Structural, Microhardness, Photoconductivity, and Dielectric ...

Research ArticleStructural Microhardness Photoconductivity and DielectricProperties of Tris(thiourea) Cadmium Sulphate Single Crystals

A P Arthi1 M Sumithra Devi2 and K Thamizharasan3

1 Department of Physics Thangavelu Engineering College Chennai 600 097 India2Department of Physics Anand Institute of Technology Chennai 603 103 India3 Department of Physics Sir Theagaraya College Chennai 600 021 India

Correspondence should be addressed to K Thamizharasan tamilsuryayahooin

Received 24 August 2014 Revised 4 November 2014 Accepted 4 November 2014 Published 20 November 2014

Academic Editor Shi J Xu

Copyright copy 2014 A P Arthi et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Semiorganic nonlinear optical tris(thiourea) cadmium sulphate (TTCS) single crystals were grown by slow evaporation methodThe crystal system cell parameter of the grown crystal was identified by powder X-ray diffraction study The self-focusing 119885-scantechnique has been employed to observe the third-order nonlinear optical property of the grown crystal The mechanical propertyof the grown crystal was examined by using Vickerrsquos microhardness test Chemical etching studies were made on the TTCS crystalusing water as an etchant The dark current and photocurrent properties of the crystal were estimated by using photoconductivitystudy The dielectric constant of grown crystal was studied in different temperature by varying applied frequencies

1 Introduction

The semiorganic nonlinear optical (NLO) materials have asignificant impact on laser technology optical communica-tion and are applied in optical storage technologies in recentyears [1 2] The organic materials have large NLO coefficientwhen compared to inorganic materials but their usage isimpeded due to their poor mechanical strength low thermalstability and low laser damage threshold [3] This organicmolecular salt exhibits interesting NLO properties because ofits strong Coulomb interactions between charged molecules[4] The inorganic materials have excellent mechanical andthermal properties but possess relatively modest optical non-linearities due to lack of extended 120587-electron delocalization[5] Both the high nonlinear optical efficiency and stablematerials are the interest of the future technological advance-ments The semiorganic material offers great materials forsecond- and third-order nonlinear optical applications Thesolution growth technique is the efficient way to producegood quality semiorganicNLO crystals [6] One such semior-ganic material is the metal complex of thioureaThe thioureamolecule is an interesting inorganic matrix modifier becauseof its large dipole moment It has good ability to form an

extensive network of hydrogen bond and has the coordina-tion capacity to form different phases of metal-thiourea com-plexes [7 8] In our study thiourea a typical polar moleculewas selected to combine with cadmium sulphate and itsresults are summarized

2 Experimental Work

The semiorganic nonlinear optical compound tris(thiourea)cadmium sulphate (TTCS) was synthesized by direct chem-ical reaction The calculated amount of AR grade thiourea(3mol) and cadmium sulphate (1mol) was dissolved indeionized water The mixtures of the reactants were stirredwell for about 6 h to avoid coprecipitation of multiple phasesThe synthesized solution produced TTCS salt and its puritywas improved by repeated recrystallization processes inaqueous solution This purified salt was then used to preparesaturated TTCS solution that was further stirred well andfiltered with high quality filter paper to avoid any impurityThe saturated growth solution was poured into a containerand isolated for inciting slow evaporation of the solventAfter 3 weeks the supersaturated mother solution yields thespontaneously nucleated TTCS crystals and the well-grown

Hindawi Publishing CorporationJournal of Solid State PhysicsVolume 2014 Article ID 153272 5 pageshttpdxdoiorg1011552014153272

2 Journal of Solid State Physics

Figure 1 As-grown TTCS crystal by slow evaporation method

10 20 30 40 50 60

50

100

150

200

(minus260)

(minus126)

(1ndash3

4)

(3ndash3

2)

(042

)(3

ndash12

)(0

ndash24

)(1

ndash40

)(minus3

ndash21

)(131

)(minus123

)(031

)(minus130

)(030

)(022

)

(102

)(minus221

)(1

ndash21

)(021

)(minus201

)

