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Electron beam induced surface modification of amorphous Sb2Se3 thin film
Journal of Non-Crystalline Solids 358 (2012) 1153–1156
Contents lists available at SciVerse ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol
Electron beam induced surface modification of amorphous Sb2Se3 thin film Oksana Shiman a,⁎, Vjaceslavs Gerbreders a, Eriks Sledevskis a, Valfrids Paskevics b a b
Innovative Microscopy Center, Daugavpils University, 1 Parades Str., Daugavpils LV-5400, Latvia Daugavpils University, 1 Parades Str., Daugavpils LV-5400, Latvia
a r t i c l e
i n f o
Article history: Received 12 December 2011 Received in revised form 6 February 2012 Available online 3 March 2012 Keywords: Amorphous and crystalline phases; Electron beam irradiation; Atomic force microscopy
a b s t r a c t The change in the surface morphology of amorphous Sb2Se3 thin films during the electron beam irradiation has been studied mainly by atomic force microscopy (AFM). Electron beam at accelerating voltages 30 kV is focused onto the surface of the specimens of 100-μm thickness, and then the surface morphology of each specimen has been observed by AFM in air. The modification of the film surface includes lateral and vertical resizing which is typically in the micrometer and sub-micrometer range. Protrusions above the surface as high as 90 nm are observed at 180 pA electron beam current, whilst trenches as deep as 97 nm are observed at 800 pA electron beam current (total thickness of thin film is 100 nm). The dependence of patterns characteristics on irradiation parameters such as exposure time and beam current has also been studied. Physical mechanisms for trench and mound formation are proposed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Nanostructure formation has been explored for many kinds of materials, and this becomes an interesting topic also for glasses with two features [1]. As is known, in single crystalline materials, one can prepare atomically flat surfaces, in which atoms can be controlled one by one. However, in amorphous materials such atomic manipulation is meaningless, since the amorphous structure is disordered at the atomic level. One of the features is that the control of nanometerscale structures could be an ultimate research subject for glassy structures. The other is that the amorphous nanostructure may yield a greater variety than the crystalline, since the bonding constraint arising from crystalline unit cells does not exist. Micro/nanostructures can be fabricated using various methods such as photolithography, femtosecond laser processing, focused ion beam and LIGA (LIthography, Electroplating and Molding) processes, etc. However, these processes are complicated, very time-consuming and expensive. When irradiating a chalcogenide surface with electron beam, micro/nanostructures can be formed in a simple one-step process. This class of material exhibits a number of structural changes when exposed to electron beams, for example, surface deformations in bulk and thin films of As2S3 [2], relief and trench formation in GeSe4 chalcogenide thin film [3], and surface modification (expansion) in Sb2S3 thin films [4] when exposed to electron beams. In his work Tanaka [1] inspected and modified the surface of chalcogenide glasses with nanometer resolution using scanning probe microscopy (SPMs).
⁎ Corresponding author. E-mail address: [email protected] (O. Shiman). 0022-3093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2012.02.013
However, studies on nano-chalcogenides are still at the beginning, and accordingly, overall features have not been discovered. In a present work we will study the nanostructures in Sb40Se60 thin films which are imaged and produced using scanning electron microscopy (SEM). 2. Experimental details Sb2Se3 thin film was prepared by thermal evaporation technique from bulk glass samples in vacuum 10 − 3 Pa onto glass substrates at room temperature. The substrate was equipped with pre-deposited Ni layer of 100 nm thickness. Film thickness was controlled during evaporation as it was shown in [5]. Thickness of prepared chalcogenide film was 100 nm. The composition and structure of the deposed layers have been analyzed using the INCA x-act detector and X-ray difractometer SmartLab Rigaku. For the tests presented here, dot patterns were exposed. Irradiation of the samples was performed by scanning electron microscope (SEM). The surface modification experiments were carried out under the following conditions: an accelerating voltage is 30 kV, electron beam (EB) current ranged between 180 and 800 pA, exposure time of 1, 5, 10, 30, 60, 150, 300, 450 and 600 s. A set of film treating/irradiation under the same conditions have been done. Study results presented here concern only extreme/polar values of the EB current (180 and 800 pA), because they are the most striking (and typical at the same time) for the entire series of experiments. EB current of 200 pA was considered to be a watershed: effect of EB current less than 200 pA causes the increasing of the thin film total thickness (high mound formation in the center of the irradiated spot); if the EB current exceeds 200 pA, the total thickness is decreased after the irradiation process.
