Carbon 43 (2005) 87–94

www.elsevier.com/locate/carbon

Composite graphitic nanolayers prepared by self-assemblybetween finely dispersed graphite oxide and a cationic polymer

Tamas Szabo a, Anna Szeri a, Imre Dekany a,b,*

a Department of Colloid Chemistry, University of Szeged, Aradi vertanuk tere 1, H-6720 Szeged, Hungaryb Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Aradi vertanuk tere 1, H-6720 Szeged, Hungary

Received 30 June 2004; accepted 23 August 2004

Available online 5 October 2004

Abstract

Chemical flaking of graphite has been performed by reacting natural graphite with a strong oxidizing agent, NaClO3/HNO3. The

formed hydrophilic, negatively charged graphite oxide (GO) colloids can be dispersed in water which allows the deposition of thin

GO/cationic polymer (poly(diallyldimethylammoniumchloride, PDDA) multilayer films on a glass substrate by wet-chemical self-

assembly. The feasibility of the charge-regulated layer-by-layer deposition is demonstrated by mutual charge titrations of the

film-forming species. Visible-light spectroscopy revealed progressive growth of the film thickness with the number of deposition

of steps, while XRD and AFM showed that partially exfoliated, highly anisometric (aspect ratio >50) graphite oxide platelet aggre-

gates were deposited with an average thickness of the stacked graphite oxide platelets of 10 carbon layers (7.4nm). Reduction of

multilayer assemblies of GO and PDDA on glass yielded a non-conductive turbostratic carbon nanofilm. The original, conductive

graphite-like structure was restored by reduction with N2H4 and annealing at 400 �C which, by gradual ordering of the carbon crys-

tallites, caused a significant decrease in the resistivity.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: A. Graphite oxide, Carbon films; B. Graphitization; C. X-ray diffraction; D. Electrical (electronic) properties

1. Introduction

Graphite/polymer nanocomposites have long been

investigated and used as structural materials because

of their markedly superior mechanical [1] and thermal

properties [2] in comparison with conventional compos-

ites. The most important step of their preparation is thecleavage of coarse graphite crystals to finer, exfoliated

stacks of graphene sheets. A possible way for the flaking

of graphite along its cleavage planes is the chemical [3]

or electrochemical [4] oxidation, by which graphite can

be disaggregated to spherical particles with diameters

as low as 40nm [5]. The formed graphite oxide (GO) is

built of unoxidized aromatic islands of variable size that

0008-6223/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbon.2004.08.025

* Corresponding author. Tel.: +36 62 544210; fax: +36 62 544042.

E-mail address: i.dekany@chem.u-szeged.hu (I. Dekany).

are separated from each other by aliphatic six-mem-

bered rings containing double bonds, C–OH, COOH

and epoxide groups and their quantity depends on the

degree of oxidation [6,7].

Various graphite oxide/polymer [8–10] or expanded

graphite/polymer [11] composites have recently been pre-

pared and their outstanding physicochemical propertiesdemonstrated [12]. However, as pointed out by Kotov

et al. [13], availability of ultrathin films of graphite–poly-

mer composites is required for the construction of ad-

vanced electro-optical devices and sensors. For the

preparation of nanostructured graphite films we have

chosen wet-chemical layer-by-layer self-assembly that

we had successfully applied before for the deposition of

thin multilayer films of different charged colloidal parti-cles and polymers [14,15]. Although self-assembled GO/

polymer films have been fabricated previously [16,17],

88 T. Szabo et al. / Carbon 43 (2005) 87–94

their reduction was only performed by Kotov et al. [13].

They reported that reduction caused a change from an

insulating towards a conductive-like state, but restoration

of the graphite structure has not been proved. We show

here that during hydrazine reduction of a polymer/GO

film a turbostratic carbon film forms the conductivity ofwhich increases significantly when it is converted back

to a nanostructured graphitic film by heat treatment.

Fig. 1. Schematic representation of the layer-by-layer deposition of

S-(PDDA/GO)n films.

1 During the reduction step Zn2+ ions could react with unreduced

GO lamellae by ion-exchange. Besides, the high surface-area amor-

phous carbon film formed could also adsorb significant amounts of

Zn2+.

2. Experimental

2.1. Materials

The host graphite was a natural specimen provided

by Kropfmuhl AG, Germany. The fraction of 250–

500lm was used. Its ash content was less than

0.1wt.% as proved by a thermoanalytical measurement.

