TWI633957B - High stability nano metal particles, manufacturing method and stabilizer - Google Patents

Abstract

A high-stability nano metal particle comprising: a nano metal particle; and an antioxidant protective film coated on the outside of the nano metal particle; the antioxidant protective film is an organic compound containing a benzene ring or a nitrogen-containing compound It is composed of a heterocyclic compound. The antioxidant protective film prolongs the antioxidant time of the nano metal particles, extending from the conventional 1-2 days to a minimum of 14 days.

Description

High stability nano metal particles, manufacturing method and stabilizer

The present invention relates to how to enhance the oxidation resistance of nano metal particles, and to maintain the catalytic activity of the nano metal particles having the antioxidant ability.

A number of methods for synthesizing nano metal particles have been proposed so far, for example, reduction of metal ions originally dissolved in a solution into nano-sized metal particles by reduction. However, nano-sized metal particles are prone to agglomeration and precipitation due to the effect of van der Waals. In addition to the problem of agglomeration, the problem of poor oxidation resistance of the synthesized nano metal particles (such as nano copper), nano copper can only maintain about 1 to 2 days to produce significant oxidation. The above problems affect the commercial availability of nano metal particles.

In order to solve these problems, a protective agent is added to the solution of the synthesized nano metal particles to form a functional protective film on the surface of the synthesized nano metal particles to resist the cohesion of the van der Waals force, and to prolong the oxidation resistance time of the nano metal particles. . The main components of the functional protective film include bifunctional molecules (as disclosed in the Chinese Patent Publication No. 200907113), polymers (such as the Republic of China invention patent publication 200640596), ascorbic acid (C ₆ H ₈ O ₆ ) and Dibutylhydroxytoluene (C ₁₅ H ₂₄ O) (eg, Republic of China invention patent I341756). However, such a functional protective film deteriorates the conductivity of the nano metal particles. Therefore, before the nano metal particles coated with the protective agent are applied to the electroplating process, a special cleaning step of removing the protective agent is required to protect The agent is removed from the surface of the nano metal particles. However, this removal step increases the trouble of manufacturing and the problem of increased cost.

The Republic of China Patent Publication No. 201023999 discloses a method for producing nano metal particles, wherein the surface of the prepared nano metal particles has a self-cleavable protective agent composed of self-cracking molecules, and the protective agent can be used. Rice metal has anti-agglomeration and anti-oxidation functions. The self-cracking protectant produces a self-cracking phenomenon at a specific temperature range (less than 200 ° C), causing the protective agent to detach from the surface of the nano metal particles. This patent document solves the problem of the cleaning step of removing the protective agent, but when using such a type of nano metal particles, it is necessary to set an operating temperature at which the protective agent can be self-cracked, which still makes commercial use. The range is limited. For example, an electroless plating bath operating at a temperature of 25 ° C is not suitable because the protective agent cannot produce self-cracking.

One. The problem of poor oxidation resistance of nano metal particles. (The antioxidant capacity can only last for 1 to 2 days in the air).

two. The problem of easy agglomeration of nano metal particles.

three. Nano metal particles coated with a protective film of anti-oxidation or anti-agglomeration result in problems of poor conductivity or catalytic activity.

four. It is necessary to recover the conductivity or catalytic activity of the nano metal particles by the cleaning step of removing the protective film, but the problem of cumbersome process and increased cost is derived.

Fives. It is necessary to use a self-cracking film at a specific operating temperature, and the application range of the nano metal particles is limited.

A high-stability nano metal particle comprising: a nano metal particle; and an antioxidant protective film coated on the outside of the nano metal particle; the antioxidant protective film is an organic compound containing a benzene ring or a nitrogen-containing compound It is composed of a heterocyclic compound.

a stabilizer added to a solution for producing nano metal particles, the stabilizer having an outer surface of the nano metal particles produced by the solution; the composition of the stabilizer is the following formula Optional one:

Where X is N or S; Y is N or C; Z is N or S; R is an alternative to H, SH, and SCH ₃

R ₁ is H; R ₂ is H or SH; and R ₃ is H or OH.

