Nanoparticles Characterization Using AFM


        Nanoparticles, a unique subset of the broad field of nanotechnology, include any type of particle with at least one dimension of less than 500 nanometers. Nanoparticles play an important role in a wide variety of fields including advanced materials, pharmaceuticals, and environmental detection and monitoring.
        The atomic force microscope (AFM) is ideally suited for characterizing nanoparticles. It offers the capability of 3D visualization and both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Statistical information, including size, surface area, and volume distributions, can be determined as well. A wide range of particle sizes can be characterized in the same scan, from 1 nanometer to 8 micrometers. In addition, the AFM can characterize nanoparticles in multiple mediums including ambient air, controlled environments, and even liquid dispersions.
        While nanoparticles are important in a diverse set of fields, they can generally be classified as one of two types: engineered or nonengineered. Engineered nanoparticles are intentionally designed and created with physical properties tailored to meet the needs of specific applications. They can be end products in and of themselves, as in the case of quantum dots or pharmaceutical drugs, or they can be components later incorporated into separate end products, such as carbon black in rubber products. Either way, the particle’s physical properties are extremely important to their performance and the performance of any product into which they are ultimately incorporated.
         Nonengineered nanoparticles, on the other hand, are unintentionally generated or naturally produced, such as atmospheric nanoparticles created during combustion. With nonengineered nanoparticles, physical properties also play an important role as they determine whether or not ill effects will occur as a result of the presence of these particles. Depending on the application of interest, nanoparticles may be known by a number of alternative and trade-specific names, including particulate matter, aerosols, colloids, nanocomposites, nanopowders, and nanoceramics.

Qualitative Analysis
         Using the AFM, individual particles and groups of particles can be resolved. Microscope images are essential in research and development projects and can be critical when troubleshooting quality control issues. The AFM offers visualization in three dimensions. Resolution in the vertical, or Z, axis is limited by the vibration environment of the instrument: whereas resolution in the horizontal, or X-Y, axis is limited by the diameter of tip utilized for scanning. Typically, AFM instruments have vertical resolutions of less than 0.1 nm and X-Y resolutions of around 1 nm. In material sensing mode, the AFM can distinguish between different materials, providing spatial distribution information on composite materials with otherwise uninformative topographies.
Quantitative Analysis

        Software-based image processing of AFM data can generate quantitative information from individual nanoparticles and between groups of nanoparticles. For individual particles, size information (length, width, and height) and other physical properties (such as morphology and surface texture) can be measured. Statistics on groups of particles can also be measured through image analysis and data processing. Commonly desired ensemble statistics include particle counts, particle size distribution, surface area distribution and volume distribution. With knowledge of the material density, mass distribution can be easily calculated. Whenever data from single-particle techniques is processed to provide statistical information, the concern over statistical significance exists. It is easy to attain greater statistical significance in AFM by combining data from multiple scans to obtain information on the larger population.
Experimental Media

         AFM can be performed in liquid or gas mediums. This capability can be very advantageous for nanoparticle characterization. For example, with combustion-generated nanoparticles, major component of the particles are volatile components that are only present in ambient conditions. Dry particles can be scanned in both ambient air and in controlled environments, such as nitrogen or argon gas. Liquid dispersions of particles can also be scanned, provided the dispersant is not corrosive to the probe tip and can be anchored to the substrate. Particles dispersed in a solid matrix can also be analyzed by topographical or material sensing scans of cross-sections of the composite material. Such a technique is useful for investigating spatial nanocomposites.

In many industries, the ability to scan from the nanometer range into the micron range is important. With AFM, particles anywhere from 1nm to 5μm in height can be measured in a single scan. It is important to note that AFM scanning is done with a physical probe in either direct contact or near contact. Therefore, particles must be anchored to the sample surface during the scan. Multiple scans can be performed, however, to provide greater statistical accuracy.
Sample Preparation for AFM Nanoparticle Characterization
       Nanoparticles typically fall into one of two categories when it comes to sample preparation. The first category is nanoparticles rigidly attached to a solid structure. The second category is nanoparticles with weak adhesion to the substrate, such as dispersions of nanoparticles in liquid or dry mediums. A good example of the first category is nanoparticles imbedded a solid matrix, as in the case of nanocomposites or nanoprecipitates3. In such cases, typically a cross-section of the composite material is scanned to determine such properties as average particle size and spatial distribution.
Examples of nanoparticles in the second category are quantum dots, diesel soot particles, carbon black, and colloidal suspensions.4 Sample preparation for the second category of nanoparticles involves the stable attachment of particles onto the substrate. Because the AFM works by scanning a mechanical probe across the sample surface, any structure being imaged must have greater affinity to the flat surface than to probe tip. When nanoparticles do accidentally attach to the probe, the resulting images typically show reduced resolution. Streaking will occur in the images if nanoparticles are not rigidly attached to the flat surface while scanning in contact mode. To avoid such artifacts, close contact mode (near contact) or CFM (crystal sensing) is strongly recommended for such samples.
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Be Systematic, and You’ll Find the Red Line across Your Physics Problems


        We should know that learning productivity is not marked as achieved value. But, the true meaning is put on ourselves that we can say as thinking satisfaction. Have you ever questioned yourself about your achievement, does it impress you? Or does it represent your competence? Sometimes we just neglect it by said “whatever, but I got a good mark”, short sentence that can shut up the rebellion inside our mind.

