1) Evaporated and sputtered InSb films have different crystallization properties. Evaporated films have a lower activation energy of 1.39 eV and crystallize by three-dimensional growth on existing nuclei.
2) Sputtered films have a higher activation energy of 2.7 eV and crystallize by nucleation and subsequent growth on the nuclei. The Avrami exponent indicates sputtered films require crystalline nuclei to form before crystallization can begin.
3) Transmission electron microscopy images show evaporated films have existing nuclei while sputtered films have no visible crystallites in the as-deposited state, requiring nucleation.
Effect of Temperature on Structural, Morphological and Optical Properties of ...RSIS International
The Pure zinc oxide (ZnO) thin films of different substrate temperature have been prepared on well cleaned glass substrate by improved spray pyrolysis technique. The gross structure of the annealed films have been examined by X- ray diffraction (XRD) technique using powder X- ray diffractometer which reveals the enhancement of crystallinity with increase in the deposition temperature. Surface morphology of the synthesized ZnO thin films have been analyzed by means of atomic force microscopy (AFM) which reveals average particle size of as synthesize ZnO thin films has been found to be 79 nm. The band gap as deposited ZnO have been examined by UV-Vis spectroscopy carried out in absorption mode by Double Beam UV- VIS Spectrophotometer with radiations in the range of 훌= 190 nm to 1100 nm which is in the range of 3.03 eV to 3.16 eV.
NAFEN™ - THE REVOLUTIONARY MATERIAL AT THE HEART OF A NEW TECHNOLOGICAL FUTURE
Aluminum Oxide Nano fibers - NAFEN™ provides the unique combination of properties including controllable diameter of 7 and 40 nm, lengths up to 15 centimeters, Young’s modulus over 400 GPa, a vast surface area of over 150 m2/g, high aspect ratios, chemical inertness, stability against radiation, and thermal stability up to 1200 C.
All of these amazing attributes are represented in NAFEN™, which ANF Technology produces in industrial volumes -- with unlimited scale-up potential -- to meet the growing market demand for these innovative nano products.
NAFEN™ IS THE ONLY SUPERIOR-QUALITY NANOFIBER ON THE MARKET PRODUCED IN INDUSTRIAL VOLUMES
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
Effect of Temperature on Structural, Morphological and Optical Properties of ...RSIS International
The Pure zinc oxide (ZnO) thin films of different substrate temperature have been prepared on well cleaned glass substrate by improved spray pyrolysis technique. The gross structure of the annealed films have been examined by X- ray diffraction (XRD) technique using powder X- ray diffractometer which reveals the enhancement of crystallinity with increase in the deposition temperature. Surface morphology of the synthesized ZnO thin films have been analyzed by means of atomic force microscopy (AFM) which reveals average particle size of as synthesize ZnO thin films has been found to be 79 nm. The band gap as deposited ZnO have been examined by UV-Vis spectroscopy carried out in absorption mode by Double Beam UV- VIS Spectrophotometer with radiations in the range of 훌= 190 nm to 1100 nm which is in the range of 3.03 eV to 3.16 eV.
NAFEN™ - THE REVOLUTIONARY MATERIAL AT THE HEART OF A NEW TECHNOLOGICAL FUTURE
Aluminum Oxide Nano fibers - NAFEN™ provides the unique combination of properties including controllable diameter of 7 and 40 nm, lengths up to 15 centimeters, Young’s modulus over 400 GPa, a vast surface area of over 150 m2/g, high aspect ratios, chemical inertness, stability against radiation, and thermal stability up to 1200 C.
All of these amazing attributes are represented in NAFEN™, which ANF Technology produces in industrial volumes -- with unlimited scale-up potential -- to meet the growing market demand for these innovative nano products.
