TWI571640B - Method for measuring electric double layer potential, stern layer thickness, and ion concentration - Google Patents

Description

Method for measuring electric double layer potential, tight layer thickness and ion concentration

The present invention relates to a method for measuring electric double layer potential, compact layer thickness and ion concentration, and more particularly to a method for measuring electric double layer potential, compact layer thickness and ion concentration using an atomic force microscope.

The development of science and technology has evolved from generation to generation. Information technology, semiconductor/microelectronics, micro-electro-mechanical systems, nanotechnology, biotechnology, energy technology, etc. have followed suit. This evolution has obviously trended toward light, thin, short, small, and advanced. The theory of micro-nanotechnology related to micro-manufacturing technology is developing very rapidly, and thus the related basic sciences deserve to be further explored, such as electroosmosis (Electroosmosis), electrophoresis (Electrophoresis), and electrowetting related to electrokinetic phenomena. (Electrowetting) and so on.

Among them, the theory of interface electric phenomenon is closely related to the electric double layer (EDL). Today, there are analytical instruments such as Scanning Electrochemical Potential Microscopy (SECPM) or Zeta Potential Analyzer. However, under different interface conditions, it is still impossible to fully explain the characteristics of the electric double layer model, such as the surface of different materials, electrolytes with different concentrations and price points. Therefore, the inventors aim to provide a simple and accurate method for measuring the electric double layer potential distribution, the tight layer thickness and the ion concentration.

The technical problem to be solved by the present invention is to provide a measuring method for easily measuring the electrical double layer potential distribution, the tight layer thickness and the ion concentration between different solid-liquid samples without complicated sample pretreatment.

In accordance with some embodiments of the present invention, a method of measuring the electric double layer potential is provided. The method comprises: using an atomic force microscope to measure the surface force of a sample located in a solution; resolving the surface force electrostatic force; converting the electrostatic force into a charge density; and converting the charge density into an electric double layer potential.

In accordance with some embodiments of the present invention, a method of measuring the thickness of a compact layer is provided. The method comprises: using an atomic force microscope to measure the surface force of the sample located in the solution; analyzing the surface force to exit the curve; and analyzing the exit curve to obtain the thickness of the tight layer.

In accordance with some embodiments of the present invention, a method of measuring ion concentration is provided. The method includes: providing an electrolyte and a sample comprising a first ion, wherein the first ion has a first concentration; adding a second ion to the electrolyte, wherein the second ion has a second concentration, and the second ion has a different price point a valence of the first ion; measuring a surface force of the sample in the electrolyte by the method described above, and converting the surface force into a potential of an electric double layer; converting the potential to the first concentration a ratio to the second concentration; and by the ratio, the first concentration of the first ion is calculated.

The following disclosure provides many different embodiments or examples to implement various features of the invention. The composition and layout of the specific examples are described below to simplify the present invention. Of course, these are only examples and are not intended to be limiting.

1 is a schematic flow diagram of a method 100 of measuring the thickness of a compact layer, the potential distribution of an electrical double layer, and the ion concentration using an atomic force microscope, in accordance with some embodiments. Additional steps may be provided before, during, and after the method 100, and some of the steps described therein may be deleted or substituted for other embodiments of the method. The schematic diagram of the configuration of the atomic force microscope and the sample used to measure the thickness of the compact layer, the potential distribution of the electric double layer, and the ion concentration is shown in Fig. 2.

Method 100 includes sample preparation (step 102), measurement of sample surface force (step 104), measurement of tight layer thickness (step 106), measurement of potential distribution (step 108), and measurement of ion concentration (step 108) Step 110). Wherein, the sample preparation comprises the following steps: chemical mechanical polishing (CMP) of the substrate; selective deposition of a passivation layer on the surface of the sample to form a portion of the sample; and surface cleaning of the sample.

A schematic diagram of the arrangement of the atomic force microscope and the sample used in the method 100 of the present disclosure is as shown in FIG. 2, and mainly includes the sample 10, the electrolyte 20, the probe 30, the laser light source 40, and the photodetector 50. The electrolyte 20 near the surface of the sample 10 forms an electrical double layer 26. The probe 30 includes a microcantilever 32 and a needle tip 34.