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Fig. 1. An AFM image of the modified surface topography in 3D for the EB irradiated area in Sb40Se60 thin films. Exposition time (from the left to right) is 5 s, 1 min and 10 min, respectively; EB current is 800 pA.
Optical microscopy (confocal laser-scanning microscope Leica TCS-SPE) and scanning electron microscopy, SEM (TESCAN VEGA), were used to study the modification induced by e-beam irradiation of thin films. The topography of the structures drawn on the substrate was measured using Atomic Force Microscope (AFM) Veeco CP II in tapping mode.
Fig. 2. Dependence of surface deformation (width and depth) on exposure time and for a 100 nm thickness Sb2Se3 film. The depth is shown as dashed lines, whereas the spot size (width) is shown as solid lines.
The height was measured from the extrema of the deformations (either peak or trough bottom) to the common reference point (the unperturbed film surface) at the edge of the scan window; dimples were recorded as negative height (depth). 3. Results In the beginning of electron beam (EB) irradiation process, a dimple is formed at the EB irradiation point, and the shrinking volume increases radially and in-depth with increasing exposition time. As exposition time increases further, a cone is produced at the center of the dimple. The height of the cone increases with radiation time, as shown in Fig. 1. The dynamics of changes in depth and width of the patterns is shown in Fig. 2. With increasing an exposure time, depth and width (spot size) of the dimple increase regardless of beam parameters. Particularly rapid growth is observed for long exposure with 800 pA e-beam current. After 10 min exposure the dimple parameters reach their maximum value: 17 μm in width and 97 nm deep, whilst a total thickness of the chalcogenide layer is 100 nm. Such large size of the dimple probably indicates that a secondary process occurred in the sample around the irradiated spot and caused by indirect effects of EB irradiation. The electron beam current, together with exposition time t, was found to be a crucial variable in the formation of different types of profiles. The dynamics of modification of Sb2Se3 thin film during EB exposure is shown on Fig. 3. There are two types of profile obtained by irradiation: U- and W-type. The use of a low-current (180 pA)
Fig. 3. Height measurements of cross-sectional profiles of electron beam induced relief in Sb40Se60 thin film. EB current is 800 pA (a) and 180 pA (b).
O. Shiman et al. / Journal of Non-Crystalline Solids 358 (2012) 1153–1156
1155
Fig. 4. An AFM image of the modified surface topography in 3D for the e-beam irradiated area in Sb40Se60 thin films. Exposition time (from the left to right) is 5 s, 1 min and 10 min, respectively; EB current is 180 pA.
electron beam with t b 5 s or a higher current (more than 200 pA) electron beam with t b 60 s tended to produce U-type profile. The dimples width varies from 0.23 to 1.9 μm, depth from 1.9 to 31 nm. The maximum parameters were obtained at 800 pA current and t = 10 min; minimum at 180 pA current and t = 1 s. As mentioned above, the electron beam can produce a cone on the dimple bottom (W-type profile). The cone forming begins within 1 min high-current EB irradiation (current exceeds 200 pA); the cone height increases with exposure time, but it does not exceed the dimple depth (peak does not exceed the film surface), as it is shown in Figs. 1 and 3a. If the sample is irradiated by EB current less than 200 pA, the cone formation and growth begins much earlier (after 5 s exposure) and reached mound height considerably exceeds the dimple depth (Figs. 3b, 4, and 5): the cone rises up to 90 nm above thin film surface. It was observed that the decreasing of the thin film thickness occurs due to high-current EB irradiation; irraidation by EB of lower current (less then 200 pA) leads to increasing of the total thickness of the irradiated area (Fig. 5). The highest patterns and narrowest widths were found at EB current 180 pA, t = 10 min. 4. Discussions There are a number of hypotheses explaining the mechanism of electron beam induced surface modification. The electron beam represents a source of electronic subsystem excitation [6] (exciting electron–hole pairs), that leads to bond-weakening effect and consequently to athermal softening [3]. One can consider the electron beam as a source of electron injection into the material. Tanaka showed that injecting electrons
Fig. 5. Dependence of surface deformation height on exposure time for 180 and 800 pA EB current.
