Grigonis, A.

Medvid, A.

Micko, A.

Rutkuniene, Z.

Vinciunaite, V.

Zabels, R.

Electronic Sumy State University Institutional Repository

196                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              IR, VIS, AND UV LASER LIGHT IRRADIATION OF AMORPHOUS CARBON FILMS Alfonsas Grigonis1, Živilơ Rutkǌnienơ1,*, Vinga Vinciǌnaitơ1, Roberts Zabels2, Artur Medvid3, Alexsandr Miþko3  1 Kaunas University of Technology,  Studentǐ st. 50,LT-51368, Kaunas, Lithuania 2 Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga, LV1063, Latvia 3 Riga Technical University, 14 Azenes St., LV-1048 Riga, Latvia  ABSTRACT Coherent laser irradiation of amorphous carbon films formatted on Si substrate by ion beam deposition (IBD) and plasma enhanced chemical vapor deposition methods (PECVD) were analyzed in this work. a-C:H films have various sp3/sp2 phases ratio and different quantity of hydrogen, so they were conditional called as diamond like (DLC) (IBD formation method, quantity of H = (25 – 35) % , hardness by Vickers (HV) = 15 – 25 GPa) and graphite like carbon films (PECVD method,  H < 20 %, HV = 6 – 12 GPa).  Films were irradiated with nanosecond Nd:YAG laser (Ekspla NL301G) at  the first (1064 nm; 6 ns),  the second (532 nm, 4.2 ns) and the fourth  (266 nm, 3 ns) harmonic by scanning or repeating (10 pulse to one point) regime. The same power was in both regimes, intensity was increased to the threshold of ablation.  Irradiation by the first laser harmonic with the power density (30 – 70) MW/cm2 stimu-lates  minor increasing of graphite phase.  The peaks at  ~ 800 cm-1(intensive) and at ~ 970 cm-1 (weak) showed SiC formation. Formation of carbides was observed at the second and superior harmonics irradiation when intensity of irradiation is low (< 10 MW/cm2). Graphitization becomes more intensive when intensity of radiation increased and films transform to the glass carbon and nano/micro crystallite compound at inten-sive ablations regime (second harmonic~ 24 MW/cm2). Ellipsometry measurements show not only the reduction but also high dispersion of film thickness. Micro relief analysis showed that film swelling proceeded during the graphitization process.   Key words: amorphous carbon films, laser irradiation.  INTRODUCTION Amorphous carbon films are perspective materials for many applications because of their unique optical, mechanical, electrical, and chemical properties. The physical properties of plasma-deposited amorphous hydrogenated carbon (a-C:H) films are determined by carbon sp3/sp2 bonding ratio and by hydrogen content [1-3].  Depending on the type of predominating bonds, the a-C:H films are divid-ed into three groups: (i) diamond-like carbon (DLC) with sp3 bonds, (ii) graph-                                               * e-mail: zirut@ktu.lt, tel. (+370) 686 54543 Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              197  ite-like carbon (GLC) with sp2 bonds, and (iii) polymer-like carbon (PLC) with sp3 bonds and a high concentration of hydrogen. The hydrogen concentration and hence the physical properties of a-C:H films can be varied by laser irradia-tion because of the energy of bonds C-H (and C-C) is considerably smaller than that  of  C=C or  CŁC bonds.  In  general,  the  effect  of  laser  irradiation  on  DLC films is determined by superposition of three processes: graphitization, spalla-tion, and evaporation, that are characterized by different threshold intensities [4]. The laser-induced graphitization of the surface layer has the lowest thresh-old and causes the changes of material properties. Among these changes, a noticeable reduction of the mass density is the most important for the surface morphology, as it leads to a pronounced surface swelling. Two other processes (spallation and evaporation) cause the material removal and lead to the for-mation of characteristic surface profiles. The effect of multilevel spallation in DLC films manifests itself in peeling and removal of one or more layers, whose lateral size is comparable with irradiated area and the thickness is much less than the film thickness [4]. The aim of the present work was to study optical properties of laser-irradiated a-C:H films. The critical values of irradiation for essential structural transformations were estimated. The corresponding changes in bonding and concentration of sp3 bonds were discussed. METHODS OF SAMPLE MANUFACTURING AND ANALYSIS Amorphous carbon films of a thickness up to 250 nm were formed on Si (100) and (111) wafers by applying a direct ion beam deposition method at room temperature. The substrates were degreased by immersing twice for 10 min in a chemically pure dimetilformamide. The substrates were cleaned for 1 to 10 min by hydrogen plasma before deposition. The films were formed from pure acetylene. The following deposition conditions such as ion energy 700 eV, ion current density ~ 0.12 mA/cm2, pressure below 10-2 Pa, deposition duration 30 min were used. The details of deposition procedure were presented else-where [5,6].  