Referring to Figures 1 and 2, method 100 begins at step 102, which is performed prior to sample processing. Sample 10 can comprise any solid to create an electrical double layer between sample 10 and electrolyte 20. In this embodiment, the sample 10 is a gold plated wafer and a glass wafer. The pre-treatment of the sample comprises planarizing the surface of the sample, forming a passivation layer, and cleaning the surface of the sample, wherein the step of forming the passivation layer is only selectively applied to a specific sample (eg, germanium wafer), which will be described in detail later. In addition, the steps involved in the pre-treatment of the sample can be arbitrarily adjusted in order. For example, the step of forming a passivation layer can be performed before or after planarizing the sample.

The step of planarizing the surface of the sample prior to processing (step 102) of the sample provides a sample having a flat surface to enhance the accuracy of subsequent surface force measurements. The manner in which the surface of the sample is planarized includes, but is not limited to, a chemical mechanical polishing (CMP) method. In the present embodiment, the chemical mechanical polishing method is attached to the polishing pad using a polishing liquid containing an acid, a base, and abrasive grains, and the effect of flattening is achieved by the relative abrasion of the surface of the sample 10 via the polishing pad. The optimum grinding conditions can be achieved by appropriately adjusting the process parameters of the CMP, such as the downforce, the rotational speed of the carrier, the rotational speed of the disk surface, the pH of the polishing solution, the particle size of the abrasive particles, and the type of polishing pad.

The step of forming a passivation layer in the sample prior treatment (step 102) forms a passivation layer on the surface of the sample 10 to avoid substances (eg, bubbles) generated by the chemical reaction of the sample 10 with the electrolyte 20, resulting in The accuracy of the surface force measurement is reduced. In this embodiment, since the germanium wafer may chemically react with the electrolyte solution 20, a passivation layer is formed on the surface of the germanium wafer. The material of the passivation layer can be any precious metal or a non-metal that is chemically less active. In this embodiment, the material of the passivation layer is gold. The gold-plated germanium wafer is deposited on the surface of the germanium wafer by an electron beam evaporation process (EB-PVD) to form a gold plating layer (not shown). In some embodiments, a chrome plating (not labeled) is formed between the gold plating and the sample 10 to increase the adhesion of the gold plating. It is worth noting that the electron beam evaporation process (EB-PVD) for forming the passivation layer can be performed before or after the planarization process of the germanium wafer. In the present embodiment, the electron beam evaporation process (EB-PVD) is performed after the planarization of the germanium wafer.

The step of cleaning the surface of the sample in the pre-treatment (step 102) of the sample is performed after planarizing the glass wafer and vapor-depositing the gold layer on the germanium wafer to improve the accuracy of the subsequent surface force measurement. The cleaning process can be any suitable process. In the present embodiment, the cleaning process removes organic contaminants on the surface of the sample 10 by means of a UV Ozone Cleaner. The ozone and oxygen ions generated by the ultraviolet ozone scrubber can excite organic pollutants and combine them with oxygen ions to form a gas. Finally, the gas is used to remove the gas to achieve the effect of cleaning the surface.

After the sample preparation (step 102), the surface roughness of the cleaned sample 10 was examined by an Atomic Force Microscopy (AFM) and an optical image detector (JSM-2500). The gold-plated tantalum wafer after cleaning has a center line average roughness (Ra) of 1.009 nm and a maximum roughness (Ry) of 8.26 nm. The cleaned glass wafer had a center line average roughness (Ra) of 0.92 nm and a maximum roughness (Ry) of 6.05 nm. Overall, the surface roughness of sample 10 is within the range of surface forces measurable.

Referring to Figures 1 and 2, the method 100 proceeds to step 104, which measures the surface force of the sample 10. Prior to measuring the surface force, the pretreated sample 10 is placed in the electrolyte 20 such that the surface of the sample 10 has an electrical double layer 26. Electrolyte 20 can be any suitable electrolyte solution. In the present embodiment, the electrolyte 20 is a sodium chloride solution, a magnesium chloride solution, and combinations thereof. Further, the concentration of the electrolyte 20 is between 0.001 mM and 10 M. In some embodiments, the concentration of electrolyte 20 is between 0.01 mM and 1 M. In the present embodiment, the concentration of the electrolyte 20 is 1 mM. The results obtained by combining the different samples 10 and the electrolyte 20 will be compared in the subsequent measurement of the surface force measurement, the potential distribution, and the ion concentration. It is to be noted that the electrolyte 20 is an electrolyte solution containing any monovalent ion, divalent ion, trivalent ion, tetravalent ion, pentavalent ion or any combination thereof, and is not limited to the sodium chloride in the embodiment. And magnesium chloride solution.

