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Photodeposited diffractive optical elements of computer generated masks
Applied Surface Science 248 (2005) 509–513 www.elsevier.com/locate/apsusc
Photodeposited diffractive optical elements of computer generated masks N. Mirchin a,*, A. Peled a, I. Baal-Zedaka a, R. Margolin a, M. Zagon a, I. Lapsker b, A. Verdyan b, J. Azoulay b a
Electrical and Electronics Engineering Department, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102, Israel b Physics Department, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102, Israel Available online 5 April 2005
Abstract Diffractive optical elements (DOE) were synthesized on plastic substrates using the photodeposition (PD) technique by depositing amorphous selenium (a-Se) films with argon lasers and UV spectra light. The thin films were deposited typically onto polymethylmethacrylate (PMMA) substrates at room temperature. Scanned beam and contact mask modes were employed using computer-designed DOE lenses. Optical and electron micrographs characterize the surface details. The films were typically 200 nm thick. # 2005 Elsevier B.V. All rights reserved. Keywords: Photodeposition; Optical gratings; Optical microelements; Diffractive optical elements; DOE
1. Introduction Several methods are used for materials processing with light beams. Among them, one finds photodeposition (PD) of thin films [1,2], photoelectrochemical etching [3], photodoping [4], laser ablation [5], laser writing and machining [6], photodiagnostics [7] and chemical processing with lasers [8,9]. The PD resolution is limited theoretically only by the smallest particles in the photoactive solution, thus, near-field imaging is possible in principle in contrast to the emulsion-based photography which suffers from * Corresponding author. Fax: +972 3 502 6643. E-mail address: [email protected] (N. Mirchin).
photon imaging diffusion [10,11]. The best experimental resolution achieved by the PD technique was 490 nm with holographic interference using an argon laser [10]. PD can be used for depositing material patterns of macroscopic or microscopic dimensions to obtain typical components such as diffractive optical elements (DOE), filters, zone lenses, mirrors, beamsplitters, birefringent elements, refractive elements and phase-gratings. 2. Photodeposition from colloids in the liquid phase By photoexcitation in the liquid phase [2], photon– material interaction can create thin layer structures or
0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.03.036
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N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
clusters of atoms on the surfaces and colloid nucleation centers in the bulk. Photodeposition systems [12–17] incorporate three functions: light ‘‘harvesting’’ centers known as chromophores, dissolved ions which decompose or react during the photoexcited state of the chromophores and a substrate. The chromophores may or may not decompose and be precipitated by photoredox reactions creating solid phase agglomeration or adsorbing on the surfaces [18–21]. In the case of amorphous selenium (a-Se) PD [12–15], the photochemically assisted reaction is given by: hv
H2 SeO3 þ 2SO2 þ H2 O!Se # þ 2H2 SO4 The method involves the preparation of a metastable mixture of Se colloid particles co-existing in hydrosol with Se+4 ions of H2SeO3 and a reducing agent such as SO2. The stabilized photoactive hydrosol has typically a pH of about 1.4 and the solvated Se ions in the solution with a concentration of 2.5 g/l. The Se elemental colloid particles are suspended in the solution and function as chromophores when activated by blue spectrum light or shorter wavelengths. They catalyze the reducing reaction by shifting the equilibrium to the right side of the above mentioned equation. Activation by light induces a simultaneous photoprecipitation, photoadsorption and electroless film growth of the precipitate on virtually any insulating substrate and also on the colloid particles in the bulk of the solution. This process is autocatalytic in the case of a-Se since the ion source, photoelectrons, precipitated material and substrate all are of the same material, i.e. a-Se. The transport of the photoreduced material onto the substrates from the solution is assumed to be controlled by Brownian motion, and the adsorption step itself, thermally and photon absorption activated [16,17].
For thin-film patterning, the image is projected onto the window/substrate of the cell which contains the photoactive aqueous colloid medium. The ‘surface’ PD [9] creates nanometer particles which are deposited on the transparent insulating substrate, typically made of polymethylmethacrylate (PMMA). These particles then grow, coalesce and create a continuous film in the areas irradiated by the photons [22–24]. Thus, by irradiating the solution with a laser or appropriate beam of light through accurately defined optical masks, dots, lines and more intricate patterns can be directly recorded photographically in one step on solid interfaces which are in contact with the solution.
