We introduce a new technique using diffusing colloidal probes to obtain three dimensional images of physically and chemically patterned surfaces. By using colloids as probes to map energy landscapes on microfabricated patterns, these measurements provide energetic (kT) and spatial (nm) information useful for designing template directed assembly processes. The basic concept is to use optical microscopy methods to monitor numerous freely diffusing colloidal probes sampling energy landscapes modulated by physical pattern features. Images of energy landscapes are generated from many-body statistical mechanical analyses that interpret equilibrium colloidal distributions as three dimensional position dependent potentials due to conservative forces. Analysis of dynamic probe trajectories as self diffusivities demonstrates a consistent interpretation of multi-body dissipative forces while measuring energy landscapes.

Our initial experiments have imaged height contours on lithographically patterned glass surfaces and 5-20 nm thick gold films patterned on glass substrates that modulate local electrostatic and dispersion forces. Energy landscapes of physically patterned surfaces display quantitative agreement with Atomic Force Microscopy images, and maps of patterned gold films are in excellent agreement with theoretical predictions. In dilute interfacial colloidal fluids, particle height histograms on different pattern features are analyzed using Boltzmann's equation produces particle-surface potentials, whereas inverse density functional theory is required to extract the interaction of single particles with patterned surfaces in concentrated colloidal fluids. Colloidal probe size and concentration as well as pattern feature dimensions are varied to investigate image resolution and acquisition times.

These non-intrusive, in-situ measurements of colloidal interactions and structures on energy landscapes provide information to design surface templates for directing the assembly of desired colloidal microstructures. Future extensions of this work are expected to produce additional approaches to interrogate physical, chemical, and biomolecular patterned surfaces and structures with diffusing colloidal probes.