The samples were irradiated in a scanning mode with the step of 25 Pm, and pulse to one point by a q-switched YAG:Nd laser ((Ekspla NL15100TH) with pulses repetition rate of 12.5 Hz. The hydrogen concentration was determined by elastic-recoil detection  using a 2.4 MeV 4He2+ beam. The optical properties of laser-irradiated a-C:H films were studied by Raman scattering (Yvon Jobin), infrared (Perkin Elmer) spectroscopy, null- ellipsometry (Gaertner L117). The Rutherford backscatter-ing spectroscopy and elastic recoil detection measurements indicated that the films consist of carbon (73 at.%) and hydrogen (27 at.%). These films are at-tributed to the typical diamond-like carbon (DLC) films. The properties of films before and after laser irradiation by first harmonic are shown in Table 1. 198                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              The IR-laser irradiation at both 35 mw/cm2 and 70 mw/cm2  intensities led to an insignificant graphitization of the DLC films. The formation of the SiC started at the interface between the substrate and the films. The presence of the sic phase was confirmed by the appearance of the peaks at 800 cmí1 and 960 cmí1 in the RS spectra. However, despite the graphitization and SiC formation, the films had good adhesion with the substrate. The microhardness of the laser-irradiated thin films decreased slightly with the increase of the energy density (Table 1). The irradiation with infrared light did not change the films’ structure, and the films still remained as DLC. The ellipsometric calculations were per-formed with or without the SiC layer depending on the rs results. The irradia-tions with the first harmonics led to a lower refractive index and thicker DLC and SiC layers (Table 1). These results indicate that the graphitization process of films was initiated.   Table 1 – The conditions of irradiation (O – wavelength, laser intensity) and char-acteristics of the films’ refractive index (n), extinction coefficient (k), film thickness (d), microhardness (HV). Sample Oѽ nm Irrad. int. MW/cm2 Model n k dDLC, (dGC ) Nm dSiC, nm HV, GPa B4 - - DLC/Si 2.41 0.16 145 - 23 B4-1 1064 70 DLC/SiC/Si 2.36 0.27 169 50 17 B4-2 1064 35 DLC/SiC/Si 2.13 0.4 165 10 19  The DLC films were found to be more sensitive to the VIS (532 nm) and UV laser irradiation (266 nm). The dispersion of film thickness showed that evaporation and surface swelling took place, and the transformation of sp3/ sp2 conditioned. When the intensity of irradiation is >1 MW/cm2, the Si and C diffusion also took place and caused the formation of the high intensity SiC peaks in the Raman spectra (at 800 cmí1and 960 í 1000 cmí1, respectively). Simultaneous processes, such as spallation and phase conversion, stimulated transformation  of  the  sp3  bond  to  the  sp2  bonds  and  the  DLC  films  to  the  graphite-like carbon/glass carbon.   Table 2 – The conditions of irradiation (O-wavelength, laser intensity), ellipsome-try data  and the fitting parameters of the Raman spectra Sample Onm Irrad. int. MW/cm2 D, cm-1 'D, cm-1 G, cm-1 'G, cm-1 ID/IG n k B4   1312  1540  0.4 2.41 0.16 B4-1  70 1322  1545  0.6 2.36 0.27 B4-2  35 1365  1546  1.06 2.13 0.4   24 1346  1598  1.33 1.9 0.11   42 1385  1584  1.23 2.47 0 Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              199  The RS spectra of DLC films were fitted to determine the D and G peaks position, the full width at half-maxima of the D (ǻD) and G (ǻG) bands, and the integral intensity ratio between the D and G peaks (ID/IG) (Table 2). The Gaussian fitting results demonstrated that the G peak narrowed (86 and 111 cmí1) and shifted to the higher wave numbers (58 and 44 cmí1), and the (ID/IG) ratio increased. The films can be called a mixture of DLC/GLC with the glassy carbon phase inserts [2,7]. CONCLUSIONS The investigations showed that thin DLC films are resistant to IR-laser ir-radiation (1.16 eV). Irradiation by the first harmonics of a Nd:YAG laser stimu-lated formation of SiC and a slight hydrogenization of Si at the interface region. The films’ graphitization and formation of the SiC clusters took place by in-creasing the photon energy.   Acknowledgements This research was funded by a grant (No. MIP-59/2010) from the Re-search Council of Lithuania. REFERENCES [1] K.P. Chu, L. Li, Mater. Chem. Phys. 96, 253 (2006). [2] J. Robertson, J. Mater. Sci. Eng. R 37, 129 (2002). [3] M.G. Beghi, A.C. Ferrari, et al. Appl. Phys. Lett. 81, 3804 (2002). [4] T.V. Kononenko, V.G Ralchenko, E.D Obraztsova et al. Appl. Surf. Sci. 86, 234 (1995). [5] A. Grigonis, Ž. Rutkuniene, A. Medvids, Vacuum, 82, 1 212 (2008). [6] A. Grigonis, A. Medvid, P. Onufrijevs et al. Opt. Mater. 30, 749 (2008). [7] L. Marcinauskas, A. Grigonis, V. Valincius, J. Non-Cryst. Solids 355, 1240 (2009)    

