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A Van Gogh underneath a Van Gogh
RESEARCH NEWS
Slower speeds win
A Van Gogh underneath a Van Gogh CHARACTERIZATION
Vincent van Gogh, one of the founding fathers of modern painting, was known to save canvas in a very particular way: He reused the canvases of abandoned paintings by covering them with layers of white and then painted over them. It is estimated that about a third of his paintings bear other artwork underneath. Recently, researchers collaborating from a range of institutions have developed a technique to reveal the hidden paintings in astonishing detail using X-ray fluorescence (XRF) elemental mapping (Dik et al., Anal. Chem. 2008, DOI 10.1021/ac800965g). Older methods for investigating covered paintings involve X-ray radiation transmission radiography (XRR) and Infrared Reflectography (IRR), both of which can reveal hidden paintings, but without much detail. Joris Dik of the Delft University of Technology in Holland and his co-workers have used non-destructive XRF elemental mapping, to investigate van Gogh’s painting Patch of Grass. Previous analyses had shown that this painting covers the image of a female head, but the details were blurred. Dik and colleagues scanned a 300 cm2 area of the painting with a narrow beam (0.5 x 0.5 mm2) of quasi-monochromatic synchrotron radiation, using a counting time of 2 seconds per pixel. The whole scan took about two days, separately recording the fluorescence spectra for each pixel. The idea is to identify certain elements by their fluorescence fingerprint. In particular, the distribution of Hg, Sb and Zn reveals the presence of specific paints
(a)
(c)
important as electronic devices continue to decrease in size. Cavity optomechanics may ultimately find applications in many areas; the ability to provide targeted cooling of nano and micromechanical oscillators, is one key area under investigation. Applications will also include areas such as scanning probe techniques and gravitational wave detection. Another application area of great interest is in gradient-force control of mechanical structures using cavity optomechanical effects. Radiation-pressure coupling has opened an extremely broad scope of application, both applied and fundamental, and with the continuing demand for ever smaller components and devices it will become an increasingly important phenomenon. Cavity optomechanics may well provide a way to probe the quantum environment of mechanical systems and give rise to entirely new ways of controlling mechanics, light or both. Techniques and applications may also be found in the area of device cooling and signal amplification.
It is widely believed that interactions at metal surfaces increase with an increase in molecular velocity. Scientists in California have presented findings that actually contradict this belief. [Nahler et al., Science, 321 (2008) 1191] Studies in heterogenous catalysis, essentially the chemistry between two different phases i.e., solid, liquid, and gas began the more general study of surface science. The Born-Oppenheimer (BO) Approximation which is the assumption that the electronic motion and the nuclear motion in molecules can be separated has contributed a great deal to the understanding of surface science and heterogenous catalysis. There are however many cases where we see a breakdown in the BO approximation; many of these cases showing a decrease in excitation as the velocity of the molecules contacting the surface decrease. Nahler et al, report when highly excited nitric oxide molecules are fired at the surface of a metal they witnessed greater molecular activity as the velocity of the incoming molecules decreased. A simple model is presented to explain this observation, it suggests that it is not the motion of the nitric oxide molecules relative to the surface that effects this observation, but the relative vibrations of the N and O bond. As the bonds expand attraction to the surface metal become greater thus aiding molecular interactions, and at slow speeds the efficiency of this effect is enhanced. Further work will take place to better understand the forces at play. This work will aid the understanding of the dynamics of molecules on metal surfaces.
Jonathan Agbenyega
Jonathan Agbenyega
(b)
(d)
Distribution of (a) Pb, (b) Hg, (c) Sb and (d)Zn using XRF (black, represents low intensity and white high intensity.
