Materials Science and Engineering B 106 (2004) 308–312

Electrodeposition route to prepare graphite-like carbon nitride

Chao Lia,b, Chuan-Bao Caoa,∗, He-Sun Zhua, Qiang Lva, Jia-Tao Zhanga, Xu Xianga

a Research Center of Materials Science, Beijing Institute of Technology, Beijing 100081, PR Chinab Department of Chemical Engineering, Zhengzhou Institute of Light Industry, Zhengzhou 450002, PR China

Received 3 July 2003; accepted 10 October 2003

Abstract

Carbon nitride thin films were deposited on Si(1 0 0) substrate from saturated acetonitrile solution of 2,4,6-trichloro-1,3,5-triazine and2,4,6-triamino-1,3,5-triazine by electrochemistry route at room temperature. The films were characterized by X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). These results indicate that crystalline g-C3N4 wasobtained in the as-deposited films. The molar ratio of precursors in the reaction system had effects on the chemical composition, chemicalbond states of C and N, and crystal structure of samples.© 2003 Elsevier B.V. All rights reserved.

Keywords: Carbon nitride; Thin films; g-C3N4; Electrodeposition

1. Introduction

A new C–N compound�-C3N4 with the mechanical prop-erties similar to those of diamond was predicted through theab initio calculations of Liu and Cohen[1,2] in 1989. Andthen, other CN structures, such as�-C3N4, cubic (c-C3N4),pseudocubic (p-C3N4) and graphitic (g-C3N4), were pro-posed[3–6]. As one of C3N4 forms, graphite-like C3N4(g-C3N4) were predicted to be relatively more stable thanthe other C3N4 phases at ambient[3,4,7]. For its potentialas ceramic semiconductor and as precursor of super hardC3N4 materials, g-C3N4 attracted attentions of many groups[7–16].

Melamine was always chosen as precursor to prepareg-C3N4 because of its honey-comb atomic arrangementwhich is very close to the expected one for g-C3N4. Alveset al. and Montigaud et al.[8,12,14], using a solvother-mal process: the pyrolysis of melamine in presence of anitriding solvent (NH2NH2) in high-pressure conditions(P = 3 GPa, 800≤ T ≤ 850◦C), prepared the graphiticform of C3N4. They proposed a new structural model forgraphitic form of the carbon nitride. With a system ofmelamine and Lewis-acid at 600–700◦C in an autoclave,

∗ Corresponding author. Tel.:+86-10-68913792;fax: +86-10-68912001.

E-mail address: cbcao@bit.edu.cn (C.-B. Cao).

Komatsu [15] synthesized melamine-based quasi-carbonnitride with an orthorhombic layer structure, which wasdifferent from g-C3N4 proposed by Teter and Hemley[4]in the structure. Demazeau et al.[10] synthesized a bulkcrystalline graphitic-like phase with only a single broadX-ray reflection observed through a solvothermal reactionof cyanuric chloride and melamine at 130 MPa and 230◦C.Analysis of their sample revealed a significant contami-nation by both chlorine and hydrogen. Recently, Zhanget al. [9], through a solid-state reaction of cyanuric chlo-ride and melamine (molar ratio 2:1) at 1.0–1.5 GPa and500–550◦C, prepared a carbon nitride compound with sto-ichiometry C6N9H4Cl, which possessed a two-dimensionalC6N9H3 framework that is structurally related to the hy-pothetical graphitic phase of C3N4. In these works, highenergy such as high temperature, high pressure, etc., wereapplied to the reaction system of melamine or/and cyanuricchloride in order to form covalent carbon and nitrogennetworks.

In this work, electrodeposition method was used to de-posit the graphitic carbon nitride thin films on Si(1 0 0)substrate from a saturated acetonitrile solution of cyanuricchloride and melamine at room temperature. The resultsdemonstrated that crystalline g-C3N4 was obtained in theCNx films, and the molar ratio of precursors in the re-action system had effects on the chemical composition,chemical bond states of C and N, and crystal structure ofsamples.