NAFEN™ IS THE ONLY SUPERIOR-QUALITY NANOFIBER ON THE MARKET PRODUCED IN INDUSTRIAL VOLUMES
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
Rosa alejandra lukaszew a review of the thin film techniques potentially ap...thinfilmsworkshop
SRF is a surface phenomenon where only ~10 penetration depths are needed (l=40 nm for niobium), thus it has been recognized for some time now that it would be economically convenient to use thin film coated cavities. But problems arise with defects within 1 or 2 l of the surface or on the surface, and insufficient attention has been paid to this topic, including trapping of impurities like oxygen in defects as well as surface roughness enabling magnetic field pinning sites. Earlier attempts at CERN applied standard sputter PVD methods, but the grain size for the CERN Nb/Cu films was 100 nm, which is 10,000 times smaller than for conventional SRF cavities with the ensuing problems that appear at grain boundaries. Thus, these prior attempts showed higher surface resistance and worst Q-slope than bulk. I will review more modern approaches using higher energetic PVD methods for thin film deposition which offer promise to achieve thin films with improved superconducting performance.
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.
Keywords: FTO, annealing in open air, spray pyrolysis, porosity, packing density, dielectric constant.
Effect of Bi Content on Optical Properties of Se-Sb-Bi Chalcogenide Amorphous...ijsrd.com
Se90-xSb10Bix (x=0, 2, 4, 6, 8 & 10) chalcogenide glasses were prepared by well-established melt quenching technique. The glassy nature was verified by X-ray diffraction (XRD). Thin films of these samples were deposited on glass substrate using thermal evaporation technique at room temperature. The transmission spectra of thin films have been taken using UV-VIS-NIR spectrophotometer (Varian Cary 500) in the wavelength range 200 nm to 1500 nm. The refractive index and film thickness are calculated by using envelope method proposed by Swanepoel. The results indicate that n increases with the increasing Bi content which is related to the increased polarizability of the larger Bi atomic radius 1.46 Å compared with the Se atomic radius 1.16 Å. The value of absorption coefficient (α) and hence extinction coefficient (k) has been determined from transmission spectra. Optical band gap (Eg) is estimated using Tauc's extrapolation and is found to decrease from 1.46eV to 1.24 eV with the Bi addition. This behavior of optical band gap is interpreted in terms of electronegativity difference of the atoms involved and cohesive energy of the system. The variation of optical band gap with Bi content has been studied. This study is aiming to examine such structures if they are employed as photonic devices such as photo-detectors, LED's and optical switches.
Vapor phase cutting of carbon nanotubes using a nanomanipulator platform-ms&t...Paul McClure
This presentation by Xidex at MS&T'10 shows how Xidex's NanoBot system, equipped with gas delivery, can be used to "edit" carbon nanotube based nanodevices. For more details, please visit www.xidex.com.
Rosa alejandra lukaszew a review of the thin film techniques potentially ap...thinfilmsworkshop
SRF is a surface phenomenon where only ~10 penetration depths are needed (l=40 nm for niobium), thus it has been recognized for some time now that it would be economically convenient to use thin film coated cavities. But problems arise with defects within 1 or 2 l of the surface or on the surface, and insufficient attention has been paid to this topic, including trapping of impurities like oxygen in defects as well as surface roughness enabling magnetic field pinning sites. Earlier attempts at CERN applied standard sputter PVD methods, but the grain size for the CERN Nb/Cu films was 100 nm, which is 10,000 times smaller than for conventional SRF cavities with the ensuing problems that appear at grain boundaries. Thus, these prior attempts showed higher surface resistance and worst Q-slope than bulk. I will review more modern approaches using higher energetic PVD methods for thin film deposition which offer promise to achieve thin films with improved superconducting performance.
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.
Keywords: FTO, annealing in open air, spray pyrolysis, porosity, packing density, dielectric constant.