A method for producing high-stability nano metal particles, wherein the stabilizer is placed in a liquid phase relative to a solid phase heterogeneous reaction solution, and the stabilizer is placed after the reaction solution has prepared nano metal particles, and the stabilization is performed. The agent is an expression of nano metal particles to form an antioxidant protective film.

One. The high-stability nano metal particles have significant antioxidant capacity, and the antioxidant time is extended from the conventional 1-2 days to at least 14 days.

two. The high stability nano metal particles have good dispersibility in solution.

three. The high stability nano metal particles retain catalytic catalytic activity.

four. The high-stability nano metal particles can be directly applied to the electroless plating as a catalytic catalyst, without the step of removing the anti-oxidation protective film, eliminating the traditional protective agent cleaning and removing steps, reducing the labor trouble and cost.

Fives. Highly stable nano metal particles can be used in various known electroplating fields.

six. It can replace palladium catalyst for electroless plating and reduce catalyst cost.

<<Nano-coated metal particles coated with anti-oxidation protective film>>

The first figure (a), (b) and (c) are views of the nano metal particles of the present invention under an electron microscope. The nano metal particles 10 are nano copper, and the outer surface of the nano metal particles 10 is coated with an oxidation resistant protective film 11. The oxidation-resistant protective film 11 is composed of a benzene ring-containing organic compound or a nitrogen-containing heterocyclic compound. For convenience of explanation, the nano metal particles 10 coated with the oxidation resistant protective film 11 are hereinafter referred to as high-stability nano metal (copper) particles.

This antioxidant protective film 11 is composed of a compound of the general formula [1].

General formula [1], X is N or S; Y is N or C; Z is N or S; R ₁ is H; R ₂ is H or SH; and R ₃ is H or OH.

Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzotriazole (BTAOH), thiol benzothiazole (Mercaptobenzothiazole, MBT), Benzimidazole (BIMD), and Mercaptobenzimidazole (MBIMD) may be selected as the above-mentioned antioxidant protective film 11.

The antioxidant protective film 11 can also be composed of a compound of the general formula [2].

In the general formula [2], R is an alternative to H, SH, and SCH ₃ .

The organic compound of the general formula [2] 3-amino-1,2,4-triazole (3-amino-1,2,4 triazole, ATA), 3-amino-5-hydrogen sulfide-1,2 , 4-amino-5-mercapto1, 2,4 triazole, AMT, 3-amino-5-methylthio-1,2,4-triazole (3-amino-5-methylthio1,2 The alternative to Sodium 2-mercaptoethanesulfonate (MES) can be used as the above-mentioned antioxidant protective film 11.

<<Synthesis method of high stability nano metal particles>> Embodiment 1:

Step one, selecting a solid polyamic acid (PAA) containing a metal ion; the metal ion may be Cu ²⁺ ; in step 2, selecting a reducing solution containing an additive; the reducing liquid is dimethyl An aqueous solution of an amine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), which is a thiol compound selected, for example: MPS (3-Mercapto-1-pronaesulfoante)

MPE(3-Mercapto-1-propanol)

MPA (3-Mercapto-propionic acid)

MES(Sodium2-Mercaptoethanesulfonate)

TGC(Sodium thioglycolate)

DMPS (2,3-Dimercapto-1-propanesulfonic acid sodium)

Step 3, the solid polyimidic acid is placed in the reducing solution to reduce the metal ion to a metal atom, and the metal atom at this stage is still attached to the poly-proline; then, the metal atom is oxidized to the metal ion by the additive Forming a metal ion with an additive suspended in the reducing solution, and the metal ion with the additive is reduced by the reducing liquid into a nano metal particle (metal atom) with an additive; in step 4, the stabilizer is placed in the reducing liquid In the ultrasonic wave stirring for 10 minutes, the stabilizer is adsorbed and surrounded on the surface of the nano metal particles to form the high-stability nano metal (copper) particles of the present invention; the stabilizer comprises any of the above organic compounds, benzene Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzotriazole (BTAOH), Mercaptobenzothiazole (MBT), benzimidazole Benzimidazole, BIMD), thiothiabenzimidazole (Mercaptobenzimidazole, MBIMD), 3-amino-1,2,4-triazole (ATA), 3-amino-5-hydrogen sulfide-1,2,4 3-amino-5-mercapto1,2,4 triazole (AMT), 3-amino-5-methylthio-1,2,4-triazole (3-amino-5-methylthio1,2,4, AMTT), sodium 2-mercaptoethanesulfonate (MES).

