Large scale synthesis of germanium selenide glass and germanium selenide glass compounds

Systems and methods for large scale synthesis of germanium selenide glass and germanium selenide glass compounds are provided. Up to about 750 grams of a germanium selenide glass or a glass compound can be synthesized at a time in about eight hours or less. Stoichiometrically proportional amounts of germanium and selenium are placed in an ampoule. A variable may also be placed in the ampoule. The ampoule is heated to above the softening temperature of the glass or glass compound being synthesized. The ampoule is then rocked for a period of time while the temperature is held constant. The temperature of the ampoule is then brought down to above the softening temperature of the glass or glass compound being synthesized and then quenched.

BACKGROUND OF THE INVENTION

This invention relates to systems and methods for synthesizing germanium selenide glass and germanium selenide glass compounds. More particularly, this invention relates to systems and methods for large scale synthesis of germanium selenide glass and germanium selenide glass compounds in reduced time.

As used herein, a germanium selenide glass compound includes germanium, selenium, and a variable (e.g., a dopant).

Germanium selenide glass is widely used in the fabrication of semiconductor devices. However, in a known technique for producing Ge3Se7, which is one type of germanium selenide glass, only about ten grams of that glass can be produced at one time. Moreover, this technique requires about 50 hours in order to produce those ten grams of germanium selenide glass.

The known technique involves placing stoichiometric proportions of germanium and selenium (totaling no more than about ten grams) in an ampoule at atmospheric pressure (i.e., at about 1 atm.). An ampoule is a small, hermetically sealed quartz-glass vessel that is typically used to hold chemical solutions or materials. A vacuum is established in the ampoule, which is then flame sealed to seal the contents under vacuum. The ampoule is placed in a furnace and heated to about 300° C. and typically left at this temperature overnight. The next morning, the ampoule is heated to about 750° C. at a rate of about 0.5° C./minute. The ampoule is left at this temperature until the following morning to ensure that the germanium has melted and that the selenium has reacted with the germanium. If the melting and reaction do not occur, the selenium can exhibit a vapor pressure of about 10 atm. at about 900° C., which may burst the ampoule. The following morning, the temperature of the ampoule is increased to about 940° C. at a rate of about 0.5° C./minute. This ensures that the contents of the ampoule have melted. Once the temperature reaches about 940° C., the ampoule is rocked back and forth (typically by a rocking mechanism connected to the furnace) for at least about six hours. During rocking, the ampoule is allowed to cool down to a range of about 800° C. to about 780° C. After the ampoule has cooled down, it is quenched in a cooling bath of ice water. The ampoule is then cracked to retrieve the germanium selenide glass.

The only known way to scale-up the synthesis of this germanium selenide glass using this known technique is to run multiple small scale reactions concurrently, in which each reaction produces only about ten grams of glass per 50 hours. Clearly, this technique is very time consuming and impractical for large scale production.

Germanium selenide glass is particularly used in the fabrication of semiconductor devices, such as, for example, PCRAM (programmable cell random access memory). In the fabrication of known PCRAM devices, a thin layer of a conductive material (e.g., silver) is deposited over a germanium selenide glass substrate. The conductive material is typically irradiated with electromagnetic energy resulting in a doped or photodoped substrate (i.e., a germanium selenide glass compound). If care is not taken while irradiating the conductive material, such an irradiation may unpredictably change the properties of the substrate as well as result in an unpredictable amount of doping. Such changes or unpredictable amounts of doping may unpredictably, and usually undesirably, alter the electrical and performance characteristics of the PCRAM device being fabricated.

Moreover, similar to the synthesis of germanium glass, there is no known technique for synthesizing germanium selenide glass compounds on a large scale.

In view of the foregoing, it would be desirable to be able to synthesize more than ten grams of a germanium selenide glass or a germanium selenide glass compound in one reaction.

It would also be desirable to be able to synthesize a germanium selenide glass or a germanium selenide glass compound in one reaction in less than about 50 hours.

It would further be desirable to be able to synthesize a germanium selenide glass compound having substantially known properties and a substantially known amount of doping.

SUMMARY OF THE INVENTION

It is an object of the invention to synthesize more than ten grams of a germanium selenide glass or a germanium selenide glass compound in one reaction.

