Essay: Metal chalcogenides, nanomaterials

The metal chalcogenides form a vast, almost infinite area of research. It is almost imposible in a single review to cover all the aspects of this chemistry, including synthesis, crystal and electronic structure, physical properties of the solids, chemical properties, and applications. The task is made easier since reviews devoted to different aspects of the metal chalcogenide chemistry have been appearing frequently, trying to keep up with the new compounds while the synthesis and characterization of new transition metal (TM) chalcogenides (including relatively binary chalcogenide) continues unabated [1-16].
A chalcogenide is a chemical compound consisting of at least one chalcogen ion and one or more electropositive element(s). Although all group VI (oxygen family) elements of the periodic table are defined as chalcogens, the term is more commonly reserved for sulfides, selenides, and tellurides, rather than oxides [17]. The word “chalcogen” derives from Greek words being “copper-former,” and is strongly related to metal-bearing minerals that have formed water-insoluble compounds with the metals in ores. The important metal chalcogenides include nickel selenides (NiSe), copper selenides (CuSe), lead selenides (PbSe) cadmium sulphide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), zinc sulphide (ZnS), and lead telluride (PbTe).

A metal chalcogenide is a compound made from a metallic element and a member of the chalcogenide family, namely the elements under oxygen–sulfur, selenium, and tellurium. In generally, the term metal chalcogenide is not really used to refer to metal oxides, however, although technically speaking metal oxides are metal chalcogenides. Chalcogenide semiconductors are very much interesting for the PV industry because of their unique electrical and physical properties (such as band gap, refractive index).

Nickel Selenide is the inorganic compound with the formula NiSe. It is usually nonstoichiometric and is often described by the formula Ni1-xSe, with 0 < x <0.15. These materials are all black semi-conducting solids when obtained as fine powders and silvery materials when obtained as larger crystals. The nickel selenides are insoluble in all solvents but can be degraded by strong oxidizing acids [18].

Nickel selenide (NiSe) is a semiconductor which shows excellent electronic and magnetic properties. NiSe has several applications in materials science field mostly in solar cells and in chemical sensors, because the band gap of NiSe lies between nickel oxide and nickel sulphide Recently, NiSe2 new application exhibit due to electrochemical properties . So many researches are focused mainly on these semiconductors over the past one decade.[19].

Copper selenide is an interesting metal chalcogenide semiconductor material. It can exists in many phases and structural forms: stoichiometric compositions such as copper (I) selenide [Cu2Se], copper (II) selenide [CuSe] and [CuSe2] with various crystallographic forms as well as non-stoichiometric such as Cu2-xSe. It has a number of applications in solar cells, super ionic conductors and photo-detectors [20].It is a semiconductor with p-type conductivity, a property useful in the solar cell production. It has both direct and indirect band gap. It has been reported to have a direct band gap of 2.2 eV and indirect band gap of 1.4 eV [21]. Copper selenide has also reported to have a direct band gap of 2.18 eV [22].

Copper selenide nanoparticles have been investigated and confirmed to exhibit higher properties required for efficient solar cells.

Lead selenide (PbSe) or lead (II) selenide is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct band gap of 0.27 eV at room temperature and it is a grey crystalline solid material [23].

It is used for manufacture of infrared detectors for thermal imaging operating at wavelengths between 1.5–5.2 µm. It does not require cooling, but performs better at lower temperatures. The peak sensitivity depends on temperature and varies between 3.7–4.7 µm.

Lead selenide has a wide range of applications including optical switching, optical computing, telecommunication components, photovoltaics, thermoelectrics, photodetectors, and infrared detectors, mid infrared lasers, solar cells, and chemical sensor [24].

It have been intensively investigated for their potential applications in the area of alternative energy sources, particularly solar energy [25], as light absorbing material for third generation solar cells.

1.1 Nanomaterials

Nanomaterials describe, in principle, materials of which a single unit is sized (in at least one dimension) between 1 and 1000nanometers (10−9 meter) but is usually 1—100 nm (the usual definition of nanoscale [26].

Nanomaterials research takes a materials science-based approach to nanotechnology, leveraging advances in materials metrology and synthesis which have been developed in support of micro fabrication research. Materials with structure at the nanoscale frequently have unique optical, electronic, or mechanical properties.

