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Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser.

Kalachyova Y, Lyutakov O, Slepicka P, Elashnikov R, Svorcik V - Nanoscale Res Lett (2014)

Bottom Line: The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity.The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure.Most regular grating structures were obtained on polymer films deposited on atomically 'flat' Si substrates.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Solid State Engineering, Institute of Chemical Technology, Prague 166 28, Czech Republic.

ABSTRACT
In this work, we describe laser modification of poly(methyl methacrylate) films doped with Fast Red ITR, followed by dopant exclusion from the bulk polymer. By this procedure, the polymer can be modified under extremely mild conditions. Creation of surface ordered structure was observed already after application of 15 pulses and 12 mJ cm(-2) fluence. Formation of grating begins in the hottest places and tends to form concentric semi-circles around them. The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity. The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure. Most regular grating structures were obtained on polymer films deposited on atomically 'flat' Si substrates. After laser patterning, the dopant was removed from the polymer by soaking the film in methanol.

No MeSH data available.


Related in: MedlinePlus

Dependence of grating amplitude on the initial thickness of PMMA-FR films irradiated by laser. The laser has 50 pulses and 12 mJ cm−2; the concentration of FR was 18%.
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Figure 8: Dependence of grating amplitude on the initial thickness of PMMA-FR films irradiated by laser. The laser has 50 pulses and 12 mJ cm−2; the concentration of FR was 18%.

Mentions: The dependence of grating periodicity on incidence angle taken from the surface normal is shown in Figure 6. Two distinct regions are apparent from the graph. The region above 50° corresponds to the formation of more regular surface pattern. For angles below 50°, formation of irregular, partially destroyed quasi periodical pattern was observed. The deviation from the proposed behavior may be due to surface structure coalescence and structure degradation. For the sake of clarity, we also show several AFM scans measured on samples modified under different angles (see Figure 7). The modification under angles close to surface normal leads to surface structure in the form of a disrupted structure. If the angle of incidence increases, the structures become more regular. At 50°, the prepared structure is highly ordered and seems to be closed to ‘ideal’. One of the possible explanations consists in changes of laser energy distributions. When the angle of the laser beam incidence is close to surface normal, significant part of light energy penetrates into the polymer film, reflects from silicon substrate, and comes back to interact with the incident light. In this case, amplitude of interference pattern is pronounced, but degradation of polymer films occurs. When the angle of the laser beam incidence is moving away from the surface normal, the amount of penetrated light decreases and grating becomes more regular. When the certain value of ‘optimal’ angle is achieved, high regular grating with approximately 500 nm periodicity is produced (Figures 6 and 7). Another possible explanation consists in the transition from laser interference-induced pattern to so-called light-induced periodical surface (LIPPS) [45]. This transition means two different types of incident beam interaction - with reflected light from substrate in the case of grating and interference with light scattered along surface in the case of LIPPS formation. When the angle of the laser beam incident is moving away from the surface normal, a so-called Brewster's angle is achieved and light does not penetrate into polymer films. At these conditions (and at greater angle), light is predominantly reflected or scattered/transmitted along the sample surface. In this case, interaction of incident light with scattered light takes place and LIPPS formation occurs. So, both explanations are possible, and further experiments are in progress to choose the right explanation.We also studied the grating creation based on the initial PMMA-FR thickness. The observed results are given in Figure 8. As can be expected, the grating amplitude is an increasing function of the initial polymer thickness. The amplitude achieves a saturated value when the film thickness exceeds 0.75 μm and then it remains constant. The saturation can be due to limited depth of penetration of the laser light. Due to high absorption coefficient of the PMMA-FR film, the penetration of UV light is restricted only to the near-surface layer. For that reason, there is no difference between the films of larger but different thicknesses. Breakpoint at 0.75 μm can be evaluated as a critical point, at which the amount of transmitted energy is insufficient to induce polymer ablation. Like the previous case, an alternative explanation can be that LIPPS-induced pattern transits into interference-induced pattern. When the polymer thickness is small, light can penetrate through the polymer film twice - to the substrate and from the substrate. So, interference between incident and reflected light is dominant. Increasing the polymer thickness leads to attenuation of light through film thickness. In this case, the interference between scattered light along the surface and the incident light seems to be more possible - LIPPS formation occurs.Ultra-thin polymer films were studied separately, and related AFM scans are presented in Figure 9. The thickness of the polymer film is smaller than the applied wavelength in this case. In this case, a modification of the surface was observed, but the creation of regular pattern was not confirmed. The modified surface rather represents a system of random distributed holes. When the film thickness is close to laser wavelength, the prepared structure becomes more regular and comprises a system of spots. With further increase in film thickness, formation of regular grating pattern occurs. The possible explanation also is that LIPPS interferes with pattern transition: less regular structures in the case of thin films, where interference of reflected and incident beams occurs, and more regular for thick films, where LIPPS structures can be expected.


Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser.

Kalachyova Y, Lyutakov O, Slepicka P, Elashnikov R, Svorcik V - Nanoscale Res Lett (2014)

Dependence of grating amplitude on the initial thickness of PMMA-FR films irradiated by laser. The laser has 50 pulses and 12 mJ cm−2; the concentration of FR was 18%.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4215891&req=5

Figure 8: Dependence of grating amplitude on the initial thickness of PMMA-FR films irradiated by laser. The laser has 50 pulses and 12 mJ cm−2; the concentration of FR was 18%.
Mentions: The dependence of grating periodicity on incidence angle taken from the surface normal is shown in Figure 6. Two distinct regions are apparent from the graph. The region above 50° corresponds to the formation of more regular surface pattern. For angles below 50°, formation of irregular, partially destroyed quasi periodical pattern was observed. The deviation from the proposed behavior may be due to surface structure coalescence and structure degradation. For the sake of clarity, we also show several AFM scans measured on samples modified under different angles (see Figure 7). The modification under angles close to surface normal leads to surface structure in the form of a disrupted structure. If the angle of incidence increases, the structures become more regular. At 50°, the prepared structure is highly ordered and seems to be closed to ‘ideal’. One of the possible explanations consists in changes of laser energy distributions. When the angle of the laser beam incidence is close to surface normal, significant part of light energy penetrates into the polymer film, reflects from silicon substrate, and comes back to interact with the incident light. In this case, amplitude of interference pattern is pronounced, but degradation of polymer films occurs. When the angle of the laser beam incidence is moving away from the surface normal, the amount of penetrated light decreases and grating becomes more regular. When the certain value of ‘optimal’ angle is achieved, high regular grating with approximately 500 nm periodicity is produced (Figures 6 and 7). Another possible explanation consists in the transition from laser interference-induced pattern to so-called light-induced periodical surface (LIPPS) [45]. This transition means two different types of incident beam interaction - with reflected light from substrate in the case of grating and interference with light scattered along surface in the case of LIPPS formation. When the angle of the laser beam incident is moving away from the surface normal, a so-called Brewster's angle is achieved and light does not penetrate into polymer films. At these conditions (and at greater angle), light is predominantly reflected or scattered/transmitted along the sample surface. In this case, interaction of incident light with scattered light takes place and LIPPS formation occurs. So, both explanations are possible, and further experiments are in progress to choose the right explanation.We also studied the grating creation based on the initial PMMA-FR thickness. The observed results are given in Figure 8. As can be expected, the grating amplitude is an increasing function of the initial polymer thickness. The amplitude achieves a saturated value when the film thickness exceeds 0.75 μm and then it remains constant. The saturation can be due to limited depth of penetration of the laser light. Due to high absorption coefficient of the PMMA-FR film, the penetration of UV light is restricted only to the near-surface layer. For that reason, there is no difference between the films of larger but different thicknesses. Breakpoint at 0.75 μm can be evaluated as a critical point, at which the amount of transmitted energy is insufficient to induce polymer ablation. Like the previous case, an alternative explanation can be that LIPPS-induced pattern transits into interference-induced pattern. When the polymer thickness is small, light can penetrate through the polymer film twice - to the substrate and from the substrate. So, interference between incident and reflected light is dominant. Increasing the polymer thickness leads to attenuation of light through film thickness. In this case, the interference between scattered light along the surface and the incident light seems to be more possible - LIPPS formation occurs.Ultra-thin polymer films were studied separately, and related AFM scans are presented in Figure 9. The thickness of the polymer film is smaller than the applied wavelength in this case. In this case, a modification of the surface was observed, but the creation of regular pattern was not confirmed. The modified surface rather represents a system of random distributed holes. When the film thickness is close to laser wavelength, the prepared structure becomes more regular and comprises a system of spots. With further increase in film thickness, formation of regular grating pattern occurs. The possible explanation also is that LIPPS interferes with pattern transition: less regular structures in the case of thin films, where interference of reflected and incident beams occurs, and more regular for thick films, where LIPPS structures can be expected.

Bottom Line: The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity.The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure.Most regular grating structures were obtained on polymer films deposited on atomically 'flat' Si substrates.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Solid State Engineering, Institute of Chemical Technology, Prague 166 28, Czech Republic.

ABSTRACT
In this work, we describe laser modification of poly(methyl methacrylate) films doped with Fast Red ITR, followed by dopant exclusion from the bulk polymer. By this procedure, the polymer can be modified under extremely mild conditions. Creation of surface ordered structure was observed already after application of 15 pulses and 12 mJ cm(-2) fluence. Formation of grating begins in the hottest places and tends to form concentric semi-circles around them. The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity. The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure. Most regular grating structures were obtained on polymer films deposited on atomically 'flat' Si substrates. After laser patterning, the dopant was removed from the polymer by soaking the film in methanol.

No MeSH data available.


Related in: MedlinePlus