rus
Issue #4/2017
I.Yaminsky, G.Meshkov, A.Akhmetova
Methods of nanoscopy in study of carbon materials and biopolymers
Methods of nanoscopy in study of carbon materials and biopolymers
With the aim of establishing the relationship between the local structure of surface of carbon and polymer materials and of their electrophysical properties, it has been developed a device for combined atomic force microscopy and scanning capillary microscopy that allows to study the morphology and properties of 2D nanoscale structures and also to conduct their controlled deposition.
Теги: scanning capillary microscopy scanning probe microscopy surface nanostructure наноструктура поверхности сканирующая зондовая микроскопия сканирующая капиллярная микроскопия
2D nanoscale structures based on carbon materials and biopolymers are promising for the energy storage. It is advisable to use the methods and apparatus of scanning probe microscopy for the development and subsequent diagnosis of such nanostructured materials. In the present work we propose the experimental system for combined capillary, electrochemical and piezo-electrochemical microscopy of the surface of materials. This equipment allows to carry out detailed analysis of the physical-chemical properties of the surfaces such as the nanostructured surface of graphite. At the same time, it can be used for targeted delivery of the required reagents to the selected area of surface by the ion-conductance microscopy with the use of a multichannel capillary probe [1].
Manufacturing of capillaries was carried out in the P-1000 Pipette Puller (Sutter Instrument) system in the selected modes (Fig.1). Zeiss LEO 912 AB transmission electron microscope was used for control of the output diameter of the nano-capillary.
The development of a combined AFM and capillary microscope was carried out on the basis of FemtoScan multifunctional scanning probe microscope and FemtoScan X high-speed atomic force microscope (Fig.2).
FemtoScan Online software was used for control and data processing [2]. Fig.3. shows interface of the software.
Technical parameters of the experimental system are given in the table.
The capabilities of the experimental system:
• atomic force microscopy;
• scanning resistive microscopy;
• scanning capillary microscopy;
• piezoelectric microscopy;
• piezo-electrochemical microscopy;
• nanolithography.
Examples of different geometry of images on the highly oriented pyrolytic graphite are shown in Fig.4. By using the technique of local anodic oxidation, the surface nanostructures consisting of conductive regions of graphite and dielectric inclusions of graphite oxide were obtained. Local electric resistance measured by conducting probe of the atomic force microscope in the mode of scanning resistive microscopy varies from a few Ohms for areas of graphite to 100 MΩ for graphite oxide.
Creation of a lithographic pattern on the surface of graphite or other materials – silicon, titanium, aluminium – in the case of local anodic oxidation occurs with the participation of the molecules of O2, H2O, etc., being in the environment. As it has been shown earlier [3], the effectiveness of local anodic oxidation depends significantly on the air humidity.
Controlled delivery of substances, such as oxidants and catalysts, into a specified area of the surface requires a quartz or glass nano-capillary with an outlet opening of the nanometer diameter. For the manufacture of nano-capillaries the tubes of borosilicate glass with outer and inner diameters of 1.0 mm and 0.58 mm, respectively, were used. Depending on the heating conditions, speed and effort of extraction the nano-capillaries with outlet opening of 10–100 nm were obtained. The electrical resistance of the conical shaped capillary filled with electrolyte with resistivity ρ, can be estimated using the formula:
R= ρL/πr1r2,
where L is the capillary length, r1 and r2 are the diameters of the inlet and outlet holes. The electric resistance of a capillary with L = 2 cm, r1 = 0.58 mm and r2 = 10 nm filled with a saline solution (ρ = 62.6 Ωcm) is about 690 MΩ. If you increase the diameter of the nano-capillary to 100 nm, the electrical resistance will drop to 6.9 MΩ.
In case of dual capillary one of the channels is used for delivery of the reagent and the other one – for positioning of the nano-capillary above the surface of the sample.
Fig.5 shows images of phospholipid films deposited on the surface of graphite. The measurements showed that the local electrical resistance of such films with a thickness of about 5 nm is by several orders of magnitude more than of the clean graphite surface.
Study of 2D nanoscale structures of catalysts and energy accumulators requires obtaining not only information about surface topography, but also measuring the set of electrophysical parameters. One of such parameters is the local electrical resistance. In the scanning resistive microscopy, the measured resistance R depends on the resistivity of the local near-surface area and on the radius of the probe used. The resistance of the circuit for the simplest model can be described by the formula:
R= Rзонда+ρ/2πr,
where ρ is the resistivity of the sample surface, r is the radius of the probe. The resistance of the probe Rзонда is small and during the measurement, as a rule, does not change.
In the case of local contact, the experimental system allows the following measurements:
• the dependence of the current on the applied voltage I(U) (current-voltage characteristic);
• the dependence of the current on the frequency of the applied signal with a selected voltage amplitude I(ω,U) (amplitude-frequency characteristic).
To conduct these measurements the signal in the range from –10 V to +10 V with frequency range from units of Hz to 10 MHz is supplied. Tuning of the signal frequency is carried out using a generator board based on digital frequency synthesizer of AD7008. The accuracy of frequency tuning is 0.01 Hz. The measured current is in the range from 1 pA to 100 nA.
In the study of energy accumulators, the system allows the measurements of currents of charge and discharge. In this case, the contact area is depended on the radius of the cantilever or the diameter of the outlet hole of nano-capillary.
