DE1519861A1 - Pure representation of elements and compounds by sublimation - Google Patents

Description

31ΖΓ.ϋ - :: · ί3-8CHUCKERTWERKE Erlangen, don ¹ ^ '- ^ν · ' ■ ' ^οΑ _

Aktiengesellschaft Werncr-von-Siomena-Str.

1519831

■ "T AS Α ° \ Μ,

PLA 64/1149

Pure representation · of clusters and connections

by sublimation

/ J .; It has been observed that there are gains in the gas phase atomic »and molecular substances on the surface of something alien to them Substance does not condense even if the temperature of the surface is below the normal condensation point de;:; concerned /: ar; f-jrmifren fabrics :; on artefactic material ILe / j-t. Vi-jlmohr erwie; e :; as necessary, the surface bia to one far below these Condensation point possibly below the melting point. Temperature to cool down to achieve a progressive condensation. sat Lon. The latter sets depending on the material of the condensation surface at one a certain temperature quite sharply.

009843/1342

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BATH ORIGINAL

Dio relationships are expressed by the following equation:

^N A - ^N E ^{c N} A - ^N ad ^A exp (-E _ad / kT)

In it is:

N. the number of atoms or
^A molecules,

Ng is the number of atoms or atoms evaporating in the unit of time.
Molecules,

N, the number of particles currently present on the surface,

E * is the molar adsorption energy,
A a puncture from T and E ,,
T the absolute, temperature and
k is Boltzraann's constant.

Whether the difference N. - N "is greater or greater at a given temperature
smaller al :? Is zero, so depends on E.

"Species" in the context of the present explanations is in the simplest form the substance to be condensed itself. In the broader sense, however, a condensation surface is still referred to as intrinsic if the substance to be condensed is the same on this condensation surface
or has approximately the same molar adsorption energy E ^ as on a surface which is chemically the same as the substance to be condensed.

With a given particle current density N. and a given adsorption energy E, the occurrence of condensation depends only on the temperature. At a certain temperature, according to the above equation, the difference N. - Np becomes greater than NuLl. Since progressive condensation begins at this temperature, this temperature is called the "limit temperature for progressive condensation". The- .-, '· hnnp'L a "! -Ο before A -r \ fatur v.:,f■K^d^n^ationafluche and that of the Eu

P - BAD ORIGINAL

condensing substance. If the gaseous substance condenses on the foreign surface due to purely physical adsorption forces, the limit temperature mentioned is below the normal condensation temperature. - However, if any chemical binding forces are added, the condensation temperature may increase very sharply. - These relationships are for example described by H. Mayer (Physics of Thin Films, ^{T-: y} il II, knowledge sheep ti publishing Ges Stuttgart 1955, in particular S ₀ iton 74 and 82..).

The method according to the invention uses this little attention so far ·? Appearance for the purification of atomic and without decomposition evaporable or sublimable ■ chemical substances and thus shows a way to reduce the cleaning effect without condensation in the solid phase noticeably increased compared to known cleaning processes increase. The sublimation process of the invention is particular for cleaning arsenic and similarly sublimable elements suitable.

The invention consists in that the substance to be cleaned on the pure Unrelated condensation surfaces, which, except for the last, are specific to the impurities, and a temperature above the limit temperature for the progressive condensation of the pure substance, and that the last condensation surface is kept below this limit temperature.

According to the invention, metals such as silver, aluminum, cadmium, mercury, zinc etc. or atomic or molecular non-metals such as iodine can be cleaned. In particular, according to the method according to the invention for shark leaks, rsto ¹ . Unnecessary materials, al ho

009 843/1342

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if

those for which an extremely high degree of purity is required, for example arsenic, has been purified.

Of the three processes involved in the well-known sublimation process, evaporation, the transport via the gas phase and the condensation int only the latter is important for the process according to the invention and should therefore be briefly explained: The normal condensation occurs not with the usual sublimation al: · a reversal of the evaporation with the only difference that i the Vapor pressure ratios different according to the lower temperature are. The condensation takes place in the ratio of these vapor pressures ;; tatt, as long as there are no deviations due to interaction between the pure Substance and the admixtures enter.

The cleaning effect through sublimation is with the corresponding known ancestors are therefore limited; in particular, there is a limit concentration for each impurity that was previously caused by sublimation could not be undercut.

Due to the above-mentioned phenomenon, namely that of The condensation temperature on a different type of surface differs from the condensation temperature on a surface of the same type, but the cleaning effect can be significantly increased. These are for the inventive Ancestors the cases of importance where there are deviations in the sense of a necessary undercooling of the condensation; "- flat acts, where a purely physical adsorption takes place .

