- Email: [email protected]
The synthesis by successive ionic layer deposition of SnMo0.6Oy·nH2O nanolayers on silica
Thin Solid Films 440 (2003) 74–77
The synthesis by successive ionic layer deposition of SnMo0.6OyØnH2O nanolayers on silica L.B. Gulina, V.P. Tolstoy* St.-Petersburg State University, Department of Chemistry, University St.26, St.Peterhof, St.Petersburg 198504, Russia Received 11 February 2003; received in revised form 15 April 2003; accepted 25 April 2003
Abstract The conditions for the layer-by-layer synthesis by the method of the successive ionic layer deposition of Sn(IV)Mo(VI,V)0.6OyØnH2O nanolayers on a silica surface were determined for the first time. The nanolayer thickness was controlled by the number of successive cycles. The composition and structure of these films were determined using Fourier transform infrared and UVyVis transmission spectroscopy, X-ray photoelectron spectroscopy, X-ray difraction, and electron microprobe. It was found that under heating up to 200 8C, molecular water and hydroxyl groups are removed from the nanolayers, the bonds Mo–O–Mo and Sn–O–Mo are formed, and Mo(V) is oxidized to Mo(VI). 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Tin oxide; Molybdenum oxide; Deposition process; X-ray photoelectron spectroscopy
1. Introduction Layers of tin and molybdenum oxides are famed for their unique combination of electrophysical and optical properties, which has found practical use, e.g. in the construction of electrochromic displays, electrochemical cells, resistive heaters which are transparent in the visible spectral range and gaseous sensors. The aim of the present work is to determine conditions for the successive ionic layer deposition (SILD) of Sn–Mo–O-containing layers and to do their analysis. The SILD method is based on multiple and alternate treatment of support with ionic solutions. One SILD cycle consists of conditioning the support with a solution of a cation-containing salt, washing, conditioning with a solution of an anion-containing salt, and washing again. The conditions for each elementary procedure are selected so that one cycle produces on the support, a nanolayer of a hard-to-dissolve compound. As shown w1–5x, an important advantage of the SILD method is the possibility to prescribe the thickness of the resulting layer with an accuracy in the order of fractions and units of nanometer. This special feature is the key to synthesize oxide multilayers containing two or more *Corresponding author. Fax: q7-812-428-57-12. E-mail address: [email protected] (V.P. Tolstoy).
oxides of different composition. It is evident that varying the thickness and composition of each elementary layer, can change physical properties of the complex multilayer. The conditions of synthesis by the SILD method of one of such a complex multilayer is reported in the present article. 2. Experimental As supports, fused quartz (Russian mark KU) and single crystals Si (001) (Russian mark KEF-7.5), polished to 14 class, were used. The choice of these materials for supports was determined by the fact that their surface chemistry is now better understood. To conduct the layer synthesis, such a support was pretreated in order to uniformly silanolize its surface. Furthermore, quartz and silicon supports are convenient for characterizing the deposited layers spectroscopically. Namely, layers on quartz can be probed by the spectrophotometry in the UVyVis spectral range, while layers on silicon can be studied using Fourier transform infrared (FT-IR) spectroscopy, X-Ray difraction (XRD), ellipsometry, and X-ray photoelectron spectroscopy (XPS). After polishing, the quartz supports were washed with acetone, and conditioned for 10 min with a solution of
0040-6090/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090Ž03.00684-9
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
concentrated nitric acid at 90–100 8C. Afterward, the supports were washed with distilled water, a solution of KOH (pH 9), and again with water. To obtain a silicon oxide layer on the surface and remove organic contamination, silicon is heated at 750 8C for 1 h. To hydroxylize this layer, the supports were conditioned for 0.5 h in double distilled water at 90–100 8C. For the SILD of the Sn–Mo–O-containing layers, a reaction scheme analogous to that used to synthesize MnO2 layers w5x was used. Namely, the layer was formed on the surface as a result of a succession of redox reactions between the adsorbed cation in the lowest oxidation degree (in the present case, Sn2q) and the adsorbed anion in the highest oxidation degree (molibdate-ions containing Mo6q). The reagents were aqueous solutions of SnCl2, (NH4)2MoO4Ø or (NH4)6Mo7O24Ø4H2O. To determine reproducible conditions for the synthesis, we varied the salts concentration, pH of the reagents and washing solutions and the time of treatments. As known, reduction of Mo6q to Mo5q in molibdate–ion is only possible in acidic media. y3 Under these conditions (pH 3.0–5.5 and Cy ), MoO4)10 molibdate solutions, composed mainly from heptomolibdate–ions Mo7O6y and their protonated forms 24 4y 3y w6x. This HMo7O5y , H Mo O and H3Mo7O24 24 2 7 24 explains that similar results were obtained by the use of (NH4)2MoO4Ø or (NH4)6Mo7O24Ø4H2 O as reagents. It was experimentally