David Wieliczka - Academia.edu (original) (raw)

Papers by David Wieliczka

Four techniques were developed to determine the optical constants of liquids and solids. Two cell... more Four techniques were developed to determine the optical constants of liquids and solids. Two cells were designed and constructed to obtain the optical constants of liquids, a wedge-shaped cell and an internal reflectance cell. The wedge-shaped cell was used to determine the optical constants of 11 liquids in the spectral range 500-12500 cm-1. The techniques of Querry and Avery were used in conjunction with the internal reflectance cell to obtain the complex refractive index of water and SF-96. The complex refractive indices of illite, kaolin, and montmorillinite were obtained from applying the techniques of Querrys and Averys. The error associated with each of the four techniques was also examined and is summarized. Keywords: Absorption, Reflectance, Optical constants, Refractive indices, Carbon dioxide laser, Infrared.

A wedge-shaped-cell has been developed that avoids serious errors during the measurements on the ... more A wedge-shaped-cell has been developed that avoids serious errors during the measurements on the Lambert absorption coefficient of liquids. The cell is a modification of a design previously used by Tyler, Taylor, and Querry. After assembling the cell the vertex angle of the air wedge film is determined using the interference fringes produced from a He-Ne laser. Without disassembling the cell the sample fluid is injected into the wedge by employing a manifold and syringe. In this way they can accurately determine the sample thickness. The Lambert absorption coefficient and the imaginary part of the complex refractive index of water and SF96 have been determined in the range of 3703.7 9cm⁻¹) to 25,000 (cm⁻¹). The range of the data is limited by the windows currently being used. This range will be extended into the UV and Ir by employing fused silica and ZnSe windows, respectively.

Plasmas and Polymers

An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethy... more An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethylsilane (TMS) monomer gas has the ability to modify the characteristics of the primary plasma polymer significantly in a favorable manner for many applications. The effect of the second plasma polymerization on the primary plasma polymer of TMS depends on the nature of the second monomer. Plasma of F-containing monomer, hexafluoroethane (HFE) and perfluoromethane (CF4), decreases the ESR signal of TMS and no detectable signal due to F-containing monomer was found. The decay rate of the signal decreased significantly. In contrast to this situation, CH4 plasma treatment yields an ESR signal that is a composite of that observed from TMS and CH4 films individually. The overall signal increased in this instance, but didn't show appreciable decay in 24 hr period. A second treatment by nonpolymer forming plasmas also decreased the ESR signal of TMS, and decreased the decay rate, indicating ...

UV pulsed laser radiation was applied to synthetic polycrystalline hydroxyapatite, the mineral th... more UV pulsed laser radiation was applied to synthetic polycrystalline hydroxyapatite, the mineral that is the main component of bone. The process was carried out in deionized water. The ablated nanoparticles have been studied with Raman spectroscopy, TEM and XPS. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of ˜ 100 nm. Raman spectroscopic analysis indicated that particles had the same structure as the original crystal. XPS demonstrated that the surface chemical composition is similar to that of the original material. The advantage of this method in comparison with ablation in vacuum and gas is that due to the confinement conditions produced by the water, the composition of the ablated nanoparticles remains the same as the target material. Another advantage is in the simplicity of the method in comparison to both ablation in vacuum or low pressure gas and to chemical methods for nanoparticle synthesis.

Lasers in Dentistry, 1995

Physical Review B, 1982

Photoemission studies of the γ-α phase transition in cerium show changes in two 4f-related featur... more Photoemission studies of the γ-α phase transition in cerium show changes in two 4f-related features in the valence band (0.3 and 2 eV below EF) and broadening of the multiplet structure in the region of the 4d-4f transitions. We show that the observed features can be explained by increased hybridization of the 4f wave function upon entering the α phase.