(minus102

)(101

)

(0ndash1

1)

(0ndash1

1)

Inte

nsity

(cps

)

2120579

(100

)

Figure 2 Powder X-ray diffraction pattern of TTCS crystal

TTCS crystals were harvested in a period of 4-5 weeks Theoptically transparent TTCS crystals whose dimension is upto 10 times 5 times 4mm3 were obtained as shown in Figure 1 Thegood quality crystals were used for further characterizations

3 Results and Discussion

31 X-Ray Diffraction Study The powder X-ray diffractionpattern of TTCS crystal was recorded by SIEFERT X-ray dif-fractometer using Cuk

120572(k120572= 154 A) radiation The

recorded powder X-ray diffraction pattern of TTCS crystalis shown in Figure 2 The disclosure of well-defined Braggrsquospeaks at specific 2120579 angle shows the high crystallinity of TTCScrystals The cell parameters of the as-grown TTCS singlecrystals were evaluated The values belonged to triclinic sys-tem of centrosymmetric 119875

1space group with cell dimensions

of 119886 = 871 A 119887 = 904 A 119888 = 973 A 120572 = 9176∘ 120573 = 11058∘and 120574 = 9555∘ and volume (119881) = 713 A3 The observed cellvalues agreed with reported values [9 10]

minus6 minus4 minus2 0 2 4 6008

012

016

020

024

028

Nor

mal

ized

Z (mm)

Z (mm)

CA


00

02

04

06

08

10 OA

tran

smitt

ance

Nor

mal

ized

tr

ansm

ittan

ce

Figure 3 Open aperture (OA) and closed aperture (CA) 119885-scancurves of TTCS crystal

32 119885-Scan Measurement Third-order nonlinear opticalproperty of TTCS crystal was studied by 119885-scan techniqueThemagnitude and sign of the nonlinear refractive index (119899

2)

and nonlinear absorption coefficient (120573) of the crystals werecalculated from the 119885-scan data [11ndash13] The open aperture(OA) and closed aperture (CA) 119885-scan methods are usedfor the measurement of nonlinear absorption coefficient andnonlinear optical refraction for optical materials In thisexperiment Gaussian laser beam was used for molecularexcitation and its propagation direction has been taken asthe 119885-axis of the optically polished crystal The beam wasfocused using a convex lens and the focal point has been takenas 119885 = 0 The monochromatic continuous wave (cw) laserlight 6328 nm with power of 20mW beam from He-Ne laserwas used The optically polished 1mm thick crystal samplewas fixed in the travel range of 12mm The input energy andthe energy transmitted by the sample were measured usinga power meter The normalized transmittance for the posi-tioned crystal sample wasmeasured at different positions andwas used to calculate third-order nonlinear optical propertyof the crystal The peak followed by a valley of normalizedtransmittance is the signature for nonlinearity of thematerialThe 119885-scan curves in closed and open aperture modes areillustrated in Figure 3 It reveals that nonlinear refractiveindex 119899

2= 183 times 10minus11m2W and nonlinear absorption

coefficient120573= 139times 10minus5 cmWThe imaginary and real partsof the third-order susceptibility values were determined asIm 1205943 = 967 times 10minus12 esu and Re 1205943 = 15974 times 10minus11 esurespectively

33 VickerrsquosMicrohardness Test Thehardness property of thecrystals played a key role in device fabrication The transpar-ent crystals free fromcracks were selected formicrohardnessmeasurement Microhardness test for the grown crystals wascarried out using a Leitz Metallux-II microscope with acalibrated ocular at the magnification of ldquoX500rdquo Vickerrsquos

Journal of Solid State Physics 3

20 30 40 50 60 70 80 90 10084

86

88

90

92

94

96

98

100

102

104

106

Load P (g)

Vick

errsquos

hard

ness

num

ber (

kg m

mminus2)

(a)

280 285 290 295 300 305 310 315 32013

14

15

16

17

18

19

20

n = 1753

logP

log d

(b)

