共查询到20条相似文献,搜索用时 31 毫秒
1.
P. N. Vinod 《Journal of Materials Science: Materials in Electronics》2009,20(10):1026-1032
The SEM and specific contact resistance measurements of the Ag metal contact formed by applying a fire-through process on
the shallow emitter region of the silicon solar cell have been investigated. The metal contact consists of screen-printed
Ag paste patterned on the silicon nitride (Si3N4) deposited over the n+-Si emitter region of the solar cell. The sintering step consists of a rapid firing step at 800 °C or above in air ambient.
This is followed by an annealing step at 450 °C in nitrogen ambient. It enables to drive the Ag metal paste onto the Si3N4 layer and facilitates the formation of an Ag metal/p-Si contact structure. It serves as the top metallization for the screen-printed
silicon solar cell. The SEM measurement shows that sintering of the Ag metal paste at 800 °C or above causes the Ag metal
to firmly coalesce with the underlying n+-Si surface. A thin layer of conductive glassy layer is also presents at the interface of the Ag metal and n+-Si surface. The electrical quality of the contact structure was characterized by measuring the specific contact resistance,
ρ
c
(in Ω-cm2) using the iteration technique based on the power loss calculation for the solar cell. It shows that best value of ρ
c
= 2.53 × 10−5 Ω-cm2 is estimated for the Ag metal contact sintered at temperature above 800 °C. This value of ρ
c
is two orders of magnitude lower than the typical value of ρ
c
= 3 × 10−3 Ω-cm2 reported previously for the Ag contacts of the solar cell. Such low value of ρ
c
for the Ag metal contacts indicates that fire-through process results in excellent ohmic properties. The plot of the ρ
c
versus impurity doping level (N
s
) shows that measured value of the ρ
c
follows a linear relationship with the N
s
as predicted by the theory for the heavily doped semiconductor surface. Hence, carrier injection across the Schottky barrier
height is quite appropriate to explain the observed ohmic properties of the Ag metal contacts on the n+-Si surface of the silicon solar cell.
相似文献
P. N. VinodEmail: |
2.
P. N. Vinod 《Journal of Materials Science: Materials in Electronics》2011,22(9):1248-1257
The specific contact resistance of the screen-printed Ag contacts in the silicon solar cells has been investigated by applying
two independent test methodologies such as three-point probe (TPP) and well-known transfer length model (TLM) test structure
respectively. This paper presents some comparative results obtained with these two measurement techniques for the screen-printed
Ag contacts formed on the porous silicon antireflection coating (ARC) in the crystalline silicon solar cells. The contact
structure consists of thick-film Ag metal contacts patterned on the top of the etched porous silicon surface. Five different
contact formation temperatures ranging from 725 to 825 °C for few minutes in air ambient followed by a short time annealing
step at about 450 °C in nitrogen ambient was applied to the test samples in order to study the specific contact resistance
of the screen-printed Ag metal contact structure. The specific contact resistance of the Ag metal contacts extracted based
on the TPP as well as TLM test methodologies has been compared and verified. It shows that the extraction procedure based
on the TPP method results in specific contact resistance, ρ
c
= 2.15 × 10−6 Ω-cm2 indicating that screen-printed Ag contacts has excellent ohmic properties whereas in the case of TLM method, the best value
of the specific contact resistance was found to be about ρ
c
= 8.34 × 10−5 Ω-cm2. These results indicate that the ρ
c
value extracted for the screen-printed Ag contacts by TPP method is one order of magnitude lower than that of the corresponding
value of the ρ
c
extracted by TLM method. The advantages and limitations of each of these techniques for quantitatively evaluating the specific
contact resistance of the screen-printed Ag contacts are also discussed. 相似文献
3.