found that the optimum conditions are: C(NH4)2MoO4s0.1 M, CSnCl2s0.01 M, pHSnCl2s2, and pH(NH4)2MoO4s3. The pH was regulated using a solution of HCl. The synthesis technique for the SnMoxOyØnH2O was as follows: After the standard pretreatment, the supports were fixed in the holders of an automated set-up controlled by a computer. This set-up dips the support into a solution of tin chloride, distilled water, a solution of ammonium molybdate, again in distilled water, and so on. The time of treatment for each reagent was 30 s. One cycle produced one nanolayer. To study the nanolayers, obtained FT-IR and UVyVis transmission spectroscopy, ellipsometry, XRD, electron microprobe and XPS were used. The FT-IR spectra were obtained with a FT-IR spectrometer Perkin-Elmer 1760X equipped with a DTGS detector. The spectra are averages of 20–50 scans at a resolution of 4 cmy1. The UVyVis spectra were measured with a Lambda-9 spectrophotometer (Perkin-Elmer) at a scanning rate of 50 nmymin and slit program of 2 nm. The electron microprobe analysis was performed at a scanning electron microscope ‘Camscan-4’ coupled with a semiconductor spectrometer of characteristic X-ray radiation AN10000. The data are processed using a program ZAF 4– FLS. Ellipsometry was performed using a home-made ellipsometer at ls632.8 nm and the angle of incidence of 458. Before the ellipsometry, the samples had been dried in air for 2 h. The layer thickness was determined
75
Fig. 1. Transmission spectra of SnMoxOy nH2O nanolayers, synthesized on a fused quartz surface. The number of the SILD cycles: (1) NSILDs15 (2) NSILDs30 and (3) the sample (1) after heating 0.5 h in air at 200 8C.
as the average of the results of 5–6 measurements at the sample surface. The XPS analysis was conducted with a Perkin-Elmer 5400 spectrometer, operated with unmonochromatized Mg Ka irradiation standard resolution 0.8 eV. The reported ratios of concentrations of elements in the layers under study are the average for three samples. XRD was measured using a DRON-3.0 X-ray diffractometer with Cu Ka irradiation. 3. Results and discussion Absorbance spectra of the SnMoxOyØnH2O nanolayers on quartz, obtained by 15 and 30 cycles of the SILD are reported in Fig. 1. It is seen that absorbance between 300–850 nm region is higher for increasing thicker layer, which testifies that the layer thickness increases with increasing number of cycles. According to the ellipsometry measurements, the thickness of a layer deposited in 15 cycles was 9.5 nm, while after 30 cycles the thickness was 18.9 nm, which corresponds to the average increase of the thickness per cycle of 0.63 nm. The observed linear increase in the layer thickness with increasing number of the SILD cycles implies that the thickness of the final layer can accurately be regulated by the synthesis procedure. In our opinion, this result is very important, since it opens a way to synthesize multilayers of a more complex in-depth composition and thereby specifically regulate their surface properties. The UVyVis spectrum also allows determination of the layer composition. The intensive band at 400–200 nm can be assigned to Mo(VI) and Sn(IV) oxides, while the band at 740 nm is consistent with Mo(V) oxide w7x. As follows from the XPS spectrum (Fig. 2), apart from ions Mo6q (experimental BE of the 3d5y2 electrons is 232.9 eV), the film contains Sn4q ions which are characterized by a peak at 487.3 eV w8x. It is y important that the counter ions NHq 4 and Cl , which could be introduced in the film structure from the
76
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
structure of the reduced molibdate. The other bands observed near 600 cmy1 in this spectrum and in spectra 2 and 3 (Fig. 3) appear to arise due to incomplete compensation of the most intensive band of the oxygen impurity in Si, and thus, may be disregarded. The bands in the high-wavenumber region of spectrum 3 are due to a low signal-to-noise ratio that results from the atmosphere absorption. After the thermal heating in air at 200 8C for 0.5 h (Fig. 1, sample 3), the optical spectra demonstrate disappearance of the band at 740 nm and a shift of the absorption edge from 300 to 350 nm, which can be associated with Sn2q, incorporated in the Sn(IV) oxide. It can be suggested that under the conditions mentioned below, the redox reaction takes place. 2Mo5qqSn4q™2Mo6qqSn2q However, partial oxidation of Mo5q ions by the air oxygen cannot be excluded. The FTIR spectra (Fig. 3) also testify that the composition and structure of the synthesized oxide layer change. After heating at 100 8C, the intensities of the band at 3300, 1640, 1440 and 960 cmy1 decreases, while a broad absorption band appears at 850–600 cmy1. Heating at 200 8C results in further decrease of the bands at 3200, 1640 and 1440 cmy1, and appearance of intensive bands with the maxima at 1075 and 790 cmy1. This spectrum behavior shows that molecular water and hydroxy-groups are removed from the oxide nanolayer, while the Mo_ O bond in its structure is replaced by the Mo–O–Mo and Mo–O–Sn bonds. However, as follows from the XRD data, this Fig. 2. XPS spectrum of the SnMoxOyØnH2O nanolayer obtained on a surface of crystalline silicon by 30 SILD cycles: (a) survey spectrum; (b) the Mo region, and (c) the Sn region.
