M. Nowell - Academia.edu (original) (raw)

Papers by M. Nowell

Acta materialia, Jan 1, 2007

The texture and grain boundary structure of recrystallized materials are dependent upon the chara... more The texture and grain boundary structure of recrystallized materials are dependent upon the character of the deformed matrix and the selective nucleation and growth of crystallites from the deformation structure. Annealing twin boundary formation in materials of low to medium stacking fault energy is not only a product of the recrystallized structure, but also plays an important role in the recrystallization process itself. In situ and ex situ recrystallization experiments were performed on pure copper (99.99% pure) previously deformed by equal channel angular extrusion. Intermittent characterization of the structure on the surface of bulk specimens was accomplished using electron backscatter diffraction. The character of the structure where nucleation preferentially occurs is presumed to be in heavily deformed regions as nuclei were first observed in such microstructures as viewed from the specimen surface. Grain growth is observed to be heavily dependent upon twinning processes at the low temperatures used for in situ experiments, with twinning occurring to aid the recrystallization process. It is shown at these temperatures that the slowest growing grains obtain the highest fraction of twin boundaries as the new twin orientations presumably increase the boundary energy at positions where there is insufficient driving force to continue growth.

Abstract Microstructural evolution during elevated temperature annealing of sputter deposited cop... more Abstract Microstructural evolution during elevated temperature annealing of sputter deposited copper (Cu) films was investigated by electron backscatter diffraction (EBSD). Analysis of films was performed both in situ using a heating stage, and by ex-situ observation of microstructural evolution. It was noted that not only is the Cu film texture and grain size a function of film thickness, but also that the fraction of twin boundaries present in the material is strongly dependent upon film thickness.

2001 Symposium on VLSI Technology. Digest of Technical Papers (IEEE Cat. No.01 CH37184), 2000

Abstract The effect of different post electroplating anneals on dual damascene Cu microstructures... more Abstract The effect of different post electroplating anneals on dual damascene Cu microstructures and via chain yields using both rapid thermal processing and furnace anneal were investigated. It was found that the grain size,(111) texture, Cu line resistance, ...

Microscopy and Microanalysis

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Electron backscatter diffraction (EBSD) has been used to characterize the grain size, grain bound... more Electron backscatter diffraction (EBSD) has been used to characterize the grain size, grain boundary structure, and texture of sputtered CdTe at varying deposition pressures before and after CdCl2 treatment in order to correlate performance with film microstructure. It is known that twin boundaries may have different electrical properties than high-angle grain boundaries and in this work we have included the effects of twin boundaries. We found better correlation of solar cell device performance to the twincorrected grain size than to the standard grain size. In addition, we have correlated the photoluminescence (PL) spectra with device performance and with the EBSD results. We find that sputtering at 18 mTorr yields the highest efficiency, largest twin-corrected grain size and the strongest PL.

MRS Proceedings, 2010

Cu2ZnSnS4 (CZTS) is a promising alternative for Cu(In,Ga)Se2 (CIGS) absorber layers in thin film ... more Cu2ZnSnS4 (CZTS) is a promising alternative for Cu(In,Ga)Se2 (CIGS) absorber layers in thin film solar cells and is comprised of commodity elements which will enable scale-up of chalcopyrite panel production unhindered by elemental supplies and costs. Various CZTS synthesis ...

Microscopy and Microanalysis, 2005

ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu,... more ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Microscopy and Microanalysis, 2005

Microscopy and Microanalysis, 2005

The automated analysis of electron backscatter diffraction (EBSD) patterns for orientation imagin... more The automated analysis of electron backscatter diffraction (EBSD) patterns for orientation imaging has become a well established technique for materials and earth sciences. This technique allows for quantitative microstructural measurements of crystal orientation and texture, grain boundary character and classification, and phase identification. Combining this technique with in-situ heating of the sample allows for the direct observation and comparison of microstructural transitions that can occur during phenomena such as ...