Nano-capillary can be used to transport various materials such as gold nanoparticles, proteins and other chemical compounds. At the same time, as already mentioned, they can be used for scanning with nano-resolution and for electrophysical measurements. The advantages of this technology are obvious when scanning biological objects, as the force of the interaction between the nano-capillary and sample can be smaller than in conventional atomic force microscope. You can extend the capabilities of nano-capillaries and make them ion-selective, allowing to determine the local concentration of ions of sodium, potassium, calcium, etc. ■
The study was performed with financial support of RFBR in the framework of research project No. 16-29-06290 "Development of new methods of nanoscopy for determination and directed modification of the structure, physical-chemical and electrophysical characteristics of the 2D nanoscale structures for energy storage and catalysts based on carbon materials and biopolymers".
Manufacturing of capillaries was carried out in the P-1000 Pipette Puller (Sutter Instrument) system in the selected modes (Fig.1). Zeiss LEO 912 AB transmission electron microscope was used for control of the output diameter of the nano-capillary.
The development of a combined AFM and capillary microscope was carried out on the basis of FemtoScan multifunctional scanning probe microscope and FemtoScan X high-speed atomic force microscope (Fig.2).
FemtoScan Online software was used for control and data processing [2]. Fig.3. shows interface of the software.
Technical parameters of the experimental system are given in the table.
The capabilities of the experimental system:
• atomic force microscopy;
• scanning resistive microscopy;
• scanning capillary microscopy;
• piezoelectric microscopy;
• piezo-electrochemical microscopy;
• nanolithography.
Examples of different geometry of images on the highly oriented pyrolytic graphite are shown in Fig.4. By using the technique of local anodic oxidation, the surface nanostructures consisting of conductive regions of graphite and dielectric inclusions of graphite oxide were obtained. Local electric resistance measured by conducting probe of the atomic force microscope in the mode of scanning resistive microscopy varies from a few Ohms for areas of graphite to 100 MΩ for graphite oxide.
Creation of a lithographic pattern on the surface of graphite or other materials – silicon, titanium, aluminium – in the case of local anodic oxidation occurs with the participation of the molecules of O2, H2O, etc., being in the environment. As it has been shown earlier [3], the effectiveness of local anodic oxidation depends significantly on the air humidity.
Controlled delivery of substances, such as oxidants and catalysts, into a specified area of the surface requires a quartz or glass nano-capillary with an outlet opening of the nanometer diameter. For the manufacture of nano-capillaries the tubes of borosilicate glass with outer and inner diameters of 1.0 mm and 0.58 mm, respectively, were used. Depending on the heating conditions, speed and effort of extraction the nano-capillaries with outlet opening of 10–100 nm were obtained. The electrical resistance of the conical shaped capillary filled with electrolyte with resistivity ρ, can be estimated using the formula:
R= ρL/πr1r2,
where L is the capillary length, r1 and r2 are the diameters of the inlet and outlet holes. The electric resistance of a capillary with L = 2 cm, r1 = 0.58 mm and r2 = 10 nm filled with a saline solution (ρ = 62.6 Ωcm) is about 690 MΩ. If you increase the diameter of the nano-capillary to 100 nm, the electrical resistance will drop to 6.9 MΩ.
In case of dual capillary one of the channels is used for delivery of the reagent and the other one – for positioning of the nano-capillary above the surface of the sample.
Fig.5 shows images of phospholipid films deposited on the surface of graphite. The measurements showed that the local electrical resistance of such films with a thickness of about 5 nm is by several orders of magnitude more than of the clean graphite surface.
Study of 2D nanoscale structures of catalysts and energy accumulators requires obtaining not only information about surface topography, but also measuring the set of electrophysical parameters. One of such parameters is the local electrical resistance. In the scanning resistive microscopy, the measured resistance R depends on the resistivity of the local near-surface area and on the radius of the probe used. The resistance of the circuit for the simplest model can be described by the formula:
R= Rзонда+ρ/2πr,
where ρ is the resistivity of the sample surface, r is the radius of the probe. The resistance of the probe Rзонда is small and during the measurement, as a rule, does not change.
In the case of local contact, the experimental system allows the following measurements:
• the dependence of the current on the applied voltage I(U) (current-voltage characteristic);
• the dependence of the current on the frequency of the applied signal with a selected voltage amplitude I(ω,U) (amplitude-frequency characteristic).
To conduct these measurements the signal in the range from –10 V to +10 V with frequency range from units of Hz to 10 MHz is supplied. Tuning of the signal frequency is carried out using a generator board based on digital frequency synthesizer of AD7008. The accuracy of frequency tuning is 0.01 Hz. The measured current is in the range from 1 pA to 100 nA.
In the study of energy accumulators, the system allows the measurements of currents of charge and discharge. In this case, the contact area is depended on the radius of the cantilever or the diameter of the outlet hole of nano-capillary.
Nano-capillary can be used to transport various materials such as gold nanoparticles, proteins and other chemical compounds. At the same time, as already mentioned, they can be used for scanning with nano-resolution and for electrophysical measurements. The advantages of this technology are obvious when scanning biological objects, as the force of the interaction between the nano-capillary and sample can be smaller than in conventional atomic force microscope. You can extend the capabilities of nano-capillaries and make them ion-selective, allowing to determine the local concentration of ions of sodium, potassium, calcium, etc. ■
The study was performed with financial support of RFBR in the framework of research project No. 16-29-06290 "Development of new methods of nanoscopy for determination and directed modification of the structure, physical-chemical and electrophysical characteristics of the 2D nanoscale structures for energy storage and catalysts based on carbon materials and biopolymers".
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