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Journal of Wuhan University of Technology-Mater. Sci. Ed. www.jwutms.net Oct.2017
989
DOI 10.1007/s11595-017-1700-0
Electrical and Optical Properties of Nano Aluminum
Film/Particle Structure
MENG Qingyun1, LI Siqi1, KANG Yixin1, ZHAI Xiaoyu1, WEI Sitao1, HE Huimei1,
WANG Yun1*, YIN Ziwen2*
(1. Faculty of Science, Beijing University of Chemical Technology, Beijing 100029, China; 2. China Electronics Technology Group
Corporation No. 45 Research Institute, CETC Beijing Electronic Equipment Co., Ltd., Beijing 101100, China)
Abstract: The electrical and optical effects of particles on the nano aluminum film deposited by thermal
evaporation was investigated. From the characterization results of scanning electron microscope (SEM), the
accumulation in tens of nanometers had been observed. The current-voltage (I-V) curve of the sample indicates
its nonlinear electrical characters expecting the corresponding nonlinear optical properties. By the theoretical
calculation, nonlinear conduction of the carrier transportation may result from the barrier-well-barrier structure,
where negative resistance and Coulomb blockade effect appears. The simulation results are approximately
matched with the experimental results. By testing the fluorescence emission spectrum of the sample, peaks
were found to be located at 420 and 440 nm. In addition, the full width at half maximum (FWHM) had been
obviously broadened by means of adding 2, 5-diphenyloxazole (DPO). Therefore, discrete energy levels could
be estimated inside those particles.
Key words: nonlinear conduction properties; fluorescence emission; aluminum nano particle
1 Introduction
With the highest content among metal elements
on the earth, aluminum (Al) has received much
attention due to the low density and excellent electro
conductibility. The unique properties of nano materials
broaden the application fields, such as nano aluminum
used in high explosive and solid rocket propellant[1,2].
Aluminum has a relatively strong activity in the
periodic table of elements. When it is prepared as
nano materials, its activity is significantly enhanced.
Due to the above phenomenon, we conclude that the
nano aluminum will have better physical properties.
Currently, researches on nanometer Al are mainly
focused on the preparation of nano Al particles,
macroscopic properties, microscopic structure and
application. Vladimir An?s team prepared nano
Al particles through electric blasting method and
demonstrated the existence of structure defect with
¦uhan University of Technology and Springer Verlag Berlin Heidelberg 2017
(Received: Oct. 20, 2016; Accepted: May 4, 2017)
MENG Qing-yun: (???): Prof.; Ph.D.; E-mail: mqybuct@
163.com
* C o r r e s p o n d i n g a u t h o r : WA N G Yu n ( ? ? ) : E - m a i l :
2415718321@qq.com; YIN Ziwen(???): E-mail: Yinziwen1989
@163.com
Supported by the 973 Program (No. 2014CB932103), the 863
Program (No. 2013AA032501), and the National Natural Science
Foundation of China (NSFC No.21676015)
X-ray[3], and lattice distortion was found in particles
caused by structure defect. Yuhua Zhou[4] measured
the microstrain of particles by different preparation
methods with X-ray refinement method. Yuma
Ohkura?s team had studied the oxidation mechanism
of Al nano particles with instantly-lighted method[5].
Compared to bulk structure, the electrical and optical
properties of nano Al films are more excellent, which
attracts more attention for investigation, such as
studying the impact from Al on the crystallization and
electrical properties of ZnO by changing its doping
concentration in ZnO film[6], observing the variation
of the luminous reflectance through ion injection
with different materials into Al film [7] and studying
the surface smoothness of Al film prepared by DC
sputtering on different substrates[8], and the physical
properties of composite films which are composed of
Al and other materials[9]. Because of its larger surface
area, and higher surface energy, nano aluminum
and other materials can easily interact. Previously,
more concerns had been shown on the single atom
of aluminum element or the interaction between bulk
aluminum and other materials. Until now, the interaction
of nano aluminum and DPO molecules has not been
reported. DPO is a widely-used photoluminescence
fluorescent substance, but with a peak close to violet
and ultraviolet wave band. If the red-shift of the peak
wavelength was achieved with the assistance of nano
990
Vol.32 No.5 MENG Qingyun et al: Electrical and Optical Properties of Nano Aluminum...
aluminum, we must consider the issue that aluminum
would have interacted with DPO. How then to over-ride
the chemical synthesis barriers? We use low-vacuum
thermal evaporation deposition to prepare the thin
films. These films, which will implement the regulation,
have a nano aluminum and DPO alternating sandwich
structure. The interaction between Al nano film and
DPO nano film leads to the shift of fluorescence
peak[10], which broadens the wavelength range of DPO.
In this paper, Al nano films were prepared with thermal
evaporation deposition for analyzing the conductive
properties, and Al/DPO nano films were fabricated for
characterizing the change in fluorescence spectrum.
Both were used to investigate the structure of Al nano
film and explored the mechanism which was impacted
by the internal structure of Al nano particles and barrier
between Al nano particles. Simple simulation was used
to analysis the structure with barrier through model.