To have very small materials, it is required to have a way to form materials in the architectures and the morphology that you desire. Traditional methods of forming materials into precise shapes and devices include cutting, chipping, pounding, extruding, and other such bulk procedures. Nanotechnology is different. Whereas bulk procedures begin from a larger structure and form it into smaller structures, nanotechnology procedures can also include beginning at the atomic level and building up into larger, nanoscale structures. Where formation of smaller materials from larger is known as “top-down” technology, the formation of materials from atomic or molecular structures is known as “bottom-up.” [27].

Figure 1. 1 Top Down to Bottom Up Pattern

Some of the properties of nanomaterials includes; Agglomeration state, Size distribution, Surface morphology, Structure, including crystallinity and defect structure, Solubility, reactivity, strength and electrical properties.

1.2 Classification of Nanoparticles

There are various ways for classification of nanomaterials. Nanoparticles are classified based on one, two and three dimensions. [28].

1.2.1 One dimension nanoparticles

One dimensional structure, such as thin film or manufactured surfaces, has been used for decades in electronics, chemistry and engineering. Production of thin films (sizes1-100 nm) or monolayer is now common place in the field of solar cells or catalysis. These thin films are using in diverse technological applications, including information storage systems, chemical and biological sensors, and fibre-optic systems, magneto-optic and optical device.[29].

1.2.2 Two dimension nanoparticles

Carbon nanotubes (CNTs) are hexagonal network of carbon atoms, 1 nm in diameter and 100 nm in length, as a sheet of graphite rolled up into cylinder. CNTs are of two types, single walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) .The small dimensions of carbon nanotubes, combined with their remarkable physical, mechanical and electrical properties make them exceptional materials. They exhibit metallic or semi conductive properties, depending on how the carbon leaf is wound on itself. The current density that nanotubes can carry is extremely high and can reach one billion amperes per square meter making it a superconductor. The mechanical strength of carbon nanotubes is sixty times greater than the best steels. Carbon nanotubes have a great capacity for molecular absorption and present a three dimensional configuration. Moreover they are chemically and chemically very Stable.[29].

1.2.3 Three dimension nanoparticles

Fullerenes (carbon 60) are spherical cages containing from 28 to more than 100 carbon atoms, contain C60. This is a hollow ball composed of interconnected carbon pentagons and hexagons, like a soccer ball. Fullerenes are class of materials displaying unique physical properties. They can be subjected to a very high pressure and regain their original shape when the pressure is released. These molecules do not combine with each other, hence giving them major potential for application as lubricants. They have interesting electrical properties and it has been recommended to use them in the electronic field, ranging from data storage to production of solar cells. Fullerenes are offering potential application in the rich area of nanoelectronics. Because fullerenes are empty structures with dimensions similar to several biological active molecules, they can be filled with different substances and find potential medical application.[30].

1.2.4 Application of Nanoparticles

Application of nanotechnology in the different field is summarized in table 1.[31].

Applied field Application

Nanomedicines Nano drugs, medical devices, tissue engineering

Chemical and Cosmetics Nanoscale chemicals and compound, spaint, coatings etc

Materials Nanoparticles, carbon nanotubes, biopolymers, paints, coatings.

Food Sciences Processing, nutracetical food, nanocapsules

Environment and Energy Water and air purification filters, fuel cells, photovoltaic.

Military and Energy Biosensors, weapons, sensory enhancement

Electronics Semiconductors chips, memory storage, photonica, optoelectronics.

Scientific Tools Atomic force, microscopic and scanning tunnelling microscope

Agriculture Atomic force, microscopic and scanning tunnelling microscope

Table 1.1: Application of nanotechnology in the different field

1.3 Preparation of nanoparticles

1.3.1 Chemical vapour Deposition and control of particle Agglomeration

Chemical vapour deposition (CVD) is one of the commonly used gas-phase aerosol processes for producing high-purity nanoparticles though generated nanoparticles are in the form of aggregates due to their coagulation at the high temperatures used. Non agglomerated spherical oxide (SiO2, TiO2, and ZrO2) nanoparticles having diameters in the range of 10–40 nm has been prepared using an electro spray assisted chemical vapour deposition (ES-CVD) method [4]. ES-CVD represents a process that can be used to control the size and morphology of synthesized particles in gas-to-particle conversion processes. [32].

1.3.2 Preparation through spray route

Spray pyrolysis is a liquid-based gas phase technique and electro spray is capable of generating fine droplets as well as nanoparticles. We report a novel synthesis way by spray pyrolysis (salt assisted spray pyrolysis (SASP)) for the continuous synthesis of nanoparticles with adjustable sizes, a narrow size distribution, high crystallinity, and good stoichiometry. In this technique, many kinds of single crystalline nanoparticles (oxide; Y2O3-ZrO3, CeO2, NiO, Eu doped Y2O3, ZnO, Ba-Sr-Ti-O, Mn doped ZnS, metal; Ag-Pd) can be prepared. This route can offer excellent controllability of particle size, chemical composition, and material crystallinity, all of which are important for advanced materials.[32].