Solid State Communications, 2000

High surface area, nano-phase materials exhibit many interesting properties quite different from ... more High surface area, nano-phase materials exhibit many interesting properties quite different from their bulk counterparts, and are the focus of much technical investigation and engineering development based on these properties. Earlier experiments using X-ray diffraction have indicated that a new phase of alumina exists upon non-hydrostatic compression of 67 nm particles of galumina to above 35 GPa and quasi-hydrostatic compression to pressures over 50 GPa. This phase is quenchable on decompression to 0 GPa, allowing for additional analysis that are unmanageable in the diamond anvil cell (DAC). For the present paper, imaging X-ray photoelectron spectroscopy (XPS), which is ideally suited for surface chemistry measurements of the small samples required in the DAC, is used. The collection of Bremsstrahlung excited Auger electrons in combination with photoelectrons allows for a better comparison of chemical shifts, through the Auger parameter. No dramatic change was observed, as is the case with many alumina polymorphs, but slight differences between the gamma phase and the new highpressure phase are noted, supporting the earlier X-ray results. Additionally, an extremely low adventitious carbon level was observed on a g-phase sample and is discussed.

Progress in Organic Coatings, 2002

ABSTRACT DC cathodic polymerization of trimethylsilane (TMS) and its mixtures with argon was cond... more ABSTRACT DC cathodic polymerization of trimethylsilane (TMS) and its mixtures with argon was conducted in a closed reactor system. The TMS deposition behavior and plasma parameters were examined with discharge time during the deposition process. The chemical composition of TMS plasma polymers was investigated by X-ray photoelectron spectroscopy (XPS) analysis. It was found that the TMS plasma coatings obtained under such operations have a distinct chemical structure that gradually changes from silicon rich at the interface with the substrate to carbon rich at the top surface. The coating characteristics of TMS plasma polymers were evaluated in terms of refractive index, linear polarization resistance, and adhesion performance to subsequent spray paint primers. Experimental data indicated that DC cathodic polymerization of TMS in a closed reactor system produced plasma coatings with superior-coating properties, such as higher refractive index and stronger primer adhesion, to those obtained in a flow reactor system as employed in parts 1 and 2 of this series. As a result, the plasma interface engineered-coating systems of IVD/plasma polymer/non-chromated primer obtained under such an operation showed excellent corrosion protection of IVD Al-coated Al alloys which outperformed the chromate conversion-coated IVD controls after 4 weeks of SO2 salt spray and 12 weeks of Prohesion salt spray tests.

Journal of Dental Research, 1996

The use of x-ray photoelectron spectroscopy for the study of biological materials has provided mi... more The use of x-ray photoelectron spectroscopy for the study of biological materials has provided mixed results. The experimental difficulties associated with the application of this technique to the study of biological materials include the effects of ultra-high vacuum, x-ray exposure, surface charging, and, for insulating materials, the inherent lack of an intrinsic energy reference. Since most biological materials are insulators, the lack of an intrinsic energy reference complicates one's ability to draw direct comparisons between different studies. In this paper, the results from two different apatites are compared with the results obtained from the use of two conventional techniques for referencing binding energies. The results presented here are referenced only to the Pt Fermi level; no further energy modifications are performed. A comparison with the results of other investigators indicates a large difference in binding energies for all involved core levels. These results in...

Journal of Dental Research, 2000

To date, the dentin/adhesive (d/a) bond has primarily been studied by morphologic analysis in con... more To date, the dentin/adhesive (d/a) bond has primarily been studied by morphologic analysis in conjunction with bond strength measurement. Although these analyses have enhanced our understanding, numerous questions about the chemistry have not been answered. The purpose of this study was to determine, at the molecular level, quantitative differences in the composition of the d/a interface formed under "wet" bonding conditions. The occlusal one-third of the crown was removed from 10 extracted, unerupted human third molars. The prepared dentin surfaces were treated, per manufacturers' instructions, with either Single Bond (3M) or One-Step adhesive (Bisco). Three-micron-thick sections of the d/a interface were cut and stained with Goldner trichrome for light microscopy. Companion slabs were analyzed with micro-Raman spectroscopy; the sample was placed at the focus of a 100x microscope objective, and spectra were acquired at 1-μm intervals across the d/a interface. Referenc...