Embodiment 2:

Step one, selecting a solid polyamic acid (PAA) containing a metal ion; the metal ion may be Cu ²⁺ ; in step 2, selecting a reducing solution containing an additive; the reducing liquid is dimethyl An aqueous solution of an amine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), which is a thiol compound selected, for example: MPS (3-Mercapto-1-pronaesulfoante)

MPE(3-Mercapto-1-propanol)

MPA (3-Mercapto-propionic acid)

MES(Sodium2-Mercaptoethanesulfonate)

TGC(Sodium thioglycolate)

DMPS (2,3-Dimercapto-1-propanesulfonic acid sodium)

Step 3, the solid polyimidic acid is placed in the reducing solution to reduce the metal ion to a metal atom, and the metal atom at this stage is still attached to the poly-proline; then, the metal atom is oxidized to the metal ion by the additive Forming a metal ion with an additive suspended in the reducing liquid, and the metal ion with the additive is reduced by the reducing liquid into a nano metal particle (metal atom) with an additive; in step 4, the aqueous solution type nano metal particle is added In an antioxidant solution, the antioxidant solution comprises water (or ethanol) and a stabilizer, and the stabilizer is any of the above organic compounds, benzotriene Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzotriazole (BTAOH), Mercaptobenzothiazole (MBT), Benzimidazole (Benzimidazole, BIMD), Mercaptobenzimidazole (MBIMD), 3-amino-1,2,4-triazole (ATA), 3-amino-5 Hydrogen sulfur-1,2,4 triazole (3-amino-5-mercapto1,2,4 triazole, AMT), 3-amino-5-methylthio-1,2,4-triazole (3-amino -5-methylthio1,2,4,AMTT), sodium 2-mercaptoethanesulfonate (MES); ultrasonically stirred for 10 minutes to surround the surface of the nanoparticle by adsorption of the stabilizer. High stability nano metal (copper) particles are formed.

<<High stability nano metal (copper) particles antioxidant experiment >>

In the second figure, the high-stability nano copper particles of the present invention were observed in the air together with the ordinary nano copper particles not coated with the antioxidant protective film.

From day 0 to day 5, the high-stability nano-copper particles were still uniformly suspended in the solution without oxidation and precipitation, and generally the nano metal particles were almost completely oxidized on the third day with a very small amount of precipitation. Only the fifth day is shown in the figure, but in fact the antioxidant capacity of the high stability nano copper particles of the present invention lasts for fourteen days.

The third figure is an ultraviolet visible spectrum (UV-Vis) of nano copper particles, wherein (a) is a high stability nano copper particle, and (b) is a general nano copper particle. It can be found that there is a UV absorption peak caused by surface plasma resonance phenomenon (SPR) of the copper particles at 550 nm, and the absorption peak is consumed over time, but does not exhibit significant shift, if nano copper When the particles are oxidized, their absorption peaks shift to the right, that is, toward the high wavelength. (a) There is still a significant absorption peak on the 6th day, (b) The absorption peak is only maintained for 3 days.

<<Experimental activity of high stability nano copper particles>>

This experiment demonstrates that the high stability nano copper particles of the present invention still have good catalytic catalytic activity by electroless plating. Although there are still many factors that affect the performance of electroless plating, the most important one is the activation step, which determines the reaction rate and reaction mechanism when depositing metals. The non-metal substrate itself is not active. To perform electroless plating on the surface of the non-metal substrate for metallization, it is necessary to first adsorb the catalyst on the surface of the non-metal substrate to promote dehydrogenation, oxidation and release of electrons to reduce the metal ions. Deposited on the surface of the catalytically active substrate to form a metal layer. Conventional electroless plating catalysts typically use palladium, however palladium metal is extremely expensive.

