Table Of ContentAksimentyevaetal.NanoscaleResearchLetters2013,8:29
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NANO EXPRESS Open Access
The chemical exfoliation phenomena in layered
GaSe-polyaniline composite
Olena Igorivna Aksimentyeva1, Pavlo Yuriyovich Demchenko1, Volodymyr Pavlovich Savchyn2
and Olexiy Alexandrovich Balitskii2*
Abstract
Toelucidatethe nature of polyaniline (PANI)-GaSe mutual interaction, we carried out structural studies of
nano-GaSe powders encapsulatedby PANI, exploiting X-ray diffraction and high resolution transmission electron
microscopy (HRTEM). Mechanically and ultrasonically dispersed GaSe crystals were mixed with aniline, which then
underwent polymerization. After such treatment, GaSe nanocrystals (as shown byHRTEM) consist offew elementary
monolayer sandwiches of hexagonal GaSe structure along thecrystallographic axisc with a meandiameterof
9.2nm.Therewasasignificantexpansionofinterplanardistances(upto0.833nm)forallofthenanocrystalsobserved
comparedto0.796nmforthesinglecrystals.
Keywords:Chemicalexfoliation,Galliumselenide,Layeredcompound
Background solutions [12-14] further underwent self-organization into
Two dimensional (2D) semiconductor nanocrystals fabri- more complicated structures [13,14] and fabricated by
cated in the plate-like form have been intensely investi- aqueous- or alcohol-based ultrasonification of GaSe pow-
gated since the invention of single-layer graphene. The ders[15,16].Themainproblemintheapplicationofsuch
majority of binary compounds among them are either objectsissynthesisandstabilizationchemistrytoberather
metal dichalcogenides (of molybdenum, vanadium, tung- nonreproducible and hardly to be controlled as a rule.
sten) or indium and gallium monochalcogenides. Gallium That usually results in unwanted electronic processes on
selenide with chemically passive selenium-terminated surface-passivator boundaries and requires of the strongly
(11–20) surfaces has been applied as effective optical ma- binding ligands, preferably unreactive in respect to the
terial for IR [1,2] and terahertz [3,4] ranges, termination ambient. Recent perspective [17] indicates that 2D plate-
layers in heterointerface fabrication [5-7], etc. Unique like nanoparticles (including those of GaSe) are excellent
structure properties stand GaSe among materials suitable luminescent emitters due to the suppression of the
for production single layer 2D plates, even extracted and absorption strengths into one electronic state in contrary
isolated from bulk. Although several groups have already to the band for a bulk material. Not long ago, we found
succeeded in mechanical- [8,9], thermal-, and laser- that the mutual interaction of components in the hybrid
induced [10] GaSe exfoliation, fabrication of free single composites containing GaSe and conducting polyaniline
sheetparticleswasfoundtobenotaneasytask.Theprop- (PANI) polymer leads to an increased essential conducti-
erties of those GaSe foils are essentially substrate- vity, UVshifting in GaSe luminescence spectra, plate-like
dependent in the mechanical procedures, while higher particle formation, etc. [18]. The aim of the presented
temperature growth is accompanied by rolling of the communication is an elucidation of the nature of the
sheetsintomorethermodynamicallyfavorable[11]tubular above-mentioned phenomena by means of structural stu-
3D structures. Other successful attempts resulted in syn- dies of micro- (nano-) GaSe powders encapsulated by
thesis of colloidal single-layered nanoparticles in organic PANI, exploiting X-ray diffraction (XRD) and high reso-
lutiontransmissionelectronmicroscopy.
*Correspondence:[email protected]
2DepartmentofElectronics,LvivIvanFrankoNationalUniversity,
DragomanovStr.50,Lviv79005,Ukraine
Fulllistofauthorinformationisavailableattheendofthearticle
©2013Aksimentyevaetal.;licenseeSpringer.ThisisanOpenAccessarticledistributedunderthetermsoftheCreative
CommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,and
reproductioninanymedium,providedtheoriginalworkisproperlycited.