Journal of Biomedical Optics, 1999

The potential environmental risks associated with mercury release have forced many European count... more The potential environmental risks associated with mercury release have forced many European countries to ban the use of dental amalgam. Alternative materials such as composite resins do not provide the clinical function for the length of time characteristically associated with dental amalgam. The weak link in the composite restoration is the dentin/adhesive bond. The purpose of this study was to correlate morphologic characterization of the dentin/adhesive bond with chemical analyses using micro-Fourier transform infrared and micro-Raman spectroscopy. A commercial dental adhesive was placed on dentin substrates cut from extracted, unerupted human third molars. Sections of the dentin/adhesive interface were investigated using infrared radiation produced at the Aladdin synchrotron source; visible radiation from a Kr+ laser was used for the micro-Raman spectroscopy. Sections of the dentin/adhesive interface, differentially stained to identify protein, mineral, and adhesive, were examined using light microscopy. Due to its limited spatial resolution and the unknown sample thickness the infrared results cannot be used quantitatively in determining the extent of diffusion. The results from the micro-Raman spectroscopy and light microscopy indicate exposed protein at the dentin/adhesive interface. Using a laser that reduces background fluorescence, the micro-Raman spectroscopy provides quantitative chemical and morphologic information on the dentin/adhesive interface. The staining procedure is sensitive to sites of pure protein and thus, complements the Raman results. © 1999 Society of Photo-Optical Instrumentation Engineers.

Journal of Applied Polymer Science, 2002

The adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrate... more The adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrates depends on the cleanliness of the substrate surface and the state of oxides on the aluminum alloy surface. Both factors are dependent on what type of alloy is used, and consequently, the best preparation of the substrate surface differs on the type of aluminum alloy. Oxygen plasma treatment is effective for the elimination of organic surface contamination, but plasma treatment, such as that of mixed argon and hydrogen, cannot be used to modify the surface state of oxides on these alloys. This is because oxides of aluminum are stable and thus resist plasma modification, and prolonged plasma treatment has been observed to change concentrations of alloy components at the surface due to the heating of the alloy. Chemical cleaning of the surface is necessary before the application of the plasma polymer used for corrosion protection enhancement. Once the surface was properly prepared, a plas...

Journal of Applied Physics, 1989

The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV... more The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV photon energy range to investigate their value as high-efficiency, customizeable photocathode materials. The yield spectra resemble the weighted sum of the absorption spectra of the constituent rare earths, but the amplitude of the yield spectra were compressed relative to the absorption coefficient data due to the large electron escape depths in these materials.

Journal of Applied Physics, 2008

Synthetic polycrystalline hydroxyapatite was ablated in water with 337 nm radiation from a UV nit... more Synthetic polycrystalline hydroxyapatite was ablated in water with 337 nm radiation from a UV nitrogen pulsed laser. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of ∼80 nm. Raman spectroscopic analysis demonstrated that particles had the same structure as the original crystal. X-ray photoelectron spectroscopy showed that the surface chemical composition was close to that of the original material. The characteristics of the ablated particles and estimations of the temperature rise of the hydroxyapatite surface under laser irradiation are consistent with the mechanism of explosive boiling being responsible for ablation. The experimental observations offer the basis for preparation of hydroxyapatite nanoparticles by laser ablation in water.

Biomaterials, 1998

Earlier studies have failed to establish a consensus on the amount of mercury vapour released fro... more Earlier studies have failed to establish a consensus on the amount of mercury vapour released from dental amalgam restorations. The purpose of this study was to accurately and quantitatively measure the equilibrium mercury vapour pressure from dental amalgam. The vapour pressure was measured using a quartz crystal microbalance as a function of the load from 0-5.4 MPa. Auger spectra were collected of the as-formed and argon ion sputter cleaned dental amalgam surface. For the as-formed surface the mercury vapour density is zero with no load and increases to 0.6 microg m(-3) at 5.4 M Pa. Following cleaning the mercury, vapour density increased to a maximum value of 15 microg m(-3). The Auger spectra of the as-formed surfaces were dominated by features associated with carbon and oxygen. These spectral results in concert with the mercury vapour density measurements indicate that the oxide film on the as-formed surfaces inhibited the release of mercury vapour. The results of this experiment provide an upper limit for the amount of mercury vapour released by dental amalgams. Under conditions simulating the oral cavity this value would be reduced by oxides that form on the surface of dental amalgam restorations.

