Transport properties of nanowires - Diaspora Stiintifica · Outline Introduction Fabricating...

Functional nanostructures

Ionut Enculescu

Functional Nanostructures group

Multifunctional Materials and Structures Lab

National Institute of Materials Physics

Magurele, Romania

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

Outline

Introduction


Metallic nanowires




Nanofiber devices


Conclusions

Fibers

Tubes

Wires

Rods

One-dimensional (1D) structures: high aspect ratio

Spectacular look – lots of preparation methods: wet,

physical, chemical, top down or bottom up

1-D Nanostructures

5

Applications of 1D structures

Electronics

Optoelectronics

Sensors

Catalysis

Solar cells

Biomimetics

Outline

Introduction


Metallic nanowires




Nanofiber devices


Conclusions

Ionut Enculescu, National Institute of Materials Physics, Magurele, Romania

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

How to prepare a nanoporous membrane by swift heavy ion irradiation

NaOH + CH3OH

Synthesizing nanowires – producing the template

Polycarbonate foil (PC)

Cylindrical pores in PC

Au thin film

Cu thick film

Anode

Reference electrode

Cathode

Polycarbonate foil (PC)

E

V

A

Electrolytic solution

Synthesizing nanowires - electrodeposition

Outline

Introduction


Metallic nanowires




Nanofiber devices


Conclusions

Metallic nanowires

NiCu

12

SEM images of NiCu alloy nanowires: (a) -800 mV, (b) -900 mV, (c) -1000

mV si (d) -1050 mV.

X ray diffraction of 130 nm diameter

nanowire arrays, electrodeposited at: (a) -800

mV, (b) -900 mV,

(c) -1000 mV si (d) -1050 mV.

NiCu nanowire arrays prepared by

electrochemical template replication

13

J Nanopart Res (2013) 15:1863

Magnetic properties

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) -1000 mV and (d) -1050 mV

(c) (a)

(b) (d)

Ni=20%

Ni=54%

Ni=75%

Ni=92%

Photolithography

Camelia - Florina FLORICA

Design of a photomask with an interdigitated electrod used for 2 probe points measurements of nanostructures

Final pattern of Ti/Au interdigated electrodes on SiO2/Si wafer obtained in the cleanroom facility of NIMP

BioSun, 17-19 of July 2013

(a) (b)

(d)

(c)

(e)

(a) Nanofire plasate pe substratul de SiO2/Si, intre electrozii metalici interdigitati obtinuti prin fotolitografie; (b) Alinierea

substratului de SiO2/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.

Transport properties of NiCu alloy 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.

Electrical contacts on single NiCu nanowires

17

NiCu magnetoresistance

18

Ni=20%

Ni=75%

Ni=54%

Ni=92%

Electrodeposited nanowires’ magnetoresistance as a function of nickel content

Electrodeposited alloy nanowires


Semiconducting nanowires

ZnO electrochemical deposition was employed for fabricating nanowires.

Nitrate bath 2e- +NO3

- + H2O→NO2- + 2OH- (1)

Zn2+ + 2OH-→Zn(OH)2→ZnO↓ +H2O (2)

or global reaction: Zn(NO3)2 +2e-→ZnO↓ +NO3

- + NO2- (3)

PVP was used as an additive in order to improve pore wetting


Using templates:

Photolithography

1 mm

Optical microscope image of the AZ5214E image reversal photoresist after being developed

Metallic deposition

SEM image of the Ti/Au thin film deposited on the previously processed wafer

SEM image of the Ti/Au interdigitated contacts deposited on SiO2/Si

e–beam lithography

Graphical representation of nanowires on SiO2 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

0 2 4 6 8 10 12 14 16

0.00

1.50x10-8

3.00x10-8

4.50x10-8

6.00x10-8

7.50x10-8

Vg = 0 V

Vg = 2 V

Vg = 4 V

Vg = 6 V

Vg = 8 V

Vg = 10 V

Vg = 12 V

Vg = 14 V

Vg = 16 V

Vg = 18 V

I D [A

]

VDS

[V]

VGS

1 μm

Gate

Field effect transistor based on electrodeposited ZnO single nanowire

Uniform arrays of CdTe nanowires

Cd2+ + HTeO2+ + 3H+ + 6e ̄ → CdTe + 2H2O.

Synthesizing CdTe nanowires

0 10 20 30 40 50 60 70

0

50

100

150

200

250

300

Cu

(2

00

)

CdT

e(3

11)

Cu (111)

CdT

e(2

20)

CdT

e(1

11)

I(a

.u.)

