Patent ID: 8689652

Claim:
A method of determining the mean surface radius r D or the density n D of particles of a powder in a sample in levitation in a plasma of volume V formed between a first electrode powered by an RF voltage and a second electrode taken to a ground voltage, the method being characterized in that: n D = 1 4 ⁢ π ⁢ ⁢ K 2 ⁢ V ⁢ ⁢ Δ ⁢ ⁢ A B × ( 1 V RF - 1 V RF ⁡ ( 0 ) ) 2 ⁢ ⁢ n r D = K ⁢ Δ ⁢ ⁢ A B ( 1 V RF - 1 V RF ⁡ ( 0 ) ) n with ⁢ : K = ɛ 0 ⁢ C q ⁢ ⁢ V ⁢ ⁢ D n , Δ ⁢ ⁢ A B = δ ⁡ ( t ) δ ⁡ ( 0 ) - 1 1 A M ⁢ ⁢ 0 + 1 A B ⁢ ⁢ 0 , δ ⁡ ( t ) = π arccos ⁡ ( V DC V RF ) - 1 and ⁢ : δ ⁡ ( 0 ) = π arccos ⁡ ( V DC ( 0 ) V RF ⁡ ( 0 ) ) - 1 V RF designating the amplitude at measurement instant t of the RF voltage feeding the first electrode when the powder is present in the plasma; V RF(0) designating the amplitude of said RF voltage feeding the first electrode in the absence of powder in the plasma; V DC designating the self-bias voltage of the first electrode at instant t when the powder is present in the plasma; V DC(0) designating the self-bias voltage of the first electrode in the absence of powder in the plasma; ΔA B designating the variation in the surface area of the second electrode in the presence of powder at instant t relative to a powder-free situation, A B0 and A M0 designating the effective surface area of the electrodes in the absence of powder; and the values of n and K being determined by calibration by plotting a curve giving r D as a function of ΔA B and of V RF using experimental data obtained from powders having a known particle diameter by measuring V RF , V RF(0) , V DC , and V DC(0) , and by performing regression on said curve.