DSpace Collection:http://inet.vidyasagar.ac.in:8080/jspui/handle/123456789/10832024-03-28T17:40:48Z2024-03-28T17:40:48ZPreparation and characterization of some Binary II-VI Nanocrystalline CompoundsSamanta, Aninditahttp://inet.vidyasagar.ac.in:8080/jspui/handle/123456789/62732021-10-28T09:47:55Z2021-10-04T00:00:00ZTitle: Preparation and characterization of some Binary II-VI Nanocrystalline Compounds
Authors: Samanta, Anindita
Abstract: i
Nanotechnology is an emergent technique for developing our global life in versatile arena
such as engineering, electronics and communication, power generation, disease detection and
treatment etc. Nanoparticles exhibit potentiality for application in multi-functional nano-
devices that are helpful in optoelectronics, spintronics, chemical and biosensors, drug
delivery, catalysis, etc. Zinc Oxide (II-VI metal oxide semiconductor) and its modified
nanocrystalline compounds have generated a growing interest among researchers due to the
ease in tuning the electrical, optical, multiferroic properties of the compounds suited to the
needs of the specific devices. ZnO is an n-type direct wide band gap (3.37 eV)
semiconductor with high exciton binding energy of 60 meV, high electron mobility, high
redox potential, stable chemical composition and have strong luminescence at room
temperature. It reveals a strong excitonic emission peak in UV region mainly due to the
recombination of free excitons. Attracting luminescent property of ZnO, positions it as a
promising candidate for various optoelectronic devices. ZnO has promising applications in
chemical sensor, low voltage phosphor material, varistor, solar cells and photocatalysis etc.
Dilute magnetic semiconductor (DMS), wherein both the semiconducting and magnetic
properties coexist, are in high demand in the electronic industry. Application capability of
diluted magnetic semiconductors in spintronic and multiferroic devices has drawn an intense
interest of recent researchers. Multiferroicity in DMS is one of the necessary requirements
for spintronic device application. The doping of transition metal ions (Mn, Co, Ni, V and Fe)
in ZnO matrix develops room temperature ferromagnetism (RTFM) in addition to the change
in band gap and other associated properties and is a strong member in the DMS category of
materials. Ferromagnetic properties in some non-magnetic element like magnesium (Mg)
and lithium (Li) doped ZnO also have been observed. Although, ferromagnetism in transition metal modified ZnO is forecasted in the year 2000, reports on the magnetoelectric (ME)
coupling and multiferroicity of these compounds are very few.
ii
The degree of magnetization in these DMS compounds depends on the particle size and
shape of the nanoparticles which vary according to the growth technique. TM doped ZnO
nanostructures can be synthesized using various growth techniques, such as co-precipitation,
sol-gel, hydrothermal, microemulsion
,
pyrosol and electrochemical method. The chemical
precipitation and sol-gel method result in the synthesis of the ZnO based DMS nanoparticles
with controlled sizes (10-30 nm) and shapes and are inexpensive and easy compared to other
classical methods of synthesis.
Further, the effluents of textile industries with major amounts of non-fixed dyes, azo dyes
and inorganic salts are a major source of environment pollution. Destruction of industrial
pollutants through photocatalytic degradation is considered to be a trendy method. Nanoscale
wide band gap semiconductors are attracting worldwide attention for their enhanced
photocatalytic degradation properties. Suitably doped ZnO nanostructures have a bright
prospect as a fruitful photocatalyst for the degradation of organic pollutants and furthering
sustainable ecology. Mg
2+
doping in ZnO matrix is expected to accomplish such enhanced
photocatalytic activities. Addition of rare earth elements in some compounds results in better
optical and photocatalytic effects. Recently, it has also been conveyed that optically active
rare earth Nd
3+
ion doped ZnO nanoparticles perform as interesting photocatalyst for the
purification of pollutant water.
The main focus of this research exertion is to establish doped ZnO nanoparticles as
potential candidate for optoelectronic devices and striking DMS material for spintronic and
multiferroic applications. We thus inspired to study the optical, electrical, magnetic and
magnetoelectric coupling properties of ZnO nanoparticles synthesized through simple and
inexpensive chemical precipitation and sol-gel technique using hydroxyoxalate type materials. Also the other important objective has been to study the prospect of modified ZnO
as an enriched photocatalyst for degradation of aqua pollutants.
