Iron Sulfide (FeS 2 ) Thin Films From Single-Source Precursors by Aerosol-Assisted Chemical Vapor Deposition (AACVD)
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133 Mat. Res. Soc. Symp. Proc. Vol. 606 ©2000 Materials Research Society
above precursors by LP-MOCVD and AACVD techniques and as analyzed by XRD, EDAX and SEM. EXPERIMENTAL Chemicals Carbon disulfide, sodium hydroxide, methylisopropyl amine (MeiPrNH), dibutyl amine (nBu 2NH) and iron (III) chloride were purchased from Aldrich chemical Company Ltd. Methanol and THF were from BDH and used without further purification. Instrumentation X-Ray diffraction (XRD): XRD patterns were measured using a Siemens D500 series automated powder diffractometer using Cu-Kcx (radiation at 40 kV/40 mA) with a secondary
graphite crystal monochromator. Samples were mounted on glass slides (5 x 5cm) and scanned from 10 -60 °C in steps of 0.040 with a count time of 2 sec. Energy Dispersive X-ray microanalysis (EDAX) was performed on a LINK QX2000 energy dispersive X-ray microanalysis unit. Scanning Electron microscopy (SEM): the samples were gold-coated using a Balzers SCD 030 sputter coating unit before electron microscopy was carried out on a JEOL JEM-1200 EX-II microscope. Preparation of sin2le-source precursors The precursors were prepared by literature methods14 and analyzed by CHN and IR. Solutions of sodium salts of the ligands were prepared by adding 0.05 mol of CS 2 to a solution of 0.05 mol of the amine in ethanol (50 cm 3 ). 6 M NaOH (10 cm 3) was added with stirring. The complexes were prepared by mixing 0.017 mol of 60% w/v FeCl 3 aqueous solution with the solution from the ligand preparation. A black-brown precipitate immediately formed and was recovered by vacuum filtration, washed with ethanol and air dried. The complex was recrystallised by dissolution in hot CHC13 (30 cm 3) (in a fume hood), vacuum filtration, and addition of ethanol (30 cm 3 ) to the filtrate. Black or dark brown solids formed on cooling; the solids were recovered by vacuum filtration and were washed with ethanol and air dried. Preparation of FeS 2 thin films by AACVD Typically the precursor (0.3 g) was dissolved in THF (30 ml) at room temperature and injected into the growth apparatus with the substrate at various temperatures. The system was allowed to run for 2 h., with a constant nitrogen flow rate of 200 sccm (carrying the precursor from the flask to the substrate), at which point the substrates were removed. Preparation of FeS2 thin films by LP-MOCVD The reactor was a cold wall, horizontal reactor. Glass, GaAs(1 11) and InP(1 11) substrates were heated by a tungsten halogen lamp and precursor by a Carbolite tube furnace with the system under a dynamic vacuum at approx. 10.2 Torr. The iron complexes as above (- 20 mg) were used in each experiment. RESULTS AND DISCUSSION The precursors used in this work have two advantages; they are air stable and soluble in most organic solvents. The preparation of the sodium salt in situ and the subsequent precipitation
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of the iron salt is a clean and efficient method of producing high yields of crystalline compounds. Two different types of CVD techniques were employed; low-pressure chemical vapor depositi
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