bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual imaging-unit atomic force microscope for nanometer order length metrology based on reference scales
Authors: Zhang Haijun , Zhang Dongxian , Lin Xiaofeng
Published: October 2002

This article reports results from a dual imaging-unit atomic force microscope (DIU-AFM) used for length metrology based on reference scales. The DIU-AFM, suitable for most samples with different conductivity, was developed in view of the fact that the application field of a dual tunneling-unit scanning tunneling microscope was strongly limited by sample conductivity. Two atomic force microscopy (AFM) units were combined in the DIU-AFM, one as a reference unit, and the other a test one. Their probes with Z piezoelements and tips were horizontally set in parallel at the same height to reduce errors due to geometric asymmetry. A reference sample and a test sample were attached to one single XY scanner on same surface, and were imaged by the AFM units at the same time. The two images have the same lateral size, and thus, the length of the test sample image could be accurately measured by counting the periodic features in the reference one. The most remarkable advantages of the DIU-AFM include: Scanning errors caused by the nonlinearity or hysteresis of the piezoscanner can be successfully avoided; moreover, it is able to measure conductive and/or nonconductive samples. We present a discussion about the setup and control of the DIU-AFM. Some comparison experiments, respectively, using periodic features of porous alumina film and grating as reference scales were demonstrated for simultaneous length calibration. Experiments show a satisfactory result of matching and calibration between the two imaging units when covering a wide scan range up to 8 μm. On the basis of different reference scales, the DIU-AFM is capable of realizing nanometer and/or submicron accuracy length metrology of test samples with any conductivity.
Resist trimming in high-density CF4/O2 plasmas for sub-0.1 μm device fabrication
Authors: Sin Chian-Yuh , Chen Bing-Hung , Loh W. L. , Yu J. , Yelehanka P. , See A. , Chan L.
Published: October 2002

Resist trimming using a CF4/O2 plasma generated by an inductively coupled high-density plasma source is investigated. Results show that the resist trimming process is applicable for the fabrication of a sub-0.1 μm polysilicon gate electrode with conventional 248 nm lithography. The trim rate depends strongly on gas composition, temperature, rf source power, bias voltage, reactor pressure and total gas flow. The trim rate increases with increasing temperature, rf source power and reactor pressure but decreases with higher bias voltage. For a typical trimming condition at gas composition of CF4 and O2 with a ratio of 3.3:1, the resist trim rates are 1.0 and 1.2 nm/s for dense and isolated lines, respectively. By examining the effect of various process parameters, it is found that the trimming process is dominated by the neutral reactant species. Angle-resolved x-ray photoelectron spectroscopy shows that a fluorinated carbon oxyfluoride polymer is deposited on the sidewall of photoresist. The degree of carbon fluorination of the film is influenced by the process parameters. A more fluorinated film, obtained at lower bias voltage and higher source power, gives more trimming.
Electrical properties of TiN films deposited by filtered cathodic vacuum arc
Authors: Cheng Y. H. , Tay B. K. , Lau S. P.
Published: October 2002

High quality TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. The influence of deposition pressure, substrate bias, and deposition temperature on the structure and electrical resistivity of TiN films were systematically studied. As the deposition pressure is increased, the film structure evolves from hexagonal α-TiN0.30 to cubic TiN, and the electrical resistivity decreases drastically at the pressure below 2×10−4 Torr, then increases slightly with the further increase of deposition pressure. With the increase of substrate bias, the electrical resistivity decreases drastically, reaching the minimum of 45 μΩ cm at a substrate bias of −100 V, then increases greatly, which results from the variation of N content in TiN films with increasing substrate bias. The increase in the deposition temperature results in a significant decrease in the defect density and a slight increase in the grain size, which accounts for a linear decrease in the electrical resistivity. Our results indicate that the main factors that affect the electrical resistivity of TiN films are the N content, phase structure, and defect density in the films. The grain size plays only a minor role in the electrical resistivity of TiN films.
Nanocrystal metal-oxide-semiconductor memories obtained by chemical vapor deposition of Si nanocrystals
Authors: Ammendola G. , Vulpio M. , Bileci M. , Nastasi N. , Gerardi C. , Renna G. , Crupi I. , Nicotra G. , Lombardo S.
Published: October 2002

We have realized nanocrystal memories by using silicon quantum dots embedded in silicon dioxide. The Si dots with the size of few nanometers have been obtained by chemical vapor deposition on very thin tunnel oxides and subsequently coated with a deposited SiO2 control dielectric. A range of temperatures in which we can adequately control a nucleation process, that gives rise to nanocrystal densities of ∼3×1011 cm−2 with good uniformity on the wafer, has been defined. The memory effects are observed in metal-oxide-semiconductor capacitors or field effect transistors by significant and reversible flat band or threshold voltage shifts between written and erased states that can be achieved by applying gate voltages as low as 5 V. The program-erase window does not exhibit any change after 105 cycles on large area cells showing that the endurance of such a memory device which uses a thinner tunnel oxide is potentially much higher than that of standard nonvolatile memories. Moreover, good retention results are observed in spite of the low tunnel dielectric thickness.
Exposed area ratio dependent etching in a submicron self-aligned contact etching
Authors: Kim J. , Chu C. W. , Kang C. J. , Han W. S. , Moon J. T.
Published: October 2002