Effect of Bi Content on Optical Properties of Se-Sb-Bi Chalcogenide Amorphous...ijsrd.com
Se90-xSb10Bix (x=0, 2, 4, 6, 8 & 10) chalcogenide glasses were prepared by well-established melt quenching technique. The glassy nature was verified by X-ray diffraction (XRD). Thin films of these samples were deposited on glass substrate using thermal evaporation technique at room temperature. The transmission spectra of thin films have been taken using UV-VIS-NIR spectrophotometer (Varian Cary 500) in the wavelength range 200 nm to 1500 nm. The refractive index and film thickness are calculated by using envelope method proposed by Swanepoel. The results indicate that n increases with the increasing Bi content which is related to the increased polarizability of the larger Bi atomic radius 1.46 Å compared with the Se atomic radius 1.16 Å. The value of absorption coefficient (α) and hence extinction coefficient (k) has been determined from transmission spectra. Optical band gap (Eg) is estimated using Tauc's extrapolation and is found to decrease from 1.46eV to 1.24 eV with the Bi addition. This behavior of optical band gap is interpreted in terms of electronegativity difference of the atoms involved and cohesive energy of the system. The variation of optical band gap with Bi content has been studied. This study is aiming to examine such structures if they are employed as photonic devices such as photo-detectors, LED's and optical switches.
Vapor phase cutting of carbon nanotubes using a nanomanipulator platform-ms&t...Paul McClure
This presentation by Xidex at MS&T'10 shows how Xidex's NanoBot system, equipped with gas delivery, can be used to "edit" carbon nanotube based nanodevices. For more details, please visit www.xidex.com.
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.
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.
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.
Transparent and Conducting TiO2 : Nb Thin Films Prepared by Spray Pyrolysis T...arj_online
To date, only sputtering and pulsed laser deposition (PLD) techniques have been employed
successfully to fabricate highly conducting and transparent TiO2:Nb (TNO) films. In this article, we demonstrate
that transparent and conducting
TiO2
: Nb
films can be made by the spray pyrolysis technique. The films were
deposited on Corning 7059 glass substrates at 500
15˚C using an alcoholic precursor solution consisting of
titanium (iv) isopropoxide and
NbCl5
. The influence of increasing
Nb
concentration on the electrical, optical
and structural properties was investigated. The minimum resistivity, 3.36
-3 10
Ω cm, for
Ti1-xNbxO2
film (x
= 0.15) was obtained after 1 hour post deposition annealing in hydrogen atmosphere at 500˚C. The x-ray
diffraction of hydrogen annealed films showed a polycrystalline anatase (004)-oriented phase without any second
phases. The optical band gap for undoped and doped films lay in the range 3.38 – 3.47 eV. Using dispersion
analysis, optical constants were determined from spectro-photometric measurements for films on glass.
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.
This is a power point presentation of project work on preparing Zinc oxide thin films by using SILAR technique and CBD technique and studying its characteristics.
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.
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 Se90S10-xCdx thin filmsIOSR Journals
Thin films of different thicknesses of Se90S10-xCdx, (x=0 and 5) were deposited by thermal evaporation technique onto glass substrates. X-ray diffraction patterns (XRD), differential thermal analysis (DTA) and energy dispersive X-ray spectroscopy (EDX) studies were carried out for samples in powder and thin film forms. XRD indicates that all the deposited thin films have an amorphous structure. The transmittance at normal incidence for these films was measured in the wavelength range 350–2500 nm. Applying Swanepoel's method successfully enabled to determine, with high accuracy, the film thickness, the real index of refraction and imaginary part of index of refraction. Regarding the optical absorption measurements; the type of optical transition and optical band gap were estimated as a function of photon energy. The effect of Cd addition on the refractive index, absorption coefficient and the optical band gap were investigated. The high frequency dielectric constant, the single oscillator energy, the dispersion energy and refractive index dispersion parameter were evaluated. Solar cell criterions have been considered. The results are interpreted in terms of concentration of localized states.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
2. 234
the crystallization. The dimensions of the probe
beam and the film thickness are small enough to 550 500 450 400
consider the temperature uniform over the
2 InSb
volume probed. 20 ~
The samples that we have investigated consist
of a single InSb layer on a thick (1.2 mm) glass oo
/
substrate. The heat diffusivity D and heat con-
ductivity K of the substrate are D = 4.90 x 10 ~ /
m 2 s 1 and K = 1.1 W K t, respectively. From /
/
these thermal properties it can be deduced that /
the rise time of the temperature is approximately -2 /
200 /~s [2]. The temperature distribution has
/
-3
/
been calculated using the expression of Pittaway
for a surface heat source on a semi-finite sub- 1.8 2.0 2.2 2.4 2.6
strate [3]. The InSb layers were prepared by
IO00/T [K1] ......
sputtering or by flash evaporation. The composi-
tion of the film was determined by X-ray fluores- Fig. I. Arrhenius plot of the transformation time r', as
cence (XRF) to be InSb within 2 at.%. The deduced from the transmittivity, vs. the temperature. The
slope of the line gives the activation energy. The sample was a
non-crystallinity of the samples was checked with 20 nm InSb film prepared by evaporation.
