Browsing by Author "Sewvandi, GA"

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item: Article-Full-text
Antiferroelectric Nature of CH3NH3PbI3-xClx Perovskite and Its Implication for Charge Separation in Perovskite Solar Cells
(Nature Portfolio, 2016) Sewvandi, GA; Kodera, K; Ma, H; Nakanishi, S; Feng, Qi
Perovskite solar cells (PSCs) have been attracted scientific interest due to high performance. Some researchers have suggested anomalous behavior of PSCs to the polarizations due to the ion migration or ferroelectric behavior. Experimental results and theoretical calculations have suggested the possibility of ferroelectricity in organic-inorganic perovskite. However, still no studies have been concretely discarded the ferroelectric nature of perovskite absorbers in PSCs. Hysteresis of P-E (polarization-electric field) loops is an important evidence to confirm the ferroelectricity. In this study, P-E loop measurements, in-depth structural study, analyses of dielectric behavior and the phase transitions of CH3NH3PbI3−xClx perovskite were carried out and investigated. The results suggest that CH3NH3PbI3−xClx perovskite is in an antiferroelectric phase at room temperature. The antiferroelectric phase can be switched to ferroelectric phase by the poling treatment and exhibits ferroelectric-like hysteresis P-E loops and dielectric behavior around room temperature; namely, the perovskite can generate a ferroelectric polarization under PSCs operating conditions. Furthermore, we also discuss the implications of ferroelectric polarization on PSCs charge separation.
item: Article-Full-text
Antiferroelectric-to-Ferroelectric Switching in CH3NH3PbI3 Perovskite and Its Potential Role in Effective Charge Separation in Perovskite Solar Cells
(American Physical Society, 2016) Sewvandi, GA; Hu, D; Chen, C; Ma, H; Kusunose, T; Tanaka, Y; Nakanishi, S; Feng, Q
Perovskite solar cells (PSCs) often suffer from large performance variations which impede to define a clear charge-transfer mechanism. Ferroelectric polarization is measured numerically using CH3NH3PbI3 (MAPbI3) pellets to overcome the measurement issues such as pinholes and low uniformity of thickness, etc., with MAPbI3 thin films. MAPbI3 perovskite is an antiferroelectric semiconductor which is different from typical semiconducting materials and ferroelectric materials. The effect of polarization carrier separation on the charge-transfer mechanism in the PSCs is elucidated by using the results of ferroelectric and structural studies on the perovskite. The ferroelectric polarization contributes to an inherent carrierseparation effect and the I–V hysteresis. The ferroelectric and semiconducting synergistic chargeseparation effect gives an alternative category of solar cells, ferroelectric semiconductor solar cells. Our findings identify the ferroelectric semiconducting behavior of the perovskite absorber as being significant to the improvement of the ferroelectric PSCs performances in future developments.
item: Conference-Abstract
Bismuth chalcohalides for optoelectronic applications
(Department of Materials Science and Engineering, University of Moratuwa., 2023-12-14) Jayawardane, JTST; Sewvandi, GA; Buddhima, P; Indeewari, A; Gurusinghe, Y; Konalingam, K
Bi-based halide perovskites are an interesting class of material because of their rich structural diversity and the ability to exist in a wide range of coordination geometries (from cluster to 1D, 2D, or even 3D) makes them particularly useful for designing novel compounds for optoelectronic applications. Bismuth halides such as BiI3, A3Bi2I9 (where A is Cs+ or CH3NH3+), chalcogenides (Bi2S3, Bi2Se3), and chalcohalides (BiSI, BiSeI, BiSI5,Bi2Te2Br,(AlCl4)6), exhibit interesting electrical, magnetic, and optical properties. In this investigation, we report electronic structure, connection to the crystal geometry, density of states and band structure of BiSeI, BiSeBr, Bi3Se4Br and BiSI Bismuth chalcohalides as potential optoelectronic materials. All calculations are performed within the framework of density functional theory using the plane-wave pseudopotential method as implemented in the Vienna Ab-initio Simulation Package (VASP). Crystal structures of the bismuth chalcohalides two distinct crystal structures can be identified. BiSeBr, BiSeI, BiSI possess an orthorhombic structure (space group Pmmn,Pnma, Pnma ) and Bi3Se4Br possess a monoclinic crystal structure (space group C2/m). According to the band structure analysis BiSeI, BiSeBr, Bi3Se4Br and BiSI are found to possess optical band gaps in between 1-1.9 eV. The crystal structure of BiSeBr, and BiSeI has chains of atoms running along the c-axis and have similar electronic properties, including similar optical band gaps of 1.54 eV and 1.56 eV, respectively. The crystal structure of Bi3Se4Br shows atomic chains, along the b axis and the calculated band structure is indicates an indirect bandgap (~1.04 eV) with the CBM at k point along the -M direction and VBM along the N-Z direction. BiSI shows well-separated groups of bands and reveal that BiSI crystal has an indirect forbidden gap (1.87eV). The minimum of the conduction band is located at ƛ point and the maximum of the valence band appears nearly midway between the Z and ƛ points. Generally, band gap greater than 1.5 eV can be used for radiation detection applications and further analysis could be carried out to find potential as room-temperature radiation detection materials. According to this study, the band gaps of BiSeI, BiSeBr,Bi3Se4Br and BiSI are in the range of band gap required for photovoltaics. Furthermore, other electronic properties, including the effective mass, optical absorption. should be investigated to check the applicability in various optoelectronic devices.