It is also an object of the invention to synthesize a germanium selenide glass or a germanium selenide glass compound in one reaction in less than about 50 hours.

It is further an object of the invention to synthesize a germanium selenide glass compound having substantially known properties and a substantially known amount of doping.

In accordance with the invention, large scale synthesis of germanium selenide glass of many different stoichiometries is provided. Moreover, the invention can synthesize these different types of glass in about eight hours or less. The amount of glass that can be synthesized is scalable. That is, germanium selenide glass weighing up to about 750 grams can be made at one time in one reaction. The invention synthesizes glass composed of about 15% to about 42% germanium.

Also in accordance with the invention, germanium selenide glass can be predictably doped with a variable. Such glass compounds may include a variable such as lithium, vanadium, chromium, manganese, cobalt, molybdenum, ruthenium, silver, praseodymium, neodymium, iridium, gold, and lead. Other suitable variables can be alternatively used. The variable included in such glass compounds can be in elemental form (e.g., pure lithium) or in compound form (e.g., silver selenide). Known amounts of the variable react with known amounts of germanium and selenium.

In one embodiment of the invention, a quartz-glass ampoule is preferably first cleaned using HCl or HCl/HNO3. The ampoule is then dried inside a dry box. For pure germanium selenide glass, 99.999% germanium and 99.999% selenium are placed in the ampoule while the ampoule is still inside the dry box. The selenium is preferably placed inside the ampoule away from the opening to prevent the selenium from subliming when the ampoule is sealed (a flame torch is preferably used to seal the opening of the ampoule). Any volatile variable placed in the ampoule should also be placed away from the opening to prevent the variable from subliming when the ampoule is sealed. The contents of the ampoule are subjected to a vacuum, and the ampoule is sealed such that the contents inside the ampoule remain under vacuum.

The sealed ampoule is placed in a furnace or other heating device, and heated to the softening temperature of the glass being synthesized or preferably higher. The softening temperature is the glass transition temperature. The ampoule is then rocked to ensure that the germanium and selenium completely mix. Rocking time depends on the amount of glass being synthesized (e.g., for about 450 grams of germanium and selenium, about 5 to 6 hours of rocking is sufficient). After thorough mixing, the composition is then cooled to between the softening temperature of the glass being synthesized and 20° C. higher than the softening temperature (i.e., no lower than the softening temperature). After cooling (which may not be necessary if heated to no more than 20° C. above the softening temperature), the ampoule is quenched in ice water. For a synthesis of about 400 grams of germanium and selenium, the reaction takes about eight hours. Thus, with one set of apparatus, about three reactions per day are possible. Therefore, one or more kilograms of germanium selenide glass can be produced per day with one apparatus.

For a germanium selenide glass doped with a variable, the germanium, selenium, and variable are similarly placed in an ampoule while inside a dry box. The contents of the ampoule are subjected to a vacuum, and the ampoule is sealed such that the contents remain under vacuum. After placing the sealed ampoule in a furnace or other heating device, the ampoule is heated. Once the ampoule is heated to at least the softening temperature of the compound being synthesized, the ampoule is rocked to ensure that the variable is evenly distributed. The compound is cooled to a range of about the softening temperature of the compound to about 20° C. above the softening temperature, if the compound is not already within that range. After cooling (if necessary), the compound is quenched.

More generally in accordance with the invention, germanium and selenium (and a variable if desired) can be placed in any appropriate container. The contents of the container are then subjected to a vacuum, and the container is sealed such that the contents inside the container remain under vacuum. The contents are then heated to the softening temperature of the glass or glass compound being synthesized, mixed, cooled, and quenched using any suitable means.

DETAILED DESCRIPTION OF THE INVENTION

The invention can preferably produce upwards of about 750 grams of germanium selenide glass per reaction depending on the stoichiometry of the glass being synthesized. For a synthesis of about 400 grams, the reaction takes about eight hours. For a 30 gram synthesis of a germanium-selenium-manganese compound (Ge25Se75; 3% atomic weight of manganese), the reaction takes about six hours. The invention also produces upwards of about 750 grams of a germanium selenide glass compound depending on the variable chosen and the ratios of the germanium and selenium to each other and to the variable. The initial cleaning of the equipment, which is important, is not included in the reaction times.

