The document discusses electrospinning techniques for fabricating semiconductor nanofibers. It begins with an introduction to semiconductors and electrospinning. It then explains how electrospinning parameters like solution concentration and applied voltage affect fiber morphology. Different electrospinning setups and collection methods are also reviewed. Examples are given of using electrospinning to produce gallium nitride and zinc oxide nanofibers for applications in transistors, photodetectors, and other devices. In conclusion, electrospinning provides a simple way to fabricate high quality semiconductor nanofibers for various applications.

1. By: Becker G. Budwan
Materials Science and Technology Program, College of Arts and
Sciences
Qatar University
Special topics, MATS 590
Supervised by: Dr. Talal Al Tahtamouni

2. • Introduction.
• Electrospinning Technique.
• Electrospinning parameters.
• Types of electrospinning.
• Effects of different types.
• Experimental.
• Results and discussion.
• Applications.
• Conclusions.
• References.
2

3. • Semiconductor (s/c) is a
materials conducts electricity
more than an insulators but
less than a pure conductors.
• Semiconductors are usually
very small and complex
devices, and can be found in
thousands of products such
as computers, cell phones
and medical equipment.
3

4. • Yu et al. 2010 synthesized
metal catalyst seed-free 1D
nanowires by using the vapor-
phase transport deposition
technique.
• Ho et al. 2010 developed
multi-junction 1D nanowire
arrays using a chemical
process.
• Bulovic et al. 2013 developed
1D nanowire arrays using Sol-
Gel.
• Presently, the electrospinning
preparation of 1D nanofibers. 4

5. • Electrospinning definition, is a simple and highly versatile
technique for generating fibers with diameters ranging from
a few micrometers to tens of nanometers.
• Many parameters affecting of the fibers fabrication and the
properties as polymer solution viscosity, flow rate of polymer
solution, voltage amount, the distance between the nozzle
and collector.
• This in turn appears some
of the changes in the
mechanical and thermal
properties, porosity, voids,
sorption capacity and
separation efficiency.
5

6. • ELECTROBLOWING.
• Combination of forces of
electric field applied and the
air flow.
• increases the efficiency of
the electrospinning process.
• Air flow accelerates the
evaporation of solvent from
the solution.
• Speed and temperature of air
flow affects the morphology
of the nanofibers.
• ELECTROSPRAYING.
deposition of materials in the
form of small beads with a
diameter of tens of
nanometres (nanoparticles) to
several micrometres
(microparticles).
6

7. Electrospinning system
consists of three major
components:
1. High voltage power
supply.
2. Spinneret (e.g., a
pipette tip).
3. Collector.
7
(1)
(2)
(3)

8. • Solution parameters:
1. Concentration: the concentrations of polymer solution play an
important role in the fiber formation during the electrospinning
process.
• If the concentration is very low, mean low viscosity and beads
form.
• If the concentration is little higher, a mixture of beads and fibers
will be obtained.
8
• When the
concentration is
suitable, smooth
nanofibers can be
obtained.
• If the concentration is
very high, helix-
shaped micro-ribbons
will be observed.
SEM images of the evolution of the products with different
concentrations from low to high during the electrospinning

9. 2. Molecular weight: Molecular weight of the polymer also has an
important effect on morphologies of electrospun fiber.
• lowering the molecular weight of the polymer tends to form
beads rather than smooth fiber.
• Increasing the molecular weight, smooth fiber will be obtained.
• Further increasing the molecular weight, micro-ribbon will be
obtained.
9
showing the typical structure in the electrospun polymer for various molecular
weights. (a) 9000-10,000 g/mol, (b) 13,000-23,000 g/mol, and (c) 31,000-50,000
g/mol (solution concentration: 25 wt. %).

10. • Process parameters:
1. Applied Voltage:
• The strength of the applied electric field controls formation of
fibers.
• At lower applied voltages the Taylor cone is formed at the tip of
the pendent drop. however, as the applied voltage is increased
the volume of the drop decreases until the Taylor cone was
formed at the tip of the capillary.
10
Effect of varying the
applied voltage on the
formation of the Taylor
cone.

