Length Regime Research Articles

Highly suppressed short-channel effects in ultrathin SOI n-MOSFETs

We have investigated short-channel effects of ultrathin (4-18-nm thick) silicon-on-insulator (SOI) n-channel MOSFET's in the 40-135 nm gate length regime. It is experimentally and systematically found that the threshold voltage (V/sub th/) roll-off and subthreshold slope (S-slope) are highly suppressed as the channel SOI thickness is reduced. The experimental 40-nm gate length, 4-nm thick ultrathin SOI n-MOSFET shows the S-slope of only 75 mV and the /spl Delta/V/sub th/ of only 0.07 V as compared to the value in the case of the long gate-length (135 nm) device. Based on these experimental results, the remarkable advantage of an ultrathin SOI channel in suppressing the short-channel effects is confirmed for future MOS devices.

Facet‐Free Selective Silicon Epitaxy by Reduced‐Pressure Chemical Vapor Deposition Process Evaluation and Impact on Shallow Trench Isolation

A facet‐free, selective epitaxy process has been identified using the chemistry in single‐wafer reduced‐pressure chemical vapor deposition. The process window has been explored with respect to shallow trench isolation, simultaneous polycrystalline silicon (polysilicon) deposition, facet formation, and electrical parameters of polysilicon sheet resistance and junction leakage current. The isolation structure can be severely degraded by aggressive pre‐epitaxy bakes through volatile SiO formation; however, the impact is minimized when the prebake is limited to 900°C, 60 s. Concurrent deposition of polysilicon and silicon epitaxy can result in significantly different deposition rates. Low process pressures result in greater relative epitaxy growth rates and high pressures result in lower relative epitaxy deposition rates. The facet‐free process depends heavily on both the gate sidewall structure and the process conditions, where the combination of an undercut into the pad oxide and the nitride sidewall with the process pressure yield a reliably facet‐free process. Electrical results demonstrate that standard Ti or Co self‐aligned silicidation can be extended into a 0.1 μm gate length regime. © 1999 The Electrochemical Society. All rights reserved.

Multiscale modeling of thin film growth

Advances have been made in multiscale modeling strategies for thin film growth by physical and chemical vapor deposition techniques. Considerable efforts have been devoted in the past decade to develop physical models and simulation strategies within each length and time-scale regime. As a result of this progress, it has become feasible to construct thin film growth model spanning length scale from the atomic level to process equipment size. Examples include chemical vapor deposition of diamond and GaAs. Two major areas of length scale-linking activitiesare firstly, macro- to microscale (depositon system to film morphology); and secondly, micro- to atomic scale (film morphology to atomic level description of reaction processes).

Viscoelasticity of Concentrated Isotropic Solutions of Semiflexible Polymers. 1. Model and Stress Tensor

The viscoelastic behavior of entangled solutions of semiflexible chains is discussed. After identifying the different possible regimes of concentration and chain length in such a solution, attention is focused on a “tightly-entangled” regime in which the polymer is confined to a tube of diameter less than its persistence length. A tube model analogous to the Doi−Edwards model is introduced to describe this regime. A general expression for the stress tensor of a solution of wormlike chains is derived, which may be applied to any concentration regime, and three intramolecular stress contributions are identified: a curvature contribution arising from forces that oppose transverse deformation or rotation of chain segments, a tension contribution arising from tangential forces that resist stretching or compression of the chain, and an orientational contribution that reduces in the appropriate limit to the Brownian stress of a rigid-rod solution. Intermolecular stress contributions are also calculated. A quali...

Electron heating effects in diffusive metal wires

We have investigated the electron heating in metallic diffusive wires of varying length at liquid-helium temperature by measuring the electric noise. The local increase of the electron temperature can be essential already for small currents and is well described by a heat-diffusion equation for the electrons. Depending on the electron thermal conductance and the electron–phonon coupling in the wire, different length regimes are identified. The quantitative knowledge of the electron temperature is important for analysis of nonequilibrium effects involving current heating in mesoscopic wires.

Phase Distribution in a Disordered Chain and the Emergence of a Two-Parameter Scaling in the Quasiballistic to the Mildly Localized Regime

We study the phase distribution of the complex reflection coefficient in different configurations as a disordered 1D system evolves in length, and its effect on the distribution of the 4-probe resistance R4. The stationary (L → ∞) phase distribution is almost always strongly non-uniform and is in general double-peaked with their separation decaying algebraically with growing disorder strength to finally give rise to a single narrow peak at infinitely strong disorder. Further in the length regime where the phase distribution still evolves with length (i.e. in the quasiballistic to the mildly localized regime), the phase distribution affects the distribution of the resistance in such a way as to make the mean and the variance of log (1+R4) diverge independently with length with different exponents. As L → ∞, these two exponents become identical (unity). Obviously, these facts imply two relevant parameters for scaling in the quasiballistic to the mildly localized regime finally crossing over to one-parameter scaling in the strongly localized regime.