2

XRD spectrum of CdTe wires showing zinc cubic blend structure

1.4 1.6 1.8 2.00

4

8

12

16

Eg=1.48 eV

Photon energy (1240/) [eV]

F(R

)2

Kubelka-Munk function versus the photon energy for determining the energy bandgap of the CdTe nanowires (Eg=1.48 ev)

-700 -650 -600 -550 -500 -450

44

46

48

50

52

54

56

Cd

(%

)

U (mV)

-700 -650 -600 -550 -500 -450

44

46

48

50

52

54

56

Te

(%

)

U (mV)

Contacting single CdTe nanowires Photolithography

Ion gun

(CH3)3Pt(CH3)

Pt

Deposition of Pt from an organo-metallic gas with the help of an ion beam

Contacting single CdTe nanowires Focused Ion Beam Induced Deposition (FIBID)

Ion gun

(CH3)3Pt(CH3)

Pt

SEM image of Pt stripes deposited with the help of FIB at different currents of the ion beam

Deposition of Pt from an organo-metallic gas with the help of an ion beam

Contacting single CdTe nanowires FIBID

Contacting single CdTe nanowires FIBID

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

-2.0x10-9

-1.0x10-9

0.0

1.0x10-9

2.0x10-9

non-passivated

passivated with PMMA

I (A

)

U (V)

Pt-CdTe(nw)-Pt FIBID

Electrical properties of single CdTe nanowires

0 3 6 9 12

0.0

3.0x10-9

6.0x10-9

9.0x10-9


I DS (

A)

VDS (V)

VG

0 V

6 V

12 V

18 V

0 2 4 6 8 10 12

0.0

3.0x10-9

6.0x10-9

9.0x10-9

1.2x10-8


PMMA passivation

VG

0 V

6 V

12 V

18 V

VDS (V)

I DS (

A)

Field effect transistor based on electrodeposited CdTe single nanowire

Typical one obtains polycrystalline films with crystallite morphology influenced by

substrate, bath composition and deposition temperature:

In the concentration range 10-

2 – 10-3 M Zn2+ ions we deal

with arrays of hexagonal

prisms or platelets

E. Matei, I. Enculescu,

Materials Research Bulletin

2011.

In the concentration range 10-3 – 10-4 M

Zn2+ 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.

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. 2012.

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

In the concentration range 10-3 – 10-4 M

Zn2+ 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.

When employing the appropriate electrodes one can directly electrodeposit self contacted arrays of nanowires which can be

further employed as electronic devices

43

V

Xray diffraction data for arrays of nanowires

deposited at different overvoltages (a)-800 mV,

(b) -1000 mV si (c) -1100 mV.

Templateless deposited ZnO nanowires

44

SEM images of arrays of nanowires deposited onto interdigitated electrodes at different

overvoltages (a, b) -800 mV; (c, d) -1000 mV and (e, f) -1100 mV.

45

(a) Refleiton spectra employed for determining the band gap using the Kubelka Munk representation


46

(a) (b)

(a) Reflection spectra employed for determining the band gap using the Kubelka Munk representation

Photoluminescence spectra of the arrays of nanowires deposited at different voltages and ratio between excitonic peak and defect peak heights


47

IV characteristics measured at different temperatures for samples

deposited at different overvoltages

(a) -800 mV, (b) -1000 mV si (c) -1100 mV.


-800 mV -800 mV

-1000 mV -1000 mV

-1100 mV -1100 mV

Log – log representations of the I-V curves

48

-exponential distribution of traps

𝑱𝑺𝑪𝑳𝑪𝒆 = µ𝒐𝑵𝒄𝒒𝟏−γ[𝜺γ

𝑵𝒕(γ+𝟏)]γ(

𝟐γ+𝟏

γ+𝟏)γ+𝟏 𝑼γ+𝟏

𝒅𝟐γ+𝟏

γ = 𝑻𝟎/𝑻

; 𝜶 =𝑪

𝒒𝒅𝑲𝑻

𝟏

𝑵𝒕

Space charge limited current -linear distribution of traps

𝑱𝑺𝑪𝑳𝑪𝒍 =𝟗

𝟖𝜺µ𝑶

𝒒𝒏𝑶

𝑪

𝑼

𝒅𝟐𝒆𝒙𝒑(𝜶𝑼)

IV characteristics measured at different

temperatures for samples deposited at different

overvoltages

(a) -800 mV, (b) -1000 mV si (c) -1100 mV.


49

ln(R) vs. 1000/T for nanowires grown at (a) -800 mV, (b) -

1000 mV si (c) -1100 mV; evidentiind prezenta a doua zone.


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

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.

Thermochromic devices

Schematic of the process for attaching the web electrodes to the substrates.

SEM images of metal-covered polymer fiber webs attached to substrates.

Textile

Paper

GOLD SILVER


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.


Temperature vs. time as a function of the applied voltage for metal-covered polymer fiber webs attached to substrates.

Au/Glass

Ag/Textile

Ag/Paper


Electrochromism and electroactivity

Schematic of the electrochromic device fabrication.


Transmission spectra of polymer fiber webs attached to glass substrates.


SEM images of polyaniline-covered fiber webs. Chronoamperogram for polyaniline deposition on polymer fiber webs.


ZnO electrodeposition on fiber webs

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


SEM images of ZnO-covered fiber webs.

Transmission spectra of fiber webs

before and after ZnO electrodeposition.

XRD patterns of electrodeposited ZnO.


PL emission spectra excited at 350 nm of electrodeposited ZnO.


Photocatalytic degradation curves of MB

under UV irradiation for electrodeposited ZnO

webs.

PL emission spectra excited at 350 nm of electrodeposited ZnO.

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

Ionut Enculescu Elena Matei Nicoleta Preda Monica Enculescu

Andreea Costas; Alex Evanghelidis; Camelia Florica; Mihaela Oancea; Cristina Busuioc

Thank you for your attention!

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Transport properties of nanowires - Diaspora Stiintifica · Outline Introduction Fabricating...

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