3. Optical elements obtained by laser scanning beam An argon laser beam operated at 488 nm wavelength was used for scanned mode photodeposition. Fig. 1 shows half a cylindrical Fresnel DOE lens obtained by scanned writing. The pattern was obtained with a fluence of 90 J/cm2 and scanning velocity of 150 mm/s.
4. Surface morphological characterization by SEM Similar to vacuum deposited films, the morphology of the structures consist initially of a discrete random array of individual particles adsorbed on the substrate, as observed by SEM and shown in Fig. 2. The particles grow in size and coalesce as the deposition proceeds. The pre-compact structures shows that the deposition is assisted also by a-Se material flow
Fig. 1. (a) Optical micrograph of a cylindrical DOE made by PD scanning mode. (b) Optical density profile of the element.
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
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Fig. 2. SEM micrographs showing the coverage of the substrate as the film grows: (a) early stage of single particles deposition on the substrate; (b) coalescing of particles at a later stage; (c) continuous film.
through diffusion, growth, bridging and coalescence [2,12,14,24]. The nanostructure of the photodeposited film was obtained by AFM, and the typical morphology at this level shows the amorphous structure of a-Se atoms arranged mainly in meandering long chains and a few rings, see Fig. 3.
5. Prototypes of DOE with contact masks Fresnel lenses with zonal widths of a few micrometers operate as diffractive lenses for optical couplers in the communication industry. Diffractive Fresnel lenses (DFL) with small groove widths of the order of microns are fabricated by various methods including lithography, ion milling and etching. To investigate the practical technological possibilities offered by PD, we have designed and prototyped DFL. The diffractive Fresnel lenses utilize constructive interference between each aperture to produce a
common focal point. The alternating regions of the transparent and opaque regions are shown in Fig. 4. The zone radii from the center required to achieve constructive or destructive interference at a distance f 1 on the optical axis are given by: r2N ¼ ð f1 þ Nl=2Þ2 f12
(1)
where rN is the radius to the Nth boundary and l is the wavelength of light. At radius r1, the first dark zone begins (encircling the central transparent zone) due to a difference of l/2 in the paths of r2N and z2 which creates a destructive condition. At r2, the second transparent zone begins due to an integral difference of l in the paths taken by the rays along r2N and z2, thus, creating a constructive condition at z2 = f 1. The following zones, i.e. N > 2 continue this alternating trend. For l f 1, which is a condition occuring for most practical FDL cases, one obtains for the firstorder focal distance, the following approximate design equation for the alternating zones radii: r2N N f1 l
(2)
which gives the ‘parabolic’ approximation for the zones radii: pffiffiffiffiffiffiffiffi pffiffiffiffi rN ¼ N r1 and r1 ¼ f1 l (3) According to the lens formula (see Fig. 4): f 1 = z1z2/ (z1 + z2). Thus, the FDL will act as a lens with focal length of f 1 for light with a wavelength l. FDLs are, thus, very useful for optics involving a monochromatic or nearly monochromatic light. Setting N = 1 leads to a simple equation to determine the focal length for the FDL: Fig. 3. AFM micrograph showing the nanolevel surface morphology of the photodeposited a-Se film.
f ¼ f1 ¼
r21 l
(4)
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N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
Fig. 4. Fresnel DOE lens configuration with three-zones (N = 1, 2, 3) details: ABC ¼ r1N þ r2N ¼ z1 þ z2 þ 12 r2N ðz11 þ z12 Þ þ .
However, unlike a standard lens that uses refraction, an FDL has multiple focal points. The other focal points of higher orders, m > 1 are located at: fm ¼
f1 ¼ r21 ðmlÞ m
m ¼ odd
(5)
giving for the FDL, a series of focal points at f 1, f 1/3, f 1/5, f 1/7, f 1/9, etc. For an FDL with diameter D, the total maximum number of alternating zones, i.e. dark and transparent included, is given by: 2 3 !1=2 2 1 4 D ðD=2Þ2 Nmax ¼ þ f12 f1 5 l 2 ðl f1 Þ (6) The transmission efficiency is approximated by the ratio of the opaque area to the total area of the FDL. Since the alternating rings of the FDL are of equal area, the transmission efficiency of a FZL is 50% if N is even.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi z21 þ r2N þ z22 þ r2N
6. Results and discussion The DOE elements in our investigation were Fresnel lenses with profile thicknesses which could be increased or decreased depending on the colloid concentration and irradiation dose delivered by the UV source. The lens whose micrograph is shown in Fig. 5a has the following design parameters: 10 opaque zones, overall lens aperture of 8 mm with central open zone diameter of 1450 mm. The measured transmission of the lens in Fig. 5 was T 45%. The film thickness evaluated from calibrated optical transmission measurements was about 200 nm for a fluence of 64 J/cm2. From Fig. 5b, one observes that the lens profile exhibits an almost constant thickness for the first 7 circles, while the next three lines have a smaller thickness. This is due to different growing rates of the film beneath the various mask apertures widths. This problem can be corrected by compensating for the
Fig. 5. (a) Photomicrograph of a FZL obtained by writing an element of 10 lines using a fluence of 64 J/cm2 derived from Dr. Hohnle Model: Blue Point UV curing fiber illuminator with exit maximum intensity of 1.35 W/cm2 in the spectral band 280–390 nm. (b) Radial optical profile density of the Fresnel Lens from the central zone out.