2 Experimental
2.1 Reagents and materials
Al (purity ? 99.99%) and DPO (purity: 99.0%)
were purchased from J&K. Microscope slides (25.4
mm�.2 mm�mm) were obtained with the brand
name of ?SAILBOAT?. Acetone solvent (mass
fraction > 99.5%) and anhydrous ethanol solution
(mass fraction: 99.7%) were purchased from Beijing
Chemical Works. All the solvents were used without
further purification.
2.2 Instrument
The Al/DPO nano films were prepared with
a DH2010 multi-functional vacuum experimental
instrument (Hangzhou Dahua Instrument Co., Ltd).
The surface morphology was recorded on a Hitachi
S-4700 SEM. Al and DPO were weighed with a DT100 analytical balance with single plate (Beijing
Optical Instrument Factory). Electric measurement
was performed on a TR-KDY-type 1 four-point probe
resistivity meter (Beijing Tong De Technology Co.,
Ltd). I-V curve was measured on an HP4145 type
semiconductor parameter analyzer (Hewlett Packard
Development Company). Solid-state fluorescence
spectra were recorded on a Hitachi Model F-7000
FL Spectrophotometer with 360 nm excitation light.
The width of the excitation slit was10.0 nm, while the
emission slit was 5.0 nm, and the PMT voltage was 600
V for all measurements.
2.3 Preparation of films
Microscope slides were rinsed with deionized
water, anhydrous ethanol solution and acetone solvent
for more than 10 minutes respectively in ultrasonic
environment, then microscope slides were rinsed
repeatedly with deionized water. Al/DPO nano films
were prepared with evaporation coating method, where
Al film (60 nm) was prepared before DPO film (200
nm) was prepared, and the above steps were repeated.
3 Results and discussion
3.1 Theory and simulation
3.1.1 Simulation of electric current density of carrier
throughout double barrier
We assume nano particle as wells (also known
as Coulomb island), and the contact between the
nano particles is considered as a barrier, then onedimensional double-barrier model is shown in Fig.1.
We tried to use such a simple model of the electrooptical properties of nano aluminum to make a simple
analysis and discussion. The nonlinear resistance
effect can be obtained in electrical properties test
and the optical properties of the Coulomb island
will be clarified after discussing the transition of
an electron-emitting issue in Coulomb island. For
this purpose, we assume that the energy of incident
particle is E, and d1, d2 and d0 are the barrier width
and barrier spacing respectively. Considering E>V1,
V 2 , j 1 , j 2 , j 3 , j 4 , and j 5 are the wave function
?,
in Fig.1, and according to
k 2=
?. There is only transmitted wave in
x>d1+d0+d2, with particles incident from left. According
to the standardized conditions of wave function,
formula (1) can be got:
(1)
3.1.2 Simulation of I-V curve of double barrier
According to Fig.1, the current density at the area
is shown in the expression of electric current density
. On introducing j 2 ,
the current density is obtained as:
Journal of Wuhan University of Technology-Mater. Sci. Ed. www.jwutms.net Oct.2017
Fig. 1 Double barrier model
According to the current density expression, the
result is obtained as is shown in Fig.2 by the simulation
through matlab software to take analog computation
on I-V curve of double barrier. Fig.2(a) is voltage
characteristic curve of well wide variation with barrier
constant. The value of d1 and d2 is 2 nm, and d0 is 2, 4,
6 and 8 nm respectively in computation. As can be seen
from Fig.2, oscillation phenomenon appears in the low
voltage region, quantum effect is weakened with the
increase of voltage. I-V curve is consistent with classic
one in the high voltage region.
991
I-V changes the width of the barrier only. The width of
the barrier is selected as 2, 4, 6, 8 nm in the calculation.
Simulation results are shown in Fig.2(b). Oscillation
effect can also be seen in Fig.2(b). With increasing
barrier width, peak moves to high-voltage region,
the number of periodic oscillation increases. But the
voltage corresponding to the respective peak keeps
unchanged. In high voltage region, the curve shades in
straight line, which is consistent with the classical I-V
curve.
3.2 Experimental measurement of currentvoltage curve of the aluminum film
Fig.3 presents the current-voltage curve of the
aluminum film. Curves a and b indicate the currentvoltage curve of the aluminum film of which the
thickness is 60 and 30 nm respectively. Curve c is the
consequence of highly-smoothed results from curve b.
The tendencies of curves c and a are similar, but the
clue of shock and the stage effect can be concluded
from curve c which is on account of quantum effect
of the potential barrier penetration. Because of the
unexpected effects happened during the measurement,
curve b has a large fluctuation. As the similar
experiment result can be obtained repeatedly, this could
result from the real physic phenomena. As can be seen
in Fig.3, one basic step appears when voltage is less
than 2 V, and 2-4 V is another one. The results in Fig.3
is approximately matched with the fitted curve in Fig.2.