used at van Gogh’s time, namely vermillion (Hg), Naples yellow (Sb) and white (Zn), so revealing a much more detailed image of a woman’s head. To confirm these results, Dik and his colleagues examined another van Gogh paining, Head of a woman, with a portable XRF unit. As expected, they found Hg in red areas, such as lips, and Sb and Zn in light areas. Using this new technique, researchers might be able to uncover other hidden paintings, thus providing better understanding of the Artist’s life and habits. Michel Fleck
Interferometers feel the pressure CHARACTERIZATION Many methods can be employed to measure mechanical displacement; the coupling of optical and mechanical degrees of freedom is behind many of these techniques. This mutual coupling of optical and mechanical degrees of freedom in an optical cavity has been explored in interferometers; better and known as cavity optomechanics. Researchers from Germany and the United States [Kippenberg et al., Science (2008) 321, 1172] discuss the phenomenon of back-action of photons caused by radiation pressure which can influence the dynamics of such systems, leading to a plethora of new phenomena, some of which may spurn innovative technologies as well as aiding the further understanding of fundamental science. Kippenberg et al., present a concise review, providing some thoughts and solutions in this area and insights in to some of the applications for this technology in the future. The paper discusses the increasing importance of the radiation pressure which takes place during the reflection of the photons. This phenomenon will become increasingly
8
SURFACE SCIENCE
OCTOBER 2008 | VOLUME 11 | NUMBER 10
Slower speeds win
A Van Gogh underneath a Van Gogh CHARACTERIZATION
Vincent van Gogh, one of the founding fathers of modern painting, was known to save canvas in a very particular way: He reused the canvases of abandoned paintings by covering them with layers of white and then painted over them. It is estimated that about a third of his paintings bear other artwork underneath. Recently, researchers collaborating from a range of institutions have developed a technique to reveal the hidden paintings in astonishing detail using X-ray fluorescence (XRF) elemental mapping (Dik et al., Anal. Chem. 2008, DOI 10.1021/ac800965g). Older methods for investigating covered paintings involve X-ray radiation transmission radiography (XRR) and Infrared Reflectography (IRR), both of which can reveal hidden paintings, but without much detail. Joris Dik of the Delft University of Technology in Holland and his co-workers have used non-destructive XRF elemental mapping, to investigate van Gogh’s painting Patch of Grass. Previous analyses had shown that this painting covers the image of a female head, but the details were blurred. Dik and colleagues scanned a 300 cm2 area of the painting with a narrow beam (0.5 x 0.5 mm2) of quasi-monochromatic synchrotron radiation, using a counting time of 2 seconds per pixel. The whole scan took about two days, separately recording the fluorescence spectra for each pixel. The idea is to identify certain elements by their fluorescence fingerprint. In particular, the distribution of Hg, Sb and Zn reveals the presence of specific paints
(a)
(c)
important as electronic devices continue to decrease in size. Cavity optomechanics may ultimately find applications in many areas; the ability to provide targeted cooling of nano and micromechanical oscillators, is one key area under investigation. Applications will also include areas such as scanning probe techniques and gravitational wave detection. Another application area of great interest is in gradient-force control of mechanical structures using cavity optomechanical effects. Radiation-pressure coupling has opened an extremely broad scope of application, both applied and fundamental, and with the continuing demand for ever smaller components and devices it will become an increasingly important phenomenon. Cavity optomechanics may well provide a way to probe the quantum environment of mechanical systems and give rise to entirely new ways of controlling mechanics, light or both. Techniques and applications may also be found in the area of device cooling and signal amplification.
It is widely believed that interactions at metal surfaces increase with an increase in molecular velocity. Scientists in California have presented findings that actually contradict this belief. [Nahler et al., Science, 321 (2008) 1191] Studies in heterogenous catalysis, essentially the chemistry between two different phases i.e., solid, liquid, and gas began the more general study of surface science. The Born-Oppenheimer (BO) Approximation which is the assumption that the electronic motion and the nuclear motion in molecules can be separated has contributed a great deal to the understanding of surface science and heterogenous catalysis. There are however many cases where we see a breakdown in the BO approximation; many of these cases showing a decrease in excitation as the velocity of the molecules contacting the surface decrease. Nahler et al, report when highly excited nitric oxide molecules are fired at the surface of a metal they witnessed greater molecular activity as the velocity of the incoming molecules decreased. A simple model is presented to explain this observation, it suggests that it is not the motion of the nitric oxide molecules relative to the surface that effects this observation, but the relative vibrations of the N and O bond. As the bonds expand attraction to the surface metal become greater thus aiding molecular interactions, and at slow speeds the efficiency of this effect is enhanced. Further work will take place to better understand the forces at play. This work will aid the understanding of the dynamics of molecules on metal surfaces.
Jonathan Agbenyega
Jonathan Agbenyega
(b)
(d)
Distribution of (a) Pb, (b) Hg, (c) Sb and (d)Zn using XRF (black, represents low intensity and white high intensity.
used at van Gogh’s time, namely vermillion (Hg), Naples yellow (Sb) and white (Zn), so revealing a much more detailed image of a woman’s head. To confirm these results, Dik and his colleagues examined another van Gogh paining, Head of a woman, with a portable XRF unit. As expected, they found Hg in red areas, such as lips, and Sb and Zn in light areas. Using this new technique, researchers might be able to uncover other hidden paintings, thus providing better understanding of the Artist’s life and habits. Michel Fleck
Interferometers feel the pressure CHARACTERIZATION Many methods can be employed to measure mechanical displacement; the coupling of optical and mechanical degrees of freedom is behind many of these techniques. This mutual coupling of optical and mechanical degrees of freedom in an optical cavity has been explored in interferometers; better and known as cavity optomechanics. Researchers from Germany and the United States [Kippenberg et al., Science (2008) 321, 1172] discuss the phenomenon of back-action of photons caused by radiation pressure which can influence the dynamics of such systems, leading to a plethora of new phenomena, some of which may spurn innovative technologies as well as aiding the further understanding of fundamental science. Kippenberg et al., present a concise review, providing some thoughts and solutions in this area and insights in to some of the applications for this technology in the future. The paper discusses the increasing importance of the radiation pressure which takes place during the reflection of the photons. This phenomenon will become increasingly
8
SURFACE SCIENCE
OCTOBER 2008 | VOLUME 11 | NUMBER 10