Unique capabilities of the scanning atom probe, atomically high resolution and atom-by-atom mass analysis, were utilized to investigate the compositional distribution in the individual apexes of a silicon microtip array and fine grains of chemical vapor deposition diamonds. The dry-etched silicon tips contain a large amount of carbon and hydrogen and the HF-treated tips contain even oxygen and fluorine. Although the carbon concentration of the uppermost surface layer is. as high as 50% for the. dry-etched tip, it decreases to less than 10% for the second layer and approaches to the constant concentration of less than 2% at the depth of 20 nm suggesting the carbon intermixture during the fabrication and/or etching process of the microtip array. The-carbon concentration in the HF-treated tip decreases from 18% to 8% at the depth of 30 nm. On the other hand, the oxygen concentration stays fairly constant at around 25% throughout the analysis. The high hydrogen concentration in the diamonds is attributed to the large difference between tbe,activation energies for hydrogen desorption, 21 kcal/mol, and for methane adsorption, 7.3 kcal/mol.