Aksimentyevaetal.NanoscaleResearchLetters2013,8:29 Page2of5
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Methods (up to few nanometers in height and up to 100 nm in
Aniline monomer, para-toluene-sulfonic acid, ammo- length) anddiscswith rather broaddiameterdistribution
niumpersulfate ((NH ) S O )asoxidantwerepurchased (see Figure 1f). Beside the majority of particles are
4 2 2 8
from Aldrich Co., St. Louis, USA. Nanodispersed GaSe located inside 5 to 15 nm size region (mean size was
powder was obtained by mechanical milling of GaSe estimated as 9.2 nm with 5.2 nm value of standard devi-
crystals, followed by ultrasonication inbutanol. Both un- ation), there are also several ultrasmall (less than 5 nm)
treated GaSe single crystal plates and dried-in-vacuum and ultralarge (>20 nm) objects. The stripes and discs
GaSe nanopowders were used for the synthesis of hybrid underwent atomic resolution on HR-TEM (Figure 1c,d,e),
nanocomposites with polyaniline. which magnifies boxed areas on Figure 1a,b. As
Preparation of composites was carried out under con- shown by HRTEM (Figure 1c,d), the heights of such
ditions of oxidative polymerization of aniline under stripes consist of GaSe elementary sandwiches, packed
(NH ) S O in an aqueous medium in the presence of along с crystallographic axis. It should be noted that
4 2 2 8
toluene sulfonic acid (TSA) as a doping and stabilizing there is an essential broadening of lattice plane spacing
agent. The method of obtaining the composite consists in this direction, yielding 0.833 nm (this value does not
of several stages. Originally, the method was performed vary for many nanocrystals from different sample areas).
by dispersing of about 45 to 150 mg GaSe plates (such Comparing with the same value for bulk GaSe material
samples are further called PANI-GaSe sample) or GaSe (0.796 nm for (0002) planes spacing), the c lattice par-
powderwithparticlesizeof60to80nm(PANI-powdered ameter increased by about 4.4%. Some of the nanocrys-
GaSe sample) in a solution of surfactant 0.12 M tals are so well resolved in order to obtain even fringes
TSA using ultrasonication for 30 min. Then, 0.205 g of from higher (0004) planes with the same value of
monomer droplets was injected in the GaSe dispersion increasing c lattice parameter. The elementary tetra-
with continuous stirring, and after 10 min, the solution layers of GaSe structure along (11–20) direction are
was added with 0.005 ml of 0.47 M solution of oxidant somehow bended by mechanical stresses, applied nor-
(NH ) S O .TheprocesswascarriedoutatT=293Kfor mally to above-mentioned direction on the whole parti-
42 2 8
24 h. Finally, a dark dispersion of composite was iso- cles (Figure 1c,d), but we did not observe any extended
lated in the form of precipitate by centrifuging. For defects or elementary tetralayer fractures. The number
investigations,wetooksampleswithinorganiccomponent of such monolayer (ML) per particles could vary from
with10to12%wt. 10 to 20 (5 to 10 lattice parameters). The smaller parti-
For transmission electron microscopy (TEM) andelec- cles (1 to 2 ML) during the interaction with electron
tron dispersive X-ray (EDX) characterization, a small beam, collinear to edges in plate-like particle geometry,
amount of PANI-powdered GaSe sample(due to untran- simply do not effectively scatter electrons to make them
sparency of bulk GaSe for electrons, PANI-GaSe sample visible by TEM, but were detected by optical measure-
was not suitable for TEM characterization) was diluted ments earlier [18] and as thin lattice resolved discs on
in anhydrous acetone and centrifuged; few drops of Figure 1a,e. That is easily proved by comparing contrast
supernatant then were spread over a carbon-coated cop- of 10 and 15 to 17 ML particles in corresponding TEM
per grip followed by drying (in a nitrogen atmosphere). images. The nature of disc-like particles is elucidated
That removes the traces of acetone and PANI capsules through analyzing Figure 1e. They are the same particles
from GaSe nanocrystals. For X-ray diffraction measure- in Figure 1c,d, but their face plane oriented normally to
ments, GaSe-PANI and PANI-powdered GaSe samples the electron beam. We can also observe lattice fringed
were placedbetweentwo plasticslides. on one well oriented plane in respect to the electron
XRD patterns were recorded in transmittance mode beam. This time, the lattice spacing yields 0.969 nm, co-
on a STOE STADI Pspectrometer (STOE & Cie GmbH, inciding exactly with triple value of (10–10) lattice plane.