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
light diminution in the outer zones. A similar though more enhanced effect can be observed in Fig. 1 for the cylindrical lens obtained by the laser scanned technique.
7. Conclusions The primary motivation for the development of the DOE by PD was to investigate the convenience of the method in terms of in situ one step patterning capabilities. We have used PD to obtain patterns of 25–250 mm linewidth in various forms for cylindrical and circular Fresnel lenses without the need of using complex photolithography and chemical etching steps. The foremost specific advantages of the direct one step process are the inherently local low temperatures used, i.e. room temperatures and below, and better spatial exploitation as compared to the other thin film definition techniques. Acknowledgement The authors wish to thank Ami M. Peled for his involvement during the computerized design of the DOE elements. References [1] A. Peled, Editor, Thin Solid Films 218 (1–2) (1992) 80–201 (special issue).
513
[2] A. Peled, N. Mirchin, in: A. Peled (Ed.), Photoexcited Processes, Diagnostics and Applications, Kluwer Academic Publishers, Boston, 2003, pp. 251–280 (Chapter 9). [3] C.I.H. Ashby, Thin Solid Films 218 (1992) 252. [4] J. Malinowski, A. Buroff, Contemp. Phys. 19 (1978) 99. [5] J. Dieleman,U.K.P. Bierman, P. Hess (Guest Eds.) Appl. Surf. Sci., 86 (1–4) (1995) 4–74. [6] D.J. Ehrlich, J.Y. Tsao (Eds.), Laser Microfabrication: Thin .Film Processes and Litography, Academic Press, Boston, 1989 [7] D. Bauerle (Ed.), Laser Processing and Diagnostics, vol. 39, Springer Ser., Chem. Phys., Springer, Heidelberg, 1984. [8] D. Bauerle, Chemical Processing with Lasers, Springer-Verlag, Berlin, 1986. [9] A. Peled, Y. Dror, Opt. Eng. 27 (6) (1988) 482. [10] A. Peled, V. Weiss, D. Rosenblatt, A.A. Friesem, Opt. Eng. 31 (1) (1991) 70. [11] V. Weiss, A. Peled, A.A. Friesem, Appl. Opt. 33 (22) (1994) 4988. [12] M. Perakh, A. Peled, Z. Feit, Thin Solid Films 50 (1978) 273. [13] M. Perakh, A. Peled, Thin Solid Films 50 (1978) 283. [14] M. Perakh, A. Peled, Thin Solid Films 50 (1978) 293. [15] A. Peled, L. Grantman, M. Ochayon, A.A. Friesem, Appl. Surf. Sci. 106 (1996) 306. [16] A. Peled, D. Naot, Colloid Polym. Sci. 265 (1987) 986. [17] A. Peled, M. Perakh, J. Colloid Interface Sci. 122 (1) (1988) 193. [18] H. Yoneyama, Crit. Rev. Solid State Mater. Sci. 18 (1) (1993) 69. [19] T. Kobayashi, Y. Taniguchi, H. Yoneyama, H. Tamura, J. Phys. Chem. 87 (1983) 768. [20] R.K. Montgomery, T.D. Mantei, Appl. Phys. Lett. 48 (7) (1986) 493. [21] R.H. Micheels, A.D. Darrow, R.D. Rauh, Appl. Phys. Lett. 39 (5) (1981) 418. [22] A. Peled, J. Mater. Res. 4 (1) (1989) 177. [23] A. Peled, A.A. Friesem, K. Vinokur, Thin Solid Films 218 (1) (1992) 201. [24] I. Lapsker, J. Azoulay, M. Rubnov, Z. Regev, R.C. Peled, A. Peled, Appl. Surf. Sci. 106 (1996) 316.
