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The characterization of lubricant on ME tape by TOF-SIMS analysis
Journal of Magnetism and Magnetic Materials 235 (2001) 183–186
The characterization of lubricant on ME tape by TOF-SIMS analysis Yukikazu Ohchia,*, Fumiyo Tojyoub a
AVCPDC, Matsushita Electric Industrial Co. Ltd., Kadoma-shi, 571-5803, Japan b Matsushita Technoresearch INC., Moriguchi-shi, 570-8501, Japan
Abstract By using time of flying secondly ion mass spectroscopy, lubricant was observed on the surface of metal evaporated tape. The difference of lubricant types showed the presence. It was also suggested that the surface free energy of lubricant have relation to the frictional coefficient. r 2001 Published by Elsevier Science B.V. Keywords: Metal evaporated (ME) tape; Lubricant; Time of flying secondly ion mass spectroscopy (TOF-SIMS); Surface free energy
1. Introduction Metal evaporated (ME) tape is considered as the ultimate tape media for high-density recording. The application of ME tape is not only to DV (Digital VCR for consumer-use) [1–3] but also to data storage. In order to realize wide application of ME tape, making advance in magnetic layer, tribology (lubricant, protective layer, surface asperities) and drive/media interface is required. Superior lubricant is essential for the reliabilities of ME tape. As lubricant used on magnetic media, there are materials that contain with Fluorocarbon or perfluoropolyether. We have designed original lubricant, and have developed the prominent lubricant layer for ME tape. Also, various analysis techniques have been tried to magnetic media. Time of flying secondly ion mass spectroscopy (TOF-SIMS) analysis [4] is the latest techniques in this field. It is suited to the characterization of fluoro-lubri*Corresponding author.
cants, because of its surface sensitivity, wide mass range, high mass resolution, high spatially resolved ion image and so on. We have tried to analyze lubricant on the surface of ME tape by TOFSIMS, so that we found that it was effective to develop ME tape. One way to characterize the tape surface is by means of contact angle goniometry. From contact angles of known liquids on tape surface, the surface free energy, gs can be calculated. The surface free energy can be broken up in dispersive energy, gd ; polarization energy, gp and hydrogen bonding energy, gh : The dispersive energy is a measure of the Van der Walls forces it exerts. The polar energy is dependent on the sum of the dipole moment on the surface. The hydrogen bonding energy is dependent on the sum of the hydrogen bond on the surface. Interpretation of contact angle data can give the surface condition of lubricant on tape, which is not readily available from complicated surface sensitive technique such as TOF-SIMS. In this study, we focus on the surface properties, the influence of
0304-8853/01/$ - see front matter r 2001 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 0 3 3 4 - 1
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Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186
the lubricant type to the presence on tape, in view of the surface free energy of lubricant type.
2. Experiment Samples used in this work summarized in Table 1. We prepared three types of ME tape with different appliance of lubricant. Lubricant A (acid type), lubricant B (ester type) and mixture of them (1 : 1 in weight) were applied in each tape. A schematic cross sectional view of ME tape is shown in Fig. 1. Polyethylene-terephthalate (PET) film was used as a non-magnetic substrate. An under coat layer was formed to distribute fine asperities which had a height of 20 nm with a density ranging from 105 to 109 asperities/mm2 according to AFM analysis. Co–CoO ferromagnetic metal thin film was deposited by an oblique vapor deposition method while applying oxygen gas. Diamond like carbon (DLC) film which was prepared to a thickness of 10 nm by a plasma CVD method using methane and argon gas was applied as a protective layer over the Co–CoO layer. Finally, fluorine-containing lubricant was formed
m ¼ 2=p InðT2 =10Þ; where T2 is the tension generated on the other end of the tape. Frictional coefficients were obtained by moving sample tapes forward and reverse against a steel pin for 100 cycles [5].
