Philip Lippel | Massachusetts Institute of Technology (MIT) (original) (raw)

Papers by Philip Lippel

Research paper thumbnail of Positron annihilation spectroscopy of vacancy-related defects in semiconductors

Microelectronics Reliability, 1994

ABSTRACT

Research paper thumbnail of Positron annihilation spectroscopy of the equilibrium vacancy ensemble in aluminium

Journal of Physics F Metal Physics

One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and ... more One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR data are compared with calculated 2D ACAR spectra for positrons annihilating from the Bloch state and from monovacancy- and divacancy-trapped states. The theoretical formalism incorporates many-body enhancement effects into supercell band-structure calculations for the defects; lattice constants appropriate to the experimental temperatures were used. Assuming the consequences of dynamic temperature effects to be small, the experimental 2D ACAR results can be accounted for the fraction of monovacancy-trapped positrons increasing with temperature, along with an additional and continually increasing contribution from divacancy-trapped positrons at high temperatures (above 613K). The analysis indicates that about 44% of the trapped positrons annihilate from a divac...

Research paper thumbnail of ONLINE EDUCATION POLICY INITIATIVE Online Education: A Catalyst for Higher Education Reforms TABLE OF CONTENTS FOREWORD iii OEPI MEMBERS vi EXECUTIVE SUMMARY viii

G iven the accelerating changes in the landscape of higher education, and given the advances in l... more G iven the accelerating changes in the landscape of higher education, and given the advances in learning science fields and in education technology over recent years, what are the implications of online education on higher education? What are education research, cognitive psychology, neuroscience and other fields telling us about how to improve education in both online and blended learning settings? How could these reforms be implemented? What are the policy implications for university presidents, for faculty, for policy makers, for funding agencies and for governments in the United States?

Research paper thumbnail of Online Education: A Catalyst for Higher Education Reforms

G iven the accelerating changes in the landscape of higher education, and given the advances in l... more G iven the accelerating changes in the landscape of higher education, and given the advances in learning science fields and in education technology over recent years, what are the implications of online education on higher education? What are education research, cognitive psychology, neuroscience and other fields telling us about how to improve education in both online and blended learning settings? How could these reforms be implemented? What are the policy implications for university presidents, for faculty, for policy makers, for funding agencies and for governments in the United States?

Research paper thumbnail of Positron annihilation spectroscopy of the equilibrium vacancy ensemble in aluminium

Journal of Physics F: Metal Physics

ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation... more ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR data are compared with calculated 2D ACAR spectra for positrons annihilating from the Bloch state and from monovacancy- and divacancy-trapped states. The theoretical formalism incorporates many-body enhancement effects into supercell band-structure calculations for the defects; lattice constants appropriate to the experimental temperatures were used. Assuming the consequences of dynamic temperature effects to be small, the experimental 2D ACAR results can be accounted for the fraction of monovacancy-trapped positrons increasing with temperature, along with an additional and continually increasing contribution from divacancy-trapped positrons at high temperatures (above 613K). The analysis indicates that about 44% of the trapped positrons annihilate from a divacancy-trapped state at 903K. Comparison of these results with those from previous measurements concerning the equilibrium vacancy ensemble in aluminium indicates that the ratio of positron trapping rates at divacancies and monovacancies ( mu 2v/ mu 1v) is about two. The present results regarding the contributions from divacancies are found to be consistent with those from the quantitative analysis of the peak-count rate 1D ACAR data using a monovacancy-divacancy analysis, which is presented elsewhere.

Research paper thumbnail of Positron-annihilation study of the equilibrium vacancy ensemble in aluminum

Research paper thumbnail of Positron Diffraction Experiments with a Brightness - Slow Positron Beam

Abstract The construction of a high brightness slow positron beam has enabled us to extend Low En... more Abstract The construction of a high brightness slow positron beam has enabled us to extend Low Energy Positron Diffraction (LEPD) measurements well beyond the previously accessible range of energies. Details of the design and construction of this beam, which ...

Research paper thumbnail of Health and medicine in the national nanotechnology initiative

Nanomedicine: Nanotechnology, Biology and Medicine, 2006

Research paper thumbnail of Determination of atom positions at stacking-fault dislocations on Au(111) by scanning tunneling microscopy

Perspectives in Condensed Matter Physics, 1989

... system. We would like to thank Professor JP Toennies for the loan of the Au(l 1) singlecrysta... more ... system. We would like to thank Professor JP Toennies for the loan of the Au(l 1) singlecrystal, Dr. VM Hallmark for providing an epitaxially grown Au( 111) thin film on mica, and J. Shyu for assistance with computer program-ming. ...

