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A nanometre-scale resolution interference-based probe of interfacial phenomena between microscopic objects and surfaces.

Contreras-Naranjo JC, Ugaz VM - Nat Commun (2013)

Bottom Line: Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces.But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach.Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object's contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus.

View Article: PubMed Central - PubMed

Affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas, USA.

ABSTRACT
Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces. But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach. Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object's contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus. The unique view-from-below perspective of reflection interference contrast microscopy also reveals previously unseen deformations and allows the first direct observation of femtolitre-scale capillary condensation dynamics underneath micron-sized particles. Our implementation of reflection interference contrast microscopy provides a generally applicable nanometre-scale resolution tool that can be potentially exploited to dynamically probe ensembles of objects near surfaces so that statistical/probabilistic behaviour can be realistically captured.

No MeSH data available.


Related in: MedlinePlus

Fringe-spacing analysis based on simplified non-planar RICM.(a) Simplified non-planar RICM image formation model. The intensity I(x) is produced by the interference of rays I1 and I2, which correspond to the single set of complementary rays I0 with the maximum OPLD (determined by geometric parameters S(xβ), β and θR defined at position xβ) among all possible contributions (shaded area). Complementary I0 originate from within the illumination cone (θ1≤αIA, where αIA is given by the illumination numerical aperture, INA, of the microscope); then, they are reflected back from planar (substrate/layer 1 at x) and non-planar (layer 1/object at xβ) interfaces producing rays I1 and I2, respectively, which interfere at position x only if they are incident within the cone of detected light (θ2≤αDA, where αDA is determined by the numerical aperture, NA, of the objective). (b) The formulation of the simplified non-planar RICM model is completed when NRL/non-NRL regimes are identified at OPLDmax, as illustrated with a normalized OPLD plot for the range of detection angles corresponding to a series of wedge inclination angles with INA=0.48 and water surroundings. (c) Despite the intrinsic fringe-spacing variability, which produces the scattered data points, the behaviour of ΔSPf/Δxf with inclination angle observed in simulations from several different wedge systems is in excellent agreement with equation (4), where INA, n1 (surroundings composition) and θR (reflected light regime) are the main parameters. (d) Percentage error of inclination angles retrieved from the averages of all fringe-spacing values originated from simulations of comparable wedge systems. Closed and open symbols represent βretrieved, using NRL and non-NRL models, respectively. In all figures, simulations are performed with numerical aperture=1.25 for wedge angles ranging from 0° to βmax.
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f4: Fringe-spacing analysis based on simplified non-planar RICM.(a) Simplified non-planar RICM image formation model. The intensity I(x) is produced by the interference of rays I1 and I2, which correspond to the single set of complementary rays I0 with the maximum OPLD (determined by geometric parameters S(xβ), β and θR defined at position xβ) among all possible contributions (shaded area). Complementary I0 originate from within the illumination cone (θ1≤αIA, where αIA is given by the illumination numerical aperture, INA, of the microscope); then, they are reflected back from planar (substrate/layer 1 at x) and non-planar (layer 1/object at xβ) interfaces producing rays I1 and I2, respectively, which interfere at position x only if they are incident within the cone of detected light (θ2≤αDA, where αDA is determined by the numerical aperture, NA, of the objective). (b) The formulation of the simplified non-planar RICM model is completed when NRL/non-NRL regimes are identified at OPLDmax, as illustrated with a normalized OPLD plot for the range of detection angles corresponding to a series of wedge inclination angles with INA=0.48 and water surroundings. (c) Despite the intrinsic fringe-spacing variability, which produces the scattered data points, the behaviour of ΔSPf/Δxf with inclination angle observed in simulations from several different wedge systems is in excellent agreement with equation (4), where INA, n1 (surroundings composition) and θR (reflected light regime) are the main parameters. (d) Percentage error of inclination angles retrieved from the averages of all fringe-spacing values originated from simulations of comparable wedge systems. Closed and open symbols represent βretrieved, using NRL and non-NRL models, respectively. In all figures, simulations are performed with numerical aperture=1.25 for wedge angles ranging from 0° to βmax.

Mentions: Although contact phenomena can be directly observed and quantified (typically as an area in the RICM image), accurate analysis of the interference pattern requires a link between the intensities and the object’s geometry (Fig. 3). Instead of applying the complete non-planar interface image formation theory, where all possible contributions to the observed intensity must be individually determined16, we consider a simplified two-dimensional model whereby a single set of complementary rays, I0, interfere to produce the intensity observed at a position x in the interferogram, I(x). For the single-layer system in Fig. 4a, I(x) depends on the interference of rays I1 and I2 in terms of their optical path length difference OPLD (term in square brackets) as follows.


