Theoretical studies have shown that new physical properties such as tunable gap opening or quantu... more Theoretical studies have shown that new physical properties such as tunable gap opening or quantum spin Hall effect could be expected from group IV graphene analogues (silicene, germanene, stanene). While there have been numerous studies of growth of such Si, Ge, Sn monolayers, the demonstration of their hexagonal organization has been often based on postgrowth characterization and their analogy to graphene has remained controversial. Our realtime scanning tunneling microscopy (STM) observation during Ge deposition on Ag(111) in the [380 K-430 K] temperature range reveals that Ag atoms are involved in all the structures observed before the formation of a second layer, rejecting the possible formation of germanene on this substrate within these experimental conditions. The observation by STM of Ge atomic diffusion shows that easy exchange between Ag and Ge atoms is responsible for the Ge-Ag surface alloying at such temperatures.
Adsorption of the Glycine–Proline (Gly–Pro) dipeptide has been investigated using surface science... more Adsorption of the Glycine–Proline (Gly–Pro) dipeptide has been investigated using surface science complementary techniques on Au(110) and Ag(110), showing some interesting differences both in the chemical form and surface organization of the adsorbed peptide. On Au(110), Gly–Pro mainly adsorbs in neutral form (COOH/NH2), at low coverage or for a short interaction time; the surface species become zwitterionic at a higher coverage or longer interaction time. These changes are accompanied by a complete reorganization of the molecules at the surface. On Ag(110), only anionic molecules (COO−/NH2) were detected on the surface and only one type of arrangement was observed. These results will be compared to some previously obtained on Cu(110), thus providing a unique comparison of the adsorption of the same di-peptide on three different metal surfaces; the great influence of the substrate on both the chemical form and the arrangement of adsorbed di-peptides was made clear.
Typically photoelectron holographic imaging (PHI) only produces atomic images for nearest and fre... more Typically photoelectron holographic imaging (PHI) only produces atomic images for nearest and frequently next-nearest-neighbor atoms to the photoemitter [1]. A new method-the derivative transform-is presented which generally yields third and sometimes fourth nearest-neighbor atoms. As a result the assignments of atomic species to the peaks in the experimentally obtained image are facilitated. The methods is exemplified by experiments for several
... 111… H. Cruguel, B. Lépine, S. Ababou, F. Solal, and G. Jézéquel UMR-CNRS-Université 6627, Ph... more ... 111… H. Cruguel, B. Lépine, S. Ababou, F. Solal, and G. Jézéquel UMR-CNRS-Université 6627, Physique des Atomes, Lasers, Molecules et Surfaces, Equipe surfaces-interfaces, Av. Gal. Leclerc, 35042 Rennes-Cédex, France ...
ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene lay... more ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas.We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered ð4 � 4Þ, ð ffiffiffiffiffi 13 p � ffiffiffiffiffi 13 p Þ R13.9�, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms
ABSTRACT The origin of the catalytic activity of gold nanoparticles remains debated despite exten... more ABSTRACT The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO2(110) during CO oxidation. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O2, Ar, or a mixture of O2 + CO and of Ar + CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidation induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle’s diameter of 2.1 ± 0.3 nm and a height of about six atomic layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different experimental conditions shows consistency of these results with published data using both “model” and “real” catalysts.