X-ray diffraction (XRD) by the absence of sharp
peaks. It appeared that evaporated films thicker
than 100 nm were at least partially microcrystal-
line. In our experiments we used evaporated films 30 t • oo
with thicknesses between 20 and 90 nm, and I 2.5 •
sputtered films between 20 and 160 nm.
2.0F
> i
3. Results uZ 1.5~ :: s
o
At constant temperature T the crystalline frac-
tion x(t) during the transformation is usually
described by the Avrami equation [4] k k
0 4~0 8~0 120 160 200
x(t) = 1 -exp{ -(t/r)'"} d (nm) ---,,.
where m is the Avrami exponent. For an activated Fig. 2. Activation energy vs. film thickness for a number of
lnSb films. The full circles represent samples prepared by
process the temperature dependence of the sputtering, the open circles films prepared by flash evapora-
characteristic transformation time r can be tion.
written as
r = r 0 exp(EacJkT ) Transformation times longer than 1 ms are
where East is the activation energy. included only, since for shorter times the non-
This activation energy can be deduced directly isothermal part of the process cannot be neglec-
from measurements of the transmittivity. In our ted. The crystallization time varies rapidly over a
samples the transmittivity increases during the temperature range less than 200 K. Also, the
amorphous-to-crystalline transition. For this experimental points can be fitted with a straight
purpose let us define the transformation time r' line. This indicates that the crystallization process
as the time needed for the transmittivity to cross a can be described with one activation energy only.
level that is 1.15 times the start level. This r' is The same conclusions can be made for the other
proportional to the transformation time r. How- samples that have been measured.
ever, it should be noted that the proportionality From the slope of the line in Fig. 1 the activa-
constant is different for different samples. From a tion energy can be calculated. In Fig. 2 the activa-
plot of log r' against l/T, the activation energy tion energies for a number of evaporated and
Eac t c a n be calculated. In Fig. 1 the result for an sputtered samples are shown. The activation
evaporated sample of 20 nm of InSb is shown. energy is independent of the film tl-fickness. There
3. 235
is a large difference, however, between sputtered
I
and evaporated films. The average activation
energy for an evaporated film is 1.39(5) eV
atom-~, while for sputtered films it is 2.7(1) eV
g120
140
u~ 100
/
/
atom ~.
To investigate this difference further, we have
80 /"
60
determined the Avrami exponent m for one sput- d c = 1.08 d a
40
tered and one evaporated sample. From the
20
Avrami exponent it can be deduced whether the
i i
crystallization starts on existing nuclei or not and 0 2'0 4'0 6'0 dO 100 120 140
what the dimensionality of the growth process of da (nm) --
the crystallites is (see e.g. ref. 5). However, the Fig. 3. Film thickness after crystallization, d~, vs. film thick-
measurement of rn is less trivial than that of E~,,t. ness of the amorphous phase, d,, for films prepared by
To obtain accurate values of m, the crystalline evaporation. The solid line corresponds to d = 1.08(4)d..
.fraction x(t) has to be calculated from the experi-
mental reflectivity and transmittivity. For this we
need to know the values of the optical constants
of the amorphous and crystalline phases at the
temperature at which the transmittivity and
reflectivity have been measured. Since accurate
values for thin films are available only at room
0 1 2 3 4 5 6
temperature [6], the following procedure was
In(t/tp)
applied. The sample is heated with a short laser
pulse from the heating laser. After the sample has Fig. 4. Avrami plot of the cryslallinc fraction x(t) for an
evaporated sample of 70 nm; tr is the pulse time of the
cooled down, the transmittivity and reflectivity heating pulse.
