- Email: [email protected]
Carbon nitride films synthesized by dual ion beam sputtering
J$.&
Nuclear Instruments
and Methods in Physics Research B 122 ( 1997) 534-537
B
__ IXIOMI
__
Beam Interactions with Materials 6 Atoms
!!iJ ELSEVIER
+
000
Carbon nitride films synthesized by dual ion beam sputtering P. Prieto a, C. Quir6s ‘, E. Elizalde a, A. Femandez a Drpurtumento b lnstitut
de CiPnciu de Muterides
’ Depurtement
de Techdogie
de FLicu
Apl~udu
C-XII.
Univer.dul
b, J.M Martin ‘, J.M. Sanz ” *
Auto’noma de Mudrid.
E-28049 Madrid,
de Sevillu (CSIC Univ. Sevillu) P.O. Box I I IS. Avda. Reinu Mercedes des Surjtices.
URA CNRS 855. Ecole Centrale
s/n.
de Lyon. P.O. Box 162. F-69131
Sporn E-41080 Ecully
Seville. Spuin Cedex. France
Abstract Carbon nitride films CN, have been obtained in a dual ion beam sputtering system using Arf to deposite graphite and low energy (i.e. < 100 eV) N$-ions to irradiate the film during its growth. The films have been characterized by Fourier transform infrared spectroscopy (FIIR), transmission electron microscopy (EM) and X-ray photoelectron spectroscopy (XPS). The results indicate the formation of small crystallites of P-C,N, (- 20 nm) embedded in a polymer-like CN, amorphous layer. Both, the nitrogen content and the formation of different C-N bonds is observed to depend on the energy and current density of the N?+ ions used to assist the deposition. In the present work we report on films with a nitrogen content close to 45 at% as estimated from the infrared spectra.
1. Introduction In 1989 Liu and Cohen [I] predicted that P-C,N, would have a bulk modulus comparable to that of diamond. Since then, several groups have attempted to synthesize this ultrahard material using a large variety of techniques [2- 141, however experimental evidence for its existence has been scarce. In fact, only very recently, some images and electron diffraction patterns of P-C,N, crystallites with typical dimensions of - 50 nm have been published [2-71. In this paper we report on CN, films, obtained in a dual ion beam sputtering system, with a nitrogen content close to 45 at% as determined by infrared spectroscopy (IRR).We also give experimental evidence of the formation of small P-CsN, nanocrystallites embedded in a polymer like CN, amorphous layer.
2. Experimental CN, films were deposited on freshly cleaved surfaces of KC1 in a dual ion beam sputtering system (base pressure, 10m7 Torr) equipped with a rotable water cooled substrate holder. The method consists in the deposition of carbon via Ar+ sputtering of a graphite target (purity 99.999%) using a 3 cm Kaufmann ion source, whereas an end-Hall ion source is used for simultaneous bombardment
* Corresponding author. [email protected]. 0168-583X/97/$17.00 PII
Fax:
Copyright
SO168-583X(96)00566-6
+ 34-1-397-3969;
email:
jo-
of the growing film with NC-ions ( < 100 eV). During the deposition, the pressure in the chamber rises up to 4 X 10m4 Torr. due to the feed gases. The sputtering conditions (Ar+, 500 eV, - I mA cm- 2, and the total deposition time (5 h) were kept constant for all the samples, whereas the current density J and the energy E of the N: ions were varied according to the values collected in Table I. Under these conditions, the nitrogen to carbon arrival rate ratio on the substrate was always larger than I. Actually, according to the nominal thickness and assuming the density of graphite, the N/C atomic arrival rate ratio increased from I .6 for sample A 1 up to 4.3 for sample A7 (cf. Table 1). The films have been characterized by IR (between 7000 and 560 cm-‘) in a Bruker IFS66V Fourier-transform infrared spectrometer with a resolution of 4 cm ‘. Some
Table I Energy and current density of the Nt ions used to assist the deposition of carbon films, averaged nitrogen to carbon atomic arrival rate ratio (ARR) and averaged atomic composition [Nl/[Cl as determined by XPS Sample
Energy (eV)
Current density (mA/cm’)
ARR
[Nl/[Cl (XPS)