item: Conference-Full-text
Computational modeling of perovskite structured methylammonium lead iodide as a solar absorber
(IEEE, 2018-05) Nanayakkara, HATV; Sewvandi, GA; Chathuranga, D
Halide Perovskite materials play a prominent role in solar cell industry as they comprise with advanced photovoltaic properties. Research is mainly based on the objective of investigating basic fundamental properties of CH3NH3PbI3 using Viana Ab-Initio Simulation Package(VASP). Before go to the experimental data analysis we have simulated fundamental photovoltaic properties of Methyl Ammonium Lead Iodide using computational method. CH3NH3PbI3 perovskite undergoes a phase transition between orthorhombic, tetragonal and cubic around 165K and 327K. Then the most stable structures are tetragonal and cubic phases. Therefore, in this research we have focused to study the basic crystallographic orientations, Energy band gap variation, Density of states in P, S orbitals and effective mass values of cubic and tetragonal phases in Methyl Ammonium Lead Iodide. Basic Density Function (DFT) theories like Local-density approximation of Kohn-Sham theory, Exchange correlation functional are basically used for theoretical calculations in this computational study.
item: Article-Full-text
Controlling dye coverage instead of addition of organic acid to reduce dye aggregation in dye-sensitized solar cells
(Elsevier, 2020) Sewvandi, GA; Kakimoto, M; Chen, C; Hu, D; Abeygunawardhana, PKW; Feng, Q
The photo-generated electron injection yield of dye-sensitized solar cells (DSSCs) based on donor-acceptor conjugated dyes is lowered by the aggregation of surface adsorbed organic dyes that pose a low-photoenergy conversion efficiency. Coadsorbates used to prevent the aggregation cause to decompose or detach the dye molecules anchored on the TiO2 surface. In this study, the effect of coadsorption of organic acid and organic dyes on photovoltaic performances was systematically scrutinized by means of adsorption isotherms and photovoltaic measurements. Our laboratory synthesized {0 1 0}-faceted TiO2 (PA TiO2) and P25 TiO2 were used as mesoporous nanocrystals, D149 organic dye was used as a sensitizer and cheno-deoxycholic acid, CDA, was used as a coadsorbate. The coadsorption of CDA reduces the adsorption parameters, maximum adsorption density (Qm) and adsorption constant (Kad), and the reduction depended on the type of TiO2. The photovoltaic performance indicates that the D149 dye has the best dye coverage at around 70% for the effective photovoltaic energy conversion. The coadsorption of CDA increased the photovoltaic performances of DSSCs based on P25 TiO2 but, CDA decreased the photovoltaic performances of DSSCs based on PA TiO2 due to the reduction of the dye coverage below 70%. The results suggest that the coadsorption of organic acids is not necessary if the particular TiO2 can maintain its coverage at the best coverage. Thus, the requirement of coadsorbates to reduce the dye aggregation depends on the type of TiO2 used in DSSCs.
