanoporous membrane by swift heavy ion irradiation Irradiation Ions: - conditions to obtain continuous etchable tracks Swift kinetic energy higher than 4MeV/nucleon Heavy Mass>Xe When passing through the material deposit energy cylindrical defect zone possibility of selective etching

9 Synthesizing nanowires producing the template NaOH + CH 3 OH

10 Synthesizing nanowires - electrodeposition Cylindrical pores in PC Polycarbonate foil (PC) Au thin film Cu thick film A V Electrolytic solution E Anode Reference electrode Polycarbonate foil (PC) Cathode

11 Outline Introduction Fabricating nanowires by template methods Metallic nanowires Semiconductor nanowires Nanowire devices and transport properties Electrospinning process and nanofibers Nanofiber devices Fibers and wires hierarchical structures Conclusions

12 Metallic nanowires NiCu 12

13 NiCu nanowire arrays prepared by electrochemical template replication SEM images of NiCu alloy nanowires: (a) -800 mv, (b) -900 mv, (c) mv si (d) mv. X ray diffraction of 130 nm diameter nanowire arrays, electrodeposited at: (a) -800 mv, (b) -900 mv, (c) mv si (d) mv. 13

14 Magnetic properties (a) (c) J Nanopart Res (2013) 15:1863 Ni=20% Ni=75% (b) (d) Ni=54% Ni=92% Hysteresis curves mmeasured at low and high temperatures (10 K and 300 K), magnetic fields up to 10 K Oe applied paralel and perpendicular to the nanowires grown at: (a) -800 mv, (b) -900 mv, (c) mv and (d) mv

15 Photolithography Design of a photomask with an interdigitated electrod used for 2 probe points measurements of nanostructures Final pattern of Ti/Au interdigated electrodes on SiO 2 /Si wafer obtained in the cleanroom facility of NIMP BioSun, of July 2013 Camelia - Florina FLORICA

16 Transport properties of NiCu alloy nanowires (a) (b) (c) (d) (e) (a) Nanofire plasate pe substratul de SiO 2 /Si, intre electrozii metalici interdigitati obtinuti prin fotolitografie; (b) Alinierea substratului de SiO 2 /Si cu suportul de probe al microscopului; (c) Proba acoperita cu un film subtire de polimer de sacrificiu (PMMA) depus prin centrifugare; (d) Iradierea stratului de PMMA in vederea conectarii capetelor nanofirului cu electrozii interdigitati; (e) Imagini SEM ale unui nanofir de NiCu contactat prin EBL.

17 Electrical contacts on single NiCu nanowires (a),(c) si (d) Imagini SEM (la mariri diferite) ale unui nanofir din aliaj de NiCu contactat prin EBL si (b) Analiza EDX a distributiei elementelor in proba. 17

18 NiCu magnetoresistance Ni=20% Ni=54% Ni=75% Ni=92% 18

19 Electrodeposited alloy nanowires Electrodeposited nanowires magnetoresistance as a function of nickel content

20 Ionut Enculescu, National Institute of Materials Physics, Magurele, Romania Semiconducting nanowires ZnO electrochemical deposition was employed for fabricating nanowires. Nitrate bath 2e - +NO H 2 O NO OH - (1) Zn OH - Zn(OH) 2 ZnO +H 2 O (2) or global reaction: Zn(NO 3 ) 2 +2e - ZnO +NO NO 2 - (3) PVP was used as an additive in order to improve pore wetting

21 Using templates: Ionut Enculescu, National Institute of Materials Physics, Magurele, Romania

22 Photolithography 1 mm SEM image of the Ti/Au thin film deposited on the previously processed wafer Optical microscope image of the AZ5214E image reversal photoresist after being developed Metallic deposition SEM image of the Ti/Au interdigitated contacts deposited on SiO 2 /Si

23 e beam lithography Graphical representation of nanowires on SiO 2 between micrometric contacts Aligning the writing field with the sample area Scanning the desired pattern for making the contact between the nanowire and the micrometric electrodes EDX mapping of the Pt contacts on a ZnO nanowire