The mechanism of selective SiO2 etching over Si3N4 has been studied with the simulation of a ladder-type surface profile and specially designed experiments in a submicron self-aligned contact (SAC) etching process. The ladder-type profile, which is the boundary of broken shoulder Si3N4, is normally observed during a highly selective SAC etching. The structure of two adjacent SiO2 and Si3N4 lines is prepared and etched in a surface wave plasma (SWP) etching system in order to investigate the effect of fluorocarbon polymer deposition on the selectivity and the ladder profile. This designed experiment shows that the removal (adding) of fluorocarbon polymer in a SAC etching directly decreases (increases) the selectivity and changes the ladder-type profile. A new surface reaction model for SiO2 etching has been developed to simulate the behavior of polymer and the ion enhanced dry etching. The simulation reasonably recovers the ladder-type profiles with the effects of polymer deposition and SiO2 etch byproducts, which are thought to be the main control factors of surface reactions in a submicron SAC etching. From the results of simulation and experiment, it is suggested that the structure for SAC process has to be optimized to maximize the selectivity of shoulder Si3N4 and photoresist at the same time.
Interfaces in copper nanoconnections
Authors: Heino P. , Ristolainen E.
Published: October 2002

Decreasing linewidth in electronics packages leads to structures that have to be described atomistically. Currently copper is among the most interesting materials in electronics due to its electrical and thermal properties. We have developed interatomic potentials to model interfaces in copper metallization. Currently an embedded-atom method potential for a Cu–Ta system and a modified embedded-atom method potential for a Ta–Si system are available. We have used the molecular dynamics method with these potentials to study the energy and microstructure of several low-index Cu–Ta and Ta–Si interfaces. Yield stress of the Cu–Ta system is correlated with the energy of the interface. In addition, more realistic Cu–Ta interfaces are generated by depositing copper atoms on a tantalum surface and tantalum atoms on copper surfaces. Tantalum atoms are seen to mix on copper surfaces, while copper atoms stay on tantalum surfaces. We discuss this with bonding energy arguments.
Two-dimensional profiling of carriers in a buried heterostructure multi-quantum-well laser: Calibrated scanning spreading resistance microscopy and scanning capacitance microscopy
Authors: Ban D. , Sargent E. H. , Dixon-Warren St. J. , Grevatt T. , Knight G. , Pakulski G. , SpringThorpe A. J. , Streater R. , White J. K.
Published: October 2002

We report results of a scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM) study of the distribution of charge carriers inside multi-quantum-well (MQW) buried heterostructure (BH) lasers. We demonstrate that individual quantum-well–barrier layers can be resolved using high-resolution SSRM. Calibrated SSRM and SCM measurements were performed on the MQW BH laser structure, by utilizing known InP dopant staircase samples to calibrate the instrumentation. Doping concentrations derived from SSRM and SCM measurements were compared with the nominal values of both p- and n-doped regions in the MQW BH lasers. For n-type materials, the accuracy was bias dependent with SSRM, while for SCM, excellent quantitative agreement between measured and nominal dopant values was obtained. The SSRM was able to measure the dopant concentration in the p-type materials with ∼30% accuracy, but quantitative measurements could not be obtained with the SCM. Our results demonstrate the utility of combining calibrated SSRM and SCM to delineate quantitatively the transverse cross-sectional structure of complex two-dimensional devices such as MQW BH lasers, in which traditional one-dimensional probing using secondary ion mass spectroscopy provides only a partial picture of internal device structure.
Modeling oxide etching in a magnetically enhanced reactive ion plasma using neural networks
Authors: Kim Byungwhan , Kwon Kwang-Ho , Kwon Sung-Ku , Park Jong-Moon , Yoo Seong Wook , Park Kun-Sik , Kim Bo-Woo
Published: October 2002

Oxide films etched in a CHF3/CF4 plasma were qualitatively modeled using neural networks. The etching was conducted using a magnetically enhanced reactive ion etcher. A statistical 24-1 experimental design plus one center point was used to characterize relationships between process factors and etch responses. The factors that were varied include a radio frequency power, pressure, CHF3 and CF4 flow rates. The resultant nine experiments were used to train neural networks and trained networks were subsequently tested on eight experiments not belonging to the training data. A total of 17 experiments were thus conducted for modeling. Etch responses modeled are etch rate and etch profile. Root-mean-squared prediction errors of optimized models are 111 Å/min and 3.50° for the etch rate and etch profile, respectively. Interaction effects between the factors were examined from the prediction models. Besides the dc bias, the F and CF2 intensities measured with an optical emission spectroscopy were related to the etch responses. Polymer deposition effect was transparent in the etch rate for a variation in CHF3, but little for the one in CF4. Conflicting effects between CHF3 and CF4 were noticed with respect to either etch response. Pressure-induced dc bias played an important role in determining etch responses.
Comparison of experimental and theoretical scanning capacitance microscope signals and their impact on the accuracy of determined two-dimensional carrier profiles
Authors: Kopanski J. J. , Marchiando J. F. , Rennex B. G.
Published: October 2002