Epitaxy and chainlength dependent strain in self-assembled monolayers

We use grazing incidence x-ray diffraction to systematically study the structure of an archetypal self-assembled monolayer as a function of the hydrocarbon chain length, n. The monolayers consists of n-alkyl thiol molecules, CH3(CH2)n−1SH (Cn, 10⩽n⩽30), self-assembled on single crystal Au(111) surfaces. At room temperature, the 2D structure is described by a C(4×2) unit mesh for all chain lengths. However, we demonstrate that there is a systematic dependence of the tilt structure (i.e., the tilt angle and tilt direction) of the hydrocarbon chains as a function of the chain length. Furthermore, we show that the monolayer structures are characterized by distinct “long’’ (n⩾16) and “short’’ (n⩽14) chain length regimes, as well as a smooth variation of the structural parameters within each regime. We associate these systematic structural changes with the conflicting requirements of epitaxy and molecular packing, and argue that the driving force is the changing intra-layer interaction strength (which is proportional to hydrocarbon chain length). We believe that these phenomena should be characteristic of the behavior of self-assembled monolayers, as well as the more general class of “soft/hard’’ interfaces.

A numerical simulation of muscle spindle ensemble encoding during planar movement of the human arm.

We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located within muscles of this limb. To accomplish this we developed a numerical simulation which could provide estimates of the length regimes experienced by a set of model receptors located within some of the principal muscles of the human arm during planar movement of this limb. These receptors were assumed to have characteristics analogous to those associated with a simple model of muscle spindle signalling of movement. To this end each spindle had proprioceptive 'channels' associated with it. These corresponded to primary and secondary spindle afferent fibers which could provide independent afferent output regarding the parent muscle the spindle monitored. The angles of the shoulder and elbow joints attained by subjects performing a task requiring movement of the right arm in a horizontal plane to a static visual target were recorded. For this angular data the lengths and rates of change of lengths experienced by muscle fascicles, and hence the model spindles, during movement were calculated by means of the numerical simulation. The discharge rates of the simulated spindles during the movement were calculated to derive a measure of the depth of modulation, induced by the movement, for each spindle. These values were then summed for all spindles to provide a first-order approximation of spindle ensemble coding of the movement. Significant correlations (P < 0.0001, Spearman's rank order) were found between the resulting ensemble encodings and, in order of significance, the angular velocity of the shoulder joint (rS = 0.945), the tangential velocity of the hand (rS = 0.942), and the angular velocity of the elbow joint (rS = 0.917). Correlations between the angular positions of the shoulder (rS = -0.623) and elbow (rS = 0.628) were lower. These findings indicate that the ensemble profiles of the simulated muscle spindles, encode information regarding kinematic parameters of movements related to both intrinsic and extrinsic coordinate systems. This suggests that motor structures capable of deriving such an ensemble encoding would be in a position to perform the sensory-motor transformations between intrinsic and extrinsic frames of reference necessary for controlling movements planned in extrinsic coordinates.

Method for Measuring Short‐Crack R‐Curves without Calibration Parameters: Case Studies on Alumina and Alumina/Aluminum Composites

A method to measure short‐crack R‐curves is introduced which does not require an independent determination of calibration factors and which utilizes an equilibrium crack shape condition to compute the shape factor of a surface crack, R‐curves of an alumina with two different grain sizes and of an aluminum/alumina composite were measured in the crack length regime of below 100 μm up to almost 1000 μm. Calculated and experimentally obtained crack depth profiles were in good agreement with deviations being between −22% and +26% for the crack ellipticity and confirmed the reliability of the method.

Physics in 100 Tesla

Within Europe, plans are well advanced for the construction of a 100 Tesla prototype magnet. The availability of such fields, having a duration of several milliseconds, creates an opportunity for much new science. By considering the new regimes of magnetic length and cyclotron energy, some promising areas for such research are identified, with examples drawn from the fields of semiconductors, metals, magnetism and superconductivity.

Dynamics of DNA molecules in agarose gel under sinusoidal electric fields.

The dynamics of DNA molecules in agarose gel has been studied by measuring the birefringence in sine wave electric fields. It was found that the birefringence is the sum of a direct current (dc) component and several harmonics of the field frequency. A detailed study of these components was performed. It was found that the dynamics of DNA molecules under these conditions can be explained by a W conformation which is not detected under dc electric fields. The variation of the field frequency gives several relaxation modes in the birefringence signal, reflecting the known dynamic behavior of DNA molecules found in the reputation with elongation of the tube length regime.

