This document examines the influence of film thickness on the structural, electrical, and photoluminescence properties of aluminum tris(8-hydroxyquinoline) (Alq3) thin films deposited on silicon substrates via vacuum evaporation. Fourier transform infrared spectroscopy, current-voltage, capacitance-voltage, and photoluminescence spectroscopy measurements were performed on Alq3 films of varying thicknesses. The results showed that molecular structure was unaffected by thickness but photoluminescence intensity and emission energy increased with thickness. Turn-on voltage and transition voltage from current-voltage and capacitance-voltage measurements also increased with thicker films.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
SYNTHESIS AND DIELECTRIC CHARACTERIZATION OF BARIUM SUBSTITUTED STRONTIUM BIS...ijrap
The strontium bismuth niobate, SrBi2Nb2O9 (SBN) is a bismuth layered perovskite oxide
compound with potentially useful ferroelectric properties which offer several advantages such as fatigue
free, lead free, low operating voltages, relatively high Curie temperature; and most importantly, their
ferroelectric properties are independent of film thickness. These materials are also important for Fe-RAM
applications having large remanent polarization and low coercivity accompanied by high Curie
temperature for better performance and reliable operation. Present paper describes synthesis, dielectric
properties and impedance studies to reveal the important properties of barium substituted strontium
bismuth niobate, Sr0.85Ba0.15Bi2Nb2O9 in the system Sr1-xBaxBi2Nb2O9(x=0.15).
Morphological study of aluminum tris(8 hydroxyquinoline) thin films using inf...John Clarkson
R.J. Curry, W.P. Gillin, J. Clarkson & D.N. Batchelder, “Morphological study of aluminum tris(8-hydroxyquinoline) thin films using infrared and Raman spectroscopy”, J. Appl. Phys., 92 (4), 1902-1905, 2002.
undamentals of Crystal Structure: BCC, FCC and HCP Structures, coordination number and atomic packing factors, crystal imperfections -point line and surface imperfections. Atomic Diffusion: Phenomenon, Fick’s laws of diffusion, factors affecting diffusion.
Graphene: the world's first 2D material. Since graphene's isolation in 2004, it has captured the attention of scientists, researchers, and industry worldwide.
Electrospinning, a broadly used technology for electrostatic fiber formation which utilizes electrical forces to produce polymer fiber with diameters ranging from 2 nm to several micrometers using polymer solutions of both natural and synthetic polymers.
IOSR Journal of Applied Physics (IOSR-JAP) is an open access international journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
SYNTHESIS AND DIELECTRIC CHARACTERIZATION OF BARIUM SUBSTITUTED STRONTIUM BIS...ijrap
The strontium bismuth niobate, SrBi2Nb2O9 (SBN) is a bismuth layered perovskite oxide
compound with potentially useful ferroelectric properties which offer several advantages such as fatigue
free, lead free, low operating voltages, relatively high Curie temperature; and most importantly, their
ferroelectric properties are independent of film thickness. These materials are also important for Fe-RAM
applications having large remanent polarization and low coercivity accompanied by high Curie
temperature for better performance and reliable operation. Present paper describes synthesis, dielectric
properties and impedance studies to reveal the important properties of barium substituted strontium
bismuth niobate, Sr0.85Ba0.15Bi2Nb2O9 in the system Sr1-xBaxBi2Nb2O9(x=0.15).
Morphological study of aluminum tris(8 hydroxyquinoline) thin films using inf...John Clarkson
R.J. Curry, W.P. Gillin, J. Clarkson & D.N. Batchelder, “Morphological study of aluminum tris(8-hydroxyquinoline) thin films using infrared and Raman spectroscopy”, J. Appl. Phys., 92 (4), 1902-1905, 2002.
undamentals of Crystal Structure: BCC, FCC and HCP Structures, coordination number and atomic packing factors, crystal imperfections -point line and surface imperfections. Atomic Diffusion: Phenomenon, Fick’s laws of diffusion, factors affecting diffusion.
Graphene: the world's first 2D material. Since graphene's isolation in 2004, it has captured the attention of scientists, researchers, and industry worldwide.
Electrospinning, a broadly used technology for electrostatic fiber formation which utilizes electrical forces to produce polymer fiber with diameters ranging from 2 nm to several micrometers using polymer solutions of both natural and synthetic polymers.
Annealing and Microstructural Characterization of Tin-Oxide Based Thick Film ...Anis Rahman
Abstract. The sheet resistance of tin oxide based thick-film resistors exhibits two regions of temperature dependence,
described by hopping (23°C-200°C) and diffusion mechanisms (200°C-350°C), respectively.