Table 1 The characteristics of sample tape
Lubricant Type Protective layer
on DLC film. The average roughness of the tape surface, Ra, was 20 nm. We investigated the surface and the tape characteristics of each sample. Surface analysis was performed by using TOF-SIMS(Phsysicalelectoronics; TRIFT II). The surface free energy was determined by an extended Fowkes theory [6] to which the contact angle was applied (Kyowa Kaimen Kagaku; CVA). The contact angle was determined at ambient temperature. The surface free energy, gs was determined by contact angles, which were measured by dropping three kinds of liquids (abromonaphthalene, methylene iodide, water). As lubricity investigation, frictional coefficients for each ME tape were measured in 251C and 40% R.H. atmosphere. Frictional coefficient against a stainless steel pin (SUS303) with a diameter of 2 mm and a surface roughness Rmax of 200 nm were measured by an apparatus as shown schematically in Fig. 2. After applying a tension of 0.01 kg to one end of the tape, the other end was moved at the rate of 18.8 mm/s. Coefficient of friction m is calculated by the following equation:
Sample-1
Sample-2
Sample-3
Lube.A Acid DLC
Lube.B Ester DLC
Lube.A+Lube.B mixture (1 : 1) DLC
Fig. 1. A schematic cross sectional view of ME tape.
3. Results and disucssion Fig. 3 shows how the lubricant is presented on ME tape by the CF ion image of TOF-SIMS. The
Fig. 2. Friction measurement apparatus.
Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186
185
exhibits uniform presence of lubricant. We consider that the influence of lubricant B causes the uniform of image, though the lubricant of sample 3 contains lubricant A (50%) in weight. Fig. 4 shows the surface free energy against lubricant A/lubricant B ratio. Though lubricant B contains 70% in weight, the surface free energy is similar to the behavior of lubricant A (100%). It is found that the lubricant A becomes effective to make the free energy low. The graph in Fig. 5 illustrates the frictional coefficient of each sample. Sample 2 is higher in
Fig. 4. Surface free energy of ME tape.
Fig. 3. CF ion images of lubricant on ME tape by TOF-SIMS.
CF ion image of sample 1 (lubricant A) indicates unmethodical presence of the lubricant. On the other hand, the image of sample 2 (lubricant B) shows that the lubricant is uniform in presence. Moreover, we see that sample 3, which consists of combination of lubricant A and lubricant B,
Fig. 5. Frictional coefficient of ME tape.
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Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186 Table 2 Lubricant conditions and characteristics of ME tape samples
Lubricant TOF-SIMS image Surface energy(mN/m) Frictional coefficient
Sample 1
Sample 3
Sample 2
A: Acid Unmethodical 27 0.21
A+B (1 : 1) Uniform 29 0.22
B: Ester Uniform 41 0.29
characteristic of tape samples was summarized in Table 2.
4. Conclusions
Fig. 6. Surface free energy of ME tape.
lubricity. Sample 1 with lubricant A exhibits lower frictional coefficient and is more stable than sample 2. Lubricant A, which is acid type, is more effective than lubricant B in view of decreasing frictional coefficient. As well, the frictional coefficient of sample 3 exhibits low and stable values. This is similar to the pattern of sample 1. Fig. 6 shows the relationship between the surface free energy and the frictional coefficient of each sample. The surface free energy of sample 1 is 27 mN/m. The value of sample 2 is 41 mN/m, the polarization energy, gp in the surface energy increases against sample 1. It is considered that the gp appears in sample 2, because of the ester unit of lubricant B molecule. But the property of surface free energy in sample 3 (mixture) is similar to the property of sample 1. The fact that sample 3 is similar to sample 1 suggests that lubricant A is mainly present on the top layer in sample 3. The
We made the following observations about lubricant on ME tape by TOF-SMIS analysis. The information from TOF-SIMS suggested how the lubricant was present on ME tape. The difference of the presence depended on the polar end-group or material property of lubricant. The surface free energy of lubricant was related to the frictional coefficient of ME tape. Lower the surface energy of lubricant seems effective to decrease frictional coefficient of ME tape.
References [1] H. Yosida, Y. Nishizawa, H. Ouhata, IEEE Trans. Magn. 31 (6) (1995) 2940. [2] M. Murai, K. Takahashi, M. Odagiri, J. Inst. Television Eng. Jpn 49 (7) (1995) 907. [3] H. Seki, K. Kuwahara, et al., Proceedings of the PMRC ’94, 1994, pp. 541–544. [4] A. Benninghoven, Angew. Chem. Int. Ed. Engl. 33 (1994) 1023. [5] Y. Ohchi, K. Kuwahara, M. Murai, Proceedings of the PMRC ’97, 1997, pp. 99–102. [6] F.M. Fowkes, Ind. Eng. Chem. 56 (1964) 40.
