Thin Polymeric Films Produced by Ion Implantation from Frozen Organic Molecules
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THIN POLYMERIC FILMS PRODUCED BY ION IMPLANTATION FROM FROZEN ORGANIC MOLECULES
L. CALCAGNO, K. L. SHENG* AND G. FOTI Instituto Dipartimentale de Fisica, UniversitA di Catania, Corso Italia 57, 195129, Catania, Italy
ABSTRACT The synthesis of polymeric films under ion bombardment of frozen benzene has been investigated for the dependence of the thickness on the fluence and beam energy of keV proton and argon ions. Chemical analyses have been performed to characterize the films.
INTRODUCTION The physical and chemical properties of polymers can be heavily changed when they are irradiated with ion beams. Electrical resistivity [1] or solubility [2] of organic films has been modified by several orders of magnitude after implantation of keV ions in the fluence range 1 4 16 2 10 -10 /cm . Polymeric films can be produced by irradiation of monomers deposited on cold substrates in high vacuum environments. Such an approach is a potential method for ion beam lithography [3] because of the low scattering of the incoming beam. In beams,
this work we show the polymerizing process induced by energetic ion with frozen benezene acting as the monomer.
EXPERIMENTAL METHOD A solid layer of benzene was formed by condensation from the gas phase on a cold substrate (77K) in a vacuum chamber (%10- 7 torr). The thickness of the deposited layer was directly measured with X-ray emission induced by a 100 keV proton beam on the gold substrate [4]. This technique is sensitive to the energy loss of the proton beam and the thickness of the 2 film will be given as carbon atoms/cm because the energy loss for hydrogen is negligible. After growing the film, the target was bombarded at low temperature with proton and argon ions at different energies. The 2 beam flux was maintained below 10+2 nA/cm and the fluence ranged 2 between 1014 and 1016 ions/cm . After bombardment the sample was warmed-up and the volatile molecules which came out from the target were measured with a gas chromatography system. The thickness of the stable organic film at room temperature was measured by using the X-ray emission technique and chemical composition was analyzed with Auger Electron Spectroscopy. *Permanent address: Institute of Nuclear Research, Academia Sinica, Visiting scientist on the basis of INFN - Academia Sinica cultural exchange plan.
Mat. Res.
Soc. Symp. Proc. Vol.
27 (1984) GElsevier Science Publishing Co.,
Inc.
550
RESULTS AND DISCUSSION Fig.l reports the thickness of synthesized residue as a function of All the experimental points are obtained fluence for proton irradiation. with the same starting thickness of the deposited film (To=1.5xlOl8 2 carbon atoms/cm ), which is small compared with the range of 100 keV 1 8 2 The residual thickness protons (8.6xi0 carbon atoms/cm ) in carbon. T is proportional to fluence (4) for low values, while for high fluence it thickness of reaches a saturation level which coincides with the initial deposited film To.
1.5-To ;71
0 Fig.l. Number of bonded carbon
0O 0
E S1.0 C
atoms in the film obtained with d
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