NaClO3, N2H4 (Aldrich), fuming HNO3 (Fluka) and

HCl (Reanal) were analytical grade chemicals. As a cat-

ionic polymer poly(diallyldimethylammoniumchloride)

(PDDA) was chosen and from the series of AldrichChemical products the one with medium molecular

weight (MW = 2 · 105�3 · 105) was used as a 20wt.%

aqueous solution. Aqueous dispersions were made by

distilled water filtered with a Millipore Milli-Q system.

2.2. Preparation of graphite oxide

Graphite oxide (denoted as GO) was prepared by thetraditional Brodie method [3]. 10 grams of graphite and

85g of NaClO3 were mixed in a round flask. 60mL of

fuming HNO3 was added from a dropping funnel in

210min with constant stirring. The mixture was then left

aging for a night�s period. Next day it was gradually

heated to 60 �C by a basket heater and kept at

60 ± 5 �C for 8h. The solid GO sample was washed with

1L of 3M HCl solution and at least with 7 · 1L distilledwater until it was chloride ion free (tested with AgNO3

solution). Finally, the suspension was filtered and dried.

2.3. Layer-by-layer deposition of polymer/graphite

oxide nanofilms

Multilayer GO films were prepared by the layer-by-

layer self-assembly process by means of a home madeautomated device, the dipping time and the rate of lift-

ing were controlled by a microprocessor. The deposition

steps and the simplified structure of the assemblies are

presented in Fig. 1.

Glass slides (Menzel Super Frost, Fischer Sci. Ltd.)

were used as substrates in all experiments. After a prelim-

inary cleaning procedure (cleaning with a detergent solu-

tion and soaking in concentrated H2SO4 saturated withK2Cr2O7 for 1h) the slide was immediately dipped into

a 1g/L PDDA solution for 20min, creating an adsorbed

monolayer of PDDA. The weakly adsorbed polymer

molecules were removed from the surface by rinsing withwater for about 1min. After drying, the glass slide was

immersed into a beaker containing freshly ultrasonicated

GO suspension (1g/L, pH = 4.03) which was prepared

by wet-grinding GO powder with water in an agate ball

mill for 4 · 30min (average particle size 62lm). Theimmersion time was chosen again to 20min to let the

adsorption process take place (other authors found

15min or even less to be sufficient for charge overcom-pensation [18,19] in case of different materials generally

used for self-assembly: azo dyes, polymers, etc.). Next,

the same rinsing followed as in the first dipping step.

We must note here that traces of weakly bound polymer

would dissolve from the glass surface and could have the

GO colloidal particles flocculated unless the rinsing pro-

cedure was precisely performed. The dipping/deposition

steps were continued to get further PDDA/GO bilayersdeposited. By this procedure we prepared thin films of

alternating PDDA and GO layers up to 25 bilayers (de-

noted as S-(PDDA/GO)25).

2.4. Reduction of PDDA/GO thin films to more

conductive carbon materials

Earlier bulk experiments indicated the possibility toreduce suspended GO by a nascent hydrogen generator

(Zn powder in HCl solution) or hydrazine [13,20]. The

former may seem to be more effective, yet, we chose to

reduce graphite oxide by N2H4 since its oxidation pro-

duces an inert gas (N2) while oxidation of Zn would

have lead to dissolved Zn2+ ions. 1

T. Szabo et al. / Carbon 43 (2005) 87–94 89

2.5. Characterization of the samples

Visible spectra of the composite films were taken on a

UVIKON 930 dual-beam spectrophotometer (Kontron

Instruments).

X-ray diffraction measurements were performed on aPhilips PW 1830 diffractometer operating with Cu anode

(40kV voltage, 30mA cathodic current). CuKb radia-

tion was absorbed by Ni filters. Basal distances (d002)

were calculated by the Bragg equation. Besides inter-

layer distance determination, crystallite size can be cal-

culated from X-ray line broadening using Scherrer�sequation [21]:

Lc ¼0:9k

bhkl cos hhklð1Þ

where k, h and b are the wavelength of X-rays, the

Bragg�s angle and the pure diffraction line broadening(in radians), respectively. The latter is defined here as

the observed diffraction peak breadth at half-maximum

intensity corrected for the instrumental line broadening

(determined by macrocrystalline K2Cr2O7). Lc is the

mean dimension of the crystallite perpendicular to the

diffracting plane (hk l). Lc-values can be determined by

Eq. (1) with ±5% precision in our experimental

conditions.Atomic force microscopy (AFM) images of the orig-

inal and the treated S-(PDDA/GO)25 films were ob-

tained with a Digital Instruments Nanoscope III

Multimode atomic force microscope operating in tap-

ping mode. 1cm · 1cm pieces of the slides were carefully

cut and fixed to the sample holder, and 1lm · 1lmareas were scanned by etched silicon tapping mode tips

(125lm length) that were purchased from VeecoGmbH.