Photodeposited diffractive optical elements of computer generated masks N. Mirchin a,*, A. Peled a, I. Baal-Zedaka a, R. Margolin a, M. Zagon a, I. Lapsker b, A. Verdyan b, J. Azoulay b a
Electrical and Electronics Engineering Department, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102, Israel b Physics Department, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102, Israel Available online 5 April 2005
Abstract Diffractive optical elements (DOE) were synthesized on plastic substrates using the photodeposition (PD) technique by depositing amorphous selenium (a-Se) films with argon lasers and UV spectra light. The thin films were deposited typically onto polymethylmethacrylate (PMMA) substrates at room temperature. Scanned beam and contact mask modes were employed using computer-designed DOE lenses. Optical and electron micrographs characterize the surface details. The films were typically 200 nm thick. # 2005 Elsevier B.V. All rights reserved. Keywords: Photodeposition; Optical gratings; Optical microelements; Diffractive optical elements; DOE
1. Introduction Several methods are used for materials processing with light beams. Among them, one finds photodeposition (PD) of thin films [1,2], photoelectrochemical etching [3], photodoping [4], laser ablation [5], laser writing and machining [6], photodiagnostics [7] and chemical processing with lasers [8,9]. The PD resolution is limited theoretically only by the smallest particles in the photoactive solution, thus, near-field imaging is possible in principle in contrast to the emulsion-based photography which suffers from * Corresponding author. Fax: +972 3 502 6643. E-mail address: [email protected] (N. Mirchin).
photon imaging diffusion [10,11]. The best experimental resolution achieved by the PD technique was 490 nm with holographic interference using an argon laser [10]. PD can be used for depositing material patterns of macroscopic or microscopic dimensions to obtain typical components such as diffractive optical elements (DOE), filters, zone lenses, mirrors, beamsplitters, birefringent elements, refractive elements and phase-gratings. 2. Photodeposition from colloids in the liquid phase By photoexcitation in the liquid phase [2], photon– material interaction can create thin layer structures or
0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.03.036
510
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
clusters of atoms on the surfaces and colloid nucleation centers in the bulk. Photodeposition systems [12–17] incorporate three functions: light ‘‘harvesting’’ centers known as chromophores, dissolved ions which decompose or react during the photoexcited state of the chromophores and a substrate. The chromophores may or may not decompose and be precipitated by photoredox reactions creating solid phase agglomeration or adsorbing on the surfaces [18–21]. In the case of amorphous selenium (a-Se) PD [12–15], the photochemically assisted reaction is given by: hv
H2 SeO3 þ 2SO2 þ H2 O!Se # þ 2H2 SO4 The method involves the preparation of a metastable mixture of Se colloid particles co-existing in hydrosol with Se+4 ions of H2SeO3 and a reducing agent such as SO2. The stabilized photoactive hydrosol has typically a pH of about 1.4 and the solvated Se ions in the solution with a concentration of 2.5 g/l. The Se elemental colloid particles are suspended in the solution and function as chromophores when activated by blue spectrum light or shorter wavelengths. They catalyze the reducing reaction by shifting the equilibrium to the right side of the above mentioned equation. Activation by light induces a simultaneous photoprecipitation, photoadsorption and electroless film growth of the precipitate on virtually any insulating substrate and also on the colloid particles in the bulk of the solution. This process is autocatalytic in the case of a-Se since the ion source, photoelectrons, precipitated material and substrate all are of the same material, i.e. a-Se. The transport of the photoreduced material onto the substrates from the solution is assumed to be controlled by Brownian motion, and the adsorption step itself, thermally and photon absorption activated [16,17].
For thin-film patterning, the image is projected onto the window/substrate of the cell which contains the photoactive aqueous colloid medium. The ‘surface’ PD [9] creates nanometer particles which are deposited on the transparent insulating substrate, typically made of polymethylmethacrylate (PMMA). These particles then grow, coalesce and create a continuous film in the areas irradiated by the photons [22–24]. Thus, by irradiating the solution with a laser or appropriate beam of light through accurately defined optical masks, dots, lines and more intricate patterns can be directly recorded photographically in one step on solid interfaces which are in contact with the solution.
3. Optical elements obtained by laser scanning beam An argon laser beam operated at 488 nm wavelength was used for scanned mode photodeposition. Fig. 1 shows half a cylindrical Fresnel DOE lens obtained by scanned writing. The pattern was obtained with a fluence of 90 J/cm2 and scanning velocity of 150 mm/s.