Figure 4 (a) Variation of Vickerrsquos microhardness number (119867119881) with applied load (119875) for TTCS crystal (b) Variation between log119875 and log 119889

of TTCS crystal

microhardness study had been used to analyze the hardnessproperty of the grown TTCS crystals using a Leitz micro-hardness tester fitted with a diamond pyramidal indenter Awell-polished TTCS crystal was used for the study and it wasplaced on the platform of Vickerrsquos microhardness The loads(119875) of different magnitudes were applied over a fixed intervalof time with an indentation time of 8 s for all the loads Thehardness number was calculated using the relation

119867119881= 18544

119875

1198892Kgmm2 (1)

where ldquo119867119881rdquo is the Vickerrsquos microhardness number ldquo119875rdquo is

the applied load in ldquoKgrdquo and ldquo119889rdquo is the diagonal lengthof the indentation impression The plot between hardnessnumber (119867

119881) and applied load (119875) is shown in Figure 4(a)

and it shows that hardness number decreases with increasein applied load The Meyerrsquos index (119899) is used to determineif the material belonged to soft category or hard categoryAccording to Onitsch [14] the value (119899) ranges between 1 and16 for hardmaterials and is greater than 16 for softmaterialsThe Meyerrsquos index number was calculated using Meyerrsquos lawas follows

119875 = 119870119889119899

log119875 = log 119896 + 119899log119889(2)

where ldquo119896rdquo is the constant for a material and ldquo119899rdquo is the Meyerrsquosindex In order to find the value of ldquo119899rdquo a graph was plottedbetween applied loads ldquolog119875rdquo and ldquolog 119889rdquo which resulted inthe formation of a straight line The slope value of the plot inFigure 4(b) was identified as 119899 = 1753 thus confirming thatthe TTCS crystal belonged to soft category

34 Chemical Etching The NLO property of the crystalpurely depends on the perfection of the grown crystalMicro-structure analysis was carried out on the grown crystal by

Figure 5 Etch pit pattern of TTCS crystal with water in 10 s

using optical microscope in the reflective mode The well-polished crystal was used for surface treatment using water asan etchant in 10 seconds The atoms at the grain boundariesare chemically more active consequently dissolve more read-ily than those within the grain forming small grooves Thegrooves become discernible when viewed under microscopebecause of reflected light with different angle The recordedetch pit pattern of TTCS crystal is shown in Figure 5 in thescale of 100 120583m From the etching analysis revealed that therod like etchpit pattern observed in TTCS crystal

35 Photoconductivity Studies Photoconductivity is theincremental change in the electrical conductivity of a sub-stance upon illumination which is generated by the absorp-tion of photons [15] The relevant photoexcitation of freecarriers and photoconductivity are expected when the crystalis illuminated with visible or near-infrared wavelengthsThe polished defect-free TTCS crystal sample which wasrectangular in size was used for the study Photoconductivityproperty of the grown TTCS crystal was measured in the


0 500 1000 1500 2000 2500 30000

50

100

150

200

250

300

350

400

450

Dark current Photocurrent

Applied field (Vcm)

Curr

ent (120583

A)

Figure 6 Photoconductivity measurement of TTCS crystal

range of 0ndash2800Vcm using a Keithley picoammeter Theelectrical contacts were made with the sample by silver paintand it was connected by copper wire that was used as anelectrodeThe light from halogen lamp of 100Wwas focusedon the sample using convex lens In addition the appliedvoltage was increased by 0ndash2800V and the correspondingphotocurrent was measured with respect to the appliedvoltage The variations of photocurrent (119868

119875) and dark current

(119868119889) with applied fieldwere shown in Figure 6 It was observed

that both dark current and photocurrent of the crystalsincrease linearly with the applied electric field but if the darkcurrent is less than the photocurrent photoconductivity ofthe TTCS crystal is positive