P. Narayanan Vinod 《Journal of Materials Science: Materials in Electronics》2008,19(7):594-601
The front grid contact is particularly important and requires a low contact resistance which represents the resistance associated
with the barrier at the interface of the metal and semiconductor contact structure. Often applied metal contacts are fired
at a higher temperature (typically above 700 °C) in air ambient, which produces ohmic contact on both surface of the photovoltaic
device. The specific contact resistance is one of the important device parameter on studying the interfacial properties of
the metalization system. Therefore, a reliable methodology to assess the ohmic losses of the applied metal contact structure
is required. It shows that it is rather simple and reliable to assess the electrical quality of the applied metal contacts
by quantifying the total ohmic losses of the solar cell associated with the various resistive components of the solar cell
normalized to unit cell area. It has been recently demonstrated that with a new experimental procedure, namely iteration method
based on the calculation of power loss (ICPL) associated with the contact resistance of the front Ag thick-film metal contacts,
a much reliable value of the specific contact resistance of the order of ≅10−5 Ω cm2 can be extracted for the planar ohmic contacts. In this work, the specific contact resistance of the planar ohmic contacts
formed on the heavily doped n+ region of the solar cells were studied on large number of finished cells by two independent methods: (i) standard three-point
probe (TPP) and (ii) iteration technique based on the calculation of the power loss (ICPL) associated with the contact resistance
of the front Ag contacts of the solar cell normalized to unit cell area. It shows that the value of specific contact resistance
measured by both methods are desirably much lower than the expected value of 10−3 Ω cm2 for the screen-printed Ag metal contacts of the photovoltaic cells used for the A.M. 1.5 applications. Using the iteration,
each resistive components of the solar cell normalized to unit cell area were directly evaluated. It is shown that by combining
the measurements of specific contact resistance of the planar ohmic contacts and ohmic losses of the cell, it gives a direct
and non-destructive diagnostic tool to qualitatively check the electrical quality of the applied Ag metal contacts.
相似文献
P. Narayanan VinodEmail: |
4.
P. N. Vinod 《Journal of Materials Science: Materials in Electronics》2010,21(7):730-736
Porous silicon has been considered as a promising optoelectronic material for developing a variety of optoelectronic devices
and sensors. In the present study, the electrical properties and metallurgical process of the screen-printed Ag metallization
formed on the porous silicon surface of the silicon solar cell have been investigated. The contact structure consists of thick-film
Ag metal contact patterned on the top of the porous silicon surface. The sintering process consists of a rapid firing step
at 750–825 °C in air ambient. It results in the formation of a nearly perfect contact structure between the Ag metal and porous
silicon/p-Si structure that forms the top metalization for the screen-printed silicon solar cells. The SEM picture shows that
Ag metal firmly coalesces with the silicon surface with a relatively smooth interfacial morphology. This implies that high
temperature fire-through step has not introduced any signs of adverse effect of junction puncture or excessive Ag indiffusion,
etc. The three-point probe (TPP) method was applied to estimate the specific contact resistance, ρ
c (Ω-cm2) of the contact structure. The TPP measurement shows that contact structure has excellent ohmic properties with ρ
c = 1.2 × 10−6 Ω-cm2 when the metal contact sintered at 825 °C. This value of the specific contact resistance is almost three orders of magnitude
lower than the corresponding value of the ρ
c = 7.35 × 10−3 Ω-cm2 obtained for the contact structure sintered at 750 °C. This improvement in the specific contact resistance indicates that
with increase in the sintering temperature, the barrier properties of the contact structure at the interface of the Ag metal
and porous silicon structure improved which in turn results a lower specific contact resistance of the contact structure. 相似文献
5.
Santosh S. Hosmani Ralf E. Schacherl Eric J. Mittemeijer 《Journal of Materials Science》2009,44(2):520-527
The microstructure of the compound (“white”) layer formed on the surface of Fe–4wt.%V alloy, by nitriding in a gas mixture
of ammonia and hydrogen at 580 °C, has been investigated by employing light and scanning electron microscopy, X-ray diffraction
and electron probe microanalysis. The compound layer is dominantly composed of γ|-Fe4N nitride. Quantitative analysis of the composition data demonstrated that V is present in the compound layer as VN precipitates,
i.e. V is not taken up significantly in (Fe, V) nitrides. A mechanism for compound-layer formation has been proposed.
相似文献
Santosh S. HosmaniEmail: |
Ralf E. Schacherl (Corresponding author)Email: |
Eric J. MittemeijerEmail: |
6.
