Naoko Sano - Academia.edu (original) (raw)
Papers by Naoko Sano
Chemical Geology, 2017
Decontamination of geological samples by gas cluster ion beam etching or ultra violet/ozone.
Journal of Materials Science: Materials in Electronics, 2018
If citing, it is advised that you check and use the publisher's definitive version for pagination... more If citing, it is advised that you check and use the publisher's definitive version for pagination, volume/issue, and date of publication details. And where the final published version is provided on the Research Portal, if citing you are again advised to check the publisher's website for any subsequent corrections.
Applied Surface Science, 2016
Conducting this study has demonstrated that not only SEM-EDX but also XPS can be an efficient too... more Conducting this study has demonstrated that not only SEM-EDX but also XPS can be an efficient tool for characterising watercolour paint surfaces. We find that surface effects are mediated by water. Once the powdered components in the watercolour come into contact with water they dramatically transform their chemical structures at the surface and show the presence of pigment components with a random dispersion within the gum layer. Hence the topmost surface of the paint is confirmed as being composed of the gum binder components. This result is difficult to confirm using just one analytical technique (either XPS or SEM-EDX). In addition, peak fitting of C1s XPS spectra suggests that the gum binder in the commercial watercolour paints is probably gum arabic (by comparison with the reference materials). This identification is not conclusive, but the combination techniques of XPS and SEM shows the surface structure with material distribution of the gum binder and the other ingredients of the watercolour paints. Therefore as a unique technique, XPS combined with SEM-EDX may prove a useful method in the study of surface structure for not only watercolour objects but also other art objects; which may in future help in the conservation for art.
Surface and Interface Analysis, 2016
In situ ion beam sputter deposition and X-ray photoelectron spectroscopy (XPS) of multiple thin l... more In situ ion beam sputter deposition and X-ray photoelectron spectroscopy (XPS) of multiple thin layers under computer control for combinatorial materials synthesis.
Surface and Interface Analysis, 2016
Principal component analysis (PCA) and other multivariate analysis methods have been used increas... more Principal component analysis (PCA) and other multivariate analysis methods have been used increasingly to analyse and understand depth-profiles in XPS, AES and SIMS. For large images or three-dimensional (3D) imaging depth-profiles, PCA has been difficult to apply until now simply because of the size of the matrices of data involved. In a recent paper, we described two algorithms, random vector 1 (RV1) and random vector 2 (RV2), that improve the speed of PCA and allow datasets of unlimited size, respectively. In this paper, we now apply the RV2 algorithm to perform PCA on full 3D time-of-flight SIMS data for the first time without subsampling. The dataset we process in this way is a 128 × 128 pixel depth-profile of 120 layers, each voxel having a 70 439 value mass spectrum associated with it. This forms over a terabyte of data when uncompressed and took 27 h to process using the RV2 algorithm using a conventional windows desktop personal computer (PC). While full PCA (e.g. using RV2) is to be preferred for final reports or publications, a much more rapid method is needed during analysis sessions to inform decisions on the next analytical step. We have therefore implemented the RV1 algorithm on a PC having a graphical processor unit (GPU) card containing 2880 individual processor cores. This increases the speed of calculation by a factor of around 4.1 compared with what is possible using a fast commercially available desktop PC having central processing units alone, and full PCA is performed in less than 7 s. The size of the dataset that can be processed in this way is limited by the size of the memory on the GPU card. This is typically sufficient for two-dimensional images but not 3D depth-profiles without sampling. We have therefore examined efficient sampling schemes that allow a good approximate solution to the PCA problem for large 3D datasets. We find that low-discrepancy series such as Sobol series sampling gives more rapid convergence than random sampling, and we recommend such methods for routine use. Using the GPU and low-discrepancy series together, we anticipate that any time-of-flight SIMS dataset, of whatever size, can be efficiently and accurately processed into PCA components in a maximum of around 10 s using a commercial PC with a widely available GPU card, although the longer RV2 approach is still to be preferred for the presentation of final results, such as in published papers.
