Research and monitoring of surface
properties with nano-scale resolution

FIELDS OF APPLICATION

• Thin films and coatings
• Nanophase and composite materials
• Superhard materials and alloys
• Diamonds and diamond powders
• Surfaces for micro-engineering
  and microelectronics

Main advantages

Specialties and advantages of the NanoScan system [1] in different kinds of investigations are provided by the use of hard piezoresonance probe and dynamic resonance scanning method as well as by application of diamond tips and tips of ultrahard fullerite C60.

The device makes simultaneous high-resolution measurement of the surface relief, mechanical properties of materials, including elastic modulus and hardness.

Original design and operational principles of the probe gives the possibility to distinguish viscous and elastic components of the interaction force between the probe tip and an investigated surface. This feature allows to observe a hard surface under a contamination viscous layer and to make measurements on the open air without a special preparation of the samples.

Unusually high spring constant of the probe (10⁴ - 10⁵ N/m) allows applying unprecedented high loads during indentation and sclerometry (up to 20 g). At the same time, dynamic resonance scanning mode allows to perform nondestructive surface testing of quite soft materials (polymers) and to investigate surface structure with the help of mechanical properties maps (like Phase Mode and Force Modulation). The use of diamond and fullerite tips allows studying of hard and ultrahard materials, what is impossible using standard SFM cantilevers. So, the advantages of the NanoScan over the other similar systems come out especially when studying hard and ultrahard materials and thin films.

Among the known commercial probes the maximum stiffness value (800 N/m) belongs to the special probe designed by Digital Instruments company. According to the theoretical assumptions the dependency between the cantilever stiffness and measured elastic modulus is given in table 1 [3]. The use of extra stiff cantilever in NanoScan makes it possible to perform Young modulus measurements for very stiff materials (elastic modulus up to 1000 GPa).

Table 1. The Young modulus and the appropriate spring constants for the measurement of the modulus.

Hard: Metals Medium: Polymers Soft: Biomaterials Modulus E (GPa) 10 - 1000 0.1 - 10 0.0001 - 0.1 Appropriate kc (N/m) 1000 - 10000 100 - 1000 0.01 - 100

The use of such a stiff cantilever allows applying unprecedented high loads during indentation and sclerometry (up to 10 g) [4]. This gives the possibility to measure hardness of superhard materials (hardness up to 150 GPa).

To correctly measure the properties of hard and elastic materials it is necessary to use the tip (indenter) with the appropriate mechanical properties. The diamond tips for SPM are manufactured only by DI. The use of diamond and fullerite tips in NanoScan [4] allows studying of hard and superhard materials, what is impossible using standard SFM cantilevers.

The device control is carried out by a personal computer completely. The controlling software works under Windows 2000/XP.

Reliability and easy-to-use of the device and simplicity in tuning and controlling give the possibility to use it not only at research laboratories, but during technology processes in manufacturing conditions.

Superhard materials. Diamonds and diamond powders

A new procedure for the hardness measurements of superhard materials including diamond using NanoScan Measurement System with an ultrahard fullerite C60 tip has been developed [4]. Diamond is plastically deformed under the indentation by the ultrahard fullerite indenter at room temperature. Now the correct measurements of the diamond hardness have become possible. The new procedure gives the possibility to perform the sub-micron hardness and mechanical tests also for thin films and fibers, for nanophase and composite materials.

Table 2. Hardness measurements using NanoScan.

material Vickers hardness GPa s NS hardness GPa s quartz 11 ± 1 11 ± 1 topaz 17 ± 1 19 ± 1 garnet 19 ± 1 19 ± 1 sapphire 23 ± 1 23 ± 1 cubic ZrO2 24 ± 2 27 ± 1 cubic BN - - 60 ± 3 type IIa diamond (100) - - 137 ± 6 type IIa diamond (111) - - 167 ± 5 ultrahard fullerite - - 310 ± 40

Typical examples of different scratches of the sclerometry tests are shown in Figs. 1-2. The hardness measured by the sclerometry procedure with use of the NanoScan are in good conformity with the hardness measured by the indentation procedure with use of the micro-hardness tester.

Fig. 1. The image of the scratch of the sclerometry test on (100) diamond face of saw-grade diamond in the<110> direction. The image size is 2x4 µm; vertical scale is 15 nm.	Fig. 2. The image of the scratch of the sclerometry test on (111) diamond face of saw-grade diamond. The image size is 3x5 µm; vertical scale is 10 nm.