with energies on the order of several volts using a scanning tunneling microscope leads to expansions in the material and that surface modification is produced through electronically induced fluidity [1]. In any case, non-Coulomb interactions represent a pure extension. The results presented here give reason to assert, that initially the electron beam acts on the amorphous substance with low electroconductivity. As a result, a static electric field is produced in irradiated area; incident electrons make the region negatively charged and the Coulomb repulsive force is generated. Coulomb repulsion (electrostatic force) causes the material to move/flow away of the acting electron beam. Thus, the material moves from the center of the irradiated area to the periphery. That eventually leads to the dimple formation in the center and a small insignificant elevation around the irradiated spot. Similar results can be found in Hoffman et al. study of amorphous GeSe4 thin films [3]. Upon EB irradiation process crystalline phase is appeared in Sb-Se thin films [7,8]. Gaussian EB that is focused to a small spot spreads out rapidly as it propagates away from that spot. This implies that crystallized band appears at the centre and then expands radially. The sheet resistance difference of SbxSe100-x films before and after transformation (crystallization) is larger than 10 4 Ω per square [9,10]. Crystallization process leads to a catastrophic reduction of the Coulomb forces; the difference in pressure at dimple bottom and sides is formed. This difference in pressure results in a net force that tends to push a crystallized area upwards; the cone appeared and grew in the center of the dimple (W-type profile). Complete crystallization of the irradiated area ceases the proces. There are some remarks arising from recent research: during the irradiation process the volume does not remain constant (see the example in Fig. 3); the surface modification maximum is directed along the electron beam axis; local expansion increases along the line of the e-beam spot movement; the total invested energy in the case of electron irradiation (E = U·q, q = I·t) was 14 mJ for 800 pA EB current and 3 mJ for EB current of 180 pA. This difference reveals the importance of the direct energy conversion (possibly the number of generated charge carriers or simultaneously created defects) for the realization of structural transformations in such chalcogenide layers. The non-linearity of the e-beam stimulated modification on exposition at high power (current) densities can be attributed to the heating effects [11]. The increase in temperature would influence not only the rate of charge and defect generation, but also the viscosity. It would also increase exponentially the efficiency of mass transport, defect migration and structural changes which would then contribute to the volume changes. If the defects and appropriate localized charge carriers belong to different structural elements (chains and sheets) [12], the Coulomb interaction could also contribute to the volume change. It is possible only under the condition of decreased viscosity of the irradiated glass volume. We should note that the initial structure and composition can have very important and sometimes unpredictable influence [13] on the above discussed modification process. They can be the reasons of the discrepancies in the published results. Additional experiments on the influence of some metal sublayers on the stimulated modification in
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O. Shiman et al. / Journal of Non-Crystalline Solids 358 (2012) 1153–1156
thin film are under progress, that will help us verify the above explanation and clarify the process occuring in the thin films. 5. Conclusions Electron beam induced effect of surface modification has been observed in Sb2Se3 thin film. It has been shown that generated patterns depend on the electron beam current density and exposure time. The origin of surface deformation can be explained in terms of static electric field and enhanced fluidity and the mechanism is athermal in nature as a one-step process provides an effective and simple way to prepare micro- and nanostructures and various microscopic optoelectronic devices such as gratings, etc. Acknowledgements This work was supported by ESF (project “Atbalsts Daugavpils Universitātes doktora studiju īstenošanai,” Nr. 2009/0140/1DP/ 1.1.2.1.2/09/IPIA/VIAA/015). The authors thank the colleague from the Institute of Solid State Physics R.Grants, who have carried out skillful AFM experiments with patience. References [1] K. Tanaka, Nanostructured chalcogenide glasses, J. Non-Cryst. Solids 326–327 (Oct. 2003) 21–28.
