CN101630536B - Method for preparing carbon nano-tube AFM probe based on electromagnetic field - Google Patents

Abstract

The invention relates to a method for preparing a carbon nano-tube AFM probe based on an electromagnetic field, which comprises the steps of: establishing a dielectrophoretic force theoretical model of carbon nano-tubes in a solution under an external electric field; adjusting the voltage amplitude between the prior AFM probe and a conductive substrate or the gap between the prior AFM probe and the conductive substrate, and controlling the field strength between the prior AFM probe and the conductive substrate; imposing an alternating current electric field between the prior AFM probe and the conductive substrate through a waveform signal generator; under the monitoring of an optical microscope, dripping the carbon nano-tube solution into the space between the prior AFM probe and the conductive substrate until the tail end of a tip of the prior AFM probe is immersed; and keeping the probe stand for 5 to 50 seconds, and then disconnecting an external alternating current signal to finish the preparation. The method has easy control, simple manufacturing conditions and low cost, and has the characteristics of environmental protection, energy conservation and the like.

Description

Preparation method based on the carbon nano-tube AFM probe of electromagnetic field

Technical field

The present invention relates to a kind of atomic force microscope probe, specifically a kind of preparation method of the carbon nano-tube AFM probe based on electromagnetic field.

Background technology

Atomic force microscope (AFM) probe structure has significant effects to resolution, sensitivity and the investigation depth of nanostructured surface scanning imagery.Conventional AFM probe is processed by photoetching process usually, has pyramidal contour structures, and cone angle is about 30 °, and length is at 15-20 μ m, and the radius-of-curvature of silicon needle point is 30-100nm less than the radius-of-curvature of 20nm, conductive pinpoint.Along with going deep into of research, such as the sign of biomolecule (DNA, chromosome and range protein) structure, conventional AFM probe can not satisfy high-resolution requirement, and biomolecule is subjected to the destruction and the damage of conventional AFM probe tip easily.For overcoming these difficulties, be necessary to study atomic force microscope probe based on carbon nano-tube point.

Carbon nano-tube (CNT) has minor diameter, high aspect ratio, high strength and high resiliency, good abrasion resistance properties and unique electricity and chemical characteristic, makes it be particularly suitable for making high-resolution atomic force microscope probe needle point.Minor diameter and high aspect ratio help to obtain high-resolution scan image, reduce the one-tenth image distortion of deep trench pattern; High strength can make probe avoid accidental striker and damage; High resiliency can limit the acting force of needle point at sample surfaces, has protected fragile organic sample to avoid the damage of needle point effectively; Good abrasion resistance properties can improve the serviceable life of expensive probe, reduces cost greatly; Unique electricity and chemical characteristic can make probe avoid or reduce the situation of sample and external pollution, particularly scanning or operation soft material in imaging and operating process; In addition, through chemistry and bio-modification, chemical sensitivity that carbon nano-tube showed and one's own thing characteristic make it become favourable prospecting tools.

The common way of preparation carbon nano-tube AFM probe is manual formula assembling and the growth of chemical vapor deposition (CVD) method.Yet, manual formula assemble method operating difficulties, waste time and energy, be difficult to realize make in batches on a large scale; The CVD growth method can be realized making in batches, but catalyst deposit position and density control difficulty, length of carbon nanotube that grows into and direction are difficult to control, and the complexity of creating conditions, and be with high costs.

Summary of the invention

At the above-mentioned defective that exists in the prior art, the technical problem to be solved in the present invention provide a kind of easy and simple to handle, cheaply based on the carbon nano-tube AFM probe preparation method of electromagnetic field.

For addressing the above problem, the technical solution used in the present invention is:

The preparation method of a kind of carbon nano-tube AFM probe based on electromagnetic field of the present invention may further comprise the steps: set up under the extra electric field dielectrophoretic force theoretical model of carbon nano-tube in the solution; Regulate the gap of voltage magnitude between conventional AFM probe and the conductive substrates or conventional AFM probe and conductive substrates, control the field intensity between conventional AFM probe and conductive substrates; Between conventional AFM probe and conductive substrates, apply AC field by waveform generator; Under optical microscope monitors, drip carbon nano-tube solution between conventional AFM probe and the conductive substrates, until the conventional AFM probe tip of submergence end; After leaving standstill 5～50 seconds, disconnection adds AC signal and promptly finishes.