The surface force between the sample 10 and the electrolyte 20 (step 104) is measured by atomic force microscopy (AFM). As shown in Fig. 2, the main structure of the atomic force microscope includes a probe 30, a microcantilever 32, a needle tip 34, a laser light source 40, and a photodetector 50. In the present embodiment, the probe 30 is made of tantalum nitride to avoid generation of a magnetic force with the sample 10, which will be described in detail later. The surface force is measured by the beam deflection technique, which causes the cantilever beam to be slightly displaced by the atomic force between the tip and the test piece. Next, the photodetector 50 detects the amount of deflection of the laser beam hitting the tip 34 to detect the interaction between the probe 30 and the surface of the sample 10, such as tunneling current, atomic force, magnetic force, and electromagnetic waves.

However, the data obtained by atomic force microscopy is the laser offset-distance relationship, which must be converted to surface force by force spectroscopy by the relationship between the sample surface and the probe and the probe elastic coefficient. Distance relationship, while simplifying the analysis of surface forces by setting experimental parameters. The surface force of the probe 30 measured on the surface of the sample 10 is composed of an electrostatic force, a Van der Waals force, a magnetic force, and a Solvation force. As described above, since the probe 30 is not composed of a magnetic substance, the influence of the magnetic force can be excluded. In addition, by setting the probe speed to 0.25 μm/sec, the influence of the solvent force can be removed. Therefore, the surface force measured by the probe 30 is the combination of the electrostatic force (F _el ) and the van der Waals force (F _van ). Among them, Van der Waals will be subtracted from the content described later by the appropriate formula, and only the remaining electrostatic force will be converted into potential by the subsequent mathematical equation, which will be detailed later.

After measuring the surface force of the sample 10, a measurement of the tight layer thickness (step 106), a measurement of the potential distribution (step 108), and a measurement of the ion concentration (step 110) will be performed, which will be described in detail later.

In step 106 of measuring the thickness of the compact layer, the Approach and Retraction of the combination of the different samples 10 and the electrolyte 20 are measured, respectively. As shown in Fig. 3, it shows the measured force-distance map of the glass wafer in a 1 millimolar (1 mM) sodium chloride solution. This force-distance map includes a forcing curve 302 and an exit curve 304. Wherein, the thickness of the tight layer can be calculated from the horizontal axis distance corresponding to the exit curve 304 where the gradient is extremely large (such as the dashed line 310 in FIG. 3). At the same time, the force value of the surface force can also be measured.

The reason for causing such a large gradient of the exit curve 304 is that the step can not be separated once. During the separation of the probe 30 from the surface of the sample 10, as the surface gap between the probe 30 and the sample 10 increases, the counter ion will be filled into the dense layer of the surface of the sample 10 or the probe 30, and will be closely adsorbed. The surface of sample 10 or probe 30 is such that probe 30 cannot be separated from the surface of sample 10 at one time. When the restoring force of the microcantilever 32 of the atomic force microscope is greater than the electrostatic attractive force, the probe 30 is separated from the surface of the sample 10 while causing a large gradient of the exit curve.

The stern layer thickness and force values measured for the combination of different samples 10 (gold plated wafers and glass wafers) with electrolyte 20 (sodium chloride and magnesium chloride) are shown in Table 1 below. Table 1: Variation of tight layer thickness and force value of different sample-electrolyte combinations         <TABLE border="1" borderColor="#000000" width="_0004"><TBODY><tr><td> Sample-electrolyte</td><td> Tight layer thickness (nm) </td><td > Force value change (nN) </td></tr><tr><td> Gold-plated silicon wafer-sodium chloride</td><td> 0.779 </td><td> 0.074 </td>< /tr><tr><td> Gold-plated germanium wafer-magnesium chloride</td><td> 0.784 </td><td> 0.045 </td></tr><tr><td> Glass wafer-chlorination Sodium</td><td> 0.751 </td><td> 0.134 </td></tr><tr><td> Glass wafer-magnesium chloride</td><td> 0.684 </td><td> 0.210 </td></tr></TBODY></TABLE> The tight layer thickness of the glass wafer in the sodium chloride solution is 0.751 nm, which is close to the theoretical value of 0.662 nm. On the other hand, the tight layer thickness of the glass wafer in the magnesium chloride solution is 0.684 nm, which is very close to the theoretical value of 0.632 nm. Therefore, the thickness of the tight layer can be calculated by the exit curve of the surface force.       