Ultramicroscopy, 2012
The characterisation of nanoscale surface properties of textile and hair fibres is key to develop... more The characterisation of nanoscale surface properties of textile and hair fibres is key to developing new effective laundry and hair care products. Here, we develop nanomechanical methods to characterise fibres using an atomic force microscope (AFM) to give their nanoscale modulus. Good mounting methods for the fibre that are chemically inert, clean and give strong mechanical coupling to a substrate are important and here we detail two methods to do this. We show, for elastic nanoindentation measurements, the situation when the tip radius significantly affects the result via a function of the ratio of the radii of the tip and fibre and indicate the importance of using an AFM for such work. A valid method to measure the nanoscale modulus of fibres using AFM is thus detailed and exampled on hair to show that bleaching changes the nanoscale reduced modulus at the outer surface.
Japanese Journal of Applied Physics, 2002
We investigated the thermotropic phase behavior of rigid-rod poly(γ-octadecyl L-glutamate) (PG18)... more We investigated the thermotropic phase behavior of rigid-rod poly(γ-octadecyl L-glutamate) (PG18) with an average molecular weight M w = 36, 000. Two polymers with narrow molecular weight distributions (M w /M n), PG18-A with M w /M n = 1.12 and PG18-B with M w /M n = 1.05, were prepared by gel permeation chromatography (GPC) fractionation. Both were found to form a smectic A phase by means of microscopic observations of the focal conic texture and by the small-angle X-ray method. The smectic A phase of PG18-A was transformed into a cholesteric phase at approximately 140-170 • C while that of PG18-B stably existed in the entire thermotropic temperature range from 60 • C to 220 • C (decomposition temperature). This dependence of smectic stability on the molecular weight polydispersity qualitatively corresponds to the theoretical prediction based on the excluded volume effect.
Journal of Fiber Science and Technology, 2018
Chemical Geology, 2021
Abstract Earlier investigations have suggested that an extensive deep biosphere with a significan... more Abstract Earlier investigations have suggested that an extensive deep biosphere with a significant fungal component is present within the sub-oceanic crust. To investigate this further, the organic material in the lithic sections of a sub-oceanic volcaniclastic tuff obtained from the eastern lobe of the Ontong Java Plateau (OJP tuff) were characterised using X-ray photoelectron spectroscopy and thermal hydrolysis and methylation coupled to gas chromatography/mass spectrometry. In the investigation here, the chemical and molecular composition of plant and fungal structural biopolymer standards were characterised using the same techniques and then compared to the organic material from the OJP tuff. This was conducted on untreated material and after hydrous pyrolysis, a process that simulated the physical and thermal decomposition of organic material that occurs during late diagenesis. The characteristics of the organic material in the OJP tuff matched the products of hydrous-pyrolysed chitin. This result suggested that OJP tuff contained organic material that could have been derived from fossilised chitin, implying that the OJP tuff potentially contained the remnants of a microbial community with a fungal component.
Applied Surface Science, 2018
Indium phosphide (InP) surfaces develop a pronounced nanostructured texture upon irradiation by e... more Indium phosphide (InP) surfaces develop a pronounced nanostructured texture upon irradiation by energetic ion beams. We have observed the mechanism of nanostructure evolution of InP under irradiation by an Ar gas cluster ion beam (GCIB) using helium ion microscopy (HIM). Initially, metallic indium nanoparticles form on the surface after removal of the topmost oxide layer. These nanoparticles form a mask which shadows the underlying InP. As the ion dose is increased, the masking effect results in substantial nanostructured topography in the form of pillars or nanocones, oriented along the axis of the incident GCIB. The surface sensitivity and high resolution of the HIM facilitates the direct observation of the metallic indium cap at the top of the pillars.
