Apparatus To Measure the Vapor Pressure of Slowly Decomposing Compounds from 1 Pa to 10⁵ Pa

Abstract

This article describes an apparatus and method for measuring vapor pressures in the range from 1 Pa to 105 Pa. Its three distinctive elements are : (1) the static pressure measurements were made with only a small temperature difference between the vapor and the condensed phase, (2) the sample was degassed in situ, and (3) the temperature range extended up to 200 °C. The apparatus was designed to measure metal-organic precursors, which often are toxic, pyrophoric, or unstable. Vapor pressures are presented for naphthalene, ferrocene, diethyl phthalate, and TEMAH (tetrakisethylmethylaminohafnium). Also presented are data for the temperature-dependent decomposition rate of TEMAH.

Toolbox for atomic layer deposition process development on high surface area powders

“…Vapor pressure can be determined by thermogravimetric analysis and subsequent calculations based on the Langmuir equation 24,25 or by directly measuring it with a capacitance manometer. [26][27][28] If the necessary vapor pressure cannot be reached below the decomposition temperature, the precursor has to be replaced by a more volatile one. Therefore, pre-selection of suitable precursors for ALD should always be the first step in process development.…”

Experiment-based modeling of a vapor draw ampoule used for low-volatility precursors

“…Recent work in determining the vapor pressures of slowly decomposing compounds (including one alkylamide similar to PDMAT) could provide a means to rule out systematic measurement errors. 30,31 Finally, we extend our model to demonstrate how it might be used to predict long-term precursor delivery. By varying the height of the ampoule in the simulation, the effect of varying the fill level of precursor can be examine d. The flow of Ar is 1 L/min (STP), the pressure is 3650 Pa, and the temperature is 75 °C.…”

Correcting “Static” Measurements of Vapor Pressure for Time Dependence Due to Diffusion and Decomposition

“…Such in situ degassing is especially useful for a decomposing sample because the more volatile decomposition products can be removed between sets of vapor pressure measurements. The companion article [1] gives a complete description of the apparatus and its operation.…”

“…Temperature equilibration was assumed to be finished after t first = 400 s [1], and the following equation, which was fit to the data at times t > t first , accounted for the other processes: $$P_{\text{fit}}\left(t\right)=P_{\text{fit}}\left(0\right)+P_B\left(\infty \right)\left(1-e^{-1/{\tau }_B}\right)+P_1\left(\frac{1}{1+\gamma }\right)e^{-t/{\tau }_B}\left(1-e^{-t/{\tau }_D}\right)$$…”

“…(61), but that some values of k B were comparable to k D . (See Figure 21 of the companion article [1]. ) Removing the requirement of Eq.…”