item: Conference-Full-text
Effect of ch3nh3i concentration on performances of the perovskite solar cells
(IEEE, 2020-07) Anuruddha, WAI; Arush, KM; Sewvandi, GA; Weeraddana, C; Edussooriya, CUS; Abeysooriya, RP
Perovskite solar cells have attracted significant attention from the scientist and the industrialists because of the high efficiency. But the fabrication of high-quality film which controls the cell performances is a very difficult task. In this study methylammonium lead iodide perovskite (CH3NH3PbI3) material was synthesized using a two-step spin coating method; first, apply lead iodide (PbI2) and then methylammonium iodide (CH3NH3I, MAI). Fabricated films were analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). It confirmed that the methylammonium lead iodide (CH3NH3PbI3) perovskite structured material with an average crystal size of 350 nm was formed. And also, the effect of morphological changes with the concentration of MAI was studied. SEM images show the enhancement of the film quality by decreasing the MAI concentration. And also. the maximum fill factor of 0.32 has been achieved with the lowest MAI concentration (0.1M).
item: Conference-Full-text
Effect of halide ion in the perovskite on perovskite solar cell performances
(IEEE, 2021-07) Ranasinghe, SS; Kuruppu, YL; Sewvandi, GA; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
In this paper, a p-i-n perovskite solar cell was studied using Solar Cell Capacitance Simulator (SCAPS). A perovskite solar cell with MAPbI 3 and a perovskite solar cell with MAPbBr 3 as the light-absorbing materials have been simulated and compared the effect of the halide ion on solar cell performances. The efficiency of MAPbI 3 and MAPbBr 3 were reached 16.8% and 5.14% respectively. Also, the thickness of each MAPbI 3 and MAPbBr 3 was varied from 0.1 μm to 1.2 μm and the best results were observed at 0.5 μm and 0.4 μm thickness of MAPbI 3 and MAPbBr 3 films, respectively. A considerable effect of halide ions on perovskite solar cell performances can be attributed to the variation of light absorption with the halide ions.
item: Conference-Extended-Abstract
Effect of Reflux temperature on synthesis of hdroxyapatite by wet chemical precipitation technique
(2011) Adikary, SU; Jayaweera, JMN; Sewvandi, GA
In this study, hydroxyapatite HA, [(Ca>o(P04)6(OHi:,j] was synthesized using wet chemical precipitation technique at different reflux temperatures. Calcium hydroxide [Ca(OH)J powder and Phosphoric acid [H3PO4] solution were used as starting materials. Variation in PH value of Ca(OHsuspension during the addition of H}P04 solution was analyzed. The effect of reflux temperature for the synthesis HA was investigated. Characteristics of synthesized powder were analyzed by Fourier transformed infrared (FTIR) spectroscopy and X-ray dijfraction (XRD). The powder characteristic has demonstrated that, the reflux temperature played an important role in the synthesis of pure and single phase HA powder.
item: Conference-Full-text
Enhancing the perovskite solar cell performance through a cu2o buffer layer at perovskite/hole transport layer interface: a numerical study
(IEEE, 2023-12-09) Jayaneththi, YH; Akmal, UKDM; Sewvandi, GA; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
This research study focuses on a numerical study of the impact of a Copper(I) Oxide buffer layer at the interface between the perovskite layer and the hole transport layer. The influence of incorporating a Cu2O layer on device performance was examined using solar cell capacitance simulator software (SCAPS-1D). The findings indicated that the inclusion of a Cu2O layer effectively enhances hole extraction through defect passivation, resulting in reduced charge recombination and ion migration. Consequently, the performance of the perovskite solar cell with the Cu2O buffer layer exhibited significant improvements compared to the reference solar cell architecture. Before incorporating the Cu2O buffer layer, the power conversion efficiency (PCE) was reported as 22.12% while it was reported as 24.48% after the introduction of the buffer layer. These findings demonstrated the promising potential of incorporating a Cu2O buffer layer to enhance the performance of experimental perovskite solar cells.