Dong-Il Shin François Gitzhofer Christian Moreau 《Journal of Materials Science》2007,42(15):5915-5923
Predicting “in-service” lifetime of ceramic thermal barrier coatings (TBCs) is difficult due to the inherent brittle nature
of ceramics used. Therefore, the study of metal-based thermal barrier coatings (MBTBCs) has been initiated to challenge the
current problems of ceramic-based TBCs (CBTBCs) and create a new generation of thermal barrier coatings (TBCs). In this work,
nano/amorphous structured MBTBCs, for use in internal combustion engines, have been produced using high frequency induction
plasma spraying (IPS) of iron-based nanostructured alloy powders. Coatings were deposited by IPS using various spray parameters
and heat treated up to 850 °C to study the thermal stability of the coating. The thermal diffusivity (α) properties of MBTBCs were measured using a laser flash method. Density (ρ) and specific heat (C
p
) of the MBTBCs were also measured for calculating thermal conductivity (k = αρC
p
).
相似文献
Dong-Il ShinEmail: |
7.
Tadashi Ishigaki Kenji Toda Tomoaki Watanabe Naonori Sakamoto Nobuhiro Matsushita Masahiro Yoshimura 《Journal of Materials Science》2008,43(14):4749-4752
In order to synthesize compounds of various Perovskite-related structures, we have utilized a novel “melt synthesis technique”
for phosphors rather than the conventional solid state reaction techniques. The solid state reactions require multi-step processes
of heating/cooling with intermediate grindings to make homogeneous samples. However, for the melt synthesis, it is possible
to make a homogeneous sample in a single step within a short period of time (1–60 s) due to the liquid phase reaction in the
molten samples, which were melted by strong light radiation in an imaging furnace. In this study, we have prepared a red-phosphor
CaLaGaO4:Eu3+ which has a perovskite—related layered K2NiF4 structure. Well-crystallized CaLa1−x
Eu
x
GaO4 samples with the K2NiF4 structure have been obtained up to x = 0.25, but there was the formation of an olivine phase when x = 0.5–1.0. The red emission at 618 nm increased with the increasing value of x up to x = 0.25.
相似文献
Tadashi IshigakiEmail: |
Masahiro Yoshimura (Corresponding author)Email: |
8.
Spark Plasma sintering (SPS) technique allows powders to be compacted at low temperature with a very short holding time. The
powder loaded into a carbon die is heated via direct current pulses and simultaneously submitted to an uni-axial pressure
of several MPa. Full density of the sample is achieved within minutes. This process is used to study Cu and Ag metals interactions
with V2O5 oxide. Syntheses of M
x
V2O5 phases (M = Cu, Ag) have been achieved within minutes. Thus Cu and Ag atoms penetrate microcrystals of V2O5 oxide at a high speed, shearing its crystal network and simultaneously rebuilding the crystal structures of the prototype
networks β, β′, ε or δ M
x
V2O5. To account for the formation of these phases identified by X-ray diffraction, structural mechanisms are proposed. Cu and
Ag atomic diffusion parameters have been determined from energy dispersive X-ray spectroscopy (EDX) and electron micropobe
analysis (EPMA) line scans. High values of diffusion coefficients have been determined. Cu atoms diffuse faster than Ag, D
Cu ≈ 4 × 10−8 m2/s and D
Ag ≈ 0.5–1 × 10−9 m2/s in ε and δ M
x
V2O5 phases, respectively. Their formation may also be used as a model for further investigations into the diffusion mechanisms
of atoms in solids and for a better understanding of the SPS process.
相似文献
Jean GalyEmail: |
9.
