Rational Design of Etchants For Electroless Porous Silicon Formation

From fundamental considerations of the surface chemistry of Si etching in fluoride solutions as well as pore formation and propagation, we develop a mechanistic understanding of what must be known for rational development of etchants: (1) an acidic fluoride solution because the presence of OH- promotes step flow etching, (2) sufficiently high fluoride concentration compared to the oxidant concentration, (3) the oxidant must be able to inject holes into the Si valance band at a sufficient rate, hence E degrees \u3e similar to 0.7 V is required, (4) oxide formation needs to be slow or nonexistent so as to avoid the formation of a uniform oxide and associated electropolishing, (5) reduction of the oxidant must lead to soluble products, (6) film homogeneity is enhanced if the oxidant\u27s half-reaction does not evolve gas, and finally (7) the net etching reaction has to be sufficiently anisotropic to support pore nucleation and propagation

Electroless Etching of Si with IO-3 and Related Species

We have previously derived seven requirements for the formulation of effective stain etchants and have demonstrated that Fe3+, Ce4+, and VO2 (+) + HF solutions are highly effective at producing nanocrystalline porous silicon. Here, we show that Cl-2, Br-2, I-2, ClO3 (-), BrO3 (-), IO3 (-), I-, and I-3 (-) induce etching of silicon when added to HF. However, using the strict definition that a pore is deeper than it is wide, we observe little evidence for porous layers of significant thickness but facile formation of pits. Iodate solutions are extremely reactive, and by the combined effects of IO3 (-), I-3 (-), I-2, and I-, these etchants roughen and restructure the substrate to form a variety of structures including (circular, rectangular, or triangular) pits, pyramids, or combinations of pits and pyramids without leaving a porous silicon layer of significant thickness

Charge-Dissipative Electrical Cables

Electrical cables that dissipate spurious static electric charges, in addition to performing their main functions of conducting signals, have been developed. These cables are intended for use in trapped-ion or ionizing-radiation environments, in which electric charges tend to accumulate within, and on the surfaces of, dielectric layers of cables. If the charging rate exceeds the dissipation rate, charges can accumulate in excessive amounts, giving rise to high-current discharges that can damage electronic circuitry and/or systems connected to it. The basic idea of design and operation of charge-dissipative electrical cables is to drain spurious charges to ground by use of lossy (slightly electrically conductive) dielectric layers, possibly in conjunction with drain wires and/or drain shields (see figure). In typical cases, the drain wires and/or drain shields could be electrically grounded via the connector assemblies at the ends of the cables, in any of the conventional techniques for grounding signal conductors and signal shields. In some cases, signal shields could double as drain shields

Working group written presentation: Trapped radiation effects

The results of the Trapped Radiation Effects Panel for the Space Environmental Effects on Materials Workshop are presented. The needs of the space community for new data regarding effects of the space environment on materials, including electronics are listed. A series of questions asked of each of the panels at the workshop are addressed. Areas of research which should be pursued to satisfy the requirements for better knowledge of the environment and better understanding of the effects of the energetic charged particle environment on new materials and advanced electronics technology are suggested

Spatially and Temporally Distinct Encoding of Muscle and Kinematic Information in Rostral and Caudal Primary Motor Cortex

The organizing principle of human motor cortex does not follow an anatomical body map, but rather a distributed representational structure in which motor primitives are combined to produce motor outputs. Electrophysiological recordings in primates and human imaging data suggest that M1 encodes kinematic features of movements, such as joint position and velocity. However, M1 exhibits well-documented sensory responses to cutaneous and proprioceptive stimuli, raising questions regarding the origins of kinematic motor representations: are they relevant in top-down motor control, or are they an epiphenomenon of bottom-up sensory feedback during movement? Here we provide evidence for spatially and temporally distinct encoding of kinematic and muscle information in human M1 during the production of a wide variety of naturalistic hand movements. Using a powerful combination of high-field functional magnetic resonance imaging and magnetoencephalography, a spatial and temporal multivariate representational similarity analysis revealed encoding of kinematic information in more caudal regions of M1, over 200 ms before movement onset. In contrast, patterns of muscle activity were encoded in more rostral motor regions much later after movements began. We provide compelling evidence that top-down control of dexterous movement engages kinematic representations in caudal regions of M1 prior to movement production

Regenerative Electroless Etching of Silicon

Regenerative electroless etching (ReEtching), described herein for the first time, is a method of producing nanostructured semiconductors in which an oxidant (Ox1) is used as a catalytic agent to facilitate the reaction between a semiconductor and a second oxidant (Ox2) that would be unreactive in the primary reaction. Ox2 is used to regenerate Ox1, which is capable of initiating etching by injecting holes into the semiconductor valence band. Therefore, the extent of reaction is controlled by the amount of Ox2 added, and the rate of reaction is controlled by the injection rate of Ox2. This general strategy is demonstrated specifically for the production of highly luminescent, nanocrystalline porous Si from the reaction of V2O5 in HF(aq) as Ox1 and H2O2(aq) as Ox2 with Si powder and wafers

Perceptually relevant remapping of human somatotopy in 24 hours

Experience-dependent reorganisation of functional maps in the cerebral cortex is well described in the primary sensory cortices. However, there is relatively little evidence for such cortical reorganisation over the short-term. Using human somatosensory cortex as a model, we investigated the effects of a 24 hr gluing manipulation in which the right index and right middle fingers (digits 2 and 3) were adjoined with surgical glue. Somatotopic representations, assessed with two 7 tesla fMRI protocols, revealed rapid off-target reorganisation in the non-manipulated fingers following gluing, with the representation of the ring finger (digit 4) shifted towards the little finger (digit 5) and away from the middle finger (digit 3). These shifts were also evident in two behavioural tasks conducted in an independent cohort, showing reduced sensitivity for discriminating the temporal order of stimuli to the ring and little fingers, and increased substitution errors across this pair on a speeded reaction time task