Applied Catalysis A: General, 2018
Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduct... more Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduction or hydroformylation reactions. In this work instead, we explored the capabilities of Rh nanoparticles as an oxidation catalyst, applied to the oxidation of benzyl alcohol to benzaldehyde under very mild conditions (100°C, and atmospheric pressure) as a model reaction. Here we report the preparation of novel Rh/C catalysts by using an impregnation protocol, with particular emphasis on the pre-treatment of the carbon supports by using HNO 3 and HCl, as well as the characterization of these materials by using an array of methods involving TEM, XPS and XRPD. Our preparation method led to a wide Rh particle size distribution ranging from 20 to 100 nm, and we estimate an upper limit diameter of Rh nanoparticles for their activity towards benzyl alcohol oxidation to be ca. 30 nm. Furthermore, a HNO 3 pre-treatment of the activated carbon support was able to induce a smaller and narrower particle size distribution of Rh nanoparticles, whereas a HCl pre-treatment had no effect or sintered the Rh nanoparticles. We rationalise these results by HNO 3 as an acid able to create new nucleation sites for Rh on the carbon surface, with the final effect of smaller nanoparticles, whereas for HCl the effect of sintering was most likely due to site blocking of the nucleation sites over the carbon surface. The roles of acid centres on the carbon surfaces for the oxidation reaction was also investigated, and the larger their amounts the larger the amounts of by-products. However, by treatment with HNO 3 we were able to convert neutral or basic carbons into supports capable to enhance the catalytic activity of Rh, and yet minimised detrimental effects on the selectivity of the oxidation to benzaldehyde.
Catalysis Science & Technology, 2017
Rh nanoparticles that were inactive in toluene, were converted into a powerful catalyst for aryl ... more Rh nanoparticles that were inactive in toluene, were converted into a powerful catalyst for aryl alcohol oxidation by the presence of water in the reaction media.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2016
Surface and Interface Analysis, 2016
This work is licensed under a Creative Commons Attribution 4.0 International License Newcastle Un... more This work is licensed under a Creative Commons Attribution 4.0 International License Newcastle University ePrints-eprint.ncl.ac.uk
Surface and Interface Analysis, 2012
ABSTRACT The authors have observed for the first time that x-ray exposure of certain polymers of ... more ABSTRACT The authors have observed for the first time that x-ray exposure of certain polymers of “degrading” type can greatly enhance the sputter rate of these polymers by gas cluster ion beam (GCIB) profiling. They have observed craters of similar dimensions to the x-ray spot well within the perimeter of sputter craters, indicating that x-rays can assist GCIB sputtering very significantly. This can be a major source of the loss of depth-resolution in sputter depth profiles of polymers. The authors have measured experimentally sputter craters in 14 different polymers by white-light interferometry. The results show that x-ray exposure can introduce much more topography than might previously have been expected, through both thermal and direct x-ray degradation and cross-linking. Within the region exposed to x-rays, the response of the polymer surface depends on its chemistry, with degrading (also known as type II) polymers being susceptible to large increases in sputter rate in some cases. For example, this leads to a sputter rate increase of a factor of 3 in poly-L-lactic acid (PLLA) compared to cluster-ion sputtering in the absence of x rays under typical experimental conditions. By comparison, crosslinking (also known as type I) polymers show either the same sputter rate or a reduced sputter rate due to crosslinking. The authors model this behavior using the bond scission parameter (GS) and crosslinking parameter (GX) used to model radiation damage in polymers. Agreement is good, allowing us to provide guidelines to assist in planning XPS depth-profiling experiments, in particular, for polymers such as PMMA and PLLA, where any requirement for uniform sputter rate is a more stringent limit to x-ray exposure than the requirement for the XPS spectra to represent chemical states quantitatively without damage.