In the present invention, an electroless plating activation liquid is prepared by using high-stability nano copper particles, and the non-metal substrate is washed and dried, then immersed in the activation liquid of the present invention, taken out and dried, that is, electroless plating is performed. The plating bath formulation for electroless copper plating is as known, including a copper ion source, a chelating agent, a reducing agent, and a pH adjusting agent. After electroless plating, the substrate was taken out, and the adhesion test of the conductive metal layer and the non-metal substrate was performed with a 3M tape (adhesion test tape).

In order to highlight the high stability of the nano copper particles to retain the catalytic activity of copper particles due to their long-term oxidation resistance, the experiment is based on high-stability nano copper particles placed in the air for 6 days as a catalytic catalyst, and The general nano copper particles were used as a catalytic catalyst for comparison. The experimental results are shown in the fourth figure, (a) is the result of electroless plating using general nano copper particles as a catalytic catalyst; (b) is the result of electroless plating using high stability nano copper particles as a catalytic catalyst. It can be seen that only part of the surface of the substrate of (a) is plated, and (b) exhibits a comprehensive plating. This result shows that 6 is placed in the air The general nano-copper particles of the day lose their catalytic activity due to the oxidation phenomenon, but the high-stability nano copper particles of the present invention retain good catalytic activity due to their superior oxidation resistance.

As shown in the fourth figure (C), the substrate of (b) is tested for adhesion of the conductive metal layer to the non-metal substrate with a 3M tape (adhesion test tape), and a small amount of conductive metal is attached to the tape to indicate that the conductive metal layer is non-metallic. The adhesion of the metal substrate meets industrial requirements.

Based on the above experimental results, the high-stability nano copper particles of the present invention can replace palladium as a catalyst for electroless plating.

<<The high-stability nano copper particles are fixed to the substrate by chemical grafting>>

This experiment was grafted on a substrate by the method of the Republic of China Invention Patent Publication No. 201230744 (hereinafter referred to as the 744 case), which is one of the inventors of the present invention, as a catalytic catalyst for electroless plating seed layer. The results of the hole-fill plating show that the high-stability nano copper particles of the present invention can be applied to the field of semiconductors.

The grafting method is performed on a tantalum substrate having a cavity having a high aspect ratio, and the inner wall of the hole is preset with a barrier layer. The pore diameters were 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm. The high-stability nano copper particles that have just been synthesized are used.

Step 1: contacting the ruthenium substrate with a first solution to form a first graft unit on the surface of the barrier layer; the first solution comprises 3-aminopropyltrimethoxymethane and a grafting substance, The grafting substance may be an amine group-containing compound; in step 2, the ruthenium substrate having the first graft unit is contacted with a second solution; the second The solution comprises a compound having high stability nano copper particles, such as thioglycolic acid comprising high stability nano copper particles; the first grafting unit chemically bonds with the compound having nano metal particles, making the invention high The stable nano copper particles are grafted on the first grafting unit to form a high stability nano copper particle grafting layer; in the third step, the high stability nano copper particle grafting layer is electrolessly plated. The upper layer of copper seed layer is formed; in step 4, copper is plated on the copper seed layer by electroplating copper hole filling technology to complete the hole filling.

The fifth figure is the SEM image of the hole-filling results. The holes are filled in the pores of each pore diameter, which shows that the high-stability nano copper particles of the present invention do have catalyst catalytic effect, so that the copper seed layer is indeed fixed and the pore filling is performed. The effectiveness of plating.

<<Conclusion>>

In summary, the above experiments all prove that the high-stability nano copper particles of the invention have remarkable antioxidant capacity, and the oxidation time thereof is extended from the conventional 1-2 days to at least 14 days.

The above electroless plating experiment results show that the high-stability nano copper particles can be directly used as a catalyst for electroless plating without removing the anti-oxidation protective layer on the surface, and the non-conductive substrate can be smoothly electrolessly plated.

The results of the above-mentioned hole-filling electroplating experiment show that the high-stability nano-copper particles do not need to remove the anti-oxidation protective layer on the surface, and can also be grafted on the ruthenium substrate, and the hole-fill plating is successfully completed.

10‧‧‧Nano metal particles

11‧‧‧Antioxidant protective film

The first figure (a), (b) and (c) show the state of the high-stability nano copper particles of the present invention under an electron microscope.