It is well known that free magnetic nanoclusters display novel properties including enhanced magn... more It is well known that free magnetic nanoclusters display novel properties including enhanced magnetic moments in ferromagnetic metals, ferrimagnetism in antiferromagnetic metals and the appearance of magnetism in non-magnetic metals. A contemporary challenge is to build some of the intrinsic novel behaviour into macroscopic materials. XMCD measurements of exposed mass-selected Fe clusters in the size range 180-700 atoms deposited in situ onto HOPG substrates reveal that adsorbed clusters show an enhancement in both orbital and spin moments relative to the bulk. Coating the exposed Fe clusters with Co increases the spin moment still further without significantly changing the orbital moment. Increasing the surface density of Fe clusters to induce a significant interaction reduces the orbital moment to its small bulk value but an enhancement in the spin moment remains even in thick cluster-assembled films. The anisotropy in isolated Fe and Co clusters embedded in Ag matrices is shown to be uniaxial with the anisotropy axes randomly oriented in three dimensions. Thick cluster films adopt a domainless correlated super-spin glass magnetic configuration as a result of the frustration between the inter-cluster exchange coupling and random anisotropy. This state is magnetically soft, which is a valuable technological attribute in high-moment films. #
A transform-k derivative spectra (KDS) transform-is introduced for construction of an atomic-stru... more A transform-k derivative spectra (KDS) transform-is introduced for construction of an atomic-structure image from photoelectron diffraction data. A phenomenological theory is used to show that the transform of spectrum derivatives enhances the image peaks by the square of the emitter-scatter distance when used in conjunction with the small cone method. In comparison with the standard transform used in photoelectron holography, the KDS transform allows more distant neighbors (scatterers) to be ``seen'' by the emitter and suppresses strong forward scattering. The ability to experimentally observe more neighbors of a photoelectron emitter expands the applicability of holographic imaging. The procedure is applied to experimental data obtained from the As/Si(111)-(1×1) and C2H4/Si(100)-(2×1) surface structures. The letter results show that C2H4 adsorption does not break the Si dimer bond.
The origin of the catalytic activity of gold nanoparticles remains debated despite extensive stud... more The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO 2 (110) during CO oxidation. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O 2 , Ar, or a mixture of O 2 þ CO and of Ar þ CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidation induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle's diameter of 2.1 ( 0.3 nm and a height of about six atomic layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different experimental conditions shows consistency of these results with published data using both "model" and "real" catalysts.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1999
Gallium nitride (GaN) materials are very useful for fabricating electronic and electro-optic devi... more Gallium nitride (GaN) materials are very useful for fabricating electronic and electro-optic devices, such as high power electronics, blue and ultraviolet light emitting diodes (LED), detectors, and laser devices. 1,2,3 However, the development of III-V nitride materials and devices has suffered from the lack of the availability of low-dislocationdensity, lattice-matched substrates for device synthesis. Recently, epitaxial lateral overgrowth (ELO) technique 4 produces GaN with a remarkable reduction of the dislocation density to about 10 4 per cm 2 or less. This method starts with a layer of GaN on sapphire (or SiC) which is then patterned with SiO 2 stripes of about 15 µm wide separated by 3 µm windows. The final MOVPE growth starts in the windows growing up and over the SiO 2 stripes because the film will not "seed" on it. Between two adjacent final stripes is where the growth fronts meet and coalesce. It is above the middle of the SiO 2 stripes.
We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy to probe the locali... more We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy to probe the localized electronic states at GaN free surfaces, metal-GaN contacts, and GaN/InGaN quantum well interfaces. These depth-resolved measurements reveal the presence of deep electronic states near GaN interfaces whose energies and relative densities depend sensitively on the local chemical structure and growth conditions. The physical properties of these states correlate with mobility variations in thin GaN films grown by molecular beam epitaxy, Fermi level positions at Mg and Al/GaN Schottky barriers, and the appearance of new phases localized near GaN/InGaN/GaN quantum well interfaces. The growth and processing dependence of deep GaN levels highlights new methods to understand and control the fundamental electronic structure of GaN heterointerfaces.
The energies of trivalent rare earth ions relative to the host valence band were measured for a s... more The energies of trivalent rare earth ions relative to the host valence band were measured for a series of rare-earth-doped yttrium aluminum garnets, R x Y 3-x Al 5 O 12 (R=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and 0<x<3), using ultraviolet photoemission spectroscopy. The 4f photoemission spectra were acquired using synchrotron radiation, exploiting the 4d to 4f "giant resonance" in the 4f electron photoemission cross-section to separate the 4f contribution. Theoretical valence band and 4f photoemission spectra were fit to experimental results to accurately determine electron energies. The measured 4f n ground state energies of these ions range from 700 meV above the valence band maximum for Tb 3+ to 4.7 eV below the valence band maximum for Lu 3+ , and all ground state energies, except for Tb 3+ , are degenerate with valence band states. An empirical model is successful in describing the relative energies of the 4f n ground states for rare earth ions in these materials. This model is used to estimate the positions of the lighter rare earth ions, giving good agreement with published excited state absorption and photoconductivity measurements on Ce 3+ in yttrium aluminum garnet. It is shown that the energies of the 4f electrons relative to the valence band can be estimated from the photoemission spectrum of the undoped host, providing a simple method for extending these results to related host crystals. The success of this model suggests that further studies of additional host compounds will rapidly lead to a broader picture of the effect of the host lattice on the 4f electron binding energies.
ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene lay... more ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas.We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered ð4 � 4Þ, ð ffiffiffiffiffi 13 p � ffiffiffiffiffi 13 p Þ R13.9�, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms
Rare-earth ions have a multitude of technological applications as optically active impurities in ... more Rare-earth ions have a multitude of technological applications as optically active impurities in insulators and semiconductors. Knowledge of the energies of the host crystal's electronic band states relative to the 4f N or 4f N-1 5d 1 states responsible for the ion's optical transitions is important for understanding the properties and performance of each material since energy and electron transfer between these states influences the material's efficiency and stability. 1 Little is known about the relationships between these states, but there is growing motivation to explore these properties for developing ultraviolet laser materials, phosphors for applications including plasma displays and mercury-free lamps, scintillator materials for medical imaging, and optical data processing and storage technologies based on photorefractivity or photon-gated photoionization holeburning. Continued advances in optical technologies require knowledge of the systematic trends and behavior of rare-earth energies relative to crystal band states so that the properties of current materials may be fully understood and new materials may be logically developed.
Theoretical studies have shown that new physical properties such as tunable gap opening or quantu... more Theoretical studies have shown that new physical properties such as tunable gap opening or quantum spin Hall effect could be expected from group IV graphene analogues (silicene, germanene, stanene). While there have been numerous studies of growth of such Si, Ge, Sn monolayers, the demonstration of their hexagonal organization has been often based on postgrowth characterization and their analogy to graphene has remained controversial. Our realtime scanning tunneling microscopy (STM) observation during Ge deposition on Ag(111) in the [380 K-430 K] temperature range reveals that Ag atoms are involved in all the structures observed before the formation of a second layer, rejecting the possible formation of germanene on this substrate within these experimental conditions. The observation by STM of Ge atomic diffusion shows that easy exchange between Ag and Ge atoms is responsible for the Ge-Ag surface alloying at such temperatures.
Adsorption of the Glycine–Proline (Gly–Pro) dipeptide has been investigated using surface science... more Adsorption of the Glycine–Proline (Gly–Pro) dipeptide has been investigated using surface science complementary techniques on Au(110) and Ag(110), showing some interesting differences both in the chemical form and surface organization of the adsorbed peptide. On Au(110), Gly–Pro mainly adsorbs in neutral form (COOH/NH2), at low coverage or for a short interaction time; the surface species become zwitterionic at a higher coverage or longer interaction time. These changes are accompanied by a complete reorganization of the molecules at the surface. On Ag(110), only anionic molecules (COO−/NH2) were detected on the surface and only one type of arrangement was observed. These results will be compared to some previously obtained on Cu(110), thus providing a unique comparison of the adsorption of the same di-peptide on three different metal surfaces; the great influence of the substrate on both the chemical form and the arrangement of adsorbed di-peptides was made clear.
Typically photoelectron holographic imaging (PHI) only produces atomic images for nearest and fre... more Typically photoelectron holographic imaging (PHI) only produces atomic images for nearest and frequently next-nearest-neighbor atoms to the photoemitter [1]. A new method-the derivative transform-is presented which generally yields third and sometimes fourth nearest-neighbor atoms. As a result the assignments of atomic species to the peaks in the experimentally obtained image are facilitated. The methods is exemplified by experiments for several
... 111… H. Cruguel, B. Lépine, S. Ababou, F. Solal, and G. Jézéquel UMR-CNRS-Université 6627, Ph... more ... 111… H. Cruguel, B. Lépine, S. Ababou, F. Solal, and G. Jézéquel UMR-CNRS-Université 6627, Physique des Atomes, Lasers, Molecules et Surfaces, Equipe surfaces-interfaces, Av. Gal. Leclerc, 35042 Rennes-Cédex, France ...
ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene lay... more ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas.We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered ð4 � 4Þ, ð ffiffiffiffiffi 13 p � ffiffiffiffiffi 13 p Þ R13.9�, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms
ABSTRACT The origin of the catalytic activity of gold nanoparticles remains debated despite exten... more ABSTRACT The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO2(110) during CO oxidation. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O2, Ar, or a mixture of O2 + CO and of Ar + CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidation induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle’s diameter of 2.1 ± 0.3 nm and a height of about six atomic layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different experimental conditions shows consistency of these results with published data using both “model” and “real” catalysts.
It is well known that free magnetic nanoclusters display novel properties including enhanced magn... more It is well known that free magnetic nanoclusters display novel properties including enhanced magnetic moments in ferromagnetic metals, ferrimagnetism in antiferromagnetic metals and the appearance of magnetism in non-magnetic metals. A contemporary challenge is to build some of the intrinsic novel behaviour into macroscopic materials. XMCD measurements of exposed mass-selected Fe clusters in the size range 180-700 atoms deposited in situ onto HOPG substrates reveal that adsorbed clusters show an enhancement in both orbital and spin moments relative to the bulk. Coating the exposed Fe clusters with Co increases the spin moment still further without significantly changing the orbital moment. Increasing the surface density of Fe clusters to induce a significant interaction reduces the orbital moment to its small bulk value but an enhancement in the spin moment remains even in thick cluster-assembled films. The anisotropy in isolated Fe and Co clusters embedded in Ag matrices is shown to be uniaxial with the anisotropy axes randomly oriented in three dimensions. Thick cluster films adopt a domainless correlated super-spin glass magnetic configuration as a result of the frustration between the inter-cluster exchange coupling and random anisotropy. This state is magnetically soft, which is a valuable technological attribute in high-moment films. #
A transform-k derivative spectra (KDS) transform-is introduced for construction of an atomic-stru... more A transform-k derivative spectra (KDS) transform-is introduced for construction of an atomic-structure image from photoelectron diffraction data. A phenomenological theory is used to show that the transform of spectrum derivatives enhances the image peaks by the square of the emitter-scatter distance when used in conjunction with the small cone method. In comparison with the standard transform used in photoelectron holography, the KDS transform allows more distant neighbors (scatterers) to be ``seen'' by the emitter and suppresses strong forward scattering. The ability to experimentally observe more neighbors of a photoelectron emitter expands the applicability of holographic imaging. The procedure is applied to experimental data obtained from the As/Si(111)-(1×1) and C2H4/Si(100)-(2×1) surface structures. The letter results show that C2H4 adsorption does not break the Si dimer bond.
The origin of the catalytic activity of gold nanoparticles remains debated despite extensive stud... more The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO 2 (110) during CO oxidation. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O 2 , Ar, or a mixture of O 2 þ CO and of Ar þ CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidation induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle's diameter of 2.1 ( 0.3 nm and a height of about six atomic layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different experimental conditions shows consistency of these results with published data using both "model" and "real" catalysts.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1999
Gallium nitride (GaN) materials are very useful for fabricating electronic and electro-optic devi... more Gallium nitride (GaN) materials are very useful for fabricating electronic and electro-optic devices, such as high power electronics, blue and ultraviolet light emitting diodes (LED), detectors, and laser devices. 1,2,3 However, the development of III-V nitride materials and devices has suffered from the lack of the availability of low-dislocationdensity, lattice-matched substrates for device synthesis. Recently, epitaxial lateral overgrowth (ELO) technique 4 produces GaN with a remarkable reduction of the dislocation density to about 10 4 per cm 2 or less. This method starts with a layer of GaN on sapphire (or SiC) which is then patterned with SiO 2 stripes of about 15 µm wide separated by 3 µm windows. The final MOVPE growth starts in the windows growing up and over the SiO 2 stripes because the film will not "seed" on it. Between two adjacent final stripes is where the growth fronts meet and coalesce. It is above the middle of the SiO 2 stripes.
