Файл: М.М. Герасимцева Тексты для аудиторного и внеаудиторного чтения (Английский язык).pdf

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Several recent studies have been devoted to the synthesis of conjugated ω-amino ketones containing a heterocyclic fragment, which influences appreciably the physicochemical properties of these compounds.

4. Say in English:

Фундаментальная теоретическая проблема, донор, акцептор, химические преобразования, метил-кетон, модификация β-аминовинил кетона, соли лития, активная метиловая группа, метиленовый элемент, как правило, обычные методы, полиметиленовая цепь, карбонильная группа, физико-химические свойства.

5.Answer the following questions:

What is the gist of fundamental theoretical problems?

What do traditional methods for the synthesis of β-aminovinyl ketones consist of?

What is the difference between the NMC2 and CO groups?

Do these compounds exhibit unusual spectral luminescence properties? Where are alkoxy ketones used with amines and methyl ketones with ω-

amino ketones?

What influences the heterocyclic fragment?

2. Guess the meaning of the following words:

Microscope, conductor, an injector, scanning tunnel design, physics, chemistry, object, modification, digital video disks, model base, lenses,

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microelectronic chemistry, vacuum, to examine, service system, atom-power microscope, varieties of graphite, semiconductors, voltage, tunnel microscopes, gene engineering, orthodox.

MICROSCOPE SCANS ATOM

Using a regular optical microscope, we can inspect objects down to 0.25 mm in size, while its electronic counterpart allows us to make out details equal to 0.1 nanometers (nm), with nanometer being a billionth part of a meter. Hence a new trend in science - nanotechnology, which caters to a range of disciplines from molecular technology and gene engineering to solid-state physics, electrochemistry and microelectronics. Since here one deals with magnitudes on the scale of molecules and atoms, microscopes with much higher resolving power become necessary. Orthodox models are not satisfactory to this end.

In 1981 two Swiss scientists, T. Bining and G. Rohrer, designed the world's first scanning tunnel microscope, an achievement that won them a Nobel prize in 1986. With it we can observe atoms singly, and in assigned points at that. The main sounding element, or probe, of this microscope is an electric conductor stylus (needle) made of tungsten or platinum alloys.

Here's how this microscope works. Fixed voltage is applied to the needle that scans the surface of an object and to the object itself; after the needle and the object have approached each other to a distance of decimal fractions of an angstrom (A), a tunnel current starts flowing between them - hence the name of the microscope, a tunnel microscope. This current is sustained at a constant value with the aid of a servo system which either lifts or lowers the scanner depending on the relief of the surface. A computer keeps a tab on these movements and processes the data thus obtained; thereupon one can inspect the object at required resolution.

Yet such tunnel microscopes have certain constraints on their employment. By and large, they are used in high (fine) vacuum. Otherwise, say, in the air or in water only particular varieties of graphite and some lamellar semiconductors can be scanned at atomic resolution. The main constraint: the examined surface should be an electric current conductor.

In 1986 a second generation of sounding microscopes – atom-power ones

– entered the stage.

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The scanning microscope unit has a scanner, a measuring head and a cantilever as essential components. A computer, too, is important: it processes the data and flashes the results on the display.

Depending on what kind of operation is carried out in particular and on the size of an object, the scanner either moves this object at a desired pace or controls the cantilever's movements. The latest models are equipped with a pitch engine to move the object under the microscope back and forth. This is a high-precision manipulation taking account of decimal fractions of a micron. It thus becomes possible to scrutinize one and the same site of the surface for days on end, which is a necessary procedure when dealing with sluggish processes. The measuring heads allow to vary the operational modes and obtain high-resolution images (even at atomic resolution); besides, we can measure more than 20 different characteristics of examined samples and modify their surface (in what we term the lithography modes).

Yet it is the cantilever needles that are the most essential part of a modern high-performance scanning microscope. They had their second birth in 1990 when methods of silicon micromechanics were suggested for their production. That was a modified classical procedure of microelectronic technology with the use of doping, oxide layer formation and photolythographic processes. Selective etching is of particular importance for the making of cantilever needles, for it becomes possible to manufacture actually identical needles to a tolerance of several units on the nanometer scale. Such needles are fastened on beams which, in their turn, are made to preassigned thickness either by doping silicon with boron or phosphorus to required depth or by sputtering adequate film structures.

