Awardee Interviews | Biography: Scott A. Chambers

Robert Celotta

Robert Celotta
Robert Celotta received his B.S. degree in Physics from the City College of New York in 1964 and went on to get his Ph.D. in Physics at New York University in 1969. His research career actually started while he was an undergraduate working part time as a Research Assistant at IBM Watson Labs (at Columbia University) on the construction of a high current cyclotron conceived by L.H. Thomas. His graduate work at NYU included atomic beam determinations of tensor polarizabilities and electron-atom collision cross sections under the supervision of Ben Bederson, currently the Editor-in-Chief at APS. Celotta then accepted a Postdoc with Jan Hall at the Joint Institute of Laboratory Astrophysics in Boulder Colorado to establish a new way to accurately determine molecular electron affinities via laser photodetachment spectrometry.

In 1971, Celotta joined the Electron Physics Group at NIST (then the National Bureau of Standards) and led an effort in monochromatic electron scattering from gases, primarily determining oscillator strengths over a very wide spectral range and exploring negative ion resonance phenomena. Then, in 1975, Dan Pierce, fresh from participating in the discovery at ETH in Zurich that GaAs could be made to emit spin polarized electrons, joined Bob Celotta on the staff of the Electron Physics Group. Thus began a period of scientific collaboration and friendship that continues to the present day. They shared the conviction that a great deal could be learned about atoms and surfaces if the electron spin parameter could be controlled and measured much more effectively then had been to date. Together with their colleagues, Pierce and Celotta set out to develop the first low energy GaAs spin polarized electron gun. This electron gun produced beams similar in current and other characteristics to conventional electron guns, yet the spin direction of the electron beam could be modulated while the current remained constant. This allows the spin dependent part of any subsequent electron interaction to be determined. The source was first used to study the spin-orbit effect in spin polarized LEED and then observed spin splittings in electron surface states. But, by 1979, they realized that surface magnetism was the most exciting application of the new spin polarization techniques and they had made their first observation of a surface hysteresis curve by using polarized electron diffraction. In the years immediately following, they proposed the transverse magnetization configuration for spin-dependent photoemission, observed the effect of electron polarizaton on elastic and inelastic electron scattering from ferromagnets, observed the spin and energy of secondary electrons from ferromagnets, utilized the detection of polarized electrons in scanning electron microscopy (SEMPA) to provide images of magnetic domains, made spin polarized, inverse photoemission measurements, determined the temperature dependence of surface magnetization, and developed two new types of spin polarization detectors. Starting in the early 1980's, Celotta also led a project at NIST to measure the interactions between polarized electrons and spin polarized atom beams, in some cases making such complete scattering measurements that quantum phases and amplitudes were obtainable instead of less complete cross section information.

Currently, Celotta and his colleagues use polarization techniques in, for example, SEMPA studies of exchange coupling between magnetic layers using nanofabrication methods to produce wedge shaped crystal structures of accurate dimensions and precise structure. He is also interested in the possibility of a spin-dependent tunneling probe of magnetic structure.

Most recently, Celotta and colleagues have demonstrated that laser fields can be used to focus neutral atomic beams to form nanostructures on surfaces.

Polarized electron experiments are notoriously complex and much of the work mentioned above could not have been done without the collaborative efforts of many highly talented scientists, including former and present members of the NIST Electron Physics Group, and the highly supportive environment provided by NIST.

Robert Celotta is an author of more than 200 publications, is the Editor-in-Chief of Methods of Experimental Physics, and is a holder of three patents ranging from polarization detection to nanolithography. He has received the Distinguish Young Scientist Award from the Maryland Academy of Sciences, two IR-100 awards, the Federal Laboratory Consortium Award for Excellence in Technology Transfer, the Outstanding and Distinguished Career in Science Award of the Washington Academy of Sciences and, from NIST, the Silver Medal and Gold Medal Awards, the E.U. Condon Award, and the W.P. Slichter Award. He is a NIST Fellow, a Fellow of the American Physical Society and is the Leader of the NIST Electron Physics Group.