Related Clues:

• Physicist's study
• Tad
• Minute amount
• Slight amount
• Least bit
• Molecule part
• Item of interest to Niels Bohr
• Theta-kappa go-between
• Itty-bitty bit
• First half of the files?
• Physics subject
• Smashed item
• Tiny part
• Molecule component
• Greek vowel