Successful learning or productive learning can be obtained when we’re able to transfer our knowledge to the others, by meaning of self-understanding about the subject we learned. In education world, the term of evaluation is introduced, both as test and quiz or other assignment. Evaluation becomes transfer medium of information and knowledge from student to teacher. How much understanding that student have, will be evaluated by teacher via general examination, with the mark of 60, 75, 90, 100, or A, B, C, D as quantitative benchmark that shows final result.
As succinctly described above, we know that the key of evaluation process is how to transfer our knowledge with objective appraisal. It is simply said that student who answer the question systematically will be highly regarded than the student who answer the question practically.
        Talking about systematic thinking, we should also do the same thing in order to learn Physics. In Physics, there are a lot of problems describing natural phenomenon and its circumstances that must be solved. Sometimes we feel dizzy, what kind of equation we should put off, or generally how we can solve them.  Basically, if we think systematically and write down the problem systematically, we will be able to find the answers at least we can transfer the problem we face on to the reader. That’s why the systematic answer in Physics problem has advantages both the answerer and the reader.
Here, the steps are:

* Given                         : (Attaching all data provide in problem set).
* Find                            : (Re-writing the main question)
* Schematic                  : (Illustrating the problem into sketch/diagram physics)
* Assumptions             : (Writing down the problem circumstances)
* Solution:
       – Basic theories      : (Showing up all theories used in solving problem)
       – Analysis               : (Corresponding the data, main question, diagram physic, and problem circumstances with basic theories to find out the solution)
       – Comments           : (Giving some notes to the answer)
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A Basic Chemical Reaction, REDOX


     化学反応(かがくはんのう)とは、原子間の結合の生成、あるいは切断によって異なる物質を生成する変化のことであるAny chemical reaction in which the oxidation numbers (oxidation states) of the atoms are changed is an oxidation – reduction reaction. Such reactions are also known as redox reactions, which is shorthand for reduction-oxidation reactions.
Oxidation and Reduction
Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number. Usually the change in oxidation number is associated with a gain or loss of electrons, but there are some redox reactions (e.g., covalent bonding) that do not involve electron transfer. Depending on the chemical reaction, oxidation and reduction may involve any of the following for a given atom, ion, or molecule:

·         Oxidation – involves the loss of electrons or hydrogen OR gain of oxygen OR increase in oxidation state
·         Reduction – involves the gain of electrons or hydrogen OR loss of oxygen OR decrease in oxidation state
Reactions involving oxidation and reduction processes are very important in our everyday world. They make batteries work and cause metal to corrode (or help to prevent their corrosion). They enable us to obtain heat by burning fuels–in factories and in our bodies.
Many redox reactions are complex. However, combustion and synthesis (from elements) are two ordinary examples which require very little description. Just a little more involved is the displacement reactions. These processes are divided into three categories: hydrogen displacement, metal displacement, halogen displacement.
Example of an Oxidation Reduction Reaction
The reaction between hydrogen and fluorine is an example of an oxidation-reduction reaction:
H2 + F2 → 2 HF
The overall reaction may be written as two half-reactions:
H2 → 2 H+ + 2 e (the oxidation reaction)
F2 + 2 e → 2 F (the reduction reaction)
There is no net change in charge in a redox reaction so the excess electrons in the oxidation reaction must equal the number of electrons consumed by the reduction reaction. The ions combine to form hydrogen fluoride:
H2 + F2 → 2 H+ + 2 F → 2 HF
Importance of Redox Reactions
Oxidation-reduction reactions are vital for biochemical reactions and industrial processes. The electron transfer system in cells and oxidation of glucose in the human body are examples of redox reactions. Redox reactions are used to reduce ores to obtain metals, to produce electrochemical cells, to convert ammonia into nitric acid for fertilizers, and to coat compact discs.
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Infrared Thermal Imaging: See The Unseen


