HEAVY CLUSTER IMPACT DESORPTION OF LARGE MOLECULES

THE LONG-TERM OBJECTIVES OF THIS PROJECT ARE THREEFOLD: TO PROVIDE IMPROVED COMMERCIAL INSTRUMENTATION FOR PARTICLE-INDUCED DESORPTION OF LARGE, FRAGILE MOLECULES, TO INCREASE OVERALL SECONDARY ION YIELD EFFICIENCIES OF LOW MASS IONS AS WELL AND TO ADD ADDITIONAL INSIGHT FOR IMPROVING EXISTING THEORIES THAT MODEL THE DESORPTION PROCESS OF MACROMOLECULES. WE WILL MEET THESE OBJECTIVES BY DEVELOPING A BIPOLAR, MULTIPLY CHARGED, HEAVY CLUSTER PRIMARY BEAM PROBE FOR MORE EFFICIENT SPUTTERING OF SECONDARY SAMPLE IONS. THE ADVANTAGES OF HEAVY CLUSTER BEAMS ARE MANY. BECAUSE THEY ARE MULTIPLY CHARGED WHEN FORMED, THEY ARE CAPABLE OF PROVIDING IMPACT ENERGIES UP TO L MEV USING ONLY MODERATE ACCELERATING VOLTAGE. SECOND, THEIR LARGER MASS ASSURES HIGH TARGET IMPACT MOMENTUM. THIRD, THEIR MASSIVENESS ALLOWS TESTING OF HYPOTHESES WHICH ADVOCATE IMPROVED SPUTTERING YIELDS AS THE SPATIAL EXTENT OF THE BOMBARDING SPECIES INCREASES. UNLIKE UNIPOLAR OPERATION OF MOST ION SOURCES, CLUSTERS FORMED BY ELECTROHYDRODYNAMIC (EH) IONIZATION CAN BE GENERATED EITHER POSITIVELY OR NEGATIVELY CHARGED. THIS BIPOLAR FEATURE PERMITS POSITIVE ION DESORPTION (USING A NEGATIVE PRIMARY BEAM), E. G., ON MAGNETIC SECTOR INSTRUMENTS WITHOUT THE NEED FOR HIGH VOLTAGE FLOATING AND ISOLATION OF THE PRIMARY BEAM SOURCE HARDWARE.