Annealing these samples causes the sheet resistance to increase in both regions. In the post-annealed samples,
the hopping conduction range is extended by 50°C (23°C-250°C) while the hopping parameter, To, is decreased by
more than 50%. The activation energy of diffusion (0.60 eV) is the same for both pre- and post annealed samples, but
the magnitude of resistance in the diffusion controlled region is increased significantly as a result of annealing. These
changes are explained in terms of a net decrease in the concentration of tin ions in the glass matrix. From a careful
microstructural study it was found that a conduction path composed of tin-oxide grains or their clusters in contact
with each other does not exist in the present system. HREM micrographs showed the presence of nanocrystalline
tin-oxide particles in the glass phase separating the tin-oxide grain clusters. Estimated average separation between
the nanocrystals in 4 nm, consistent with a variable-range hopping conduction via the dissolved tin ions in the glass
matrix.
Properties and applications of graphene.
More introductions about graphene are in Alfa Chemistry.
https://www.alfa-chemistry.com/products/graphene-38.htm
Production and characterization of nano copper powder using electric explosio...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
As a new type of nanomaterials with the most thin, the maximum intensity and most conductive conductivity, graphene is known as "black gold" and "king of new materials". https://www.alfa-chemistry.com/products/graphene-38.htm
Heat treatment of BFO film deposited on Si (111): Spectroscopic studyiosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice
The name ‘graphene’ comes from graphite + -ene = graphene
Comparison of Morphological, Electrical and Optical Properties of as-deposite...IJERA Editor
Indium selenide (InSe) thin films have been deposited on to glass substrate by e-beam evaporation technique. Scanning Electron Microscopy (SEM) has been used to study the surface morphology of the films. It is observed that the as-deposited InSe films have no sign of grains and the surfaces are almost smooth and uniform. While a number of grain boundaries are observed in the annealed films. Three different slopes in the conductivity vs temperature curves exhibits in as-deposited InSe films. If it is associated with three types of conduction mechanisms, then it might be interesting. The conductivity of annealed InSe films increases continuously with increasing temperature showing normal semiconducting behaviour. The direct optical band is found to decrease from 1.79 eV to 1.57 eV after annealing.
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
Copper indium sulphide films were deposited by the
pulse plating technique with different OFF times in the range of
5s – 30s and at a constant current density of 5 mA cm-2. The
films exhibited single phase copper indium sulphide. The grain
size increased with decrease of OFF time. Optical band gap of the
films increased from 1.44– 1.497 eV with decrease of OFF time.
Optical constants (refractive index, n, and extinction co-efficient,
k) of the films have been obtained in the wavelength range 800 -
1700 nm by using spectrophotometric measurement. The
obtained results concerning the absorption index yield the energy
gap in addition to the type of the allowed optical transitions.
N/m* ratio has been obtained from refractive index data. The
dispersion of refractive index is analyzed by using a single
oscillator model.
Annealing and Microstructural Characterization of Tin-Oxide Based Thick Film ...Anis Rahman
Abstract. The sheet resistance of tin oxide based thick-film resistors exhibits two regions of temperature dependence,
described by hopping (23°C-200°C) and diffusion mechanisms (200°C-350°C), respectively.
Annealing these samples causes the sheet resistance to increase in both regions. In the post-annealed samples,
the hopping conduction range is extended by 50°C (23°C-250°C) while the hopping parameter, To, is decreased by
more than 50%. The activation energy of diffusion (0.60 eV) is the same for both pre- and post annealed samples, but
the magnitude of resistance in the diffusion controlled region is increased significantly as a result of annealing. These
changes are explained in terms of a net decrease in the concentration of tin ions in the glass matrix. From a careful
microstructural study it was found that a conduction path composed of tin-oxide grains or their clusters in contact
with each other does not exist in the present system. HREM micrographs showed the presence of nanocrystalline
tin-oxide particles in the glass phase separating the tin-oxide grain clusters. Estimated average separation between
the nanocrystals in 4 nm, consistent with a variable-range hopping conduction via the dissolved tin ions in the glass
matrix.
Properties and applications of graphene.