[2] K. Tanaka, Electron beam induced reliefs in chalcogenide glasses, Appl. Phys. Lett. 70 (2) (Jan. 1997) 261. [3] G.B. Hoffman, W.-C. Liu, W. Zhou, R. Sooryakumar, P. Boolchand, R.M. Reano, Relief and trench formation on chalcogenide thin films using electron beams, J. Vac. Sci. Technol. B 26 (6) (2008) 2478. [4] R. Debnath, A. Fitzgerald, Electron beam induced surface modification of amorphous SbS chalcogenide films, Appl. Surf. Sci. 243 (1–4) (Apr. 2005) 148–150. [5] V. Gerbreders, J. Teteris, E. Sledevskis, A. Bulanovs, Photoinduced changes of optical reflectivity in As2S3 -Al system, J. Optoelectron. Adv. Mater. 9 (10) (2007) 3153–3156. [6] Arun Madan, Melvin P. Shaw, The Physics and Applications of Amorphous Semiconductors, Academic Press Inc, Boston, 1988, p. 545. [7] S. Elsayed, Electron beam and gamma irradiation effects on amorphous chalcogenide SbSe2.5 films, Nucl. Instrum. Methods Phys. Res. B 225 (4) (Oct. 2004) 535–543. [8] M. Kurumada, Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film, J. Cryst. Growth 250 (3–4) (Apr. 2003) 444–449. [9] M.J. Kang, et al., Electrical properties and crystallization behavior of Sb x Se100−x thin films, Microsyst. Technol. 13 (2) (May 2006) 153–159. [10] O. Shiman, V. Gerbreder, E. Sledevsky, A. Bulanov, Electric conductivity of Sb/Se thin film micro-scale structures, Latv. J. Phys. Tech. Sci. (1) (2011) [Online]. Available: http://versita.metapress.com/content/6888k50k14085u1m/fulltext.pdf [Accessed: 26-Aug-2011]. [11] V. Takáts, et al., Surface pattern recording in amorphous chalcogenide layers, J. Non-Cryst. Solids 355 (37–42) (Oct. 2009) 1849–1852. [12] K. Shimakawa, A. Ganjoo, J. Optoelectron. Adv. Mater. 3 (2) (2001) 167–176. [13] E. Vateva, Giant photo- and thermo-induced effects in chalcogenides, J. Optoelectron. Adv. Mater. 9 (10) (2007) 3108–3114.
Contents lists available at SciVerse ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol
Electron beam induced surface modification of amorphous Sb2Se3 thin film Oksana Shiman a,⁎, Vjaceslavs Gerbreders a, Eriks Sledevskis a, Valfrids Paskevics b a b
Innovative Microscopy Center, Daugavpils University, 1 Parades Str., Daugavpils LV-5400, Latvia Daugavpils University, 1 Parades Str., Daugavpils LV-5400, Latvia
a r t i c l e
i n f o
Article history: Received 12 December 2011 Received in revised form 6 February 2012 Available online 3 March 2012 Keywords: Amorphous and crystalline phases; Electron beam irradiation; Atomic force microscopy
a b s t r a c t The change in the surface morphology of amorphous Sb2Se3 thin films during the electron beam irradiation has been studied mainly by atomic force microscopy (AFM). Electron beam at accelerating voltages 30 kV is focused onto the surface of the specimens of 100-μm thickness, and then the surface morphology of each specimen has been observed by AFM in air. The modification of the film surface includes lateral and vertical resizing which is typically in the micrometer and sub-micrometer range. Protrusions above the surface as high as 90 nm are observed at 180 pA electron beam current, whilst trenches as deep as 97 nm are observed at 800 pA electron beam current (total thickness of thin film is 100 nm). The dependence of patterns characteristics on irradiation parameters such as exposure time and beam current has also been studied. Physical mechanisms for trench and mound formation are proposed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Nanostructure formation has been explored for many kinds of materials, and this becomes an interesting topic also for glasses with two features [1]. As is known, in single crystalline materials, one can prepare atomically flat surfaces, in which atoms can be controlled one by one. However, in amorphous materials such atomic manipulation is meaningless, since the amorphous structure is disordered at the atomic level. One of the features is that the control of nanometerscale structures could be an ultimate research subject for glassy structures. The other is that the amorphous nanostructure may yield a greater variety than the crystalline, since the bonding constraint arising from crystalline unit cells does not exist. Micro/nanostructures can be fabricated using various methods such as photolithography, femtosecond laser processing, focused ion beam and LIGA (LIthography, Electroplating and Molding) processes, etc. However, these processes are complicated, very time-consuming and expensive. When irradiating a chalcogenide surface with electron beam, micro/nanostructures can be formed in a simple one-step process. This class of material exhibits a number of structural changes when exposed to electron beams, for example, surface deformations in bulk and thin films of As2S3 [2], relief and trench formation in GeSe4 chalcogenide thin film [3], and surface modification (expansion) in Sb2S3 thin films [4] when exposed to electron beams. In his work Tanaka [1] inspected and modified the surface of chalcogenide glasses with nanometer resolution using scanning probe microscopy (SPMs).