Applied Surface Science, 1998

. Ž . X-ray photoelectron spectroscopy XPS and scanning electron microscopy SEM have been applied... more . Ž . X-ray photoelectron spectroscopy XPS and scanning electron microscopy SEM have been applied to investigate the surface chemistry and morphology of InP wafers photochemically etched under 308 nm illumination from a XeCl excimer Ž . laser. The etching experiments were carried out at ambient temperature and in a low-pressure 1 mbar atmosphere of Cl 2 Ž . 2 10% diluted in He. During the process, the samples were exposed to laser radiation with fluences of 73 mJrcm or 114 mJrcm 2 . Both fluence values are below the ablation threshold of 140 mJrcm 2 for InP. The mapping of the photoelectron Ž . Ž . Ž . spectral line intensities of In 3d , Cl 2p , and P 2p displayed the distribution of In-Cl and In-P compounds on 5r2 3 r2 3 r2 the surface of the wafer. The chemical composition and morphology of the etched surface were found to be dependent on laser fluence. Surfaces with a fine granular structure were observed at a lower fluence, while at higher fluences, surfaces with a linear grating-like structure were formed. More chlorine is bound to the surface prepared at a higher fluence. q 1998 Elsevier Science B.V.

Applied Spectroscopy, 1997

The clinical success of dental composites depends critically upon the adhesive bond that secures ... more The clinical success of dental composites depends critically upon the adhesive bond that secures it to the tooth. Previous efforts to characterize the adhesive/dentin interface have generally required sample preparation that alters or damages the interface. Using micro-Raman spectroscopy, we have collected chemical and morphologic information on the dentin/adhesive interface with minimal sample preparation. Results from this technique have provided direct evidence of adhesive penetration and demineralization depth for two adhesive systems.

Applied Spectroscopy, 1996

The degree of adhesive penetration into dentin has been studied through micro-Raman spectroscopic... more The degree of adhesive penetration into dentin has been studied through micro-Raman spectroscopic examination of the dentin/adhesive interface. In contrast to previous studies, for the specimen examined in this work the adhesive penetrates less than 2 μm into the acid-etched and, thus, decalcified dentin. There is strong spectroscopic evidence that, upon acid etching of the dentin surface, which is typically performed immediately before the adhesive is applied, the collagen matrix collapses upon itself.

Four techniques were developed to determine the optical constants of liquids and solids. Two cell... more Four techniques were developed to determine the optical constants of liquids and solids. Two cells were designed and constructed to obtain the optical constants of liquids, a wedge-shaped cell and an internal reflectance cell. The wedge-shaped cell was used to determine the optical constants of 11 liquids in the spectral range 500-12500 cm-1. The techniques of Querry and Avery were used in conjunction with the internal reflectance cell to obtain the complex refractive index of water and SF-96. The complex refractive indices of illite, kaolin, and montmorillinite were obtained from applying the techniques of Querrys and Averys. The error associated with each of the four techniques was also examined and is summarized. Keywords: Absorption, Reflectance, Optical constants, Refractive indices, Carbon dioxide laser, Infrared.

A wedge-shaped-cell has been developed that avoids serious errors during the measurements on the ... more A wedge-shaped-cell has been developed that avoids serious errors during the measurements on the Lambert absorption coefficient of liquids. The cell is a modification of a design previously used by Tyler, Taylor, and Querry. After assembling the cell the vertex angle of the air wedge film is determined using the interference fringes produced from a He-Ne laser. Without disassembling the cell the sample fluid is injected into the wedge by employing a manifold and syringe. In this way they can accurately determine the sample thickness. The Lambert absorption coefficient and the imaginary part of the complex refractive index of water and SF96 have been determined in the range of 3703.7 9cm⁻¹) to 25,000 (cm⁻¹). The range of the data is limited by the windows currently being used. This range will be extended into the UV and Ir by employing fused silica and ZnSe windows, respectively.

Plasmas and Polymers

An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethy... more An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethylsilane (TMS) monomer gas has the ability to modify the characteristics of the primary plasma polymer significantly in a favorable manner for many applications. The effect of the second plasma polymerization on the primary plasma polymer of TMS depends on the nature of the second monomer. Plasma of F-containing monomer, hexafluoroethane (HFE) and perfluoromethane (CF4), decreases the ESR signal of TMS and no detectable signal due to F-containing monomer was found. The decay rate of the signal decreased significantly. In contrast to this situation, CH4 plasma treatment yields an ESR signal that is a composite of that observed from TMS and CH4 films individually. The overall signal increased in this instance, but didn't show appreciable decay in 24 hr period. A second treatment by nonpolymer forming plasmas also decreased the ESR signal of TMS, and decreased the decay rate, indicating ...