1.3.3 Laser pyrolysis/photothamal synthesis

An alternate means of heating the precursors to make the reaction and homogeneous nucleation is absorption of laser energy. Compared to heating the gases in a furnace, this allows greatly localized heating and rapid cooling, because only the gas (or a portion of the gas) is heated, and its heat capacity is small. Heating is normally done using an infrared (CO2 ) laser, whose energy is either absorbed by one of the precursors or by an inert photosensitizer such as sulfur hexafluoride. The silicon particles were prepared in the laboratory by laser pyrolysis of silane. Nanoparticles of many materials have been made using this method. A few recent examples are MoS2 nanoparticles prepared by Borsella et al. SiC nanoparticles prepared by Kamlag et al. and Si nanoparticles produced by Ledoux et al use a pulsed CO2 laser, thereby limiting the reaction time and allowing preparation of even smaller particles.[33].

1.3.4 Thermal plasma synthesis

However, another means of providing the energy needed to induce reactions that lead to supersaturation and particle nucleation is to inject the precursors into thermal plasma. This normally decomposes them fully into atoms, which can then react or condense to form particles when cooled by mixing with cool gas or expansion through a nozzle. Heberlein et al. have applied these methods to the production of nanoparticles of SiC and TiC for nanophase hard coatings.[33].

1.3.5 Flame spray synthesis

Rather than injecting vapour precursors into the flame, one can directly spray liquid precursor into it. This method is generally called flame spray pyrolysis. This procedure allows use of precursors that do not have sufficiently high vapour pressure to be delivered as a vapour. Madler et al. presented a very detailed study of this method, as applied to the synthesis of silica particles from hexamethyldisiloxane. [33].

1.3.6 Low temperature reactive synthesis

For particular materials, it is possible to react vapour phase precursors directly without external addition of heat, and without considerable production of heat. Sarigiannis et al. produced ZnSe nanoparticles from dimethylzinc-trimethylamine and hydrogen selenide by mixing them in a counter-flow jet reactor at room temperature. In fact the heat of reaction was sufficient to allow crystallization of the particles without substantially increasing the gas temperature. This is an interesting result, because it is one of few methods reported for vapour-phase preparation of compound semiconductor nanoparticles that are usually produced by colloidal chemistry [33].

1.4 Objectives of Proposed Work

The main objectives of proposed work are:

 Synthesis of Ni, Cu, & Pd selenide nanomaterials by chemical route method.

 Characterization of synthesized nanomaterials by various techniques such as X-ray diffraction, UV-VIS spectroscopy, Scanning electron microscopy, Transmission electron microscopy, Conductivity and I-V characteristics.

 If possible, materials of good electrical and optical properties will be used for fabrication of suitable device.

1.5 Literature Review

In 2014, S. Mostafa Hosseinpour-Mashkani, MajidRamezani, MortezaVatanparast. Worked on “Synththesis and characterization of lead selenide nanostructures through simple sonochemical method in the presence of novel precursor” PbSe nanostructures have been synthesized by using [bis (salicylate) lead (II)]; [Pb (Hsal) 2] as lead precursor in the presence of sonochemical method in aqueous solution. Moreover, the effects of reaction time, ultrasonic power, and surfactant on the morphology and particle size of products were studied by SEM images. It was found out that the size and morphology of the products obtained were greatly influenced by these parameters. The XRD studies indicated the production of pure cubic PbSe nanostructures can only happen in the presence of ultrasonic radiation. The average diameter of the PbSe nanostructures was 12nm. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Photo-luminescence (PL) and EDX analysis. By comparing this method and other ones, it was found that the present technique is simple, low cost and fast. Additionally, they have used a non-toxic precursor and solvent. The XRD results indicated that pure cubic PbSe without any impurities could be obtained in the presence of ultrasonic irradiation. [34].

