Ben Meester

ELECTROSTATIC SOL–SPRAY DEPOSITION OF NANOSTRUCTURED CERAMIC THIN FILMS

Abstract Electrospraying has been developed into an electrostatic spray deposition technique for the deposition of ceramic thin films. The cone-jet spraying mode appears to be the most preferable for this purpose, and the domain where the cone-jet mode exists was found to depend strongly on the nozzle design. A nozzle with a large diameter and a tilted outlet widens the windows for both the applied high DC voltage and the flow rates of a precursor liquid keeping the cone-jet mode intact. The results of three nozzle designs are compared, one of which has been selected for feeding two different precursor liquids simultaneously. With three relevant sols as precursor liquids, nanostructured thin films of ZnO, ZrO 2 , and Al 2 O 3 have been deposited. Their morphologies are dependent on the preparation of the precursor sols and the deposition temperature. Highly porous films were obtained by using a high deposition temperature and a sol prepared from a metal alkoxide or a metal acetate.

Laser-induced chemical vapor deposition of nanostructured silicon carbonitride thin films

Laser-induced chemical vapor deposition of silicon carbonitride thin films has been investigated using a continuous wave CO2 laser in parallel configuration with the substrate. The reactant gases in this process, hexamethyl disilazane and ammonia, are rapidly heated by CO2 laser radiation due to their absorption of the laser energy. Polymerlike silicon carbonitride films or agglomerated nanosized particles are formed depending on process conditions. Dense, smooth films or nanostructured deposits have been synthesized at low substrate temperatures (Ts<300 °C) on quartz, copper, and silicon and can be obtained with controlled microstructures. Surface morphology, composition, and type of chemical bonding have been studied with electron microscopy and spectroscopic analysis and are correlated to the most important laser process parameters. X-ray photoelectron spectroscopy and reflectance Fourier transform infrared spectroscopy show that the deposits consist of Si–N, Si–C, and Si–O bonds, linked together in a ...

Nanoporous TiO2/Cu1.8S heterojunctions for solar energy conversion

Thin films of p-type Cu 1.8 S have been deposited onto smooth and nanoporous n-type TiO 2 with Atomic Layer Chemical Vapor Deposition (AL-CVD). As precursors, Cu(thd) 2 and H 2 S have been used and self-limited deposition takes place between 125 and 240 °C. The crystalline phase and growth rate strongly depend on the process conditions; below 175 °C CuS and above this temperature, Cu 1.8 S is formed. Photospectroscopy shows that Cu 1.8 S has a bandgap of 1.75 eV and an absorption coefficient of 2.3 X 10 4 cm -1 at 500 nm. A 35-nm-thick Cu 1.8 S film on flat TiO 2 substrates shows a short circuit photocurrent of 30 μA/cm 2 and an open circuit photovoltage of 200 mV at broad-band irradiation of 2.8 kW/m 2 . The internal quantum efficiency is 6% at 500 nm.

CuInS2–TiO2 heterojunctions solar cells obtained by atomic layer deposition

Abstract Chalcopyrites are being studied widely as a promising absorber material for high-efficiency, low-cost, thin-film solar cells. The present paper deals with the growth of CuInS 2 thin films by atomic layer deposition. CuInS 2 films are grown on glass, F-doped SnO 2 coated glass, and TiO 2 thin films at a pressure of 2 mbar and in the temperature range of 350–500 °C using CuCl, InCl 3 and H 2 S as precursors. The influence of the process conditions on the structural and the electrical properties is examined. The growth temperature, the purge time and the vapor pressure of the precursors are found to be the decisive parameters. The composition of the thin films is investigated with X-ray diffraction and Raman spectroscopy. Depending on the process conditions single phase CuInS 2 or a mix of Cu x S, CuInS 2 and CuIn 5 S 8 are formed. The effect of annealing the CuInS 2 films in an H 2 S or O 2 atmosphere is studied as well.

Synthesis of pyrite (FeS2) thin films by low-pressure MOCVD

Thin films of iron disulfide have been prepared by low-pressure CVD (LPCVD) from iron(III) acetylacetonate (Fe(acac) 3 ), tert-butyldisulfide (TBDS), and hydrogen. The influence of the relevant CVD parameters on the growth rate, chemical composition (stoichiometry), morphology, crystalline phases, and contaminants has been examined. Pyrite thin films with a uniformity variation of less than 5 % over a length of 10 cm are obtained in a hot-wall LPCVD reactor. The present study shows that these films are deposited without detectable iron sulfide (FeS) phases at temperatures from 300 °C up to 340 °C on glass and silicon substrates. Growth rates vary between 0.2 nm min -1 and 12 nm min -1 . In all cases, the films are polycrystalline pyrite with an indirect bandgap of 0.95 ± 0.05 eV, and a dark specific resistance of 0.5-1.0 Ω cm. The absorption coefficient of the films is 3 ± 1 × 10 5 cm -1 at λ = 500 nm.

In situ mass spectrometric study of pyrite (FeS2) thin film deposition with metallorganic chemical vapor deposition

Pyrite, FeS{sub 2}, thin films have been prepared by metallorganic chemical vapor deposition using tert-butyl disulfide (TBDS) and iron(III) acetylacetonate [Fe(acac){sub 3}] as the precursors and H{sub 2} as co-reactant. The reaction mechanism is studied with in situ mass spectrometry. The thermal decomposition of TBDS and Fe(acac){sub 3} has been investigated, as well as the synthesis of FeS{sub 2}. A complicated gas-phase reaction chain occurs in the deposition reaction. In the first 1--2 cm of the deposition zone, thick rough films are formed, but further downstream in the reactor a smooth FeS{sub 2} film is deposited. This remarkable change in morphology is accounted for in the proposed reaction mechanism.

Preparation of thin porous titania films on stainless steel substrates for heat exchange (HEX) reactors

A porous titania film with pores of few micrometer sizes was prepared on a stainless steel support for a composite material of metal and inorganic oxide. The combination of a porous catalyst layer and a metal support improves the thermal conductivity compared with a traditional inorganic powder catalyst by an aid of a metal support. A porous titania film was obtained on a stainless steel support by the electrostatic sol-spray deposition (ESSD) method. Water in the parent sol was a key factor to obtain porous films. These porous films were cracked by a rapid temperature change during the cooling procedure after the deposition by the difference of the thermal expansion rate of stainless steel and titania. The parent sol was aged before a deposition to obtain a flexible structure to keep its structure. The obtained porous films comprised an aggregation of fibrous titania with few micrometer pores by SEM observation. This film was stable for a rapid temperature change. A porous titania film without any cracks were obtained on a stainless steel substrate using the ESSD method by an aging of the parent sol.

In-situ mass spectrometric study of the reaction mechanism in MOCVD of Pyrite (FeS2)

Pyrite, FeS 2 , thin films have been prepared by MOCVD using tert-butyldisulfide (TBDS), iron(III) acetylacetonate (Fe(acac) 3 ), and H 2 as the precursors. The reaction mechanism is studied by using in-situ mass spectrometry. The thermal decomposition of TBDS and Fe(acac) 3 has been investigated, as well as the synthesis of FeS 2 . A complicated gas-phase reaction chain occurs in the deposition reaction. In the first 1-2 cm of the deposition zone, a thick, rough film is formed, but further downstream in the reactor, a smooth FeS 2 film is obtained. This change in morphology is accounted for in the proposed reaction mechanism.