UV pulsed laser radiation was applied to synthetic polycrystalline hydroxyapatite, the mineral th... more UV pulsed laser radiation was applied to synthetic polycrystalline hydroxyapatite, the mineral that is the main component of bone. The process was carried out in deionized water. The ablated nanoparticles have been studied with Raman spectroscopy, TEM and XPS. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of ˜ 100 nm. Raman spectroscopic analysis indicated that particles had the same structure as the original crystal. XPS demonstrated that the surface chemical composition is similar to that of the original material. The advantage of this method in comparison with ablation in vacuum and gas is that due to the confinement conditions produced by the water, the composition of the ablated nanoparticles remains the same as the target material. Another advantage is in the simplicity of the method in comparison to both ablation in vacuum or low pressure gas and to chemical methods for nanoparticle synthesis.

Lasers in Dentistry, 1995

Physical Review B, 1982

Photoemission studies of the γ-α phase transition in cerium show changes in two 4f-related featur... more Photoemission studies of the γ-α phase transition in cerium show changes in two 4f-related features in the valence band (0.3 and 2 eV below EF) and broadening of the multiplet structure in the region of the 4d-4f transitions. We show that the observed features can be explained by increased hybridization of the 4f wave function upon entering the α phase.

Solid State Communications, 2000

High surface area, nano-phase materials exhibit many interesting properties quite different from ... more High surface area, nano-phase materials exhibit many interesting properties quite different from their bulk counterparts, and are the focus of much technical investigation and engineering development based on these properties. Earlier experiments using X-ray diffraction have indicated that a new phase of alumina exists upon non-hydrostatic compression of 67 nm particles of galumina to above 35 GPa and quasi-hydrostatic compression to pressures over 50 GPa. This phase is quenchable on decompression to 0 GPa, allowing for additional analysis that are unmanageable in the diamond anvil cell (DAC). For the present paper, imaging X-ray photoelectron spectroscopy (XPS), which is ideally suited for surface chemistry measurements of the small samples required in the DAC, is used. The collection of Bremsstrahlung excited Auger electrons in combination with photoelectrons allows for a better comparison of chemical shifts, through the Auger parameter. No dramatic change was observed, as is the case with many alumina polymorphs, but slight differences between the gamma phase and the new highpressure phase are noted, supporting the earlier X-ray results. Additionally, an extremely low adventitious carbon level was observed on a g-phase sample and is discussed.

Progress in Organic Coatings, 2002

ABSTRACT DC cathodic polymerization of trimethylsilane (TMS) and its mixtures with argon was cond... more ABSTRACT DC cathodic polymerization of trimethylsilane (TMS) and its mixtures with argon was conducted in a closed reactor system. The TMS deposition behavior and plasma parameters were examined with discharge time during the deposition process. The chemical composition of TMS plasma polymers was investigated by X-ray photoelectron spectroscopy (XPS) analysis. It was found that the TMS plasma coatings obtained under such operations have a distinct chemical structure that gradually changes from silicon rich at the interface with the substrate to carbon rich at the top surface. The coating characteristics of TMS plasma polymers were evaluated in terms of refractive index, linear polarization resistance, and adhesion performance to subsequent spray paint primers. Experimental data indicated that DC cathodic polymerization of TMS in a closed reactor system produced plasma coatings with superior-coating properties, such as higher refractive index and stronger primer adhesion, to those obtained in a flow reactor system as employed in parts 1 and 2 of this series. As a result, the plasma interface engineered-coating systems of IVD/plasma polymer/non-chromated primer obtained under such an operation showed excellent corrosion protection of IVD Al-coated Al alloys which outperformed the chromate conversion-coated IVD controls after 4 weeks of SO2 salt spray and 12 weeks of Prohesion salt spray tests.

