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Submitted on 1 Jan 1988
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CRYSTALLINE TO AMORPHOUS
TRANSFORMATION IN B+ ION IMPLANTED Fe
FILMS
Si-Yun Bi, Yue-Lu Zhang, Lliang-Mo Mei
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Supplement au no 12, Tome 49, dkcembre 1988
CRYSTALLINE TO AMORPHOUS TRANSFORMATION
INB+
ION IMPLANTED
Fe
FILMS
Si-yun Bi, Yue-lu Zhang and Lliang-mo Mei
Department of Physics, Shandong University, Jinan, China
Abstract. - The transformation of crystalline Fe films to amorphous alloy by implanting B+ ions was studied by using the technique of conversion electron Mossbauer spectroscopy. The analysis of the fraction of the amorphous phase and its hf parameters as functions of B+ ion dose and the phases formed after crystallizing show that chemical short-range order (CSRO) plays an important part in the formation and stability of the ion-induced amorphous phases.
Polycrystalline Fe films can be transformed into amorphous Fe-B alloy by implanting B ions [I]. In this paper the influence of implanted B ion dose on amor- phization and the formed amorphous product were studied by means of conversion electron Mossbauer spectroscopy (CEMS).
Polycrystalline Fe films of 1 500
k
thickness were deposited on single crystal silicon wafers by thermal evaporation. Then, 30, 60 and 100 Kev B ions were implanted into the Fe films in turn with the dose ra- tio 20:35:45. The conversion electron Mossbauer spec- tra of as-deposited and implanted films were recorded by using a constant accelerated Mossbauer set up with 5 7 ~ o / ~ h source. The computer fitting of the Mossbauer spectra was carried out using the standardMOSFUN program on PDP11/34 computer system. Figure 1 shows the Mossbauer spectra recorded for an as-deposited sample and after implanting 10 x 1016,
20 x 1016, 30 x 1016 and 40 x
loz6
ions/cm2 as well the fitted results.It can be seen from figure 1 that the amorphous phase is formed in the implanted Fe films when the dose of the implanted ions is beyond a critical value and this fraction increases with the B ion dose. How- ever, the corresponding hyperfine structure basically remains unchanged. The amount of the amorphous material in the implanted film as a function of the B
ion dose is shown in figure 2. In figure 1 and figure 2
it can be seen that when the dose of the implanted ions is less than 10 x 1016 ions/cm2 the effects of im- planting B ions in the Fe film result in a broadening of the linewidths, which suggests there are defects due to implanted damage [2], and increasing the intensities of lines 2 and 5, which shows the magnetization in the implanted film gradually lies in the film plane, but the crystal structure of the film is still a-Fe. In the case of small and moderate doses, the amorphous amount increases almost linearly, while the corresponding hy- perfine field and isomer shift remain constant until all the film is amorphized completely. From the average hyperfine field (255 KOe) and isomer shift (0.11 mm/s) it can be infered that the formed amorphous phase is basically the Fe75B25 alloy [3].
Fig. 1.
-
The conversion electron Mossbauer spectra of polycrystalline Fe films after implantin B ions with dif- ferent doses, 0, 10 x loL6, 20 x 1018, 30 x 1016 and40 x 10'' ions/cm2.
C8
-
1366 JOURNAL DE PHYSIQUEIn order to study the distribution of the amorphous phase in the implanted film, 400 was removed by ion etching from the surface of the film implanted 30x 1016.
Then the Mossbauer spectrum at room temperature was recorded, as shown in figure 3a. It can be seen that the Mossbauer spectral structure is almost the same as before, which implies that the distribution of the implanted B ions and the amorphous phase formed in the implaated film is basically homogeneous. This result maybe is due to implanting ions in turn at three different energy.
The Mossbauer spectra b, c and d in figure 3 are those of the film after annealing respectively at 150°, 300' and 400 "C in vacuum for an hour. After anneal- ing at low temperature, the linewidths of a-Fe phase in the Mossbauer spectrum become narrow, but the ratio of the two phases did not change at all, which shows that the recovery of implanted damage plays an im- portant part in low temperature annealing. After an- nealing at 300 OC, the amount of the amorphous phase decreases remarkably, which indicates that B atoms in the amorphous phase begin to diffuse into the a-Fe. Annealing at 400 OC, the amorphous phase in the film has crystallized and the new phases after crystallizing are the mixture of a-Fe and FezB crystallites [4].
The above experimental results show that when the dose of B ions implanted into the Fe film is beyond a certain critical value the amorphous clusters are first formed in the local small areas in which B ion concen- tration reaches an adequate threshold, that is, 25 % in
L . . . j
-6
-4
-2O
24
cjV
(mm/s)
Fig. 3. - The conversion electron Miissbauer spectra of the
Fe film implanted with the dose, 30 x 1.0'' ions/cm2 af-
ter removing 400
A
from the surface of the film at room temperature and after annealing at 150°, 300° and 400 OCin vacuum for an hour.
our implanting condition and the formed amorphous phase is basically Fe75B25 alloy. So chemical short- range order (CSRO) plays an important part in the formation and stability of the ion-induced amorphous phases.
111 Mei Liang-mo, et al., J. Magn. .Magn. Mater. 59
(1986) 346.
[2] Gibbons, J. F., Proc. IEEE 60 (1972) 1062. 131 Dennis, John R. ,and Hale, Edward B., J. Appl.
Phys. 49 (1978) 1119.