IR, VIS, and UV laser light irradiation of amorphous carbon films

SocioEconomic Challenges Journal (Sumy State University)

196                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I             
 
IR, VIS, AND UV LASER LIGHT IRRADIATION OF 
AMORPHOUS CARBON FILMS 
Alfonsas Grigonis1, Živilơ Rutkǌnienơ1,*, Vinga Vinciǌnaitơ1, Roberts Zabels2, 
Artur Medvid3, Alexsandr Miþko3 
 
1 Kaunas University of Technology,  Studentǐ st. 50,LT-51368, Kaunas, Lithuania 
2 Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga, LV1063, Latvia 
3 Riga Technical University, 14 Azenes St., LV-1048 Riga, Latvia 
 
ABSTRACT 
Coherent laser irradiation of amorphous carbon films formatted on Si substrate by 
ion beam deposition (IBD) and plasma enhanced chemical vapor deposition methods 
(PECVD) were analyzed in this work. a-C:H films have various sp3/sp2 phases ratio and 
different quantity of hydrogen, so they were conditional called as diamond like (DLC) 
(IBD formation method, quantity of H = (25 – 35) % , hardness by Vickers (HV) = 15 – 
25 GPa) and graphite like carbon films (PECVD method,  H < 20 %, HV = 6 – 12 GPa).  
Films were irradiated with nanosecond Nd:YAG laser (Ekspla NL301G) at  the 
first (1064 nm; 6 ns),  the second (532 nm, 4.2 ns) and the fourth  
(266 nm, 3 ns) harmonic by scanning or repeating (10 pulse to one point) regime. The 
same power was in both regimes, intensity was increased to the threshold of ablation.  
Irradiation by the first laser harmonic with the power density (30 – 70) MW/cm2 stimu-
lates  minor increasing of graphite phase.  The peaks at  ~ 800 cm-1(intensive) and at ~ 
970 cm-1 (weak) showed SiC formation. Formation of carbides was observed at the 
second and superior harmonics irradiation when intensity of irradiation is low (< 10 
MW/cm2). Graphitization becomes more intensive when intensity of radiation increased 
and films transform to the glass carbon and nano/micro crystallite compound at inten-
sive ablations regime (second harmonic~ 24 MW/cm2). Ellipsometry measurements 
show not only the reduction but also high dispersion of film thickness. Micro relief 
analysis showed that film swelling proceeded during the graphitization process.  
 
Key words: amorphous carbon films, laser irradiation. 
 
