Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2000-04-03
2001-04-17
Turner, Archene (Department: 1775)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C252S501100, C252S518100, C252S519100, C252S519140, C252S519400, C423S592100, C423S618000, C423S624000, C423S596000, C423S598000, C423S606000, C423S608000, C423S610000, C423S635000, C423S641000, C423S566200, C423S566300, C427S331000, C427S335000, C427S372200, C508S108000
Reexamination Certificate
active
06217843
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is the national stage under 35 U.S.C. 371 of PCT/IL97/00390, filed Nov. 27, 1997.
FIELD OF THE INVENTION
The present invention relates to a method for the preparation of nanoparticles of metal oxides containing inserted metal particles and to metal-intercalated and/or metal-encaged “inorganic fullerene-like” (hereinafter IF) structures of metal chalcogenides obtained therefrom. According to the invention, either heating a metal I material with water vapor or electron beam evaporation of said metal I material with water or another suitable solvent, in the presence of a metal II salt, produces metal II-doped metal I oxides, and subsequent sulfidization, yields bulk quantities of metal II-intercalated or metal II-encaged IF structures (nested fullerenes, nanotubes, and structures with negative curvature) of metal I chalcogenides. The intercalated and/or encaged IF structures form stable suspensions, e.g. in alcohol, and electrophoretic deposition from said suspensions yields thin films of the intercalated IF materials, with a range of potential applications such as the photosensitive element in solar cells, for the fabrication of inert scanning probe microscope (SPM, that includes both STM=scanning tunneling microscope and SFM=scanning force microscope) tips, secondary batteries and electrochromic devices. The metal-intercalated or metal-encaged IF structures can further be used as solid lubricants.
BACKGROUND OF THE INVENTION
Nanoclusters of various inorganic layered compounds, like metal dichalcogenides—MX
2
(M=Mo,W;X=S,Se), are known to be unstable in the planar form and to form a hollow cage—inorganic fullerene-like (IF—MX
2
) structures such as nested fillerenes and nanotubes (Tenne et al., 1992; Feldman et al., 1995 and 1996; published European Patent application No. EP 0580019) and structures with negative curvature (Schwartzites). Not surprisingly, nanoparticles of hexagonal boronitrides with graphite-like structure behaved similarly (Stephan et al., 1994; Chopra et al., 1995). Furthermore, nested fullerene-like polyhedra of MoS
2
were synthesized at room temperature by a stimulus from an electron beam (José-Yacamán et al., 1996) in analogy to carbon-nested fullerenes (Ugarte, 1992), and also by application of an electric pulse from the tip of a scanning tunneling microscope (STM) (Homyonfer et al., 1996).
Intercalation of carbon nanotubes with alkali metal atoms from the vapor phase was recently described (Zhou et al., 1994). The intercalated films were found to arrange in stage-1 (n=1) superlattice, i.e. alkali-metal layers were stacked between each two carbon layers. The composite nanostructures were found to disintegrate when exposed to air, and complete shattering of the nanotubes (exfoliation) was obtained upon immersion in water. The intercalation of 2 H—MoS
2
and 2 H—WS
2
compounds was discussed in detail (Brec and Rouxel, 1986; Friend and Yoffe, 1987; Somoano et al., 1973), but staging was not observed in either of the former compounds, i.e. the alkali atoms were found to have a random distribution. Here too, deintercalation occurs upon exposure to air and exfoliation upon immersion in water.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a new method for the synthesis of large quantities of IF structures of metal chalcogenides that affords intercalation of the IF structures with various metal atoms. Metal intercalation has a remarkable influence on the solubility of these IF structures in aprotic solvents. The formations of stable suspensions from the metal-intercalated or metal-encaged IF structures permits deposition of thin films, with a range of potential applications such as the use of such films as the photosensitive element in solar cells, for the fabrication of inert SPM tips, secondary batteries and electrochromic devices.