Growth of juvenile halibut ( Hippoglossus hippoglossus) related to temperature, day length and feeding regime

Experimental studies with farmed juvenile halibut, Hippoglossus hippoglossus, were undertaken to optimize rearing procedures. Extended feeding period and/or day length did not significantly increase growth rates of juvenile halibut of 5 to 20 g wet weight. Growth was strongly affected by temperature, and highest growth rates were obtained at 13°C followed by 10, 16 and 7°C for juveniles of 20 to 90 g. Growth rate declined with size in one of two experiments in this size interval. Q 10 of daily growth rate between 7 and 10°C varied from 2.5 to 3.0. Individual growth always varied highly within the temperature treatments (overall range −0.3 – 3.5%·d −1), but significant size rank correlations were maintained during the 12-week experiment. Juvenile halibut grew approximately isometrically from 20 to 90 g. Weight-specific oxygen consumptions of 80 g juveniles averaged 140 and 200 mg O 2 (kg·h) −1 at 10 and 16°C, respectively, and this is comparable to rates measured for other flatfish species.

Group velocity of large-amplitude electromagnetic waves in a plasma.

The nonlinear group velocity of a laser pulse propagating in a cold underdense unmagnetized plasma is examined. Analytical expressions for the group velocity are derived for various pulse length regimes. These expressions reduce to the usual \ensuremath{\partial}\ensuremath{\omega}/\ensuremath{\partial}k form for small amplitude and are verified for aribtrary amplitude using particle in cell simulations on a cyclic mesh. We find that the leading edge of a pulse moves at the linear group velocity and that the phase velocity of the excited wake is less than the group velocity of the pulse for symmetrically shaped pulses. The techniques used can be applied to other waves in a plasma.

Stable growth and kinetic roughening in electrochemical deposition.

We studied kinetic roughening of copper which was electrodeposited at slow rates. The surfaces showed a unique scaling. In the shorter length regime, the interface width scaled with the length scale $L$ as ${L}^{\ensuremath{\alpha}}$ ($\ensuremath{\alpha}=0.87\ifmmode\pm\else\textpm\fi{}0.05$). In the longer length regime, the width scaled with the deposition time $t$ as ${t}^{\ensuremath{\beta}}$ ($\ensuremath{\beta}=0.45\ifmmode\pm\else\textpm\fi{}0.05$). The value of $\ensuremath{\alpha}+\frac{\ensuremath{\alpha}}{\ensuremath{\beta}}$, 2.8, is much larger than 2 predicted for the case where the growing direction is normal to the surface everywhere. The scaling behavior is interpreted as the result of enhanced growth of the protrusions owing to nonlocal Laplacian growth effect.

Life Cycle and Population Structure of the Polychaete Ficopomatus enigmaticus (Serpulidae) in Mar Chiquita Coastal Lagoon, Argentina

Ficopomatus enigmaticus, a polychaete inhabiting the subtidal zone in the Mar Chiquita coastal lagoon, builds reef-like aggregates that facilitate silt accumulation. To describe the life cycle, samples were take monthly from September 1984 to September 1985. In contrast with other polychaetes, it has two oocyte generations per year; maturation of the oocytes takes approximately 4 mo. Temperature level and day length regime do not appear as environmental signals to the onset of oogenesis, although they possibly affect oogenesis growth. Two periods of spawning and recruitment were observed in November–December and April–May, when water temperature is above 18°C. Hermaphroditic individuals were not found. Sex ratio was male-biased in all months, significantly in November, February, and August (p<0.001). Monthly size-frequency distributions show distinct year-classes with early (November–December) and late (April–May) recruitment. Early recruited cohorts have two spawning periods during a 24-mo lifespan. Late cohorts have one spawning period during their 20-mo lifespan. The life cycle of this species can be summarized as follows: annual iteroparous—1 to 2 batches of small eggs per female during each lifespan, free spawning, planktotrophic larvae, sedentary suspension-feeder worms.

Performance of modulation-doped charge-coupled devices (MD-CCD's) in the microwave and millimeter-wave bands

A two-phase, modulation-doped charge coupled device (MD-CCD) has been characterized by both phase shift and charge transfer efficiency (CTE) measurements from 1.25 MHz to 16.4 GHz. Both two-dimensional transient simulations and experimental evidence support the conclusion that the cutoff frequency for transport of discrete charge packets emulates the cutoff frequency of small signal HEMT devices in the short gate length regime. These simulations predict a CTE of almost 0.999 at 40 GHz for an In/sub 0.53/Ga/sub 0.47/As channel device. The device is fabricated using conventional MMIC processing techniques. In addition, measurement methods used for characterization of a prototype 5-stage delay line chip agree well with simulations using a new CCD SPICE model. >

Fine structure of the free-living parakeet pineal in relation to the breeding cycle.