The dielectrophoretic force theoretical model of described carbon nano-tube in solution refers to: in the carbon nano-tube solution inhomogeneous field between conventional AFM probe and conductive substrates, and the dielectrophoretic force model that the carbon nano-tube after the electric polarization is suffered, specific as follows:

$F_{\mathrm{DEP}}=\frac{1}{6}{\mathrm{\&pi;r}}^{2}l{\mathrm{\&epsiv;}}_m\mathrm{Re}\left[K\left(\mathrm{\&omega;}\right)\right]\&dtri;{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="S2008100123839E00011.png"\; state="\{\{state\}\}">E</figure-callout>}}^2$

$K\left(\mathrm{\&omega;}\right)=\frac{{\mathrm{\&epsiv;}}_p^{*}-{\mathrm{\&epsiv;}}_m^{*}}{{\mathrm{\&epsiv;}}_m^{*}}$

${\mathrm{\&epsiv;}}^{*}=\mathrm{\&epsiv;}-j\frac{\mathrm{\&sigma;}}{\mathrm{\&omega;}}$

Wherein, E is an electric field intensity,

Be the gradient symbol, r is the radius of carbon nano-tube, and l is the length of carbon nano-tube, and ε is a specific inductive capacity, and σ is a conductance, $j=\sqrt{-1},$ ω is the angular frequency of extra electric field, and subscript p and m represent carbon nano-tube and solution respectively, and what K (ω) described is the degree of polarization of carbon nano-tube in electric field, i.e. repolarization rate.

What described carbon nano-tube dielectrophoretic force model adopted is positive dielectrophoretic force, and in the carbon nano-tube solution inhomogeneous field between conventional AFM probe and conductive substrates, the electric field strength of conventional AFM probe end is the strongest.

Described conventional AFM probe is new and old doped silicon probe, metal probe and the conducting probe that is wrapped with layer of metal film.

Described conductive substrates is the doped silicon based end, metallic substrates and graphite base.

Field intensity＞10 between described conventional AFM probe and conductive substrates ⁵V/m; The size of field intensity determines that by the amplitude of extra electric field and conventional AFM probe and conductive substrates spacing wherein the amplitude of extra electric field is 2.5～10V, and conventional AFM probe and conductive substrates spacing are 5～25 μ m.

The frequency range of described AC field is 100Hz～10MHz.

Described carbon nano-tube solution is for being equipped with ultrasonic dispersing, dilution good carbon nano-tube alcoholic solution, carbon nano-tube acetone soln in advance or having contained the carbon nano-tube aqueous solutions of 1% sodium dodecylsulphonate.

The time preferably that carbon nano-tube solution leaves standstill after being added drop-wise between conventional probe and the conductive substrates is 10～25 seconds.

The present invention has following beneficial effect and advantage:

1. the position of carbon nano-tube AFM probe and density, length and direction are easy to control, and it is simple to create conditions, and cost is low.The inventive method produces that eelctric dipole is subjected to the electric field force effect and the dielectrophoresis ultimate principle of moving based on carbon nano-tube polarization, carbon nano-tube is subjected to positive dielectrophoretic force and moves towards the strongest conventional AFM probe 1 needle point of electric field strength, by regulating electric field strength position and density, length and the direction of controlling carbon nanotube AFM probe easily, technology is simple, and cost is low.

2. environmental protection and energy saving.The conventional AFM probe of the usefulness that adopts can be the disabled discarded conventional AFM probes of wearing and tearing in the inventive method.

Description of drawings

The principle schematic that the carbon nano-tube that Fig. 1 polarizes for the inventive method is moved by dielectrophoretic force;

Fig. 2 is the carbon nano-tube AFM probe preparation method synoptic diagram that the present invention is based on electromagnetic field.

Embodiment

As shown in Figure 1, the invention provides a kind of preparation method of the carbon nano-tube AFM probe based on electromagnetic field, polarization produces that eelctric dipole is subjected to the electric field force effect and the dielectrophoresis ultimate principle of moving to this method based on carbon nano-tube.When applying when being biased in conventional AFM probe 1 (positive electrode) and conductive substrates 2 (negative electrode), the inhomogeneous field 3 of generation produces the polarization charges of equivalent contrary signs on carbon nano-tube 4 surfaces.The polarization charge of these equivalent contrary signs forms dipole in pairs, and dipole is subjected to 5 effects of non-vanishing clean electrostatic force and moves in inhomogeneous field.The dielectrophoretic force direction vector of each position, space is by arrow 6 expressions.