are measured. This is repeated a large number of
times on the same area of the sample. In this way
the sample is crystallized gradually while the denced by XRF and Rutherford backscattering
transmittivity and reflectivity are measured at measurements.
room temperature. This allows us to use the opti- In Fig. 4 an Avrami plot is shown of the crys-
cal constants that have been determined for sput- talline fraction x(t) resulting from an experiment
tered InSb at room temperature: for amorphous on a 70 nm InSb layer produced by flash evapor-
InSb n = 4 . 8 2 - 1.95i and for crystalline InSb ation. If the crystallization process could be
n = 4 . 0 7 - 0 . 7 5 5 i [6]. The dielectric constant of described completely by the Avrami equation,
the mixture of the amorphous and crystalline this would be a straight line with slope m. How-
phase is calculated using an effective medium ever, the curve deviates strongly from the simple
theory [2, 7]. This is valid if the crystalline phase Avrami behaviour. This is typical for all samples
appears homogeneously distributed throughout considered, both sputtered and evaporated. This
the volume of the film. deviation is not unexpected for a thin film. In the
The effective optical constants are used to derivation of the Avrami expression the im-
extract the crystalline fraction x(t). The calcula- pingement of crystallites is taken into account.
tion includes volume changes during the transi- However, it is assumed that the material extends
tion. For sputtered films Holtslag and Scholte [6] infinitely in all directions. This is obviously not
observed that the film thickness d changes slightly true for a thin film. Therefore one may expect the
during crystallization: d c = 1.015 d a. In flash- crystallization to become lower dimensional
evaporated films the volume change is much when the crystallites reach the interfaces of the
larger (see Fig. 3): d~=l.08d~. The volume film [9]. Also, one cannot neglect the effect of the
change upon fusion of lnSb is reported to be stress induced by the volume expansion during
11.4%-13.7% [8]. Therefore the density of the the crystallization. This may become especially
evaporated sample is comparable to the density important when the crystals start to impinge.
of the liquid. The sputtered sample is less dense. From the slope at the beginning of the curve,
This can be attributed to the incorporation the Avrami exponent at the start of the crystalliza-
of a considerable amount of argon, as evi- tion process can be calculated. For an evaporated
4. 236
film of 70 nm m = 1.5(2) was found. For a sput- Combined with the high vaiues ot the Avrami
tered film of 92 nm rn = 3(1). The value for the exponent and the activation energy, this indicates
sputtered film is rather inaccurate owing to the that crystalline nuclei first have to be formed
high activation energy of the film. To obtain before crystallization can start. The value of the
enough points at the start of the crystallization, a Avrami exponent is in accordance with t ; ; - 2.5
short pulse time has to be used: 0.1 ms vs. 10 ms This value corresponds to a crystallization pro-
for an evaporated film. Consequently, the non- cess that is similar to that in the evaporated layer
isothermal part of the crystallization may have plus an extra nucleation step. Also, as one might
influenced the experimental value of the Avrami expect, the value of the activation energy in the
exponent. However, within the given limits the
experimental value for the Avrami exponent is
correct.
4. Discussion and conclusions
In Table 1 the results for sputtered and evap-
orated InSb are summarized. It is clear that the
crystallization properties depend strongly on the
preparation method. Unfortunately, there is no
unique relationship between the value of the
Avrami exponent and the characteristics of the
crystallization process. Different processes may
give the same value for the Avrami exponent [5].
To understand these differences we have to com-
bine the results of the optical measurements with
the results of T E M experiments on a sputtered
and an evaporated layer of InSb on Si3N 4 sub-
strates [10].
First consider the evaporated layer. From the
Fig. 5. TEM pholograph of an amorphous lnSb layer
low value of the Avrami exponent m = 1.5(2) it is prepared by evaporation. The number of crystalline nuclei
highly unlikely that the crystallization starts with visible corresponds to approximately I() ~ crystatlites m ~'
the formation of crystalline nuclei. This is evi-
denced by Fig. 5, in which a section of an evap-
orated layer is shown. The number of crystallites
visible corresponds to 1 0 ~~ crystalhtes m - .-
- "
Therefore it can be concluded that in evaporated
InSb the crystallization proceeds by three-dimen-
sional diffusion-limited growth on already exist-
!
ing nuclei. In sputtered InSb the situation is
different. As can be seen from Fig. 6, no visible
crystallites are present in the as-deposited layer.