4. Surface morphological characterization by SEM Similar to vacuum deposited films, the morphology of the structures consist initially of a discrete random array of individual particles adsorbed on the substrate, as observed by SEM and shown in Fig. 2. The particles grow in size and coalesce as the deposition proceeds. The pre-compact structures shows that the deposition is assisted also by a-Se material flow
Fig. 1. (a) Optical micrograph of a cylindrical DOE made by PD scanning mode. (b) Optical density profile of the element.
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
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Fig. 2. SEM micrographs showing the coverage of the substrate as the film grows: (a) early stage of single particles deposition on the substrate; (b) coalescing of particles at a later stage; (c) continuous film.
through diffusion, growth, bridging and coalescence [2,12,14,24]. The nanostructure of the photodeposited film was obtained by AFM, and the typical morphology at this level shows the amorphous structure of a-Se atoms arranged mainly in meandering long chains and a few rings, see Fig. 3.
5. Prototypes of DOE with contact masks Fresnel lenses with zonal widths of a few micrometers operate as diffractive lenses for optical couplers in the communication industry. Diffractive Fresnel lenses (DFL) with small groove widths of the order of microns are fabricated by various methods including lithography, ion milling and etching. To investigate the practical technological possibilities offered by PD, we have designed and prototyped DFL. The diffractive Fresnel lenses utilize constructive interference between each aperture to produce a
common focal point. The alternating regions of the transparent and opaque regions are shown in Fig. 4. The zone radii from the center required to achieve constructive or destructive interference at a distance f 1 on the optical axis are given by: r2N ¼ ð f1 þ Nl=2Þ2 f12
(1)
where rN is the radius to the Nth boundary and l is the wavelength of light. At radius r1, the first dark zone begins (encircling the central transparent zone) due to a difference of l/2 in the paths of r2N and z2 which creates a destructive condition. At r2, the second transparent zone begins due to an integral difference of l in the paths taken by the rays along r2N and z2, thus, creating a constructive condition at z2 = f 1. The following zones, i.e. N > 2 continue this alternating trend. For l f 1, which is a condition occuring for most practical FDL cases, one obtains for the firstorder focal distance, the following approximate design equation for the alternating zones radii: r2N N f1 l
(2)
which gives the ‘parabolic’ approximation for the zones radii: pffiffiffiffiffiffiffiffi pffiffiffiffi rN ¼ N r1 and r1 ¼ f1 l (3) According to the lens formula (see Fig. 4): f 1 = z1z2/ (z1 + z2). Thus, the FDL will act as a lens with focal length of f 1 for light with a wavelength l. FDLs are, thus, very useful for optics involving a monochromatic or nearly monochromatic light. Setting N = 1 leads to a simple equation to determine the focal length for the FDL: Fig. 3. AFM micrograph showing the nanolevel surface morphology of the photodeposited a-Se film.
f ¼ f1 ¼
r21 l
(4)
512
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
Fig. 4. Fresnel DOE lens configuration with three-zones (N = 1, 2, 3) details: ABC ¼ r1N þ r2N ¼ z1 þ z2 þ 12 r2N ðz11 þ z12 Þ þ .
However, unlike a standard lens that uses refraction, an FDL has multiple focal points. The other focal points of higher orders, m > 1 are located at: fm ¼
f1 ¼ r21 ðmlÞ m
m ¼ odd
(5)
giving for the FDL, a series of focal points at f 1, f 1/3, f 1/5, f 1/7, f 1/9, etc. For an FDL with diameter D, the total maximum number of alternating zones, i.e. dark and transparent included, is given by: 2 3 !1=2 2 1 4 D ðD=2Þ2 Nmax ¼ þ f12 f1 5 l 2 ðl f1 Þ (6) The transmission efficiency is approximated by the ratio of the opaque area to the total area of the FDL. Since the alternating rings of the FDL are of equal area, the transmission efficiency of a FZL is 50% if N is even.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi z21 þ r2N þ z22 þ r2N
6. Results and discussion The DOE elements in our investigation were Fresnel lenses with profile thicknesses which could be increased or decreased depending on the colloid concentration and irradiation dose delivered by the UV source. The lens whose micrograph is shown in Fig. 5a has the following design parameters: 10 opaque zones, overall lens aperture of 8 mm with central open zone diameter of 1450 mm. The measured transmission of the lens in Fig. 5 was T 45%. The film thickness evaluated from calibrated optical transmission measurements was about 200 nm for a fluence of 64 J/cm2. From Fig. 5b, one observes that the lens profile exhibits an almost constant thickness for the first 7 circles, while the next three lines have a smaller thickness. This is due to different growing rates of the film beneath the various mask apertures widths. This problem can be corrected by compensating for the
Fig. 5. (a) Photomicrograph of a FZL obtained by writing an element of 10 lines using a fluence of 64 J/cm2 derived from Dr. Hohnle Model: Blue Point UV curing fiber illuminator with exit maximum intensity of 1.35 W/cm2 in the spectral band 280–390 nm. (b) Radial optical profile density of the Fresnel Lens from the central zone out.