Suitable variables for germanium selenide glass compounds in accordance with the invention include lithium, vanadium, chromium, manganese, cobalt, molybdenum, ruthenium, silver, praseodymium, neodymium, iridium, gold, and lead. Other suitable variables may also be used. The variable included in such glass compounds can be in elemental form (e.g., pure lithium) or in compound form (e.g., silver selenide). Known amounts of the variable are reacted with known amounts of germanium and selenium.

FIG. 1shows a preferably quartz-glass ampoule2connected to a preferably quartz-glass tube8at opening3. Ampoule2and tube8may be made of other suitable material or materials besides quartz-glass. Ampoule2and tube8are preferably cleaned with a cleaning agent such as HCl or HCl/HNO3. Ampoule2and tube8are then heated for about twenty-four hours in a furnace of about 120° C. Ampoule2and tube8are preferably further cleaned by refilling ampoule2and tube8with a dry inert gas such as Ar or N2and then subjecting them to a vacuum. Ampoule2and tube8may be refilled with a dry inert gas and subjected to a vacuum several more times to further ensure cleanliness.

The cleanliness of ampoule2and tube8and the purity of the germanium, selenium, and the variable (if present) is important in order to preserve the integrity of the mean coordination in the backbone structure of the glass.

After ampoule2and tube8are cleaned, 99.999% pure germanium4and 99.999% pure selenium6are placed in ampoule2through tube8via openings3and9. A variable5may also be placed in ampoule2. Germanium4, selenium6, and variable5are preferably in the form of solid pellets. Germanium4and selenium6may be obtained in this form from Cerac, Inc., of Milwaukee, Wis. Alternatively, germanium4, selenium6, and variable5may be in liquid form.

The amounts of germanium4, selenium6, and variable5placed in ampoule2preferably fill most of ampoule2. This decreases the amount of selenium, germanium, or variable that may evaporate or sublime out of the liquid or solid phase, respectively. Such evaporation or sublimation may cause the glass or compound to synthesize with other than the desired stoichiometric proportions. However, the amounts of germanium4, selenium6, and variable5placed in ampoule2should not fill the entire volume of ampoule2in order to allow the germanium4, selenium6, and variable5to thoroughly mix inside ampoule2. For example, in an ampoule 20 cm. long and 4.6 cm. in diameter, about 50 grams of germanium, about 218 grams of selenium, and about 8 grams of manganese are acceptable amounts. For this ampoule, tube8can be, for example, 15 cm. long and 1.3 cm. in diameter.

Germanium4, selenium6, and variable5(if desired) are preferably placed in ampoule2inside a dry box (not shown). Selenium6and any variable that is volatile (e.g., susceptible to sublimation) are preferably placed in ampoule2at the end opposite opening3. This placement makes those variable materials (including selenium) less likely to sublime when ampoule2is sealed (ampoule2is preferably sealed with a flame torch—described below).

An adapter (not shown) for connection to a commercially available vacuum line (not shown) is preferably fitted to ampoule2inside the dry box. The adapter preferably has a valve or switch such that the adapter and in turn, opening9of tube8may be selectively opened and closed. The adapter and ampoule2are taken out of the dry box and connected to the vacuum line. The contents of ampoule2are then subjected to a vacuum. To ensure cleanliness, the adapter is closed before the adapter and ampoule2are taken out of the dry box. The adapter remains closed until it is ready to be connected to the vacuum line. This will ensure that air does not enter tube8or ampoule2and interact with germanium4, selenium6, and variable5(if present).

Ampoule2is preferably sealed while its contents are still subjected to the vacuum. Germanium4, selenium6, and variable5are preferably at room temperature (about 25° C.) when they are sealed in ampoule2. Alternatively, germanium4, selenium6, or variable5may be at a temperature other than room temperature when they are sealed in ampoule2.

However, at lower temperatures, the quantity of each material placed in ampoule2can be measured with more preciseness. For example, germanium4, selenium6, variable5or any combination of them may be chilled, for example, by refrigeration to a temperature below room temperature. Advantageously, less germanium4and selenium6may sublime out of the solid phase. Some germanium4and selenium6may sublime when they are subjected to a vacuum or when ampoule2is sealed with a heat source (described below). Unless accounted for, such a sublimation may be detrimental because the synthesized glass or compound may have a stoichiometry different than the desired stoichiometry.