As shown in Figure 2, preparation method's step of carbon nanotube atomic force microscope probe of the present invention is:

At first set up under the extra electric field dielectrophoretic force theoretical model of carbon nano-tube in the solution: in carbon nano-tube solution 11 inhomogeneous fields of 2 of conventional AFM probe 1 and conductive substrates, the dielectrophoretic force model that the carbon nano-tube after the electric polarization is suffered, specific as follows:

$F_{\mathrm{DEP}}=\frac{1}{6}{\mathrm{\&pi;r}}^{2}l{\mathrm{\&epsiv;}}_m\mathrm{Re}\left[K\left(\mathrm{\&omega;}\right)\right]\&dtri;{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="S2008100123839E00011.png"\; state="\{\{state\}\}">E</figure-callout>}}^2$

$K\left(\mathrm{\&omega;}\right)=\frac{{\mathrm{\&epsiv;}}_p^{*}-{\mathrm{\&epsiv;}}_m^{*}}{{\mathrm{\&epsiv;}}_m^{*}}$

${\mathrm{\&epsiv;}}^{*}=\mathrm{\&epsiv;}-j\frac{\mathrm{\&sigma;}}{\mathrm{\&omega;}}$

Wherein, E is an electric field intensity,

Be the gradient symbol, r is the radius of carbon nano-tube, and l is the length of carbon nano-tube, and ε is a specific inductive capacity, and σ is a conductance, $j=\sqrt{-1},$ ω is the angular frequency of extra electric field, and subscript p and m represent carbon nano-tube and solution respectively, and what K (ω) described is the degree of polarization of carbon nano-tube in electric field, i.e. repolarization rate.As the real part Re[K of K (ω) (ω)] symbol be timing, carbon nano-tube is subjected to positive dielectrophoretic force effect and moves towards the strongest position of electric field intensity; Otherwise, as Re[K (ω)] symbol when negative, carbon nano-tube is subjected to the negative dielectrophoretic force effect and towards the most weak regional movement of electric field intensity;

After setting up above-mentioned electrophoretic force theoretical model, carry out following operation:

Conventional AFM micro cantilever probe 7 is fixed on the probe anchor clamps 8;

Under the supervision of the optical microscope 9 of being with the CCD camera, adjust micromotion platform 10 conductive substrates 2 and the spacing of conventional AFM probe 1 end are controlled in 5～25 mu m ranges; Optical microscope 9 by band CCD camera can be easily monitors whether the moving of micromotion platform, conventional AFM probe 1 semi-girder touch that conductive substrates 2 is out of shape and the dropping process of carbon nano-tube solution 11 subsequently from display.

Between conventional AFM micro cantilever probe 7 and conductive substrates 2, apply AC signal and produce the dielectrophoresis inhomogeneous field by AC signal generator 12; The frequency range of AC signal is 100Hz～10MHz, and present embodiment adopts 10kHz-5MHz;

Under the supervision of optical microscope 9, drip carbon nano-tube solution 11 between conventional AFM micro cantilever probe 7 and the conductive substrates 2, until the end of the conventional AFM micro cantilever probe 7 of submergence with micropipettor; Carbon nano-tube solution 11 is for being equipped with ultrasonic dispersing, dilution good carbon nano-tube alcoholic solution, carbon nano-tube acetone soln in advance or having contained the carbon nano-tube aqueous solutions of 1% sodium dodecylsulphonate (SDS);

In the present embodiment in the carbon nano-tube solution inhomogeneous field of 2 of conventional AFM probe 1 and conductive substrates, control conventional AFM probe 1 terminal needle point and conductive substrates 2 distances are the shortest, the electric field strength that then can obtain conventional AFM probe 1 needle point is the strongest.Based on dielectrophoresis ultimate principle shown in Figure 1, carbon nano-tube is subjected to positive dielectrophoretic force and moves towards the strongest conventional AFM probe 1 needle point of electric field strength.

For guaranteeing that carbon nano-tube has time enough to move to the needle point of conventional AFM probe 1 in the carbon nano-tube solution 11, in the present embodiment, after dripping carbon nano-tube solution 11, leave standstill 5～50 seconds (present embodiment is 10～25 seconds), disconnection subsequently adds AC signal, separates the making that conventional AFM probe 1 and conductive substrates 2 are promptly finished carbon nano-tube AFM probe.