Microscopy and Microanalysis, 2005

ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu,... more ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Microscopy and Microanalysis, 2005

Automated analysis of Electron Backscatter Diffraction (EBSD) patterns for orientation imaging an... more Automated analysis of Electron Backscatter Diffraction (EBSD) patterns for orientation imaging and phase identification in materials and earth sciences has become a widely accepted microstructural analysis tool. To briefly review, EBSD is a scanning electron microscope (SEM) based technique where the sample is tilted approximately 70 degrees and the electron beam is positioned in an analytical spot-mode within a selected grain. An EBSD pattern is formed due to the diffraction of the electron beam by select crystallographic planes within the material. The EBSD pattern is representative of both the phase and crystallographic orientation of the selected area. The pattern is imaged by a phosphor screen and recorded with a digital CCD camera and then analyzed. For orientation imaging, EBSD patterns are systematically collected and analyzed from a specified array of measurement points. The microstructure can then be visualized by coloring points on the array according to information derived from the EBSD pattern. For example, orientation imaging maps from a duplex stainless steel sample are shown in . In , the colors represent the crystallographic directions aligned with the sample normal direction. The shaded stereographic triangle provides the color key. In , the colors represent the phases within the material; red is BCC ferrite while blue is FCC austenite. In , measurement points of similar crystallographic orientation are grouped together to define the grains within the material. The measured grains are then randomly colored to illustrate the grain size and morphology. Each of these maps is derived from the same acquired data, and many other analytical possibilities exist. In addition, quantitative microstructural and orientation measurements can be made. For example, in this duplex stainless steel the average grain size has a diameter of 32 microns assuming a circular grain shape. However, analysis of the grain shape shows this is not the case. By fitting an ellipse to the points defining a grain, the aspect ratio of the minor to major axes can be calculated. In this example the average aspect ratio is 0.34. The average grain size can then be more accurately defined as an average grain area of 828 square microns. EBSD patterns are generated within a small interaction volume located at the surface of a sample with a penetration depth typically less than 50-100 nm. Because of this, EBSD pattern quality is extremely sensitive to the integrity of the crystallographic lattice order at the surface of the sample. While some samples, such as ECD deposited metal films, require no preparation prior to analysis, often samples must be sectioned and prepared to obtain useable EBSD patterns . When considering how to prepare a sample for EBSD analysis, it is important to recognize that in order to obtain highquality patterns the surface deformation that is typically introduced during standard metallographic preparation should be minimized. This deformation will disturb the crystallographic lattice and will result in more diffuse diffraction bands and a loss of intensity and contrast within the pattern. While EBSD patterns can be obtained from rough surfaces, the topography of the surface will often block the diffraction signal from reaching an EBSD detector, and will in turn reduce the yield of usable EBSD patterns obtained across such a surface. For orientation imaging, a flat surface is therefore desirable. Proper sample preparation will result in optimized pattern quality and subsequent high-confidence orientation imaging data. In this work, the sample preparation procedure developed to obtain high-quality EBSD patterns from a nickel-based superalloy will be presented.

Microscopy and Microanalysis, 2011

Microscopy and Microanalysis, 2011

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2012

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2008

Metallurgical and Materials Transactions A, 2006

Tungsten carbide grains are usually prism-shaped triangular platelets in cemented tungsten carbid... more Tungsten carbide grains are usually prism-shaped triangular platelets in cemented tungsten carbide materials, owing to the highly anisotropic nature of tungsten carbide grains. The misorientation distribution function (MODF) shows a preferred misorientation relationship between WC/WC crystals. The misorientation relationship is characterized as 90 deg misorientation about the axis. The carbide-carbide boundaries with 90 deg rotation about the axis are low-energy boundaries and play an important role in grain growth and densification during sintering. In this study, the evolution of carbide-carbide boundaries with 90 deg rotation about the axis during the sintering process is determined quantitatively using orientation imaging microscopy (OIM). The evolution of boundaries is correlated with grain growth. The rapid grain growth at early stages of sintering is attributed to coalescence of grains along the 90 deg low-energy boundaries. The origin of these boundaries and their role in grain growth during sintering are also discussed.

Journal of Microscopy, 2004

Electron backscatter diffraction (EBSD) and orientation imaging microscopy have become establishe... more Electron backscatter diffraction (EBSD) and orientation imaging microscopy have become established techniques for analysing the crystallographic microstructure of single and multiphase materials. In certain instances, however, it can be difficult and/or time intensive to differentiate phases within a material by crystallography alone. Traditionally a list of candidate phases is specified prior to data collection. The crystallographic information extracted from the diffraction patterns is then compared with the crystallographic information from these candidate phases, and a best-fit match is determined. Problems may arise when two phases have similar crystal structures. The phase differentiation process can be improved by collecting chemical information through X-ray energydispersive spectroscopy (XEDS) simultaneously with the crystallographic information through EBSD and then using the chemical information to pre-filter the crystallographic phase candidates. This technique improves both the overall speed of the data collection and the accuracy of the final characterization. Examples of this process and the limitations involved will be presented and discussed.