item: Conference-Full-text
Evaluating the thermal conductivity of three-phase insulation composite using analytical and numerical methods
(IEEE, 2022-07) Chamath, LG; Srimal, LKT; Sewvandi, GA; Rathnayake, M; Adhikariwatte, V; Hemachandra, K
Sustainable insulation materials have been more attractive in the last two decades due to biodegradability, low embodied energy, availability, and non-toxicity. Those materials are primarily fabricated as composite materials using natural plant fibres. Then, the material contains three phases, i.e., fibre, binder, and air void. The volume fraction of each phase will decide the material’s insulation properties and can be analyzed using experimental, analytical, and numerical methods. Numerical and analytical methods are more attractive compared to experimental methods due to cost-effectiveness and less time consumption. However, only a limited number of studies have attempted to find the effective thermal conductivity (K eff ) of a three-phase composite by these methods. In this study, the authors have suggested a plan to find the K eff of this composite using a numerical method and validated through the analytical techniques. This study, coir fibre was used as a fibre material and latex as a binder material. The results show that the numerical model should be changed based on the air void fraction. It was concluded that the close-pores structure model applies to the pore volume fraction of 0.65 and the open-pores structure model for pore fractions above 0.65 for numerical analysis.
item: Conference-Abstract
Fabrication of dye sensitized solar cells using locally available sensitizers
(2017) Samanchandra, AR; Tharanga, D; Sewvandi, GA
Dye sensitized solar cells (DSSC) were fabricated using the dyes extracted from locally available natural plants of Mangosteen, Centella, Beetroot, Turmeric. Extracted dyes were analyzed using UV-vis spectrometer. Photo anodes were prepared by using regent grade TiO2 Powder. The TiO2 films were coated on Fluorine doped Tin Oxide (FTO) using doctor blade method and spray coating method. The film quality was examined using X-ray diffractometer and Scanning electron microscope (SEM). The film prepared using spray coating method has better uniformity. DSSCs fabricated using the dye extracted from mangosteen have shown high efficiency than the DSSCs of other dyes. Combined dye absorptions of X (mangosteen and centella) and Y (mangosteen and turmeric) were done to increase the efficiency. The DSSC fabricated with mangosteen and centella combination of dyes yielded the maximum performance.
item: Article-Full-text
Facile size-controllable synthesis process, bandgap blue shift, and enhanced photocatalytic performances of [111]-faceted anatase TiO2 nanocrystals
(Royal Society of Chemistry, 2017) Xu, L; Sewvandi, GA; Uemura, S; Kusunose, T; Nakanishi, S; Feng, Q
The facet exposed on a nanocrystal surface strongly affects the physicochemical properties of the crystal surface but it is not easy to control in the synthesis process. Herein we demonstrate a facile synthesis process for size-controllable [111]-faceted anatase TiO2 nanocrystals by hydrothermal treatment of a mixed solution of tetramethylammonium hydroxide solution and titanium isopropoxide. The [111]-faceted cubic anatase single nanocrystals are formed by a topochemical transformation reaction of nanosized titanate nanosheets to anatase nanofragments and Ostwald ripening crystal growth of the nanofragments. By using the size-controlled anatase nanocrystals, we have unveiled for the first time that the bandgap blue shift with reducing crystal size is dependent on the crystal-facet, and increases in the order of non-facet < [111]-facet < {010}-facet. The quantitative relationships between the bandgap and the surface area are given for the non-faceted, [111]-faceted, and {010}-faceted anatase nanocrystals. The photocatalytic studies on the [111]-faceted anatase TiO2 nanocrystals, a commercial P25 sample, and a non-faceted ST-20 anatase nanocrystal sample reveal that the increasing photocatalytic activity order matches the increasing bandgap order.
item: Article-Full-text
First-principles calculation on electronic properties of Bismuth-halide inorganic perovskites for solar cell
(2021) Sewvandi, GA; Jayawardane, JTST
Solar energy is a commonly used alternate source of energy and it can be utilized based on the principle of the photovoltaic effect. The photovoltaic effect converts sun energy into electrical energy using photovoltaic devices (solar cells).