The second graph depicts the variation of the high stability nano copper particles of the present invention with the conventional nano copper particles not coated with the antioxidant protective film for several days in the air.

The third figure is an ultraviolet visible spectrum (UV-Vis) of nano copper particles, (a) is a high-stability nano copper particle of the present invention, and (b) is a general nano copper particle.

The fourth diagram (a) is the result of electroless plating using general nano copper particles as a catalytic catalyst; (b) the result of electroless plating using the high stability nano copper particles of the present invention as a catalytic catalyst; The adhesion test results of the conductive metal layer and the non-metal substrate were performed on the substrate of (b) with a 3M tape (adhesion test tape).

The fifth figure describes that the high-stability nano copper particles of the present invention are grafted onto the barrier layer of a high aspect ratio hole by a chemical grafting method, and serve as a catalyst for the copper seed layer to complete the copper seed layer. The electroless plating, and the SEM image of the hole filling on the copper seed layer.

Claims (8)

A high-stability nano metal particle comprising: one nano metal particle; the nano metal particle is a nano copper particle; an anti-oxidation protective film coated on the outside of the nano copper particle; the antioxidant protective film is It is composed of an organic compound containing a benzene ring; wherein the organic compound containing a benzene ring is Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzene triazole (1- Hydroxybenzotriazole (BTAOH), Mercaptobenzothiazole (MBT), Benzimidazole (BIMD), Mercaptobenzimidazole (MBIMD); Nanoparticle coated with the antioxidant film Copper particles have catalytic catalytic activity in electroless plating systems. A high-stability nano metal particle, comprising: a nano metal particle, wherein the nano metal particle is a nano copper particle; an anti-oxidation protective film coated on the outside of the nano copper particle; the anti-oxidation protective film is The nitrogen-containing heterocyclic compound is 3-amino-1,2,4-triazole (3-amino-1,2,4 triazole, ATA), 3-amino group -5 hydrogen sulfide-1,2,4 triazole (3-amino-5-mercapto1,2,4 triazole, AMT), 3-amino-5-methylthio-1,2,4-triazole (3 -amino-5-methylthio1,2,4,AMTT), sodium 2-mercaptoethanesulfonate (MES). A stabilizer for producing high-stability nano metal particles as described in claim 1 of the patent application, a stabilizer is added to the solution of the synthetic nano copper particles, the stabilizer has an anti-oxidation protective film on the outside of the nano copper particles produced by the solution, and the nano copper particles coated with the anti-oxidation protective film Catalytic activity in electroless plating systems; Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzotriazole (BTAOH) , Mercaptobenzothiazole (MBT), Benzimidazole (BIMD), Mercaptobenzimidazole (MBIMD). A stabilizer for producing high-stability nano metal particles as described in claim 2, the stabilizer being added to a solution of synthetic nano copper particles, the stabilizer producing nano copper produced by the solution The outer part of the particle has an anti-oxidation protective film, and the nano copper particles coated with the anti-oxidation protective film have catalytic catalytic activity in the electroless plating system; the stabilizer is 3-amino-1,2,4-three 3-amino-1,2,4 triazole, ATA, 3-amino-5-mercapto1,2,4 triazole, AMT , 3-amino-5-methylthio-1,2,4-triazole (3-amino-5-methylthio1,2,4,AMTT), sodium 2-mercaptoethanesulfonate (Sodium 2-mercaptoethanesulfonate, MES). A method for producing high-stability nano metal particles according to claim 1, comprising: step one, selecting a solid polyamic acid (PAA) containing copper ions; a stock solution; the reducing liquid is selected from an aqueous solution of dimethylamine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), the additive is a thiol compound; Polyamic acid is placed in the reducing liquid to produce nano copper particles in the reducing liquid; in step three, a stabilizer is placed in the reducing liquid, and the reducing liquid is stirred to cause the stabilizer to be adsorbed and surrounded by a surface of the copper-copper particles forms an anti-oxidation protective film on the surface of the nano-copper