If germanium4, selenium6, and variable5are at a temperature higher than room temperature, less heating and mixing time is required. For example, if germanium4, selenium6, and manganese were all in liquid form when they are placed in ampoule2, only about 3 hours of heating and mixing should be required for a 450 gram synthesis.

A suitable heat source such as an H2/O2torch can be used to seal ampoule2by melting a portion of tube8about 1 cm away from opening3. This causes the rest of tube8to break off from ampoule2. Note that portion10of tube8inFIG. 2was melted to seal opening3of ampoule2.

FIG. 2shows germanium4, selenium6, and variable5sealed under vacuum. The appropriate stoichiometric proportions of 99.999% pure germanium4, 99.999% pure selenium6, and variable5required to synthesize the selected compound are sealed inside. If a pure germanium selenide glass were being synthesized, the appropriate stoichiometric proportions of germanium4and selenium6would be sealed inside. The amount of germanium4, selenium6, and variable5shown in ampoule2is merely illustrative.

After ampoule2is sealed, it is placed in an assembly such that the contents of ampoule2(i.e., the germanium4, selenium6, and variable5) can be homogeneously heated in a furnace or other heating device.FIG. 3shows a cross-sectional view of such an assembly. Assembly12includes tube14and extension tube16. Tube14and extension tube16may be made of quartz-glass or other comparable material or materials. Tube14and tube16preferably have the same outer diameter and are also preferably connected. Tube14is preferably sealed at the end connected to tube16by seal18. Seal18is preferably made of quartz-glass or other suitable material or materials that can prevent ampoule2from sliding further inward. Tube16and seal18keep ampoule2positioned in the homogeneous heating zone of a furnace or other heating device. An alternative to seal18is having tube16with a closed end. Ampoule2is then in contact with the closed end of tube16. As a second alternative, tube14may have a closed end. In both cases, tube14and tube16do not need to be connected and seal18is unnecessary. Tube16will be in contact with the closed end of tube14which will be in contact with ampoule2.

The opposite end of tube14preferably has opening15to allow ampoule2to be placed in, and taken out of, assembly12. The inner diameter of tube14is preferably slightly larger than the outer diameter of ampoule2. Tube14is preferably long enough such that a portion of tube14extends outside the furnace when assembly12is placed in the furnace.

After ampoule2is placed inside tube14of assembly12, a portion of a tube20having an outer diameter preferably slightly smaller than the inner diameter of tube14is slid into tube14. Tube20is preferably slid into tube14such that the end of ampoule2with tube portion10is in contact with seal18, and the opposite end of ampoule2is in contact with tube20. Tube20is preferably long enough such that when tube20is in contact with an end of ampoule2and tube portion10is in contact with seal18, a portion of tube20extends outside the furnace beyond tube14.

Preferably, quartz wool22and24are placed inside tube16and tube20, respectively, to help ensure that all of ampoule2is heated to substantially the same temperature. Furthermore, quartz wool24helps insulate ampoule2from any cool air that may enter via tube20.

After assembly12is complete (i.e., ampoule2and tube20are slid inside of tube14such that the end of tube20is in contact with an end of ampoule2and tube portion10is in contact with seal18), assembly12is placed inside a tube furnace. Alternatively, tubes14and16with ampoule2inside may be first placed inside the furnace and then tube20slid inside tube14. Or, tubes14and16may be placed first in the furnace and then ampoule2and tube20slid inside tube14.

FIG. 4shows a cross-sectional view of tube furnace40in accordance with the invention. Alternatively, furnace40can be other types of heating devices that can heat ampoule2while the contents of ampoule2are motionless or in motion. Preferably, furnace40is a multi-position tube furnace such as an EW-33903-10 by Cole-Parmer of Vernon Hills, Ill. When such a tube furnace is motionless, an ampoule placed inside the furnace (e.g., as part of assembly12) can be heated without the contents of the ampoule or the ampoule itself moving. Preferably, such a tube furnace includes a rocking device or other mechanism that can move the tube furnace rhythmically (e.g., from a starting point to an intermediary point and back to the starting point). Note that rhythmic movement is not required. Any movement of the furnace that causes the contents inside the ampoule to completely mix is sufficient.