item: Conference-Full-text
Impact of drying temperature on morphology and the crystallinity of ch3nh3pbi3 thin films
(IEEE, 2021-07) Yasassri, MAH; Sewvandi, GA; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
Today, solar power is considered one of the most promising energy sources to satisfy the growing global energy demands and resolve the increasing energy crisis due to the reduction of fossil fuels. Solar cells are in continuous development; scientists focus more on discovering many ways to increase the photoelectric conversion efficiency of organic-inorganic perovskite solar cells. The quality of the perovskite film is directly affecting the performance of the device. The present work reports the influences of drying temperature on the film morphology and crystal structure of CH3NH3PbI3 thin film. A Two-step spin coating method was used to prepare the thin films and dried them at different drying temperatures to transform MAI.PbI 2 .DMSO into pure CH3NH3PbI3. X-ray diffraction data indicate the improvement of the crystallinity as the drying temperature rises. Furthermore, the grain size increase with the drying temperature forming larger grains at 150°C. The larger grains help increase the fill factor, decrease the crystal boundaries, and decrease the charge carrier recombination. UV visible absorption spectra reveal that the bandgap of corresponding CH 3 NH 3 PbI 3 thin films is around 1.55 eV.
item: Conference-Full-text
Potential of chalcogenide halide bismuth perovskites ch3nh3bichi2 (ch = s, se,) as solar absorbers based on theoretical study
(IEEE, 2022-07) Jayawardane, JTST; Sewvandi, GA; Rathnayake, M; Adhikariwatte, V; Hemachandra, K
Organo lead halide perovskite has received a great deal of attention in the past couple of years due to its excellent optoelectronic properties. However, the presence of toxic lead in these materials is a significant concern for human health. Therefore, it is essential to select the elements for solar cell design that are environmentally friendly and conducive to human health. Many non-toxic alternatives can be used to solve this problem. Among those alternatives, Bismuth-based perovskite has become a promising alternative due to similar photovoltaic properties and enhanced environmental stability. Bismuth ternary based halide has interected due to their superior stability, but the main disadvantage is their wide band gap for single junction solar cells. The incorporation of the chalcogenide anions into bismuth chalcogenides was reported to have smaller bandgaps than that of the halide bismuth perovskites, which could reduce their bandgaps without affecting their photovoltaic properties. Band gap and dominant band to band absorption could be predictable from electronic property calculations using ground state density functional theory (DFT) as the lowest energy difference between the conduction band minimum (CBM) and the valence band maximum (VBM). As a result, for photovoltaic applications, the structural and band gap properties of mixed chalcogen and halogen anions, CH 3 NH 3 Bi (Ch, X)3 (Ch = chalcogen; X = halogen), were calculated using a combination of density- functional theory calculations. Results reveal that the band gaps of CH 3 NH 3 BiChI 2 S and CH 3 NH 3 BiChI 2 Se are 1.39 eV and 1.34 eV, which are in the range of band gaps required for photovoltaics.
item: Thesis-Abstract
Removal of heavy metals from waste water using locally derived chitosan
(2014-06-05) Sewvandi, GA; Adikary, SU
In this research work natural bio polymer “chitosan” was synthesized using locally available shrimp shells and adsorption of chromium by chitosan was studied. Synthesize of chitosan involved four main stages as preconditioning, demineralization, deprotenisation and deacetylation. “Preconditioning” process is a new step introduced in this research, to remove loosely bound protein. In the preconditioning, the skeletal matrix structure is first weakened which makes easier to remove soluble protein by washing with water. Therefore during deproteination process less alkali concentration can be used. Effect of deacetylation conditions such as alkali concentration, number of times of deacetylation performed and reaction temperature was investigated. Chitosan was characterized using Fourier Transform Infrared Spectroscopy (FTIR), Differential Thermal analysis (DTA), Thermal Gravimetric Analysis (TGA) and X-ray diffraction (XRD). These characterization techniques confirm the existence of chitosan. Degree of deacetylation was calculated using FTIR spectra. This value was highly depending on reaction temperature, reaction time, alkali concentration and number of times of deacetylation. Both characterization techniques confirm the existence of chitosan. The affinity of chitosan for chromium was studied using K2Cr2O7 solution as the heavy metal solution containing Cr (VI) ions. Adsorption of chromium ions by chitosan was investigated under different conditions. The effect of reaction temperature, particle size of chitosan and pH of solution were studied. Amount of chromium absorbed under different conditions was evaluated using atomic absorption spectroscopy.