The accuracy with which two-dimensional carrier profiles can be extracted from scanning capacitance microscopy (SCM) images of doped structures in silicon depends on the model used to interpret the SCM differential capacitance data. This work validates models of the SCM by comparing the calculated SCM signal to the measured signal for a variety of sample parameters, measurement conditions, and capacitance sensors from different manufacturers. The magnitude of the capacitance sensor high-frequency voltage is measured and its effect on ΔC–V curves and extracted carrier profiles is quantified. Two nonidealities commonly observed in SCM signals, U-shaped C–V curves and double zero crossing in the SCM signal at the p–n junctions, are related to the measurement parameters and explained.
Modification of thiol-derived self-assembling monolayers by electron and x-ray irradiation: Scientific and lithographic aspects
Authors: Zharnikov M. , Grunze M.
Published: October 2002

This article reviews recent experiments on the modification of thiol-derived self-assembling monolayers (SAMs) by electron and x-ray irradiation. Several complementary experimental techniques such as near-edge x-ray absorption fine structure spectroscopy, x-ray photoelectron spectroscopy and microscopy, and infrared reflection absorption spectroscopy were applied to gain a detailed knowledge on the nature and extent of irradiation-induced damage in these systems. The reaction of a SAM to electron and x-ray irradiation was found to be determined by the interplay of the damage/decomposition and cross-linking processes. Ways to adjust the balance between these two opposing effects by molecular engineering of the SAM constituents are demonstrated. The presented data provide the physical–chemical basis for electron-beam patterning of self-assembled monolayers to extend lithography down to the nanometer scale.
Accuracy and precision of measuring cross-sectional area in stem disks of Douglas-fir infected by Armillaria root disease
Authors: Cruickshank Mike G
Published: October 2002

Stem cross-sectional areas were checked for accuracy and precision of area measurements in healthy and Armillaria ostoyae (Romagn.) Herink infected 18-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Ten trees were randomly selected in each combination of two size classes and four infection classes, and stem disks were taken at the soil line (0 m) and at 1.3 m. Disks were marked at the longest radius, 90° to the longest radius, the shortest radius, and at radii determined by the sum of the largest diameter and the diameter at 90° divided by four. These radii were used to calculate cross-sectional area, then these calculated areas were compared with the corresponding digitized areas. Cross-sectional areas calculated from radial measurements were generally not within 5% of digitized areas. Radii were also drawn on the disks corresponding to the positions at which healthy and infected roots arose from the root collar below. For 0-m disks, the stem radii over healthy roots averaged 7 mm longer than over infected roots. At 1.3 m, the stem radii over healthy roots were 4 mm longer, but this was reduced with increasing infection of the root system. Offset piths and irregular shapes formed because of radial reduction over infected roots, and corresponding radial expansion over healthy roots affected the accuracy of disk area estimation.
Fine root turnover in a northern hardwood forest: a direct comparison of the radiocarbon and minirhizotron methods
Authors: Tierney Geraldine L , Fahey Timothy J
Published: October 2002

We examined fine root turnover using both the minirhizotron and radiocarbon methods within the organic horizon of a northern hardwood forest to better understand discrepancies in turnover estimates obtained using these methods. The recently developed radiocarbon method estimates the mean age of organic matter by comparing its radiocarbon content to recorded atmospheric radiocarbon levels, which peaked in the 1960s as a result of thermonuclear weapons testing. The radiocarbon content of fine roots harvested from minirhizotron tubes did not differ from that of roots collected from the soil, suggesting these two methods sampled the same population of fine roots. However, long-term observation of fine root survivorship using minirhizotrons showed that root age distribution is positively skewed, causing systematic overestimation of fine root turnover by the minirhizotron method and underestimation by the radiocarbon method. We developed a parametric regression model of fine root survivorship. Our estimate of fine root turnover (about 30% per year) using this variation of the minirhizotron method was supported by radiocarbon data considered in conjunction with fine root age distribution.
HIGH PRESSURE TRANSPORT STUDY OF NON-FERMI LIQUID BEHAVIOUR IN U2Pt2In AND U3Ni3Sn4
Authors: DE VISSER A. , ESTRELA P. , NAKA T.
Published: October 2002

The strongly correlated metals U 2 Pt 2 In and U 3 Ni 3 Sn 4 show pronounced non-Fermi liquid (NFL) phenomena at ambient pressure. Here we review single-crystal electrical resistivity measurements under pressure (p ≤ 1.8 GPa) conducted to investigate the stability of the NFL phase. For tetragonal U 2 Pt 2 In (I ‖ a) we observe a rapid recovery of the Fermi-liquid T2-term with pressure. The Fermi-liquid temperature varies as T FL ~ p-p c , where p c =0 is a critical pressure. The analysis within the magnetotransport theory of Rosch provides evidence for the location of U 2 Pt 2 In at a p=0 antiferromagnetic critical point (QCP). In the case of cubic U 3 Ni 3 Sn 4 we find T FL ~ (p-p c )1/2. The analysis provides evidence for an antiferromagnetic QCP in U 3 Ni 3 Sn 4 at a negative pressure p c = -0.04±0.04 GPa
High Field Magnetotransport in CeRh1-xIrxIn5 Heavy Electron Alloys
Authors: CHRISTIANSON A. D. , LACERDA A. H. , PAGLIUSO P. G. , MORENO N. O. , HUNDLEY M. F. , SARRAO J. L.
Published: October 2002