Furnace40preferably includes a hose clamp42clamped to the portion of the outer surface of tube14that extends outward from furnace40. Wires44are preferably connected to hose clamp42and to screws46. Wires44may be wrapped around screws46or wires44may be pinned between screws46and the outer surface of the face of furnace40. Screws46are preferably diametrically opposed on the outer surface of the face of furnace40. This arrangement secures tube14(and tube16) inside tube furnace40.

Furnace40also preferably includes a hose clamp48clamped to the portion of the outer surface of tube20that extends beyond tube14. Wires50are preferably connected to hose clamp48and to screws52. Wires50may be wrapped around or screws52or pinned between screws52and the outer surface of the face of furnace40. Screws52are preferably diametrically opposed on the outer surface of the face of furnace40. This arrangement secures tube20and prevents ampoule2from moving along the longitudinal axis of assembly12.

Hose clamps42and48may alternatively be clamped onto tubes14and20, respectively, before tubes14and20are placed in furnace40.

Tubes14and20are secured inside furnace40such that neither tube (nor ampoule2) can move, or can only move very little, along the longitudinal axis of furnace40when furnace40is in motion.

The outer diameter of tube14is preferably slightly smaller than the inner diameter of tube54of furnace40such that tube14does not shake around, or only shakes very little, inside furnace40when30furnace40is in motion. For example, if the inner diameter of tube54is about 5 cm, the outer diameter of tube14can be about 4.6 cm.

Similarly, the outer diameters of ampoule2and tube20are preferably slightly smaller than the inner diameter of tube14such that ampoule2and tube20do not shake around, or only shake very little, inside tube14when furnace40is in motion.

After ampoule2and assembly12are secure inside furnace40, ampoule2is heated. The temperature inside furnace40is increased to at least the softening temperature of the glass or compound being synthesized and preferably higher. The temperature is typically increased to between about 400° C. and 800° C. and preferably no higher than about 850° C. A germanium-selenium phase diagram is shown in FIG.5. The melting temperatures of germanium selenide glass with different stoichiometries are roughly indicated by transition lines56. The melting temperature is no higher than the temperature at which the glass being synthesized changes to L2phase58. If a small amount of a variable is involved in a germanium selenide compound, the germanium-selenium phase diagram may be used as a rough guideline to determine the softening temperature of that compound. As is known in the art, the softening temperature of a germanium-selenium compound is approximately half the melting temperature of that compound. For example, for 12% Ge/88% Se, the glass transition temperature (i.e., the softening temperature) is about 107° C.; for 24% Ge/76% Se, the glass transition temperature is about 229° C.; for 30% Ge/70% Se, the glass transition temperature is about 335° C.; for 40% Ge/60% Se, the glass transition temperature is about 347° C.

The temperature inside furnace40is preferably increased at a rate ranging from about 20° C./minute to about 30° C./minute. If the temperature inside furnace40is raised too fast, a substantial amount of selenium6may not react with germanium4or the other variable. The unreacted selenium6may then exhibit a vapor pressure strong enough to burst the ampoule. Care also should be exercised when increasing the temperature in a germanium selenide glass compound reaction involving a variable that exhibits a large vapor pressure.

After the temperature inside furnace40has reached or exceeded the softening temperature of the glass or glass compound being synthesized, the temperature is held constant and furnace40is preferably rocked or moved to mix the contents of ampoule2into a homogenous molten mixture. The temperature may be held constant at, for example, no lower than 400° C. For a synthesis of about 400 grams of germanium selenide glass, furnace40should be rocked or moved for about five to six hours to ensure that all of germanium4and selenium6completely mix. For a synthesis of about 750 grams, about 8 hours of rocking should be sufficient to allow all of germanium4and selenium6to mix. Generally, the larger the synthesis, the more time is necessary to allow germanium4and selenium6to react. Similarly, for larger syntheses of glass compounds, more time is necessary to allow germanium4, selenium6, and variable5to react.

FIGS. 6 and 7illustrate furnace40equipped with a rocking mechanism60that causes the tube furnace to move rhythmically. As shown, rocking mechanism60causes furnace40to pivot about the mid-point61of the longitudinal axis of furnace40. Rocking mechanism60may be controlled by a variable speed controller (not shown). Furnace40is preferably moved from an ‘up’ position (FIG. 6) to a ‘down’ position (FIG. 7) and back to the ‘up’ position once every four seconds or so while mixing to ensure complete and homogeneous softening and mixing of the contents of ampoule2. Furnace40preferably rocks through an angle of about 60° to 80°.