Al A2 A3 A4 A5 A6 A7
55 65 71 73 76 81 87
0.03 I 0.055 0.066 0.072 0.077 0.077 0.083
1.6 2.9 3.4 3.7 4.0 4.0
0.32 0.32 0.41 0.49 0.5 I 0.60
4.3
0.58
0 1997 Elsevler Science B.V. All rights reserved
P. Prieto et ul./Nucl.
535
Instr. and Meth. in Phys. Res. B 122 (1997) 534-537
of the films were floated off in water and supported on a copper grid coated with a holey carbon film for TEM. This was performed in a Philips CM10 microscope operated at 100 keV in the Ecole Centrale de Lyon. The C/N atomic ratio of the films was determined by quantitative XPS analysis of the respective surfaces using the sensitivity factors given by the manufacturer and neglecting the effect of contamination. The spectra were taken in a PHI-3027 spectrometer equipped with a double pass CMA using MgKcl radiation (hv= 1486.6 eV).
1.0
A
a
A n
A
‘X8-
A
iz 0,6-
Am
‘m
E e 0.4-
l A
_
n
2100cm-1
A
1350 cm-l
n
3. Results and discussion Fig. I shows FTIR spectra (3000-600 cm-‘) corresponding to samples Al to A7 as labelled (cf. Table 1). At first glance, the spectra are characterized by two intense vibrational bands, whose relative intensity changes gradually as the assistance with NT is increased. Whereas the intensity of the broad peak around 1300 cm- ’ decreases continuously as we move from Al to A7, the feature around 2 100 cm- ’ grows and becomes the preponderant band in samples A6 and A7. These bands are in good agreement with those reported in previous studies [7-121 and identified in the study carried out by Kaufman et al. [13]. The broad peak between 1100 and 1700 cm-’ includes several overlapping absorption bands associated
Al OD-_
i 3000
c
I
’
2500
I
2000
m
IV
I
1500
1000
-’
Wavenumber (cm-l) Fig. 1. Infrared Table 1).
spectra
of different
CN,
film?., as labelled
(cf,
1 1
’
I
2
-
I
3
’
I
4
’
I-
I
5
6
’
I
’
7
J*E(eVmA/cmz) Fig. 2. (a) normalized area of the cm-’ (A) and at 2100 cm-’ (m) J X E of the N: ions. (b) [N]/[C] XPS as a function of the product J
IR absorption band at 1350 as a function of the product atomic ratio as determined by X E of the N: ions.
with stretching modes of sp2 and sp carbon in graphitic and disordered structures, as well as with the formation of C-N and C=N bonds [ 131. The absorption band around 2100 cm-’ is attributed to the stretching mode of the nitrile group (i.e. C=N) [7-131. The appearance and continuous growth of this band constitutes the main effect to be observed in Fig. 1. Its enhancement indicates an increasing nitrogen content from sample Al to A7. In fact, sample A7 only shows the absorption band associated with the nitrile group, which would indicate a nitrogen content close to 45at%, as we apparently do not see any other absorption band associated either with carbon-carbon or carbon-nitrogen. Deposition parameters such as the current density and energy of the N,+ ions are shown to play a significant role, both in the nitrogen content of the film and the formation of different C-N bonds and phases. This dependence is better observed in Fig. 2a, where the normalized areas of the two IR active absorption bands (i.e. at 1300 cm-’ and 2 100 cm - ’ ) has been depicted as a function of the product J X E of the nitrogen ions (cf. Table 1). As a whole the IR data suggest the formation of a polymer like CN, phase in which nitrogen substitutes carbon in increasing amounts as
III. ION BEAMS
the J X E is increased and can reach a value close to 4.5 at%. However, it is important to note that the formation of P-C,N, requires not only a higher nitrogen incorporation (i.e 57 at%) but also an sp3 hybridization of carbon. which can not be unambiguously identified by IR. In addition, we have performed an XPS analysis of the surface of the films. The [N]/[C] atomic ratio of the different films was roughly estimated in terms of the total intensities of the respective C I s and N 1s XPS peaks corrected by the sensitivity factors given by the manufacturer (i.e. 0.477 for N Is and 0.296 for Cls). The results are shown in Fig. 2b as a
Fig. 3. TEM micrographs
and electron diffraction
function of the product J X E and have also been included in Table I. The surface composition [N]/[C] of the films, as determined by XPS, ranges between 0.32 and 0.6, clearly below the compositions suggested by IR, at least for samples A6 and A7. However. the surface composition determined by XPS shows a similar dependence on J X E, ;1s the normalized area of the IR absorption band associated with the nitrile group (cf. Fig. 2a). This fact confirms the idea that the nitrogen content of the film increases from sample Al to sample A7, but its absolute determination requires more detailed quantification procedures
pattern of sample A4: (a) bright and (b) dark field images of different zones of the sample.