11. 2. Flow rate:
• The flow rate of the polymer solution within the syringe is another
important process parameter.
• lower flow rate is more recommended as the polymer solution will get
enough time for polarization.
• If the flow rate is very high, bead fibers with thick diameter will form rather
than the smooth fiber with thin diameter and short drying time.
11
SEM images of the effect of the flow rate on the morphologies of the polysulfone
PSF fibers from 20% PSF/DMAC solution at 10 kV. Flow rates of (a) and (b) are
0.40 and 0.66 ml/h, respectively.

12. 3. Collector distance:
• The distance (H) between the collector and the tip can also
affect the fiber diameter and morphologies.
• If the distance is too short, the fiber will not have enough time
to solidify before reaching the collector, whereas if the distance
is too long, bead fiber can be obtained.
12
SEM images of the electrospun PSF fibers from 20 wt. % PSF/DMAC solution at 10 kV with
different distances. The distances of (a) and (b) are 10 and 15 cm, respectively. The
diameters of (a) and (b) are 438 ± 72 and 368 ± 59 nm, respectively.

13. • Spinneret (tip):
• Single tip
• Double tip
• Multi tip
• Core-shell tip
13

14. • Collecting:
1. Plate type: very simple and delivers nanofiber layers with a
random internal structure.
2. Rotating type: At slow speeds, the fibers are randomly
deposited on the drum surface, but at higher speeds, fibers
are deposited on the drum surface in the preferred direction.
14

15. • Types of electrospinning set-up:
a) Vertical set-up.
• Shaft type.
• Converse type.
b) Horizontal set-up.
15

16. Effects of different types in
electrospinning process:
1. The directions of gravity and
electric field forced on fibers.
2. The average fiber diameter.
• Thinner fibers.
• Thicker fibers.
3. The fiber distribution.
• widest size distribution.
• narrowest size
distribution.
16
(a) and (c) SEM image, (b) and (d)
Statistical chart of diameter size
distribution.

17. 17

18. • Hui Wu et al. 2009
18
Ga(NO3)3
Alcohol and
Deionized
water (1:1)
Polyvinylpyrrolido
ne PVP
under
stirrin
g
Electrospinnin
g
Calcinati
on 500 oC
Ga2O3
nanofibe
r
under
850 oC
Ammonia
NH3
GaN
nanofibe
r
in tube
furnace

19. • Mali et al. 2013
19
Zn(NO3)2 Deionized
water
Polyvinylpyrrolido
ne PVP
under
stirrin
g
Electrospinnin
g
Calcinati
on 500 oC
ZnO
nanofibe
r

20. • Hui Wu et al. 2009
20
SEM image of (a) electrospun PVP/Ga(NO3)3 precursor
nanofibers, (b) Ga2O3 nanofibers synthesized by
calcinations of sample (a) at 500 oC for 4 hours, (c)
GaN nanofibers.
a b
PL spectrum at room
temperature of GaN
nanofibers. The
excitation wavelength
is 325nm from a He-
Cd laser.
c

21. • Mali et al. 2013
21
(a) FESEM
images of as
synthesized
PVP-ZnO
nanofibers
and (b) after
annealing at
520 °C.
a
b
XRD patterns of (a) as-synthesized PVP-ZnO
nanofibers and (b) after annealing at 520 °C.

22. 22
Transistors
Photodetectors
Photocatalysis
Gas sensors

23. • Electrospinning is simple technique for
fabricating nanofibers.
• Changing in electrospinning parameters
affect in fiber diameter and morphologies.
• High quality semiconductor nanofibers
synthesized by electrospinning technique.
23

24. • http://www.investopedia.com/terms/s/semiconductor.asp
• Yu D., Trad T., McLeskey J. T. Jr., Craciun V., Taylor C. R.,
Nanoscale Res. Lett. 2010, 5, 1333-1339.
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• http://uotechnology.edu.iq/dep-
materials/lecture/thirdclass/polymerfiberstechnology3.pdf
• M Kevin, Y H Fou, A S W Wong, G W Ho, Nanotechnology 2010, 21,
315602-315610.
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Liming Wang, Annual Report Conference on Electrical Insulation and
Dielectric Phenomena, 2009.
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Pan, Adv. Mater. 2009, 21, 227-231.
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