In addition, as can be seen from Table 1, the force value of the gold-plated germanium wafer is less than that of the glass wafer. This phenomenon is caused by the difference in Isoelectric Points (IEP) of the probe 30, the sample 10, and the electrolyte 20. The tantalum nitride used for the probe 30 has an IEP of 6; the surface of the gold-plated tantalum wafer is gold with an IEP of 7; and the IEP of the glass wafer is about 2. In an environment where the pH of the electrolyte 20 (1 mM sodium chloride and 1 mM magnesium chloride) is about 6.5, the gold-plated tantalum wafer is electrically different from the probe strip, so that an electrostatic force is absorbed. The glass wafer is electrically identical to the probe strip, so that it generates repulsive power. Since the gold-plated germanium wafer and the probe have an electrostatic force that attracts each other, the force value displayed is smaller than the force value between the glass wafer and the probe.

In step 108 of measuring the potential distribution, it converts the measured surface force into a potential distribution. In this step, the surface force is first analyzed to the electrostatic force, and the electrostatic force is converted into the charge density by a mathematical model of the electrostatic force. Finally, the charge density is converted to a potential by the 1D Poisson Boltzmann equation.

<TABLE border="1"borderColor="#000000"width="_0005"><TBODY><tr><tdwidth="267"height="0"></td></tr><tr><Td></td><td><imgwi="110"he="42"file="02_image001.jpg"img-format="jpg"></img></td></tr></TBODY></TABLE> As described above, by appropriately selecting the material of the probe 30 and the moving speed of the control probe 30, the surface force measured by the probe 30 is electrostatic force (F _el ) and Van der Waals. The combination of force (F _van ). Among them, the van der Waals force is independent of the charge density, so the surface force measured by the probe 30 is deducted from the _van der force (F _van ) in the following formula (1) to obtain the electrostatic force (F _el ), so as to facilitate The surface potential distribution curve is obtained by a mathematical model of electrostatic force and a 1D Pozmann equation. Formula (1) wherein D represents the distance between the probe 30 and the surface of the sample 10, R is the radius of the probe, and A _H is the Hammaker Constant.

<TABLE border="1"borderColor="#000000"width="_0006"><TBODY><tr><tdwidth="132"height="0"></td></tr><tr><Td></td><td><imgwi="379"he="46"file="02_image003.jpg"img-format="jpg"></img></td></tr></TBODY></TABLE> Next, after subtracting the van der Waals (Fvan), the resulting electrostatic force (Fel) is brought into the mathematical model of the electrostatic force, as shown in the following formula (2). Equation (2) where ε is the dielectric constant, ε ₀ is the vacuum dielectric constant, R is the radius of the probe, λ _D is the Debye length, σ _T is the charge density of the probe 30, and σ _S is The charge density of the surface of sample 10. By appropriately setting the value of the charge density (σ _T ) of the probe 30, the charge density (σ _S ) of the surface of the sample 10 can be obtained by Matlab software calculation under the condition of the known electrostatic force (Fel). The size. Then, the difference between the charge density (σ _T ) of the probe 30 and the charge density (σ _S ) on the surface of the sample 10 is brought into the 1D Poisson Boltzmann equation describing the relationship between potential and charge density in the space and combined with Gouy. The -Chapman model gives the potential distribution at different distances between the probe 30 and the surface of the sample 10. The 1D Possonzmann equation is as follows (3) <TABLE border="1"borderColor="#000000"width="85%"><TBODY><tr><tdwidth="251"height="0"></td></tr><tr><td></td><td><imgwi="129"he="43"file="02_image005.jpg"img-format="jpg"></Img></td></tr></TBODY></TABLE>. Wherein σ _St represents the difference between the charge density (σ _T ) of the probe 30 and the charge density (σ _S ) of the surface of the sample 10, and Ψ _St represents the potential at that point.