Based on dielectrophoresis ultimate principle shown in Figure 1, carbon nano-tube is subjected to positive dielectrophoretic force and moves towards the strongest conventional AFM probe 1 needle point of electric field strength.The carbon nano-tube that moves to conventional AFM probe 1 needle point is attached on the end of conventional AFM probe 1 needle point under the effect of electric field force, and the axis of carbon nano-tube tends to parallel with the direction of this place's electric field lines.In addition, impurity such as the non-type carbon in the solution also can be adsorbed onto the end of conventional AFM probe 1 needle point by electric field force, thereby play the intensity of sticking of strengthening carbon nano-tube and conventional AFM probe 1.The carbon nano-tube AFM probe of principle making satisfies AFM conventional imaging operating function in view of the above.

Claims (8)

1. preparation method based on the carbon nano-tube AFM probe of electromagnetic field is characterized in that may further comprise the steps: set up under the extra electric field dielectrophoretic force theoretical model of carbon nano-tube in the solution; Regulate the gap of voltage magnitude between conventional AFM probe (1) and the conductive substrates (2) or conventional AFM probe (1) and conductive substrates (2), control the field intensity between conventional AFM probe (1) and conductive substrates (2); Between conventional AFM probe (1) and conductive substrates (2), apply AC field by waveform generator (12); Under optical microscope (9) monitors, drip carbon nano-tube solution (11) between conventional AFM probe (1) and the conductive substrates (2), until conventional AFM probe (1) tip end of submergence; After leaving standstill 5～50 seconds, disconnection adds AC signal and promptly finishes;

The dielectrophoretic force theoretical model of described carbon nano-tube in solution refers to: in carbon nano-tube solution (11) inhomogeneous field between conventional AFM probe (1) and conductive substrates (2), and the dielectrophoretic force model that the carbon nano-tube after the electric polarization is suffered, specific as follows:

$F_{\mathrm{DEP}}=\frac{1}{6}{\mathrm{\&pi;r}}^{2}l{\mathrm{\&epsiv;}}_m\mathrm{Re}\left[K\left(\mathrm{\&omega;}\right)\right]\&dtri;E^2$

$K\left(\mathrm{\&omega;}\right)=\frac{{\mathrm{\&epsiv;}}_p^{*}-{\mathrm{\&epsiv;}}_m^{*}}{{\mathrm{\&epsiv;}}_m^{*}}$

${\mathrm{\&epsiv;}}^{*}=\mathrm{\&epsiv;}-j\frac{\mathrm{\&sigma;}}{\mathrm{\&omega;}}$

Wherein, E is an electric field intensity,

Be the gradient symbol, r is the radius of carbon nano-tube, and l is the length of carbon nano-tube, and ε is a specific inductive capacity, and σ is a conductance,

ω is the angular frequency of extra electric field, and subscript p and m represent carbon nano-tube and solution respectively, and what K (ω) described is the degree of polarization of carbon nano-tube in electric field, i.e. repolarization rate;

Field intensity＞10 between described conventional AFM probe (1) and conductive substrates (2) ⁵V/m.

2. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: what described carbon nano-tube dielectrophoretic force model adopted is positive dielectrophoretic force, in the carbon nano-tube solution inhomogeneous field between conventional AFM probe (1) and conductive substrates (2), the electric field strength of conventional AFM probe end is the strongest.

3. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: described conventional AFM probe (1) is new and old doped silicon probe, metal probe and the conducting probe that is wrapped with layer of metal film.

4. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: described conductive substrates (2) is the doped silicon based end, metallic substrates and graphite base.

5. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: the size of field intensity is determined with conductive substrates (2) spacing by the amplitude and the conventional AFM probe (1) of extra electric field, wherein the amplitude of extra electric field is 2.5～10V, and conventional AFM probe (1) is 5～25 μ m with conductive substrates (2) spacing.

6. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: the frequency range of described AC field is 100Hz～10MHz.

7. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: described carbon nano-tube solution (11) is for being equipped with ultrasonic dispersing, dilution good carbon nano-tube alcoholic solution, carbon nano-tube acetone soln in advance or having contained the carbon nano-tube aqueous solutions of 1% sodium dodecylsulphonate.

8. according to the preparation method of the described carbon nano-tube AFM probe based on electromagnetic field of claim 1, it is characterized in that: the time that carbon nano-tube solution (11) leaves standstill after being added drop-wise between conventional probe (1) and the conductive substrates (2) is 10～25 seconds.

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