techology » chemical

Atomic Force Microscopy

techicien — Sun, 28 Feb 2010 15:45:09 +0000

DESCRIPTION OF TECHNIQUE

Atomic force microscopy (AFM) is a form of scanning probe microscopy (SPM), where a small probe is scanned across the sample to obtain information on the sample surface. The information gathered by the interaction of the probe with the surface can be as simple as physical topography or other material such as measurements of physical, magnetic, or chemical properties. These data are collected as the probe is scanned in a raster pattern through the sample to form a map of the property measured from the XY position. Thus, the AFM microscope image shows the change in the property measured, for example. height or magnetic domains, over the image area.

The AFM probe tip has a very sharp, often less than 100 in diameter, at the end of a small cantilever beam. The probe is connected to a piezoelectric tube scanner, which scans the probe in a selected area of the surface of the sample. Interatomic forces between the probe tip and the sample surface cause the cantilever to deflect the topography of the sample surface (or other property) changes. A laser light reflected from the back of the cantilever measures the deflection of the cantilever. This information is sent back to a computer, which generates a map of topography and / or other properties of interest. All square as large as about 100 ìm square less than 100 nm can be resumed.

INFORMATION ANALYSIS

Modes of contact AFM – The AFM probe is scanned at a constant force between the probe and the sample surface to obtain a 3D topographical map. When the probe cantilever is deflected by topographic changes, the scanner changes the position of the probe to restore the original cantilever deflection. The location information of the scanner is used to create a topographic image. Lateral resolution of <1 style = “font-weight: bold;”> intermittent contact (tapping mode) AFM – In this mode, the cantilever probe is oscillated or at its resonant frequency. The oscillating probe tip is then scanned at a height where it barely touches or “taps” the surface of the sample. The system monitors the position of the probe and the amplitude of oscillation to obtain information on topographic properties and others. Precise topographic information can be obtained even for very delicate surfaces. Optimum resolution is about 50 Å lateral and <1 style = “font-weight: bold;”> Lateral Force Microscopy – This method of measuring the lateral deviation of the cantilever probe tip is scanned across the sample in contact mode. Changes in lateral bending forces are on the friction between the probe tip and the sample surface.

Detection phase microscopy with the operating system in tapping mode, the cantilever oscillation is damped by the interaction with the sample surface. The phase delay between the signal units and actual cantilever oscillation is monitored. Changes in the phase lag indicate variations in surface properties such as viscoelasticity or mechanical. Image phase, typically collected simultaneously with a topographic image, maps the local changes in physical properties and mechanical properties of the material.

Magnetic Force Microscopy – this image to local variations in the magnetic forces on the sample surface. The tip of the probe is coated with a thin film of ferromagnetic material that reacts to magnetic domains on the surface of the sample. The magnetic forces between the tip and the sample are measured by monitoring the cantilever deflection, while the probe is scanned at a constant height above the surface. A map showing the sample natural forces or applied magnetic domain structure.

Image analysis – Since the images are collected in digital format, a wide range of image manipulation are available for the AFM data. Quantitative topographic information, such as the lateral spacing, step height and the roughness of the surface are readily obtained. Images can be presented as two-dimensional or three-dimensional representations on paper or as digital image files for electronic transfer and publication.

Nanoindentation – A tip of the probe is forced specializes in the sample surface to obtain a measure of the mechanical properties of the material in areas as small as a few nanometers. (See Manual nanoindentation hardness tests.)

TYPICAL APPLICATIONS

* 3-dimensional topography of IC device
* Measures of roughness for the chemical mechanical polishing
* Analysis of the distribution phase microscopic polymer
* Measures of physical and mechanical properties of thin films
* Imaging magnetic domains on digital storage media
* Pictures of the phases of submicron in metals
* Imaging defect in IC failure analysis
* Microscope images of biological samples fragile
* Metrology Stampers compact disk

SAMPLE REQUIREMENTS

No sample preparation is usually necessary. Samples can be taken up in the air or liquid. Sample height is limited to about 1.5 inches. Areas up to 8 inches in diameter can be completely crossed without repositioning. Larger samples may be automatic for imaging in a limited area. Roughness of the surface total image area should not exceed about 6 microns.

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Biocatalyst introduction

techicien — Sun, 28 Feb 2010 07:16:34 +0000

Over the past 20 years, many reservations have been expressed with respect to catalysis, arguing that: (i) enzymes only feature limited substrate specificity, (ii) there is only limited availability of enzymes, (iii) only a limited number of enzymes are enzymes; yield (iv) the stability of catalytic proteins is limited, (v) enzymatic reactions have limited space-time, and (vi) require complicated cosubstrates as cofactors.

Following the discovery of many new enzymes by recombinant DNA technology, which allows both the production more efficient and focused combinatorial or alteration of individual enzymes, and the process of development towards greater stability and volumetric productivity, routes of synthesis in which one or all of the steps are biocatalytic have advanced dramatically in recent years. Design rules for improving biocatalysts are increasingly precise and easy to use.