P. Priers et 01. /Nucl.
Instr. und Nrth. in Phys. Res. B 122 (1997) 534-537
[ 14,151. In fact, both the respective information depth and sensitivity to the different species is quite different in the two techniques. Both the Cls and Nl s XPS spectra show a complex structure formed by several overlapping features, which have been accounted for as a whole, instead of separately. Furthermore, their quantification is influenced by the presence of surface contaminants like oxygen, due to the exposure of the samples to the air, or by the smaller thickness of the more strongly assisted films, where Cl and K from the substrate were also detected. This could be due to the presence of some patches of uncovered KCI in the sample. In any case the higher nitrogen content of sample A7 corresponds to the observation of a predominant absorption band associated to C=N. It is worth noting that although the total deposition time and the sputtering conditions were kept constant, the thickness of the films decreased significantly as the assistance (current density and energy) increased. Nominal values, as given by the thickness monitor, ranged from 1700 ,& for sample Al to 450 A for sample A7. This effect has been confirmed by AES depth profiling of equivalent samples deposited on Si. It seems that increasing the energy of assistance leads to preferential sputtering of the graphitelike phase and the consequent enrichment of the nitrile groups, which on the other hand improve the hardness of the films [8] but causes significant stresses and poor adhesion to KCI. The structure of the films was investigated by TEM. Fig. 3 shows the bright (a) and dark (b) field TEM images of different zones of the sample A4. The electron diffraction pattern is included in the inset of Fig. 3a. The sample shows diffractions rings, that although diffused, indicate a certain degree of crystallization. Fig. 3b shows the corresponding dark field image. It shows the tiny crystallites which caused the halo rings observed in Fig. 3a. They appear embedded in an amorphous CN., layer with sizes ranging between 4 and 25 nm. The analysis of the diffraction rings enabled us to assign them to the following interplanar spacings, 3.55, 2.5, 2.05 and I.61 A. These show an acceptable agreement with values reported and also calculated previously [2-71 for B-C,N,. In fact, the observed spacings can be indexed as (100). ( 101). (210) and (2 I I) respectively [2,3].
4. Conclusions Different CN, films have been deposited in a dual ion beam sputtering system using Ar-ions (500 eV) for sputtering of a graphite target and low energy (< 100 eV) NC ions for irradiation of the growing film. The films have been characterized by FHR, XPS and TEM. The results
537
show that Nl assisted deposition of graphite enables to obtain CN., films whose nitrogen content can be as high as [C]/[N] = 1 depending on the deposition parameters. Both XPS and IR indicate the formation of an amorphous polymer like solid with different C-N bonds and phases. Increasing the energy of the Ni-ions causes a higher nitrogen incorporation and the formation of nitrile groups, but a significant decrease of the film thickness. All that could be caused by preferential sputtering effects of the graphite-like phase and the corresponding enrichment of the nitrile groups. In addition we have also shown that assisting with 70-80 eV NC-ions leads to the formation of nanocrystallites of B-C3N,.
Acknowledgements This work has been financially supported by the CICYT of Spain under contract MAT 96/0676. The collaboration and technical support of J.A. Rodriguez are also acknowledged.