solutions were not detected by XPS. Unfortunately, XPS did not allow for indentification of Mo5q, if any, due to the overlapping of the signals originated from Mo6q and Mo5q. It might be caused by a low concentration of Mo5q ions with respect to that of Mo6q ions. The electron microprobe gave the SnyMo atomic ratio to be 1.67. The FT-IR spectra (Fig. 3) showed that the film under study contains molecular water (the bands at 3300 and 1640 cmy1) and hydroxyls (1440 cmy1), probably forming the Sn–OH and Mo–OH bonds with the film metals. However, due to the absence of standards, unambiguous interpretation of the 1440 cmy1 band is impossible. In addition, the FT-IR spectra exhibit the bands at 960, 876 and 710 assigned to stretching vibrations of Me–O groups in the MosO, MoyOy Mo and MoyOySn w9,10x units, and the absorption band at 540 cmy1 can be assigned to the Sn–O–Sn bond w11x, which implies that tin is included into the
Fig. 3. FT-IR transmission spectra of the initial SnMoxOyØnH2O nanolayer deposited on a surface of crystalline silicon by 25 SILD cycles and heated (1) at 100 8C (2) at 200 8C and (3) for 0.5 h.
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
treatment does not convert the initial amorphous oxide structure into the crystalline one. 4. Conclusions For the first time, the conditions for the SILD of the Sn(IV)Mo(VI,V)0.6 Oy ØnH2 O layers on a silica surface were determined. The layer thickness was controlled with the accuracy up to fractions of nanolayer by the number of the SILD cycles. The spectroscopic analysis of the layers revealed that under heating up to 200 8C, molecular water and hydroxyl groups are removed from the nanolayers, the bonds Mo–O–Mo and Sn–O–Mo are formed, and Mo(V) is oxidized to Mo(VI).
References w1 x w2 x w3 x w4 x w5 x w6 x w7 x w8 x w9 x w10x
Acknowledgments The work was supported by grant No 1-03-32427 from Russian Foundation for Basic Research (RFBR).
77
w11x
V.P. Tolstoy, Russ. Chem. Rev. 3 (1993) 267. V.P. Tolstoy, Thin Solid Films 307 (1997) 10. V.P. Tolstoy, A.G. Ehrlich, Thin Solid Films 307 (1997) 60. V.P. Tolstoy, Russ. J. Inorg. Chem. 38 (7) (1993) 1063. V.P. Tolstoy, I.V. Murin, A. Reller, Appl. Surf. Sci. 112 (1997) 255. M.T. Pope, Heteropoly and Isopoly Oxometalates, SpringerVerlag, Berlin–Heidelberg–New York–Tokyo, 1983. E.A. Nikitina, Heteropolycompounds, Goschimisdat, Moscow, 1962, (Russ.). J.F. Moulder, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Co., Physical Electronics Division, USA, 1995. E.N. Iurchenko, Methods of molecular spectroscopy in inorganic chemistry (Russ.), Novosibirsk, Nauka, 1986. G.M. Maksimov, G.N. Kustova, K.I. Matveev, T.P. Lasarenko, Koordinazionnaja Chimia 15 (6) (1999) 788, (Chemistry of Complex Compounds) (Russ.). J.P. Espinos, A. Fernandez, V.M. Jimenez, A.R. GonzalezElipe, A. Caballero, M. Ocana, Solid State Jonics 116 (1999) 117.