Research paper thumbnail of Evidence for threshold effects in positron diffraction from NaF and LiF

Research paper thumbnail of A monovacancy-divacancy model interpretation of positron annihilation measurements in aluminium

Journal of Physics F: Metal Physics, 1984

ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data o... more ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data of the peak-count rate, long-slit angular correlation of annihilation radiation (1D ACAR) for Al single crystals yields an apparent value for the monovacancy formation enthalpy (H1vF) of (0.76+or-0.04) eV. However, lifetime experiments of lower temperatures (293-645K) have yielded H1vF=(0.66+or-0.02) eV. A constrained monovacancy-divacancy analysis of the 1D ACAR data, incorporating theoretical predictions of the relative peak-count rates arising from monovacancy- and divacancy-trapped positrons, can resolve this apparent discrepancy between the lifetime results and momentum measurements (Doppler broadening or angular correlation) of the vacancy formation enthalpy in Al. This analysis yields a divacancy binding enthalpy of H2vb=(0.30+or-0.13) eV, and indicates that at the melting point about 60% of the positrons annihilate from divacancy-trapped states in Al, consistent with the interpretation of recent 2D ACAR results. Introduction of the ratio of the positron trapping rate into divacancies to that into monovacancies, mu 2v/ mu 1v, as deduced from the jellium-model calculations of McMullen et al. (1981) allows one to estimate the divacancy binding entropy S2vb as well. The results are compared with those of previous investigations of vacancy formation and self-diffusion in Al.

Research paper thumbnail of Resolution in the scanning tunneling microscope

Ultramicroscopy, 1992

... Holland Resolution in the scanning tunneling microscope RJ Wilson d, PH Lippel h, S Chiang a,... more ... Holland Resolution in the scanning tunneling microscope RJ Wilson d, PH Lippel h, S Chiang a, DD Chambliss d and VM Hallmark IBM Research ... STM itself is comprised of a piezoelectric tripod, which carries a tungsten tip at small distance (- 10 ) from a single crystal surface of ...

Research paper thumbnail of Study of the equilibrium vacancy ensemble in aluminum using 1D- and 2D-angular correlation of annihilation radiation

One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and ... more One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D-ACAR) data have been obtained between 293 and 903 K for single crystals of aluminum. The peak counting rates vs temperature, which were measured using the 1D-ACAR technique, provide a model independent value for the temperature dependence of the positron trapping probability. Using these results it is possible to strip out the Bloch state contribution from the observed 2D-ACAR surfaces and then compare the resulting defect ACAR surfaces to calculated 2D-ACAR surfaces for positrons annihilating from the Bloch, monovacancy, and divacancy-trapped states. The result of this comparison is that the presence of an increasing equilibrium divacancy population is consistent with the observed temperature dependence of ACAR data at high temperature in Al and that the present results when compared to earlier studies on Al indicate that the ratio of the trapping rates at divacancies and monovacanci...

Research paper thumbnail of Scanning positron microbeam

Review of Scientific Instruments, 1988

The construction and operation of a scanning positron microbeam is reported. The positrons are ob... more The construction and operation of a scanning positron microbeam is reported. The positrons are obtained from a doubly remoderated positron beam with a normalized brightness-per-volt of 1.8 x 10⁵ e/sup +/ s⁻¹ cm⁻² rad⁻² V⁻¹ Ci⁻¹. The beam of 8000 e/sup +/ s⁻¹ is brought to a 10 x 50 ..mu..m² focus by a sectored lens and is scanned across a test grid. Possible applications to defect spectroscopy and the observation of small samples will be discussed.