Darmstadt, Germany) equipped with copper X-ray tube From TEM and HRTEM images, we suggest that the
(the incident beam was passed through a germanium particles are few-ML thick to observe lattice spacing
monochromator to produce Kα1 radiation with a wave- similartomechanicallyexfoliatedGaSeflakes[9].
length of 0.154056 nm). EDX and TEM images were XRD patterns and EDX acquisition are presented in
obtained using a HR-TEM (Fei Technai G2 F20 S Twin Figure 2. EDX (Figure 2, inset) confirms the initial stoi-
microscope) operatedat 300keV. chiometry of GaSe powders, predictably denying volatil-
ity losses (since we did not carry out any of the high
Results and discussion temperature treatments). The other lines (not presented
TEM images of PANI-powdered GaSe samples are pre- on expanded EDX spectrum) came both from organic
sented in Figure 1. Expanded images (Figure 1a,b) de- components and TEM grid (copper, sulfur, nitrogen,
monstrate the presence (simultaneously with ultralarge oxygen, and carbon). After performing X-ray phase ana-
microcrystals) of two types of nano-objects: thin stripes lysis, we can conclude that the formed object is a
Aksimentyevaetal.NanoscaleResearchLetters2013,8:29 Page3of5
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Figure1TEMandHRTEMimagesofthenanoparticles.Representative(a,b)TEM,HRTEM(c,d,e)ofboxedareas(ina,b)imagesandsize
histogrammadebycountingover100particlesfrombTEM(f)ofexfoliatedbyPANI–powderedGaSenanoparticles.Inthe(c)and(d)images,the
latticeplanescouldbeattributedtothe(0001)directionalongthecrystallographiccaxis,whileinthe(e)image,tothe(10–10)directionalong
thecrystallographicaaxisofhexagonalGaSe.
complex PANI-GaSe, a new chemical compound. While spatial group P63/mmc with a = 3.75607 (10) and
indexing PANI-GaSe XRD pattern (fitting up with the c=16.15(1)Å(alreadyabout1.5%ofcparameterincreas-
best texture model using WinCSD [19]), we came to the ing) with a dominant orientation (10–10) texture model.
conclusion that the main phase in the sample is based As shown in Figure 2a, there is also one additional dif-
on hexagonal GaSe (so-called β-polytype [20,21]), the fraction peak in the interplanar distance (d = 1.917 Å) as
Aksimentyevaetal.NanoscaleResearchLetters2013,8:29 Page4of5
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Figure2XRDpatterns,EDXspectrumandschematicpresentation.XRDpatternsofPANI-GaSesample(а),PANI-powderedGaSesample(b),
typicalEDXspectrumofmainelements(inset),andschematicrepresentationofGaSecrystalstructure(β-polytype,2Hβ:spacegroupP6/mmc)
3
interactionwithPANI(c).
well as some additional diffraction peaks with very low describe the prevailing model of orientation, creates the
intensity (in particular, at d = 1.107 Å). Also, the applied additional diffraction reflections, and is clearly eluci-
texture model does not precisely describe the experi- dated by HRTEM. When utilizing the single-crystal
mental diffractogram: the highest intensity reflection is plates, this composite phase is apparently saved, but
(11–20), while according to the theoretical diffraction, it thereissimplyhexagonalGaSeincontrarytothesample
should be (10–10). The XRD of the PANI-powdered PANI-powdered GaSe. As it was mentioned earlier
GaSe sample showed that during the milling, the crystal [18,22], powdered (i.e., fractured) GaSe samples exhibit
texture predictably decreases, and the diffractogram con- numerous extended defects-cleavage stairs on the sur-
tains other diffraction reflections, characteristic for GaSe face. The aniline molecules diffuse through them more
(Figure 2b). There is also the possibility of partial transi- effectively, filling van der Waals gap of particles
tion of β-GaSe polytype into the so-called ε-polytype (Figure 2c). That forms few ML composite particles
GaSe (2Hα, space group P-6 m2), which shows in part- based on GaSe-PANI compounds. As we have not
icular, the ratio of intensities of reflections (10–10) and observed any lattice fringes that exceeded 8.33 Å for
(10–11). Note that the diffraction peak in the interplanar (0002) GaSe crystal planes, we conclude that this is a
distance d = 1.917 Å persists. In fact, for that sample, critical parameter of GaSe-PANI composites based on
any crystallographic refinement is generally unstable be- GaSe crystal structure. Furtherhindrance of PANI in the
cause of essential difference between the FWHM of van der Waals gap unambiguously leads to the forma-
reflections (they are either narrower or broader than tion of free isolated particles. The low-temperature syn-
theoretical). The simple calculations of angular positions thesis procedure and the presence of PANI on GaSe
of the reflections with third Miller index not equal to edges permit to avoid thermodynamically preferable rol-
zeroprovideacparameterveryclosetothatoneobserved ling of plane-like particles into tubular, onion [10], or
byTEM. belt-like[23]3Dstructures.