The synthesis by successive ionic layer deposition of SnMo0.6OyØnH2O nanolayers on silica L.B. Gulina, V.P. Tolstoy* St.-Petersburg State University, Department of Chemistry, University St.26, St.Peterhof, St.Petersburg 198504, Russia Received 11 February 2003; received in revised form 15 April 2003; accepted 25 April 2003
Abstract The conditions for the layer-by-layer synthesis by the method of the successive ionic layer deposition of Sn(IV)Mo(VI,V)0.6OyØnH2O nanolayers on a silica surface were determined for the first time. The nanolayer thickness was controlled by the number of successive cycles. The composition and structure of these films were determined using Fourier transform infrared and UVyVis transmission spectroscopy, X-ray photoelectron spectroscopy, X-ray difraction, and electron microprobe. It was found that under heating up to 200 8C, molecular water and hydroxyl groups are removed from the nanolayers, the bonds Mo–O–Mo and Sn–O–Mo are formed, and Mo(V) is oxidized to Mo(VI). 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Tin oxide; Molybdenum oxide; Deposition process; X-ray photoelectron spectroscopy
1. Introduction Layers of tin and molybdenum oxides are famed for their unique combination of electrophysical and optical properties, which has found practical use, e.g. in the construction of electrochromic displays, electrochemical cells, resistive heaters which are transparent in the visible spectral range and gaseous sensors. The aim of the present work is to determine conditions for the successive ionic layer deposition (SILD) of Sn–Mo–O-containing layers and to do their analysis. The SILD method is based on multiple and alternate treatment of support with ionic solutions. One SILD cycle consists of conditioning the support with a solution of a cation-containing salt, washing, conditioning with a solution of an anion-containing salt, and washing again. The conditions for each elementary procedure are selected so that one cycle produces on the support, a nanolayer of a hard-to-dissolve compound. As shown w1–5x, an important advantage of the SILD method is the possibility to prescribe the thickness of the resulting layer with an accuracy in the order of fractions and units of nanometer. This special feature is the key to synthesize oxide multilayers containing two or more *Corresponding author. Fax: q7-812-428-57-12. E-mail address: [email protected] (V.P. Tolstoy).
oxides of different composition. It is evident that varying the thickness and composition of each elementary layer, can change physical properties of the complex multilayer. The conditions of synthesis by the SILD method of one of such a complex multilayer is reported in the present article. 2. Experimental As supports, fused quartz (Russian mark KU) and single crystals Si (001) (Russian mark KEF-7.5), polished to 14 class, were used. The choice of these materials for supports was determined by the fact that their surface chemistry is now better understood. To conduct the layer synthesis, such a support was pretreated in order to uniformly silanolize its surface. Furthermore, quartz and silicon supports are convenient for characterizing the deposited layers spectroscopically. Namely, layers on quartz can be probed by the spectrophotometry in the UVyVis spectral range, while layers on silicon can be studied using Fourier transform infrared (FT-IR) spectroscopy, X-Ray difraction (XRD), ellipsometry, and X-ray photoelectron spectroscopy (XPS). After polishing, the quartz supports were washed with acetone, and conditioned for 10 min with a solution of
0040-6090/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090Ž03.00684-9
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
concentrated nitric acid at 90–100 8C. Afterward, the supports were washed with distilled water, a solution of KOH (pH 9), and again with water. To obtain a silicon oxide layer on the surface and remove organic contamination, silicon is heated at 750 8C for 1 h. To hydroxylize this layer, the supports were conditioned for 0.5 h in double distilled water at 90–100 8C. For the SILD of the Sn–Mo–O-containing layers, a reaction scheme analogous to that used to synthesize MnO2 layers w5x was used. Namely, the layer was formed on the surface as a result of a succession of redox reactions between the adsorbed cation in the lowest oxidation degree (in the present case, Sn2q) and the adsorbed anion in the highest oxidation degree (molibdate-ions containing Mo6q). The reagents were aqueous solutions of SnCl2, (NH4)2MoO4Ø or (NH4)6Mo7O24Ø4H2O. To determine reproducible conditions for the synthesis, we varied the salts concentration, pH of the reagents and washing solutions and the time of treatments. As known, reduction of Mo6q to Mo5q in molibdate–ion is only possible in acidic media. y3 Under these conditions (pH 3.0–5.5 and Cy ), MoO4)10 molibdate solutions, composed mainly from heptomolibdate–ions Mo7O6y and their protonated forms 24 4y 3y w6x. This HMo7O5y , H Mo O and H3Mo7O24 24 2 7 24 explains that similar results were obtained by the use of (NH4)2MoO4Ø or (NH4)6Mo7O24Ø4H2 O as reagents. It was experimentally found that the optimum conditions are: C(NH4)2MoO4s0.1 M, CSnCl2s0.01 