INTRODUCTION 
Amorphous carbon films are perspective materials for many applications 
because of their unique optical, mechanical, electrical, and chemical properties. 
The physical properties of plasma-deposited amorphous hydrogenated carbon 
(a-C:H) films are determined by carbon sp3/sp2 bonding ratio and by hydrogen 
content [1-3].  
Depending on the type of predominating bonds, the a-C:H films are divid-
ed into three groups: (i) diamond-like carbon (DLC) with sp3 bonds, (ii) graph-
                                               
* e-mail: zirut@ktu.lt, tel. (+370) 686 54543 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              197 
 
ite-like carbon (GLC) with sp2 bonds, and (iii) polymer-like carbon (PLC) with 
sp3 bonds and a high concentration of hydrogen. The hydrogen concentration 
and hence the physical properties of a-C:H films can be varied by laser irradia-
tion because of the energy of bonds C-H (and C-C) is considerably smaller than 
that  of  C=C or  CŁC bonds.  In  general,  the  effect  of  laser  irradiation  on  DLC 
films is determined by superposition of three processes: graphitization, spalla-
tion, and evaporation, that are characterized by different threshold intensities 
[4]. The laser-induced graphitization of the surface layer has the lowest thresh-
old and causes the changes of material properties. Among these changes, a 
noticeable reduction of the mass density is the most important for the surface 
morphology, as it leads to a pronounced surface swelling. Two other processes 
(spallation and evaporation) cause the material removal and lead to the for-
mation of characteristic surface profiles. The effect of multilevel spallation in 
DLC films manifests itself in peeling and removal of one or more layers, whose 
lateral size is comparable with irradiated area and the thickness is much less 
than the film thickness [4]. 
The aim of the present work was to study optical properties of laser-
irradiated a-C:H films. The critical values of irradiation for essential structural 
transformations were estimated. The corresponding changes in bonding and 
concentration of sp3 bonds were discussed. 
METHODS OF SAMPLE MANUFACTURING AND ANALYSIS 
Amorphous carbon films of a thickness up to 250 nm were formed on Si 
(100) and (111) wafers by applying a direct ion beam deposition method at 
room temperature. The substrates were degreased by immersing twice for 10 
min in a chemically pure dimetilformamide. The substrates were cleaned for 1 
to 10 min by hydrogen plasma before deposition. The films were formed from 
pure acetylene. The following deposition conditions such as ion energy 700 eV, 
ion current density ~ 0.12 mA/cm2, pressure below 10-2 Pa, deposition duration 
30 min were used. The details of deposition procedure were presented else-
where [5,6].  
The samples were irradiated in a scanning mode with the step of 25 Pm, 
and pulse to one point by a q-switched YAG:Nd laser ((Ekspla NL15100TH) 
with pulses repetition rate of 12.5 Hz. 
The hydrogen concentration was determined by elastic-recoil detection  
using a 2.4 MeV 4He2+ beam. The optical properties of laser-irradiated a-C:H 
films were studied by Raman scattering (Yvon Jobin), infrared (Perkin Elmer) 
spectroscopy, null- ellipsometry (Gaertner L117). The Rutherford backscatter-
ing spectroscopy and elastic recoil detection measurements indicated that the 
films consist of carbon (73 at.%) and hydrogen (27 at.%). These films are at-
tributed to the typical diamond-like carbon (DLC) films. The properties of 
films before and after laser irradiation by first harmonic are shown in Table 1. 
198                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I             
 
The IR-laser irradiation at both 35 mw/cm2 and 70 mw/cm2  intensities led to an 
insignificant graphitization of the DLC films. The formation of the SiC started 
at the interface between the substrate and the films. The presence of the sic 
phase was confirmed by the appearance of the peaks at 800 cmí1 and 960 cmí1 
in the RS spectra. However, despite the graphitization and SiC formation, the 
films had good adhesion with the substrate. The microhardness of the laser-
irradiated thin films decreased slightly with the increase of the energy density 
(Table 1). The irradiation with infrared light did not change the films’ structure, 
and the films still remained as DLC. The ellipsometric calculations were per-
formed with or without the SiC layer depending on the rs results. The irradia-
tions with the first harmonics led to a lower refractive index and thicker DLC 
and SiC layers (Table 1). These results indicate that the graphitization process 
of films was initiated.  
 
