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Papers by Mohammed Yousif
Cement and concrete …, 2006
Raman spectrometry has received attention for the past 3 decades in its application to the charac... more Raman spectrometry has received attention for the past 3 decades in its application to the characterisation of pure cement phases, white and grey cements. Various configurations of instrumentation and laser excitation sources have been used, as reported in a limited number of papers. The first demonstrated investigation in 1976 by Bensted, illustrated the characterisation of various pure mineral cement phases with the use of a visible excitation source and a standard dispersive configuration. This was soon followed by an investigation of pure phases, as well as white and grey cements in 1980 by Conjeaud and co-workers using a microprobe configuration and visible excitation. Considerable difficulties with excessive fluorescence phenomena, especially with grey cements, have however been reported from the initial to the most recent publication. This review aimed to report on Raman studies of pure synthesized cement phases, cement phases as found in white and grey cements, various forms of gypsum and related compounds as found in cement and concrete, hydration of pure cement phases, as well as those of white and grey cement and lastly carbonation effects. Results reported are discussed and tables of summarized observed Raman shifts are given. D
Advances in Dental Research, 1997
The Raman spectroscopic technique enables us to obtain vibrational (IR and far-IR) spectra of min... more The Raman spectroscopic technique enables us to obtain vibrational (IR and far-IR) spectra of minerals by analyzing scattered light caused by (visible or near-visible) monochromatic laser excitation. The method possesses several advantages over IR absorption, including simple sample preparation, easy spectral/band analysis, and linear-response to mineral/chemical concentrations. In micro-Raman spectrometer systems, samples are positioned under an optical microscope, and specimens can be scanned with a lateral resolution (approximately 1 mm). In this paper, recent applications of micro-Raman spectroscopy and near-infrared Fourier transform Raman spectroscopy in the study of dental hard tissues and of calculus are reviewed. Special attention is given to mineral components in enamel, dentin, and calculus, and to calcium fluoride formed in/on enamel. The results from the use of an Ar(+)-laser/grating-based micro-Raman spectrometer show that: CaF2 formed in/on enamel by APF treatment is detectable and different from pure CaF2; and with the technique, the crystallite orientation in enamel can be determined. A Raman spectrometer based on Fourier transform and a diode-laser-pumped Nd:YAG laser (1.06 mm) can be used to obtain fluorescence-free Raman signals from biological materials, and identification of mineral components present in dental calculus is possible.
Review of Scientific Instruments, 2010
A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for meas... more A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for measuring interfacial phenomena with chemical specificity and high axial resolution perpendicular to the interface. The instrument platform is an inverted optical microscope with added automated variable angle optics to control the angle of an incident laser on a prism/sample interface. These optics include two motorized translation stages, the first containing a focusing lens and the second a variable angle galvanometer mirror. The movement of all instrument components is coordinated to ensure that the same sample location and area are probed at each angle. At angles greater than the critical angle, an evanescent wave capable of producing Raman scatter is generated in the sample. The Raman scatter is collected by a microscope objective and directed to a dispersive spectrometer and charge-coupled device detector. In addition to the collected Raman scatter, light reflected from the prism/sample interface is collected to provide calibration parameters that enable modeling the distance over which the Raman scatter is collected for depth profiling measurements. The developed instrument has an incident angle range of 25.5°-75.5°, with a 0.05° angle resolution. Raman scatter can be collected from a ZnSe/organic interface over a range of roughly 35-180 nm. Far from the critical angle, the achieved axial resolution perpendicular to the focal plane is approximately 34 nm. This is roughly a 30-fold improvement relative to confocal Raman microscopy.