0-9843 / 1342 ORIGINAL BATHROOM

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In order to allow the contaminated substance in the gas phase to run through the condensation apparatus as unhindered as possible - above all without interaction with other materials, it is proposed according to the further invention to generate _{a vacuum, in particular less than 10 Torr r, in the condensation chamber to carry out the process} .

According to the invention, the contaminated one is in the gas phase First of all, the fabric is moved past the unrelated surfaces of the pure fabric. The temperature of the surfaces is chosen so that below the given Density ratio is the normal condensation temperature of the pure substance is undershot, but the temperature of the con-'ionation.'ifflatten is still higher than the temperature for dio progressively e condensation of the pure substance, so that this just not yet ■: hro .-. Chi '.' Den will.

The same uder similar substances, "- 'JW-UhIt, which are also contained as impurities in the gas flow, are used for the surfaces mentioned, so that Impurities whose condensation temperature is above the above-mentioned limit purature for progressive condensation of the pure substance are therefore separated from the gas phase of the contaminated substance, while the remaining gas flow continues through the evacuated Rf- .

I! i '-'.! l i the gas flow reaches an area which is the same as the pure substance is also alien, but whose temperature is below the limit temperature

tur i '<tr for t.ichroi lunde condensation (Jf;:; pure substances li ^ gt, so

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BAD ORFGINAL

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U ι «; υ υ ι

<i'i !. ^{J the} latter condensed. The latter condensation .; Γ Liic'-io 1-yjnn -now assist a substance of which the pure? The substance is to be removed and thus collected without being re-contaminated. Γη in this sense can be used as a condensation.5f.Iache for the pure substance, e.g. quartz glass.

V .'- v: itir rhin is the for; lori pure matter vorf einher. '. · Feces: den;: - ntior: sf ^ äeh · au er. alien to the impurities that have not yet been separated from the gas flow on the first surfaces. In addition, if these impurities are not reflected on the areas intended for the pure substance, it is advisable to ensure that the covering of this area with the pure substance is not too great and thus possibly suitable for the named impurities. This can happen, for example, that the condensation. ^ Pool for the pure: material moves through the condensation space at a constant speed; becomes, in such a way, that ¹ , * the pure substance is deposited only in an extremely thin layer on the Kondon.vitionflache. For example, a disk can be provided which rotates around its axis in such a way that part of its surface always protrudes into the condensation space and another part into a space in which the pure substance is collected. In the first space Then four pure substances are deposited on the pane and in the second room the Sohoibe is heated in such a way that the pure substance evaporates from it again.

An example of a device for performing the method according to The invention is shown schematically in a figure:

Kin jacket tube 1, in particular made of quartz glass, for example bO cm in length and 4 cm in diameter is at the center to more than half of its

0 0 9 8 4 3/1 342

₆ _ ORIGINAL BATHROOM

Wrapped with a heating coil 2 for a long time. In the jacket tube 1 there is also a liquid-cooled double-walled tube 3, in particular made of quartz glass, which is almost as long as the jacket tube. The pipe is cooled by the supply lines 8, in particular with water. On the section of the pipe 3 that is irradiated by the heating coil 2, this is covered with a film 6. This foil consists in particular of metal, for example aluminum or zinc. The closed end of the jacket tube 1, in which the substance 7 to be cleaned is located, is inserted into an oven 4, which has a higher temperature than the heating coil. On the jacket pipe 1 there is also a connection piece to a high vacuum pump, as well as an airtight closable opening ⁽ ί sum insertion of the pipe 3. The pure substance deposited on the pipe 3 is denoted by 10. - This arrangement can also be carried out the other way around, namely with cooled Jacketed pipe and heated pipe 3, the foils 6 then lying on the inner wall of the jacketed pipe.

The method according to the invention is based on the example of arsenic purification are explained: The furnace 4 had a temperature of 350 G and the heating coil 2 a temperature of about 275 G. The tube 3 and the metal tube 1 consisted of quartz glass, and a foil 6 aluminum was chosen. The condensation took place in a high vacuum, less than 10 Torr.

The limit temperature for progressive condensation int for arsenic on quartz with low particle current densities is around 25 ^° C. On aluminum it is not much higher, but the slight heating of the metal foil by radiation from the heating coil is sufficient to prevent arsenic condensation on the aluminum foil. The condensate

0Q9843 / 1342

_BATH ORIGINAL vC y _Kü

nation the arsenic can only be found above the aluminum on the quartz tube 3 (figure), where the temperature falls below the limit temperature of arsenic on quartz.

2, it has been proven that under the same conditions no arsenic is deposited on the silver and molybdenum sheet placed around the tube 3 (figure) either. Sheets of this type are also suitable for the cleaning method according to the invention. On the other hand, arsenic is deposited on a silver mirror applied to the quartz tube 3 (figure), since it is more strongly cooled by the same because of its intimate contact with the tube 3 than the silver sheet placed loosely around the tube 3. A silver mirror applied to the same above the section of the pipe 3 irradiated by the heating coil 2 (figure) can thus be used as a condensation surface for the pure substance.