⁎ Corresponding author. E-mail address: [email protected] (O. Shiman). 0022-3093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2012.02.013
However, studies on nano-chalcogenides are still at the beginning, and accordingly, overall features have not been discovered. In a present work we will study the nanostructures in Sb40Se60 thin films which are imaged and produced using scanning electron microscopy (SEM). 2. Experimental details Sb2Se3 thin film was prepared by thermal evaporation technique from bulk glass samples in vacuum 10 − 3 Pa onto glass substrates at room temperature. The substrate was equipped with pre-deposited Ni layer of 100 nm thickness. Film thickness was controlled during evaporation as it was shown in [5]. Thickness of prepared chalcogenide film was 100 nm. The composition and structure of the deposed layers have been analyzed using the INCA x-act detector and X-ray difractometer SmartLab Rigaku. For the tests presented here, dot patterns were exposed. Irradiation of the samples was performed by scanning electron microscope (SEM). The surface modification experiments were carried out under the following conditions: an accelerating voltage is 30 kV, electron beam (EB) current ranged between 180 and 800 pA, exposure time of 1, 5, 10, 30, 60, 150, 300, 450 and 600 s. A set of film treating/irradiation under the same conditions have been done. Study results presented here concern only extreme/polar values of the EB current (180 and 800 pA), because they are the most striking (and typical at the same time) for the entire series of experiments. EB current of 200 pA was considered to be a watershed: effect of EB current less than 200 pA causes the increasing of the thin film total thickness (high mound formation in the center of the irradiated spot); if the EB current exceeds 200 pA, the total thickness is decreased after the irradiation process.
1154
O. Shiman et al. / Journal of Non-Crystalline Solids 358 (2012) 1153–1156
Fig. 1. An AFM image of the modified surface topography in 3D for the EB irradiated area in Sb40Se60 thin films. Exposition time (from the left to right) is 5 s, 1 min and 10 min, respectively; EB current is 800 pA.
Optical microscopy (confocal laser-scanning microscope Leica TCS-SPE) and scanning electron microscopy, SEM (TESCAN VEGA), were used to study the modification induced by e-beam irradiation of thin films. The topography of the structures drawn on the substrate was measured using Atomic Force Microscope (AFM) Veeco CP II in tapping mode.
Fig. 2. Dependence of surface deformation (width and depth) on exposure time and for a 100 nm thickness Sb2Se3 film. The depth is shown as dashed lines, whereas the spot size (width) is shown as solid lines.
The height was measured from the extrema of the deformations (either peak or trough bottom) to the common reference point (the unperturbed film surface) at the edge of the scan window; dimples were recorded as negative height (depth). 3. Results In the beginning of electron beam (EB) irradiation process, a dimple is formed at the EB irradiation point, and the shrinking volume increases radially and in-depth with increasing exposition time. As exposition time increases further, a cone is produced at the center of the dimple. The height of the cone increases with radiation time, as shown in Fig. 1. The dynamics of changes in depth and width of the patterns is shown in Fig. 2. With increasing an exposure time, depth and width (spot size) of the dimple increase regardless of beam parameters. Particularly rapid growth is observed for long exposure with 800 pA e-beam current. After 10 min exposure the dimple parameters reach their maximum value: 17 μm in width and 97 nm deep, whilst a total thickness of the chalcogenide layer is 100 nm. Such large size of the dimple probably indicates that a secondary process occurred in the sample around the irradiated spot and caused by indirect effects of EB irradiation. The electron beam current, together with exposition time t, was found to be a crucial variable in the formation of different types of profiles. The dynamics of modification of Sb2Se3 thin film during EB exposure is shown on Fig. 3. There are two types of profile obtained by irradiation: U- and W-type. The use of a low-current (180 pA)
Fig. 3. Height measurements of cross-sectional profiles of electron beam induced relief in Sb40Se60 thin film. EB current is 800 pA (a) and 180 pA (b).