References
[I] A.Y. Liu and M.L. Cohen, Science 245 (1989) 841; Phys. Rev. B 42 (1990) 10727. [2] C. Niu, Y.Z. Lu and C.M. Lieber, Science 261 (1993) 334. 131 K.M. Yu, M.L. Cohen, E.E. Haller, W.L. Hansen, A.Y. Liu and I.C. Wu, Phys. Rev. B 49 (1994) 5034. [4] Z. Ze-Bo, L. Yin-An, X. Si-Shen and Y. Guo-Zhen, J. Mat. Sci. Lett. 14 (1995) 1742. [5] H.W. Song, F.Z. Cui, X.M. He, W.Z. Li and H.D. Li, J. Phys.: Condens. Matter 6 ( 1994) 6125. [6] Z-M. Ren, Y-C. Du, Y. Qiu, J-D. Wu, Z-F. Ying, X-X. Xiong and F-M. Li, Phys. Rev. B 5 1 ( 1995) 5274. [7] A. Femandez, P. Prieto, C. Quiros, J.M. Sanz. J.M. Martin and B. Vacher, Appl. Phys. Lett. 69 (1996). [8] H-X. Han and B.J. Feldman, Solid State Commun. 65 (1988) 921. [9] K. Ogata, J.F.D. Chubaci and F. Fujimoto, J. Appl. Phys. 76 (1994) 3791. [IO] X-A. Zhao, C.W. Ong, J.C. Tsang, Y.W. Wong, P.W. Ghan and C.L. Choy, Appl. Phys. Lett. 66 (1995) 2652. [I I] M. Ricci, M. Trinquecoste, F. Auguste. R. Canet, P. Delhaes, C. Guimon, Cl. Pfister-Guillouzo, B. Nysten and J.P. Issi, J. Mat. Res. 8 (1993) 480. (121 D. Li, S. Lopez, Y.W. Chung, M.S. Wong and W. D. Sproul, J. Vat. Sci. Technol. A I3 (1995) 1063. [I31 J.H. Kaufman, S. Metin and D.D. Saperstein, Phys. Rev. B 39 (1989) 13053. 1141 A. Bousetta, M. Lu and A. Bensaoula. J. Vat. Sci. Technol. I? (1995) 1639. [I51 I. Gouzman, R. Brener and A. Hoffman, Surf. Sci. 332-333 (I 995) 283.
III. ION BEAMS
Nuclear Instruments
and Methods in Physics Research B 122 ( 1997) 534-537
B
__ IXIOMI
__
Beam Interactions with Materials 6 Atoms
!!iJ ELSEVIER
+
000
Carbon nitride films synthesized by dual ion beam sputtering P. Prieto a, C. Quir6s ‘, E. Elizalde a, A. Femandez a Drpurtumento b lnstitut
de CiPnciu de Muterides
’ Depurtement
de Techdogie
de FLicu
Apl~udu
C-XII.
Univer.dul
b, J.M Martin ‘, J.M. Sanz ” *
Auto’noma de Mudrid.
E-28049 Madrid,
de Sevillu (CSIC Univ. Sevillu) P.O. Box I I IS. Avda. Reinu Mercedes des Surjtices.
URA CNRS 855. Ecole Centrale
s/n.
de Lyon. P.O. Box 162. F-69131
Sporn E-41080 Ecully
Seville. Spuin Cedex. France
Abstract Carbon nitride films CN, have been obtained in a dual ion beam sputtering system using Arf to deposite graphite and low energy (i.e. < 100 eV) N$-ions to irradiate the film during its growth. The films have been characterized by Fourier transform infrared spectroscopy (FIIR), transmission electron microscopy (EM) and X-ray photoelectron spectroscopy (XPS). The results indicate the formation of small crystallites of P-C,N, (- 20 nm) embedded in a polymer-like CN, amorphous layer. Both, the nitrogen content and the formation of different C-N bonds is observed to depend on the energy and current density of the N?+ ions used to assist the deposition. In the present work we report on films with a nitrogen content close to 45 at% as estimated from the infrared spectra.
1. Introduction In 1989 Liu and Cohen [I] predicted that P-C,N, would have a bulk modulus comparable to that of diamond. Since then, several groups have attempted to synthesize this ultrahard material using a large variety of techniques [2- 141, however experimental evidence for its existence has been scarce. In fact, only very recently, some images and electron diffraction patterns of P-C,N, crystallites with typical dimensions of - 50 nm have been published [2-71. In this paper we report on CN, films, obtained in a dual ion beam sputtering system, with a nitrogen content close to 45 at% as determined by infrared spectroscopy (IRR).We also give experimental evidence of the formation of small P-CsN, nanocrystallites embedded in a polymer like CN, amorphous layer.