Please refer to FIG. 4, which is a potential distribution diagram of a combination of different samples 10 (gold plated wafers and glass wafers) and different electrolytes 20 (sodium chloride and magnesium chloride). Among them, the potential value of the gold-plated germanium wafer-magnesium chloride 414 is closer to zero than the gold-plated germanium wafer-sodium chloride 412. Similarly, the potential value of the glass wafer-magnesium chloride 404 is closer to zero than the glass wafer-sodium chloride 402. The cause of this phenomenon is the ionic strength. The density of the diffusion layer in the high ionic strength solution increases. In order to neutralize the charge of the overall system, the volume of the diffusion layer decreases, so that the potential of the diffusion layer is pushed toward the surface of the sample to cause the overall potential to decrease. Since the ionic strength of magnesium chloride is higher than the ionic strength of sodium chloride, the electric double layer potential formed by the magnesium chloride electrolyte is more compressed than sodium chloride.

At the same time, the present invention proves the potential distribution obtained by the surface force by the Poisson Boltzman (PB) equation and the modified Poisson Boltzman (MPB) equation. rationality. Among them, the PB equation is suitable for the potential distribution prediction of low-concentration monovalent electrolyte, while MPB is suitable for the potential distribution prediction of multivalent electrolyte. The results show that the potential distribution of surface force-converted 1 mM sodium chloride is consistent with the potential distribution obtained by the PB equation in the length of the Debye (about 10 nm). On the other hand, the surface force conversion of 1 mM magnesium chloride is consistent with the potential distribution obtained by the MPB equation. Therefore, the surface force obtained by the AFM is converted into a potential distribution close to the theoretical value and can be used as an actual measurement.

In addition, in combination with the foregoing steps, the thickness of the compact layer (step 106) and the potential distribution value described above are obtained, and the Zeta-Potential is obtained. The combination of the different sample 10 and the electrolyte 20 measured in this embodiment is as follows. Shown. Table 2: The boundary potential of different substrates and liquids         <TABLE border="1" borderColor="#000000" width="_0007"><TBODY><tr><td> Substrate</td><td> Sodium Chloride</td><td> Magnesium Chloride</td ></tr><tr><td> gold-plated germanium wafers</td><td> -33 mV </td><td> -10 mV </td></tr><tr><td> glass Wafer</td><td> 23 mV </td><td> 8 mV </td></tr></TBODY></TABLE>

<TABLE border="1" borderColor="#000000" width="_0008"><TBODY><tr><td width="213" height="0"></td></tr><tr>< Td></td><td><img wi="217" he="45" file="02_image007.jpg" img-format="jpg"></img></td></tr></ TBODY></TABLE> is in the step 110 of measuring the ion concentration, which calculates the ion concentration ratio by mathematically calculating the potential measured in the foregoing. Next, the ion concentration is calculated from the ion concentration ratio. This mathematical equation is a New Poisson Boltzman (NPB) equation and can represent the relationship between the potential and the concentration of the first ion and the second ion. The equation is as shown in the following formula (4). Equation (4) where t represents the boundary potential, c represents the internal potential, and β1 and β2 represent the concentrations of the first ion and the second ion, respectively.       

According to the present invention, after the measurement of the potential distribution, the ratio of the first ion to the second ion is derived by adding the second ion to the electrolyte containing the first ion in the potential measurement, and the ratio of the first ion to the second ion is derived by the NPB equation. Knowing the addition of the second ion concentration, an unknown first ion concentration is calculated. It is to be noted that the first ion and the second ion are ions of different valences (for example, one, two, three, four, five, six, seven valences) or ions of different valences, respectively, and are not limited to the present invention. One of the sodium ions and the divalent magnesium ions are measured. For example, when the first ion is calcium ion, the second ion may be a non-divalent ion such as sodium ion or aluminum ion. Or when the first ion is a combination of sodium ions and calcium ions, the second ion may be a non-monovalent or divalent ion such as an aluminum ion. That is to say, when the ion concentration of a certain valence in the electrolyte is known, the ion concentration of other valences can be obtained by the above NPB equation. In some embodiments, the electrolyte 20 used is sodium chloride and magnesium chloride in the aforementioned force measurement and potential distribution calculations. Therefore, in step 110, a known concentration of magnesium chloride and sodium chloride is added to the magnesium chloride electrolyte and the sodium chloride electrolyte.