36 Dielectric Constant The dielectric constant of crystalis due to the contribution of electronic ionic orientationand space charge polarization which are predominant inthe lower frequency region [16] Dielectric measurements ofthe crystals were carried out using a HIOKI model 3532-50LCR HITESTER The dielectric measurements were carriedout from 40K to 150K at the frequencies of 1 KHzndash1MHzand were shown in Figure 7 It was noticed that variation ofdielectric constant as a function of frequency suggests that thedielectric constant is relatively higher in the low frequencyregion The dielectric constant of the crystal decreases whenfrequency increases The characteristic of lower dielectricconstant with fewer defects crystal is utilized for variousNLOapplications

4 Conclusion

Semiorganic thiourea metal complex tris(thiourea) cad-mium sulphate single crystals with dimension up to 10 times 5 times4mm3 was grown by slow evaporation technique Powder X-ray diffraction study confirmed the cell dimension values andstructure of the latticeThird-order nonlinear refractive index

30 35 40 45 50 55 6085

90

95

100

105

110

115

120

125

130

135

140

Die

lect

ric co

nsta

nt (120576

r)

40 ∘C80 ∘C

120 ∘C150 ∘C

log f(Hz)

Figure 7 Dielectric constant versus log119891 of TTCS crystal

(1198992= 183 times 10minus11m2W) nonlinear absorption coefficient

(120573 = 139 times 10minus5 cmW) and third-order nonlinear opticalsusceptibility (1205943 = 1189 times 10minus8 esu) were estimated by 119885-scan technique The hardness property of the crystal wasstudied and its Meyerrsquos index value 119899 = 1753 suggested thatTTCS is a soft material The microstructure of the growthpattern was analyzed using etch pit study The high value ofphotocurrentwas observed than the dark current for differentapplied fieldsThe dielectric constant of the crystal was foundto be high in the low frequency region and decreased withincrease in applied frequency All the results explained itsusefulness to the optical applications

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] H O Marey L F Warns M S Webb et al ldquoSecond-harmonicgeneration in zinc tris(thiourea) sulfaterdquo Applied Optics vol 31no 24 pp 5051ndash5060 1992

[2] X Q Wang D Xu D R Yuan et al ldquoSynthesis structure andproperties of a new nonlinear optical material zinc cadmiumtetrathiocyanaterdquoMaterials Research Bulletin vol 34 no 12 pp2003ndash2011 1999

[3] M Jiang and Q Fang ldquoOrganic and semiorganic nonlinearoptical materialsrdquo Advanced Materials vol 11 pp 1147ndash11511999

[4] A K Dharmadhikari B Roy S Roy J A Dharmadhikari AMishra and G R Kumar ldquoHigher-order optical nonlinearitiesin 41015840-dimethylamino-N-methyl-4-stilbazolium tosylaterdquoOpticsCommunications vol 235 no 1ndash3 pp 195ndash200 2004

[5] J Ramajothi S Dhanuskodi and K Nagarajan ldquoCrystalgrowth thermal optical and microhardness studies of tris


(thiourea) zinc sulphatemdasha semiorganic NLOmaterialrdquoCrystalResearch and Technology vol 39 no 5 pp 414ndash420 2004

[6] N Zaitseva L Carman A Glenn et al ldquoApplication of solutiontechniques for rapid growth of organic crystalsrdquo Journal of Crys-tal Growth vol 314 no 1 pp 163ndash170 2011

[7] S G Bhat and S M Dharmaprakash ldquoA new metal-organiccrystal bismuth thiourea chloriderdquoMaterials Research Bulletinvol 33 no 6 pp 833ndash840 1998

[8] G A Bowmaker J V Hanna C Pakawatchai B W Skelton YThanyasirikul and A H White ldquoCrystal structures and vibra-tional spectroscopy of copper(l) thiourea complexesrdquo InorganicChemistry vol 48 no 1 pp 350ndash368 2009

[9] L Cavaica A C Villa A Mangia and C Palmeiri ldquoThe crys-tal structure of tris(thiourea)cadmium sulphaterdquo InorganicaChimica Acta vol 4 pp 463ndash470 1970

[10] E Corao and S Baggio ldquoThe crystal structure of a five-coor-dinated cadmium(II) complex Tristhiourea-cadmium sul-phaterdquo Inorganica Chimica Acta vol 3 pp 617ndash622 1969