Biocatalysts are not operating from different scientific principles from organic catalysts. The existence of a multitude of patterns of enzymes as catalysts oligopeptidic or polypeptide shows that the entire action of enzymes can be explained by rational chemical and physical principles. However, enzymes can create unusual reaction conditions and higher pKa values as low or a high positive potential for a redox metal ion. Enzymes were always found in almost all catalyze reactions in organic chemistry.

Biotechnology and biocatalysis differ from conventional processes, not only with a different type of catalyst, they also constitute a basis of new technologies. The basic raw material of a biological process is built based on sugar, lignin, animal or plant waste in the field of biotechnology, such as unit operations membrane processes, chromatography, biocatalysis or predominate, and the range of products biotechnological processes often includes chiral molecules or biopolymers such as proteins, nucleic acids or carbohydrates.

Cost and margin pressure from competitors less expensive and cooperation with emphasis on a clean surface (or less polluted), the environment are two important developments. Less preparation, with higher yields at every step, lower costs of materials and energy, and less waste targets. Biotechnology and biocatalysis often offer options unique technology and solutions, they act as enabling technologies, in other cases, biocatalysis is to outperform competing technologies to gain access. In the field of pharmaceutical drugs, the reason this unit for the enantiomeric purity is that the vast majority of new drug targets are chiral biocatalysis as promoting the technology with the best performance of selectivity.

Biocatalytic processes to penetrate more and more the chemical industry. In a recent study, 134 industrial-scale biotransformations, on a scale of> 100 kg with whole cells or enzymes from a precursor other than a C-source, were analyzed. Hydrolase (44%), followed by oxido-reductase (30%), dominate the industrial biocatalytic applications. Data on the average performance of fine chemicals (non-pharmaceutical) applications were made 78%, a concentration of 108 g of the final product of L and a volumetric productivity of 372 g (L • D)

Applications of Biocatalysis in Industry

Chemical Industry of the Future: Manufacturing environmentally benign, green chemistry, sustainable development in the future

Because of two very strong and important driving forces of the chemical industry of the future will be very different from today’s version:

* Cost and margin pressure of competition in an increasingly open market-oriented economy, and
* Operation of the sector in a social framework that places emphasis on a clean (or cleaner) environment

Treatment with the intent of this new set of conditions focuses on the development of production chains with fewer stages of processing, with higher yields at every step, to save material and energy costs. Less waste is generated, and the treatment and disposal fall. Both the pressures encountered in the case of environmental compliance costs.

In many cases, such as the high-fructose corn syrup, or biotechnology and biocatalysis technologies offer options and solutions that are not available through any other technology, in such situations, such as acrylamide, nicotinamide or intermediates for antibiotics , biotechnology and biocatalysis act as “enabling technologies”. In the remaining situations, biotechnology and biocatalysis offer a solution among others, who all must be evaluated according to criteria developed in Chapter 2: product yield, selectivity, productivity, (bio) catalyst stability, and space-time-performance .

In this context, the three terms in the title are largely synonymous, however, that have been developed in a slightly different context:

* Production is a movement toward environmentally-friendly production systems that are both economically and environmentally sound manner;
* Sustainable development is a worldwide movement and the chemical industry represents a set of guidelines on how to manage resources so that no sources are minimized as much as possible;
* Green Chemistry is the design of chemical products and processes to reduce or eliminate the use and production of hazardous substances.

“Green Chemistry is a comprehensive approach that applies to all aspects of chemistry” (Anastas, 2002). Methods of green chemistry can be viewed through the framework of the “Twelve Principles of Green Chemistry (Anastas, 1998):

1. It ‘better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the integration of all
3. materials used in the production process of the final product. As far as practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4. The chemicals must be designed to preserve the effectiveness of the function by reducing the toxicity.
5. The use of auxiliary substances (eg solvents, separation agents, etc.) should be made unnecessary wherever possible and should be harmless if used.
6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperatures and pressures.
7. A raw material or feedstock should be renewable rather than depleting wherever technically and economically feasible.
8. Unnecessary derivatization (blocking group, protection / deprotection, temporary modification of physical / chemical processes) should be avoided wherever possible.
9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10. The chemicals must be designed so that at the end of their function will not persist in the environment and break down into innocuous degradation products.
11. Analytical methods must be further developed to allow real-time, in a process of monitoring and control prior to the formation of hazardous substances.
12. Substances and the form of a substance used in a chemical process should be chosen so as to minimize the risk of chemical accidents, including releases, explosions and fires.

Catalysis offers numerous advantages for the achievement of green chemistry: novel, high-efficiency, shortest paths process, greater selectivity and low temperatures and pressures. Biocatalysis combines the goals of all three issues mentioned above. Biocatalysts, as well as many raw materials, especially to heat, in turn, are completely renewable and for the most part, do not pose any harm to humans or animals. By reducing temperatures and high pressures and large consumption of metals and organic solvents, waste production per unit of product is drastically reduced.