Thermogravimetric analyses were carried out by a

MOM Q-1500 D Derivatograph in the temperature

range of 25–1000 �C at 5 �C/min heating rate. An inert

athmosphere was assured by N2 gas with �10cm3min�1

flow rate (STP).

Streaming potential measurements were done by

means of a PCD-02 Particle Charge Detector (MutekAnalytic GmbH, Munich, Germany). 2

2 A cylindrical test cell and a piston fitting into it (both made of

teflon) constitutes the heart of the PCD. Between them there is

concentric, narrow slit containing a solution or suspension. Some of

the dispersed charged colloids or macromolecules will adsorb on the

teflon surfaces by physical forces. Each of the adsorbed particles is

surrounded by a symmetrical charge cloud of counter-ions. In a typical

measurement, a synchron motor has the piston oscillated by �4Hzfrequency inducing thereby an intensive liquid stream that sweeps

away the counter-ions from the vicinity of the probe material. The

potential difference induced by the slipping of the counter-ion diffuse

layer from the surface is detected through two gold electrodes; it

corresponds to the so-called streaming potential.

Electrical resistivity of the thin films at ambient tem-

perature was measured by a Keithley 2400 Series Source

Meter with two-wire connections, applying a constant

voltage of 0.1V on two gold electrodes (fixed electrode

distance was 3mm). Five measurements were done at

different surface sites of the films and the values wereaveraged.

3. Results and discussion

3.1. Cyclic charge titration of the PDDA-GO system

Investigating the electrostatic interactions between theGO sheets and cationic polymers, a ‘‘cyclic charge titra-

tion’’ was performed. This term refers to the experiment

when known volumes of a 0.1g/L PDDA solution are

added to 10mL of 0.5g/L GO suspension (pH adjusted

to 9.8) with concomitant streaming potential measure-

ments. After the sign of the potential had reversed, the ti-

trant was changed to the original GO suspension and its

addition was continued until the next reversal, when thetitrant was changed again, and so on. The titration was

performed in a dynamic mode: portions of titrants were

added successively in 10min intervals. The titration curve

presented in Fig. 2a clearly indicates the feasibility of

PDDA to recharge GO surfaces and vice versa, thus,

indirectly indicating the applicability of these species

for the charge regulated self-assembly. This statement is

explained in terms of the streaming potential change (thathas the same sign as the surface charge density) over the

titration: The pure graphite oxide suspension consists of

highly negatively charged lamellae at pH = 9.8 [16,22], a

few of them adsorb on the teflon cell, so a high negative

streaming potential can be measured. Addition of PDDA

gradually decreases this value because the cationic chains

preferentially adsorb on the negative GO surfaces result-

ing in the rapid flocculation of the suspension. After aspecific amount of polyelectrolyte added, no streaming

potential can be measured, consequently, the net surface

charge of the heterocoagulated flocs is zero. Continued

titration overcompensates the original charge of graphite

oxide (high positive potential is detected). As we change

the titrant to the original GO suspension, the streaming

potential tends to decrease and even restoration of the

original charge of GO can be achieved. Subsequent alter-nate additions of the titrants cause charge reversal too,

though, the high starting potential value of GO cannot

be reached again.

In principle we would be able to determine the cation

exchange capacity (CEC) of GO at pH = 9.8 on the

basis of this experiment because the specific charge of

PDDA (meq charges/g polymer) can be calculated

from the molar weight of the monomer (1 monomerholds one positive charge in a very wide pH range)

that is 6.19meq/g. Assuming that the polyelectrolyte

Fig. 2. (a) Cyclic charge titration of the PDDA/GO system: (�) PDDA

solution (0.1g/L), (m) GO suspension (0.5g/L). (b) Equilibrium

titration of GO with PDDA.

Fig. 3. Absorption spectra of S-(PDDA/GO)n ultrathin film.