Research paper thumbnail of Positron annihilation spectroscopy of vacancy-related defects in semiconductors

Microelectronics Reliability, 1994

ABSTRACT

Research paper thumbnail of Low energy positron diffraction on Cu(111): Importance of surface loss processes at large angles of incidence

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1991

Fi.gure i Schematic diagram of the atomic geometry of C the surface cell and i Ls reciprocal lat:... more Fi.gure i Schematic diagram of the atomic geometry of C the surface cell and i Ls reciprocal lat:ic_ v the associated diffraction pa:tern [Panel(b)] primitive surface unit cell veLtors is taken t The beam positions are shown as if intersecti A==i'mr_,m,_ cgrmm==_'_-4mmllv nn_finnmH robin,liti'h(= i

Research paper thumbnail of Surface structure determination of the cleavage faces of CdSe via low-energy positron diffraction

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1989

Low energy positron diffraction intensities were measured for positron beams from CdSe(1010) and ... more Low energy positron diffraction intensities were measured for positron beams from CdSe(1010) and fourteen beams for CdSe(1120). These were compared with calculated intensities for bond-length- conserving relaxed surface structures for both surfaces. Using an R-factor methodology the best-fit structures were obtained for these surfaces corresponding to local planar tilt angles of ..omega.. = 15 +-5/degree/ for CdSe(1010) and ..omega.. = 27 +-7/degree/ for CdSe(1120). Both results are in excellent correspondence withe predicted structures based on tight-binding total-energy minimization calculations. 21 refs., 5 figs., 2 tabs.

Research paper thumbnail of Production and applications of positron microbeams

Journal of Physics: Condensed Matter, 1989

ABSTRACT

Research paper thumbnail of Observation of optically induced molecular reorientation in films of smectic C liquid crystals

Applied Physics Letters, 1983

A linearly polarized laser beam incident on a freely suspended film of a smectic C liquid crystal... more A linearly polarized laser beam incident on a freely suspended film of a smectic C liquid crystal has been observed to reorient the molecules. In films of 4,4 bis (heptyloxy) azoxybenzene, large reorientations have been observed with an incident optical power of les than 50 mW. Photographs are presented showing the change in molecular orientation as the incident polarization is

Research paper thumbnail of High-resolution imaging of copper-phthalocyanine by scanning-tunneling microscopy

Physical Review Letters

High-Resolution Imaging of Copper-Phthalocyanine by Scanning-Tunneling Microscopy. PH Lippel 1,2 ... more High-Resolution Imaging of Copper-Phthalocyanine by Scanning-Tunneling Microscopy. PH Lippel 1,2 , RJ Wilson 1 , MD Miller 1 , Ch. ...

Research paper thumbnail of Positron annihilation spectroscopy of vacancy-related defects in semiconductors

Microelectronics Reliability, 1994

ABSTRACT

Research paper thumbnail of Positron annihilation spectroscopy of the equilibrium vacancy ensemble in aluminium

Journal of Physics F Metal Physics

One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and ... more One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR data are compared with calculated 2D ACAR spectra for positrons annihilating from the Bloch state and from monovacancy- and divacancy-trapped states. The theoretical formalism incorporates many-body enhancement effects into supercell band-structure calculations for the defects; lattice constants appropriate to the experimental temperatures were used. Assuming the consequences of dynamic temperature effects to be small, the experimental 2D ACAR results can be accounted for the fraction of monovacancy-trapped positrons increasing with temperature, along with an additional and continually increasing contribution from divacancy-trapped positrons at high temperatures (above 613K). The analysis indicates that about 44% of the trapped positrons annihilate from a divac...

Research paper thumbnail of ONLINE EDUCATION POLICY INITIATIVE Online Education: A Catalyst for Higher Education Reforms TABLE OF CONTENTS FOREWORD iii OEPI MEMBERS vi EXECUTIVE SUMMARY viii

G iven the accelerating changes in the landscape of higher education, and given the advances in l... more G iven the accelerating changes in the landscape of higher education, and given the advances in learning science fields and in education technology over recent years, what are the implications of online education on higher education? What are education research, cognitive psychology, neuroscience and other fields telling us about how to improve education in both online and blended learning settings? How could these reforms be implemented? What are the policy implications for university presidents, for faculty, for policy makers, for funding agencies and for governments in the United States?

Research paper thumbnail of Online Education: A Catalyst for Higher Education Reforms

G iven the accelerating changes in the landscape of higher education, and given the advances in l... more G iven the accelerating changes in the landscape of higher education, and given the advances in learning science fields and in education technology over recent years, what are the implications of online education on higher education? What are education research, cognitive psychology, neuroscience and other fields telling us about how to improve education in both online and blended learning settings? How could these reforms be implemented? What are the policy implications for university presidents, for faculty, for policy makers, for funding agencies and for governments in the United States?