Journal of Dental Research, 1996

The use of x-ray photoelectron spectroscopy for the study of biological materials has provided mi... more The use of x-ray photoelectron spectroscopy for the study of biological materials has provided mixed results. The experimental difficulties associated with the application of this technique to the study of biological materials include the effects of ultra-high vacuum, x-ray exposure, surface charging, and, for insulating materials, the inherent lack of an intrinsic energy reference. Since most biological materials are insulators, the lack of an intrinsic energy reference complicates one's ability to draw direct comparisons between different studies. In this paper, the results from two different apatites are compared with the results obtained from the use of two conventional techniques for referencing binding energies. The results presented here are referenced only to the Pt Fermi level; no further energy modifications are performed. A comparison with the results of other investigators indicates a large difference in binding energies for all involved core levels. These results in...

Journal of Dental Research, 2000

To date, the dentin/adhesive (d/a) bond has primarily been studied by morphologic analysis in con... more To date, the dentin/adhesive (d/a) bond has primarily been studied by morphologic analysis in conjunction with bond strength measurement. Although these analyses have enhanced our understanding, numerous questions about the chemistry have not been answered. The purpose of this study was to determine, at the molecular level, quantitative differences in the composition of the d/a interface formed under "wet" bonding conditions. The occlusal one-third of the crown was removed from 10 extracted, unerupted human third molars. The prepared dentin surfaces were treated, per manufacturers' instructions, with either Single Bond (3M) or One-Step adhesive (Bisco). Three-micron-thick sections of the d/a interface were cut and stained with Goldner trichrome for light microscopy. Companion slabs were analyzed with micro-Raman spectroscopy; the sample was placed at the focus of a 100x microscope objective, and spectra were acquired at 1-μm intervals across the d/a interface. Referenc...

Journal of Biomedical Optics, 1999

The potential environmental risks associated with mercury release have forced many European count... more The potential environmental risks associated with mercury release have forced many European countries to ban the use of dental amalgam. Alternative materials such as composite resins do not provide the clinical function for the length of time characteristically associated with dental amalgam. The weak link in the composite restoration is the dentin/adhesive bond. The purpose of this study was to correlate morphologic characterization of the dentin/adhesive bond with chemical analyses using micro-Fourier transform infrared and micro-Raman spectroscopy. A commercial dental adhesive was placed on dentin substrates cut from extracted, unerupted human third molars. Sections of the dentin/adhesive interface were investigated using infrared radiation produced at the Aladdin synchrotron source; visible radiation from a Kr+ laser was used for the micro-Raman spectroscopy. Sections of the dentin/adhesive interface, differentially stained to identify protein, mineral, and adhesive, were examined using light microscopy. Due to its limited spatial resolution and the unknown sample thickness the infrared results cannot be used quantitatively in determining the extent of diffusion. The results from the micro-Raman spectroscopy and light microscopy indicate exposed protein at the dentin/adhesive interface. Using a laser that reduces background fluorescence, the micro-Raman spectroscopy provides quantitative chemical and morphologic information on the dentin/adhesive interface. The staining procedure is sensitive to sites of pure protein and thus, complements the Raman results. © 1999 Society of Photo-Optical Instrumentation Engineers.

Journal of Applied Polymer Science, 2002

The adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrate... more The adhesion of a plasma polymer and the corrosion protection offered to aluminum alloy substrates depends on the cleanliness of the substrate surface and the state of oxides on the aluminum alloy surface. Both factors are dependent on what type of alloy is used, and consequently, the best preparation of the substrate surface differs on the type of aluminum alloy. Oxygen plasma treatment is effective for the elimination of organic surface contamination, but plasma treatment, such as that of mixed argon and hydrogen, cannot be used to modify the surface state of oxides on these alloys. This is because oxides of aluminum are stable and thus resist plasma modification, and prolonged plasma treatment has been observed to change concentrations of alloy components at the surface due to the heating of the alloy. Chemical cleaning of the surface is necessary before the application of the plasma polymer used for corrosion protection enhancement. Once the surface was properly prepared, a plas...

Journal of Applied Physics, 1989

The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV... more The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV photon energy range to investigate their value as high-efficiency, customizeable photocathode materials. The yield spectra resemble the weighted sum of the absorption spectra of the constituent rare earths, but the amplitude of the yield spectra were compressed relative to the absorption coefficient data due to the large electron escape depths in these materials.