M, pHSnCl2s2, and pH(NH4)2MoO4s3. The pH was regulated using a solution of HCl. The synthesis technique for the SnMoxOyØnH2O was as follows: After the standard pretreatment, the supports were fixed in the holders of an automated set-up controlled by a computer. This set-up dips the support into a solution of tin chloride, distilled water, a solution of ammonium molybdate, again in distilled water, and so on. The time of treatment for each reagent was 30 s. One cycle produced one nanolayer. To study the nanolayers, obtained FT-IR and UVyVis transmission spectroscopy, ellipsometry, XRD, electron microprobe and XPS were used. The FT-IR spectra were obtained with a FT-IR spectrometer Perkin-Elmer 1760X equipped with a DTGS detector. The spectra are averages of 20–50 scans at a resolution of 4 cmy1. The UVyVis spectra were measured with a Lambda-9 spectrophotometer (Perkin-Elmer) at a scanning rate of 50 nmymin and slit program of 2 nm. The electron microprobe analysis was performed at a scanning electron microscope ‘Camscan-4’ coupled with a semiconductor spectrometer of characteristic X-ray radiation AN10000. The data are processed using a program ZAF 4– FLS. Ellipsometry was performed using a home-made ellipsometer at ls632.8 nm and the angle of incidence of 458. Before the ellipsometry, the samples had been dried in air for 2 h. The layer thickness was determined
75
Fig. 1. Transmission spectra of SnMoxOy nH2O nanolayers, synthesized on a fused quartz surface. The number of the SILD cycles: (1) NSILDs15 (2) NSILDs30 and (3) the sample (1) after heating 0.5 h in air at 200 8C.
as the average of the results of 5–6 measurements at the sample surface. The XPS analysis was conducted with a Perkin-Elmer 5400 spectrometer, operated with unmonochromatized Mg Ka irradiation standard resolution 0.8 eV. The reported ratios of concentrations of elements in the layers under study are the average for three samples. XRD was measured using a DRON-3.0 X-ray diffractometer with Cu Ka irradiation. 3. Results and discussion Absorbance spectra of the SnMoxOyØnH2O nanolayers on quartz, obtained by 15 and 30 cycles of the SILD are reported in Fig. 1. It is seen that absorbance between 300–850 nm region is higher for increasing thicker layer, which testifies that the layer thickness increases with increasing number of cycles. According to the ellipsometry measurements, the thickness of a layer deposited in 15 cycles was 9.5 nm, while after 30 cycles the thickness was 18.9 nm, which corresponds to the average increase of the thickness per cycle of 0.63 nm. The observed linear increase in the layer thickness with increasing number of the SILD cycles implies that the thickness of the final layer can accurately be regulated by the synthesis procedure. In our opinion, this result is very important, since it opens a way to synthesize multilayers of a more complex in-depth composition and thereby specifically regulate their surface properties. The UVyVis spectrum also allows determination of the layer composition. The intensive band at 400–200 nm can be assigned to Mo(VI) and Sn(IV) oxides, while the band at 740 nm is consistent with Mo(V) oxide w7x. As follows from the XPS spectrum (Fig. 2), apart from ions Mo6q (experimental BE of the 3d5y2 electrons is 232.9 eV), the film contains Sn4q ions which are characterized by a peak at 487.3 eV w8x. It is y important that the counter ions NHq 4 and Cl , which could be introduced in the film structure from the
76
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
structure of the reduced molibdate. The other bands observed near 600 cmy1 in this spectrum and in spectra 2 and 3 (Fig. 3) appear to arise due to incomplete compensation of the most intensive band of the oxygen impurity in Si, and thus, may be disregarded. The bands in the high-wavenumber region of spectrum 3 are due to a low signal-to-noise ratio that results from the atmosphere absorption. After the thermal heating in air at 200 8C for 0.5 h (Fig. 1, sample 3), the optical spectra demonstrate disappearance of the band at 740 nm and a shift of the absorption edge from 300 to 350 nm, which can be associated with Sn2q, incorporated in the Sn(IV) oxide. It can be suggested that under the conditions mentioned below, the redox reaction takes place. 2Mo5qqSn4q™2Mo6qqSn2q However, partial oxidation of Mo5q ions by the air oxygen cannot be excluded. The FTIR spectra (Fig. 3) also testify that the composition and structure of the synthesized oxide layer change. After heating at 100 8C, the intensities of the band at 3300, 1640, 1440 and 960 cmy1 decreases, while a broad absorption band appears at 850–600 cmy1. Heating at 200 8C results in further decrease of the bands at 3200, 1640 and 1440 cmy1, and appearance of intensive bands with the maxima at 1075 and 790 cmy1. This spectrum behavior shows that molecular water and hydroxy-groups are removed from the oxide nanolayer, while the Mo_ O bond in its structure is replaced by the Mo–O–Mo and Mo–O–Sn bonds. However, as follows from the XRD data, this Fig. 2. XPS spectrum of the SnMoxOyØnH2O nanolayer obtained on a surface of crystalline silicon by 30 SILD cycles: (a) survey spectrum; (b) the Mo region, and (c) the Sn region.
