1. Deposition rate measurements

Transcription

1 1. Deposition rate measurements A quartz crystal monitor (at a distance of 1mm from the source aperture) was used to measure the deposition rate of the clusters (note for Cu, 1Hz =.11Å). The deposition rate was measured as a function of the magnetron power for various Ar flow rates and a set aggregation length of 25 mm. 2 Deposition rate (Hz/min) Ar 25 sccm Ar 2 sccm Ar 15 sccm Ar 1 sccm Power (W) Figure 2: Deposition rate as a function of magnetron power for various flows The deposition rate was measured as a function of the Ar gas flow rate for various aggregation lengths and a fixed power of 25Watts. 16 Deposition rate (Hz/min) Distance 25 mm Distance 195 mm Distance 155 mm Distance 85 mm Ar flow (sccm) Figure 3: Deposition rate as a function of Ar gas flow rate for various aggregation lengths

2 Note that the deposition rate drops at higher Ar flow and magnetron power. This is due to the increased number of collisions between particles and thus a reduction in the mean free path of the clusters. 2. Cluster mass measurements Cluster mass with Ar flow rate The Ar flow rate was varied for a fixed power and aggregation length. The resulting mass spectra (taken using the QMF2) are shown below of negatively charged Cu clusters. Power: 38W, Agg length: minimum, He: sccm, Apertures 5mm inner, 4mm outer Cu Mass Spectra with Ar Flow Rate 1sccm 3sccm 5sccm 7sccm 9sccm 2 1 1x1 5 2x1 5 3x1 5 4x1 5 5x1 5 6x1 5 Figure 4. From these spectra the mean cluster mass can be plotted as a function of the Ar flow. This is shown below in figure 2.

3 2.4x1 5 Relationship between mean cluster mass and Ar gas flow for Cu clusters Cluster Mass (amu) 2.2x1 5 2.x x x x x1 5 1.x1 5 8.x1 4 6.x1 4 4.x Ar Flow (sccm) Figure 5 Cluster mass with He flow rate The He flow rate was varied for a fixed power, aggregation length and Ar flow rate. The resulting mass spectra (taken using the QMF2) are shown below of negatively charged Cu clusters. Power: 37W, Agg length: minimum, Ar: 2 sccm, Apertures 5mm inner, 4mm outer Cu mass spectra with He flow rate sccm 1sccm 3sccm 5sccm 7sccm 9sccm 1x1 5 2x1 5 3x1 5 4x1 5 5x1 5 6x1 5 7x1 5 Figure 6 From these spectra the mean cluster mass can be plotted as a function of the He flow. This is shown below in figure 4.

4 Relationship between mean cluster mass and He flow for Cu clusters 1.6x1 5 Cluster 1.4x x1 5 1.x1 5 8.x1 4 6.x He Flow (sccm) Figure 7 Cluster mass with magnetron power The magnetron power was varied for a fixed aggregation length, Ar and He flow rates. The resulting mass spectra (taken using the QMF2) are shown below of negatively charged Cu clusters. Agg length: minimum, Ar: 4 sccm, He: 6sccm, Apertures 5mm inner, 4mm outer Cu mass spectra with power 35W 3W 25W 2W 15W 1. 5.x1 4 1.x x1 5 2.x x1 5 3.x x1 5 Figure 8 From these spectra the mean cluster mass can be plotted as a function of the power. This is shown below in figure 6.

5 Relationship between mean cluster mass and power for Cu clusters 9x1 4 8x1 4 7x1 4 6x1 4 5x1 4 4x1 4 3x1 4 2x Power (Watts) Figure 9 Cluster mass with aggregation length The aggregation length was varied for a fixed power, Ar and He flow rates. The resulting mass spectra (taken using the QMF2) are shown below of negatively charged Cu clusters. Power: 35W, Ar: 15 sccm, He: sccm, Apertures 5mm inner, 4mm outer. Cu mass spectra with aggregation length 8. 65mm mm mm mm x1 5 2x1 5 3x1 5 4x1 5 5x1 5 6x1 5 Cluster mass (a.m.u.) Figure 1

6 Large clusters Large clusters can be acquired with the NC2U using high powers and relatively high Ar gas flows. The graph below shows such a spectrum which goes beyond the range of the QMF2. These clusters are positively charged. Power : 95W, Ar flow: 65sccm, He:, Aggregation length: maximum. 3. Large Cu clusters from the NC2U source 2.5 Ion Current (na) x1 5 1.x x1 6 2.x x1 6 3.x1 6 Figure 11

7 Small clusters Small clusters can be acquired with the NC2U using low powers and high He gas flows. The graph below shows spectra of negatively charged clusters for two different He flows. Individual cluster peaks can just be resolved. Power : 1W, Ar flow: 35sccm, He flow:11sccm, 9sccm Aggregation length: minimum QMF: f=1khz, U/V =.15, Sit=, External Keitherly nanometer input A B 11sccm He 9sccm He Figure 12

8 From the above graph the value of k (the correction factor) can be calculated. The value k is used in the calculation of the mass: M=7x1 7 (kv/f 2 d 2 ) Where M is the mass, V is the AC voltage, f is the frequency and d is the diameter of the quadrupole poles. On the graph the peaks A and B lie at 5amu and 793amu. There are five distinct peaks between these peaks giving an average separation of 48.8amu. For Cu clusters this value should be 63.5 (the atomic weight of Cu). The correction factor is therefore: k= 63.5/48.8 = 1.3 This value is comparable with the result calculated by Baker et al 1. (1.25) who determined the constant by using ionised Ar. The corrected mass spectrum is shown in figure 1. The number of atoms per cluster has been added sccm He 9sccm He Figure 13 1 S.H.Baker et al. Rev.Sci.Instrum. 68(4) p 1853, 1997.

9 3. Other measurements Beam size from cluster source The beam diameter was measured for different aperture plate arrangements at a distance of 1mm. NC2U Beam profiles with different aperture arrangements at a distance of 1mm 1. Red - 4mm inner, 5mm skimmer Black - 4mm inner, 1mm skimmer Blue - 8mm inner, 1mm skimmer Deposition rate (normalised) Distance (mm) Figure 14