The microstructure of a translucent keatite solid–solution glass–ceramic (keatite s.s.) of the LAS-system (Li2O–Al2O3–SiO2) has been analyzed with SEM, AFM, XRF, XRD, and TEM. The glass–ceramic consists mainly of keatite s.s. with minor secondary
phases such as zirconium titanate, gahnite and probably rutile. Furthermore the resistance to temperature differences (RTD)
of this glass–ceramic was investigated. It is shown that, in spite of the relatively high coefficient of thermal expansion
(CTE) of about 1 × 10−6 K−1, an improved RTD can be achieved by special ceramization treatment. With this, compressive stresses in the first 100 μm to
150 μm are induced. These stresses can presumably be contributed to a difference in CTE between the surface-near zone and
the bulk. Said CTE difference is caused by chemical gradients of CTE-relevant elements, such as Zn, K, and supposedly additional
alkali elements such as Li. These stresses are useful to increase the strength and application range of glass–ceramics based
on keatite s.s.
相似文献
Christian RoosEmail: |
10.
Raghupatruni Venkata Satya Prasad Gandham Phanikumar 《Journal of Materials Science》2009,44(10):2553-2559
Melt spinning technique was used to synthesize Ni2MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis
of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of
Ni2MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni2MnGa with a size range of 10–20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel
speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite
and γ (gamma) phases. Amorphous phase, Ni2MnGa nanoparticles, and the martensite phase are analyzed in detail.
相似文献
Raghupatruni Venkata Satya PrasadEmail: |
Gandham Phanikumar (Corresponding author)Email: |
11.
Alexander Klushin Alexander Golubov Werner Prusseit Hermann Kohlstedt 《Journal of Low Temperature Physics》1997,106(3-4):265-269
In order to optimize the series array performance of Y Ba2Cu3O7−x (YBCO) grain boundary shunted junctions, a method to determine and control the junction resistance Rs and Au/YBCO contact resistivity ρ
c
has been developed. 200 nm thick c-oriented YBCO films were grown by intermittent thermal coevaporation on bicrystal yttria-stabilized
zirconia substrates. A gold contact overlayer of thickness dn was deposited in situ. Normal junction resistances have been measured as a function of dn and shunt width w. It was shown that, in accordance with theoretical estimates, the junction shunt resistance is essentially
controlled by the c-axis Au/YBCO interface specific resistance and scales as
. The product ρ
c
ρ
n
≃ 3.10−14 Ω2
cm
3 was estimated from the experimental data, leading to ρ
c
≈ 10−8 Ωcm
2 for typical values of ρ
n
for gold thin films. 相似文献
12.
• | Drawing on the transaction costs, strategic capability and the strategic cognition perspectives, our study seeks to examine whether and how firms’ strategic orientations at the business level influence the entry mode choices that firms make in accessing foreign markets. |
• | The study uses a sample of 332 foreign market entries made by 62 U.S. based firms over a period of 6 years to test hypotheses linking firm business level strategy to the choice of foreign entry modes. |
• | Findings indicate that Prospectors are more likely to choose equity-based foreign market entry modes than Defenders. In addition, Prospectors favor full-ownership entry modes, namely, greenfield investments and full acquisitions, over shared-ownership modes such as joint ventures and partial acquisitions. |
Deepak K. DattaEmail: |
13.
Marc Nikolussi Andreas Leineweber Eric Jan Mittemeijer 《Journal of Materials Science》2009,44(3):770-777
Massive, pure cementite layers were grown on ferrite substrates by nitrocarburising in a dedicated NH3/H2/CO/N2 containing gas atmosphere at temperatures in the range of 783–843 K. From the parabolic layer-growth constants, an “apparent”
activation energy for cementite-layer growth of 109 ± 12 kJ/mol was obtained. This “apparent” activation energy can be subdivided
into a positive contribution due to the activation energy for (tracer) diffusion of carbon in cementite and a negative contribution
due to the temperature dependence of the difference of the carbon activity in cementite at the surface and at the interface
cementite/ferrite.
相似文献
Andreas LeineweberEmail: |
14.
Antolii Belous Oleg V’yunov Maya Glinchuk Valentin Laguta Darko Makovez 《Journal of Materials Science》2008,43(9):3320-3326
Barium titanate, which is characterized by a positive temperature coefficient of resistance (PTCR), is widely used in practice.
At the same time, it is unknown why only a small percentage of the introduced donor dopant takes part in the formation of
PTCR effect, which phases appear at grain boundaries, how the introduced acceptor dopants affect the properties of grains.