More introductions about graphene are in Alfa Chemistry.
https://www.alfa-chemistry.com/products/graphene-38.htm
Production and characterization of nano copper powder using electric explosio...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
As a new type of nanomaterials with the most thin, the maximum intensity and most conductive conductivity, graphene is known as "black gold" and "king of new materials". https://www.alfa-chemistry.com/products/graphene-38.htm
Heat treatment of BFO film deposited on Si (111): Spectroscopic studyiosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice
The name ‘graphene’ comes from graphite + -ene = graphene
Comparison of Morphological, Electrical and Optical Properties of as-deposite...IJERA Editor
Indium selenide (InSe) thin films have been deposited on to glass substrate by e-beam evaporation technique. Scanning Electron Microscopy (SEM) has been used to study the surface morphology of the films. It is observed that the as-deposited InSe films have no sign of grains and the surfaces are almost smooth and uniform. While a number of grain boundaries are observed in the annealed films. Three different slopes in the conductivity vs temperature curves exhibits in as-deposited InSe films. If it is associated with three types of conduction mechanisms, then it might be interesting. The conductivity of annealed InSe films increases continuously with increasing temperature showing normal semiconducting behaviour. The direct optical band is found to decrease from 1.79 eV to 1.57 eV after annealing.
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
Copper indium sulphide films were deposited by the
pulse plating technique with different OFF times in the range of
5s – 30s and at a constant current density of 5 mA cm-2. The
films exhibited single phase copper indium sulphide. The grain
size increased with decrease of OFF time. Optical band gap of the
films increased from 1.44– 1.497 eV with decrease of OFF time.
Optical constants (refractive index, n, and extinction co-efficient,
k) of the films have been obtained in the wavelength range 800 -
1700 nm by using spectrophotometric measurement. The
obtained results concerning the absorption index yield the energy
gap in addition to the type of the allowed optical transitions.
N/m* ratio has been obtained from refractive index data. The
dispersion of refractive index is analyzed by using a single
oscillator model.
Electrical Properties of Thermally Evaporated In40 Se60 Thin Filmsiosrjce
In40 Se60 thin films with different thicknesses (300,500, and 700nm) have been deposited by single
source vacuum thermal evaporation onto glass substrates at ambient temperature to study the effect of thickness
and on its structural morphology, and electrical properties. AFM study revealed that microstructure parameters
such as crystallite size, and roughness found to depend upon deposition conditions. The DC conductivity of the
vacuum evaporated In40 Se60thin films was measured in the temperature range (293-473)K and was found to
increase on order of magnitude with increase of thickness. The plot of conductivity with reciprocal temperature
suggests, there are two activation energies Ea1and Ea2 for In40 Se60 for all thicknesses which decreases with
increasing thickness .Hall effect measurement showed that low thickness In40 Se60 film exhibit p-type
conductance whereas the film exhibit n-type towards the higher thickness. The electric carrier concentration
and mobility show opposite dependence upon thickness.
Influence of Thickness on Electrical and Structural Properties of Zinc Oxide ...paperpublications3
Abstract: Zinc Oxide (ZnO) thin films were prepared on corning (7059) glass substrates at a thickness of 75.5 and 130.5nm by RF sputtering technique. The deposition was carried out at room temperature after which the samples were annealed in open air at 1500C. The electrical and structural properties of these films were studied. The electrical properties of the films were monitored by four-point probe method while the structural properties were studied by X-ray diffraction (XRD). It was found that the electrical resistance of the films decreases with increase in the thickness of the films. The XRD analysis of the films showed that the films have a peak located at 〖34.31^0-34.35〗^0with hkl (002). Other parameters calculated include the stress ( ) and the grain size (D).
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Electrochemical Supercapacitive Performance of Sprayed Co3O4 ElectrodesIJERA Editor
Nanocrystalline cobalt oxide (Co3O4) thin film electrodes were fabricated by spray pyrolysis method on conducting fluorine doped tin oxide (FTO) substrates using ammonia complexed with cobalt chloride (CoCl2. 6H2O) solution. The structural and morphological properties of Co3O4electrodes were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM).The surface morphology study showed the film formation of porous surface with clusters. The electrochemical supercapacitive properties ofCo3O4 electrodes were evaluated using cyclic voltammetry and galvanostatic charge-discharge method. The Co3O4electrodes showed maximum specific capacitance of 168 F/g in 1 M aqueous KOH electrolyte at the scan rate of 20 mV/s. The maximum specific energy and specific power of the cell are 2.2Wh/kg and 0.23 kW/kg, respectively.
