EQCM-Principles of Operation measure change in oscillation frequency ◆ Sauerbrey equation: ◆△f=2(△m/A)nf2/( quartz pauart)2 where n= overtone number Quartz shear modulus(2.95 x 10 cms pauart=density(2.65g/cms)
EQCM - Principles of Operation Measure change in oscillation frequency Sauerbrey equation: f = - 2 (m/A) n fo 2 /(quartz quartz) 1/2 where n = overtone number quartz = shear modulus (2.95 x 1011 g/cms) quartz = density (2.65 g/cm3 )
EQCM-Principles of Operation(contd) Sauerbrey equation ◆△=-2(Am/A)nf2( quartz pauart)2 ◆ Significance ◆if△ m positive,then△f ◆if△ m negative,then△f for 300 um thick quartz wafer oscillating at 5 MHz and Am=l8 ng/cm2△f≈1Hz( measurable)
EQCM - Principles of Operation (cont’d) Sauerbrey equation: f = - 2 (m/A) n fo 2 /(quartz quartz) 1/2 Significance: if m positive, then f ________ if m negative, then f ________ for 300 m thick quartz wafer oscillating at 5 MHz and m = 18 ng/cm2 f 1 Hz (measurable)
EQCM-Principles of Operation Solution exerts a dampening effect △f=-f63/2 1/2 SoIn nsoln gaurtz Quartz where nsoIn- solution viscosity Psoln=solution density
EQCM - Principles of Operation Solution exerts a dampening effect: f = - f0 3/2 [soln soln / (qaurtz quartz)]1/2 where: soln = solution viscosity soln = solution density
EOCM- Advantages ◆ Sensitivit ng/cm Hz ◆ In situ technique not a vacuum method ◆ Inexpensive ◆<$10k
EQCM - Advantages Sensitivity ng/cm2 Hz In situ technique not a vacuum method Inexpensive < $10k
EQCM-Disadvantages ◆ Selectivity ◆ mass sensor Cannot distinguish what is on surface
EQCM - Disadvantages Selectivity mass sensor Cannot distinguish what is on surface