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25 I D [A] Field effect transistor based on electrodeposited ZnO single nanowire 7.50x10-8 Vg = 0 V Vg = 2 V Vg = 4 V 6.00x10-8 Vg = 6 V Vg = 8 V Vg = 10 V Vg = 12 V 4.50x10-8 Vg = 14 V Vg = 16 V Vg = 18 V 3.00x x10-8 V GS μm V DS [V] Gate

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29 Uniform arrays of CdTe nanowires Cd 2+ + HTeO H + + 6e CdTe + 2H 2 O.

30 Cd (%) Te (%) F(R) 2 CdTe(311) I(a.u.) CdTe(220) CdTe(111) Cu (200) Synthesizing CdTe nanowires 16 E g =1.48 ev 300 Cu (111) Photon energy (1240/) [ev] Kubelka-Munk function versus the photon energy for determining the energy bandgap of the CdTe nanowires (E g =1.48 ev) XRD spectrum of CdTe wires showing zinc cubic blend structure U (mv) U (mv)

31 Contacting single CdTe nanowires Photolithography

32 Contacting single CdTe nanowires Focused Ion Beam Induced Deposition (FIBID) Ion gun (CH 3 ) 3 Pt(CH 3 ) Pt Deposition of Pt from an organo-metallic gas with the help of an ion beam

33 Contacting single CdTe nanowires FIBID Ion gun (CH 3 ) 3 Pt(CH 3 ) Pt Deposition of Pt from an organo-metallic gas with the help of an ion beam SEM image of Pt stripes deposited with the help of FIB at different currents of the ion beam

34 Contacting single CdTe nanowires FIBID

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36 I (A) Electrical properties of single CdTe nanowires 2.0x x10-9 Pt-CdTe(nw)-Pt FIBID x x10-9 non-passivated passivated with PMMA U (V)

37 I DS (A) I DS (A) Field effect transistor based on electrodeposited CdTe single nanowire 9.0x x x10-9 V G 0 V 6 V 12 V 18 V 1.2x x x10-9 V G 0 V 6 V 12 V 18 V 3.0x Pt-CdTe(nw)-Pt FIBID 0.0 Pt-CdTe(nw)-Pt FIBID PMMA passivation V DS (V) V DS (V)

38 Typical one obtains polycrystalline films with crystallite morphology influenced by substrate, bath composition and deposition temperature: In the concentration range M Zn 2+ ions we deal with arrays of hexagonal prisms or platelets E. Matei, I. Enculescu, Materials Research Bulletin 2011.

39 In the concentration range M Zn 2+ ions we deal with arrays of hexagonal nanowires e.g. arrays of nanowires obtained by electrodeposition after sputtering a ZnO seed layer I. Enculescu et al in press.

40 Deposition conditions can be made more complex e.g. pulsed deposition to form structures such as tubes or cones Deposition using inverse ramp potential leads to hollow hexagonal prisms: a deposition etching process Matei et al. Mat. Chem Phys

41 Structure is also influenced by the deposition conditions (including deposition rate, concentration of deposition bath and so on). Evolution of structure as a function of deposition parameters for ramp potential deposition: Matei et al. Mat. Chem Phys. 2012

42 In the concentration range M Zn 2+ ions we deal with arrays of hexagonal nanowires e.g. arrays of nanowires obtained by electrodeposition after sputtering a ZnO seed layer I. Enculescu et al in press.