Research paper thumbnail of Positron annihilation spectroscopy of the equilibrium vacancy ensemble in aluminium

Journal of Physics F: Metal Physics

ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation... more ABSTRACT One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D ACAR) data have been obtained as a function of temperature between 293 and 903K for single crystals of aluminium. The 2D ACAR data are compared with calculated 2D ACAR spectra for positrons annihilating from the Bloch state and from monovacancy- and divacancy-trapped states. The theoretical formalism incorporates many-body enhancement effects into supercell band-structure calculations for the defects; lattice constants appropriate to the experimental temperatures were used. Assuming the consequences of dynamic temperature effects to be small, the experimental 2D ACAR results can be accounted for the fraction of monovacancy-trapped positrons increasing with temperature, along with an additional and continually increasing contribution from divacancy-trapped positrons at high temperatures (above 613K). The analysis indicates that about 44% of the trapped positrons annihilate from a divacancy-trapped state at 903K. Comparison of these results with those from previous measurements concerning the equilibrium vacancy ensemble in aluminium indicates that the ratio of positron trapping rates at divacancies and monovacancies ( mu 2v/ mu 1v) is about two. The present results regarding the contributions from divacancies are found to be consistent with those from the quantitative analysis of the peak-count rate 1D ACAR data using a monovacancy-divacancy analysis, which is presented elsewhere.

Research paper thumbnail of Positron-annihilation study of the equilibrium vacancy ensemble in aluminum

Research paper thumbnail of Positron Diffraction Experiments with a Brightness - Slow Positron Beam

Abstract The construction of a high brightness slow positron beam has enabled us to extend Low En... more Abstract The construction of a high brightness slow positron beam has enabled us to extend Low Energy Positron Diffraction (LEPD) measurements well beyond the previously accessible range of energies. Details of the design and construction of this beam, which ...

Research paper thumbnail of Health and medicine in the national nanotechnology initiative

Nanomedicine: Nanotechnology, Biology and Medicine, 2006

Research paper thumbnail of Determination of atom positions at stacking-fault dislocations on Au(111) by scanning tunneling microscopy

Perspectives in Condensed Matter Physics, 1989

... system. We would like to thank Professor JP Toennies for the loan of the Au(l 1) singlecrysta... more ... system. We would like to thank Professor JP Toennies for the loan of the Au(l 1) singlecrystal, Dr. VM Hallmark for providing an epitaxially grown Au( 111) thin film on mica, and J. Shyu for assistance with computer program-ming. ...

Research paper thumbnail of Evidence for threshold effects in positron diffraction from NaF and LiF

Research paper thumbnail of A monovacancy-divacancy model interpretation of positron annihilation measurements in aluminium

Journal of Physics F: Metal Physics, 1984

ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data o... more ABSTRACT A monovacancy-model analysis of new temperature-dependent (in the range 293-903K) data of the peak-count rate, long-slit angular correlation of annihilation radiation (1D ACAR) for Al single crystals yields an apparent value for the monovacancy formation enthalpy (H1vF) of (0.76+or-0.04) eV. However, lifetime experiments of lower temperatures (293-645K) have yielded H1vF=(0.66+or-0.02) eV. A constrained monovacancy-divacancy analysis of the 1D ACAR data, incorporating theoretical predictions of the relative peak-count rates arising from monovacancy- and divacancy-trapped positrons, can resolve this apparent discrepancy between the lifetime results and momentum measurements (Doppler broadening or angular correlation) of the vacancy formation enthalpy in Al. This analysis yields a divacancy binding enthalpy of H2vb=(0.30+or-0.13) eV, and indicates that at the melting point about 60% of the positrons annihilate from divacancy-trapped states in Al, consistent with the interpretation of recent 2D ACAR results. Introduction of the ratio of the positron trapping rate into divacancies to that into monovacancies, mu 2v/ mu 1v, as deduced from the jellium-model calculations of McMullen et al. (1981) allows one to estimate the divacancy binding entropy S2vb as well. The results are compared with those of previous investigations of vacancy formation and self-diffusion in Al.

Research paper thumbnail of Resolution in the scanning tunneling microscope

Ultramicroscopy, 1992

... Holland Resolution in the scanning tunneling microscope RJ Wilson d, PH Lippel h, S Chiang a,... more ... Holland Resolution in the scanning tunneling microscope RJ Wilson d, PH Lippel h, S Chiang a, DD Chambliss d and VM Hallmark IBM Research ... STM itself is comprised of a piezoelectric tripod, which carries a tungsten tip at small distance (- 10 ) from a single crystal surface of ...