LGS crystal which melts congruently at 1470⁰C has been grown by Czochralski method. The langasite
crystal of length about 1cm grown along its Z-axis was cut in X and Y directions , polished and
subjected to various characterization studies. Phase and structure of the grown crystal was confirmed by
Powder XRD measurement. FTIR spectrum was carried out to confirm the functional groups present in
the grown crystals. The optical behavior was studied by UV–vis-NIR analysis. Electrical properties such as Dielectric constant, Resistivity, Conductivity and Piezoelectric coefficient have also been studied.
Это идея навязать фундаметальные резонансные частоты
колебаний фононов и/или их гармоники в известном
гелиевом сверхпроводнике другому материалу с очень
гибкой структурой
Optical Characterization of Fluorine Doped Tin Oxide Deposited By Spray Pyrol...paperpublications3
Abstract: Fluorine doped tin oxide thin (FTO) films prepared by spray pyrolysis technique at a substrate temperature of 573K. The films deposited were 100 nm thick. After the deposition, the films were then annealed at different annealing temperatures of 423K, 573K and723K respectively in open air. The optical parameters of the prepared films as transmittance, optical energy gap, refractive index, extinction coefficient, porosity, packing density and the dielectric constants were found to be influenced by varying the annealing temperatures.
Optical and Impedance Spectroscopy Study of ZnS NanoparticlesIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Similar to ThinSolidFilms 517 (2009) 5298–5300 (20)
2. Keithley 236 Source Measure Unit and a 590 CV analyser respectively
at room temperature.
3. Result and discussion
Fig. 1 shows the FTIR spectra obtained from the Alq3 thin films of
different thicknesses. The FTIR spectrum of Alq3 powder prepared on
KBr is also included as a reference. The region shown in the spectra
corresponds to the “fingerprint region” of the vibrational modes
present in Alq3 films. The FTIR spectra of all the films irrespective of
film thickness are quite similar to the spectra of Alq3 powder prepared
on KBr confirming that the same functional groups are present in all
the films and the Alq3 powder. Going down the spectral range, from
1700–1000 cm−1
, two bands centered at 1606 and 1578 cm−1
as-
signed to a CC stretching vibration involving the quinoline group
of ligands are first observed followed by the bands at 1498 and
1468 cm−1
which correspond to a CC/CN stretching + CH bending
vibration associated with both the pyridyl and phenyl groups in Alq3.
Then, vibrations at 1385 and 1328 cm−1
involving CC/CN stretching +
CH bending of the quinoline fragments of Alq3 are observed. The bands
recorded at the end of this spectral range with peak positions at 1282,
1230 and 1115 cm−1
are assigned to a CH/CCN bending + CN stretch-
ing vibrations. In the region below 1000 cm−1
, the most intense ab-
sorption is observed at 789 cm−1
which is assigned to the out-of-plane
CH wagging vibrations of the quinoline groups. No significant change
in the chemical bonding structures of Alq3 films is observed within the
detection of the FTIR spectra with an increase in film thickness. The
increase in the FTIR absorbance peak intensity with increase in film
thickness of the Alq3 film is due to the increase in the number of
molecules with increase in film thickness [6]. The PL spectra of the Alq3
films of different thicknesses are shown in Fig. 2. The measurement
was made at room temperature with an excitation wavelength of
224 nm. All films showed strong PL peaks at a wavelength of ~519 nm
in all films. The PL intensity increases and the PL emission peak energy
is red-shifted with increase in film thickness. The thickness depen-
dence of the PL emission intensity and peak energy are also displayed
in Fig. 3. With the increase in the Alq3 film thickness from 70 to 280 nm,
the PL intensity increases by a factor of 2 and the peak energy is shifted
from about 514 to 525 nm. The increase in the PL intensity with film
thickness showed that PL intensity is dependent on the number of Alq3
molecules in the film structure. The Alq3 emission peak also showed a
significant red-shift with increase in film thickness. For thinner Alq3
film, the surface component is dominant while for thicker film the
contribution from the bulk (the 3D exciton) is more dominant [2]. This
explains the red-shift of Alq3 emission peak with increase in film
thickness. Fig. 4 shows the I–V characteristics Al/Alq3/c-Si/Al devices
with Alq3 film of different thicknesses with the inset showing the
device configuration. The current increases exponentially with in-
crease in applied bias voltage. It is also evident that the organic layer
thickness has an influence on the I–V characteristics of the films. The
electron injection barrier increases as the Alq3 film thickness increases.
This may due to the different positions of the HOMO and LUMO levels
as the Alq3 film thickness increases, leading to unbalanced electron
Fig. 2. PL spectra (excited at 224 nm) of evaporated Alq3 thin film on silicon substrates.