Metrologia, 2013
ABSTRACT The stability of prototype kilogram reference masses has been a long-standing question w... more ABSTRACT The stability of prototype kilogram reference masses has been a long-standing question within the SI, with mass loss or gain at the surface being the principal concern. In papers I, III and IV of this series we showed mercury and organic carbonaceous contamination to be significant in sample surfaces exposed to typical prototype kilogram storage environments. In this work, we have examined the surfaces of six platinum mass standards manufactured in the mid-19th century. We used x-ray photoelectron spectroscopy in order to identify mercury and carbonaceous contamination, and assess the validity of our previous models for the rate of increase. We use white-light interferometry to study surface roughness and polishing damage. We see mercury on all six of the 19th century polished prototypes we analysed. For one weight, manufactured around 1830, we see a quantity of mercury roughly equivalent to 250 µg if present on the surface of a prototype kilogram at the same mass per unit area. The quantities of these contaminations calculated from our XPS spectra are in good agreement with the theoretical models developed in papers III and IV for the growth of mercury and carbonaceous contamination, respectively, and increase our confidence that these processes are indeed happening at the surface of polished kilogram prototypes in most (if not all) cases. We discuss some potential sources of mercury contamination, though the most likely source remains the accidental breakage of thermometers and barometers containing mercury in the past. Mercury in laboratory air can adsorb and diffuse into defects and grain boundaries, especially at polished surfaces. We consider some possible ways to improve the situation, for example by placing a gold foil in the proximity of a prototype to act as a ‘getter’ that will preferentially adsorb mercury.
Metrologia, 2013
ABSTRACT Mercury contamination and the build-up of carbonaceous contamination are two contributin... more ABSTRACT Mercury contamination and the build-up of carbonaceous contamination are two contributing factors to the instability observed in kilogram prototype masses. The kilogram prototypes that lie at the core of the dissemination of the SI base unit were manufactured in the late 19th century, and have polished surfaces. In papers IV and V of this series we developed a method for cleaning noble metal mass standards in air to remove carbonaceous contamination. At the core of this ‘UVOPS’ protocol is the application of UV light and ozone gas generated in situ in air. The precise nature of the carbonaceous contamination that builds up on such surfaces is difficult to mimic demonstrably or quickly on new test surfaces, yet data from such tests are needed to provide the final confidence to allow UVOPS to be applied to a real 19th century kilogram prototype. Therefore, in the present work we have applied the UVOPS method to clean a platinum avoirdupois pound mass standard, ‘RS2’, manufactured in the mid-19th century. This is thought to have been polished in a similar manner to the kilogram prototypes. To our knowledge this platinum surface has not previously been cleaned by any method. We used x-ray photoelectron spectroscopy to identify organic contamination, and weighing to quantify the mass lost at each application of the UVOPS procedure. The UVOPS procedure is shown to be very effective.It is likely that the redefinition of the kilogram will require mass comparisons in vacuum in the years to come. Therefore, in addition to UVOPS a cleaning method for use in vacuum will also be needed. We introduce and evaluate gas cluster ion-beam (GCIB) treatment as a potential method for cleaning reference masses in vacuum. Again, application of this GCIB cleaning to a real artefact, RS2, allows us to make a realistic evaluation of its performance. While it has some attractive features, we cannot recommend it for cleaning mass standards in its present form.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2013
There is a pressing need for reference data to allow sputter depth-profiling of polymers using cl... more There is a pressing need for reference data to allow sputter depth-profiling of polymers using cluster and polyatomic ion sources for the quantification of depth in XPS and SIMS. The authors have developed a new method of sputter rate measurement based on a combination of contact masking and white-light interferometry. This allowed us to measure sputter rates for 19 different polymers of technological significance, a much wider set of data than any available previously. The results show a much larger range of sputter yield than might previously have been expected. For example, the sputter yield of PMMA being more than ten times that of poly ether ether ketone when using argon ion clusters of around 4 eV/atom, with other polymers being widely distributed between these extremes. Without reference data for sputter rate this wide range could lead to major errors in depth estimation in sputter depth-profiling of polymer coatings, biomaterials, nanostructures, polymer electronic and polymer photovoltaic devices. V
Chemical Geology, 2017
Decontamination of geological samples by gas cluster ion beam etching or ultra violet/ozone.