In the present work, pure and doped ZnO nanoparticles have been synthesized
successfully through the chemical precipitation and sol-gel technique. Ni, Co, Fe, Mg and
Nd doped ZnO nanoparticles were characterized by structural, optical, electrical, magnetic
and ME characterization. All the prepared materials crystallize with hexagonal wurtzite
structure. Average crystallite size of the fabricated nanopowders remained in the range of
15-30 nm. The nanocrystalline nature and self-organization of the nanoparticles have been
confirmed through SAED study. Chemical bonding and composite elements of the samples
was detected through FTIR and EDX characterization. The variations of band gap in case of
doped ZnO were deliberated according to the Moss-Burstein band filling effect, which is
generally observed in n-type semiconductors. The intense fluorescence emission at 367 nm
has been discussed through exciton recombination corresponding to near band edge emission.
The visible emission bands have been assigned to the defect states likes oxygen vacancies
and zinc interstitials. The tuned optical properties of doped ZnO make it suitable for
application in photonic and optoelectronic devices. All these materials have low dielectric
loss. Ferroelectric loops observed in these compounds can be explained through the
interaction of dipoles in the non centro-symmetric structure. The origin of observed
ferromagnetism in doped ZnO nanocompounds at low temperature is correlated to the
relevant mechanisms referred in the literature based on bound magnetic polarons (BMP),
oxygen vacancies and zinc interstitials. The variation of room temperature ME voltage
coefficient as function of magnetic field has been studied to investigate the interplay between
charge carriers and spin ordering. The TM doped ZnO nanoparticles exhibit a strong ME
coupling coefficient which facilitates their application in multiferroic devices. It has been
shown through various characterizations that the doped ZnO nanocompounds are superior for various photonic, spintronic, magnetoelectric and multiferroic devices (tunnel magneto-
resistance, magnetic sensor, multiple state memory devices).
Photocatalytic reactions are processed through OH
•
and O
2
•
radicals created on the
surface of Mg and Nd modified ZnO nanoparticles. Photocatalytic activity enhances with
higher doping concentration due to separation efficiency of the electron–hole pairs and
modifications of physical and chemical properties. Both band gap energy and crystallite size
are monitoring factors of photocatalytic performance. The observed superior photocatalytic
properties in the Mg and Nd doped ZnO nanoparticles make them promising candidates for
efficient sunlight-assisted photocatalytic effect, self-cleaning and photovoltaic applications.
The prepared Mg and Nd doped ZnO nanoparticles are found to have sunlight assisted
photcatalytic degradation property with a rate constant far higher to that of other II-VI
semiconductor based compositions and have the capability to effectively and promptly clean
the waste water from its dye based contaminants.2021-10-04T00:00:00ZGrowth and characterization of SnS nanostructured materials and Its applicationsRana, Chandanhttp://inet.vidyasagar.ac.in:8080/jspui/handle/123456789/62712021-09-30T10:13:46Z2021-08-17T00:00:00ZTitle: Growth and characterization of SnS nanostructured materials and Its applications
Authors: Rana, Chandan
Abstract: Semiconducting materials are promising materials in different field of nanoscience
and technology. Tin Sulfide (SnS) is a significant and functional material in the
semiconductor engineering. Considering the importance and various applications of SnS
nanocrystals the work is mainly planned to grow SnS nanocrystals in a simple and cost
effective way. The research works cover the growth, characterization and applications of SnS
nanocrystals. The grown nanomaterials are applied in ethanol Gas Sensor, Si based
Heterojunction Solar Cells and natural Dye Sensitized Solar Cells. The grown nanomaterials
are also used to investigate the molecular interaction with protein.