In 2001, Junjie Zhu, Xuehong Liao, Jun Wang, Hong-Yuan Chen. Worked on “Photochemical synthesis and characterization of PbSe Nanoparticles” PbSe nanoparticles have been prepared by a simple reaction between Pb(Ac)2 and Na2SeSO3 in the presence of complexating agent using photoirradiation method. The nanoparticles were characterized by X-ray Diffraction (XRD), energy-dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS). The sizes of the sample products as prepared were calculated by Debye-Scherrer formula according to XRD spectrum to be about 25 nm. Also similar results have been obtained in the TEM images. PbSe nanoparticles have been prepared by the photochemical method. The advantages of this method are that it is a simple and efficient for producing nanoparticles. We can predict the upscaling of the process to form large quantities of nanosized PbSe. These nanoparticles could find use in photoresistors, photodetectors, and photoemitter.[35].

Also in 2008 Zhen Li, Chao Wu, Yanyan Liu, Tiebing Liu, Zheng Jiao And Minghong Wu. Worked on “Preparation of PbSe nanoparticles by electron beam irradiation Method” A novel method has been developed by electron beam irradiation to prepare PbSe nanopaticles. 2 MeV 10mA GJ-2-II electronic accelerators were used as a radiation source. Nanocrystalline PbSe was prepared rapidly at room temperature under atmospheric pressure without any kind of toxic reagents. The structure and morphology of prepared PbSe nanoparticles were analysed by X-ray diffraction, transmission electron microscope and atomic force microscope. The results indicated that the obtained products were cubic nanocrystalline PbSe with an average grain size of 30 nm. The optical properties of prepared PbSe nanocrystalline were characterized by using photoluminescence spectroscopy. The possible mechanism of the PbSe grain growth by electron beam irradiation technique is proposed. As-prepared PbSe nanoparticles were dispersed uniformly with spherical shape morphology and with a diameter range of 20– 40 nm. PL spectrum showed the blue shifting of the absorption edge, which were due to small size property of nanocrystalline PbSe. The advantages of this method exhibited that it was a simple, fast, efficient method without any kind of toxic reagent for producing nanoparticles. This technique could be used to prepare other metal selenides such as SnSe, CdSe and ZnSe.[36].

In 2010, Zeping Peng, Mingzhu Liu, Chao Yu, Zhanli Chai, Hongjie Zhang and Cheng Wang. Work on “Preparation of nanoscale PbSe particles with different morphologies in diethylene glycol” Nanoscale PbSe particles with different morphologies including octahedral, tetradecahedral and cubic shapes have been successfully prepared in diethylene glycol (DEG) at 240 oC in the presence of PVP-K30: poly(vinyl pyrrolidone),with MW = 50 000. The formation of PbSe is believed to be an elemental recombination process of corresponding elements reduced from their precursors by the solvent. Experimental results indicated that a prominent morphological variation was observed through varying the molar ratios of selenius acid to Pb2+ when Pb (Ac) 2 was used as lead precursor, while the sizes of the final PbSe products tended to increase along with the increase of the molar ratios of selenius acid to Pb2+ when Pb(NO3)2 was used as lead precursor.[37].

In 2002, Jun-Jie Zhu, Hui Wang, Shu Xu, and Hong-Yuan Chen. Worked on “Sonochemical Method for the Preparation of Monodisperse Spherical and Rectangular Lead Selenide Nanoparticles” Monodisperse lead selenide nanoparticles have been successfully prepared using a sonochemical route from an aqueous solution of lead acetate and sodium selenosulfate in the presence of complexing agents under ambient air. It was found that when trisodium citrate was used as the complexing agent, the product obtained was spherical nanoparticles with an average size of ca. 8 nm. But if potassium nitrilotriacetate was used, the product consisted of rectangles with an average size of ca. 25 nm. The products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. A probable mechanism for the sonochemical formation of PbSe was proposed. Also several factors that affected the nature and morphology of the products were discussed such as the pH value, the complexing agents, and the intensity of the ultrasound irradiation. Further studies may expand this method for the preparation of other nanocrystalline selenide semiconductors.[38].

Further more in 2010, N.A.Okerekea, A.J.Ekpunobi. Worked on “Structural, Optical Properties and Applications of Chemically Deposited Lead Selenide Thin Films” Semiconductors based on selenium are important class of semiconducting systems which have been extensively studied due to their fundamental electronic and optical properties. Intensive research has been performed in the past to study the fabrication and characterization of these compounds in the form of thin films. A number of methods for the preparation of PbSe thin films have been reported, but chemical bath deposition method is found to be very good and low cost method to fabricate the polycrystalline PbSe thin films. They have report the structural, optical properties and applications of PbSe obtained from chemical baths using SeSO3 or K2SeO4 as a source of selenide ions. XRD studies on the films product obtained from both baths suggest a clausthalite cubic structure. The optical band gap of the film is estimated to be in the range of 1.0-1.3eV. It showed a uniform distribution of particles as shown in photomicrograph. The average grain size is 3.82Å. The films were found to have high absorbance in the ultra violet region and reduce as the wavelength increased. They have generally high transmittance, high refractive index. for this reason, the film has potential for use in the solar cell fabrication, window screen and anti-reflection coatings.[39].