item: Conference-Abstract
Removal of heavy metals from wastewater using chitosan
Sewvandi, GA; Adikary, SU
In this research work natural bio polymer “chitosan” was synthesized using locally available shrimp shells and adsorption of chromium by chitosan was studied. Synthesize of chitosan involved four main stages as preconditioning, demineralization, deprotenisation and deacetylation. Chitosan was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). Both characterization techniques confirm the existence of chitosan. The affinity of chitosan for chromium was studied using K2Cr2O7 solution as the heavy metal solution containing Cr (VI) ions. Adsorption of chromium ions by chitosan was investigated under different conditions. The effect of reaction temperature, particle size of chitosan and pH of solution were studied. Amount of chromium absorbed under different conditions was evaluated using atomic adsorption spectroscopy.
item: Article-Full-text
Solvothermal reaction and piezoelectric response of oriented KNbO3Polycrystals
(ACS Publications, 2021) Yang, D; Wang, Y; Li, L; Yao, M; Zhang, W; Gu, H; Zhang, S; Fan, M; Sewvandi, GA; Hu, D
KNbO3 (KN) piezoelectric polycrystals were prepared by a two-step solvothermal reaction process with the managed organic solvents as reaction mediums at a low temperature for a short time. In the solvothermal reaction system, the formation mechanism of polycrystalline KN is mainly the dissolution–deposition mechanism. The influences of alkalinity, viscosity, and the polarity for reaction mediums on the formation of the niobates were investigated. The chemical reaction mechanisms of niobate products and formation mechanism of niobate crystals from the precursor were clarified. The regulating and controlling mechanism of the phase compositions, the morphologies, and the lattice constants for the niobates obtained in varied reaction mediums were revealed. The obtained KN piezoelectric polycrystals are constructed from oriented KN nanocrystals. Piezoelectric hysteresis loops of cuboid KN polycrystals were detected for the first time. A prepared cuboid KN polycrystal shows an average d33* value of 32 pm/V. The study provides a strategy for the development of oriented KN piezoelectric materials to apply the orientation engineering.
item: Article-Abstract
Synthesizing and characterization of natural biopolymer chitosan derived from shrimp type, penaeus monodon
Sewvandi, GA; Adikary, SU
In this study natural biopolymer "chitosan" was synthesized using locally available shrimp type of Penaeus monodon. Synthesis of chitosan involved four main stages: preconditioning, demineralization, deprotenisalion and deacetylation. The first stage, "preconditioning " process, is a new step introduced in this research. Effect of deacetylation conditions such as alkali concentration, number of limes deacetylation was performed and reaction temperature was investigated. Yields of chitin and chitosan from R monodon were calculated. Chitosan was characterized using Fourier Transform Infrared (FTIR) Spectroscopy and X-ray diffraction. Degree of deacetylation of synthesized powder was calculated using FTIR spectra. Both characterization techniques confirm the existence of chitosan.
item: Article-Full-text
Topological relations and piezoelectric responses of crystal-axis-oriented BaTiO3/CaTiO3 nanocomposites
(Royal Society of Chemistry, 2017) Hu, D; Niu, X; Ma, H; Zhang, W; Sewvandi, GA; Yang, D; Wang, X; Wang, H; Kong, X; Feng, Q
2D crystal-axis-oriented mesocrystalline BaTiO3/CaTiO3 (BT/CT) nanocomposites with high-density heteroepitaxial interfaces were synthesized by a two-step solvothermal soft chemical process. The nanostructures, formation mechanism, topological relations between the BT and CT, and piezoelectric responses of the nanocomposites were investigated. The mesocrystalline nanocomposites are polycrystals constructed from crystal-axis-oriented BT and CT nanocrystals with the same crystal-axis orientation, respectively. The directions of the [001] and [1−10] of crystalline BT correspond to the directions of the [0−10] and [100] of crystalline CT, respectively. The mesocrystalline nanocomposites were formed via an in situ topochemical mesocrystal conversion mechanism. The density of the artificial BT/CT heteroepitaxial interface in these mesocrystalline nanocomposites can be adjusted by regulating the fraction of BT and CT in the nanocomposites. The mesocrystalline BT/CT nanocomposite with the composition close to BT/CT = 1/1 presents a large piezoelectric response owing to the lattice strain derived from its heteroepitaxial interfaces with the high density in the nanocomposite.