Smooth Vertical Surfaces Research Articles

Adhesive force of a single gecko foot-hair.

Geckos are exceptional in their ability to climb rapidly up smooth vertical surfaces. Microscopy has shown that a gecko's foot has nearly five hundred thousand keratinous hairs or setae. Each 30-130 microm long seta is only one-tenth the diameter of a human hair and contains hundreds of projections terminating in 0.2-0.5 microm spatula-shaped structures. After nearly a century of anatomical description, here we report the first direct measurements of single setal force by using a two-dimensional micro-electromechanical systems force sensor and a wire as a force gauge. Measurements revealed that a seta is ten times more effective at adhesion than predicted from maximal estimates on whole animals. Adhesive force values support the hypothesis that individual seta operate by van der Waals forces. The gecko's peculiar behaviour of toe uncurling and peeling led us to discover two aspects of setal function which increase their effectiveness. A unique macroscopic orientation and preloading of the seta increased attachment force 600-fold above that of frictional measurements of the material. Suitably orientated setae reduced the forces necessary to peel the toe by simply detaching above a critical angle with the substratum.

Dry etching of Si field emitters and high aspect ratio resonators using an inductively coupled plasma source

An inductively coupled plasma (ICP) source has been used to generate a Cl2 plasma for the etching of Si field emitters and resonators. An optimized etch condition was used to etch Si field emission devices with controllable sidewall angles as well as good uniformity for large arrays of emitters. A mask erosion technique was used to control the Si emitter profile. The sidewall angle of Si emitters increased from 55° to 75° as plasma pressure was increased from 0.1 to 5.0 mTorr. Sharp tips with good uniformity and a high packing density of 6.25×106 tips/cm2 were fabricated using 200 W ICP source power, 100 W stage power at 1 mTorr with 20 sccm of Cl2 flowing and an ICP source to sample distance of 8 cm. Released Si mechanical resonators were also fabricated with a vertical etch profile and smooth surfaces. An optimized etch condition of 250 W ICP source power and 70 W stage power at 5 mTorr with 20 sccm of Cl2 flow and an ICP source to sample distance of 6 cm provided an etch rate of 219 nm/min and a selectivity to a Ni–Ti mask of 26. Due to the high selectivity and etch rate, resonators and cantilevered beams as thick as 40 μm were fabricated giving improved device performance compared to thinner devices. Submicrometer Si resonators were also fabricated that were 3.1 μm thick with 1.7 μm wide comb drive fingers and 0.2 μm gaps between them.

GaN hexagonal microprisms with smooth vertical facets fabricated by selective metalorganic vapor phase epitaxy

Selective growth of GaN was performed by low-pressure metalorganic vapor phase epitaxy using a mask-patterned GaN epitaxial layer on a (0001) sapphire substrate. GaN hexagonal microprisms of 5–16 μm in diameter, with smooth vertical facets and no ridge growth, were fabricated on a (0001) sapphire substrate. This vertical {11̄00} facet of GaN was parallel to a {112̄0} face of the sapphire substrate. Both the use of an epitaxial GaN layer on the sapphire substrate and low working pressure contributed to obtaining smooth top and vertical facet surfaces. Also, the stripe structures of GaN were obtained that had a rectangular cross section. Moreover, the selection of the mask-patterning direction was found to be important because of the 30° rotation of the crystallographic orientation between the GaN layer and the sapphire substrate.

Reactive ion etching of β-SiC in CCl 2 F 2 /O 2

For the first time, the reactive ion etching (RIE) of β-SiC in CCI2F2/O2 gas mixture is reported. The addition of oxygen to the CC12F2 does not appear to enhance the etch rate, however, the RF power and the DC bias conditions prove to be the dominant factors for controlling the etch rate. In addition, fine line structures with vertical walls and smooth etched surfaces are achieved.

Locomotor adaptations in the disc‐winged bat Thyroptera tricolor. I. Functional organization of the adhesive discs

AbstractLocomotor capability on smooth vertical surfaces is rare in mammals. The adhesive discs on thumbs and soles of bats of the family Thyropteridae are uniquely specialized for this purpose, but their functional organization remains virtually unexplored. The face of the discs is concave, has a characteristic dermatoglyphic pattern, and is permanently moist. Each disc is supported by a biconcaval fibrocartilagenous framework; its circular “rim” is divided into 60–80 chambers, each accommodating a sudoriparous gland which discharges on the disc face. Glandular form and cytology are unique, reflecting special functional adaptations. Other significant adaptations involve the epidermis, distribution of adipose tissue, extrinsic muscle insertions, disc relations to digital joints, and distribution of certain sensory endings. The discs have no intrinsic musculature and are manipulated from without. Experiments with living Thyroptera and analysis of the internal organization of the discs verify that their functional mode is suctorial rather than some other adhesive mechanisms; special relationships within the thumb discs suggest that the adhesive force may be to some extent adjustable under normal use.