The characterization of lubricant on ME tape by TOF-SIMS analysis Yukikazu Ohchia,*, Fumiyo Tojyoub a
AVCPDC, Matsushita Electric Industrial Co. Ltd., Kadoma-shi, 571-5803, Japan b Matsushita Technoresearch INC., Moriguchi-shi, 570-8501, Japan
Abstract By using time of flying secondly ion mass spectroscopy, lubricant was observed on the surface of metal evaporated tape. The difference of lubricant types showed the presence. It was also suggested that the surface free energy of lubricant have relation to the frictional coefficient. r 2001 Published by Elsevier Science B.V. Keywords: Metal evaporated (ME) tape; Lubricant; Time of flying secondly ion mass spectroscopy (TOF-SIMS); Surface free energy
1. Introduction Metal evaporated (ME) tape is considered as the ultimate tape media for high-density recording. The application of ME tape is not only to DV (Digital VCR for consumer-use) [1–3] but also to data storage. In order to realize wide application of ME tape, making advance in magnetic layer, tribology (lubricant, protective layer, surface asperities) and drive/media interface is required. Superior lubricant is essential for the reliabilities of ME tape. As lubricant used on magnetic media, there are materials that contain with Fluorocarbon or perfluoropolyether. We have designed original lubricant, and have developed the prominent lubricant layer for ME tape. Also, various analysis techniques have been tried to magnetic media. Time of flying secondly ion mass spectroscopy (TOF-SIMS) analysis [4] is the latest techniques in this field. It is suited to the characterization of fluoro-lubri*Corresponding author.
cants, because of its surface sensitivity, wide mass range, high mass resolution, high spatially resolved ion image and so on. We have tried to analyze lubricant on the surface of ME tape by TOFSIMS, so that we found that it was effective to develop ME tape. One way to characterize the tape surface is by means of contact angle goniometry. From contact angles of known liquids on tape surface, the surface free energy, gs can be calculated. The surface free energy can be broken up in dispersive energy, gd ; polarization energy, gp and hydrogen bonding energy, gh : The dispersive energy is a measure of the Van der Walls forces it exerts. The polar energy is dependent on the sum of the dipole moment on the surface. The hydrogen bonding energy is dependent on the sum of the hydrogen bond on the surface. Interpretation of contact angle data can give the surface condition of lubricant on tape, which is not readily available from complicated surface sensitive technique such as TOF-SIMS. In this study, we focus on the surface properties, the influence of
0304-8853/01/$ - see front matter r 2001 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 0 3 3 4 - 1
184
Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186
the lubricant type to the presence on tape, in view of the surface free energy of lubricant type.
2. Experiment Samples used in this work summarized in Table 1. We prepared three types of ME tape with different appliance of lubricant. Lubricant A (acid type), lubricant B (ester type) and mixture of them (1 : 1 in weight) were applied in each tape. A schematic cross sectional view of ME tape is shown in Fig. 1. Polyethylene-terephthalate (PET) film was used as a non-magnetic substrate. An under coat layer was formed to distribute fine asperities which had a height of 20 nm with a density ranging from 105 to 109 asperities/mm2 according to AFM analysis. Co–CoO ferromagnetic metal thin film was deposited by an oblique vapor deposition method while applying oxygen gas. Diamond like carbon (DLC) film which was prepared to a thickness of 10 nm by a plasma CVD method using methane and argon gas was applied as a protective layer over the Co–CoO layer. Finally, fluorine-containing lubricant was formed
m ¼ 2=p InðT2 =10Þ; where T2 is the tension generated on the other end of the tape. Frictional coefficients were obtained by moving sample tapes forward and reverse against a steel pin for 100 cycles [5].