After the contents of ampoule2are mixed into a homogenous molten mixture, the temperature of furnace40is brought down to preferably within about 20° C. of the softening temperature of the glass or glass compound being synthesized, but no lower than the softening temperature. The temperature of furnace40is brought down at a rate of preferably about 20° C./minute. For a synthesis of about 400 grams, the temperature is held within about 20° C. of the softening temperature but no lower than the softening temperature for about ten minutes. This temperature may be, for example, between 300° C. and 320° C.

Generally, the larger the synthesis, the longer the temperature should be held within about 20° C. of the softening temperature but no lower than the softening temperature. For a synthesis of about 750 grams, the temperature should be held within about 20° C. of the softening temperature but no lower than the softening temperature for about 10 minutes. Generally, the larger the diameter of the ampoule, the longer the temperature should be held. This preferably ensures that the glass or glass compound at the center of the ampoule cools to the same temperature as the rest of the ampoule and that the glass or glass compound quenches homogeneously. Glass and glass compounds that have high amounts (e.g., more than about 30%) of germanium are preferably cooled longer than glass and glass compounds that have low amounts of germanium.

The rocking movement of furnace40may be stopped prior to or after furnace40has been at the decreased temperature. Preferably, the rocking movement is not stopped until the temperature of furnace40is at the decreased temperature.

After ampoule2has been held at the decreased temperature, it is preferably left in the ‘down’ position as shown inFIGS. 7 and 8for several minutes. This allows the viscous melt to collect at the bottom of ampoule2. If this does not occur, a thin film of germanium selenide glass of slightly different stoichiometry may solidify on top of the glass being synthesized (if a glass were being synthesized). Some excess selenium may condense out of this thin film. This is undesirable because the overall stoichiometry of the glass may change. For the synthesis of a glass compound, a thin film with a different stoichiometry than the rest of the compound may solidify on top of the compound. Similarly, some excess selenium or the variable may condense out of this thin film. Unless accounted for, such condensations are undesirable.

Ampoule2is now quenched.FIG. 7shows furnace40positioned such that the opening of furnace40through which ampoule2and assembly12were placed is aligned with a tub70filled with ice water72. A cooling agent such as salt74may be placed in ice water72to further lower the temperature of ice water72. Salt74may be, for example, calcium chloride. To remove ampoule2, wires50are cut or unwrapped from screws52. Alternatively, screws52may be loosened. Tube20may then be removed. After tube20is removed, ampoule2may slide out of furnace40into tub70on its own. If ampoule2does not slide out of furnace40by itself, end41of furnace40may be tapped. If ampoule2still does not slide out or if it gets stuck at the end of tube14, metal tongs may be used to pull ampoule2out. Sliding ampoule2out of furnace40and into tub70should preferably take less than five seconds.

Metal tongs may be used to hold onto ampoule2while swirling it around tub70. This more rapidly quenches ampoule2.

FIG. 9illustrates ampoule2in tub70. Upon quenching, the contents of ampoule2solidify into a germanium selenide glass or glass compound80. The amount of time required in tub70depends on the size of ampoule2and the amount of glass or glass compound inside. For about a 20 cm. long ampoule with about a diameter of 4.6 cm., initially filled with about 50 grams of germanium and about 218 grams of selenium, ampoule2should be quenched in ice water for about ten minutes to ensure complete and homogeneous cooling.

Glass or glass compound80may be stored in ampoule2until needed. To retrieve glass or glass compound80from ampoule2, a tungsten-carbide knife may be used to score the outer surface of ampoule2(e.g., by scoring completely around the circumference of ampoule2). Ampoule2may then be cracked open by carefully placing the tip of a fine screwdriver, for example, on the score and gently tapping the butt of the screwdriver. In most circumstances, glass or glass compound80will come loose from the walls of ampoule2. If, however, glass or glass compound80does not come loose, the outer walls of ampoule2may be gently tapped with an object like a pair of tweezers. If glass or glass compound80still does not come loose, the portion of ampoule2with glass or glass compound80still stuck to the walls may be immersed in a Dewar filled with N2(liquid). Glass or glass compound80will then crack, contract, and separate from the quartz-glass walls of ampoule2. Care should be taken when choosing N2(liquid)or when a variable with properties that may cause the compound to act adversely to such an immersion is present in the glass compound.