Elucidation of the above questions is of considerable scientific and practical interest. It has been shown that the phases
Bа6Ti17O40 and Y2Ti2O7 precipitate on grains of barium titanate doped with donor dopant (yttrium). We identified paramagnetic impurities (iron, manganese,
chromium) in starting reagents. These impurities can occupy titanium sites. Therefore, the part of the donor dopant that is
spent on the charge exchange of acceptor dopants does not participate in the charge exchange of titanium Ti4+ → Ti3+, which is responsible for the appearance of PTCR effect in barium titanate. It has been found that an extra acceptor dopant
(manganese) is distributed mainly at grain boundaries and in the grain outer layer. It has been shown that manganese ions
introduced additionally (as acceptor dopants) increase the potential barrier at grain boundaries and form a high-resistance
outer layer in PTCR ceramics. The resistance of grains, outer layers, and grain boundaries as a function of the manganese
content has been investigated.
相似文献
Oleg V’yunovEmail: |
15.
A quenching apparatus for the gaseous products of the solar thermal dissociation of ZnO 总被引:1,自引:0,他引:1
D. Gstoehl A. Brambilla L. O. Schunk A. Steinfeld 《Journal of Materials Science》2008,43(14):4729-4736
Rapid cooling for avoiding the recombination of Zn vapor and O2 derived from the solar thermal dissociation of ZnO is investigated using a thermogravimeter coupled to a quenching apparatus.
The ZnO sample, which is placed in a cavity receiver and directly exposed to concentrated solar irradiation, underwent dissociation
in the temperature range 1,820–2,050 K at a rate monitored by on-line thermogravimetry. The product gases were quenched by
water-cooled surfaces and by injection of cold Ar at cooling rates from 20,000 to 120,000 K/s, suppressing the formation of
ZnO in the gas phase and at the walls. Zinc content of the collected particles downstream varied in the range 40–94% for Ar/Zn(g)
dilutions of 170 to 1,500.
相似文献
D. GstoehlEmail: |
16.
Maria Cristina Larciprete Danilo Dini Raffaella Ostuni Concita Sibilia Mario Bertolotti Xavier Alvarez-Mico Rafael Gomez-Bombarelli Mirko Cappeddu Michael Scalora Mark J. Bloemer 《Journal of Materials Science》2007,42(18):7866-7871
We present our results on a newly synthesized bis-phenylazo derivative, namely bisperfluoroalkylsulfonylamino- arylazomethylene-triphenyl-phosphorane
(BAM-TPP). Thin films of BAM-TPP in polymethylmethacrylate (PMMA) matrix were prepared. The films (thickness, d < 60 μm) were exposed to UV-vis light with variable intensity in order to stimulate the photochromic reaction of BAM-TPP.
The resulting absorption changes of the BAM-TPP/PMMA films were investigated by spectrophotometry. The absorption spectra
reveal that BAM-TPP molecules in PMMA undergo photoisomerization with resulting decrease of absorbance in the range 500–700 nm.
Finally, the time response of film transmittance at 514 nm under increasing CW light intensity was recorded, showing that
the reverse photochromic process brings the absorbance back to its pristine value. The obtained films thus proved to be suitable
for optical switching applications.
相似文献
Maria Cristina Larciprete (Corresponding author)Email: |
Danilo DiniEmail: |
Michael ScaloraEmail: |
17.
Hybrid organic–inorganic materials based on polypyrrole and 1,3-dithiole-2-thione-4,5-dithiolate (DMIT) containing dianions 总被引:1,自引:0,他引:1
Antonio Gerson Bernardo da Cruz James Lewis Wardell Ana M. Rocco 《Journal of Materials Science》2008,43(17):5823-5836
The synthesis of hybrid materials by electropolymerization of pyrrole and inorganic complexes based on the DMIT ligand (1,3-dithiole-2-thione-4,5-dithiolate),
e.g. [NEt4]2[M(DMIT)
n
] (M = Ni, Pd or Pd, n = 2; M = Sn, n = 3], in acetonitrile solution is reported. Spectroscopic data showed that DMIT-containing anions, [M(DMIT)
n
]2−, were inserted into the polypyrrole framework without chemical modification during the electropolymerization process. Cyclic
voltammetry showed that materials obtained were electroactive, undergoing redox processes related to both the conducting polymer
and the counteranions. The electrochemical results also suggest that, in the case of the transition metal containing films,
the counteranions are not trapped in the PPy matrix but undergo anion exchange during the redox cycle of PPy. However, an
opposite behaviour was observed with the film with [M(DMIT)
n
]2−. The films exhibit good thermal stabilities and have conductivity values expected for semiconductors. This study of these
hybrid materials highlights the importance of targeting specific materials for specific applications.
