1. Influence of deposition rate and Time on nucleation of Er on a-c
Khadegeh pourghrobany

2. Introduction:
nucleation kinetics of UHV deposited Er on a-c at room temperature and for atom arrival rates of ()atoms/cm s is studied.for all deposition rate, the density of nuclei increased with time to a saturation value and remained stationary.it was found that the nucleation rate is linearty dependent on the deposition rate,indicating that a single-adatom constitutes a stable nucleus.at lower deposition rate(up to R=1× atoms/ 𝑐𝑚 2 s),the saturation density is constant and independent of R but at higher rates it increases. In this work the experimental results on the influence of deposition rate and time on the nucleation of Er on a-c is reported and the atomisitic theory proposed by Venables is used to evaluate the results.

3. Experiment
Er was deposited onto a-c surfaces by thermal evaporation from 99/99% purity erbium metal using a Balzers UMS 500U UHV system .a-c films supported by copper grids were used as substrates for the electron microscope investigations.

5. Condition experiment A substrate temperature of 290-300 K.
The distance between the evaporation crucible and substrate was 54.5cm.
Evaporation was carried out at a pressure of 10 −8 mbar.

6. Temperature film The substrate temperature was controlled by an
Automated(computerized) system and measured
Using several platinum RTD sensors which were surface mounted on the substrate holder at locations as close as possible to the substrate.

11. conclusions Er adatoms on a-c substrates are mobil.
The linear dependence of the deposition rate to the nucleation rate indicates that according to Waltons theary the critical cluster size is zero .
In Waltons theory the nucleation rate is determined by the formation of stable cluster.
The relation between 𝑛 𝑠 R is obtained to be constant up to about 1× atoms/ 𝑐𝑚 2 s and thereafter is proportional about 𝑅
Using the atomistic theory of nucleation the diffusion length of adatoms, 𝑥 𝑠 =(1.53±0.01)nm.
𝐸 𝑠𝑑 =(0.12±0.01).