The interplay of magnetism and superconductivity has been a recurring theme in heavy fermion compounds. Recently, alloys of CeRhIn 5 (antiferromagnet at 3.8 K) and CeIrIn 5 (superconductor at 0.4 K) have been grown, i.e. CeRh 1-x Ir x In 5. For x = 0.5, specific heat and magnetic susceptibility measurements indicate at ~3.6 K an antiferromagnetic transition occurs. Decreasing temperature still further, a superconducting transition is observed at 0.8 K. Thus this alloy series offers the possibility of exploring the coexistence of superconductivity and magnetism in a Ce-based heavy fermion system. We have initiated a magnetotransport study from 1.4 to 300 K with applied fields to 18 T, to probe the behavior of these systems at temperatures above the possible coexistence region. In this paper we will focus on comparing the high field magnetotransport properties of CeRh 0.9 Ir 0.1 In 5 to the end compounds CeRhIn 5 and CeIrIn 5.
ULTRASONIC AND MAGNETIZATION STUDIES AT THE METAMAGNETIC TRANSITION IN UPt3
Authors: SUSLOV A. , DASGUPTA D. , FELLER J. R. , SARMA B. K. , KETTERSON J. B. , HINKS D. G.
Published: October 2002

The velocity and attenuation of longitudinal ultrasound were measured on two single crystals of UPt 3 in magnetic fields up to 33 T and temperatures down to 40 mK. For fields applied in the basal plane, a strong dip in the velocity is seen at a field of 20 T in both samples and is accompanied by a simultaneous increase in the dc magnetization. At lower temperatures the dip gets more pronounced and sharper. At a temperature around 0.6 K the velocity dip develops a second feature at a slightly higher field of ~21.6 T.
THE QUANTUM HALL EFFECT IN QUASI-ONE-DIMENSIONAL ORGANIC CONDUCTORS
Authors: YAKOVENKO V. M.
Published: October 2002

Theoretical overview of the quantum Hall effect in quasi-one-dimensional (Q1D) organic conductors (TMTSF) 2 X will be presented.1 The emphasis will be on the recent developments, such as the temperature evolution of the Hall effect2,3 and the chiral edge states.4 Time permitting, a theory of the nonchiral electron edge states in a Q1D triplet superconductor5 and the holon edge states in the charge-gap regime6 will be presented too.
THE EFFECTS OF PRESSURE AND MAGNETIC FIELD ON THE CONDUCTIVITY OF FeCl4 DOPED POLYACETYLENE: THE INFLUENCE OF SCATTERING BY LOW-ENERGY EXCITATIONS
Authors: ALESHIN A. N. , KIM T. J. , SUH D.-S. , PARK Y. W. , KANG H. , KANG W.
Published: October 2002

The effects of hydrostatic pressure and magnetic field on the conductivity of oriented polyacetylene films doped with FeCl 4- up to metallic state have been studied at T = 0.35-300 K. It was found that application of pressure up to 10 kBar increases the conductivity at 300 K by a factor of 1.3 and suppresses the resistivity minimum in ρ (T) at 270 - 280 K. At T < 2 K the temperature dependence of resistivity ρ (T) ~ ln T (at ambient pressure and at 10 kBar) which remains unaltered by a magnetic field up to 14 Tesla. Transverse magnetoresistance (MR) was found to be negative, linear and temperature independent at T < 2 K (at ambient and high pressure). We attribute the observed ρ (T) and MR behavior to weak localization accompanied by effect of electron dephasing time saturation due to scattering by two-level systems of a special type. More strong behavior of ρ (T) and MR at T > 2 K related to further suppression of weak localization due to scattering by low-energy excitations of a "glassy" type.
HIGH FIELD MAGNETOCONDUCTIVITY OF IODINE DOPED HELICAL POLYACETYLENE
Authors: SUH D.-S. , KIM T. J. , ALESHIN A. N. , PARK Y. W. , PIAO G. , AKAGI K. , SHIRAKAWA H. , QUALLS J. S. , HAN S. Y. , BROOKS J. S.
Published: October 2002

The effect of interfibrillar interaction on the charge transport of doped polyacetylene is investigated by studying the high field magnetoconductivity of iodine doped helical polyacetylene. The zero-field resistivity ratio, ρ r = ρ(1.2 K )/ρ(300 K ), is comparable to that of stretch-oriented high-density polyacetylene, which indicates the partial alignment of chains inside a polymer fiber. At low magnetic fields, the small negative component of magnetoconductivity was observed and its magnitude increases as the ρ r value increases. In the high field region, the magnetoconductivity is positive and it clearly shows the linear dependence on the magnetic field up to H = 30 T. The linear field dependence of magnetoconductivity is different from what is expected in the three-dimensional weak localization picture. For the same ρ r value samples, the magnitude of negative magnetoconductivity of S-polyacetylene is much bigger than that of R-polyacetylene, which could be attributed to the difference in the degree of helicity determining the strength of interfibrillar interaction.
SPINLESS IMPURITIES IN CUPRATES: LOCAL MAGNETISM AND KONDO EFFECT IN THE NORMAL AND SUPERCONDUCTING STATES
Authors: ALLOUL H. , BOBROFF J. , MENDELS P. , RULLIER-ALBENQUE F.
Published: October 2002

Spinless point defects in the CuO 2 planes of the cuprates have been shown for long to induce a magnetic response on the neighboring copper sites which behaves as a nearly free local moment in the under-doped case.1,2 In the case of Li + substitution on the Cu site, accurate 7 Li NMR shift data allow to evidence that the local moment susceptibility displays a ( T + T K ) -1 dependence, with a Kondo like temperature T K which increases abruptly near optimal doping.3 While a Curie paramagnetic response can be understood on general theoretical grounds in the case of undoped quantum spin systems, the Kondo screening of the moment might directly reflect the influence of charge carriers. This Kondo like behavior is also corroborated by measurements of the fluctuation time of the local moment deduced from 7 Li NMR spin lattice relaxation time.4 The local moment is found to survive in the superconducting state although a marked reduction of the screening is observed when T K > T c (see Ref. [5]), as might be expected from theoretical considerations.