The SnS nanoparticles are grown with the variation of growth conditions as well as
growth process to apply the materials in device fabrication. The effects of various growth
conditions such as growth time, growth temperature, doped as well as bio synthesis on the
growth of SnS nanocrystals have been investigated. The grown samples have been
characterized structurally through X- ray diffraction (XRD), transmission electron
microscopy (TEM), field emission scanning electron microscopy (FESEM), atomic force
microscopy (AFM) and selected area diffraction (SEAD). The elemental compositions of the
grown samples were analyzed through EDAX analysis. The optical properties of the grown
materials have been investigated through UV-VIS absorption spectroscopy and
photoluminescence (PL) spectroscopy. The optical band gap of samples has been calculated
from optical absorption spectra.
We have successfully synthesized SnS nanoparticles in a simple cost effective
chemical reduction method by varying growth time i.e 3 hours to 14 hours. The grown
samples have been ultra-sonicated in ethanol. The dispersed sample has been characterized
structurally and optically. The crystallite size increases with increase of growth time. The
band gap is maximum for 3h grown sample and decreases for samples grown for longer time. Photoluminescence spectra show possible defect states. Energy dispersive X-ray analysis
shows that stoichiometry is well maintained for sample grown for 7h.
SnS nanoparticles have been synthesized by simple wet chemical precipitation
method using triethylamine (TEA) at room temperature. The grown samples were
characterized by X-ray diffraction, Transmission electron microscopy (TEM), Field emission
Scanning electron Microscopy (FESEM), Optical absorption spectra and PL. XRD image
shows that the particles are orthorhombic structure. The TEM image shows that particles are
chain-like shape and crystal size is about 20 nm. FESEM result also support the TEM result.
AFM image shows that the surface roughness of the as prepared SnS nanocrystals is about
7.39 nm. Optical absorption study determines the band gap of the grown sample is about 1.76
eV. PL spectra of SnS shows an emission peak at 698.79 nm which is due to band to band
transition.
SnS nanocrystals were also synthesized by simple wet chemical precipitation method
with the variation of growth temperature. The growth temperature was varied from 14
70
0
C. XRD results shows that the crystals are orthorhombic in phase. TEM images indicate
that the grain sizes are almost spherical within the range 5 nm to 10 nm. A decrease in band
gap is observed as particle size increase with increase of growth temperature. The
temperature variation of p-type SnS nanocrystals indicates electrical conductivities were
ranging from 0.020 to 0.037 Ohm
10
13
cm
−3
to 1.54 × 10
14
cm
−3
.
-1
cm
−1
and carrier concentrations were varying from 7.05 ×
SnS and SnS-Ag nanocomposite were synthesized by cost effective solvothermal
technique. The as synthesized materials have been studied by structurally and optically
through various tools and techniques. Structural characterization was investigated through by
X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Field Emission
Scanning Electron Microscopy (FESEM). Elemental compositions were confirmed by
0
C to Electron Diffraction X-ray Analysis (EDAX). The Optical properties were characterized by
UV-VIS absorption spectra, Photoluminescence spectra (PL) and Time Correlated Single
Photon Counting (TCSPC). XRD results suggest that the samples are in orthorhombic
structure in phase. The particle size has been estimated from TEM study. The calculated the
band gap values were 2.04 eV and 1.80 eV of SnS and SnS-Ag nanocomposite respectively.
A decrease in the band gap energy of SnS-Ag nanocomposite was observed compared to SnS.
Pure SnS, Fe doped SnS and Mn doped SnS nanocrystals were prepared by simple
chemical precipitation method. The structural and optical properties of the as prepared
nanoparicles were studied. XRD results indicate the orthorhombic crystal phase of the as
prepared samples. TEM results show that the crystal size increase with increase of doping
and the grain size is greater for Mn doped SnS nanoparticles. A decrease in the band gap of
Mn doped SnS was observed compared to pure as well as Fe doped SnS.
SnS nanoparticles have been used to fabricate different types of devices in a cost
effective way. The as grown time varying SnS NPs are deposited on glass for the fabrication
of gas sensor. The sensing measurements were done at operating temperature ranging
between 250
0
C and 300 °C for SnS based sensor. Here we have chosen three operating
temperature i.e. 250 °C, 275 °C and 300 °C. The sensitivity in dry air conditions becomes
maximum for 7 hours SnS sample at 300 °C. The percentage of sensitivity of 7 hours samples
at 300°C was 61%. The gas sensing properties has been studied in dry air as well as humid
conditions. The stability of the sensors has been also studied over 4 weeks and this indicates
good stability.