Journal of Materials Science: Materials in Electronics, 2018
If citing, it is advised that you check and use the publisher's definitive version for pagination... more If citing, it is advised that you check and use the publisher's definitive version for pagination, volume/issue, and date of publication details. And where the final published version is provided on the Research Portal, if citing you are again advised to check the publisher's website for any subsequent corrections.
Applied Surface Science, 2016
Conducting this study has demonstrated that not only SEM-EDX but also XPS can be an efficient too... more Conducting this study has demonstrated that not only SEM-EDX but also XPS can be an efficient tool for characterising watercolour paint surfaces. We find that surface effects are mediated by water. Once the powdered components in the watercolour come into contact with water they dramatically transform their chemical structures at the surface and show the presence of pigment components with a random dispersion within the gum layer. Hence the topmost surface of the paint is confirmed as being composed of the gum binder components. This result is difficult to confirm using just one analytical technique (either XPS or SEM-EDX). In addition, peak fitting of C1s XPS spectra suggests that the gum binder in the commercial watercolour paints is probably gum arabic (by comparison with the reference materials). This identification is not conclusive, but the combination techniques of XPS and SEM shows the surface structure with material distribution of the gum binder and the other ingredients of the watercolour paints. Therefore as a unique technique, XPS combined with SEM-EDX may prove a useful method in the study of surface structure for not only watercolour objects but also other art objects; which may in future help in the conservation for art.
Surface and Interface Analysis, 2016
In situ ion beam sputter deposition and X-ray photoelectron spectroscopy (XPS) of multiple thin l... more In situ ion beam sputter deposition and X-ray photoelectron spectroscopy (XPS) of multiple thin layers under computer control for combinatorial materials synthesis.
Surface and Interface Analysis, 2016
Principal component analysis (PCA) and other multivariate analysis methods have been used increas... more Principal component analysis (PCA) and other multivariate analysis methods have been used increasingly to analyse and understand depth-profiles in XPS, AES and SIMS. For large images or three-dimensional (3D) imaging depth-profiles, PCA has been difficult to apply until now simply because of the size of the matrices of data involved. In a recent paper, we described two algorithms, random vector 1 (RV1) and random vector 2 (RV2), that improve the speed of PCA and allow datasets of unlimited size, respectively. In this paper, we now apply the RV2 algorithm to perform PCA on full 3D time-of-flight SIMS data for the first time without subsampling. The dataset we process in this way is a 128 × 128 pixel depth-profile of 120 layers, each voxel having a 70 439 value mass spectrum associated with it. This forms over a terabyte of data when uncompressed and took 27 h to process using the RV2 algorithm using a conventional windows desktop personal computer (PC). While full PCA (e.g. using RV2) is to be preferred for final reports or publications, a much more rapid method is needed during analysis sessions to inform decisions on the next analytical step. We have therefore implemented the RV1 algorithm on a PC having a graphical processor unit (GPU) card containing 2880 individual processor cores. This increases the speed of calculation by a factor of around 4.1 compared with what is possible using a fast commercially available desktop PC having central processing units alone, and full PCA is performed in less than 7 s. The size of the dataset that can be processed in this way is limited by the size of the memory on the GPU card. This is typically sufficient for two-dimensional images but not 3D depth-profiles without sampling. We have therefore examined efficient sampling schemes that allow a good approximate solution to the PCA problem for large 3D datasets. We find that low-discrepancy series such as Sobol series sampling gives more rapid convergence than random sampling, and we recommend such methods for routine use. Using the GPU and low-discrepancy series together, we anticipate that any time-of-flight SIMS dataset, of whatever size, can be efficiently and accurately processed into PCA components in a maximum of around 10 s using a commercial PC with a widely available GPU card, although the longer RV2 approach is still to be preferred for the presentation of final results, such as in published papers.