solutions were not detected by XPS. Unfortunately, XPS did not allow for indentification of Mo5q, if any, due to the overlapping of the signals originated from Mo6q and Mo5q. It might be caused by a low concentration of Mo5q ions with respect to that of Mo6q ions. The electron microprobe gave the SnyMo atomic ratio to be 1.67. The FT-IR spectra (Fig. 3) showed that the film under study contains molecular water (the bands at 3300 and 1640 cmy1) and hydroxyls (1440 cmy1), probably forming the Sn–OH and Mo–OH bonds with the film metals. However, due to the absence of standards, unambiguous interpretation of the 1440 cmy1 band is impossible. In addition, the FT-IR spectra exhibit the bands at 960, 876 and 710 assigned to stretching vibrations of Me–O groups in the MosO, MoyOy Mo and MoyOySn w9,10x units, and the absorption band at 540 cmy1 can be assigned to the Sn–O–Sn bond w11x, which implies that tin is included into the
Fig. 3. FT-IR transmission spectra of the initial SnMoxOyØnH2O nanolayer deposited on a surface of crystalline silicon by 25 SILD cycles and heated (1) at 100 8C (2) at 200 8C and (3) for 0.5 h.
L.B. Gulina, V.P. Tolstoy / Thin Solid Films 440 (2003) 74–77
treatment does not convert the initial amorphous oxide structure into the crystalline one. 4. Conclusions For the first time, the conditions for the SILD of the Sn(IV)Mo(VI,V)0.6 Oy ØnH2 O layers on a silica surface were determined. The layer thickness was controlled with the accuracy up to fractions of nanolayer by the number of the SILD cycles. The spectroscopic analysis of the layers revealed that under heating up to 200 8C, molecular water and hydroxyl groups are removed from the nanolayers, the bonds Mo–O–Mo and Sn–O–Mo are formed, and Mo(V) is oxidized to Mo(VI).
References w1 x w2 x w3 x w4 x w5 x w6 x w7 x w8 x w9 x w10x
Acknowledgments The work was supported by grant No 1-03-32427 from Russian Foundation for Basic Research (RFBR).
77
w11x
V.P. Tolstoy, Russ. Chem. Rev. 3 (1993) 267. V.P. Tolstoy, Thin Solid Films 307 (1997) 10. V.P. Tolstoy, A.G. Ehrlich, Thin Solid Films 307 (1997) 60. V.P. Tolstoy, Russ. J. Inorg. Chem. 38 (7) (1993) 1063. V.P. Tolstoy, I.V. Murin, A. Reller, Appl. Surf. Sci. 112 (1997) 255. M.T. Pope, Heteropoly and Isopoly Oxometalates, SpringerVerlag, Berlin–Heidelberg–New York–Tokyo, 1983. E.A. Nikitina, Heteropolycompounds, Goschimisdat, Moscow, 1962, (Russ.). J.F. Moulder, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Co., Physical Electronics Division, USA, 1995. E.N. Iurchenko, Methods of molecular spectroscopy in inorganic chemistry (Russ.), Novosibirsk, Nauka, 1986. G.M. Maksimov, G.N. Kustova, K.I. Matveev, T.P. Lasarenko, Koordinazionnaja Chimia 15 (6) (1999) 788, (Chemistry of Complex Compounds) (Russ.). J.P. Espinos, A. Fernandez, V.M. Jimenez, A.R. GonzalezElipe, A. Caballero, M. Ocana, Solid State Jonics 116 (1999) 117.