Fig.3 I-V curves of aluminum nano films with different thickness
Fig.2 (a) Well width varying voltage characteristic; (b) Wide
base voltage characteristic curves
With increasing width of the potential well, the
first formant corresponding voltage decreases, the
resonance peak and peak ratio increase, the negative
resistance region is narrowed. From the graphics,
resonance peak current is shown approximately at
the location of 1, 2, 3, 4-volt, with the corresponding
energy of 1-4 eV.
The well width is 2 nm in Fig.2(b). The result of
The surface topography of the aluminum films
of which the thickness is 60 and 30 nm can be seen
in Fig.4 (d in 60 nm, e in 30 nm). The particles are
uniform and the average size is 50 nm deduced from
the pictures, the aperture between two particles is very
small, but compact film is not formed. The contact of
the particles is formed by potential barrier leading to
the transportation of current carrier. So, the quantum
effect appears. The distribution in picture e is large and
992
Vol.32 No.5 MENG Qingyun et al: Electrical and Optical Properties of Nano Aluminum...
the aperture between two particles is big, including
the particles bigger than 50 nm or almost 20 nm.
Comparing picture d with e, both the particles in small
size and the aperture are increasing which amount to
the potential well becoming smaller and the barrier
becoming wider and further bringing out the obvious
shock of curve b in Fig.4.
the sample belongs to bulk material without coulomb
blockade effect and stairs effect. The simulation
compared to the equivalent width of the barrier is zero
when calculating the results. The peak position moves
to the direction of short waves with the increase of
thickness which can be concluded based on the other
samples in different thickness.
Fig.4 SEM of nano films (film thickness: (d) 60 nm; (e) 30
nm)
We want to make I-V oscillation phenomenon
of sample not occur, and return to the classic linear
relationship. When we prepare the sample during the
experiment, adjust the preparation conditions, and
increase the applied voltage and the particle size of the
sample, these methods are in favor of the transition to
the classical I-V.
It is found that I-V curves go back to the classical
linear relationship demonstrating no oscillation, when
the value of voltage is more than 10 V.
3.3 Fluorescent properties of the aluminum
film
As we know, large pieces of aluminum do not
have the fluorescent effect, because of the Fermi
level discrete on the surface of nanometer particles.
But photoluminescence appears after the aluminum
is made into nano materials. To highlight the
fluorescence efficiency of nano aluminum material,
and to investigate the microstructure and properties of
nano aluminum films, 60 nm aluminum (99.99%) was
deposited on glass substrates each time using the way
coated with a multilayer film. Sample Al1-Al5 in Fig.5
and Fig.6 presents the thickness of the film ranging in
60-300 nm. Fig.6 reveals that the photon energy is 2.93
eV when the wavelength is around 420 nm. The work
function of this is smaller than that of large pieces of
aluminum. Results exactly match with the simulation
data. A main peak and two shoulder peaks on both
sides can be seen in Fig.5. When the layer number of
the films is increased to five (300 nm), the fluorescent
peak is very weak and the fluorescent efficiency nearly
approaches to zero. At this time, the I-V nature of
Fig.5 The fluorescence emission spectra of aluminum films with
different thicknesses
Fig.6 The fluorescence emission spectra of aluminum/DPO
composite films with different thicknesses
DPO is a kind of organic fluorescent material.
Fluorescent peaks of pure DPO are in 420 and 440 nm.
The Al DOP1 in Fig.6 presents a cell fabric, which is
made by evaporating 30 nm DPO on the glass slide
which has been evaporated by 60 nm Al, and Al DPO5
means constituted by five structure layers. Fig.6 shows
that the peak shapes of fluorescence emission spectrum
of composite film are more broadened, the luminous
efficiency decreases with the increase of thickness.
This is similar to the pure aluminum but the extent is
much more, so we confirm that the fluorescent photon
launched by DPO is absorbed by aluminum film.
By comparing Fig.5 with Fig.6, the area in Fig.6 is
bigger which indicates that the fluorescence spectra
had changed due to the interaction between DPO and
nanometer aluminum.
Journal of Wuhan University of Technology-Mater. Sci. Ed. www.jwutms.net Oct.2017
4 Conclusions
The nonlinear effect of I-V curve obtained by
mathematical simulation fits the experimental curve,
which indicates that the nonlinear electric conduction
property of aluminum film is generated by potential
barrier in the touch point between particles in particle
film structure. Therefore, the quantum tunneling
effect takes place when current carrier transports in
the nanometer aluminum film leading to the nonlinear
electrical effect.
The fluorescence effect of nano aluminum
film is completely due to the nanometer effect. The
fluorescence spectra become wider after maxing DPO,
which indicates that DPO interacts with nano aluminum
due to the energy level dispersion of Al nano particles.
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Lee J H, Lee J W, Hwang S, et al. Effects of Al Concentration on
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Kang T J, Kim J G, Lee H Y, et al. Modification of Optical and
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Shanmugan S, Mutharasu D, Hassan Z, et al. A Study on the Effect
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