2. Experimental CN, films were deposited on freshly cleaved surfaces of KC1 in a dual ion beam sputtering system (base pressure, 10m7 Torr) equipped with a rotable water cooled substrate holder. The method consists in the deposition of carbon via Ar+ sputtering of a graphite target (purity 99.999%) using a 3 cm Kaufmann ion source, whereas an end-Hall ion source is used for simultaneous bombardment
* Corresponding author. [email protected]. 0168-583X/97/$17.00 PII
Fax:
Copyright
SO168-583X(96)00566-6
+ 34-1-397-3969;
email:
jo-
of the growing film with NC-ions ( < 100 eV). During the deposition, the pressure in the chamber rises up to 4 X 10m4 Torr. due to the feed gases. The sputtering conditions (Ar+, 500 eV, - I mA cm- 2, and the total deposition time (5 h) were kept constant for all the samples, whereas the current density J and the energy E of the N: ions were varied according to the values collected in Table I. Under these conditions, the nitrogen to carbon arrival rate ratio on the substrate was always larger than I. Actually, according to the nominal thickness and assuming the density of graphite, the N/C atomic arrival rate ratio increased from I .6 for sample A 1 up to 4.3 for sample A7 (cf. Table 1). The films have been characterized by IR (between 7000 and 560 cm-‘) in a Bruker IFS66V Fourier-transform infrared spectrometer with a resolution of 4 cm ‘. Some
Table I Energy and current density of the Nt ions used to assist the deposition of carbon films, averaged nitrogen to carbon atomic arrival rate ratio (ARR) and averaged atomic composition [Nl/[Cl as determined by XPS Sample
Energy (eV)
Current density (mA/cm’)
ARR
[Nl/[Cl (XPS)
Al A2 A3 A4 A5 A6 A7
55 65 71 73 76 81 87
0.03 I 0.055 0.066 0.072 0.077 0.077 0.083
1.6 2.9 3.4 3.7 4.0 4.0
0.32 0.32 0.41 0.49 0.5 I 0.60
4.3
0.58
0 1997 Elsevler Science B.V. All rights reserved
P. Prieto et ul./Nucl.
535
Instr. and Meth. in Phys. Res. B 122 (1997) 534-537
of the films were floated off in water and supported on a copper grid coated with a holey carbon film for TEM. This was performed in a Philips CM10 microscope operated at 100 keV in the Ecole Centrale de Lyon. The C/N atomic ratio of the films was determined by quantitative XPS analysis of the respective surfaces using the sensitivity factors given by the manufacturer and neglecting the effect of contamination. The spectra were taken in a PHI-3027 spectrometer equipped with a double pass CMA using MgKcl radiation (hv= 1486.6 eV).
1.0
A
a
A n
A
‘X8-
A
iz 0,6-
Am
‘m
E e 0.4-
l A
_
n
2100cm-1
A
1350 cm-l
n
3. Results and discussion Fig. I shows FTIR spectra (3000-600 cm-‘) corresponding to samples Al to A7 as labelled (cf. Table 1). At first glance, the spectra are characterized by two intense vibrational bands, whose relative intensity changes gradually as the assistance with NT is increased. Whereas the intensity of the broad peak around 1300 cm- ’ decreases continuously as we move from Al to A7, the feature around 2 100 cm- ’ grows and becomes the preponderant band in samples A6 and A7. These bands are in good agreement with those reported in previous studies [7-121 and identified in the study carried out by Kaufman et al. [13]. The broad peak between 1100 and 1700 cm-’ includes several overlapping absorption bands associated
Al OD-_
i 3000
c
I
’
2500
I
2000
m
IV
I
1500
1000
-’
Wavenumber (cm-l) Fig. 1. Infrared Table 1).
