Switchable SQUID Fabricated in Loop Geometry from Fe 0.1 Co 0.9 and Pb
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RESEARCH/RESEARCHERS Near-Field Optical Microscope Enables Submicron Direct-Write Laser Micromachining of Diamond Diamond came to the attention of the scientific community as a material that could be useful in microelectronic and microelectromechanical systems applications because of its mechanical, electrical, thermal, and chemical properties. However, diamond is very difficult to work with, due to its hardness. Igor Smolyaninov and Christopher Davis from the Department of Electrical and Computer Engineering of the University of Maryland have developed a technique for microscale processing. Using a standard scanning near-field optical-shear-force microscopy technique, they achieved high-resolution surface ablation of thick chemical-vapor-deposition-(CVD)-grown diamond films. As reported in the October 1 issue of Optics Letters, their method uses nanosecond optical pulses from a Nd:YAG laser operating at 1060-nm wavelength coupled to a multimode optical fiber with an initial core diameter of 150 µm adiabatically tapered to a 100-nm microscope tip and used as a local light source. This arrangement allowed them to deliver a power of ~100 MW/cm2 to a sample region of only 500 nm × 500 nm during a single laser pulse. This power was sufficient for ablating locally the surface of diamond. The ablation process required multiple laser pulses in a given location and may be mediated by an intermediate step in which the diamond is turned into graphite before being ablated. Patterns written on samples were investigated with a shearforce microscope, which was an intrinsic part of their system. Extended use of the optical fiber showed no damage to the tip from either exposure to the laser light or accumulation of graphite. Calculations indicate that the optimum tip diameter is ~λ/3. Thus, even though the diameter for single spots obtained was ~500 nm, the spatial resolution of this micromachining method can be further increased to 50–100 nm by using a pulsed UV laser. CLAUDIU MUNTELE
Electromagnetic Tweezers Enable Simultaneous Positioning and Viewing of Micron-Sized Magnetic Objects The advent of nanotechnology has created a need for techniques that are capable of precisely manipulating and positioning objects that range in size from atomic to micrometer dimensions. Optical trapping methods and microelectromechanical systems (MEMS) have been used for manipulating micron-scale objects of biological interest. For magnetic materials, magnetic 752
tweezers, consisting of permanent or soft coil-wound magnets with macroscopic dimensions, have been employed. Recently,a magnetic material manipulation technique that integrates a low profile magnetic coil and soft ferromagnetic probe has surfaced. This device, which is physically much smaller than other magnetic or optical tweezers, provides several advantages over these other devices, including negligible sample heating, low cost, ability to study particles suspended in a variety of solutions, and simultaneous positioning and optical viewing of samples. In the September 17 issue of Ap
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