Ultramicroscopy, 2012
The characterisation of nanoscale surface properties of textile and hair fibres is key to develop... more The characterisation of nanoscale surface properties of textile and hair fibres is key to developing new effective laundry and hair care products. Here, we develop nanomechanical methods to characterise fibres using an atomic force microscope (AFM) to give their nanoscale modulus. Good mounting methods for the fibre that are chemically inert, clean and give strong mechanical coupling to a substrate are important and here we detail two methods to do this. We show, for elastic nanoindentation measurements, the situation when the tip radius significantly affects the result via a function of the ratio of the radii of the tip and fibre and indicate the importance of using an AFM for such work. A valid method to measure the nanoscale modulus of fibres using AFM is thus detailed and exampled on hair to show that bleaching changes the nanoscale reduced modulus at the outer surface.
Japanese Journal of Applied Physics, 2002
We investigated the thermotropic phase behavior of rigid-rod poly(γ-octadecyl L-glutamate) (PG18)... more We investigated the thermotropic phase behavior of rigid-rod poly(γ-octadecyl L-glutamate) (PG18) with an average molecular weight M w = 36, 000. Two polymers with narrow molecular weight distributions (M w /M n), PG18-A with M w /M n = 1.12 and PG18-B with M w /M n = 1.05, were prepared by gel permeation chromatography (GPC) fractionation. Both were found to form a smectic A phase by means of microscopic observations of the focal conic texture and by the small-angle X-ray method. The smectic A phase of PG18-A was transformed into a cholesteric phase at approximately 140-170 • C while that of PG18-B stably existed in the entire thermotropic temperature range from 60 • C to 220 • C (decomposition temperature). This dependence of smectic stability on the molecular weight polydispersity qualitatively corresponds to the theoretical prediction based on the excluded volume effect.
Journal of Fiber Science and Technology, 2018
Chemical Geology, 2021
Abstract Earlier investigations have suggested that an extensive deep biosphere with a significan... more Abstract Earlier investigations have suggested that an extensive deep biosphere with a significant fungal component is present within the sub-oceanic crust. To investigate this further, the organic material in the lithic sections of a sub-oceanic volcaniclastic tuff obtained from the eastern lobe of the Ontong Java Plateau (OJP tuff) were characterised using X-ray photoelectron spectroscopy and thermal hydrolysis and methylation coupled to gas chromatography/mass spectrometry. In the investigation here, the chemical and molecular composition of plant and fungal structural biopolymer standards were characterised using the same techniques and then compared to the organic material from the OJP tuff. This was conducted on untreated material and after hydrous pyrolysis, a process that simulated the physical and thermal decomposition of organic material that occurs during late diagenesis. The characteristics of the organic material in the OJP tuff matched the products of hydrous-pyrolysed chitin. This result suggested that OJP tuff contained organic material that could have been derived from fossilised chitin, implying that the OJP tuff potentially contained the remnants of a microbial community with a fungal component.
Applied Surface Science, 2018
Indium phosphide (InP) surfaces develop a pronounced nanostructured texture upon irradiation by e... more Indium phosphide (InP) surfaces develop a pronounced nanostructured texture upon irradiation by energetic ion beams. We have observed the mechanism of nanostructure evolution of InP under irradiation by an Ar gas cluster ion beam (GCIB) using helium ion microscopy (HIM). Initially, metallic indium nanoparticles form on the surface after removal of the topmost oxide layer. These nanoparticles form a mask which shadows the underlying InP. As the ion dose is increased, the masking effect results in substantial nanostructured topography in the form of pillars or nanocones, oriented along the axis of the incident GCIB. The surface sensitivity and high resolution of the HIM facilitates the direct observation of the metallic indium cap at the top of the pillars.