N. Mirchin et al. / Applied Surface Science 248 (2005) 509–513
light diminution in the outer zones. A similar though more enhanced effect can be observed in Fig. 1 for the cylindrical lens obtained by the laser scanned technique.
7. Conclusions The primary motivation for the development of the DOE by PD was to investigate the convenience of the method in terms of in situ one step patterning capabilities. We have used PD to obtain patterns of 25–250 mm linewidth in various forms for cylindrical and circular Fresnel lenses without the need of using complex photolithography and chemical etching steps. The foremost specific advantages of the direct one step process are the inherently local low temperatures used, i.e. room temperatures and below, and better spatial exploitation as compared to the other thin film definition techniques. Acknowledgement The authors wish to thank Ami M. Peled for his involvement during the computerized design of the DOE elements. References [1] A. Peled, Editor, Thin Solid Films 218 (1–2) (1992) 80–201 (special issue).
513
[2] A. Peled, N. Mirchin, in: A. Peled (Ed.), Photoexcited Processes, Diagnostics and Applications, Kluwer Academic Publishers, Boston, 2003, pp. 251–280 (Chapter 9). [3] C.I.H. Ashby, Thin Solid Films 218 (1992) 252. [4] J. Malinowski, A. Buroff, Contemp. Phys. 19 (1978) 99. [5] J. Dieleman,U.K.P. Bierman, P. Hess (Guest Eds.) Appl. Surf. Sci., 86 (1–4) (1995) 4–74. [6] D.J. Ehrlich, J.Y. Tsao (Eds.), Laser Microfabrication: Thin .Film Processes and Litography, Academic Press, Boston, 1989 [7] D. Bauerle (Ed.), Laser Processing and Diagnostics, vol. 39, Springer Ser., Chem. Phys., Springer, Heidelberg, 1984. [8] D. Bauerle, Chemical Processing with Lasers, Springer-Verlag, Berlin, 1986. [9] A. Peled, Y. Dror, Opt. Eng. 27 (6) (1988) 482. [10] A. Peled, V. Weiss, D. Rosenblatt, A.A. Friesem, Opt. Eng. 31 (1) (1991) 70. [11] V. Weiss, A. Peled, A.A. Friesem, Appl. Opt. 33 (22) (1994) 4988. [12] M. Perakh, A. Peled, Z. Feit, Thin Solid Films 50 (1978) 273. [13] M. Perakh, A. Peled, Thin Solid Films 50 (1978) 283. [14] M. Perakh, A. Peled, Thin Solid Films 50 (1978) 293. [15] A. Peled, L. Grantman, M. Ochayon, A.A. Friesem, Appl. Surf. Sci. 106 (1996) 306. [16] A. Peled, D. Naot, Colloid Polym. Sci. 265 (1987) 986. [17] A. Peled, M. Perakh, J. Colloid Interface Sci. 122 (1) (1988) 193. [18] H. Yoneyama, Crit. Rev. Solid State Mater. Sci. 18 (1) (1993) 69. [19] T. Kobayashi, Y. Taniguchi, H. Yoneyama, H. Tamura, J. Phys. Chem. 87 (1983) 768. [20] R.K. Montgomery, T.D. Mantei, Appl. Phys. Lett. 48 (7) (1986) 493. [21] R.H. Micheels, A.D. Darrow, R.D. Rauh, Appl. Phys. Lett. 39 (5) (1981) 418. [22] A. Peled, J. Mater. Res. 4 (1) (1989) 177. [23] A. Peled, A.A. Friesem, K. Vinokur, Thin Solid Films 218 (1) (1992) 201. [24] I. Lapsker, J. Azoulay, M. Rubnov, Z. Regev, R.C. Peled, A. Peled, Appl. Surf. Sci. 106 (1996) 316.