spectra
of different
CN,
film?., as labelled
(cf,
1 1
’
I
2
-
I
3
’
I
4
’
I-
I
5
6
’
I
’
7
J*E(eVmA/cmz) Fig. 2. (a) normalized area of the cm-’ (A) and at 2100 cm-’ (m) J X E of the N: ions. (b) [N]/[C] XPS as a function of the product J
IR absorption band at 1350 as a function of the product atomic ratio as determined by X E of the N: ions.
with stretching modes of sp2 and sp carbon in graphitic and disordered structures, as well as with the formation of C-N and C=N bonds [ 131. The absorption band around 2100 cm-’ is attributed to the stretching mode of the nitrile group (i.e. C=N) [7-131. The appearance and continuous growth of this band constitutes the main effect to be observed in Fig. 1. Its enhancement indicates an increasing nitrogen content from sample Al to A7. In fact, sample A7 only shows the absorption band associated with the nitrile group, which would indicate a nitrogen content close to 45at%, as we apparently do not see any other absorption band associated either with carbon-carbon or carbon-nitrogen. Deposition parameters such as the current density and energy of the N,+ ions are shown to play a significant role, both in the nitrogen content of the film and the formation of different C-N bonds and phases. This dependence is better observed in Fig. 2a, where the normalized areas of the two IR active absorption bands (i.e. at 1300 cm-’ and 2 100 cm - ’ ) has been depicted as a function of the product J X E of the nitrogen ions (cf. Table 1). As a whole the IR data suggest the formation of a polymer like CN, phase in which nitrogen substitutes carbon in increasing amounts as
III. ION BEAMS
the J X E is increased and can reach a value close to 4.5 at%. However, it is important to note that the formation of P-C,N, requires not only a higher nitrogen incorporation (i.e 57 at%) but also an sp3 hybridization of carbon. which can not be unambiguously identified by IR. In addition, we have performed an XPS analysis of the surface of the films. The [N]/[C] atomic ratio of the different films was roughly estimated in terms of the total intensities of the respective C I s and N 1s XPS peaks corrected by the sensitivity factors given by the manufacturer (i.e. 0.477 for N Is and 0.296 for Cls). The results are shown in Fig. 2b as a
Fig. 3. TEM micrographs
and electron diffraction
function of the product J X E and have also been included in Table I. The surface composition [N]/[C] of the films, as determined by XPS, ranges between 0.32 and 0.6, clearly below the compositions suggested by IR, at least for samples A6 and A7. However. the surface composition determined by XPS shows a similar dependence on J X E, ;1s the normalized area of the IR absorption band associated with the nitrile group (cf. Fig. 2a). This fact confirms the idea that the nitrogen content of the film increases from sample Al to sample A7, but its absolute determination requires more detailed quantification procedures
pattern of sample A4: (a) bright and (b) dark field images of different zones of the sample.
P. Priers et 01. /Nucl.
Instr. und Nrth. in Phys. Res. B 122 (1997) 534-537
[ 14,151. In fact, both the respective information depth and sensitivity to the different species is quite different in the two techniques. Both the Cls and Nl s XPS spectra show a complex structure formed by several overlapping features, which have been accounted for as a whole, instead of separately. Furthermore, their quantification is influenced by the presence of surface contaminants like oxygen, due to the exposure of the samples to the air, or by the smaller thickness of the more strongly assisted films, where Cl and K from the substrate were also detected. This could be due to the presence of some patches of uncovered KCI in the sample. In any case the higher nitrogen content of sample A7 corresponds to the observation of a predominant absorption band associated to C=N. It is worth noting that although the total deposition time and the sputtering conditions were kept constant, the thickness of the films decreased significantly as the assistance (current density and energy) increased. Nominal values, as given by the thickness monitor, ranged from 1700 ,& for sample Al to 450 A for sample A7. This effect has been confirmed by AES depth profiling of equivalent samples deposited on Si. It seems that increasing the energy of assistance leads to preferential sputtering of the graphitelike phase and the consequent enrichment of the nitrile groups, which on the other hand improve the hardness of the films [8] but causes significant stresses and poor adhesion to KCI. The structure of the films was investigated by TEM. Fig. 3 shows the bright (a) and dark (b) field TEM images of different zones of the sample A4. The electron diffraction pattern is included in the inset of Fig. 3a. The sample shows diffractions rings, that although diffused, indicate a certain degree of crystallization. Fig. 3b shows the corresponding dark field image. It shows the tiny crystallites which caused the halo rings observed in Fig. 3a. They appear embedded in an amorphous CN., layer with sizes ranging between 4 and 25 nm. The analysis of the diffraction rings enabled us to assign them to the following interplanar spacings, 3.55, 2.5, 2.05 and I.61 A. These show an acceptable agreement with values reported and also calculated previously [2-71 for B-C,N,. In fact, the observed spacings can be indexed as (100). ( 101). (210) and (2 I I) respectively [2,3].