       Infrared thermography also called infrared thermal imaging uses thermal imagers or Infrared imaging cameras. This technique is widely used in many application fields, such as analyzing component stress in PCB, surveillance affairs, monitoring body temperature etc. Infrared thermal imaging becomes effective method as monitoring tool since every matter radiates thermal energy. In bioengineering application, this method can be used to monitor the temperature distribution of human body in hyperthermia treatment. By monitoring, the researcher can control heat distribution to specific localization in disease area.
The Spectrum
       When the sun goes down and the other sources of illumination are removed, there is no light to be reflected and most mammals, especially, cannot see anything. The unaided human eye cannot see infrared radiation, but the radiation is always present. It is heat or thermal radiation in a portion of the Electromagnetic (EM) spectrum to which our eyes do not respond. Our bodies respond to infrared, if it is intense enough, by feeling warmed, or sometimes, cooled.
       The illustration above depicts the EM spectrum ordered in terms of wavelength given in centimeters. There are 100 centimeters in one meter and 10,000 microns in one centimeter. (Most of the terminology used in infrared imaging discusses wavelength in units of micrometers, also called microns). Also shown are the common names given to the different portions of the spectrum.
        The IR or infrared portion occupies roughly the region between 10 to the minus 4 to 10 to the minus 3 centimeters, or, from about 1 micron to about 100 microns. But most commercial equipment comes designed to operate in portions of the region, for a number of reasons (lower atmospheric absorption of IR radiation -or IR “atmospheric windows”, detector availability at reasonable cost). Commercial IR thermography equipment comes in in the following wavelength bands and their filtered sub-bands. Common jargon follows approximately the terminology listed below:
·         The Near IR region and band is from about 0.7 to 1.7 microns,
·         The short wave or SW band is from about 1.8 to 2.4 microns,
·         The medium wave or MW band is from about 2.4 to 5 microns, and the
·         Long wave or LW band is from about 8 to 14 microns.
       The two principle properties of this radiation are:
1. All types travel at the speed of light in a vacuum, although they may differ in speed or not travel at all through or in some materials and,
2. Their physical interactions with various materials can be described mathematically in terms of transverse (electromagnetic) waves (TEM) or, in many cases as uncharged particles each particle having an energy of h*(nu), where (nu) is the frequency and h is a constant number known as Planck’s constant (its value differs slightly with the unit system used, but in the International System of Units (System International or SI units) it is: 6.6260693 x E-34 Joule seconds (E-34 is 10 to the -34th power or 1/1,000,000,000,000,000,000,000,000,000,000,000).
       Every object at temperatures above Absolute Zero (0 K or -273.15 °C) emits thermal radiation, much in the infrared portion of the EM spectrum. Many objects that are very hot emit thermal radiation that is in the visible and even the ultraviolet portion of the EM spectrum as well as the infrared, e.g. an incandescent light bulb or our local star that we call the Sun. See the hand-sketched graph below of thermal radiation intensity versus wavelength from several objects including the Sun; note the range of visible wavelengths. Note, too, that here the units of wavelength are in nanometers; 1000 nanometers = 1 micrometer (micron). That is a common variant found in physics courses.
       What is invisible to humans, particularly when only thermal infrared is present, can be “seen” by a thermal imager, or more precisely, a thermal imaging camera, especially at night. It works in daylight, too, and one can easily see the surprising differences in appearance of any object from emitted thermal “light” to reflected visible light. The shape will be the same but the brightness distribution and shadows look very different even in black and white and more pronounced when viewed in false colors.
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Faraday’s Law of Induction and The Correlation between Biot-Savart Concept


        Faraday’s Law and Biot-Savart equation become 2 basic concepts respectively in designing electric generator or magnetic generator that have been used in many application field, for example, producing electric power by power generator to supply town’s electricity or especially producing high frequency AC magnetic field to cause heat loss in super paramagnetic magnetic nanoparticle for hyperthermia treatment. We’ve already learned about the Biot-Savart’s equation that simply said if the magnetic field can be produced along wire carrying an electric current. Now, Faraday’s concept tells reversely.
          Any change of magnetic environment in a coil of a wire will cause a voltage (Electromotive Force: EMF) to be induced in the coil. No matter the change is produced, the voltage will be generated. The change could be produced by changing  the magnetic field strength, moving magnet toward or away from  the coil, moving the coil into or out the magnetic field, rotating the coil relative to the magnet, etc.

         Faraday’s law is fundamental relationship which comes from Maxwell’s equation. It serves as a succinct summary of the ways a voltage (or EMF) may be generated by changing magnetic environment. The induced EMF in a coil is equal to the negative of the rate of change in magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

          Understanding Faraday’s law requires understanding the concept of magnetic flux. The magnetic flux is a way of measuring the total amount of magnetic field over a surface or a surface area. An example might be the area of the coil of wire in the above experiments. If the magnetic field direction is perpendicular to the surface, then the magnetic flux is the magnetic field multiplied by the surface area. If the magnetic field is not perpendicular, then this product must also be multiplied by the cosine of the angle between the magnetic field direction and the outward pointing line perpendicular to the surface. This line perpendicular to the surface is called the normal.

じゃあ、Faraday’s Law のことが分かてしまいましたか。

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