0921-5107/$ – see front matter © 2003 Elsevier B.V. All rights reserved.doi:10.1016/j.mseb.2003.10.006

C. Li et al. / Materials Science and Engineering B 106 (2004) 308–312 309

2. Experimental

The apparatus used in our experiment is an electrolytic cellsystem. The schematic diagram of the system can refer to[17]. Melamine (2,4,6-triamino-1,3,5-triazine) and cyanuricchloride (2,4,6-trichloro-1,3,5-triazine) dissolved in acetoni-trile and formed a saturated solution, which served as elec-trolyte. All reagents were analytical grade. A p-type Si(1 0 0)substrate (10 mm× 20 mm× 0.3 mm) with the resistivityof 7� cm was mounted on a graphite cathode, which wasseparated with graphite anode from 7 mm. Before deposi-tion, the substrate was treated with dilute HF solution, andcleaned by ultrasonic treatment in the distilled water, ethanoland acetone, respectively, then dried in a vacuum drier. Thepotential of the DC power can be varied from 0 to 4000 V.In this work, all experiments were obtained under an ap-plied potential of 1200 V, temperature 25◦C and depositingtime of 3 h. The X-ray powder diffraction (XRD) patternwas recorded on a Rigaku D/max-2400 X-ray diffractometerwith Cu K� radiation (λ = 1.54056 Å). X-ray photoelec-tron spectra (XPS) were obtained on a KRATOS XSAM800electron spectrometer for chemical analysis (ESCA), usingMg K� X-ray (hν = 1486.6 eV) as the excitation source.Fourier transform infrared spectroscopy (FTIR) was takenwith a Perkin-Elmer (L-710) spectrophotometer.

3. Results and discussion

In attempts to synthesize CNx films, three precursor sys-tems were adapted in the process of cathode electrodeposi-tion. The first was acetonitrile solution containing cyanuricchloride, the second was acetonitrile solution containingmelamine, and the third was a saturated acetonitrile solutionof cyanuric chloride and melamine. The first two can obtaina light-yellow deposit on substrate after long-time reaction,which contains a large amount of O elements. Using the thirdsystem, the significant result was obtained. In the process ofelectrodeposition, gas produced in cathode, which made wetlitmus-paper red and dilute AgNO3 solution produce whiteprecipitate. It is indicated that the reaction between cyanuricchloride and melamine took place under the high electricfield, in which hydrogen chloride gas produced. After 3 h,gray thin films were observed on Si(1 0 0) substrate. In thesystem, two molar ratios of precursors were used, one wasmelamine and cyanuric chloride in molar ratio 1:1 (sampleA) while the other was that in molar ratio 2:1 (sample B).

The XRD patterns of samples A and B are shown inFig. 1. The strongest peak corresponds to the reflection ofSi(4 0 0), which comes from Si substrate. The identificationof the peaks is given inTable 1. Thed-values of the reflec-tions of samples A and B are in agreement with those ofcalculated graphite-like carbon nitride in[4]. The XRD pat-terns indicate that the existence of g-C3N4 in samples A andB. The graphitic C3N4, predicted by Teter and Hemley[4],consists of an ABAB. . . stacking of the planar structure and

10 20 30 40 50 60 70 80 90

Si(100)

(b)

(a)

Inte

nsit

y (a

.u.)

2q (degree/Cu Kα .)

(100

)

(110

)

(200

)

(302

)

(100

)

(101

)(0

02)

(110

)

(200

)

(302

)

Fig. 1. XRD diagrams of the as-deposited CNx films: (a) sample A; (b)sample B.

the unit cell with space group has 14 atoms. Each C atomis three-fold coordinated, as is one of the four N atoms perhexagonal cell. The other three N atoms are two-fold coordi-nated (resonant bonds). Comparison with the sample A, thedifference between the theoretical lattice constants and thosecalculated from the XRD data of the sample B is smaller,the intensity of those diffraction peaks from the sample B isstronger, and the peak from non-crystalline phase is weaker.It indicated that the sample B is much better crystallizedthan the deposits A.