In the present embodiment, the sample 10 is selected as a gold-plated germanium wafer, and the sodium and magnesium ion ratios of the electrolyte are preset to compare the accuracy of the sodium and magnesium ion ratios calculated by the NPB equation. Please refer to FIG. 5, which shows the potential distribution of the gold-plated germanium wafer in the electrolyte with different ratios of sodium to magnesium ions. Among them, the electrolytes 502, 504, 506, 508, 510, and 512 have sodium to magnesium ion ratios of 1, 3, 2, 1.33, 4, and 0.6, respectively. The potential distribution under various electrolytes will increase as the ionic strength increases, and the potential value will be closer to zero. Causes As mentioned above, a high ionic strength solution (i.e., a multi-valent or high concentration solution) compresses the potential distribution of its electric double layer. However, the electrolyte 510 (and the sodium to magnesium ion ratio of 4) does not conform to this phenomenon. The reason is that when the value of sodium and magnesium ions reaches 4, a significant volume effect (Steric effect) is generated, which causes an extra force between the ions, and the potential distribution curve obtained by the surface force does not conform to the above phenomenon. .

Please refer to Table 3 below, which is the result of converting the potential distribution of gold-plated germanium wafers in different sodium-magnesium ions to the concentration of sodium-magnesium ions by the NPB equation. Table 3: Configured sodium/magnesium ion ratio and calculated sodium/magnesium ion ratio         <TABLE border="1" borderColor="#000000" width="_0009"><TBODY><tr><td> Sodium Chloride (mM) </td><td> Magnesium Chloride (mM) </td>< Td> Configured sodium/magnesium ion ratio</td><td> Calculated sodium/magnesium ion ratio</td></tr><tr><td> 0.8 </td><td> 0.8 </td> <td> 1 </td><td> 0.973 </td></tr><tr><td> 1.5 </td><td> 0.75 </td><td> 2 </td><td> 1.997 </td></tr><tr><td> 2.7 </td><td> 0.9 </td><td> 3 </td><td> 3.004 </td></tr><tr ><td> 2 </td><td> 0.5 </td><td> 4 </td><td> 3.68 </td></tr><tr><td> 4 </td><td > 3 </td><td> 1.33 </td><td> 1.312 </td></tr><tr><td> 3 </td><td> 5 </td><td> 0.6 < /td><td> 0.626 </td></tr></TBODY></TABLE> can be seen from Table 3, except for electrolytes with a sodium to magnesium ion ratio of 4, different ratios of sodium to magnesium ions (1, 2, 3) The ratio of sodium to magnesium ions calculated under 1.33 and 0.6) can represent the ratio of sodium to magnesium ions in the mixed solution, and the relative error value is mostly less than 5%.       

Further, when the ion concentration ratio is calculated using the formula (4), a more precise ion concentration ratio can be obtained by appropriate parameter replacement. The potential from any distance from the surface of the sample 10 can be known from the potential distribution curve (as shown in Fig. 5). The boundary potential at the thickness of the compact layer is set to t', and the potential at the lowest potential of the set potential curve is the internal potential c'. Further, the coefficient a is set to correct the boundary potential and the internal potential, and the correction is as shown in the following formula (5). t=t'-a c=c'-a Equation (5) By the appropriate selection coefficient a, the corrected internal potential c is close to zero. Next, the corrected boundary potential t and the internal potential c are brought into the above NPB equation to obtain an ion concentration ratio, and the results are shown in Table 3.

In summary, the present disclosure provides a method of measuring compact layer thickness, electric double layer potential, and ion concentration. Through the method of the invention, only a simple sample preparation is required, and then the surface force of the sample is measured by an atomic force microscope, and after the mathematical equation is converted, the compact layer thickness, the electric double layer potential and the ion concentration can be measured. . Among them, the compact layer thickness is calculated by the exit curve in the force spectrum mode in the atomic force microscope. The electric double layer potential is obtained by analyzing the measured surface force by a mathematical model of electrostatic force, 1D Poisson Boltzmann equation and Gouy-Chapman model. The ion concentration is obtained by calculating the ion concentration ratio by the new Boltzmann equation. It is worth noting that the measurement of ion concentration can be applied to various electrolytes with ions at different valences. For example, in an electrolyte containing a valence ion of unknown concentration, the concentration of monovalent ions can be determined by the method of the present disclosure by adding a known concentration of divalent ions, and vice versa.

It is worth noting that the present invention can be considered as an additional function of an atomic force microscope (AFM) without the need to modify or add new devices. The surface force measured by the atomic force microscope can be converted into a compact layer thickness, an electric double layer potential and an ion concentration according to the conversion method of the present disclosure only after a simple sample preparation.

