Surface Patterning Technique Research Articles

Mechanisms and Resolution of Photocatalytic Lithography

Remote oxidation via the gas phase by the TiO2 photocatalyst was exploited for a novel technique for solid surface patterning, photocatalytic lithography. A TiO2-coated photomask was placed on an organic or inorganic substrate to be patterned with a small gap (12.5−100 μm), and irradiated with UV light. Heptadecafluorodecyltrimethoxysilane-, octadecyltriethoxysilane-, and methyltriethoxysilane-coated glass plates, a silicon plate, and a copper plate could be patterned in ≥10 min with resolution of 10 μm or better. Such resolution could be obtained even when the intervening gap between the TiO2 film and the substrate was 100 μm. This may be explained in terms of a double excitation scheme, in which not only TiO2 but also a chemical species diffusing from the TiO2 surface or the substrate to be oxidized is excited by the incident light.

All-photoplastic microstencil with self-alignment for multiple layer shadow-mask patterning

A rapid and simple method to fabricate tiny shadow-masks and their use in multi-layer surface patterning with in situ micromechanical alignment is presented. Instead of using silicon micromachining with through-wafer etching to define the thin membrane with etched apertures, we are using photoplastic SU-8-based resist as structural material of both membrane and support rim. Two layers, 5 and 150 μm thick, are structured by lithography and finally released from the surface. The free-standing SU-8 membranes have apertures ranging from 6 to 300 μm. They are placed and mechanically fixed to the surface, which needs to be patterned. Deposition by evaporation of Cr, Au, Al or other material through the membrane apertures results in an accurate 1:1 replication of the aperture pattern. In view of multi-layer patterning, we used in situ micromechanical alignment pins or jigs and achieved an overlay precision of <2 μm in both x- and y-directions. The reusable shadow-masks allows for a low-cost surface patterning technique without the need for photolithography related process steps. It allows unconventional surfaces to be patterned in a rapid and vacuum-clean way on arbitrary surfaces.

Fabrication and application of a full wafer size micro/nanostencil for multiple length-scale surface patterning

A tool and method for flexible and rapid surface patterning technique beyond lithography based on high-resolution shadow mask method, or nanostencil, is presented. This new type of miniaturized shadow mask is fabricated by a combination of MEMS processes and focused ion beam (FIB) milling. Thereby apertures in a 100–500 nm thick low-stress silicon nitride membrane in the size range from <100 nm to >100 μm were made. The stencil device is mechanically fixed on the surface and used as miniature shadow mask during deposition of metal layers. Using this method, aluminum micro- and nanostructures as small as 100 nm in width were patterned. The deposited micro- and nano-scale structures were used as etch mask and transferred into a sub-layer (in our case silicon nitride) by dry plasma etching. High-resolution shadow masking can be used to create micro/nanoscale patterns on arbitrary substrates including mechanically fragile or chemically active surfaces.

Patterning of Solid Surfaces by Photocatalytic Lithography Based on the Remote Oxidation Effect of TiO2

A novel technique for solid surface patterning is developed on the basis of the remote oxidation effect of TiO2 photocatalysts. A TiO2-coated quartz plate was faced to a solid substrate, that is, a glass plate modified with an ultrathin organic layer or silicon, copper, or silver plate, separated by a small gap, and the TiO2 was irradiated with UV light in air through a photomask. As a result, two-dimensional images corresponding to the photomask are obtained. Those images are based on the contrasts of nonoxidized to oxidized surfaces.

Directed assembly of one-dimensional nanostructures into functional networks.

One-dimensional nanostructures, such as nanowires and nanotubes, represent the smallest dimension for efficient transport of electrons and excitons and thus are ideal building blocks for hierarchical assembly of functional nanoscale electronic and photonic structures. We report an approach for the hierarchical assembly of one-dimensional nanostructures into well-defined functional networks. We show that nanowires can be assembled into parallel arrays with control of the average separation and, by combining fluidic alignment with surface-patterning techniques, that it is also possible to control periodicity. In addition, complex crossed nanowire arrays can be prepared with layer-by-layer assembly with different flow directions for sequential steps. Transport studies show that the crossed nanowire arrays form electrically conducting networks, with individually addressable device function at each cross point.

Polymer gels with engineered environmentally responsive surface patterns

The polymer gels called hydrogels may be induced to swell or shrink (taking up or expelling water between the crosslinked polymer chains) in response to a variety of environmental stimuli, such as changes in pH or temperature, or the presence of a specific chemical substrate1. These gels are being explored for several technological applications, particularly as biomedical materials2. When hydrogels swell or shrink, complex patterns may be generated on their surfaces3,4,5,6,7. Here we report the synthesis and controlled modulation of engineered surface patterns on environmentally responsive hydrogels. We modify the character of a gel surface by selectively depositing another material using a mask. For example, we use sputter deposition to imprint the surface of an N-isopropylacrylamide (NIPA) gel with a square array of gold thin films. The periodicity of the array can be continuously varied as a function of temperature or electric field (which alter the gel's volume), and so such an array might serve as an optical grating for sensor applications. We also deposit small areas of an NIPA gel onthe surface of an acrylamide gel; the patterned area can be rendered invisible reversibly by switching the temperature above or below the lower critical solution temperature of the NIPA gel. We anticipate that these surface patterning techniques may find applications in display and sensor technology.

Dynamics of long-pulse laser transfer of micrometer-sized metal patterns as followed by time-resolved measurements of reflectivity and transmittance

Laser-induced transfer of thin films is a simple single-step technique for surface patterning. In this paper the optimization principles and processes are outlined which led to successful application of the long-pulse laser transfer technique. The critical analysis of experiments on ns-pulse laser transfer of thin films of a variety of metals and the optimization study of the long-pulse laser transfer technique suggests that efficient deposition of high-quality patterns of micrometer dimensions can only be expected when using long laser pulses which not only produce ablation of the thin film pattern in solid phase but also maintain sufficient temperature during transfer and even on landing, to ensure film adherence. In order to identify and understand the different time-dependent processes determining the laser transfer, studies using optical and electron microscopy and static and time-resolved optical measurements were performed.

Deposition of micrometer-sized tungsten patterns by laser transfer technique

A simple single-step technique for surface patterning is presented. It is shown that well-adhering micrometer-sized patterns of 100% coverage preserving the shape and dimensions of the ablated area can be deposited by ablating and transferring tungsten thin films in the form of single solid pieces using single pulses of peak power up to 100 mW and 100 μs–1 ms duration from a diode-pumped YAG laser.