Table 1 The characteristics of sample tape
Lubricant Type Protective layer
on DLC film. The average roughness of the tape surface, Ra, was 20 nm. We investigated the surface and the tape characteristics of each sample. Surface analysis was performed by using TOF-SIMS(Phsysicalelectoronics; TRIFT II). The surface free energy was determined by an extended Fowkes theory [6] to which the contact angle was applied (Kyowa Kaimen Kagaku; CVA). The contact angle was determined at ambient temperature. The surface free energy, gs was determined by contact angles, which were measured by dropping three kinds of liquids (abromonaphthalene, methylene iodide, water). As lubricity investigation, frictional coefficients for each ME tape were measured in 251C and 40% R.H. atmosphere. Frictional coefficient against a stainless steel pin (SUS303) with a diameter of 2 mm and a surface roughness Rmax of 200 nm were measured by an apparatus as shown schematically in Fig. 2. After applying a tension of 0.01 kg to one end of the tape, the other end was moved at the rate of 18.8 mm/s. Coefficient of friction m is calculated by the following equation:
Sample-1
Sample-2
Sample-3
Lube.A Acid DLC
Lube.B Ester DLC
Lube.A+Lube.B mixture (1 : 1) DLC
Fig. 1. A schematic cross sectional view of ME tape.
3. Results and disucssion Fig. 3 shows how the lubricant is presented on ME tape by the CF ion image of TOF-SIMS. The
Fig. 2. Friction measurement apparatus.
Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186
185
exhibits uniform presence of lubricant. We consider that the influence of lubricant B causes the uniform of image, though the lubricant of sample 3 contains lubricant A (50%) in weight. Fig. 4 shows the surface free energy against lubricant A/lubricant B ratio. Though lubricant B contains 70% in weight, the surface free energy is similar to the behavior of lubricant A (100%). It is found that the lubricant A becomes effective to make the free energy low. The graph in Fig. 5 illustrates the frictional coefficient of each sample. Sample 2 is higher in
Fig. 4. Surface free energy of ME tape.
Fig. 3. CF ion images of lubricant on ME tape by TOF-SIMS.
CF ion image of sample 1 (lubricant A) indicates unmethodical presence of the lubricant. On the other hand, the image of sample 2 (lubricant B) shows that the lubricant is uniform in presence. Moreover, we see that sample 3, which consists of combination of lubricant A and lubricant B,
Fig. 5. Frictional coefficient of ME tape.
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Y. Ohchi, F. Tojyou / Journal of Magnetism and Magnetic Materials 235 (2001) 183–186 Table 2 Lubricant conditions and characteristics of ME tape samples
Lubricant TOF-SIMS image Surface energy(mN/m) Frictional coefficient
Sample 1
Sample 3
Sample 2
A: Acid Unmethodical 27 0.21
A+B (1 : 1) Uniform 29 0.22
B: Ester Uniform 41 0.29
characteristic of tape samples was summarized in Table 2.
4. Conclusions
Fig. 6. Surface free energy of ME tape.
lubricity. Sample 1 with lubricant A exhibits lower frictional coefficient and is more stable than sample 2. Lubricant A, which is acid type, is more effective than lubricant B in view of decreasing frictional coefficient. As well, the frictional coefficient of sample 3 exhibits low and stable values. This is similar to the pattern of sample 1. Fig. 6 shows the relationship between the surface free energy and the frictional coefficient of each sample. The surface free energy of sample 1 is 27 mN/m. The value of sample 2 is 41 mN/m, the polarization energy, gp in the surface energy increases against sample 1. It is considered that the gp appears in sample 2, because of the ester unit of lubricant B molecule. But the property of surface free energy in sample 3 (mixture) is similar to the property of sample 1. The fact that sample 3 is similar to sample 1 suggests that lubricant A is mainly present on the top layer in sample 3. The
We made the following observations about lubricant on ME tape by TOF-SMIS analysis. The information from TOF-SIMS suggested how the lubricant was present on ME tape. The difference of the presence depended on the polar end-group or material property of lubricant. The surface free energy of lubricant was related to the frictional coefficient of ME tape. Lower the surface energy of lubricant seems effective to decrease frictional coefficient of ME tape.
References [1] H. Yosida, Y. Nishizawa, H. Ouhata, IEEE Trans. Magn. 31 (6) (1995) 2940. [2] M. Murai, K. Takahashi, M. Odagiri, J. Inst. Television Eng. Jpn 49 (7) (1995) 907. [3] H. Seki, K. Kuwahara, et al., Proceedings of the PMRC ’94, 1994, pp. 541–544. [4] A. Benninghoven, Angew. Chem. Int. Ed. Engl. 33 (1994) 1023. [5] Y. Ohchi, K. Kuwahara, M. Murai, Proceedings of the PMRC ’97, 1997, pp. 99–102. [6] F.M. Fowkes, Ind. Eng. Chem. 56 (1964) 40.