Correlatively it will be shown that the scattering of charge carriers by spinless defects can be studied accurately in single crystals in which such defects are created by electron irradiation. The low T upturns of the resistivity can be associated with a Kondo-like T dependence of the scattering in the under-doped case. In the over-doped case, T K being very high, the scattering becomes T-independent and 2D weak localization effects dominate.6
ORBITAL MAGNETISM IN THE CUPRATES
Authors: CHAKRAVARTY SUDIP , KEE HAE-YOUNG , NAYAK CHETAN
Published: October 2002

The pseudogap phase of the cuprate superconductors is argued to be characterized by a hidden broken symmetry of d-wave character in the particle-hole channel that leads to staggered orbital magnetism. This proposal has many striking phenomenological consequences, but the most direct signature of this order should be visible in the neutron scattering experiments. The theoretical underpinning of these experiments is discussed.
MAGNETIC FIELD EFFECTS On Tc AND THE PSEUDOGAP ONSET TEMPERATURE IN CUPRATE SUPERCONDUCTORS
Authors: CHEN QIJIN , KAO YING-JER , IYENGAR ANDREW P. , LEVIN K.
Published: October 2002

We study the sensitivity of Tc and the pseudogap onset temperature, T*, to low fields, H, for cuprate superconductors, using a BCS-based approach extended to arbitrary coupling. We find that T* and Tc, which are of the same superconducting origin, have very different H dependences. The small coherence length makes T* rather insensitive to the field. However, the presence of the pseudogap at Tc makes Tc more sensitive to H. Our results for the coherence length ξ fit well with existing experiments. We predict that very near the insulator ξ will rapidly increase.
USING RADIO FREQUENCY PENETRATION DEPTH TO PROBE LAYERED SUPERCONDUCTORS
Authors: MIELKE C. H.
Published: October 2002

Measuring the electrical resistivity of layered superconductors yields interesting information regarding the mixed and normal state of the system. Because of the high degree of anisotropy of many systems it becomes impossible to distinguish between the relatively small resistivity associated with ρxy and the much larger ρzz using traditional 4 lead techniques. Moreover, dissipation associated with vortex pining masks the crossover from superconducting to normal state. Recent development of radio frequency (rf) techniques in milli-second pulsed high magnetic fields have resulted in a powerful tool to investigate metals and superconductors at extremes in H-T space. The rf technique is sensitive to changes in the most conducting regions of the sample, hence the in-plane resistivity is measured. By measuring the change in skin depth as a function of applied magnetic field and temperature, a reliable method for mapping the upper critical field is realized. Direct comparison with thermodynamic measurements such as magnetization and thermal conductivity show compelling agreement.
TRANSPORT IN MgB2 IN HIGH MAGNETIC FIELDS
Authors: SZABO P. , SAMUELY P. , JANSEN A. G. M. , KLEIN T. , MARCUS J. , FRUCHART D. , MIRAGLIA S.
Published: October 2002

Magnetotransport measurements are presented on polycrystalline MgB 2 samples. The 'resistive' upper critical magnetic field reveals a temperature dependence with positive curvature from Tc = 39.3 K down to about 20 K, then changes to slightly negative curvature reaching 26 T at 1.5 K. The 26-Tesla upper critical field is much higher than what is known so far on polycrystals of MgB 2 but it is in agreement with the recent data obtained on epitaxial MgB 2 films.1 The deviation of Hc2(T) from standard BCS might be due to the proposed two-gap superconductivity in this compound.2 Recently we have found evidence for the existence of two superconducting energy gaps in this system using Andreev reflection spectroscopy.3 The temperature dependence of the resistivity and the normal state magnetoresistance are analyzed.
EVIDENCE FOR THE PAIR FORMATION FAR ABOVE Tc IN EPITAXIAL La2-xSrxCuO4 THIN FILMS
Authors: VANACKEN J. , WECKHUYSEN L. , WAGNER P. , MOSHCHALKOV V. V.
Published: October 2002

A large positive magnetoresistivity (up to ten percent or more) is observed for both under-doped and over-doped superconducting La 2-x Sr x CuO 4 epitaxial thin films at temperatures far above the superconducting critical temperature T c . This magnetoresistivity can be related to the pairs eventually forming the superconducting phase at low temperatures. Our observations support the idea of a close relation between the pseudogap and the superconducting gap and provide new indications for the presence of pre-pairs above T c .
GEOMETRICAL FRUSTRATION, AND RELEVANCE FOR HIGH FIELD STUDIES
Authors: RAMIREZ A. P.
Published: October 2002

Geometrical Frustration arises when the symmetry of a magnetic interaction is incompatible with the spatial symmetry of the crystalline lattice. Magnetic field can break this symmetry condition and we will illustrate different classes of behavior on the pyrochlore lattice – spin ice for Ising spins and spatial symmetry projection for Heisenberg spins.
OBSERVATION OF QUANTUM OSCILLATIONS IN FOUR-LAYER BaRuO3
Authors: ALEXANDER C. S. , XIN Y. , ZHOU Z. X. , MCCALL S. , CAO G. , CROW J. E.
Published: October 2002