Research paper thumbnail of Study of the equilibrium vacancy ensemble in aluminum using 1D- and 2D-angular correlation of annihilation radiation

One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and ... more One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D-ACAR) data have been obtained between 293 and 903 K for single crystals of aluminum. The peak counting rates vs temperature, which were measured using the 1D-ACAR technique, provide a model independent value for the temperature dependence of the positron trapping probability. Using these results it is possible to strip out the Bloch state contribution from the observed 2D-ACAR surfaces and then compare the resulting defect ACAR surfaces to calculated 2D-ACAR surfaces for positrons annihilating from the Bloch, monovacancy, and divacancy-trapped states. The result of this comparison is that the presence of an increasing equilibrium divacancy population is consistent with the observed temperature dependence of ACAR data at high temperature in Al and that the present results when compared to earlier studies on Al indicate that the ratio of the trapping rates at divacancies and monovacanci...

Research paper thumbnail of Scanning positron microbeam

Review of Scientific Instruments, 1988

The construction and operation of a scanning positron microbeam is reported. The positrons are ob... more The construction and operation of a scanning positron microbeam is reported. The positrons are obtained from a doubly remoderated positron beam with a normalized brightness-per-volt of 1.8 x 10⁵ e/sup +/ s⁻¹ cm⁻² rad⁻² V⁻¹ Ci⁻¹. The beam of 8000 e/sup +/ s⁻¹ is brought to a 10 x 50 ..mu..m² focus by a sectored lens and is scanned across a test grid. Possible applications to defect spectroscopy and the observation of small samples will be discussed.

Research paper thumbnail of Positron annihilation spectroscopy of vacancy-related defects in semiconductors

Microelectronics Reliability, 1994

ABSTRACT

Research paper thumbnail of Low energy positron diffraction on Cu(111): Importance of surface loss processes at large angles of incidence

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1991

Fi.gure i Schematic diagram of the atomic geometry of C the surface cell and i Ls reciprocal lat:... more Fi.gure i Schematic diagram of the atomic geometry of C the surface cell and i Ls reciprocal lat:ic_ v the associated diffraction pa:tern [Panel(b)] primitive surface unit cell veLtors is taken t The beam positions are shown as if intersecti A==i'mr_,m,_ cgrmm==_'_-4mmllv nn_finnmH robin,liti'h(= i

Research paper thumbnail of Surface structure determination of the cleavage faces of CdSe via low-energy positron diffraction

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1989

Low energy positron diffraction intensities were measured for positron beams from CdSe(1010) and ... more Low energy positron diffraction intensities were measured for positron beams from CdSe(1010) and fourteen beams for CdSe(1120). These were compared with calculated intensities for bond-length- conserving relaxed surface structures for both surfaces. Using an R-factor methodology the best-fit structures were obtained for these surfaces corresponding to local planar tilt angles of ..omega.. = 15 +-5/degree/ for CdSe(1010) and ..omega.. = 27 +-7/degree/ for CdSe(1120). Both results are in excellent correspondence withe predicted structures based on tight-binding total-energy minimization calculations. 21 refs., 5 figs., 2 tabs.

Research paper thumbnail of Production and applications of positron microbeams

Journal of Physics: Condensed Matter, 1989

ABSTRACT

Research paper thumbnail of Observation of optically induced molecular reorientation in films of smectic C liquid crystals

Applied Physics Letters, 1983

A linearly polarized laser beam incident on a freely suspended film of a smectic C liquid crystal... more A linearly polarized laser beam incident on a freely suspended film of a smectic C liquid crystal has been observed to reorient the molecules. In films of 4,4 bis (heptyloxy) azoxybenzene, large reorientations have been observed with an incident optical power of les than 50 mW. Photographs are presented showing the change in molecular orientation as the incident polarization is

Research paper thumbnail of High-resolution imaging of copper-phthalocyanine by scanning-tunneling microscopy

Physical Review Letters

High-Resolution Imaging of Copper-Phthalocyanine by Scanning-Tunneling Microscopy. PH Lippel 1,2 ... more High-Resolution Imaging of Copper-Phthalocyanine by Scanning-Tunneling Microscopy. PH Lippel 1,2 , RJ Wilson 1 , MD Miller 1 , Ch. ...