90 T. Szabo et al. / Carbon 43 (2005) 87–94

neutralizes all charges on GO, CEC values of 0.35; 0.33;

0.34 and 0.44mmol/g were calculated from the differentcycles of the titration curve. Thus, unfortunately, this

measurement cannot be applied for quantitative analyt-

ical purposes because the amount of titrants belonging

to the hypothetic equivalence points (where streaming

potential = 0mV) do not correlate with each other in a

systematic way. The main reason for this is the ‘‘dy-

namic’’ mode of the titration: in case of titration of lay-

ered materials like GO, the reaction is rather slow as thepolymer chains must penetrate into the interlayer space,

where they neutralize the charges. So, recording such a

‘‘titration curve’’ (streaming potential) in an equilibrium

method takes days. Equilibrium measurement was per-

formed by mixing graphite oxide suspensions with differ-

ent amounts of PDDA in plastic flasks (pH was set to

9.8) that were then shaken for a week and the streaming

potential was measured. The equilibrium data are shown

in Fig. 2b. Zero streaming potential was measured at

1.19mmol added PDDA/g GO. This value is three–four

times higher than those obtained in the dynamic mode,

showing that polymer uptake of graphite oxide films

(three–four times higher than in dynamic method) can-not be completed with deposition times as short as some

minutes or some hours. However, we must emphasize

again that the aim of these experiments was to demon-

strate the suitability of PDDA and GO for the ‘‘charge

regulated’’ electrostatic self-assembly method.

3.2. Spectrophotometric and XRD investigation of

S-(PDDA/GO)n nanofilms

Self-assembly of the ultrathin films was monitored by

absorption spectrophotometry in the visible range

(k = 350–800nm). This technique is often used to char-

acterize the consecutive build-up of oppositely charged

species. Numerous papers report on the growth of the

multilayer structure by a linear fashion for polymers,

semiconductor nanoparticles, aluminosilicate platelets,etc. [15,23,24]. Former publications dealing with poly-

mer/GO self-assembly found the same build-up ten-

dency [13,16,17]. Absorption spectra of S-(PDDA/

GO)n ultrathin films (n = number of bilayers) are shown

in Fig. 3. Since the glass slide substrates showed some

light absorption even in the visible range (Amax � 0.05),

subtraction of their spectra from that of the sandwich

layers were necessary to display the real optical featureof the assemblies. The shape of the film spectra coincides

with that of GO suspensions and no changes were ob-

served after deposition of the polymer, indicating that

only the graphite oxide bears the dominant light absorp-

tion and light scattering. Absorbances of the films at dif-

ferent wavelengths are plotted against the bilayer

5 10 15 20 25 302Θ °

Inte

nsit

y (a

.u.)

n=25

n=20

n=15

n=10

500

cps

GO powder

parent

graphite

Fig. 4. XRD patterns of graphite, graphite oxide and S-(PDDA/GO)nfilms.

T. Szabo et al. / Carbon 43 (2005) 87–94 91

number in the inset of Fig. 3. Absorbances at all fre-

quencies increased proportionally with increasing n,

however, true linear correlation was only observed at

NIR wavelengths (800nm). At visible wavelengths (400

and 600nm), a break point splits the linear growing ten-

dency at n = 11. After depositing 11 bilayers, a change inthe slope occurs. The same phenomenon was reported

by Dante et al. after deposition of 20 bilayers of PDDA

and an azo dye [25]. They claimed the slope decrease was

the result of progressive disordering of chromophoric

groups and not that of reduction of transferred mass.

In our system the reason must be that if n P 11 the

thickness is so high that the bonding forces between

the outermost layers are weakened compared to the onesclose to the glass substrate so the species prefer being

solvated in the liquid phase.

Absorbance increment due to the deposition of one

graphite oxide layer differs from that found in an earlier

study [13] applying almost the same conditions. As a

matter of fact, for an S-(PDDA/GO)7 film five times

higher absorption (A400 = 1) was measured than Kotov

and co-workers found (A400 = 0.2). This apparent con-tradiction can be partly explained by the different opti-

cal properties of the applied graphite oxides. It is

known that the colour of graphite oxide depends on

the stage of oxidation [26]: the higher the O:C ratio is,

the lighter colour the GO sample has. Since the graphite

used in Ref. [13] was oxidized three times, its specific

absorbance must be lower than that of the material we

prepared. On the other hand, centrifugation was omit-ted in this case, so greater lamellae were not removed

from the GO suspension. This indicates that smaller par-

ticles build more homogeneous, but significantly thinner

films by self-assembly.