Well characterized single crystals of the four layer crystallographic form of BaRuO3 were studied at low temperatures (20 < T < 850 mK) and high magnetic fields (0 < H < 30 T). Quantum oscillations have been observed via the Shubnikov - de Haas and de Haas - van Alphen effects. In marked contrast, BaRuO3 with the nine-layer structure shows no similar behavior, suggesting a substantial change in the Fermi surface or quasi-particle relaxation times. The quantum oscillations provide insight into the ground state which, like those of other layered ruthenates, is characteristically sensitive to electron-lattice coupling. This observation is significant in that it represents the first example of quantum oscillations in a non-Ruddlesden–Popper type ruthenate and provides some insight into the Fermi surface even though a psuedo-gap is evident in other studies.
NUCLEAR MAGNETISM OF HELIUM-3 PRECIPITATES
Authors: SHVARTS V. A. , KLESS K. J. , MATSUNAGA N. , ADAMS E. D. , XIA J. X. , SCHUBERTH E. A.
Published: October 2002

Simultaneous measurements of magnetic susceptibility from 0.5 to 10 mK and pressure from 2.88 to 3.54 MPa have been made in 3He nanoclusters embedded in a 4He matrix, following phase separation. The susceptibility of the 3.54 MPa, all –solid sample behaves similarly to that of bulk 3He for v = 21.3 cm3/mole, with a Weiss constant θ = -250μK. For the 2.88 MPa, liquid-droplet sample, θ = 140μK, indicating a ferromagnetic tendency, similar to 2-D films at some coverages. At intermediate pressures, χ has a peak near 1.05 mK, but without a discontinuity. For all samples, χ had a solid-like contribution to the lowest temperatures. Magnetic ordering in nano-clusters appears to be different than the U2D2 phase of bulk 3He.
PULSE-FIELD EXPERIMENTS ON THE SPIN-LATTICE INTERACTION IN LOW-DIMENSIONAL SPIN SYSTEMS
Authors: WOLF B. , ZHERLITSYN S. , SCHMIDT S. , LÜTHI B. , LANG M.
Published: October 2002

Low-dimensional spin systems reveal new and unexpected physical phenomena such as distinct plateaus in the magnetization as a function of magnetic field. In this paper we present ultrasonic measurements for the quasi-two-dimensional spin system SrCu2(BO3)2 in magnetic fields up to 50 T. From this technique we obtained detailed information about the spin state, the magnetic excitations and their interaction with phonons. The dimerized quantum-spin system SrCu2(BO3)2 exhibits plateaus in the magnetization and shows surprisingly strong magneto-elastic effects as a function of temperature and magnetic field. The pronounced elastic anomalies indicate a resonant interaction between the sound wave and the magnetic excitations.
FORCE-DETECTED SCANNED PROBE MAGNETIC RESONANCE MICROSCOPY
Authors: HAMMEL P. C.
Published: October 2002

Magnetic Resonance Force Microscopy (MRFM) is a novel scanned probe technique that combines the three-dimensional imaging capabilities of magnetic resonance imaging (MRI) with the high sensitivity and resolution of atomic force microscopy (AFM). This emerging technology holds clear potential for resolution at the atomic scale. When fully realized, MRFM will provide a unique method for non-destructive, chemically specifc, subsurface imaging with applicability to a wide variety of materials. I will review results to date spanning applications of MRFM to nuclear spin, electron spin, and ferromagnetic resonance. I will outline the MRFM technique, discuss its present status and indicate future directions of our effort.
ULTRAFAST COHERENT TERAHERTZ SPECTROSCOPY IN HIGH MAGNETIC FIELDS
Authors: CROOKER S. A. , TAYLOR A. J.
Published: October 2002

With an aim towards measuring the high-frequency complex conductivity of correlated electron materials in the regime of low temperatures and high magnetic fields, we introduce a method for performing time-domain terahertz spectroscopy directly in the cryogenic bore of existing dc and pulsed-field magnets. Miniature, fiber-coupled THz emitters and receivers are constructed and are demonstrated to work down to 5 K and up to 6 Tesla, for eventual use in higher-field magnets. Maintaining the sub-micron alignment between fiber and antenna during thermal cycling, and obtaining ultrafast (<200fs) optical gating pulses at the end of long optical fibers constitute the major technical challenges of this project. Preliminary data on YBCO superconducting thin films is shown.
NEUTRON SCATTERING IN MAGNETIC FIELDS UP TO 17 T
Authors: PROKES K. , SMEIBIDL P. , MEISSNER M.
Published: October 2002

Neutron scattering in magnetic fields can provide important imformation regarding the magnetism of a system under study on microcsopic scale. Although pulse magnets are capable to reach very high fields, for neutron scattering mostly superconducting magnets are used. At present, a split-pair 14.5 T superconducting magnet used for user-program experiments at HMI offers the highest magnetic field for neutron scattering. With Dy-pole tips placed symmetrically around the sample position a 2.5 T enhancement is achieved. The temperature range accessible with such an insert is between 1.8 and 100 K. Temperatures down to 30 mK can be achieved with a dilution stick, which can be inserted into the 14.5 T cryomagnet. In the contribution we report on the latest neutron scattering achievements in magnetic fields obtained at HMI.
ULTRASONIC SPECTROMETERS FOR CONDENSED MATTER STUDIES AT VERY HIGH MAGNETIC FIELD
Authors: SUSLOV A. , DASGUPTA D. , FELLER J. R. , SARMA BIMAL K. , KETTERSON J. B.
Published: October 2002