In 2011, Azam Sobhania, Fatemeh Davarb, Masoud Salavati-Niasari. Worked on “Synthesis and characterization of hexagonal nano-sized nickel selenide by simple hydrothermal method assisted by CTAB” Nano-sized nickel selenide powders have been successfully synthesized via an improved hydrothermal method based on the reaction between NiCl2•6H2O, SeCl4 and hydrazine (N2H4•H2O) in water, in present of cetyltrimethyl ammonium bromide (CTAB) as surfactant, at various conditions. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray energy dispersive spectroscopy analysis. The effects of temperature, reaction time and reductant agent on the morphology, the particle sizes and the phase of the final products have been investigated. It was found that the phase and morphology of the products could be very much influenced by these parameters. The synthesis procedure is simple and uses less toxic reagents than in the past reported methods. Photoluminescence (PL) was used to study the optical properties of NiSe samples.[40].

In 2012, Azam Sobhani, Masoud Salavati-Niasari, Fatemeh Davar. Worked on “Shape control of nickel selenides synthesized by a simple hydrothermal reduction process” Nickel selenide (NiSe) nanoparticles were prepared from the reaction of a SeCl4 aqueous solution with a NiCl2.6H2O aqueous solution in the presence of polyvinyl alcohol (PVA) used as capping agent and hydrazine hydrate (N2H4.H2O) as a reductant through a hydrothermal method. The size, morphology, chemical composition and purity of these nanoparticles depend on the capping agent, reductant, reaction temperature and time.[41].

However, in 2012, Shuguang Chen, KaiZeng,YandeSong,HaibinLi,PengLiu,FujinLi.Worked on “Systematically shape evolution of hexagonal NiSe crystals caused by mixed solvents and ammoniumchloride” systematic shape evolution of hexagonal NiSe crystals is achieved via a simple Solvothermal route in a mixture of NiCl2.6H2O, elemental selenium, hydrazine hydrate and ethylenediamine. Via introducing ammoniumchloride as electrolyte and varying the volume ratios of hydrazine hydrate to ethylenediamine, shape evolution of hexagonal NiSe crystals from small hexagonal microdisks to hexagonal microdisks in larger width, microspheres, hexagonal prisms and hexagonal bitowers is successfully achieved. X-ray powder diffraction, field emission scanning electron microscopy, energy dispersion spectrometer, transmission electron microscopy and selected area electron diffraction are performed for the analyses of the products. The ionization and hydrolysis of ammoniumchloride decrease the nucleation rate of hexagonal NiSe and the diffusion rate of growth resources, whereas the adsorption of ethylenediamine at {001 facets of hexagonal NiSe crystals inhibits the crystal growth in <001> directions, thus leading to various novel architectures. Future work is in progress to gain further approaching into the performances and applications of these materials. This simple solvothermal method with the assistances of mixed solvents and electrolyte may be extended to the shape-controlled synthesis of other metal chalcogenides with unique shapes and structures.[42].

In 2014, Azam Sobhani, Masoud Salavati-Niasari. Worked on “Synthesis and characterization of a nickel selenide series via a hydrothermal process” A series of nickel selenides (NiSe and NiSe2) has been successfully synthesized from the reaction of SeCl4 with NiCl2.6H2O in the presence of cetyltrimethyl ammonium bromide (CTAB) as surfactant and hydrazine hydrate (N2H4.H2O) as reductant at 180oC for 12 h through a simple hydrothermal process. The morphology, phase structure and composition of NixSey can be controlled by adjusting the Ni/Se ratio of the raw materials, the quantity of reductant, the reaction temperature and so forth. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. It was found that when the ratio of Ni/Se is 1:1 or 3:2, flower-like assemblies of NiSe nanosheets are produced, at 180oC for 12 h. While if the ratio of Ni/Se is 1:2 at 180oC, the products are found to be the mixture of hexagonal NiSe and cubic NiSe2.By the decrease of nickel content in molar ratio of 1:2 (Ni: Se), nanospheres are agglomerated and microstructures are formed. When the reaction temperature decreasing from 180oC to 120oC, we reach pure NiSe2 nanoparticles. The formation mechanism of the nickel selenides has been investigated in detail by means of XRD and SEM analyses. The present synthetic method is a suitable process with good reproducibility and high yield, which make it possible to scale up to industrial production. Also, this method may be use to synthesize other selenide semiconductor materials.[43].