相似文献
Antonio Gerson Bernardo da CruzEmail: |
18.
C. Park X. Long S. Haberman S. Ma I. Dutta R. Mahajan S. G. Jadhav 《Journal of Materials Science》2007,42(13):5182-5187
This paper reports on the application of a miniaturized impression creep test to measure the creep behavior of pure polycrystalline
Sn, and compares the results to compression creep data on the same sample, in order to experimentally determine a scaling
constant to formulate the equivalent uniaxial creep constitutive law from the impression creep data. The creep parameters
determined via impression and compression creep are found to be identical, with n ∼ 5 and Q ∼ 42 kJ/mol, indicating that over
the tested stress–temperature range, the mechanism is core diffusion controlled dislocation creep. In conjunction with results
from previous modeling work, a single conversion factor, κn/C, which depends on material properties, is shown to be usable for converting the impression creep relation to the equivalent
uniaxial creep relation, and the experimentally determined value of κn/C for polycrystalline Sn is very close to that obtained via modeling.
相似文献
I. DuttaEmail: |
19.
James E. Kennedy Declan M. Devine John G. Lyons Luke M. Geever Clement L. Higginbotham 《Journal of Materials Science》2009,44(3):889-896
The work undertaken investigates the spectral, thermal and surface characteristics of a random styrene butadiene rubber (SBR)
with monomeric graft(s) of acrylic acid (AA), N-vinyl-2-pyrrolidinone (NVP) or N-isopropylacrylamide (NIPAAm) synthesised using UV polymerisation. The grafted materials were characterised by differential
scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), attenuated total reflectance infrared Fourier
transform spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Thermograph analysis has shown an endothermic transition
occurring at ~75 °C for all random SB-g-NVP copolymers, whereas the T
g value for random SB copolymer was found at 60 °C, thus suggesting that a chemical reaction between styrene and NVP had occurred.
Similar thermal profiles to that of random SB-g-NVP copolymers were evident when random SB was UV polymerised with AA. When
NIPAAm was grafted onto random SB, a notable exothermic transition was evident in all samples tested using DSC. It was established
using MDSC that this exothermic transition was caused by the breakdown of crosslinks as a result of UV polymerisation.
相似文献
James E. KennedyEmail: |
Declan M. DevineEmail: |
John G. LyonsEmail: |
Luke M. GeeverEmail: |
Clement L. Higginbotham (Corresponding author)Email: |
20.
When tin transforms from the β to α phase it undergoes a dramatic process. The crystal structure changes from tetragonal to
diamond cubic; the material properties transform from a ductile metal to a brittle semiconductor; however the most notable
change is the decrease in density, which goes from 7.31 g/cm3 to 5.77 g/cm3 [1]. It can be calculated that this decrease in density is equivalent to an increase in volume of about 26% [2]. Due to this volume increase and the brittleness, the transformed material progressively cracks and eventually falls apart.
This could potentially be a threat for tin-rich alloys used in electronics in low temperature applications. Due to the optimal
transformation temperature of approximately 240 K and the long time required for the transformation, a direct observation
of the phenomenon has not been possible. This study proposes a new method for observing the β/α transformation in situ using
a time-lapse photographic technique. This study concentrates on pure tin, but the applicability of the method opens new possibilities
for studying the phenomenon for other tin alloys, such as the two commonly encountered eutectics of SnCu and SnAgCu.
相似文献
D. Di MaioEmail: |