43 V When employing the appropriate electrodes one can directly electrodeposit self contacted arrays of nanowires which can be further employed as electronic devices 43

44 Templateless deposited ZnO nanowires Xray diffraction data for arrays of nanowires deposited at different overvoltages (a)-800 mv, (b) mv si (c) mv. M images of arrays of nanowires deposited onto interdigitated electrodes at different overvoltages (a, b) -800 mv; (c, d) mv and (e, f) mv. 44

45 Templateless deposited ZnO nanowires (a) Refleiton spectra employed for determining the band gap using the Kubelka Munk representation 45

46 Templateless deposited ZnO nanowires (a) Reflection spectra employed for determining the band gap using the Kubelka Munk representation (a) (b) Photoluminescence spectra of the arrays of nanowires deposited at different voltages and ratio between excitonic peak and defect peak heights 46

47 Templateless deposited ZnO nanowires IV characteristics measured at different temperatures for samples deposited at different overvoltages (a) -800 mv, (b) mv si (c) mv. 47

48 Templateless deposited ZnO nanowires -800 mv -800 mv Space charge limited current -linear distribution of traps J SCLCl = 9 8 εµ qn O U O exp(αu) C d2 ; α = C 1 qdkt N t -exponential distribution of traps J SCLCe = µ o N c q 1 γ [ γ = T 0 /T εγ N t (γ+1) ]γ ( 2γ+1 Uγ+1 )γ+1 γ+1 d 2γ mv mv mv mv IV characteristics measured at different temperatures for samples deposited at different overvoltages (a) -800 mv, (b) mv si (c) mv. Log log representations of the I-V curves 48

49 Templateless deposited ZnO nanowires ln(r) vs. 1000/T for nanowires grown at (a) -800 mv, (b) mv si (c) mv; evidentiind prezenta a doua zone. 49

50 Electrospinning process Electrospinning is simple and inexpensive method used for the synthesis of metallic, polymer and ceramic fibers. Fiber diameter ranges from tens of nanometers to several micrometers. Stationary collector nonwoven meshes Rotating collector well-aligned arrays

51 Electrospinning process Solution parameters: polymer type and molecular weight; solvent type; solution surface tension, viscosity and conductivity. Process parameters: spinneret diameter; solution feed rate; applied voltage; distance between spinneret and collector; collector type. Ambient parameters: temperature; humidity; pressure; atmosphere type.

52 Thermochromic devices Schematic of the process for attaching the web electrodes to the substrates. GOLD SILVER Textile Paper SEM images of metal-covered polymer fiber webs attached to substrates.

53 Thermochromic devices Transmission spectra of polymer fiber webs attached to glass substrates and the correlation between transmission and resistance (inset figure). SEM images of metal-covered polymer fiber webs attached to substrates.

54 Thermochromic devices Au/Glass Ag/Textile Ag/Paper Temperature vs. time as a function of the applied voltage for metal-covered polymer fiber webs attached to substrates.

55 Thermochromic devices

56 Electrochromism and electroactivity Schematic of the electrochromic device fabrication.

57 Electrochromism and electroactivity Transmission spectra of polymer fiber webs attached to glass substrates.

58 Electrochromism and electroactivity Chronoamperogram for polyaniline deposition on polymer fiber webs. SEM images of polyaniline-covered fiber webs.

59 Electrochromism and electroactivity

60 ZnO electrodeposition on fiber webs The steps in preparing the substrates for ZnO electrodeposition. Current vs. time curves for all deposition experiments.

61 ZnO electrodeposition on fiber webs Transmission spectra of fiber webs before and after ZnO electrodeposition. SEM images of ZnO-covered fiber webs. XRD patterns of electrodeposited ZnO.

62 ZnO electrodeposition on fiber webs PL emission spectra excited at 350 nm of electrodeposited ZnO.

63 ZnO electrodeposition on fiber webs PL emission spectra excited at 350 nm of electrodeposited ZnO. Photocatalytic degradation curves of MB under UV irradiation for electrodeposited ZnO webs.

64 Conclusions -1 D structures are interesting for a wide range of applications; -combination of techniques necessary for fabricating such nanostructures -integrating them into devices lithographical techniques at multiscale -there are possibilities to fabricate cheap large scale nanostructures -use of green materials possible -open up possibilities for new generation of devices

65 Ionut Enculescu Elena Matei Nicoleta Preda Monica Enculescu Andreea Costas; Alex Evanghelidis; Camelia Florica; Mihaela Oancea; Cristina Busuioc

66 Thank you for your attention!