Three ultrasonic spectrometers have been constructed for use with the continuous and pulsed magnetic field facilities of the NHMFL at the Tallahassee and Los Alamos sites. The first of these, designed for use with the dc magnets, is a heterodyne spectrometer with the capabilities of high velocity resolution and near-simultaneous measurements at several frequencies (typically near transducer harmonics). The other two spectrometers are designed for the short-pulsed magnets, with the capability of fast data acquisition. These spectrometers have been used in the study of metamagnetism in the heavy fermion materials.
HIGH PRESSURE TECHNIQUES FOR LOW TEMPERATURE STUDIES IN DC AND PULSED MAGNETIC FIELDS
Authors: TOZER S. W.
Published: October 2002

Pressure can be used to expand the parameter space available in almost any experiment and allows for the continuous tuning of the electrical and orbital properties of a material. When combined with low temperatures and high magnetic fields, it becomes a powerful tool for the exploration of the band structure and defect levels in semiconductors, exotic transport mechanisms in molecular conductors, and the coexistence of magnetism and superconductivity. We have developed a variety of miniature pressure cells to allow the user to take full advantage of these opportunities. Metallic diamond anvil cells as small as 6 mm in diameter and 8 mm in height allow the sample to be rotated in field at millikelvin temperatures. Miniature plastic DACs and sapphire ball cells, rotators, and specialized He-4 and He-3 systems have also been developed to provide similar experimental capabilities in pulsed magnetic fields. Methods and designs to generate hydrostatic pressure and techniques to perform optical and electrical measurements in DC and pulsed fields will be presented.

We would like to acknowledge the technical assistance of Richard Desilets, Howard Kolb, John Farrell, and Mike Pacheco. A portion of this work was performed at the National High Magnetic Field Laboratory, which is sponsored by NSF Cooperative Agreement No. DMR-9527035 and by the State of Florida.
Discretizing a backwardstochastic differential equation
Authors: Zhang Yinnan , Zheng Weian
Published: October 2002

We show a simple method to discretize Pardoux‐Peng′s nonlinear
backward stochastic differential equation. This discretization
scheme also gives a numerical method to solve a class of
semi‐linear PDEs.
On the maximum value for Zygmund class on an interval
Authors: Xinzhong Huang , Kwon Oh Sang , Park Jun Eak
Published: October 2002

We prove that if f(z) is a continuous real‐valued function on
ℝ with the properties f(0) = f(1) = 0 and that ‖f‖ z  = infx,t|f(x + t) − 2f(x) + f(x − t)/t|is finite for all x, t ∈ ℝ, which is called Zygmund function on ℝ, then maxx∈[0,1]|f(x)| ≤ (11/32)‖f‖z. As an
application, we obtain a better estimate for Skedwed Zygmund
bound in Zygmund class.
Seismic Isolation Systems for Developing Countries
Authors: Kelly James M.
Published: October 2002

This paper describes an experimental and theoretical study of the feasibility of using fiber reinforcement to produce lightweight low-cost elastomeric isolators for application to housing, schools and other public buildings in highly seismic areas of the developing world. The theoretical analysis covers the mechanical characteristics of multi-layer elastomeric isolation bearings where the reinforcing elements, normally steel plates, are replaced by a fiber reinforcement. The fiber in the fiber-reinforced isolator, in contrast to the steel in the conventional isolator (which is assumed to be rigid both in extension and flexure), is assumed to be flexible in extension, but completely without flexure rigidity. This leads to an extension of the theoretical analysis on which the design of steel-reinforced isolators is which accommodates the stretching of the fiber-reinforcement. Several examples of isolators in the form of long strips were tested at the Earthquake Engineering Research Center Laboratory. The tested isolators had significantly large shape factors, large enough that for conventional isolators the effects of material compressibility would need to be included. The theoretical analysis is extended to include compressibility and the competing influences of reinforcement flexibility and compressibility are studied. The theoretical analysis suggests and the test results confirm that it is possible to produce a fiber-reinforced strip isolator that matches the behavior of a steel-reinforced isolator. The fiber-reinforced isolator is significantly lighter and can be made by a much less labor-intensive manufacturing process. The advantage of the strip isolator is that it can be easily used in buildings with masonry walls. The intention of this research is to provide a low-cost lightweight isolation system for housing and public buildings in developing countries.
Versatile macrolide‐responsive mammalian expression vectors for multiregulated multigene metabolic engineering
Authors: Weber Wilfried , Marty René R. , Keller Bettina , Rimann Markus , Kramer Beat P. , Fussenegger Martin
Published: October 2002