The SnS/Si as well as SnS:Ag/Si heterojunction solar cell has been fabricated. Open
circuit voltage (V
oc
), short circuit current (J
sc
), fill factor (FF) as well as power conversion
efficiency (η) were also calculated. The efficiency of SnS-Ag/Si heterojunction is greater than the SnS/Si heteojunction. The increase in conversion efficiency is due to the scattering
effect from silver (Ag) nanoparticles.
The as grown Fe doped and Mn doped SnS nanocrystals have been applied for
fabrication of dye sensitized solar cell. Anthocyanin is a type of natural dye which was found
in the various leaves of plants, flowers and fruits. These natural dyes are used as photo
sensitizer in the fabricated dye sensitized solar cell. Acalypha Wilkesiana leaf extract was
used as natural dye which can increase the power conversion efficiency of the fabricated solar
cells. The performances of the fabricated dye sensitized solar cell were studied through the
current (I)-voltage (V) study. The open circuit voltage (V
factor (FF) as well as power conversion efficiency (η) were also studied.
oc
), Short circuit current (Jsc), Fill
SnS nanoparticles were also synthesized by the extract of Gymnema Sylvestre leaves
in aqueous medium through green synthesis. The leaves extract of Gymnema Sylvestre plant
have been employed as an efficient capping agent for the synthesis of SnS NPs. Low cost
natural dye sensitized solar cells (DSSCs) based on chemically grown as well as green
synthesized SnS NPs were fabricated. Acalypha Wilkesiana leaf extract was used as the
natural dyes as a photosensitizer. The fabricated dye sensitized solar cell has been
characterized through J-V study. Comparative studies of the efficiencies of the fabricated
solar cell have been investigated. The fill factor, open circuit voltage and short circuit current
density of the fabricated dye sensitized solar cell were also estimated.
Finally, the bimolecular interaction of bovine serum albumin (BSA) with SnS
materials has been studied through different tools and techniques. The BSA-SnS NPs
interaction, complexation formation and conformational changes of protein (BSA) with the
SnS nanoparticles were investigated by microscopic as well as spectroscopic measurements.
The quenching of fluorescence spectra under the association of SnS nanoparticles was used to
study the molecular interaction of bovine serum albumin (BSA) with SnS nanocrystals. The interaction and the formation of SnS@BSA bioconjugate also investigated using optical
spectroscopy measurements. A spontaneous binding process happened in between BSA and
SnS nanocrystals which were confirmed by UV–VIS and fluorescence spectra. A little red
shift in the optical absorption spectra of protein (BSA) was detected due to binding of protein
(BSA) with SnS NPs. The SnS nanoparticles quench the fluorescence spectra of bovine
serum albumin. The Stern–Volmer quenching constant, Hill coefficient (n), nature of binding
as well as binding constant (K
b
) of the BSA – SnS NPs conjugates were also calculated.
The objective of my thesis is to synthesize good quality SnS nanocrystals by cost
effective methods. We have synthesized different sizes of the nanocrystals by changing the
growth conditions as well as growth technique. The nanostructured SnS have been applied in
fabrication of devices as ethanol gas sensor, heterojunction solar cell with Si, dye sensitized
solar cell using natural dye. Also the molecular interaction of SnS nanocrystals with bovine
serum albumin (BSA) is studied. The thesis consists of eight chapters.2021-08-17T00:00:00ZPhotocurrent Generation and Photocatalytic Activity of Some Solution Processable RGO and MoS2 Based Composite MaterialsIbrahim, Sk.http://inet.vidyasagar.ac.in:8080/jspui/handle/123456789/60132021-05-06T09:00:57Z2021-04-19T00:00:00ZTitle: Photocurrent Generation and Photocatalytic Activity of Some Solution Processable RGO and MoS2 Based Composite Materials
Authors: Ibrahim, Sk.