Applied Catalysis A: General, 2018
Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduct... more Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduction or hydroformylation reactions. In this work instead, we explored the capabilities of Rh nanoparticles as an oxidation catalyst, applied to the oxidation of benzyl alcohol to benzaldehyde under very mild conditions (100°C, and atmospheric pressure) as a model reaction. Here we report the preparation of novel Rh/C catalysts by using an impregnation protocol, with particular emphasis on the pre-treatment of the carbon supports by using HNO 3 and HCl, as well as the characterization of these materials by using an array of methods involving TEM, XPS and XRPD. Our preparation method led to a wide Rh particle size distribution ranging from 20 to 100 nm, and we estimate an upper limit diameter of Rh nanoparticles for their activity towards benzyl alcohol oxidation to be ca. 30 nm. Furthermore, a HNO 3 pre-treatment of the activated carbon support was able to induce a smaller and narrower particle size distribution of Rh nanoparticles, whereas a HCl pre-treatment had no effect or sintered the Rh nanoparticles. We rationalise these results by HNO 3 as an acid able to create new nucleation sites for Rh on the carbon surface, with the final effect of smaller nanoparticles, whereas for HCl the effect of sintering was most likely due to site blocking of the nucleation sites over the carbon surface. The roles of acid centres on the carbon surfaces for the oxidation reaction was also investigated, and the larger their amounts the larger the amounts of by-products. However, by treatment with HNO 3 we were able to convert neutral or basic carbons into supports capable to enhance the catalytic activity of Rh, and yet minimised detrimental effects on the selectivity of the oxidation to benzaldehyde.
Catalysis Science & Technology, 2017
Rh nanoparticles that were inactive in toluene, were converted into a powerful catalyst for aryl ... more Rh nanoparticles that were inactive in toluene, were converted into a powerful catalyst for aryl alcohol oxidation by the presence of water in the reaction media.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2016
Surface and Interface Analysis, 2016
This work is licensed under a Creative Commons Attribution 4.0 International License Newcastle Un... more This work is licensed under a Creative Commons Attribution 4.0 International License Newcastle University ePrints-eprint.ncl.ac.uk
Surface and Interface Analysis, 2012
ABSTRACT The authors have observed for the first time that x-ray exposure of certain polymers of ... more ABSTRACT The authors have observed for the first time that x-ray exposure of certain polymers of “degrading” type can greatly enhance the sputter rate of these polymers by gas cluster ion beam (GCIB) profiling. They have observed craters of similar dimensions to the x-ray spot well within the perimeter of sputter craters, indicating that x-rays can assist GCIB sputtering very significantly. This can be a major source of the loss of depth-resolution in sputter depth profiles of polymers. The authors have measured experimentally sputter craters in 14 different polymers by white-light interferometry. The results show that x-ray exposure can introduce much more topography than might previously have been expected, through both thermal and direct x-ray degradation and cross-linking. Within the region exposed to x-rays, the response of the polymer surface depends on its chemistry, with degrading (also known as type II) polymers being susceptible to large increases in sputter rate in some cases. For example, this leads to a sputter rate increase of a factor of 3 in poly-L-lactic acid (PLLA) compared to cluster-ion sputtering in the absence of x rays under typical experimental conditions. By comparison, crosslinking (also known as type I) polymers show either the same sputter rate or a reduced sputter rate due to crosslinking. The authors model this behavior using the bond scission parameter (GS) and crosslinking parameter (GX) used to model radiation damage in polymers. Agreement is good, allowing us to provide guidelines to assist in planning XPS depth-profiling experiments, in particular, for polymers such as PMMA and PLLA, where any requirement for uniform sputter rate is a more stringent limit to x-ray exposure than the requirement for the XPS spectra to represent chemical states quantitatively without damage.