TABLE 1 Comparison between some parameters deter-
mining the crystallization process in thin amorphous InSb
films prepared by sputtering and by evaporation. E~t is the
activation energy for crystallization, m is the Avrami
exponent and d~ and d~ are the film thicknesses of the
crystalline and amorphous layers respectively
t~rameter E vapora~d Aput~red
E~,~, 1.39(5)eV atom t 2.7(l)eV atom
m 1.5(2) 3(1)
Fig. 6. TEM photograph of an amorphous InSb laver
d~/d. 1.08(4) 1.015(5)
prepared by sputtering.
5. 237
sputtered layer is higher than in the evaporated during sputtering. Before crystallization can start,
layer. argon first has to be removed.
Until now, transient nucleation effects have In conclusion, it has been shown that the
been neglected, since the Avrami analysis crystallization process in evaporated InSb pro-
neglects the incubation time that is needed to ceeds by three-dimensional diffusion-limited
reach a steady state nucleation rate. This is justi- growth on existing nuclei. In sputtered InSb
fied for evaporated InSb, since nuclei are already the crystallization proceeds by nucleation and
present. For sputtered InSb one has to take care. subsequent three-dimensional diffusion-limited
However, Gravesteijn has shown that it is pos- growth. The high activation energy in sputtered
sible to crystallize a thin InSb film near the melt- films is mainly due to the high barrier against
ing point in 15 ns [1]. The incubation time at that nucleation in these layers.
temperature will be even shorter. Also, a non-
negligible incubation time would have turned up
in the Arrhenius plot of the crystallization time as Acknowledgments
a deviation from linear behaviour. No such devia- The author gratefully acknowledges Mr. P. van
tion has been observed for crystallization times der Werf and Mr. N. Dreesen for the preparation
larger than 1 ms. Therefore it is not unreasonable of the samples. Dr. J. Coombs, Dr. A. Holtslag
to neglect the incubation time due to transient and Dr. G. Thomas are acknowledged for
nucleation in sputtered InSb also. critically reading the manuscript.
Now we can estimate the activation energies
for the nucleation step and the growth separately.
It can be deduced straightforwardly that the acti- References
vation energy for a sputtered film can be written
as [3, 1 1] D. J. Gravesteijn, Appl. Opt., 27(1988) 736.
C. J. van der Poel, J. Mater. Res., 3 (1988) 126.
Eac, spur= ( E n ~- E~)/rn~p~ L. G. Pittaway, Br. J. AppL Phys., 15 ( 19641967.
M. Avrami, J. ('hem. Phys., 9 (1941 ) 177.
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North-Holland, Amsterdam, 1971t, p. 47 I.
E act evap = Eg/t~lcv.lp A. H. M. Holtslag and P. M. L. O. Scholte, to be
published.
where E n and Eg are the activation energies for J. C. Maxwell Garnett, l'hil. 7)ans. R. 3oc. Lond., 203
nucleation and growth respectively and rn~p~ and 119114) 385.
rn~v,~ are the Avrami exponents of the sputtered
p N. A. Goryunova, The ('hemist O, ~1 Diamond-like Semi-
and evaporated films respectively. From this we conductors, Chapman and Halk London. 1965, p. 114.
9 M. C. Weinberg, J. Non-('ryst. Solids, 70 1985) 253.
find Eg = 2.113) eV atom i and E n = 612) eV
10 F. J. A. M. Greidanus, B. A. J. Jacobs. F. J. A. den
atom 1. The barrier against nucleation in the Broeder, J. H. M. Spruit and M. Rosenkranz, Appl. f'hvs.
sputtered film is very high. This is most likely due Lett., 54 (1989) 963.
to the argon that is incorporated in the film 11 E. A. Marseglia, .I. Non-(rvst. Solids, 41 1981)) 3 I.