Abstract: The performance of different nano scale materials change when
composite is formed by attaching with different 2 dimensional materials. In my
thesis I have tried to synthesis different reduced graphene oxide (RGO) and
molybdenum disulfide (MoS2) based composite materials by simple low cost,
solution processable and easy to achieve soft chemical route. All the
synthesized composite materials were well characterized structurally and
optically. The solar light induced photo current generation and photocatalytic
activities of these materials were studied in detail.
Solution processable Reduced Graphene Oxide – Zinc Sulfide (RGO-
ZnS) composite has been synthesized by a simple single-step one-pot
solvothermal route and is reported in chapter 2. As- synthesized composite was
characterized structurally and optically. The photo induced charge generation
of RGO-ZnS in solid phase as well as in solution phase has been investigated
under simulated solar light illumination. RGO-ZnS thin film photo detector
shows an excellent photocurrent generation with a high degree of
reproducibility. The photosensitivity (ratio of photo to dark current) of the
detector varies linearly with the light intensity. A remarkable increase of photo-
reduction efficiency of RGO-ZnS compare to controlled-ZnS or controlled-
RGO towards the reduction of 4-Nitrophenol was observed. Chapter 3 reports the solvothermal synthesis of Reduced Graphene Oxide – Cadmium Sulfide (RGO-CdS) nanorod composite. The as synthesized
composite was characterized structurally and optically by XRD, TEM, XPS,
Raman, UV-Vis and PL spectroscopy. The photocurrent generation in large
area thin-film photodetector devise is also reported. The photo catalytic activity
of the composite was examined by the degradation of tetracycline (TC)
antibiotic under solar light illumination. An enhanced photocatalytic activity of
CdS nanorods was observed after the incorporation of RGO in the composite.
Here, RGO plays a key role towards efficient photo induced charge separation
which subsequently decreases the electron-hole recombination possibility and
improves the photocatalytic activity of the RGO-CdS composite.
Chapter 4 describes the one pot single step solvothermal synthesis of
reduced graphene oxide - cadmium zinc sulfide (RGO-CdZnS) composite. The
reduction of graphene oxide (GO), synthesis of Cd 0.5 Zn 0.5 S nanorod and
decoration of nanorods onto RGO sheet was done simultaneously. The
structural, morphological and optical properties were studied thoroughly by
different techniques, such as XRD, TEM, UV-Vis and PL. The PL intensity of
CdZnS nanorods quench significantly after the attachment of RGO, confirms
photo induced charge transformation from CdZnS nanorods to RGO sheet
through the interface of RGO-CdZnS. An excellent photo current generation in
RGO-CdZnS thin film device has been observed under simulated solar light
irradiation. The photo current as well as photo sensitivity increases linearly
with the solar light intensity. Our study establishes that, the synergistic effect of RGO and CdZnS in the composite is capable of getting promising applications in the field of optoelectronic devising. The photocatalytic activity of the RGO-CdZnS composite was investigated towards the degradation of 4-Nitrophenol. A notable increase of photocatalytic efficiency of RGO-CdZnS compare to controlled CdZnS was observed. Here RGO plays a crucial role to efficient photo induced charge separation from the CdZnS, and decreases the
electron-hole recombination probability and subsequently enhanced the photocatalytic activity of the RGO-CdZnS composite material under simulated solar light irradiation. This work highlights the potential application of RGO-based materials in the field of photocatalytic degradation of organic water pollutant.