Applied Spectroscopy Reviews, 2004
ABSTRACT
Applied Spectroscopy Reviews, 2006
The calibration procedures needed for use of dispersive Raman spectrometers have been reviewed. L... more The calibration procedures needed for use of dispersive Raman spectrometers have been reviewed. Like other high‐precision spectrometers incorporating moving gratings, Raman spectrometers are subject to problems with wavenumber scale accuracy. Commercially available Raman spectrometers of types DILOR‐HORIBA LabRam and RENISHAW System 1000 have been examined for wavenumber scale stability, linearity, and reproducibility. For reliable use of the wavenumber data, daily
Analytical …, 1984
has been demonstrated in this laboratory (18) and by others (1 7) and, with the exception of pref... more has been demonstrated in this laboratory (18) and by others (1 7) and, with the exception of preformed organic ions, generally proceeds by "cationization". Third, laser desorption, as used in this instrument, appears to be a direct extension of the rapid heating experiments performed by Daves et al. (30) and ourselves (31) and described by Friedmann et al. (32) as a process which allows one to rapidly exceed the activation energy for desorption of intact species, prior to the onset of decomposition. It therefore overcomes the limitation of simple thermal desorption as a method for relatively small molecules.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011
The current paper gives an overview of the development of Raman spectrometry in gemmological labo... more The current paper gives an overview of the development of Raman spectrometry in gemmological laboratories. While before 1990s, no commercial gemmological laboratory possessed such an instrument, all larger international labs have acquired these instruments by now. The Raman spectrometer is routinely used for the detection of emerald fillers, HPHT treatment of diamonds, analysis of the nature of a gemstone, analysis of gemstone inclusions and treatments, and the characterisation of natural or colour enhanced pearls and corals. Future developments in gemstone research lie in the closer analysis of the features of Raman and PL spectra and in the combination of several instruments.► This paper gives an overview of the development of Raman spectrometer in gemmology. ► It is used for analysis of the nature of a gemstone. ► It is also used for analysis of gemstone inclusions and treatments. ► Combination of Raman spectrometer with other instruments would help gemmology.
Applied Spectroscopy, 1996
Analytical Chemistry, 1983
Review of Scientific Instruments, 2011
Cement and concrete …, 2006
Raman spectrometry has received attention for the past 3 decades in its application to the charac... more Raman spectrometry has received attention for the past 3 decades in its application to the characterisation of pure cement phases, white and grey cements. Various configurations of instrumentation and laser excitation sources have been used, as reported in a limited number of papers. The first demonstrated investigation in 1976 by Bensted, illustrated the characterisation of various pure mineral cement phases with the use of a visible excitation source and a standard dispersive configuration. This was soon followed by an investigation of pure phases, as well as white and grey cements in 1980 by Conjeaud and co-workers using a microprobe configuration and visible excitation. Considerable difficulties with excessive fluorescence phenomena, especially with grey cements, have however been reported from the initial to the most recent publication. This review aimed to report on Raman studies of pure synthesized cement phases, cement phases as found in white and grey cements, various forms of gypsum and related compounds as found in cement and concrete, hydration of pure cement phases, as well as those of white and grey cement and lastly carbonation effects. Results reported are discussed and tables of summarized observed Raman shifts are given. D
Advances in Dental Research, 1997
The Raman spectroscopic technique enables us to obtain vibrational (IR and far-IR) spectra of min... more The Raman spectroscopic technique enables us to obtain vibrational (IR and far-IR) spectra of minerals by analyzing scattered light caused by (visible or near-visible) monochromatic laser excitation. The method possesses several advantages over IR absorption, including simple sample preparation, easy spectral/band analysis, and linear-response to mineral/chemical concentrations. In micro-Raman spectrometer systems, samples are positioned under an optical microscope, and specimens can be scanned with a lateral resolution (approximately 1 mm). In this paper, recent applications of micro-Raman spectroscopy and near-infrared Fourier transform Raman spectroscopy in the study of dental hard tissues and of calculus are reviewed. Special attention is given to mineral components in enamel, dentin, and calculus, and to calcium fluoride formed in/on enamel. The results from the use of an Ar(+)-laser/grating-based micro-Raman spectrometer show that: CaF2 formed in/on enamel by APF treatment is detectable and different from pure CaF2; and with the technique, the crystallite orientation in enamel can be determined. A Raman spectrometer based on Fourier transform and a diode-laser-pumped Nd:YAG laser (1.06 mm) can be used to obtain fluorescence-free Raman signals from biological materials, and identification of mineral components present in dental calculus is possible.
