Surface Monolayer Formation Time Calculator (UHV)
For surface science researchers running UHV experiments who need to know how many seconds a freshly prepared clean surface survives at a given base pressure before one monolayer of adsorbate covers it — the number that decides whether an experiment can be done at 10⁻⁶ mbar or demands 10⁻¹⁰ mbar. This tool estimates surface contamination using the Hertz-Knudsen equation with sticking coefficient 1 (check case: N₂, 28 g/mol, at 295 K and 1×10⁻⁶ mbar gives about 3.5 s).
How to use this tool
- Enter the chamber pressure and pick its unit from the Pa / mbar / Torr dropdown.
- Set the temperature in K (295 for room temperature).
- Enter the molar mass of the dominant residual gas in g/mol (28 for N₂, 32 for O₂, 18 for H₂O).
- Adjust surface site density n₀ (default 1×10¹⁹ sites/m²) and the sticking coefficient s (default 1) if your system differs.
- Read the impingement flux and the monolayer formation time, which update after every keystroke.
FAQ
- Q: How long does it take to form one monolayer of N₂ at 1×10⁻⁶ mbar and 295 K?
- A: About 3.5 seconds — that is this tool's built-in check case (N₂, 28 g/mol, 295 K, 1×10⁻⁶ mbar).
- Q: What equation does this monolayer formation time calculator use?
- A: The Hertz–Knudsen equation: flux = P / √(2πmkT) with k = 1.380649×10⁻²³ J/K and m the molecule mass in kg, then time = n₀ / (s × flux).
- Q: Which pressure units can I enter?
- A: Pa, mbar or Torr — the tool converts mbar and Torr to Pa before applying the formula (1 mbar = 100 Pa, 1 Torr = 133.322 Pa).
- Q: Why does the monolayer time become infinite at zero pressure?
- A: Because flux = P / √(2πmkT) is zero when P = 0, so no molecules impinge and the time n₀ / (s × flux) is undefined — the tool reports "infinite — no impingement" instead of a number.