[11] R DeSalvo M Sheik-Bahae A A Said D J Hagan and EW Van Stryland ldquoZ-scan measurements of the anisotropy ofnonlinear refraction and absorption in crystalsrdquo Optics Lettersvol 18 no 3 pp 194ndash196 1993

[12] M Krishna Kumar S Sudhahar P Pandi G Bhagavan-narayana and R Mohan Kumar ldquoStudies of the structural andthird-order nonlinear optical properties of solution grown 4-hydroxy-3-methoxy-41015840-N1015840-methylstilbazolium tosylate mono-hydrate crystalsrdquo Optical Materials vol 36 no 5 pp 988ndash9952014

[13] MK Kumar S Sudhahar A Silambarasan BM Sornamurthyand R M Kumar ldquoCrystal growth structural linear and non-linear optical studies of 4-methyl-41015840-N1015840-methylstilbazoliumtosylate single crystalsrdquo Optik vol 125 no 2 pp 751ndash755 2014

[14] E M Onitsch ldquoThe present status of testing the hardness ofmaterialsrdquoMicroscope vol 95 pp 12ndash14 1950

[15] S Follonier M Fierz I Biaggio U Meier C Bosshard andP Gunter ldquoStructural optical and electrical properties of theorganic molecular crystal 4-NN-dimethylamino-41015840-N1015840-methylstilbazolium tosylaterdquo Journal of the Optical Society of AmericaB Optical Physics vol 19 no 9 pp 1990ndash1998 2002

[16] C Balarew and R Dehlew ldquoApplication of the hard and softacids and bases concept to explain ligand coordination in dou-ble salt structuresrdquo Journal of Solid State Chemistry vol 55 no1 pp 1ndash6 1984

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

Computational Methods in Physics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of


Figure 1 As-grown TTCS crystal by slow evaporation method

10 20 30 40 50 60

50

100

150

200

(minus260)

(minus126)

(1ndash3

4)

(3ndash3

2)

(042

)(3

ndash12

)(0

ndash24

)(1

ndash40

)(minus3

ndash21

)(131

)(minus123

)(031

)(minus130

)(030

)(022

)

(102

)(minus221

)(1

ndash21

)(021

)(minus201

)

(minus102

)(101

)

(0ndash1

1)

(0ndash1

1)

Inte

nsity

(cps

)

2120579

(100

)

Figure 2 Powder X-ray diffraction pattern of TTCS crystal

TTCS crystals were harvested in a period of 4-5 weeks Theoptically transparent TTCS crystals whose dimension is upto 10 times 5 times 4mm3 were obtained as shown in Figure 1 Thegood quality crystals were used for further characterizations

3 Results and Discussion

31 X-Ray Diffraction Study The powder X-ray diffractionpattern of TTCS crystal was recorded by SIEFERT X-ray dif-fractometer using Cuk

120572(k120572= 154 A) radiation The

recorded powder X-ray diffraction pattern of TTCS crystalis shown in Figure 2 The disclosure of well-defined Braggrsquospeaks at specific 2120579 angle shows the high crystallinity of TTCScrystals The cell parameters of the as-grown TTCS singlecrystals were evaluated The values belonged to triclinic sys-tem of centrosymmetric 119875

1space group with cell dimensions

of 119886 = 871 A 119887 = 904 A 119888 = 973 A 120572 = 9176∘ 120573 = 11058∘and 120574 = 9555∘ and volume (119881) = 713 A3 The observed cellvalues agreed with reported values [9 10]


012

016

020

024

028

Nor

mal

ized

Z (mm)

Z (mm)

CA


00

02

04

06

08

10 OA

tran

smitt

ance

Nor

mal

ized

tr

ansm

ittan

ce

Figure 3 Open aperture (OA) and closed aperture (CA) 119885-scancurves of TTCS crystal

32 119885-Scan Measurement Third-order nonlinear opticalproperty of TTCS crystal was studied by 119885-scan techniqueThemagnitude and sign of the nonlinear refractive index (119899