The present invention has been described in the above embodiments and embodiments, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims. Exemplary embodiments embodying the features and advantages of the present invention are described in detail in the above description. It is to be understood that the invention is capable of various modifications in the various embodiments of the invention invention.

10‧‧‧ samples
20‧‧‧ Electrolytes
26‧‧‧Electric double layer
30‧‧‧ probe
32‧‧‧Micro cantilever
34‧‧‧ needle tip
40‧‧‧Laser light source
50‧‧‧Photodetector
100‧‧‧ method
102, 104, 106, 108, 110‧ ‧ steps
302‧‧‧ Approximation curve
304‧‧‧ exit curve
402‧‧‧Glass wafer - sodium chloride
404‧‧‧Glass wafer - magnesium chloride
412‧‧‧ Gold Plated Wafer - Sodium Chloride
414‧‧‧ Gold Plated Wafer - Magnesium Chloride
502, 504, 506, 508, 510, 512‧‧‧ electrolyte

Aspects of the present invention are fully understood from the following detailed description. It is worth noting that, according to industry standard practices, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or decreased for clarity of discussion. 1 is a schematic flow diagram of a method of measuring the thickness of a compact layer, the potential distribution of an electric double layer, and the ion concentration using an atomic force microscope, in accordance with some embodiments. 2 is a schematic diagram of an atomic force microscope and sample configuration for measuring the thickness of a compact layer, the potential distribution of an electric double layer, and the ion concentration, in accordance with some embodiments. Figure 3 illustrates an approximation curve and an exit curve for the force measured by an atomic force microscope, in accordance with some embodiments. Figure 4 is a graph showing the potential distribution of various samples in combination with an electrolyte, in accordance with some embodiments. Figure 5 is a plot of the potential profile of an electrolyte having various sodium to magnesium ion ratios, in accordance with some embodiments.

10‧‧‧ samples

20‧‧‧ Electrolytes

26‧‧‧Electric double layer

30‧‧‧ probe

32‧‧‧Micro cantilever

34‧‧‧ needle tip

40‧‧‧Laser light source

50‧‧‧Photodetector

Claims (10)

A method for measuring electric double layer potential comprises: using an atomic force microscope to measure a surface force of a sample located in a solution; analyzing the surface force to obtain an electrostatic force; converting the electrostatic force into a charge density; And converting the charge density to a potential of an electric double layer. The method of claim 1, wherein the electrostatic force is converted into the charge density by a mathematical model of an electrostatic force, and the electrostatic force is converted to the charge density, wherein the mathematical model of the electrostatic force is: Where ε is the dielectric constant, ε ₀ is the vacuum dielectric constant, R is the radius of the probe of the atomic force microscope, λ _D is the Debye length, σ _{T is} the charge density of the probe of the atomic force microscope, σ _S is the charge density of the surface of the sample. The method of claim 1, wherein converting the charge density to the electric double layer is performed by a 1D Poisson Boltzmann equation combined with a Gouy-Chapman model to convert the charge density For this potential. A method for measuring the thickness of a compact layer, comprising: measuring a surface force of a sample in a solution by using an atomic force microscope; analyzing an exit curve of the surface force; and analyzing the exit curve to obtain a tight layer thickness. The method of claim 4, wherein parsing the exit curve to obtain a thickness of one of the compact layers is to calculate a horizontal distance corresponding to a portion of the exit curve whose gradient of variation is extremely large. The method of claim 4, further comprising calculating the electrical double by combining the thickness of the compact layer with the potential of the electrical double layer obtained by the method of any one of claim 1 to claim 3. One of the layers is the zeta potential. A method for measuring an ion concentration, comprising: providing an electrolyte comprising a first ion and a sample, wherein the first ion has a first concentration; and adding a second ion to the electrolyte, wherein the second ion Having a second concentration, and the price of the second ion is different from the price of the first ion; measuring one of the samples in the electrolyte by the method of any one of claim 1 to claim 3 Surface force, and converting the surface force into a potential of an electric double layer; converting the potential into a ratio of the first concentration to the second concentration; and calculating the first ion by the ratio The first concentration. The method of claim 7, wherein the first ion comprises a monovalent ion, a divalent ion, or a combination thereof. The method of claim 7, wherein the second ion comprises a monovalent ion, a divalent ion, or a combination thereof. The method of claim 7, wherein the potential is converted to a ratio of the first concentration to the second concentration by a new Bozeman (New Poisson Boltzman, NPB) equation, which is converted to this ratio.