Acta materialia, Jan 1, 2007

The texture and grain boundary structure of recrystallized materials are dependent upon the chara... more The texture and grain boundary structure of recrystallized materials are dependent upon the character of the deformed matrix and the selective nucleation and growth of crystallites from the deformation structure. Annealing twin boundary formation in materials of low to medium stacking fault energy is not only a product of the recrystallized structure, but also plays an important role in the recrystallization process itself. In situ and ex situ recrystallization experiments were performed on pure copper (99.99% pure) previously deformed by equal channel angular extrusion. Intermittent characterization of the structure on the surface of bulk specimens was accomplished using electron backscatter diffraction. The character of the structure where nucleation preferentially occurs is presumed to be in heavily deformed regions as nuclei were first observed in such microstructures as viewed from the specimen surface. Grain growth is observed to be heavily dependent upon twinning processes at the low temperatures used for in situ experiments, with twinning occurring to aid the recrystallization process. It is shown at these temperatures that the slowest growing grains obtain the highest fraction of twin boundaries as the new twin orientations presumably increase the boundary energy at positions where there is insufficient driving force to continue growth.

Abstract Microstructural evolution during elevated temperature annealing of sputter deposited cop... more Abstract Microstructural evolution during elevated temperature annealing of sputter deposited copper (Cu) films was investigated by electron backscatter diffraction (EBSD). Analysis of films was performed both in situ using a heating stage, and by ex-situ observation of microstructural evolution. It was noted that not only is the Cu film texture and grain size a function of film thickness, but also that the fraction of twin boundaries present in the material is strongly dependent upon film thickness.

2001 Symposium on VLSI Technology. Digest of Technical Papers (IEEE Cat. No.01 CH37184), 2000

Abstract The effect of different post electroplating anneals on dual damascene Cu microstructures... more Abstract The effect of different post electroplating anneals on dual damascene Cu microstructures and via chain yields using both rapid thermal processing and furnace anneal were investigated. It was found that the grain size,(111) texture, Cu line resistance, ...

Microscopy and Microanalysis

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Electron backscatter diffraction (EBSD) has been used to characterize the grain size, grain bound... more Electron backscatter diffraction (EBSD) has been used to characterize the grain size, grain boundary structure, and texture of sputtered CdTe at varying deposition pressures before and after CdCl2 treatment in order to correlate performance with film microstructure. It is known that twin boundaries may have different electrical properties than high-angle grain boundaries and in this work we have included the effects of twin boundaries. We found better correlation of solar cell device performance to the twincorrected grain size than to the standard grain size. In addition, we have correlated the photoluminescence (PL) spectra with device performance and with the EBSD results. We find that sputtering at 18 mTorr yields the highest efficiency, largest twin-corrected grain size and the strongest PL.

MRS Proceedings, 2010

Cu2ZnSnS4 (CZTS) is a promising alternative for Cu(In,Ga)Se2 (CIGS) absorber layers in thin film ... more Cu2ZnSnS4 (CZTS) is a promising alternative for Cu(In,Ga)Se2 (CIGS) absorber layers in thin film solar cells and is comprised of commodity elements which will enable scale-up of chalcopyrite panel production unhindered by elemental supplies and costs. Various CZTS synthesis ...

Microscopy and Microanalysis, 2005

ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu,... more ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Microscopy and Microanalysis, 2005

Microscopy and Microanalysis, 2005

The automated analysis of electron backscatter diffraction (EBSD) patterns for orientation imagin... more The automated analysis of electron backscatter diffraction (EBSD) patterns for orientation imaging has become a well established technique for materials and earth sciences. This technique allows for quantitative microstructural measurements of crystal orientation and texture, grain boundary character and classification, and phase identification. Combining this technique with in-situ heating of the sample allows for the direct observation and comparison of microstructural transitions that can occur during phenomena such as ...

Microscopy and Microanalysis, 2005

ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu,... more ABSTRACT Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.