X-ray diffraction is a powerful tool for the structure

analysis of layered materials like GO. Fig. 4 shows the

X-ray diffraction patterns of the starting materials and

the nanofilms, while Table 1 summarizes the XRDparameters.

The very intense and narrow peak at 2H = 26.28� cor-responds to the (002) planes of graphene layers

(d002 = 0.339nm). In the course of strong oxidation the

structure expands as oxygen-containing groups are

Table 1

XRD parameters and resistivities of the graphite oxide composite films

Sample 2H� d002 (nm)

Graphite powder 26.28 0.339

Graphite oxide powder 14.06 0.630

S-(PDDA/GO)10 11.54 0.767

S-(PDDA/GO)15 11.44 0.773

S-(PDDA/GO)20 11.24 0.787

S-(PDDA/GO)25 11.20 0.790

Red. (PDDA/GO)25 — —

Red. (PDDA/GO)25, 400 �C 25.86 0.345

incorporated between the carbon sheets: the d-spacing

is almost doubled (d002 = 0.630nm) The mean numberof GO sheets stacked along the c-axis (N) can be calcu-

lated in terms of the crystallite size and the basal spac-

ing: N = Lc/d002. Line broadening of the GO powder

diffractogram shows that Lc is nearly 22nm indicating

that parallel to layer expansion partial disaggregation

of the macrocrystalline graphite particles also occurred

(N = 35). XRD patterns of the nanofilms reveal swelling

of the GO layers to �0.77nm with concomitant linebroadening (position and breadth remained constant

after each bilayer numbers). This means that while air-

dry GO (d002 = 0.63nm) contains only few water mole-

cules (the thickness of a GO layer is 0.61nm [27]), GO

in the thin film is much more hydrated. However, since

the van der Waals diameter of H2O is 0.28nm [28], not a

monomolecular layer of water is built in the intergallery

space which would have increased d002 to 0.89nm. Thecrystallite sizes (0.76–0.78nm) and N-values (9–11) for

the GO incorporated in the nanofilms decreased signifi-

cantly which means that partial disaggregation took

place in the suspension and the self-assembly selected

these thinner platelets.

Lc (nm) N R (kX)

macroscopic — —

22 35 —

7.4 10 >2.11 · 105

7.3 9 >2.11 · 105

8.7 11 >2.11 · 105

8.5 11 >2.11 · 105

— — >2.11 · 105

6.5 19 6.6

Fig. 5. XRD pattern and absorbance (at 700nm) of the S-(PDDA/

GO)25 film as a function of reduction time.

-70

-60

-50

-40

-30

-20

-10

0

10

0 100 200 300 400 500 600 700 800T (˚C)

Mas

scha

nge

(wt%

)

DT

G,D

TA

sign

al (

a.u.

)

GO TG

GO DTG

reduced GO TG

GO DTA

Fig. 6. TG-DTA curves of pure and reduced graphite oxide under N2.

92 T. Szabo et al. / Carbon 43 (2005) 87–94

3.3. Reduction of S-(PDDA/GO)25 films

Reduction of (PDDA/GO)25 films with hydrazine was

performed at ambient temperature. It takes place in

maximally 24h [13]. So we soaked the multilayer films

on glass slides in 0.02M N2H4 and sped up the reaction

by using an elevated temperature (50 �C). XRD and

spectrophotometric measurements were done at differ-ent stages (times) of reduction (Fig. 5). The intensity

of graphite oxide reflection gradually decreased with

progressing reduction (the pattern of the starting film

was recorded with a smaller data collection time, that

is the reason for the low peak height), indicating the

destruction of the layered graphite oxide structure. After

one hour the GO was completely reduced. However, in-

stead of the sharp graphite (002) reflection near 26� 2H,only a broad halo developed that comes from the scat-

tering of the formed disordered, turbostratic carbon

[20]. A significant difference in the darkness of the par-

tially reduced films was observed visually that was sup-

ported by photometry (Fig. 5 inset). According to this

we reached an absorbance plateau (thus, completed

reaction) after 45min. This is not inconsistent with the

XRD measurement as this plateau is not caused bythe end of the reduction but the light absorption of

the black carbon film was so high that no further in-

crease of absorbance could be detected.