It is well known that gallium monoselenide crystal lat-
tice (Figure 2c) consists of tetralayers: Se-Ga-Ga-Se-, Conclusions
bounded by the weak van der Waals forces. The inter- Few ML gallium selenide-PANI nanoparticles have been
layer distance between selenium-terminated sandwiches synthesized using chemical exfoliation method. They
is approximately 3.25 Å. Due to this, it is possible to dif- possess highly crystalline structure similar to bulk GaSe,
fusively include polymeric chains of polyaniline between but with essential broadening of interplanar distances.
layers of Se-Se (the width of aniline molecule is about The obtained few-nanometer thick disk-like flakes pos-
2.8 Å in the thickest point of benzene ring). Obviously, sess broad diameter distribution with average value of
polymerization results in much larger spatial hindrance 9.2 nm. These results enlighten new frontiers for the de-
of long PANI molecules when forming crystalline com- velopment of optical nanomaterials. They extend the
positestructuresbased onhexagonalGaSe.Thischanges fabrication techniques such as mechanical and thermal
the diffraction pattern which now does not accurately procedures, not suitable either for formation of size
Aksimentyevaetal.NanoscaleResearchLetters2013,8:29 Page5of5
http://www.nanoscalereslett.com/content/8/1/29
controlled or plate-like particles and organic syntheses, 16. RybkovskiyDV,ArutyunyanNR,OrekhovAS,GromchenkoIA,VorobievIV,
drasticallyaffected bystabilizingligands. OsadchyAV,SalaevEY,BaykaraTK,AllakhverdievKR,ObraztsovaED:Size-
inducedeffectsingalliumselenideelectronicstructure:theinfluenceof
interlayerinteractions.PhysRevB2011,84:085314.
Competinginterest
17. ScholesGD:Twodimensionsarebrighter.NatureMater2011,10:906.
Theauthorsdeclarethattheyhavenocompetinginterests.
18. AksimentyevaOI,DemchenkoPY,SavchynVP,BalitskiiOA:Structure,
Authors’contributions electricalandluminescentpropertiesofthepolyaniline-GaSehybrid
nanocomposites.MolCrystLiqCryst2011,536:297.
OIAcarriedoutthesynthesisofnanocomposites.PYuDparticipatedinXRD
19. AkselrudLG,ZavaliiPY,GrinYN,PecharskiVK,BaumgartnerB,WolfelE:Use
measurementsandstructurerefinements.VPSsupervisedtheworkand
oftheCSDprogrampackageforstructuredeterminationfrompowder
finalizedthemanuscript.OABdesignedtheexperiment,participatedinthe data.MaterSciForum1993,133–136:335.
structuralinvestigationanddraftedthemanuscript.Allauthorsreadand
20. TatarinovaLI,AuleitnerYK,PinskerZG:Electron-diffractionstudyofGaSe.
approvedthefinalmanuscript.
SovPhysCrystallogr1956,1:426.
21. BenazethS,DungNH,GuittardM,LaruelleP:Affinementsurmonocristal
Authors’information delastructuredupolytype2HduséléniuredegalliumGaSeformeβ.
OIAiscurrentlytheleadingresearcherofPhysicalChemistryDepartment.
ActaCrystC1988,44:234.
PYuDisworkingasaseniorresearcherofInorganicChemistryDepartment.
22. Balyts'kyiOO:Fractureoflayeredgalliumandindiumchalcogenides.
VPSandOABareprofessorandassociateprofessor,respectively,of
MaterSci2005,41:839.
SemiconductorPhysicsDepartment.AllauthorsarefromtheLvivIvan
23. PengH,MeisterS,ChanCK,ZhangXF,CuiY:Morphologycontroloflayer-
FrankoNationalUniversity.
structuredgalliumselenidenanowires.NanoLett2007,7:199.
Authordetails
1DepartmentofChemistry,LvivIvanFrankoNationalUniversity,Kyrylaand doi:10.1186/1556-276X-8-29
MefodiyaStr,6,Lviv79005,Ukraine.2DepartmentofElectronics,LvivIvan Citethisarticleas:Aksimentyevaetal.:Thechemicalexfoliation
phenomenainlayeredGaSe-polyanilinecomposite.NanoscaleResearch
FrankoNationalUniversity,DragomanovStr.50,Lviv79005,Ukraine.
Letters20138:29.
Received:22October2012Accepted:6January2013
Published:15January2013
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