Fig. 2 shows XPS spectra of A- and B-sample. The sam-ple A consists of C, N, and a small amount of O and Clelements. Using standard XPS atomic sensitivity factors forthe C 1s, N 1s, O 1s, Cl 1s core levels, the atom content(%) of four elements 45.59, 39.57, 9.70 and 5.13 was de-termined from band intensity measurements, respectively,with a N/C ratio 0.88. The sample B consists mainly of C,N, and a small amount of O elements, whose atom content(%) is 51.14, 41.50 and 7.36, respectively, with a N/C ratio0.81. The oxygen in the films may come from adsorptionin air. The major difference of samples A and B is the ex-istence of Cl in the sample A. It indicates that the reactionof melamine and cyanuric chloride is incomplete for sam-ple A. The other difference of samples A and B comes from

Table 1The experimental and theoretical X-ray diffraction data from our samplesand [4]

Sample A Sample B (g-C3N4)theo

d (nm) Intensity d (nm) Intensity d (nm) h k l

4.142 100 4.114 100 4.107 1 0 03.735 56 3.504 1 0 13.348 51 3.360 0 0 22.353 20 2.367 76 2.371 1 1 02.040 22 2.047 45 2.053 2 0 01.227 16 1.235 38 1.268 3 0 2

310 C. Li et al. / Materials Science and Engineering B 106 (2004) 308–312

0 200 400 600 800 1000 1200

sample B

sample ACl1s

C1s

N1s

O1s

Inte

nsit

y (a

.u.)

Binding energy (eV)

Fig. 2. XPS spectra of the as-deposited films.

the lower N/C ratio for sample B. When depositing frompure acetonitrile liquid carbon films can be obtained eas-ily [18–20]. The saturated acetonitrile solution of melamineand cyanuric chloride in molar ratio 2:1 is more dilute than

Fig. 3. The binding energy (serrate lines) and the deconvoluted (smooth lines) spectra of C 1s and N 1s for the as-deposited films: (a) C 1s for sampleA; (b) N 1s for sample A; (c) C 1s for sample B; (d) N 1s for sample B.

that in molar ratio 1:1, because the solubility of melaminein acetonitrile is very small. The low N/C ratio of sample Bmay be due to the competition of the carbon films deposi-tion by the reaction of acetonitrile on the substrate surfacein more dilute acetonitrile solution.

The binding energy and the deconvoluted spectra of C1s and N 1s core levels, of A- and B-sample, are given inFig. 3. The C 1s spectra of films can be deconvoluted intotwo lines peaked at 284.5±0.1 and 287.8±0.1 eV. The peakat 284.5 ± 0.1 eV may be attributed to amorphous carbon,contaminated carbon and surface carbon. The other peak at287.8±0.1 eV indicates that the electronic density of carbonis reduced by interaction with a higher electronegative atomsuch as nitrogen and is positively charged[21]. Thus, the C1s spectra indicate that the samples include only one kind ofbonding carbon, in addition to amorphous carbon, contami-nated carbon and surface carbon. The N 1s spectra of filmscan be deconvoluted into two lines peaked at 398.8 ± 0.1and 400.2 ± 0.1 eV, respectively. The assignment of N 1score level in literature is controversial[22–29]. Based on therecent theoretical calculations of Hellgren et al.[26], we at-tribute the peak at 398.8±0.1 eV to the sp3 C–N bonds while

C. Li et al. / Materials Science and Engineering B 106 (2004) 308–312 311

4000 3500 3000 2500 2000 1500 1000 500

sample B

sample A

melamine

Tra

nsm

itta

nce

Wavenumber (cm-1)

Fig. 4. FTIR spectra of the as-deposited CNx films.

the peak at 400.2 ± 0.1 eV to the sp2 C=N bonds[22–25].Therefore, the C 1s and N 1s spectra show that the two sam-ples include two kinds of nitrogen atoms and only one kindof carbon atom, in addition to amorphous carbon, contami-nated carbon and surface carbon. In the structure of g-C3N4proposed by Teter and Hemley[4], the two-dimensionalsheet consists of two types of nitrogen atoms, one in two-foldcoordination within rings and the other in three-fold coordi-nation connecting three C3N3 rings, and one type of carbonatom in three-fold coordination with nitrogen. The results ofXPS indicate that the chemical bond states of C and N in thesamples A and B are analogous to that in the hypotheticalg-C3N4. However, the C 1s spectrum of deposits B under-lines the presence of larger amount of amorphous carbon,contaminated carbon and surface carbon. It may be the re-sult of the competition of the carbon films deposition by thereaction of acetonitrile in more dilute acetonitrile solution.