2)

and nonlinear absorption coefficient (120573) of the crystals werecalculated from the 119885-scan data [11ndash13] The open aperture(OA) and closed aperture (CA) 119885-scan methods are usedfor the measurement of nonlinear absorption coefficient andnonlinear optical refraction for optical materials In thisexperiment Gaussian laser beam was used for molecularexcitation and its propagation direction has been taken asthe 119885-axis of the optically polished crystal The beam wasfocused using a convex lens and the focal point has been takenas 119885 = 0 The monochromatic continuous wave (cw) laserlight 6328 nm with power of 20mW beam from He-Ne laserwas used The optically polished 1mm thick crystal samplewas fixed in the travel range of 12mm The input energy andthe energy transmitted by the sample were measured usinga power meter The normalized transmittance for the posi-tioned crystal sample wasmeasured at different positions andwas used to calculate third-order nonlinear optical propertyof the crystal The peak followed by a valley of normalizedtransmittance is the signature for nonlinearity of thematerialThe 119885-scan curves in closed and open aperture modes areillustrated in Figure 3 It reveals that nonlinear refractiveindex 119899

2= 183 times 10minus11m2W and nonlinear absorption

coefficient120573= 139times 10minus5 cmWThe imaginary and real partsof the third-order susceptibility values were determined asIm 1205943 = 967 times 10minus12 esu and Re 1205943 = 15974 times 10minus11 esurespectively

33 VickerrsquosMicrohardness Test Thehardness property of thecrystals played a key role in device fabrication The transpar-ent crystals free fromcracks were selected formicrohardnessmeasurement Microhardness test for the grown crystals wascarried out using a Leitz Metallux-II microscope with acalibrated ocular at the magnification of ldquoX500rdquo Vickerrsquos


20 30 40 50 60 70 80 90 10084

86

88

90

92

94

96

98

100

102

104

106

Load P (g)

Vick

errsquos

hard

ness

num

ber (

kg m

mminus2)

(a)

280 285 290 295 300 305 310 315 32013

14

15

16

17

18

19

20

n = 1753

logP

log d

(b)


of TTCS crystal


119867119881= 18544

119875

1198892Kgmm2 (1)





119875 = 119870119889119899

log119875 = log 119896 + 119899log119889(2)







0 500 1000 1500 2000 2500 30000

50

100

150

200

250

300

350

400

450


Applied field (Vcm)

Curr

ent (120583

A)







4 Conclusion


30 35 40 45 50 55 6085

90

95

100

105

110

115

120

125

130

135

140

Die

lect

ric co

nsta

nt (120576

r)

40 ∘C80 ∘C

120 ∘C150 ∘C

log f(Hz)






References
























FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




20 30 40 50 60 70 80 90 10084

86

88

90

92

94

96

98

100

102

104

106

Load P (g)

Vick

errsquos

hard

ness

num

ber (

kg m

mminus2)

(a)

280 285 290 295 300 305 310 315 32013

14

15

16

17

18

19

20

n = 1753

logP

log d

(b)


of TTCS crystal


119867119881= 18544

119875

1198892Kgmm2 (1)





119875 = 119870119889119899

log119875 = log 119896 + 119899log119889(2)







0 500 1000 1500 2000 2500 30000

50

100

150

200

250

300

350

400

450


Applied field (Vcm)

Curr

ent (120583

A)







4 Conclusion


30 35 40 45 50 55 6085

90

95

100

105

110

115

120

125

130

135

140

Die

lect

ric co

nsta

nt (120576

r)

40 ∘C80 ∘C

120 ∘C150 ∘C

log f(Hz)






References
























FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




0 500 1000 1500 2000 2500 30000

50

100

150

200

250

300

350

400

450


Applied field (Vcm)

Curr

ent (120583

A)







4 Conclusion


30 35 40 45 50 55 6085

90

95

100

105

110

115

120

125

130

135

140

Die

lect

ric co

nsta

nt (120576

r)

40 ∘C80 ∘C

120 ∘C150 ∘C

log f(Hz)






References
























FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



Structural, Microhardness, Photoconductivity, and Dielectric ...

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