Stephan J. P. Kress

• Dr. sc.
• PostDoc Position at Harvard University

In the initial proposal of the spaser – a source of coherent, intense, and narrow-band surface plasmons – colloidal quantum dots were envisioned as an ideal gain medium for compensation of the significant losses intrinsic to plasmonics. However, many spasers shown to date have required a single material to both serve as a gain medium and define the...

Colloidal nanoplatelets are atomically flat, quasi-two-dimensional sheets of semiconductor that can exhibit efficient, spectrally pure fluorescence. Despite intense interest in their properties, the mechanism behind their highly anisotropic shape and precise atomic-scale thickness remains unclear, and even counter-intuitive for commonly studied nan...

Colloidal quantum dots are robust, efficient, and tunable emitters now used in lighting, displays, and lasers. Consequently, when the spaser, a laser-like source of surface plasmons, was first proposed, quantum dots were specified as the ideal plasmonic gain medium. Subsequent spaser designs, however, have required a single material to simultaneous...

The mechanical wiring between cells and their surroundings is fundamental to the regulation of complex biological processes during tissue development, repair or pathology. Traction force microscopy (TFM) enables determination of the actuating forces. Despite progress, important limitations with intrusion effects in low resolution 2D pillar-based me...

Supplementary Figures 1-10, Supplementary Methods and Supplementary References

Migrating HUVEC on red cTFM platform (inter-disc spacing: 1.5 μm). Cell und nucleus outline (based on brightfield image) were superimposed. Scale bar: 10 μm.

Electrohydrodynamic nanodrip-printing of fluorescent quantum dot nanodiscs. Scale bar: 5 μm

Relaxation of the elastic silicone upon cell removal. HeLa cells were seeded on a red cTFM platform (inter-disc spacing: 1.5 μm). Upon imaging, cells were detached from the substrate by adding 0.01% sodium dodecyl sulfate to the medium, followed by imaging the same region again. Scale bar: 10 μm.

Mesh relaxation. Reconstruction of the original mesh and QD nanodisc's original positions through relaxation of the deformed mesh. Colorbar: 1 corresponds to maximum deformation of the triangles in the mesh and 0 to perfectly equilateral triangles. Red dots indicate QD nanodiscs whose positions are fixed as boundary for the relaxation.

Colloidal nanoplatelets - quasi-two-dimensional sheets of semiconductor exhibiting efficient, spectrally pure fluorescence - form when liquid-phase syntheses of spherical quantum dots are modified. Despite intense interest in their properties, the mechanism behind their anisotropic shape and precise atomic-scale thickness remains unclear, and even...

The fabrication of functional metamaterials with extreme feature resolution finds a host of applications such as the broad area of surface/light interaction. Non-planar features of such structures can significantly enhance their performance and tunability, but their facile generation remains a challenge. Here, we show that carefully designed out-of...

Color printing at the diffraction limit has been recently explored by fabricating nanoscale plasmonic structures with electron beam lithography. However, only a limited color range and constant intensity throughout the structure have been demonstrated. Here we show an alternative, facile approach relying on the direct, open-atmosphere electrohydrod...

Advancing open atmosphere printing technologies to produce features in the nanoscale range has important and broad applications ranging from electronics, to photonics, plasmonics and biology. Recently an electrohydrodynamic printing regime has been demonstrated in a rapid dripping mode (termed NanoDrip), where the ejected colloidal droplets from no...

Plasmonic structures can provide deep-subwavelength electromagnetic fields useful for enhancing light-matter interactions. However, because these localized modes are also dissipative, structures that offer the best compromise between field confinement and loss have been sought. Metallic wedge waveguides were initially identified as an ideal candida...

High-quality materials are critical for advances in plasmonics, especially as researchers now investigate quantum effects at the limit of single surface plasmons or exploit ultraviolet- or CMOS-compatible metals such as aluminum or copper. Unfortunately, due to inexperience with deposition methods, many plasmonics researchers deposit metals under t...

Colloidal quantum-dots are bright, tunable emitters that are ideal for studying near-field quantum-optical interactions. However, their colloidal nature has hindered their facile and precise placement at desired near-field positions, particularly on the structured substrates prevalent in plasmonics. Here, we use high-resolution electro-hydrodynamic...

Gradient fields of optical, magnetic, or electrical origin are widely used for the manipulation of micro- and nanoscale objects. Among various device geometries to generate gradient forces, sharp metallic tips are one of the most effective. Surface roughness and asperities present on traditionally produced tips reduce trapping efficiencies and limi...

Nanotechnology, with its broad impact on societally relevant applications, relies heavily on the availability of accessible nanofabrication methods. Even though a host of such techniques exists, the flexible, inexpensive, on-demand and scalable fabrication of functional nanostructures remains largely elusive. Here we present a method involving nano...

This paper presents the space-resolved temperature determination in the mixing zone of a transient free dimethyl ether jet flowing into a non-moving atmosphere via the time-resolved local molar mixture fraction, obtained with tracer added Laser-induced Fluorescence. The temperature of the mixture is calculated with an approach of an adiabatic mixin...