Table 1 – The conditions of irradiation (O – wavelength, laser intensity) and char-
acteristics of the films’ refractive index (n), extinction coefficient (k), film thickness (d), 
microhardness (HV). 
Sample Oѽ 
nm 
Irrad. int. 
MW/cm2 Model n k 
dDLC, 
(dGC ) 
Nm 
dSiC, 
nm 
HV, 
GPa 
B4 - - DLC/Si 2.41 0.16 145 - 23 
B4-1 1064 70 DLC/SiC/Si 2.36 0.27 169 50 17 
B4-2 1064 35 DLC/SiC/Si 2.13 0.4 165 10 19 
 
The DLC films were found to be more sensitive to the VIS (532 nm) and 
UV laser irradiation (266 nm). The dispersion of film thickness showed that 
evaporation and surface swelling took place, and the transformation of sp3/ sp2 
conditioned. When the intensity of irradiation is >1 MW/cm2, the Si and C 
diffusion also took place and caused the formation of the high intensity SiC 
peaks in the Raman spectra (at 800 cmí1and 960 í 1000 cmí1, respectively). 
Simultaneous processes, such as spallation and phase conversion, stimulated 
transformation  of  the  sp3  bond  to  the  sp2  bonds  and  the  DLC  films  to  the  
graphite-like carbon/glass carbon.  
 
Table 2 – The conditions of irradiation (O-wavelength, laser intensity), ellipsome-
try data  and the fitting parameters of the Raman spectra 
Sample Onm 
Irrad. int. 
MW/cm2 D, cm
-1 'D, 
cm-1 G, cm
-1 'G, 
cm-1 ID/IG n k 
B4   1312  1540  0.4 2.41 0.16 
B4-1  70 1322  1545  0.6 2.36 0.27 
B4-2  35 1365  1546  1.06 2.13 0.4 
  24 1346  1598  1.33 1.9 0.11 
  42 1385  1584  1.23 2.47 0 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 1, Part I              199 
 
The RS spectra of DLC films were fitted to determine the D and G peaks 
position, the full width at half-maxima of the D (ǻD) and G (ǻG) bands, and 
the integral intensity ratio between the D and G peaks (ID/IG) (Table 2). 
The Gaussian fitting results demonstrated that the G peak narrowed (86 
and 111 cmí1) and shifted to the higher wave numbers (58 and 44 cmí1), and 
the (ID/IG) ratio increased. The films can be called a mixture of DLC/GLC 
with the glassy carbon phase inserts [2,7]. 
CONCLUSIONS 
The investigations showed that thin DLC films are resistant to IR-laser ir-
radiation (1.16 eV). Irradiation by the first harmonics of a Nd:YAG laser stimu-
lated formation of SiC and a slight hydrogenization of Si at the interface region. 
The films’ graphitization and formation of the SiC clusters took place by in-
creasing the photon energy.  
 
Acknowledgements 
This research was funded by a grant (No. MIP-59/2010) from the Re-
search Council of Lithuania. 
REFERENCES 
[1] K.P. Chu, L. Li, Mater. Chem. Phys. 96, 253 (2006). 
[2] J. Robertson, J. Mater. Sci. Eng. R 37, 129 (2002). 
[3] M.G. Beghi, A.C. Ferrari, et al. Appl. Phys. Lett. 81, 3804 (2002). 
[4] T.V. Kononenko, V.G Ralchenko, E.D Obraztsova et al. Appl. Surf. Sci. 86, 234 
(1995). 
[5] A. Grigonis, Ž. Rutkuniene, A. Medvids, Vacuum, 82, 1 212 (2008). 
[6] A. Grigonis, A. Medvid, P. Onufrijevs et al. Opt. Mater. 30, 749 (2008). 
[7] L. Marcinauskas, A. Grigonis, V. Valincius, J. Non-Cryst. Solids 355, 1240 (2009) 
 
  


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IR, VIS, and UV laser light irradiation of amorphous carbon films

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