Journal of Applied Physics, 2008

Synthetic polycrystalline hydroxyapatite was ablated in water with 337 nm radiation from a UV nit... more Synthetic polycrystalline hydroxyapatite was ablated in water with 337 nm radiation from a UV nitrogen pulsed laser. According to transmission electron microscopy micrographs, the ablated particles were approximately spherical and had a size of ∼80 nm. Raman spectroscopic analysis demonstrated that particles had the same structure as the original crystal. X-ray photoelectron spectroscopy showed that the surface chemical composition was close to that of the original material. The characteristics of the ablated particles and estimations of the temperature rise of the hydroxyapatite surface under laser irradiation are consistent with the mechanism of explosive boiling being responsible for ablation. The experimental observations offer the basis for preparation of hydroxyapatite nanoparticles by laser ablation in water.

Biomaterials, 1998

Earlier studies have failed to establish a consensus on the amount of mercury vapour released fro... more Earlier studies have failed to establish a consensus on the amount of mercury vapour released from dental amalgam restorations. The purpose of this study was to accurately and quantitatively measure the equilibrium mercury vapour pressure from dental amalgam. The vapour pressure was measured using a quartz crystal microbalance as a function of the load from 0-5.4 MPa. Auger spectra were collected of the as-formed and argon ion sputter cleaned dental amalgam surface. For the as-formed surface the mercury vapour density is zero with no load and increases to 0.6 microg m(-3) at 5.4 M Pa. Following cleaning the mercury, vapour density increased to a maximum value of 15 microg m(-3). The Auger spectra of the as-formed surfaces were dominated by features associated with carbon and oxygen. These spectral results in concert with the mercury vapour density measurements indicate that the oxide film on the as-formed surfaces inhibited the release of mercury vapour. The results of this experiment provide an upper limit for the amount of mercury vapour released by dental amalgams. Under conditions simulating the oral cavity this value would be reduced by oxides that form on the surface of dental amalgam restorations.

Applied Surface Science, 1998

. Ž . X-ray photoelectron spectroscopy XPS and scanning electron microscopy SEM have been applied... more . Ž . X-ray photoelectron spectroscopy XPS and scanning electron microscopy SEM have been applied to investigate the surface chemistry and morphology of InP wafers photochemically etched under 308 nm illumination from a XeCl excimer Ž . laser. The etching experiments were carried out at ambient temperature and in a low-pressure 1 mbar atmosphere of Cl 2 Ž . 2 10% diluted in He. During the process, the samples were exposed to laser radiation with fluences of 73 mJrcm or 114 mJrcm 2 . Both fluence values are below the ablation threshold of 140 mJrcm 2 for InP. The mapping of the photoelectron Ž . Ž . Ž . spectral line intensities of In 3d , Cl 2p , and P 2p displayed the distribution of In-Cl and In-P compounds on 5r2 3 r2 3 r2 the surface of the wafer. The chemical composition and morphology of the etched surface were found to be dependent on laser fluence. Surfaces with a fine granular structure were observed at a lower fluence, while at higher fluences, surfaces with a linear grating-like structure were formed. More chlorine is bound to the surface prepared at a higher fluence. q 1998 Elsevier Science B.V.

Applied Spectroscopy, 1997

The clinical success of dental composites depends critically upon the adhesive bond that secures ... more The clinical success of dental composites depends critically upon the adhesive bond that secures it to the tooth. Previous efforts to characterize the adhesive/dentin interface have generally required sample preparation that alters or damages the interface. Using micro-Raman spectroscopy, we have collected chemical and morphologic information on the dentin/adhesive interface with minimal sample preparation. Results from this technique have provided direct evidence of adhesive penetration and demineralization depth for two adhesive systems.

Applied Spectroscopy, 1996

The degree of adhesive penetration into dentin has been studied through micro-Raman spectroscopic... more The degree of adhesive penetration into dentin has been studied through micro-Raman spectroscopic examination of the dentin/adhesive interface. In contrast to previous studies, for the specimen examined in this work the adhesive penetrates less than 2 μm into the acid-etched and, thus, decalcified dentin. There is strong spectroscopic evidence that, upon acid etching of the dentin surface, which is typically performed immediately before the adhesive is applied, the collagen matrix collapses upon itself.