Ss can also be different on the length of the tube 3 on top of each other the following films may be provided, in particular those that are present as an impurity in arsenic, so that for them due to the supercooling effect a deposition is caused. However, this continues presupposes that the limit temperature for advancing condensation for arsenic is not too high on these foils.

Two tables are compared as an example of the effect of a macaw cleaning carried out according to the method according to the invention. These are measured values on several gallium arsenide rods which were produced from the same purified starting material, but the arsenic used for the gallium arsenide in Table 2 being subjected to a subsequent purification according to the invention

009843/1342

. ₈ . ^ß AD ORIGINAL

ID I a ö D I

'.vurd- ?. - It should be noted that all of the arsenic was already consumed during the ordinary cleaning a normal sublimation in the hydrogen stream iurchiremacht.

The following tables indicate: In column 1 the bar number of the gallium arsenide, in column 2 the conductivity er, in column 3 the Hall constant R " _t, in column 4 the carrier mobility / U and in column 5 the charge carrier concentration η. The values given in columns 2 to 5 apply to the position with the highest impact.

Table 1

Gallium and arsenic purified using known processes and converted to gallium arsenide processed.

No.

cm)

3 ^Rh

cm (Asec)

-1

/ U
cm (V:; ec * 5 , 2 η
cm 4800 5 , 2 • 10 4800 39 , 0 . 10 4700 • 10

40

40

300

120

120

16

Table 2

Gallium arsenide as in Table 1, but with post-purified according to the invention Aroen

34 1 . 5 165 342 5600 2, 2400 BATH 5200 5 1160 5800 22nd
7, 250
009843/1
905 5600
6800 4th 1500 ORIGINAL 6000

3.8. 10

0.25. ' 10

0.54 x 10

2.5 · 10

0.69 x 10
0.42 x 10

16

16 16 16

16 16

if 9

I J I

'.Yahr ^ nd the arsenic produced with purified by known methods

ο Gallium arsenide has mobilities below 5000 cm / Vsec and charge carrier concentrations above 5 · 10 ^i:> cm "", the corresponding ".Vsrto in Table 2 are consistently above 5000 or below 5 · 10. In addition, gallium arsenide according to Table 2 is more highly resistive and has a higher Hall constant than gallium arsenide according to Table 1.

Since the cleaning method for the output elements and the method of synthesis of gallium arsenide in all cases is the same, it appears that the improvement of the values in Table 2 with respect to Table 1), the post-cleaning according to the invention is due to the arsenic.

7 claims
1 figure

009843/1342

BAD LOCAL - 10 - · ·

Claims (1)

Claims 1. Sublimation process for cleaning chemical substances, in particular Ar3s and similarly sublinable elements by condensation from the gas phase, characterized in that the substance to be cleaned on the pure substance is foreign to condensation surfaces is passed, which are specific to the last of the impurities and a temperature above the Limit temperature for the progressive condensation of the pure substance, and that the last condensation surface is below the limit temperature is maintained. 2. The method according to claim 1, characterized in that in a vacuum is being worked on. 3. Process according to claims 1 and 2, characterized in that the temperature of the condensation surfaces is chosen to be lower than the condensation temperature of the pure substance on its own , floor. 4. Device for carrying out the process according to the preceding Claims, characterized in that a heating coil (2) is wound around the middle over more than half of its length Casing tube (1), in particular made of quartz glass, is provided that a liquid-cooled double-walled tube is inserted into the casing tube (1) (3) »in particular made of quartz glass, which is almost as long as the jacket tube that is irradiated on by the heating coil (2) Section of the tube (3) dieoe3 with one or more different foils (6) following one another along its length, '009843/134 2 BATH - ——- ~~ "vC / Kö 'ft.' in particular made of metal, that the jacket tube (1) with the closed end, in which the substance to be cleaned. (7) is placed in an oven (4) which has a higher temperature has as the heating coil (2), and that at the other end of the jacket tube (1) a connecting piece (5) to a high vacuum pump and an airtightly closable opening (9) for inserting the tube (3) is provided (FIG.). ^{1 :.} Device according to claim 4, modified so that the jacket pipe (1) is cooled from the outside and the pipe (3) is heated from the inside, and there :. ^J the foils (6) are applied to the inner surface of the jacket pipe. 6. Device according to claims 4 and 5 for carrying out the method according to claims 1 to 3, characterized in that the last condensation surface consists of a material from which the condensate can be removed without further contamination, for example glass, in particular quartz glass . 7. Device according to claims 4 and 5 for performing the method according to claims 1 to 3, characterized in that the last condensation surface is a silver mirror. BATH ORIGINAL 001143/1342 - 12 -