Metrologia, 2013
ABSTRACT The stability of prototype kilogram reference masses has been a long-standing question w... more ABSTRACT The stability of prototype kilogram reference masses has been a long-standing question within the SI, with mass loss or gain at the surface being the principal concern. In papers I, III and IV of this series we showed mercury and organic carbonaceous contamination to be significant in sample surfaces exposed to typical prototype kilogram storage environments. In this work, we have examined the surfaces of six platinum mass standards manufactured in the mid-19th century. We used x-ray photoelectron spectroscopy in order to identify mercury and carbonaceous contamination, and assess the validity of our previous models for the rate of increase. We use white-light interferometry to study surface roughness and polishing damage. We see mercury on all six of the 19th century polished prototypes we analysed. For one weight, manufactured around 1830, we see a quantity of mercury roughly equivalent to 250 µg if present on the surface of a prototype kilogram at the same mass per unit area. The quantities of these contaminations calculated from our XPS spectra are in good agreement with the theoretical models developed in papers III and IV for the growth of mercury and carbonaceous contamination, respectively, and increase our confidence that these processes are indeed happening at the surface of polished kilogram prototypes in most (if not all) cases. We discuss some potential sources of mercury contamination, though the most likely source remains the accidental breakage of thermometers and barometers containing mercury in the past. Mercury in laboratory air can adsorb and diffuse into defects and grain boundaries, especially at polished surfaces. We consider some possible ways to improve the situation, for example by placing a gold foil in the proximity of a prototype to act as a ‘getter’ that will preferentially adsorb mercury.
Metrologia, 2013
ABSTRACT Mercury contamination and the build-up of carbonaceous contamination are two contributin... more ABSTRACT Mercury contamination and the build-up of carbonaceous contamination are two contributing factors to the instability observed in kilogram prototype masses. The kilogram prototypes that lie at the core of the dissemination of the SI base unit were manufactured in the late 19th century, and have polished surfaces. In papers IV and V of this series we developed a method for cleaning noble metal mass standards in air to remove carbonaceous contamination. At the core of this ‘UVOPS’ protocol is the application of UV light and ozone gas generated in situ in air. The precise nature of the carbonaceous contamination that builds up on such surfaces is difficult to mimic demonstrably or quickly on new test surfaces, yet data from such tests are needed to provide the final confidence to allow UVOPS to be applied to a real 19th century kilogram prototype. Therefore, in the present work we have applied the UVOPS method to clean a platinum avoirdupois pound mass standard, ‘RS2’, manufactured in the mid-19th century. This is thought to have been polished in a similar manner to the kilogram prototypes. To our knowledge this platinum surface has not previously been cleaned by any method. We used x-ray photoelectron spectroscopy to identify organic contamination, and weighing to quantify the mass lost at each application of the UVOPS procedure. The UVOPS procedure is shown to be very effective.It is likely that the redefinition of the kilogram will require mass comparisons in vacuum in the years to come. Therefore, in addition to UVOPS a cleaning method for use in vacuum will also be needed. We introduce and evaluate gas cluster ion-beam (GCIB) treatment as a potential method for cleaning reference masses in vacuum. Again, application of this GCIB cleaning to a real artefact, RS2, allows us to make a realistic evaluation of its performance. While it has some attractive features, we cannot recommend it for cleaning mass standards in its present form.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2013
There is a pressing need for reference data to allow sputter depth-profiling of polymers using cl... more There is a pressing need for reference data to allow sputter depth-profiling of polymers using cluster and polyatomic ion sources for the quantification of depth in XPS and SIMS. The authors have developed a new method of sputter rate measurement based on a combination of contact masking and white-light interferometry. This allowed us to measure sputter rates for 19 different polymers of technological significance, a much wider set of data than any available previously. The results show a much larger range of sputter yield than might previously have been expected. For example, the sputter yield of PMMA being more than ten times that of poly ether ether ketone when using argon ion clusters of around 4 eV/atom, with other polymers being widely distributed between these extremes. Without reference data for sputter rate this wide range could lead to major errors in depth estimation in sputter depth-profiling of polymer coatings, biomaterials, nanostructures, polymer electronic and polymer photovoltaic devices. V