O. Shiman et al. / Journal of Non-Crystalline Solids 358 (2012) 1153–1156
1155
Fig. 4. An AFM image of the modified surface topography in 3D for the e-beam irradiated area in Sb40Se60 thin films. Exposition time (from the left to right) is 5 s, 1 min and 10 min, respectively; EB current is 180 pA.
electron beam with t b 5 s or a higher current (more than 200 pA) electron beam with t b 60 s tended to produce U-type profile. The dimples width varies from 0.23 to 1.9 μm, depth from 1.9 to 31 nm. The maximum parameters were obtained at 800 pA current and t = 10 min; minimum at 180 pA current and t = 1 s. As mentioned above, the electron beam can produce a cone on the dimple bottom (W-type profile). The cone forming begins within 1 min high-current EB irradiation (current exceeds 200 pA); the cone height increases with exposure time, but it does not exceed the dimple depth (peak does not exceed the film surface), as it is shown in Figs. 1 and 3a. If the sample is irradiated by EB current less than 200 pA, the cone formation and growth begins much earlier (after 5 s exposure) and reached mound height considerably exceeds the dimple depth (Figs. 3b, 4, and 5): the cone rises up to 90 nm above thin film surface. It was observed that the decreasing of the thin film thickness occurs due to high-current EB irradiation; irraidation by EB of lower current (less then 200 pA) leads to increasing of the total thickness of the irradiated area (Fig. 5). The highest patterns and narrowest widths were found at EB current 180 pA, t = 10 min. 4. Discussions There are a number of hypotheses explaining the mechanism of electron beam induced surface modification. The electron beam represents a source of electronic subsystem excitation [6] (exciting electron–hole pairs), that leads to bond-weakening effect and consequently to athermal softening [3]. One can consider the electron beam as a source of electron injection into the material. Tanaka showed that injecting electrons
Fig. 5. Dependence of surface deformation height on exposure time for 180 and 800 pA EB current.
with energies on the order of several volts using a scanning tunneling microscope leads to expansions in the material and that surface modification is produced through electronically induced fluidity [1]. In any case, non-Coulomb interactions represent a pure extension. The results presented here give reason to assert, that initially the electron beam acts on the amorphous substance with low electroconductivity. As a result, a static electric field is produced in irradiated area; incident electrons make the region negatively charged and the Coulomb repulsive force is generated. Coulomb repulsion (electrostatic force) causes the material to move/flow away of the acting electron beam. Thus, the material moves from the center of the irradiated area to the periphery. That eventually leads to the dimple formation in the center and a small insignificant elevation around the irradiated spot. Similar results can be found in Hoffman et al. study of amorphous GeSe4 thin films [3]. Upon EB irradiation process crystalline phase is appeared in Sb-Se thin films [7,8]. Gaussian EB that is focused to a small spot spreads out rapidly as it propagates away from that spot. This implies that crystallized band appears at the centre and then expands radially. The sheet resistance difference of SbxSe100-x films before and after transformation (crystallization) is larger than 10 4 Ω per square [9,10]. Crystallization process leads to a catastrophic reduction of the Coulomb forces; the difference in pressure at dimple bottom and sides is formed. This difference in pressure results in a net force that tends to push a crystallized area upwards; the cone appeared and grew in the center of the dimple (W-type profile). Complete crystallization of the irradiated area ceases the proces. There are some remarks arising from recent research: during the irradiation process the volume does not remain constant (see the example in Fig. 3); the surface modification maximum is directed along the electron beam axis; local expansion increases along the line of the e-beam spot movement; the total invested energy in the case of electron irradiation (E = U·q, q = I·t) was 14 mJ for 800 pA EB current and 3 mJ for EB current of 