4. Conclusions Different CN, films have been deposited in a dual ion beam sputtering system using Ar-ions (500 eV) for sputtering of a graphite target and low energy (< 100 eV) NC ions for irradiation of the growing film. The films have been characterized by FHR, XPS and TEM. The results
537
show that Nl assisted deposition of graphite enables to obtain CN., films whose nitrogen content can be as high as [C]/[N] = 1 depending on the deposition parameters. Both XPS and IR indicate the formation of an amorphous polymer like solid with different C-N bonds and phases. Increasing the energy of the Ni-ions causes a higher nitrogen incorporation and the formation of nitrile groups, but a significant decrease of the film thickness. All that could be caused by preferential sputtering effects of the graphite-like phase and the corresponding enrichment of the nitrile groups. In addition we have also shown that assisting with 70-80 eV NC-ions leads to the formation of nanocrystallites of B-C3N,.
Acknowledgements This work has been financially supported by the CICYT of Spain under contract MAT 96/0676. The collaboration and technical support of J.A. Rodriguez are also acknowledged.
References
[I] A.Y. Liu and M.L. Cohen, Science 245 (1989) 841; Phys. Rev. B 42 (1990) 10727. [2] C. Niu, Y.Z. Lu and C.M. Lieber, Science 261 (1993) 334. 131 K.M. Yu, M.L. Cohen, E.E. Haller, W.L. Hansen, A.Y. Liu and I.C. Wu, Phys. Rev. B 49 (1994) 5034. [4] Z. Ze-Bo, L. Yin-An, X. Si-Shen and Y. Guo-Zhen, J. Mat. Sci. Lett. 14 (1995) 1742. [5] H.W. Song, F.Z. Cui, X.M. He, W.Z. Li and H.D. Li, J. Phys.: Condens. Matter 6 ( 1994) 6125. [6] Z-M. Ren, Y-C. Du, Y. Qiu, J-D. Wu, Z-F. Ying, X-X. Xiong and F-M. Li, Phys. Rev. B 5 1 ( 1995) 5274. [7] A. Femandez, P. Prieto, C. Quiros, J.M. Sanz. J.M. Martin and B. Vacher, Appl. Phys. Lett. 69 (1996). [8] H-X. Han and B.J. Feldman, Solid State Commun. 65 (1988) 921. [9] K. Ogata, J.F.D. Chubaci and F. Fujimoto, J. Appl. Phys. 76 (1994) 3791. [IO] X-A. Zhao, C.W. Ong, J.C. Tsang, Y.W. Wong, P.W. Ghan and C.L. Choy, Appl. Phys. Lett. 66 (1995) 2652. [I I] M. Ricci, M. Trinquecoste, F. Auguste. R. Canet, P. Delhaes, C. Guimon, Cl. Pfister-Guillouzo, B. Nysten and J.P. Issi, J. Mat. Res. 8 (1993) 480. (121 D. Li, S. Lopez, Y.W. Chung, M.S. Wong and W. D. Sproul, J. Vat. Sci. Technol. A I3 (1995) 1063. [I31 J.H. Kaufman, S. Metin and D.D. Saperstein, Phys. Rev. B 39 (1989) 13053. 1141 A. Bousetta, M. Lu and A. Bensaoula. J. Vat. Sci. Technol. I? (1995) 1639. [I51 I. Gouzman, R. Brener and A. Hoffman, Surf. Sci. 332-333 (I 995) 283.
III. ION BEAMS