So scanning cantilever microscopes give an insight into many characteristics of materials. However, the end result directly depends on a modification of needles. For instance, those with a current-conducting surface are used for measuring the relative distribution of surface resistance and capacity as well as the electric characteristics of subsurface structures. Conductor probes supplied with dielectric coating are employed for determining the distribution of subsurface magnetic fields and capacity. Needles coated with high-strength materials (boron nitride, diamond-like coats, etc.) are good for determining the surface hardness. And probes with a chemically modified structure identify and interpret the distributions of

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adhesive forces; using such probes, we learn to what extent the surface of an object is homogeneous.

The above examples do not cover all the possibilities of probing (sounding) microscopy. But they are enough to show that many cantilever modifications are needed to get to know all the various characteristics of objects. It takes time to replace cantilevers and find an appropriate one among many; indeed, it is hardly possible to choose the right cantilever and fix it at the right time and place. That is why multiprobe cartridges are designed: each cartridge is supplied with dozens of needles with different coatings and different characteristics.

New-generation microscopes possess superhigh resolution enabling them to scan not only atomic lattices but individual atoms as well. Furthermore, they are capable of modifying various surfaces and changing their structure on the nanometer scale. A subtle, miniature piece of work! Say, the portraits and biographies of all Russians (150 million) drawn this way could be fitted into a slate only 3×3 cm large.

Such high-power microscopes are a must in submicron electronics, microbiology, in polymer production (quality inspection and identification of materials obtained) for the optical industry. The application range of these unique apparatuses keeps expanding, and they are quite indispensable in many areas. For instance, in testing the quality of eye lenses, which is a rather sophisticated procedure: being transparent, such lenses should be placed into a water solution for observation. The only nondestructive method available today is through sounding microscopy, for it allows to keep the lens surface intact. The manufacture of digital video disks is yet another nonalternative application domain of such scanning microscopy. Today these disks are made by diestamping. And since the dies used in such stamping are of magnetic material, nickel in particular, no other methods but sounding microscopy are good for checking their surface.

Thus the new generation of scanning microscopes supplied with probes (cantilevers) has a good future in physical and metrological research alike.

3. Answer the questions:

When can we inspect objects down to 0,25 mm in size? What new trend of science do you know?

Who designed the first scanning tunnel microscope?

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What is the main sounding element of this model?

How does needle scan the surface?

What is the name of this microscope?

What is the current sustained with?

What does the computer do?

How can you inspect the object?

What are the constraints of the microscope?

TEXTS FOR HOME READING

TEXT 1

INTERACTION OF NITROGEN OXIDES WITH POLYMERS

The reactions with nitrogen oxides present in the atmosphere is an important factor contributing to the deterioration of the polymer properties during ageing.

The review is devoted to the mechanism of reactions of nitrogen oxides with various types of polymers.

The reactions of reactive polymer groups with gases diffusing in the polymer bulk are distributed non-uniformly throughout the bulk; this hampers the kinetic description of these processes. In addition, reaction kinetics depends on the rate of relaxation processes in the polymer. Data on ageing of polymers of various classes obtained by conventional methods are presented in the review together with the EPR studies of the processes in question.

Reactions of nitrogen oxides with various types of polymers are described in detail. Polymers containing no double bonds are not very sensitive to nitrogen oxides. Rubbers are much more sensitive to these agents (nitrogen oxides can either detach allylic hydrogen atoms or add to the double bonds). The kinetics and mechanisms of reactions of double bonds in polymers with nitrogen oxides are considered comprehensively.

In addition to double bonds, amide groups of macromolecules, fluorinated groups, hydroperoxides and peroxide macroradicals are active participants of the reactions with nitrogen oxides. The oxide reacting predominantly with amide groups is N2O4. The cross-linking and destruction processes occurring in parallel are discussed. It is shown that at high temperatures, NO can disproportionate to give N2 and active NO3 radical. This stage may be responsible for the self-acceleration of hydroperoxide decomposition in an atmosphere of nitrogen oxides.

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Particular emphasis is given to the mechanism of the formation of nitrogen-containing radicals. The known structures of stable nitrogencontaining macroradicals formed allow one to draw conclusions concerning the free-radical stages of ageing.

The simple methods of synthesis of spin-labeled macromolecules based on free-radical reactions with nitrogen oxides have been considered. These methods are of great importance in the case of insoluble and chemically inert polymers such as polyperfluoroolefins. For PTFE and in the copolymer of tetrafluoroethylene with hexafluoropropylene, the macromolecules containing paramagnetic nitroxide groups both in the middle and at the end of the polymer chain, were prepared in this way. The produced nitroxide radicals made it possible to investigate the structure and the reaction-front movement during nitration of solid polymers by means of ESR imaging technique.

Task: Make a short essay to the written text.