The pristine and reduced graphite oxide were sub-

jected to thermal analysis in N2 (Fig. 6). The GO has

a weight loss of 7–8% up to 200 �C (no DTA signal) that

is caused by the slow removal of physically adsorbed

water. A significant exothermic loss is followed thathas the maximum rate at 275 �C according to the

DTG and DTA curve. This is ascribed to the destruction

of different oxygen-containing (e.g. hydroxyl) groups

[28] by the deflagration of GO. The decomposition of

the strongly attached functional groups follows. We

think that loss at higher temperatures is due to carbon

combustion caused by the traces of oxygen gas in the

system (there is a broad exothermic hump up to

800 �C). There is a marked difference between the un-

treated and reduced GO samples. The reduced one doesnot have a water content (2% loss up to 200 �C) and it

has featureless DTG and DTA curves because hydro-

phobic carbon is formed. Also, the lack of functional

groups is evidenced by the minor weight loss up to

800 �C.Morphological changes of the nanofilm surface

brought by the reductive treatment is demonstrated in

the AFM images of Fig. 7. Scanning of the original(PDDA/GO)25 assembly visualized 25–35nm thick exfo-

liated slabs with micron-sized lateral dimensions stacked

upon each other. The aspect ratio of the anisometric

aggregates is at least 40 from the image assuming a

25nm thickness and 1000nm width, but it may be much

higher as the platelet was greater than the scanned sur-

face. Reduction has destroyed the layered graphite oxide

structure, mainly mounds of the formed turbostraticcarbon particles determine the topography which is con-

sistent with the lack of the sharp XRD reflection of well-

ordered graphite.

3.4. Postreduction treatment of S-(PDDA/carbon)25films

Formation of a conductive carbonaceous film hasprompted our effort to restore the original, more or-

dered graphitic arrangement of the layers. Heat treat-

ment of 1h in air was applied on the slides up to

400 �C (the glass substrate melts at higher temperatures).

There is a gradual shift of the scattering maximum to

higher angles (Fig. 8). The reduced (but not heated) film

Fig. 7. AFM images of freshly deposited (a) and reduced (b) S-

(PDDA/GO)25 film.

0

200

400

600

800

1000

1200

10 12 14 16 18 20 22 24 26 28 302Θ ˚

Inte

nsit

y (c

ps)

reduced

200˚C 400˚C

Fig. 8. Effect of heat treatment on the X-ray diffractogram of S-

(PDDA/GO)25.

T. Szabo et al. / Carbon 43 (2005) 87–94 93

has a broad peak near 2H = 22� that arises from carbon

layers stacked in an irregular fashion. Heating causes agradual ordering of the carbon (d002 = 0.37nm at

200 �C) and a significantly sharper peak appears at

400 �C, with d002 = 0.345nm which is typical for carbon

blacks, and close to the reflection of graphite. In conclu-

sion, three-dimensional ordering of adjacent graphene

layers was improved by the heat treatment that, in turn,

proved to improve the conductivity too. The electrical

resistivity of the reduced film showed an at least32000-fold increase upon heating (Table 1): while resis-

tivities of the (PDDA/GO) and the hydrazine-treated

nanofilms were higher than 211MX (that is the maxi-

mum measurable R), the annealed sample possessed a

resistivity of 6.6kX. Thus, we have managed to alter

the thin carbon/polymer composite from an insulator

to a conductor.

4. Conclusion

Crude graphite powder has been partly exfoliated

into thin platelet-like aggregates by a strong oxidation

process. Cyclic charge titrations of the as-prepared,

hydrophilic graphite oxide with poly(diallyldimethylam-

moniumchloride) showed that GO meets the require-ments of the layer-by-layer self-assembly method

which is the easiest, wet-chemical technique for thin film

deposition. X-ray diffractograms and AFM image of the

film consisting 25 bilayers of PDDA and GO showed

that self-assembly selects thin, anisometric graphite

oxide particule aggregates from its suspension. Reduc-

tion of the polyelectrolyte/GO composite and transfor-

mation of the formed turbostratic carbon to aconductive nanofilm was achieved by reduction with

hydrazine and subsequent heat treatment.

Acknowledgments

This work was supported by the Hungarian National

Scientific Fund OTKA (T034430). The authors thankProfessor Hanns-Peter Boehm for his valuable remarks

and for revising and improving the manuscript.

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