We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy to probe the locali... more We have used low energy electron-excited nanoluminescence (LEEN) spectroscopy to probe the localized electronic states at GaN free surfaces, metal-GaN contacts, and GaN/InGaN quantum well interfaces. These depth-resolved measurements reveal the presence of deep electronic states near GaN interfaces whose energies and relative densities depend sensitively on the local chemical structure and growth conditions. The physical properties of these states correlate with mobility variations in thin GaN films grown by molecular beam epitaxy, Fermi level positions at Mg and Al/GaN Schottky barriers, and the appearance of new phases localized near GaN/InGaN/GaN quantum well interfaces. The growth and processing dependence of deep GaN levels highlights new methods to understand and control the fundamental electronic structure of GaN heterointerfaces.
The energies of trivalent rare earth ions relative to the host valence band were measured for a s... more The energies of trivalent rare earth ions relative to the host valence band were measured for a series of rare-earth-doped yttrium aluminum garnets, R x Y 3-x Al 5 O 12 (R=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and 0<x<3), using ultraviolet photoemission spectroscopy. The 4f photoemission spectra were acquired using synchrotron radiation, exploiting the 4d to 4f "giant resonance" in the 4f electron photoemission cross-section to separate the 4f contribution. Theoretical valence band and 4f photoemission spectra were fit to experimental results to accurately determine electron energies. The measured 4f n ground state energies of these ions range from 700 meV above the valence band maximum for Tb 3+ to 4.7 eV below the valence band maximum for Lu 3+ , and all ground state energies, except for Tb 3+ , are degenerate with valence band states. An empirical model is successful in describing the relative energies of the 4f n ground states for rare earth ions in these materials. This model is used to estimate the positions of the lighter rare earth ions, giving good agreement with published excited state absorption and photoconductivity measurements on Ce 3+ in yttrium aluminum garnet. It is shown that the energies of the 4f electrons relative to the valence band can be estimated from the photoemission spectrum of the undoped host, providing a simple method for extending these results to related host crystals. The success of this model suggests that further studies of additional host compounds will rapidly lead to a broader picture of the effect of the host lattice on the 4f electron binding energies.
ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene lay... more ABSTRACT Using scanning tunneling microscopy (STM), the elaboration of the so-called silicene layer on Ag(111) is monitored in real time during Si evaporation at different temperatures. It is shown that the growth of silicene is accompanied by the release of about 65% of the surface Ag atoms from the Si covered areas.We observe that Si islands develop on the Ag terraces and Si strips at the Ag step edges, progressively forming ordered ð4 � 4Þ, ð ffiffiffiffiffi 13 p � ffiffiffiffiffi 13 p Þ R13.9�, and dotted phases. Meanwhile, displaced Ag atoms group to develop additional bare Ag terraces growing round the Si islands from the pristine Ag step edges. This indicates a strong interaction between Si and Ag atoms, with an important modification of the Ag substrate beneath the surface layer. This observation is in contradiction with the picture of a silicene layer weakly interacting with the unreconstructed Ag substrate, and strongly indicates that the structure of silicene on Ag(111) corresponds either to a Si-Ag surface alloy or to a Si plane covered with Ag atoms
Rare-earth ions have a multitude of technological applications as optically active impurities in ... more Rare-earth ions have a multitude of technological applications as optically active impurities in insulators and semiconductors. Knowledge of the energies of the host crystal's electronic band states relative to the 4f N or 4f N-1 5d 1 states responsible for the ion's optical transitions is important for understanding the properties and performance of each material since energy and electron transfer between these states influences the material's efficiency and stability. 1 Little is known about the relationships between these states, but there is growing motivation to explore these properties for developing ultraviolet laser materials, phosphors for applications including plasma displays and mercury-free lamps, scintillator materials for medical imaging, and optical data processing and storage technologies based on photorefractivity or photon-gated photoionization holeburning. Continued advances in optical technologies require knowledge of the systematic trends and behavior of rare-earth energies relative to crystal band states so that the properties of current materials may be fully understood and new materials may be logically developed.
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Papers by H. Cruguel