Formation of Metal Nitrides by Nitrogen Implantation
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Mat. Res. Soc. Symp. Proc. Vol. 54,
1986 Materials Research Society
618
identify the phases present in the thin film samples. RESULTS Two typical X-ray diffraction spectra are shown in Figures I and 2, which provide clear and definite evidence of the formation of metal nitrides. Most of the nitrides observed started to appear at implantation doses of the order of 1017 ions/cm2 . The thin metal films implanted to high doses were almost completely converted to their corresponding nitrides as revealed by the absence of the diffraction lines of the matrix metals. A summary of all the metal nitrides obtained in this study is given in Table I. Also listed in it are other nitrides not observed and those obtained by ion implantation as reported in literature. Many equilibrium nitrides did form by room temperature nitrogen implantation, while others were not observed even at very high doses. Table I. Nitride Formation by Nitrogen Implantation in 10 Selected Metals
Ti
Nitrides obtained
Nitrides not obtained
TiN
Ti 2 N
Zr
ZrN
Al
AlN
Nb
Nb2N and NbN(fcc)
Nitrides in literature* TiN
ZrN AIN Conflicting results, NbN or amorphous Cu3 N is unstable and has ordered structure, unfavoured.
Cu 3N
Cu
W
W2 N and WN
Co
Co 3 N
Structural transition needed for Ti 2 N is unfavoured.
Amorphous, tentative Co 2 N, CoN and Co4N
Co4 N, tentative Unfavourable structural transition for both Co2 N and CoN, Co4 N probably unstable
Ni
Ni 3 N
Gd
GdN
Sn
Ni 4 N S
N34
Ni3 N
Ni 4 N probably unstable Sn 3 N4 unstable and structural transition unfavoured
*See Ref. 6 and references therein. It should be pointed out that in the X-ray spectra of the high dose implanted samples many of the nitride peaks appear at a d-value(planar spacing) This may be attrilarger than the standard value given by the ASTM cards. buted to nitrogen supersaturation and/or the presence of elastic stresses. A medium temperature annealing of these as-implanted nitrides indeed caused relaxation of the structure to approach the standard spacing values.
619
4
F 1
F.I.X-ray spectrum far bulk Ti inplanted by N+ to a dose of 5X10
17
2
/an .
0
F. 0 o5
0 0
C
60
)5
50
45
40
55
26 Fig. 2.
X-ray spectrum for Ni film ( _1000R) inplanted by N+ to a dose of 17 2 5X10 /an
DISCUSSION
There have been much discussion concerning the ion beam induced phase transformation, especially from crystalline to metastable state or vice versa. Some empirical criteria are advanced to predict the amorphization induced by ion beam [5], emphasizing either on the solubility range of the compound (Brimhall et al. ), structural and kinetic consideration (Liu et al. and Hung et al. ), the heat of formation (Alonso et al. ) or polymorphic transition (Johnson et al. ). In a general discussion of metalloid implantation into metals, Rausenbach and Hohmuth [6] proposed a criterion based on Hagg's rule stating that amorphization will occur in systems where R (the ratio of the radius of the metalloid atwi to that of the metal atom) is larger than 0.59. As far as the nitrog
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