Fig. 4 shows the IR spectra of samples A and B. Forcomparison, the spectrum of melamine is also given. TheIR spectrum of melamine presents several strong bands near3000 cm−1, a series of strong bands in the 1000–1700 cm−1

and another one centered at 810 cm−1. The bands near3000 cm−1 are consistent with modes involving N–H stretch-ing vibrations. The bands observed in 1250–1650 cm−1

region are typical for molecules that contain CN heterocy-cles and are generally associated with the skeletal stretchingvibrations of these aromatic rings[9,14,21]. The absorptionat 810 cm−1 is characteristic of out-of-plane bending modesof the rings[9,12,14]. By comparison with the IR spectrumof melamine, the peaks at 810 cm−1 in samples A and Bcan be attributed to out-of-plane bending modes of CNheterocycles, the peaks observed at 1330 and 1610 cm−1

correspond to the C=N in the rings, and the bands near3000 cm−1 suggest the presence of hydrogen. The lack ofabsorption at 2200 cm−1 indicates the films do not allowC≡N triple bonds. The results of IR, indicating existenceof CN aromatic ring, support that the indexing result of

XRD pattern because the melamine-based carbon nitrideintroduced by Teter and Hemley[4] is formally depictedas a perfect de-ammonation polycondensate of melamine.In sample B, the bands near 3000 cm−1 are weaker thansample A, which can be linked with the fact that sample Ballows smaller hydrogen atoms. The better definition of thepeaks observed at 1330 and 1610 cm−1 in sample B seemsto indicate a better arrangement of the holey-type structure.

Traditional electrochemical reaction takes place in ion so-lutions or organic solutions containing a conductive medium.The reaction can be carried out under low potentials (sev-eral voltages) since the conductive ability of the solutionis high. But our deposition is carried out in an organic so-lution, which is a non-conductor and does not contain anyconductive ions. In the deposition process, when the poten-tial is applied to the electrodes, the precursors in the solventare polarized and react on the surface of electrode, in whichthe migration rate of the precursors and the retention timeon the surface of the electrodes are important factors affect-ing the reaction. Therefore, one key feature of the syntheticroute is the molar ratio of precursors in the reaction system,on which the concentration of solutions depended. Whendepositing from pure acetonitrile liquid carbon films can beobtained easily[18–20]. The saturated acetonitrile solutionof melamine and cyanuric chloride in molar ratio 2:1 is moredilute than that in molar ratio 1:1, because the solubility ofmelamine in acetonitrile is very small. In sample B, the lowN/C ratio and the presence of larger amount of amorphouscarbon, contaminated carbon and surface carbon, may bedue to the competition of the carbon films deposition by thereaction of acetonitrile on the substrate surface in more di-lute acetonitrile solution. We speculated that the amorphouscarbon depositing from pure acetonitrile might promote thereaction of depositing carbon nitride on the electrode sur-face. The speculation is supported by the experimental factthat the sample B are much better crystallized than the de-posits A. Shen et al.[30] studied the nucleation and growthof diamond on two-step pretreated Si substrates, and thoughtthat it is easier to form nucleation sites on carbon than onthe Si substrate directly, and the etching of the carbon canalso produce sites. From the results of our experiments, itwas evident that the molar ratio of precursors in the reactionsystem had important effects on the chemical composition,chemical bond states of C and N, and crystal structure ofsamples.

4. Conclusion

Carbon nitride thin films were deposited on Si(1 0 0)substrate from saturated acetonitrile solution of 2,4,6-trichloro-1,3,5-triazine and 2,4,6-triamino-1,3,5-trazine byelectrochemistry route at room temperature. XPS measure-ments suggest the film mostly consisted of C and N, andN bonded with C in the forms of C–N and C=N bond.FTIR spectroscopy indicates CN aromatic ring existed in

312 C. Li et al. / Materials Science and Engineering B 106 (2004) 308–312

the product. XRD results show that thed-values of thediffractions agree well with the data of graphite-like carbonnitride calculated in the literature. These results indicatethat crystalline g-C3N4 was obtained in the as-depositedfilms. The molar ratio of melamine and cyanuric chloridein the reaction system had effects on the chemical composi-tion, chemical bond states of C and N, and crystal structureof samples.

Acknowledgements

The financial support from the National Natural ScienceFoundation of China is gratefully acknowledged.

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