The effects of colloidal nanotopography on initial fibroblast adhesion and morphology

Colloidal lithography offers a simple, inexpensive method of producing irregular nanotopographies, a pattern not easily attainable utilizing conventional serial writing processes. Colloids with 20- or 50-nm diameter were utilized to produce such an irregular topography and were characterized by calculating the percentage area coverage of particles. Interparticle and nearest neighbor spacing were also assessed for the individual colloids in the pattern. Two-way analysis of variance (ANOVA) indicated significant differences between the number of fibroblasts adhering to planar, 20-, and 50-nm-diameter colloidal topographies, the number of fibroblasts adhering to the substrates at the time intervals studied, namely 20 min, 1 h, and 3 h and significant interaction between time and topography on fibroblast adhesion (P<0.01). Tukey tests were utilized for sensitive identification of the differences between the sample means and compounded ANOVA results. Cytoskeletal and general cell morphology were investigated on planar and colloidal substrates, and indicated cells in contact with irregular nanotopographies exhibit many peripheral protrusions while such protrusions are absent in cells on planar control surfaces. These protrusions are rich in microtubules on 20-nm-diameter colloidal surfaces while microfilaments are prevalent on 50-nm-diameter surfaces. Moreover, by 3 h, cells on the colloidal substrates initiate cell-cell adhesions, also absent in controls

SiGe p-channel MOSFETs with tungsten gate

A self-aligned SiGe p-channel MOSFET tungsten gate process with 0.1 μm resolution is demonstrated. Interface charge densities of MOS capacitors realised with the low pressure sputtered tungsten process are comparable with thermally evaporated aluminium gate technologies (5×1010cm-2 and 2×1011 cm -2 for W and Al, respectively). Initial results from 1 μm gate length SiGe p-channel MOSFETs using the tungsten-based process show devices with a transconductance of 33 mS/mm and effective channel mobility of 190 cm

Dry etching and sputtering

Dry etching is an important process for micro- and nanofabrication. Sputtering effects can arise in two contexts within a dry-etch process. Incoming ions cause removal of volatile products that arise from the interaction between the dry-etch plasma and the surface to be etched. Also, the momentum transfer of an incoming ion can cause direct removal of the material to be etched, which is undesirable as it can cause electrical or optical damage to the underlying material. This is largely avoided in dry-etch processes by use of reactive chemistries, although in some processes this component of the etching can be significant. Etch processes, both machine type and possible etch chemistries, are reviewed. Methods of characterizing the electrical and optical damage related to ion impact at the substrate are described. The use of highly reactive chemistries and molecular constituents within the plasma is best for reducing the effects of damage

The response of fibroblasts to hexagonal nanotopography fabricated by electron beam lithography

It has been known for many years that cells will react to the shape of their microenvironment. It is more recently becoming clear that cells can alter their morphology, adhesions, and cytoskeleton in response to their nanoenvironment. A few studies have gone further and measured cellular response to high-adhesion nano-materials. There have, however, been practical difficulties associated with genomic studies focusing on low-adhesion nanotopographies. Because of advancement in fabrication techniques allowing the production of large area of structure and the ability to amplify mRNA prior to microarray hybridization, these difficulties can be overcome. Here, electron beam lithography has been used to fabricate arrays of pits with 120 nm diameters, 100 nm depth and 300 nm center to center spacing in hexagonal arrangement. Electron and fluorescent microscopies have been used to observe morphological changes in fibroblasts cultured on the pits. 1.7k gene microarray was used to gauge genomic response to the pits. The results show reduction in cellular adhesion, decrease in spreading, and a broad genomic down-regulation. Also noted was an increase in endocytotic activity in cells on the pits

Issues in etching compound and Si-based devices

Ion-induced damage is an important issue in Ill-V and Si-Ge devices. The principal cause of damage is the introduction of traps and point defects by ions penetrating into the semiconductor. At the low ion energies used in modem process technology (100eV say) the bulk of the ions remain on or within a few nm of surfaces. However some channel along the (110) direction and so penetrate into the semiconductor to a depth of 30 to 50 nm. In high electron mobility transistors (HEMT's) with f(T) greater than 100 GHz, the active current carrying layer is only 30 to 50 nm below the surface. In compound semiconductors it is usually impossible to anneal such damage away. An analytic model of this channelling has been developed and its accuracy checked by measuring the penetration of ions produced by a very low energy implantation. An important finding is while atomic ions (e.g. Cl+) can channel and so cause damage, molecular ions (e.g. Cl+) do not. This can be used to predict processes that will be suitable for low damage

Imaging magnetic domain structure in sub-500 nm thin film elements

Magnetic imaging in the transmission electron microscope (TEM) has been used to examine submicron elements with the aim of discovering down to what element size complex domain patterns can form. The elements were squares, circles, triangles, and pentagons in the size range 100-500 nm and were made from 36 nm Co films or 8 nm Ni80Fe20 (NiFe) with in-plane magnetization. The magnetic domain structures in these elements were imaged at high resolution using the differential phase contrast imaging mode in a TEM. Nonuniform magnetization structures were seen in the images. Vortices were present at remanence in all shapes of 36-nm-thick Co elements down to 100 nm size and in circular NiFe elements down to 116 nm diameter. Triangular NiFe elements did not have a vortex state at remanence, instead the magnetization curved round within the element but did not achieve complete flux closure. In simulations of square and circular NiFe elements, it was found that defects at the edges of the elements encouraged reversal by a vortex mechanism, whereas for simulated elements with no defects, reversal was by rotation and occurred at much lower fields

Optimizing substrate disorder for bone tissue engineering of mesenchymal stem cells

A key tenet of bone tissue engineering is the development of scaffold materials that can stimulate stem cell differentiation in the absence of chemical treatment to become osteoblasts without compromising material properties. Recently, the authors have shown that two types of slightly disordered arrays of nanopits stimulate human mesenchymal stem cells (MSCs) to produce bone mineral in vitro, in the absence of osteogenic supplements. In this article, they aim at optimizing the topographic parameters to stimulate MSCs to form bone cells. They have developed a high-speed electron beam technique to pattern 1 cm(2) areas with 10(9) dots. In three steps, they (1) systematically changed the degree of disorder from +/- 30 to 150 nm from a perfect square arrangement with a 300 nm pitch, (2) changed the pit diameter from 50 to 193 nm, and (3) explored the importance of pits versus pillars. They found that arrays of pillars 35 nm tall with a diameter of 193 nm and a disorder of +/- 30 nm provided the optimal conditions for stimulating MSCs to form bone cell