Seasonal changes in the ultrastructure of the free-living Rose-Ringed Parakeet Psittacula krameri pineal were examined in relation to the sub-tropical environment and seasonal reproduction. Dark and light pinealocytes of the presumptive neuroendocrine cell line predominated, while supporting cells, ependymal cells, myelinated and non-myelinated nerve fibers with nerve endings, and regressed photoreceptor elements were also observed. Unlike in pineals of many animals, particularly mammals, the presence of dense-core vesicles (DCVs) with varying core density, and absence of clear vesicles and vacuoles with flocullent material, indicate the involvement of DCVs in the synthesis and secretion of pineals principle/s. In November (pre-breeding) when the day length registered a drop to LD 10:14, pinealocytes showed significantly decreased and smaller DCVs and mitochondria, nuclei with heterochromatin, and greater distribution of glycogen and lipid droplets, all indicating low pineal metabolic activity. During the shortest day regime from December to March, when the birds peaked breeding, the number and size of DCVs and mitochondria increased, and Golgi body-endoplasmic reticulum-lysosome complex (GERL) was very well defined. Images of DCVs suggested possible secretion of pineal principle/s by dissolution, and exocytosis. Coincidence of these features with peak gonadotrophic (circulating LH) and spermatogenic and testicular endocrine activity described previously suggested an active turnover of pineal products during this short day length regime when parakeets breed. In contrast, during the post-breeding season (April onwards), when the day-length increased to LD 13:11 and hypophyseal-gonadal function was down, nuclei and RER continued to show active profile, the Golgi body and associated complex were moderately seen, and the DCVs and mitochondria were significantly smaller and lesser. It is therefore probable that the pineal is an important relay to translate cues related to less drastic sub-tropical environmental change into DCV-linked neurohormones that in turn may be involved in modulating seasonal breeding in parakeets.

Scale-invariant spatial patterns in genome organization

Eukaryotic genomes are characterized by coding regions interspersed within non-coding sequences, creating irregular dispersal patterns. Fractal analysis was applied to the study of this dispersed organization of eukaryotic genomes. The results show that eukaryotic genomes possess two length regimes - a short ordered length scale, and a fractal regime with fractal dimensions ranging from 0.21±0.02 to 0.84±0.02. Fractal scaling provides clues to the origin and evolution of sequence patterns within genomes, and provides us with tools necessary to characterize such patterns in detail.

A SEX DIFFERENCE IN THE PROPENSITY TO ENTER DIRECT/DIAPAUSE DEVELOPMENT: A RESULT OF SELECTION FOR PROTANDRY.

In monandrous mating systems with discrete nonoverlapping generations males should maximize the expected number of matings by starting to emerge before females. This is known as protandry. Moreover, Evolutionarily Stable Strategies (ESS) models show that the male emergence curve should be abruptly truncated before female emergence has ceased. In temperate areas where many insects have partial second generations, we accordingly predict that males should enter diapause development at an earlier date than should females, as a result of late-emerging males being penalized in terms of fewer mating opportunities. The decision to diapause or to develop directly is usually mediated by response to environmental stimuli of which day length is the most important. Hence we predict that the mechanism by which males enter diapause at an earlier date than females will be that of the male reaction norm for diapause development being shifted towards longer day lengths when compared to that of females. As a result of the greater tendency of males to enter diapause development, partial second generations that develop directly should be female biased. As a corollary, first generations should be male biased because some males of the first generation are from the previous year. The prediction that males should enter diapause development earlier in the season, i.e., at longer day lengths, as compared to females was corroborated by rearing Pieris napi under a variety of critical day length regimes producing mixed broods of directly developing and diapausing individuals, and by outdoor rearings of cohorts of larvae of P. napi and P. rapae initiated throughout the season. The prediction that partial second generations should be female biased was corroborated by laboratory rearings at constant temperature of P. napi (Pieridae), Polygonia c-album (Nymphalidae), and Pararge aegeria (Satyridae) under critical day length conditions, producing female-biased sex ratio under direct, and male-biased sex ratio under diapause development.

A gyrotron-powered standing-wave electromagnetic wiggler experiment

Experimental results on a gyrotron-powered standing-wave electromagnetic wiggler are presented. The gyrotron interaction cavity and the standing-wave storage cavity are designed as a single unit. The gyrotron was operated at a high field intensity and short interaction length regime. The operating mode is the TE 13 mode at 129.5 GHz. A value of 0.0057 is obtained for the normalized vector potential of the wiggler field. The experimental results indicate that higher wiggler field strengths should be feasible with higher-power electron beams; such an advance would make possible the development of compact, low-voltage, near-IR FELs.