Review of Scientific Instruments, 2010
A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for meas... more A scanning angle total internal reflection (SATIR) Raman spectrometer has been developed for measuring interfacial phenomena with chemical specificity and high axial resolution perpendicular to the interface. The instrument platform is an inverted optical microscope with added automated variable angle optics to control the angle of an incident laser on a prism/sample interface. These optics include two motorized translation stages, the first containing a focusing lens and the second a variable angle galvanometer mirror. The movement of all instrument components is coordinated to ensure that the same sample location and area are probed at each angle. At angles greater than the critical angle, an evanescent wave capable of producing Raman scatter is generated in the sample. The Raman scatter is collected by a microscope objective and directed to a dispersive spectrometer and charge-coupled device detector. In addition to the collected Raman scatter, light reflected from the prism/sample interface is collected to provide calibration parameters that enable modeling the distance over which the Raman scatter is collected for depth profiling measurements. The developed instrument has an incident angle range of 25.5°-75.5°, with a 0.05° angle resolution. Raman scatter can be collected from a ZnSe/organic interface over a range of roughly 35-180 nm. Far from the critical angle, the achieved axial resolution perpendicular to the focal plane is approximately 34 nm. This is roughly a 30-fold improvement relative to confocal Raman microscopy.
Applied Spectroscopy Reviews, 2004
ABSTRACT
Applied Spectroscopy Reviews, 2006
The calibration procedures needed for use of dispersive Raman spectrometers have been reviewed. L... more The calibration procedures needed for use of dispersive Raman spectrometers have been reviewed. Like other high‐precision spectrometers incorporating moving gratings, Raman spectrometers are subject to problems with wavenumber scale accuracy. Commercially available Raman spectrometers of types DILOR‐HORIBA LabRam and RENISHAW System 1000 have been examined for wavenumber scale stability, linearity, and reproducibility. For reliable use of the wavenumber data, daily
Analytical …, 1984
has been demonstrated in this laboratory (18) and by others (1 7) and, with the exception of pref... more has been demonstrated in this laboratory (18) and by others (1 7) and, with the exception of preformed organic ions, generally proceeds by "cationization". Third, laser desorption, as used in this instrument, appears to be a direct extension of the rapid heating experiments performed by Daves et al. (30) and ourselves (31) and described by Friedmann et al. (32) as a process which allows one to rapidly exceed the activation energy for desorption of intact species, prior to the onset of decomposition. It therefore overcomes the limitation of simple thermal desorption as a method for relatively small molecules.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011
The current paper gives an overview of the development of Raman spectrometry in gemmological labo... more The current paper gives an overview of the development of Raman spectrometry in gemmological laboratories. While before 1990s, no commercial gemmological laboratory possessed such an instrument, all larger international labs have acquired these instruments by now. The Raman spectrometer is routinely used for the detection of emerald fillers, HPHT treatment of diamonds, analysis of the nature of a gemstone, analysis of gemstone inclusions and treatments, and the characterisation of natural or colour enhanced pearls and corals. Future developments in gemstone research lie in the closer analysis of the features of Raman and PL spectra and in the combination of several instruments.► This paper gives an overview of the development of Raman spectrometer in gemmology. ► It is used for analysis of the nature of a gemstone. ► It is also used for analysis of gemstone inclusions and treatments. ► Combination of Raman spectrometer with other instruments would help gemmology.
Applied Spectroscopy, 1996
Analytical Chemistry, 1983
Review of Scientific Instruments, 2011