A multiple frequency source system includes at least one frequency source tunable to a predefined target frequency, and at least one additional frequency source operable to generate a second signal at a frequency which is either higher or lower than the target frequency. The method involves milling the metal powders at elevated temperatures and in the presence of at least one liquid solvent. Other embodiments may be described and claimed. The sheath may be formed from a brittle material. Then, as the data are processed, they will be sent to a central data processing unit that integrates the data in the Brownian motion equation. With this, better connections between contact plugs and plugs connected to upper surfaces of contact plugs are achieved.