In chapter 5, the synthesis of a molybdenum disulfide–zinc phthalocyanine (MoS synthesis of MoS2 2
-ZnTTBPc) composite is reported, where the scalable was done by a simple solvothermal route followed by the
sono-chemical attachment of ZnTTBPc. The as-synthesized material acquires a
monolayer with an average thickness of 2 nm. Raman studies give sufficient evidence of the existence of monolayer MoS2 in the MoS
composite. The highly exfoliated abundant active sites available on the 2D surface of MoS2
efficiently act as photocatalytic reaction centres. Moreover,
the high energy transfer efficiency, authenticated by steady-state
photoluminescence and time-correlated single photon counting studies, makes
the MoS2 -ZnTTBPc (3:1) composite a promising optoelectronic and
photocatalytic material. The photo-generated electrons from the conduction
2-ZnTTBPc band of ZnTTBPc transfer to the conduction band of MoS2
leaving holes at the valence band of ZnTTBPc and simultaneously the photo-generated holes from
the valence band of MoS2 transfer to the valence band of ZnTTBPc. These
well-separated charges reduce the electron–hole recombination probability in
the composite, subsequently offering a positive synergetic effect among
ZnTTBPc and single-layered MoS2 sheets. It could thus have promise as a new
photo-catalyst towards removing different organic pollutants and for other
optoelectronic devices.2021-04-19T00:00:00ZEffect of Mo substitution on structural, dielectric, electrical and magnetic properties of Cobalt-Zinc spinel ferritesPradhan, Ashok Kr.http://inet.vidyasagar.ac.in:8080/jspui/handle/123456789/60122021-05-06T08:29:40Z2021-04-04T00:00:00ZTitle: Effect of Mo substitution on structural, dielectric, electrical and magnetic properties of Cobalt-Zinc spinel ferrites
Authors: Pradhan, Ashok Kr.
Abstract: Magnetic materials are widely used in different technological applications like,
power generation, communication, data storage and retrieval, sensors etc. Continuous
efforts by many researchers during the past many decades have led to the discovery of
many novel magnetic materials and properties like high-T
C
oxide superconductors,
giant and colossal magnetoresistive materials, high magneto-dielectric material, giant
magnetostrictive materials, etc. Here we report the synthesis of Molybdenum
substituted Cobalt-Zinc inverse spinel ferrites and their characterization with structural,
dielectric, complex impedance, electric modulus, electrical conductivity and magnetic
properties.
All the polycrystalline Mo doped Co-Zn ferrite samples was prepared with the
help of conventional ceramic technique. The XRD pattern affirms the formation of
exact cubic inverse spinel structure with having Fd3m space group. The calculated
lattice constant and grain size was observed to be increased with Mo concentration. The
temperature variation of dielectric constant
recommend that the origin of dielectric
constant in ferrite is four types of polarization. Also the temperature reliance of
dielectric constant can be clarified based on thermally assisted relaxation mechanism.
The dielectric dispersion of all the sample can be best illuminated in light of Maxwell-
Wagner type of interfacial polarization in agreement with Koop’s phenomenological
theory. The variation of dielectric loss tangent with temperature and frequency reveals
very low value of tanδ at room temperature and high frequency. Both the real and imaginary part of impedance decreased with frequency due to
decrease in space charge polarization. The Zʺ vs. f curves have some broad Debye peaks
at a hopping frequency and peaks are shifted to higher temperature at high frequency
due to increase in rate of electron hopping at higher temperature. The Cole-Cole plot
suggest that there is a contribution of only grain boundary in the conduction process
and also existance of non-Debye type relaxation in the materials was verified. All the
curves of electric modulus were well fitted according to modified Kohlrausch-
Williums-Watts (KWW) function proposed by Bergman. The scaling behavior gives
the concrete evidence for existence of non-Debye type relaxation in the present
samples. The activation energy of all the samples was calculated from both the
impedance and modulus spectra.
The variation of ac conductivity with frequency predict that the conduction is
because of the correlated barrier hopping mechanism. Also all the curves were well
fitted according to Jonscher’s single power law. The temperature dependence of ac
conductivity displayed the semiconducting nature of the sample. The activation energy
of all the samples in both paramagnetic and ferrimagnetic region was estimated using
the Arrhenius relation. It has been seen that the value of activation energy in
ferrimagnetic state is lower than that in paramagnetic state due to the fact that
ferrimagnetic state is ordered than the paramagnetic state. The variation of magnetic
moment with temperature showed the increase of both maturation magnetization and
Curie temperature due to Mo substitution. The low value of Tc might be because of the
disordered cation distribution in the material under study. Also the variation of real
permeability with temperature have the similar trend as M-T plot.2021-04-04T00:00:00Z