The present invention thus relates, in one aspect, to a method for the preparation of nanoparticles or nanowhiskers of a metal II-doped metal I oxide, wherein said metal I is selected from In, Ga, Sn and a transition metal and said metal II is any metal, preferably a metal selected from an alkali, alkaline earth or a transition metal, which method comprises:
(i) heating a metal I material with water in a vacuum apparatus at a base pressure of 10
−3
to 10
−5
Torr or electron beam evaporating a metal I material with water or with an oxygen-containing volatile solvent in a vacuum apparatus at a base pressure of 10
−5
to 10
−6
Torr, in the presence of a metal II salt, and
(ii) recovering the metal II-doped metal I oxide from the walls of the vacuum apparatus.
The metal I material may be the metal I itself or a mixture of 2 or more different metals I, or a substance comprising a metal I or a mixture of substances comprising 2 or more different metals I. Examples of transition metals include, but are not limited to, Mo, W, V, Zr, Hf, Pt, Re, Nb, Ta Ti, and Ru. The elctron beam evaporation embodiment is more suitable for refractory transition metals, e.g. Nb, V, Ta, Ti.
Examples of metal II salts include, but are not limited to, alkali metal chlorides such as NaCl, KCl, LiCl and CsCl. Examples of doped oxides thus prepared include, but are not limited to, Na, K, Li or Cs-doped MoO
3−x
, preferably MoO
2
and MoO
3,
, or Na, K, Li or Cs-doped WO
3−x
, preferably WO
3
and W
18
O
49
, or Na, K, Li or Cs-doped mixed oxide such as Mo
x
W
1−x
O
3
, wherein x is from 0 to 1, and Na, K, Li or Cs-doped V
2
O
5
, preferably Li-doped V
2
O
5
.
According to the invention, the metal II salt may be added to the water or to the oxygen-containing volatile solvent, or when it is NaCl or KCl, it is already present in the water.
Examples of suitable oxygen-containing volatile solvents are, without being limited to, acetone, ethanol, methanol.
The metal II-doped metal I oxides thus prepared are useful as starting products for the preparation of metal II-intercalated and/or metal II-encaged inorganic fuillerene-like (IF) structures of a metal I chalcogenide, wherein metal I and metal II are as defined above, which method comprises:
(i) heating a metal I material with water in a vacuum apparatus at a base pressure of 10
−3
to 10
−5
Torr or electron beam evaporating a metal I material with water or with an oxygen-containing volatile solvent in a vacuum apparatus at a base pressure of 10
−5
to 10
−6
Torr, in the presence of a metal II salt;
(ii) arnealing the metal II-doped metal I oxide obtained in step (i) in a reducing atmosphere with a H
2
X gas, wherein X is S, Se, or Te; and
(iii) recovering the metal II-intercalated and/or metal II-encaged inorganic fullerene-like (IF) structures of the metal I chalcogenide.
The expression “inorganic fullerene-like” (“IF”) as used herein refers to inorganic metal chalcogenide structures having one layer or nested layers which form what is known in the art as a closed cage (Tenne et al., 1992; Margulis et al., 1993) which may encage a core or may form a stuffed nested layer structure. In particular, the term refers to structures such as what is known in the art as single and double layer inorganic fullerenes (Srolovitz et al., 1995), nested layer inorganic fullerene (Tenne et al., 1992), stuffed inorganic fullerenes (Margulis et al., 1993), structures with negative curvature (Schwartzites), single layer nanotubes (Bethune et al., 1993; Iijima and Ichiashi, 1993), nested nanotubes (Iijima, 1991) and stuffed nanotubes (Ajayan and Iijima, 1993).
Thus, IF structures of metal I chalcogenides intercalated with metal II particles, said IF structures including one or more metal I chalcogenide layers of desired size and shape (e.g. spheres, nanotubes, structures with negative curvature (Schwartzites), and polyhedral shapes), being hollowed or having a metal II-doped metal I oxide core, may be produced using the method of the present invention.
As used herein, “metal II-encaged IF structures of metal I chalcogenide” refers to IF st
Feldman Yishay
Homyonfer Moshe
Tenne Reshef
Browdy and Neimark
Turner Archene
Yeda Research and Development Co. Ltd.
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