Lasse Højlund Thamdrup

Double thermal oxidation scheme for the fabrication of SiO2 nanochannels

We present a planar fabrication scheme for fluidic systems with silicon dioxide nanochannels and assess the waferscale quality and homogeneity of the fabricated devices. The nanochannels have heights h ranging from 14 to 300 nm and widths w of 2.5, 5 and 10 μm. Compared to other state-of-the-art fabrication techniques, our double thermal oxidation scheme (DTOS) displays improvements with respect to 4 inch waferscale height variation σh 1.1 nm and low surface roughness Ra 0. 5n m. Our technique is based on well-controlled growth of silicon dioxide, UV lithography, etching, with an etch-stop layer, and glass to silicon dioxide fusion bonding. The smallest achievable channel height is controlled by the precision of oxide growth. The fusion bonding protocol is capable of producing very high aspect ratios, w/h > 2500. We test the devices by measuring capillary filling speed in different channel heights, ranging from 14 to 310 nm. These tests reproduce as well as extend the results reported by Tas et al (2004 Appl. Phys. Lett. 85 3274). A systematic deviation from bulk behaviour has been observed for channel heights below 100 nm. (Some figures in this article are in colour only in the electronic version)

Light-Induced Local Heating for Thermophoretic Manipulation of DNA in Polymer Micro- and Nanochannels

We present a method for making polymer chips with a narrow-band near-infrared absorber layer that enables light-induced local heating of liquids inside fluidic micro- and nanochannels fabricated by thermal imprint in polymethyl methacrylate. We have characterized the resulting liquid temperature profiles in microchannels using the temperature dependent fluorescence of the complex [Ru(bpy)(3)](2+). We demonstrate thermophoretic manipulation of individual YOYO-1 stained T4 DNA molecules inside micro- and nanochannels.

Experimental investigation of bubble formation during capillary filling of SiO2 nanoslits

Experimental results are presented regarding the influence of bubble formation on the capillary filling speed of water in SiO2 nanoslits with heights ranging from 33to158nm. The formation of an isolated pinned bubble in a nanoslit with a height of 111nm causes an immediate decrease in the filling speed. In nanoslits with heights below 100nm, pinned bubbles are continuously formed at the advancing liquid meniscus. This observed increase in bubble density, which increases the fluidic resistance, quantitatively coincides with an observed reduction of the filling speed during filling of nanoslits with heights below 100nm.

Smart plastic functionalization by nanoimprint and injection molding

In this paper, we present a route for making smart functionalized plastic parts by injection molding with sub-micrometer surface structures. The method is based on combining planar processes well known and established within silicon micro and sub-micro fabrication with proven high resolution and high fidelity with truly freeform injection molding inserts. The link between the planar processes and the freeform shaped injection molding inserts is enabled by the use of nanoimprint with flexible molds for the pattern definition combined with unidirectional sputter etching for transferring the pattern. With this approach, we demonstrate the transfer of down to 140 nm wide holes on large areas with good structure fidelity on an injection molding steel insert. The durability of the sub-micrometer structures on the inserts have been investigated by running two production series of 102,000 and 73,000 injection molded parts, respectively, on two different inserts and inspecting the inserts before and after the production series and the molded parts during the production series.

Designing visual appearance using a structured surface

We present an approach for designing nanostructured surfaces with prescribed visual appearances, starting at design analysis and ending with a fabricated sample. The method is applied to a silicon wafer structured using deep ultraviolet lithography and dry etching and includes preliminary design followed by numerical and experimental verification. The approach comprises verifying all design and fabrication steps required to produce a desired appearance. We expect that the procedure in the future will yield structurally colored surfaces with appealing prescribed visual appearances.

Nanoimprinted polymer chips for light induced local heating of liquids in micro- and nanochannels

A nanoimprinted polymer chip with a thin near-infrared absorber layer that enables light-induced local heating (LILH) of liquids inside micro- and nanochannels is presented. An infrared laser spot and corresponding hot-spot could be scanned across the device. Large temperature gradients yield thermophoretic forces, which are used to manipulate and stretch individual DNA molecules confined in nanochannels. The absorber layer consists of a commercially available phthalocyanine dye (Fujifilm), with a narrow absorption peak at approximately 775 nm, dissolved in SU-8 photoresist (Microchem Corp.). The 500 nm thick absorber layer is spin-coated on a transparent substrate and UV exposed. Microand nanofluidic channels are defined by nanoimprint lithography in a 1.5 μm thick layer of low molecular weight polymethyl methacrylate (PMMA, Microchem Corp.), which is spin coated on top of the absorber layer. We have used a previously developed two-level hybrid stamp for replicating two V-shaped microchannels (width=50 μm and height = 900 nm) bridged by an array of 200 nanochannels (width and height of 250 nm). The fluidic channels are finally sealed with a lid using PMMA to PMMA thermal bonding. Light from a 785 nm laser diode was focused from the backside of the chip to a spot diameter down to 5 ..m in the absorber layer, yielding a localized heating (Gaussian profile) and large temperature gradients in the liquid in the nanochannels. A laser power of 38 mW yielded a temperature of 40oC in the center of a 10 μm 1/e diameter. Flourescence microscopy was performed from the frontside.