FIG. 10shows time versus temperature for the large scale synthesis of a germanium selenide glass or glass compound in accordance with the invention. An ampoule containing germanium and selenium is heated from, for example, about room temperature (at a time 0) to a temperature equal to or greater than the softening temperature of the glass or glass compound being synthesized (e.g., 940° C.), shown at point91. The temperature of the glass or glass compound is preferably increased at a rate of about 30° C./minute. This is represented by slope92.

After reaching point91, the germanium, selenium, and variable (if present) are mixed at a constant temperature until the selenium, germanium, and variable completely mix and become evenly distributed inside the ampoule. This occurs during time period93which may be, for example, about five to about six hours, depending on the amounts of germanium, selenium, and variable involved.

After reaching point94, (i.e., the point at which the germanium, selenium, and variable are heated and mixed), the mixture is cooled. The temperature of the mixture is preferably decreased at a rate of about 20° C./minute, represented by slope95. The temperature of the mixture is cooled down to within about 20° C. the softening temperature but no less than the softening temperature of the glass or glass compound being synthesized (e.g., Ge3Se7). This is shown at point96. If point94is within about 20° C. of the softening temperature but no lower than the softening temperature, the cooling may be unnecessary.

After the mixture reaches this range (e.g., within about 20° C. of the softening temperature but no lower than the softening temperature), the mixture is quenched. This is represented by slope97. The time between points96and98is preferably no more than about five seconds (depending on the amount of glass or glass compound being synthesized).

Ampoule2is held at the quenching temperature (e.g., about 0° C.) for time period99to ensure complete and homogeneous cooling. Time period99may be, for example, about fifteen minutes to about twenty minutes for a glass or glass compound of about 400 grams.

FIG. 11shows a process for large scale synthesis of a germanium selenide glass and a germanium selenide glass compound in accordance with the invention. At step102, germanium and selenium (and, if desired, a variable) are placed in a clean ampoule and then subjected to a vacuum. The amount of germanium placed in the ampoule is preferably stoichiometrically proportional to the amount of selenium for the particular glass being synthesized. If a variable is placed in the ampoule, the amount of the variable is preferably stoichiometrically proportional to the amount of germanium and selenium for the glass compound being synthesized. At step104, the ampoule is sealed. At step106, the sealed ampoule is placed in a heating device (e.g., a tube furnace).

At step108, the temperature of the heating device is increased to the softening temperature of the glass or glass compound being synthesized or above. The temperature of the heating device is preferably increased at a rate between about 20° C./minute and about 30° C./minute. At step110, the temperature of the heating device is held constant and the contents of the ampoule are mixed for about 5 to about 6 hours for a 400 gram glass synthesis to ensure that the germanium mixes with the selenium.

At step112, the temperature of the heating device is lowered to within about 20° C. of the softening temperature of the glass being synthesized (e.g., Ge3Se7or Ge2Se8) or the glass compound being synthesized (e.g., Ge25Se75; 3% atomic weight of manganese), but no lower than the softening temperature. The temperature of the heating device is preferably lowered at a rate of about 20° C./minute. If the temperature of the heating device is already within about 20° C. of the softening temperature but no lower than the softening temperature, step112may be unnecessary.

At step114, the ampoule is quenched. Ampoule2is held at the quenching temperature (e.g., for about fifteen to about twenty minutes for a 300-400 gram synthesis or for about thirty minutes for a 750 gram synthesis) to ensure complete and homogeneous cooling. This occurs at step116.

Note that the embodiments described in connection withFIGS. 1-11are merely illustrative. Germanium and selenium alone or germanium, selenium, and a variable may be placed in any clean suitable equipment (i.e., equipment as free from impurities as possible), heated in any suitable heating device, mixed in any suitable way, cooled in any suitable way, and quenched in any suitable way. For example, germanium and selenium may be subjected to a vacuum and sealed in a container that has a mixing device (e.g., a stirrer) to mix the germanium and selenium.

Thus, systems and methods for large scale synthesis of germanium selenide glass and germanium selenide glass compounds are provided. One skilled in the art will appreciate that the invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the invention is limited only by the claims which follow.