Microscopy and Microanalysis, 2005

Automated analysis of Electron Backscatter Diffraction (EBSD) patterns for orientation imaging an... more Automated analysis of Electron Backscatter Diffraction (EBSD) patterns for orientation imaging and phase identification in materials and earth sciences has become a widely accepted microstructural analysis tool. To briefly review, EBSD is a scanning electron microscope (SEM) based technique where the sample is tilted approximately 70 degrees and the electron beam is positioned in an analytical spot-mode within a selected grain. An EBSD pattern is formed due to the diffraction of the electron beam by select crystallographic planes within the material. The EBSD pattern is representative of both the phase and crystallographic orientation of the selected area. The pattern is imaged by a phosphor screen and recorded with a digital CCD camera and then analyzed. For orientation imaging, EBSD patterns are systematically collected and analyzed from a specified array of measurement points. The microstructure can then be visualized by coloring points on the array according to information derived from the EBSD pattern. For example, orientation imaging maps from a duplex stainless steel sample are shown in . In , the colors represent the crystallographic directions aligned with the sample normal direction. The shaded stereographic triangle provides the color key. In , the colors represent the phases within the material; red is BCC ferrite while blue is FCC austenite. In , measurement points of similar crystallographic orientation are grouped together to define the grains within the material. The measured grains are then randomly colored to illustrate the grain size and morphology. Each of these maps is derived from the same acquired data, and many other analytical possibilities exist. In addition, quantitative microstructural and orientation measurements can be made. For example, in this duplex stainless steel the average grain size has a diameter of 32 microns assuming a circular grain shape. However, analysis of the grain shape shows this is not the case. By fitting an ellipse to the points defining a grain, the aspect ratio of the minor to major axes can be calculated. In this example the average aspect ratio is 0.34. The average grain size can then be more accurately defined as an average grain area of 828 square microns. EBSD patterns are generated within a small interaction volume located at the surface of a sample with a penetration depth typically less than 50-100 nm. Because of this, EBSD pattern quality is extremely sensitive to the integrity of the crystallographic lattice order at the surface of the sample. While some samples, such as ECD deposited metal films, require no preparation prior to analysis, often samples must be sectioned and prepared to obtain useable EBSD patterns . When considering how to prepare a sample for EBSD analysis, it is important to recognize that in order to obtain highquality patterns the surface deformation that is typically introduced during standard metallographic preparation should be minimized. This deformation will disturb the crystallographic lattice and will result in more diffuse diffraction bands and a loss of intensity and contrast within the pattern. While EBSD patterns can be obtained from rough surfaces, the topography of the surface will often block the diffraction signal from reaching an EBSD detector, and will in turn reduce the yield of usable EBSD patterns obtained across such a surface. For orientation imaging, a flat surface is therefore desirable. Proper sample preparation will result in optimized pattern quality and subsequent high-confidence orientation imaging data. In this work, the sample preparation procedure developed to obtain high-quality EBSD patterns from a nickel-based superalloy will be presented.

Microscopy and Microanalysis, 2011

Microscopy and Microanalysis, 2011

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2012

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2009

Microscopy and Microanalysis, 2008

Metallurgical and Materials Transactions A, 2006

Tungsten carbide grains are usually prism-shaped triangular platelets in cemented tungsten carbid... more Tungsten carbide grains are usually prism-shaped triangular platelets in cemented tungsten carbide materials, owing to the highly anisotropic nature of tungsten carbide grains. The misorientation distribution function (MODF) shows a preferred misorientation relationship between WC/WC crystals. The misorientation relationship is characterized as 90 deg misorientation about the axis. The carbide-carbide boundaries with 90 deg rotation about the axis are low-energy boundaries and play an important role in grain growth and densification during sintering. In this study, the evolution of carbide-carbide boundaries with 90 deg rotation about the axis during the sintering process is determined quantitatively using orientation imaging microscopy (OIM). The evolution of boundaries is correlated with grain growth. The rapid grain growth at early stages of sintering is attributed to coalescence of grains along the 90 deg low-energy boundaries. The origin of these boundaries and their role in grain growth during sintering are also discussed.

Journal of Microscopy, 2004

Electron backscatter diffraction (EBSD) and orientation imaging microscopy have become establishe... more Electron backscatter diffraction (EBSD) and orientation imaging microscopy have become established techniques for analysing the crystallographic microstructure of single and multiphase materials. In certain instances, however, it can be difficult and/or time intensive to differentiate phases within a material by crystallography alone. Traditionally a list of candidate phases is specified prior to data collection. The crystallographic information extracted from the diffraction patterns is then compared with the crystallographic information from these candidate phases, and a best-fit match is determined. Problems may arise when two phases have similar crystal structures. The phase differentiation process can be improved by collecting chemical information through X-ray energydispersive spectroscopy (XEDS) simultaneously with the crystallographic information through EBSD and then using the chemical information to pre-filter the crystallographic phase candidates. This technique improves both the overall speed of the data collection and the accuracy of the final characterization. Examples of this process and the limitations involved will be presented and discussed.