180 pA. This difference reveals the importance of the direct energy conversion (possibly the number of generated charge carriers or simultaneously created defects) for the realization of structural transformations in such chalcogenide layers. The non-linearity of the e-beam stimulated modification on exposition at high power (current) densities can be attributed to the heating effects [11]. The increase in temperature would influence not only the rate of charge and defect generation, but also the viscosity. It would also increase exponentially the efficiency of mass transport, defect migration and structural changes which would then contribute to the volume changes. If the defects and appropriate localized charge carriers belong to different structural elements (chains and sheets) [12], the Coulomb interaction could also contribute to the volume change. It is possible only under the condition of decreased viscosity of the irradiated glass volume. We should note that the initial structure and composition can have very important and sometimes unpredictable influence [13] on the above discussed modification process. They can be the reasons of the discrepancies in the published results. Additional experiments on the influence of some metal sublayers on the stimulated modification in
1156
O. Shiman et al. / Journal of Non-Crystalline Solids 358 (2012) 1153–1156
thin film are under progress, that will help us verify the above explanation and clarify the process occuring in the thin films. 5. Conclusions Electron beam induced effect of surface modification has been observed in Sb2Se3 thin film. It has been shown that generated patterns depend on the electron beam current density and exposure time. The origin of surface deformation can be explained in terms of static electric field and enhanced fluidity and the mechanism is athermal in nature as a one-step process provides an effective and simple way to prepare micro- and nanostructures and various microscopic optoelectronic devices such as gratings, etc. Acknowledgements This work was supported by ESF (project “Atbalsts Daugavpils Universitātes doktora studiju īstenošanai,” Nr. 2009/0140/1DP/ 1.1.2.1.2/09/IPIA/VIAA/015). The authors thank the colleague from the Institute of Solid State Physics R.Grants, who have carried out skillful AFM experiments with patience. References [1] K. Tanaka, Nanostructured chalcogenide glasses, J. Non-Cryst. Solids 326–327 (Oct. 2003) 21–28.
[2] K. Tanaka, Electron beam induced reliefs in chalcogenide glasses, Appl. Phys. Lett. 70 (2) (Jan. 1997) 261. [3] G.B. Hoffman, W.-C. Liu, W. Zhou, R. Sooryakumar, P. Boolchand, R.M. Reano, Relief and trench formation on chalcogenide thin films using electron beams, J. Vac. Sci. Technol. B 26 (6) (2008) 2478. [4] R. Debnath, A. Fitzgerald, Electron beam induced surface modification of amorphous SbS chalcogenide films, Appl. Surf. Sci. 243 (1–4) (Apr. 2005) 148–150. [5] V. Gerbreders, J. Teteris, E. Sledevskis, A. Bulanovs, Photoinduced changes of optical reflectivity in As2S3 -Al system, J. Optoelectron. Adv. Mater. 9 (10) (2007) 3153–3156. [6] Arun Madan, Melvin P. Shaw, The Physics and Applications of Amorphous Semiconductors, Academic Press Inc, Boston, 1988, p. 545. [7] S. Elsayed, Electron beam and gamma irradiation effects on amorphous chalcogenide SbSe2.5 films, Nucl. Instrum. Methods Phys. Res. B 225 (4) (Oct. 2004) 535–543. [8] M. Kurumada, Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film, J. Cryst. Growth 250 (3–4) (Apr. 2003) 444–449. [9] M.J. Kang, et al., Electrical properties and crystallization behavior of Sb x Se100−x thin films, Microsyst. Technol. 13 (2) (May 2006) 153–159. [10] O. Shiman, V. Gerbreder, E. Sledevsky, A. Bulanov, Electric conductivity of Sb/Se thin film micro-scale structures, Latv. J. Phys. Tech. Sci. (1) (2011) [Online]. Available: http://versita.metapress.com/content/6888k50k14085u1m/fulltext.pdf [Accessed: 26-Aug-2011]. [11] V. Takáts, et al., Surface pattern recording in amorphous chalcogenide layers, J. Non-Cryst. Solids 355 (37–42) (Oct. 2009) 1849–1852. [12] K. Shimakawa, A. Ganjoo, J. Optoelectron. Adv. Mater. 3 (2) (2001) 167–176. [13] E. Vateva, Giant photo- and thermo-induced effects in chalcogenides, J. Optoelectron. Adv. Mater. 9 (10) (2007) 3108–3114.