TY - JOUR

T1 - Preliminary investigations into macroscopic attenuated total reflection-fourier transform infrared imaging of intact spherical domains

T2 - Spatial resolution and image distortion

AU - Everall, Neil J.

AU - Priestnall, Ian M.

AU - Clarke, Fiona

AU - Jayes, Linda

AU - Poulter, Graham

AU - Coombs, David

AU - George, Michael W.

PY - 2009/3

Y1 - 2009/3

N2 - This paper describes preliminary investigations into the spatial resolution of macro attenuated total reflection (ATR) Fourier transform infrared (FT-IR) imaging and the distortions that arise when imaging intact, convex domains, using spheres as an extreme example. The competing effects of shallow evanescent wave penetration and blurring due to finite spatial resolution meant that spheres within the range 20-140 μm all appeared to be approximately the same size (∼30-35 ∼m) when imaged with a numerical aperture (NA) of ∼0.2. A very simple model was developed that predicted this extreme insensitivity to particle size. On the basis of these studies, it is anticipated that ATR imaging at this NA will be insensitive to the size of intact highly convex objects. A higher numerical aperture device should give a better estimate of the size of small spheres, owing to superior spatial resolution, but large spheres should still appear undersized due to the shallow sampling depth. An estimate of the point spread function (PSF) was required in order to develop and apply the model. The PSF was measured by imaging a sharp interface; assuming an Airy profile, the PSF width (distance from central maximum to first minimum) was estimated to be ∼20 and 30 μm for IR bands at 1600 and 1000 cm -1, respectively. This work has two significant limitations. First, underestimation of domain size only arises when imaging intact convex objects; if surfaces are prepared that randomly and representatively section through domains, the images can be analyzed to calculate parameters such as domain size, area, and volume. Second, the model ignores reflection and refraction and assumes weak absorption; hence, the predicted intensity profiles are not expected to be accurate; they merely give a rough estimate of the apparent sphere size. Much further work is required to place the field of quantitative ATR-FT-IR imaging on a sound basis.

AB - This paper describes preliminary investigations into the spatial resolution of macro attenuated total reflection (ATR) Fourier transform infrared (FT-IR) imaging and the distortions that arise when imaging intact, convex domains, using spheres as an extreme example. The competing effects of shallow evanescent wave penetration and blurring due to finite spatial resolution meant that spheres within the range 20-140 μm all appeared to be approximately the same size (∼30-35 ∼m) when imaged with a numerical aperture (NA) of ∼0.2. A very simple model was developed that predicted this extreme insensitivity to particle size. On the basis of these studies, it is anticipated that ATR imaging at this NA will be insensitive to the size of intact highly convex objects. A higher numerical aperture device should give a better estimate of the size of small spheres, owing to superior spatial resolution, but large spheres should still appear undersized due to the shallow sampling depth. An estimate of the point spread function (PSF) was required in order to develop and apply the model. The PSF was measured by imaging a sharp interface; assuming an Airy profile, the PSF width (distance from central maximum to first minimum) was estimated to be ∼20 and 30 μm for IR bands at 1600 and 1000 cm -1, respectively. This work has two significant limitations. First, underestimation of domain size only arises when imaging intact convex objects; if surfaces are prepared that randomly and representatively section through domains, the images can be analyzed to calculate parameters such as domain size, area, and volume. Second, the model ignores reflection and refraction and assumes weak absorption; hence, the predicted intensity profiles are not expected to be accurate; they merely give a rough estimate of the apparent sphere size. Much further work is required to place the field of quantitative ATR-FT-IR imaging on a sound basis.

KW - ATR

KW - Artifacts

KW - Attenuated total reflection

KW - FT-IR spectroscopy

KW - Fourier transform infrared spectroscopy

KW - Global imaging

KW - Image distortion

KW - PSF

KW - Point spread function

KW - Spatial resolution

UR - http://www.scopus.com/inward/record.url?scp=62849107002&partnerID=8YFLogxK

U2 - 10.1366/000370209787598951

DO - 10.1366/000370209787598951

M3 - Article

C2 - 19281647

AN - SCOPUS:62849107002

SN - 0003-7028

VL - 63

SP - 313

EP - 320

JO - Applied Spectroscopy

JF - Applied Spectroscopy

IS - 3

ER -