metal particles to form high-stability nano-copper particles, and the nano-metal particles coated with the anti-oxidation protective film are in an electroless plating system Catalytic activity; the stabilizer is selected from Benzotriazole (BTA), Benthzothiadiazole (TDA), 1-hydroxybenzotriazole (BTAOH), thiol Benzothiazole (Mercaptobenzothia) Zole, MBT), benzimidazole (BIMD), Mercaptobenzimidazole (MBIMD). A method for producing high-stability nano metal particles according to claim 2, comprising: step one, selecting a solid polyamic acid (PAA) containing copper ions; a stock solution; the reducing liquid is selected from the group consisting of an aqueous solution of dimethylamine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), the additive is a thiol compound; and the second step is the solid state. Polyamic acid is placed in the reducing liquid to produce nano copper particles in the reducing liquid; in step three, a stabilizer is placed in the reducing liquid, and the reducing liquid is stirred to cause the stabilizer to be adsorbed and surrounded by The surface of the gold-plated copper particles forms an anti-oxidation protective film on the surface of the nano-copper particles to form high-stability nano-copper particles, and the nano-copper particles coated with the anti-oxidation protective film have an electroless plating system. Catalytic catalytic activity; the stabilizer is selected from the group consisting of 3-amino-1,2,4-triazole (3-amino-1,2,4 triazole, ATA), 3-amino-5-hydrogen sulfide-1 , 2,4 triazole (3-amino-5-mercapto1, 2,4 triazole, AMT), 3-amino-5-methylthio-1,2,4-triazole (3-amino-5-met Hylthio1, 2, 4, AMTT), sodium 2-mercaptoethanesulfonate (MES). A method for producing high-stability nano metal particles according to claim 1, comprising: step one, selecting a solid polyamic acid (PAA) containing copper ions; a stock solution; the reducing liquid is selected from the group consisting of an aqueous solution of dimethylamine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), the additive is a thiol compound; and the second step is the solid state. Polyamic acid is placed in the reducing solution to produce nano copper particles in the reducing solution; in step three, the nano copper particles are placed in an anti-oxidation solution, and the stabilizer is placed in the antioxidant solution. The anti-oxidation solution is stirred to adsorb the stabilizer on the surface of the nano metal particles, and an anti-oxidation protective film is formed on the surface of the nano-copper particles to form high-stability nano copper particles, and the anti-coating is coated. The nano-particles of the oxidized protective film have catalytic catalytic activity in an electroless plating system; the anti-oxidation solution contains water or ethanol, and a stabilizer selected from Benzotriazole (BTA), Toluene diamine (Benthzo Thiadiazole, TDA), 1-hydroxybenzotriazole (BTAOH), Mercaptobenzothiazole (MBT), Benzimidazole (BIMD), Mercaptobenzimidazole (Mercaptobenzimidazole, MBIMD). A method for producing high-stability nano metal particles according to claim 1, comprising: step one, selecting a solid polyamic acid (PAA) containing copper ions; a stock solution; the reducing liquid is selected from the group consisting of an aqueous solution of dimethylamine borane ((CH ₃ ) ₂ NHBH ₃ , DMAB), an aqueous solution of sodium borohydride (NaBH ₄ ), the additive is a thiol compound; and the second step is the solid state. Polyamic acid is placed in the reducing solution to produce nano copper particles in the reducing solution; in step three, the nano copper particles are placed in an anti-oxidation solution, and the stabilizer is placed in the antioxidant solution. The anti-oxidation solution is stirred to adsorb the stabilizer on the surface of the nano metal particles, and an anti-oxidation protective film is formed on the surface of the nano-copper particles to form high-stability nano copper particles, and the anti-coating is coated. The nano metal particles of the oxidized protective film have catalytic catalytic activity in an electroless plating system; the antioxidant solution contains water or ethanol, and a stabilizer selected from the group consisting of 3-amino-1,2,4- Triazole (3-amino-1, 2, 4 triazole, ATA), 3-Amino-5-mercapto-1,2,4 triazole (AMT), 3-amino-5-methylthio-1,2,4-tri A choice of azozolium (3-amino-5-methylthio1,2,4,AMTT) and sodium 2-mercaptoethanesulfonate (MES).