Proposed magneto-electrostatic ring trap for neutral atoms

We propose a novel trap for confining cold neutral atoms in a microscopic ring using a magneto-electrostatic potential. The trapping potential is derived from a combination of a repulsive magnetic field from a hard drive atom mirror and the attractive potential produced by a charged disk patterned on the hard drive surface. We calculate a trap frequency of [29.7, 42.6, 62.8] kHz and a depth of [16.1, 21.8, 21.8] MHz for [133Cs, 87Rb, 40K], and discuss a simple loading scheme and a method for fabrication. This device provides a one-dimensional potential in a ring geometry that may be of interest to the study of trapped quantum degenerate one-dimensional gases.Comment: 4 pages, 2 figures; revised, including new calculations and further discussio

Production of carbonized micro-patterns by photolithography and pyrolysis

The preparation of carbon micro-patterns is reported in this paper. Different carbon micro-patterns were created using photolithography of the epoxy-based negative photoresist SU-8. Photoresist patterns were optimized in terms of resolution and aspect ratio and subsequently subjected to pyrolysis to obtain carbonized and conductive 3D structures. The latter step requires the optimization of the resist cross-linking time as well as the temperature and time of the resist post-bake. This step is crucial in order to avoid any severe modification of the geometry of the patterns produced during the actual pyrolysis. By observing optical and scanning electron microscope images, the morphology of the structures before and after pyrolysis was studied and the same patterns were also characterized by a laser probe profilometer. Finally, the thus obtained carbon patterns on Si wafers were used to carry out cell culture tests with Neural Stem Cells (NSC). The adhesion and the arrangement of the stem cells were analyzed to verify the ability of the patterned substrates to guide the orientation and, therefore, the differentiation of the cells

Capillary origami: spontaneous wrapping of a droplet with an elastic sheet

The interaction between elasticity and capillarity is used to produce three dimensional structures, through the wrapping of a liquid droplet by a planar sheet. The final encapsulated 3D shape is controlled by tayloring the initial geometry of the flat membrane. A 2D model shows the evolution of open sheets to closed structures and predicts a critical length scale below which encapsulation cannot occur, which is verified experimentally. This {\it elastocapillary length} is found to depend on the thickness as $h^{3/2}$, a scaling favorable to miniaturization which suggests a new way of mass production of 3D micro- or nano-scale objects.Comment: 5 pages, 5 figure

Fabrication of Resorcinol-Formaldehyde Xerogel based High Aspect Ratio 3-D Hierarchical C-MEMS Structures

We demonstrate a novel method to fabricate arrays of resorcinol- formaldehyde xerogel (RFX) based high aspect ratio (HAR) three- dimensional (3-D) hierarchical C-MEMS structures. Starting from a master pattern of HAR 3-D posts fabricated in SU-8 negative photoresist by photolithography, a negative PDMS stamp with arrays of holes was prepared by micromolding. The PDMS stamp was then used to fabricate HAR 3-D RFX posts by replica molding. The 3-D RFX posts thus fabricated were electrosprayed with SU-8 or an RF sol in the form of submicron or nano sized droplets and followed by pyrolysis to yield HAR 3-D hierarchical carbon posts. To characterize their use in C-MEMS based batteries, galvanostatic (charge and discharge) experiments on RFX derived carbon showed that it can be reversibly intercalated with Li ions and possesses superior intercalation properties as compared to SU- 8 derived carbon which is a widely used material in C-MEMS

Surface scattering velocities in III-nitride quantum well laser structures via the emission of hybrid phonons

We have theoretically and numerically studied nitride-based quantum well (QW) laser structures. More specifically, we have used a QW made with III-nitride where the width of the barrier region is large relative to the electron mean free path, and we have calculated the electron surface capture velocities by considering an electron flux which is captured into the well region. The process is assisted by the emission of the longitudinal optical phonons as predicted by the hybrid (HB) model. The results of surface capture velocities via the emission of HB phonons are compared to the emission of the dielectric continuum phonons (Zakhleniuk et al 1999 Phys. Status Solidi a 176 79). Our investigation shows that the two different phonon models predict almost the same results for the non-retarded limit. Furthermore, the surface capture velocities strongly depend on the size of the structure and the heterostructure materials. Lastly, a comparison to the recent experimental values shows that our model could accurately describe the experimentally measured parameters of the quantum capture processes

A comparative investigation of thickness measurements of ultra-thin water films by scanning probe techniques

The reliable operation of micro and nanomechanical devices necessitates a thorough knowledge of the water film thickness present on the surfaces of these devices with an accuracy in the nm range. In this work, the thickness of an ultra-thin water layer was measured by distance tunnelling spectroscopy and distance dynamic force spectroscopy during desorption in an ultra-high vacuum system, from about 2.5 nm up to complete desorption at 1E-8 mbar. The tunnelling current as well as the amplitude of vibration and the normal force were detected as a function of the probe-sample distance. In these experiments, a direct conversion of the results of both methods is possible. From the standpoint of surface science, taking the state-of-the-art concerning adsorbates on surfaces into consideration, dynamic force spectroscopy provides the most accurate values. The previously reported tunnelling spectroscopy, requiring the application of significantly high voltages, generally leads to values that are 25 times higher than values determined by dynamic force spectroscopy

Decoupled cantilever arms for highly versatile and sensitive temperature and heat flux measurements

Microfabricated cantilever beams have been used in microelectromechanical systems for a variety of sensor and actuator applications. Bimorph cantilevers accurately measure temperature change and heat flux with resolutions several orders of magnitude higher than those of conventional sensors such as thermocouples, semiconductor diodes, as well as resistance and infrared thermometers. The use of traditional cantilevers, however, entails a series of important measurement limitations, because their interactions with the sample and surroundings often create parasitic deflection forces and the typical metal layer degrades the thermal sensitivity of the cantilever. The paper introduces a design to address these issues by decoupling the sample and detector section of the cantilever, along with a thermomechanical model, the fabrication, system integration, and characterization. The custom-designed bi-arm cantilever is over one order of magnitude more sensitive than current commercial cantilevers due to the significantly reduced thermal conductance of the cantilever sample arm. The rigid and immobile sample section offers measurement versatility ranging from photothermal absorption, near-field thermal radiation down to contact, conduction, and material thermal characterization measurements in nearly identical configurations.United States. Dept. of Energy. Division of Materials Sciences and Engineering (DE-FG02-02ER45977)United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (UIUC FA9550-08-1-0407