Metal-organic CVD of Y2O3 Thin Films using Yttrium tris-amidinates By S. Karle, V.-S. Dang, M. Prenzel, D. Rogalla, H.-W. Becker, A. Devi
This essay is dedicated to the history of creation and development of the molecular layering technique (ML) which, in the modern community of non-Russian scientists, is commonly referred to as atomic layer deposition (ALD). Basic research in the field of chemical transformations of solid surfaces using the ML method in the light of the “framework” hypothesis proposed by V. B. Aleskovskii in 1952 is discussed. A number of questions raised by international scientists including those involved in the Virtual Project on the History of ALD (VPHA, 2013), and scientists from conferences in Helsinki (Finland, May 2014.), Kyoto (Japan, June 2014), and personal communications amongst peers are addressed. For the first time in English, this article provides information about V. B. Aleskovskii and S. I. Kol'tsov who are closely associated with development of the ML technique in the Soviet Union. This paper also informs the scientific community about research groups currently engaged in ML research in Russia and introduces the scientific school of “Chemistry of highly organized substances”, founded and supervised by V. B. Aleskovskii.
A field-emission scanning electron microscopy image showing a desert rose-like aggregation found as outgrowth on the homogeneous morphology of a VO2 (B) phase film grown at 200 °C by MOCVD.
Chem. Vap. Deposition, 2015, 21, 375.
DOI: 10.1002/cvde.201507191
The original article presented the modeling for non-steady evaporation processes of liquid solution droplets injected into a pumped-down low-pressure vessel having a specified wall temperature. Numerical simulations were carried out for one of the few precursors with sufficient physical property data, TTIP. The authors compared the droplet evaporation processes for two possible solvents, toluene and hexane. Unfortunately, a discrepancy in the unit systems of the property references (molar units vs mass units) was not detected during the modeling used in this paper. We present here the correct property values, the corrected figures and updated discussion. The sensitivity analysis and stages of the vaporization process elicited in the simulations are not affected by this error. Updated Figures 5, 6, 7, 8 and 9 showing corrected droplet evaporation times for a process, normalized to 10 s cycles, are given here.
The correct enthalpy of vaporization for TTIP is ΔHvap = 219.2 kJ kg−1 (instead of 62.3 kJ kg−1) and for toluene ΔHvap = 401.6 kJ kg−1 (instead of 38.1 kJ kg−1). In consequence, the vaporization times for TTIP and toluene mixtures were underestimated. The vaporization time of a mixture of TTIP and hexane is 3.81 s (instead of 2.35 s). The vaporization time of a mixture of TTIP and toluene is 4.68 s (instead of 1.89 s).
The main consequence of the unit error is the discussion in Section 3.2 where we use the model results to consider the choice of solvent. In MOCVD it is sometimes possible to choose between chemically compatible solvents for a given precursor. The main motivation for this study was to understand how the physical properties of vapor pressure, specific heat and enthalpy of vaporization might influence the precursor vaporization. We have many years of experience with toluene, but have not yet tried hexane as a vaporization solvent for TTIP. There is no reported experimental comparison in the literature. Hexane has six times higher vapor pressure than toluene, so one might conclude that hexane would be a vastly superior choice. However in our recently reported preliminary study of pp-MOCVD alumina deposition using different precursors and solvents, we did not get markedly different results due to solvent alone.1 The erroneous shorter drop life for toluene seemed to possibly fit with one aspect of our previous results, but this could definitely be due to one of many other factors like solvent and precursor chemistry and variability of working conditions.
The model shows how vaporization kinetics are mainly controlled by enthalpy of vaporization, not vapor pressure. Toluene and hexane have similar enthalpy of vaporization. This aspect of the mathematical description of the problem, the study with pure hexane, the sensitivity
A systematic study into the MOCVD of V-O films using the vanadyl-acetylacetonate [VO(acac)2] precursor is carried out. The films are prepared via low pressure MOCVD on Si(001) substrates. The nature and quality of films are examined by varying operational parameters, e.g., deposition temperature, precursor vaporization rate, and flow of oxygen reacting gas. X-ray diffraction data point to the formation of crystalline films in the range 200−550 °C. Outside of this temperature ranges amorphous phases were obtained. Field-emission scanning electron microscope (FESEM) images indicate very homogeneous surfaces with grain shape and dimensions depending on operational conditions. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses point to the absence of any C contamination.
This paper describes the results of experimental evaluation of titanium dioxide thin films formed by CVD as active layers in semiconductor, resistive sensors for detection of ethanol vapors. TiO2 layers with a thickness of 90 nm are formed by CVD in the TTIP-O2-O3-Ar reaction system. Sensors manufactured with titania films formed under all the deposition conditions studied exhibit good electrical response to the ethanol vapors, with quick response-recovery characteristics in the temperature range 170–300 °C. Sensor performance is determined by the relative amount of anatase phase and grain size in the films. The response value (Rair/Rethanol) of the sample with the highest degree of crystallinity reached 37 at an operating temperature of 200 °C.
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