TEXT 2

MECHANOCHEMICAL SYNTHESIS OF INTERMETALLIC

COMPOUNDS

In recent decades, the mechanochemical method has been often used to prepare intermetallic compounds. The review presents the current state of research in the field of mechanochemical synthesis in metallic systems with both negative and positive enthalpies of mixing.

It is demonstrated that this method of synthesis of intermetallic compounds and solid solutions can be performed for many pairs of metals. Numerous examples are given.

In practice, the method is especially significant when the components have very high melting points (synthesis of MoSi2), when the difference between the melting points and densities of the components is great (Mg-Ti); in those cases where the temperatures of the conventional synthesis are too high; and also when phases with a nanometer grain size are required. This method is also used for the pretreatment of components prior to thermal synthesis.

The mechanochemical approach is the most promising for the synthesis of metastable phases, supersaturated solid solutions and amorphous phases.

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The most pronounced extension of the concentration regions of supersaturated solid solutions is attained in those systems in which components have similar atomic radii and can undergo phase transitions to related structural types.

A specific feature of materials obtained by the mechanochemical route is high dispersity (in most cases, they include nano-sized particles), which permits one to influence substantially their physicochemical properties.

The main factors influencing the concentration boundaries of the nonequilibrium solid solutions prepared by mechanochemical method are elucidated.

Structural transformations occurring in the material during treatment in a mill are analysed. As a result of high plastic deformation, the components react to give either equilibrium or non-equilibrium chemical compounds (intermetallic compounds and solid solutions). The mechanisms of the processes are discussed in detail. Several hypotheses are stated and analysed.

It is demonstrated for numerous examples that the process of formation of solid solutions can be represented by several stages including (1) the formation of layered composite structures with simultaneous dispersion of the initial components to nanometer sizes (i.e. the formation of a large contact area of the components); (2) synthesis of intermetallic compounds in nano-sized layered composites; (3) dissolution of the resulting intermetallic compounds in the solvent metal to give a solid solution.

Task: Make a short essay to the written text.

TEXT 3

SILICON IS THE ELEMENT OF THE 21st CENTURY

Discussions on the main results of the work on the Project were on the agenda of the Second Conference on Material Studies and Physico-chemical Basics of Technologies of Production of Alloyed Silicon Crystals. The conference, which met in Moscow early this year, was attended by scientists from Moscow and the Moscow Region, St. Petersburg, Nizhni Novgorod, Novosibirsk, Krasnoyarsk, Irkutsk, Kiev and Minsk - a total of more than 120 participants. Speakers at the conference stressed that so far only four countriesthe United States, Japan, Germany and Russia - have mastered the technologies for polysilicon production although the demand for it is steadily growing. This

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stems from the needs of such branches as microelectronics and solar power generation which will provide a tangible contribution to electricity generation in the 21st century.

The development of technologies of manufacture of silicon monocrystals is oriented at producing ingots of larger size with mounting demands for getting more perfect crystalline structures and greater uniformity in the distribution of electrophysical properties throughout the volume of the material. The most serious problem encountered in this connection is the need to reduce the size of microflaws which have the strongest impact on the performance characteristics of integrated circuits. Speakers at the conference discussed the results of studies (Institute of Semiconductor Physics) of new types of what are called extension defects in silicon crystals and also the method of modelling of processes of heat and mass transfer, crystallization and defect formation (Institute of Heat Physics) which help reduce the numbers of surface submicronic defects.

Polished silicon plates have been mainly used so far for the production of integrated circuits. But with the current transition to submicronic and nanometer levels preference is being given to what are called epitaxial* structures especially in view of the prospects of using them for super-fast circuits of the future. Today epitaxial processes (chiefly molecular-ray ones), combined with ionic implantation* and pulsed radiation processing of materials are becoming increasingly important for the formation of silicon structures.

There has been growing interest among experts in recent time towards what are called microcrystalline and amorphous silicon films upon glass and metal base. These can be used as solar panels, fine-film transistors for liquidcrystal displays, light emitters and photocells. What is more, methods have been developed of producing such films with preset characteristics. One of the most effective of these consists in using a supersonic gas jet with gas activation by an electron beam. And the rate of precipitation of silicon layers by this technique has turned out to be the greatest.

The attention of experts has also been attracted by yet one more modification of this remarkable material – porous silicon. When some of the associated problems (ensuring stability and reproducibility) are resolved the new material will have a future as light emitter in the visible band. So far, however, there have been even more successful studies into what experts call controlled formation of pores massif of preset, configuration in the process of deep photoanodic etching, or scouring of silicon. This kind of structures can be