Fig. 3. Variation of PL emission intensity and energy with film thickness of evaporated
Alq3 films.
Fig. 4. I–V characteristic of Al/Alq3/c-Si/Al structure thin films.
Table 1
Turn-on and operating voltage of Al/Alq3/c-Si/Al structure for different Alq3 layer
thickness.
Alq3 layer thickness
(±5 nm)
Turn-on voltage (Von)
(±2 V)
Operating voltage (Vop)
(±2 V)
70 8 8.0–11.5
120 9 9.0–12.0
180 10.5 10.5–13.0
230 11.5 11.5–15.0
Fig. 1. FTIR spectra of evaporated Alq3 thin films and powder prepared on KBr.
5299J.Y. Koay et al. / Thin Solid Films 517 (2009) 5298–5300
3. and hole current. Therefore, in order to achieve the same current
density in the devices, the applied bias voltage has to be increased with
increase in Alq3 film thickness. The results given in Table 1 shows that
the turn-on voltage, Von and operating voltage, Vop increase when the
Alq3 layer thickness increases. This is because the Alq3 layer thickness
plays a role in improving the balance of electron and hole current [7], as
the cathode contact for electron injection in all the devices was the
same. The Von for the device is controlled by the majority carrier
injection from the electrode to gate. Since the electron is the majority
carrier, the turn-on voltage, Von is mainly determined by the organic–
electrode interface barrier. The higher Vop for the thicker films shows
that the contribution of the minority carrier current to the total current
becomes more significant [8,9] as the film thickness increases. Fig. 5
shows the Fowler–Nordheim (FN) plots obtained from the I–V curves
of the Alq3 films. According to the FN model, assuming that the current
is limited by high injection barriers at the electrodes, implying that no
space charges are present, for a given electric field the current should
be independent of the film thickness. However, the current for a given
field decreases when the film thickness increases from 70 to 230 nm.
This clearly contradicts the theoretical models based on pure injection
limitation [10]. They show a linear variation at high field which
deviates to a power law evolution at lower fields. This behavior shows
that either holes or electrons can be injected to the organic layer by
tunneling through the existing barriers existing at the organic–
electrode interfaces. The deviation from the linear portion of the
curve is supposed to be due to the thermionic emission (Richardson–
Schottky) contribution. The linear part of the curves plotted in Fig. 5
has gradually shifted to lower fields with increase in Alq3 layer
thickness. This behavior can be related to the development of a space
charge region near the Alq3/Al interface [11]. Fig. 6 shows the C–V
characteristic of a single Alq3 layer of thickness ranging from 70 to
230 nm. The transition voltage, VT is strongly dependent on the
thickness of the Alq3 layer. Fig. 7 shows the dependence of the VT
(taken as the inflection point of the C–V curves) [12] on the Alq3
thickness. As the Alq3 film thickness increases, VT obviously increases
linearly to a more positive value within the error limits.
4. Conclusion
The effects of film thickness on the chemical bonding, PL and
electrical properties of Alq3 films deposited by thermal evaporation on
c-Si substrates have been studied. The FTIR results have shown that
increasing film thickness produces no significant change in the
chemical bonding structures. However, increasing film thickness
increases the number of Alq3 molecules in the film structure and
this is represented by the increase in the absorption band intensity of
the vibrational modes present in the film. The PL intensity also
increases with increase in film thickness showing dependence of PL
intensity on the number of Alq3 molecules. Decrease in film thickness
produces a blue shift in PL emission peak energy as a result in
dominance of the surface component for thinner films. I–V measure-
ment results show that thicker films result in higher Von and higher
Vop indicating that the total current is mainly contributed by minority
carriers in thinner films. Thinner films are more favorable for current
injection into the organic layer by tunneling through the barriers as
these films can easily produce higher fields at small applied voltage.
Shifting of the linear part of the FN plots to lower fields for thicker
films shows indication of development of space charge region near the
Alq3/Al interface. An increase in capacitance is produced by thinner
film and VT increases with increase in film thickness.
References
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Fig. 6. C–V characteristic of Al/Alq3/c-Si/Al structure thin films.
Fig. 7. Variation of transition voltage with film thickness for the Al/Alq3/c-Si/Al
structure.
Fig. 5. Fowler–Nordheim equation plots for the Al/Alq3/c-Si/Al structure for different
Alq3 layer thickness.
5300 J.Y. Koay et al. / Thin Solid Films 517 (2009) 5298–5300