A new procedure for numerical Young modulus measurements of superhard materials has been recently developed [5]. The procedure is based on the loading curves measurement and analysis. The method allows performing the non-destructive measurements with nanoscale resolution, which is useful for multiphase materials and thin films investigation. The error of proposed method does not exceed 10%.

Table 3. Young modulus measurements using NanoScan.

Material E (NanoHardness Tester by CSM Instruments*), GPa Е (NanoScan), GPa Glass < SiO2 PbO > 86 ± 4 95 ± 5 Quartz < SiO2 (100) > 107 ± 5 120 ± 5 Lithium niobate < LiNbO3 (0001) > 215 ± 15 225 ± 10 Gadolinium-gallium garnet < Gd3Ga5O12 (110) > 270 ± 15 270 ± 35 Yttrium-aluminum garnet < Y3Al5O12 (111) > 347 ± 20 345 ± 20 Sapphire < Al2O3 (100) > 441 ± 25 375 ± 35 Silicon - carbide < SiC (001) > 514 ± 26 404 ± 40 Tungsten carbide < WC > + 8% Co 545 ± 30 700 ± 70 Diamond type II a (111) - 1000 ± 100

* Methods of nanoindedentation proposed by Oliver, Pharr [6].

Thin films and coatings

One of the new developing applications of the SPM methods is investigation of thin films adhesion to the substrate. Shortly, this method is based on scratching the film with variable (increasing) load and determining conditions of the film detachment from the substrate. The NanoScan system makes it possible to carry out such investigations for different types of films within a wide range of thickness (from several microns up to several tens of nanometers) and hardness (from about 1 GPa and up to 100 GPa) [2].

Fig. 3 shows the example of the investigation of film of dense monolayers of nanotubes same-oriented in regard to substrate. This is the film with nanotubes 45 -oriented to the substrate.

Fig. 3. 45-degree film, the traces from 4 scratches with depth of 30, 60, 90 and 120 nm (from bottom to the top accordingly); a) - surface relief; b) - elastic modulus map. Size of the image: 5.9 mkm x 5.9 mkm x 166 nm

Submicro- and nano-phase materials. Superhard alloys

The testing of a structure of hard alloys that include hard component in form of grains sizing from a few microns to nanometers and metal bond as well, is the most important industrial task. Today the testing of such alloys is performed by observing of microsections with use of a special optical microscope. But development of hard-alloy technologies has resulted in diminishing of the grain sizes of the hard phase to 0.1 mkm and even less. In addition, the necessity of testing of the border areas between different components of alloy has appeared. Regularly, this task is solved by methods of translucent electron microscopy. The technique for testing of hard alloys and analyzing of their mechanical properties with use of the NanoScan measurement system is proposed (Fig. 4).

The investigations performed confirm the efficiency of use of the SPM NanoScan for testing of hard alloys, since it gives the necessary resolution, requires neither special treatment nor processing of samples and only a few minutes for a measurement. In addition, the proposed method holds much promise for investigations of mechanical properties of alloys on a scale from a few tens micrometers with the resolution up to 10 nm.

Fig. 4. The image of metal-fullerite C60 composit surface with a grain size 0.4-0.8 m; a) the relief of surface; b) the elastic modulus map. (Image size is 3.5 x 3.5 mkm x 50 nm.)

Surfaces for micro-engineering and microelectronics

The investigation technique of the structure using NanoScan allows investigating the structure and quality of the surface. It gives possibility to calculate different parameters of surface roughness.

The results of the researches carried out have demonstrated efficiency of NanoScan for the investigation of surfaces structure and quality.

References:

1. Gogolinsky K., Reshetov V., Industrial laboratory (Testing of materials), V. 64, № 6 (1998) p. 30
2. Gogolinsky K., Kosakovskaya Z., Reshetov V., Chaban A., Acoustical Physics, 6 (2002)
3. Heuberger M., Dietler G., Schlapbach L., Nanotechnology, № 5 (1994) p.12
4. Blank V., Popov M., Lvova N., Gogolinsky K., Reshetov V., J. Mater. Res., № 12 (1997), p. 3109
5. Useinov А, Instruments and experimental techniques, № 1 (2004) p. 134
6. Oliver W.C., Pharr G.M., J. Mater. Res. - № 7 (1992) p. 1564

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