Further more in 2011, Anuar Kassim, Ho Soon Min, Tan Wee Tee and Yazid Rosli. Worked on “preparation and characterization of chemical bath deposited NiSe thin films” Nickel selenide thin films were deposited on microscope glass substrates using the chemical bath deposition method. The deposition was carried out using nickel sulphate as a Ni2+ ion source and sodium selenite as a Se2- ion source in the presence of Na2EDTA as a complexing agent. The structural and morphological properties of NiSe films product were investigated using X-ray diffraction and atomic force microscopy. X-ray diffraction patterns showed that the films were polycrystalline NiSe with hexagonal structure with (100) preferential orientation. Based on the atomic force microscopy analysis, all the samples showed complete coverage of the substrate surface with the thickness of the films about 156-664 nm. When the bath temperature was increased from 55 to 75 °C, the grain size was increased but the band gap was decreased from 1.89 to 1.80 eV.[44].

In 2014, M. Kristl, j. Kristl. Worked on “Sonochemical Process for the Preparation of Nanosized Copper Selenides with Different Phases” The family of copper selenides has attracted significant interest due to its many phases and a variety of compounds. Many studies prove the applicability of copper selenides as important solar cell materials. A simple sonochemical process was developed to synthesize various copper selenides in aqueous solutions, using Cu(CH3COO)2 as copper source and Na2SeSO3, elemental Se and selenourea as selenium sources. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and chemical analysis confirmed that different copper selenides with crystallite sizes between 9 and 28 nm were obtained in high yield. The following nanosized copper selenides with crystallite sites between 9 and 28 nm were prepared: Cu2Se, Cu2-xSe, Cu3Se2, β – CuSe. The synthesis from sodium selenosulfate and water/EDTA solutions of copper acetate provides the possibility of changing the product composition and particle size by using different molar ratio of precursors and applying the complexing agent. The method allowed them the preparation of Cu2Se, which has not been prepared sonochemically by now. The second method, involving the dissolution of Se in NaOH solutions, also enables changing of the product composition by changing the precursor ratio, while the addition of the complexing agent seems to have no significant control on the product in this case. The synthesis from copper acetate and thiourea yields pure β – CuSe. The method investigated herein demonstrates the possibility to produce stoichiometric copper selenides as well as nonstoichiometric compounds from convenient copper and selenium sources using a facile sonochemical method. Further investigation are expected to give better understanding of the influence of reaction time and complexing agents on the composition and morphology of the products.[45].

However in 2012, T.Arokiya Mary and Joe Jesudurai. Worked on “A simple hydrothermal route for synthesizing copper Selenide Nano-Flakes” Copper selenide Cu2Se nanopowders have been synthesized by low cost and effective hydrothermal technique at temperature of 200oC.The synthesized nanoparticles were characterized by a different techniques like XRD, UV, FTIR, SEM and EDAX. XRD and SEM analysis confirms that the synthesized particles to be of the cubic structure exhibited a hexagonal flake –like morphology in the [111] plane. While a UV and FTIR study informs us about the optical properties of Cu2Se nanoparticles. EDAX reveals the composition of the synthesized material. The estimated optical band gap for the particles was

Found to be within the reported range.[46].

Further more in 2012, D. Patidar n, N.S.Saxena. Worked on “Characterization of single phase copper selenide nanoparticles and their growth mechanism” The high quality Cu3Se2 phase of copper selenide nanoparticles have been synthesized through the solution-phase chemical reaction between copper and selenium. In this synthesis procedure, hydrazine hydrate acts as reducing agent where as ethylene glycol controls the nucleation and growth of particles. An attempt has been made to explain the growth mechanism to form copper selenide nanoparticles through the coordination of selenium to the Cu2+ complexes with OH groups of ethylene glycol. Result indicates the formation of Cu3Se2 single phase nanoparticles.The particles with the average particle size 25nm is spherical in shape having tetragonal structure. The particles are well crystallized having 94% degree of crystallinity. An effort has also been made to find out the energy band gap of copper selenide nanoparticles through the absorption spectra. The band gap shifts towards higher value by 1.82 eV as compared to bulk band gap due to quantum confinement effect.[47].

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