A nanometre-scale resolution interference-based probe of interfacial phenomena between microscopic objects and surfaces.

Contreras-Naranjo JC, Ugaz VM - Nat Commun (2013)

Fringe-spacing analysis based on simplified non-planar RICM.(a) Simplified non-planar RICM image formation model. The intensity I(x) is produced by the interference of rays I1 and I2, which correspond to the single set of complementary rays I0 with the maximum OPLD (determined by geometric parameters S(xβ), β and θR defined at position xβ) among all possible contributions (shaded area). Complementary I0 originate from within the illumination cone (θ1≤αIA, where αIA is given by the illumination numerical aperture, INA, of the microscope); then, they are reflected back from planar (substrate/layer 1 at x) and non-planar (layer 1/object at xβ) interfaces producing rays I1 and I2, respectively, which interfere at position x only if they are incident within the cone of detected light (θ2≤αDA, where αDA is determined by the numerical aperture, NA, of the objective). (b) The formulation of the simplified non-planar RICM model is completed when NRL/non-NRL regimes are identified at OPLDmax, as illustrated with a normalized OPLD plot for the range of detection angles corresponding to a series of wedge inclination angles with INA=0.48 and water surroundings. (c) Despite the intrinsic fringe-spacing variability, which produces the scattered data points, the behaviour of ΔSPf/Δxf with inclination angle observed in simulations from several different wedge systems is in excellent agreement with equation (4), where INA, n1 (surroundings composition) and θR (reflected light regime) are the main parameters. (d) Percentage error of inclination angles retrieved from the averages of all fringe-spacing values originated from simulations of comparable wedge systems. Closed and open symbols represent βretrieved, using NRL and non-NRL models, respectively. In all figures, simulations are performed with numerical aperture=1.25 for wedge angles ranging from 0° to βmax.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675327&req=5

f4: Fringe-spacing analysis based on simplified non-planar RICM.(a) Simplified non-planar RICM image formation model. The intensity I(x) is produced by the interference of rays I1 and I2, which correspond to the single set of complementary rays I0 with the maximum OPLD (determined by geometric parameters S(xβ), β and θR defined at position xβ) among all possible contributions (shaded area). Complementary I0 originate from within the illumination cone (θ1≤αIA, where αIA is given by the illumination numerical aperture, INA, of the microscope); then, they are reflected back from planar (substrate/layer 1 at x) and non-planar (layer 1/object at xβ) interfaces producing rays I1 and I2, respectively, which interfere at position x only if they are incident within the cone of detected light (θ2≤αDA, where αDA is determined by the numerical aperture, NA, of the objective). (b) The formulation of the simplified non-planar RICM model is completed when NRL/non-NRL regimes are identified at OPLDmax, as illustrated with a normalized OPLD plot for the range of detection angles corresponding to a series of wedge inclination angles with INA=0.48 and water surroundings. (c) Despite the intrinsic fringe-spacing variability, which produces the scattered data points, the behaviour of ΔSPf/Δxf with inclination angle observed in simulations from several different wedge systems is in excellent agreement with equation (4), where INA, n1 (surroundings composition) and θR (reflected light regime) are the main parameters. (d) Percentage error of inclination angles retrieved from the averages of all fringe-spacing values originated from simulations of comparable wedge systems. Closed and open symbols represent βretrieved, using NRL and non-NRL models, respectively. In all figures, simulations are performed with numerical aperture=1.25 for wedge angles ranging from 0° to βmax.
Mentions: Although contact phenomena can be directly observed and quantified (typically as an area in the RICM image), accurate analysis of the interference pattern requires a link between the intensities and the object’s geometry (Fig. 3). Instead of applying the complete non-planar interface image formation theory, where all possible contributions to the observed intensity must be individually determined16, we consider a simplified two-dimensional model whereby a single set of complementary rays, I0, interfere to produce the intensity observed at a position x in the interferogram, I(x). For the single-layer system in Fig. 4a, I(x) depends on the interference of rays I1 and I2 in terms of their optical path length difference OPLD (term in square brackets) as follows.

Bottom Line: Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces.But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach.Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object's contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus.

View Article: PubMed Central - PubMed

Affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas, USA.

ABSTRACT
Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces. But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach. Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object's contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus. The unique view-from-below perspective of reflection interference contrast microscopy also reveals previously unseen deformations and allows the first direct observation of femtolitre-scale capillary condensation dynamics underneath micron-sized particles. Our implementation of reflection interference contrast microscopy provides a generally applicable nanometre-scale resolution tool that can be potentially exploited to dynamically probe ensembles of objects near surfaces so that statistical/probabilistic behaviour can be realistically captured.

No MeSH data available.


Related in: MedlinePlus