Processes for the production of zintl compounds,...

Details Processes for the production of zintl compounds,... Processes for the production of zintl compounds,...

2000-12-22

2003-01-07

Sheehan, John (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

C148S253000, C148S261000, C427S226000

Reexamination Certificate

active

06503342

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to processes for the production of Zintl compounds, processes for the production of intermetallic compounds and processes for manufacturing electronic components including intermetallic compounds. In particular, this invention relates to the application of intermetallic compounds in the manufacture of electronic components. More specifically, this invention relates to a method of applying intermetallic compositions onto the surface of electronic components.
BACKGROUND OF THE INVENTION
Intermetallic compounds and Zintl phases have been known for some time. Zintl compounds are binary compounds formed between alkali or alkaline earth elements and post transition elements [(see for example, “Chemistry, Structure, and Bonding of Zintl Phases and Ions”, Ed. Susan M. Kauzlarich, VCH Publishers, (1996)]. One of the earliest examples of Zintl ions were those formed by the reaction of sodium in liquid ammonia with a variety of Group 14 metals, such as lead, to form, e.g. 4[Na(NH
3
)
n
+
][Pb
9
]
4−
. These complexes are unstable due to the facile liberation of NH
3
, which can occur at low temperatures to form intermetallic compositions of the type NaPb
x
.
The isolation of solid derivatives of Zintl anions using ethylenediamine in the place of ammonia has been reported in which the alloy composition NaSn
2.4.2.5
, on slow dissolution in warm ethylenediamine followed by precipitation on the addition of THF or monoglyme, generates the species Na
4
(en)
7
Sn
9
(en=ethylenediamine).
Macrocyclic ligands, such as 2,2,2-crypt, have been used in place of ammonia or ethylenediamine due to their effective sequestering capabilities. The stability of these cryptate complexes, an example of which includes [2(2,2,2-crypt-K)
+
[Pb
5
]
2+
, have enabled extensive characterisation of their crystal structures.
However, hitherto, the available techniques for producing Zintl compounds, have been cumbersome, especially where it is desired to produce Zintl compounds with predetermined stoichiometries. For example, the majority of these compounds have been obtained by dissolving pre-formed stoichiometric alloys of metals in ammonia. This route, which is required to obtain stoichiometric control of the product, involves high-temperature methods and highly specialised techniques. As a result, Zintl compounds, particularly of the heaviest (most metallic) post-transition elements, have generally only been prepared in very small scale (10-50 mg) and have therefore not been broadly accessible to the majority of synthetic chemists or useful in industrial processes.
SUMMARY OF THE INVENTION
As indicated, the invention also relates to processes for producing intermetallic compounds. Intermetallic compounds, which may be defined as mixed metal compounds of the type M
1
x
M
2
y
. . . M
3
z
, possess properties that do not necessarily resemble the respective alloys and often exhibit properties which are intermediate between their component elements.
The majority of intermetallic alloys behave as semi-conductors and have thus found extensive applications in the electronics industry. Some intermetallic compounds display photoactive properties and these have been employed in photodetector components. The properties of the intermetallic layer are dependent upon the stoichiometry of the metal components. Thus the stoichiometric control of the metal components is important in order to achieve the desired electrical properties of the intermetallic layers.
The existing process for the manufacture of electronic components such as vacuum photodiodes having intermetallic layers based on antimony and alkali metals, involve the high temperature formation of antimony/alkali metal intermetallic layers using metal vapours. This deposition process typically involves predepositing an antimony layer onto the surface of the electronic component, followed by the addition of an alkali metal in vapour form. This process is highly labour intensive and the characteristics of the intermetallic films deposited are often variable as a consequence of inherently poor control of their stoichiometry.
It would therefore be highly desirable to improve the method in which intermetallic layers can be deposited onto electronic components during their manufacture. In addition, it would be advantageous to obtain a higher degree of stoichiometric control than those offered by the existing vapour deposition method.
Thus, it is a further object of the present invention to provide an improved process of forming intermetallic layers for use in the manufacture of electronic components. Such electronic components include photomultipliers and other photodetectors used in, e.g., medical scanners and scientific instruments.
Another object of the present,invention is to provide a method of producing intermetallic layers in which the stoichiometry can be controlled to furnish films with essentially consistent characteristics.
The present invention in all its aspects followed from the development of a novel procedure for producing Zintl compounds from stable precursors. This procedure enabled for the first time the production of Zintl compounds by a convenient route in a manner which permitted the Zintl compounds to be produced with preselected stoichiometries between the metal components thereof.
Advantageously, the use of a stable precursor to generate a Zintl compound that may be subsequently converted to an intermetallic alloy according to the present invention, allows the possibility for the deposition of the intermetallic alloy from solution at low temperature. Such a method provides a substantial improvement over existing vapour phase deposition techniques. The method of the present invention provides a convenient route to the formation of Zintl compounds on a gram or multi-gram scale.
Thus, the invention provides a novel application of Zintl compounds, especially when produced in accordance with the first aspect of the invention, in the manufacture of electronic components having surface coatings formed from intermetallic compounds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, there is provided a process for the production of a Zintl compound comprising subjecting a heterometallic phosphinidene complex to thermal decomposition.
The heterometallic phosphinidene complex typically comprises at least two metals. Preferably one of the metals may be a metal of Group 13, 14 or 15 of the Periodic Table. Particularly preferred metals are those from Group 15 of the Periodic Table, including As, Sb and Bi.
The second of the metals is preferably a metal of Group 1 of the Periodic Table, e,g, Li, Na, K, Rb or Cs.
The heterometallic phosphinidene complex used in the process of the invention preferably contains one or more phosphinidene ligands [PR], which may be the same or different. The phosphorus atom of each phosphinidene ligand is covalently linked to a substituted or unsubstituted hydrocarbyl group, R.
The unsubstituted or substituted hydrocarbyl group, R, typically contains 1 to 15, preferably 4 to 10 carbon atoms, and may be selected from alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, and alkaryl. Typical substituents include F and alkylsilyl groups.
A particularly preferred phosphinidene ligand is PCy (Cy=cyclohexyl, C
6
H
11
), wherein the phosphorus atom is linked to a cyclohexyl group. Other examples of possible substituents include
t
Bu [tertiary butyl, (CH
3
)
3
C—],
i
Pr [isopropyl, (CH
3
)
2
CH—], bis(trimethylsilyl)methyl [(CH
3
Si)
2
CH—], tris(trimethylsilyl)methyl {[(CH
3
)
3
Si]
3
C—}, trimethylsilyl [(CH
3
)
3
Si] and fluorinated groups such as pentafluorophenyl (C
6
F
5
).
The phosphorus atom of each phosphinidene ligand in the heterometallic phosphinidene complex is generally coordinated to four metal atoms. It is preferred that the phosphorus atom is coordinated to three Group I metal atoms and one metal atom of Groups

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