The novel macrolide‐inducible and ‐repressible mammalian gene regulation systems (E.REX) have been cloned into a variety of sophisticated expression configurations including (1) multi‐purpose expression vectors, (2) pTRIDENT‐based artificial operons, (3) dual‐regulated expression strategies for independent control of two different transgenes, (4) autoregulated vectors for one‐step installation of adjustable multigene expression, and (5) oncoretroviral and lentiviral plasmids for transduction of macrolide‐, streptogramin‐ and tetracycline‐dependent transactivators and production of cell lines supporting independent control of three different transgenes. This vector portfolio represents a construction kit‐like toolbox for efficient installation of adjustable gene expression responsive to clinically licensed antibiotics and enables the design of multiregulated multigene metabolic engineering strategies required for biopharmaceutical manufacturing, gene therapy, and tissue engineering. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 691–705, 2002.
Simultaneous HPLC determination of 5‐fluorouracil and its metabolites in plasma of cancer patients
Authors: Casale F. , Canaparo R. , Muntoni E. , Serpe L. , Zara G.P. , Pepa C. Della , Berno E. , Costa M. , Eandi M.
Published: October 2002

5‐Fluorouracil (5‐Fu) is a commonly used anticancer agent for treatment of solid tumours. Certain studies have reported conflicting results between individual plasma concentration levels and toxicity or therapeutic effects. For this reasons some authors proposed to evaluate the plasma levels of 5‐Fu metabolites 5‐fluorouridine, 5‐fluoro‐2′‐deoxyuridine and 5‐fluoro‐5,6‐dihydro‐uracil. The aim of the present work is to develop and validate a new HPLC method simultaneously determining 5‐fluorouracil and its three metabolites, to be used to study the plasma levels, therapeutic effects and toxicity in cancer patients. The analytes were separated on a 4.6 × 250 mm ODS1 (5 µm) not end‐capped column, operating at room temperature. Elution was performed under isocratic conditions, employing a 1.5 mM K3PO4 mobile phase (pH 5). 5‐Bromo‐5,6‐dihydro‐uracil was used as internal standard. The limits of quantitation were 0.5 µg/mL for 5‐fluorouracil, 1 µg/mL for 5‐fluoro‐5,6‐dihydro‐uracil, 3 µg/mL for 5‐fluoro‐2′‐deoxyuridine and 5‐fluorouridine; the stability, recovery, linearity, accuracy and specificity of the compounds were evaluated according to the criteria widely accepted. Using this method we measured plasma samples of 18 cancer patients treated with folinic acid (100 mg/m2) by intravenous administration, followed by an i.v. bolus of 5‐Fu (400 mg/m2). The concentration levels of 5‐fluorouracil and for 5‐fluoro‐5,6‐dihydro‐uracil were detectable in all the subjects while 5‐fluorouridine and 5‐fluoro‐2′‐deoxyuridine were present only in eight patients. Copyright © 2002 John Wiley & Sons, Ltd.
Effect of Saccharomyces cerevisiae fermentation conditions on expanded bed adsorption of heterologous cutinase
Authors: Calado Cecília R C , Cabral Joaquim M S , Fonseca Luis P
Published: October 2002

The effect of culture media composition, and fermentation conditions and strategy on the growth and cutinase production of recombinant Saccharomyces cerevisiae and subsequent cutinase purification by expanded bed adsorption (EBA) was studied. The reduction in the amount of yeast extract used as nitrogen source from 20 g dm−3 to 10 g dm−3 in batch cultures led to a 29% decrease in the heterologous cutinase production, while the 5% cutinase dynamic adsorption capacity (q5%) on the cation Streamline SP XL was increased 6.7‐fold. By dilution of the whole fermentation broth, performed with the lowest yeast extract content, which reduces conductivity, the q5% was additionally increased by 1.9‐fold. After implementation of a fed‐batch strategy the cutinase concentration, cutinase yield on carbon source, cutinase yield on nitrogen source and productivity were increased by 10.8‐, 2.9‐, 5.3‐ and 6.4‐fold, respectively, in relation to the previously‐mentioned batch fermentation. However, the increased cutinase production was compromised by heterologous protein loss during the EBA recovery operation and the cutinase dynamic adsorption capacity and purification productivity decreased by 90% and 75%, respectively. Thus, target protein production by S cerevisiae fermentation and a downstream process with EBA cannot be considered as separate entities, where the understanding of the factors that affect the interactions among them are crucial towards optimization of the overall production process of heterologous proteins.

© 2002 Society of Chemical Industry
Perinatal imaging findings of inherited Sotos syndrome
Authors: Chen Chih‐Ping , Lin Shuan‐Pei , Chang Tung‐Yao , Chiu Nan‐Chang , Shih Shin‐Lin , Lin Chen‐Ju , Wang Wayseen , Hsu Hong‐Chih
Published: October 2002

Objectives

Although most cases of Sotos syndrome are sporadic, familial cases have been described. In familial cases, the most likely mode of inheritance is autosomal dominant with variable expressivity. We present the perinatal imaging findings of an inherited case.

Case

This was the second pregnancy of a 32‐year‐old woman with Sotos syndrome. She had given birth to her first child with macrocephaly, ventriculomegaly, macrocisterna magna and neonatal death at 28 weeks' gestation. During this pregnancy, prenatal ultrasonography at 18 weeks' gestation showed only mild dilatation of lateral ventricles. The pregnancy was uneventful until 31 weeks' gestation when fetal macrocephaly, right hydronephrosis, and polyhydramnios began to develop. At 33 weeks' gestation, dilatation of the third ventricle and fetal overgrowth were obvious. At 34 weeks' gestation, macrodolichocephaly, hypoplasia of the corpus callosum, enlargement of the lateral ventricles with prominent occipital horns, and macrocisterna magna were noted. At 36 weeks' gestation, a male baby was delivered with macrodolichocephaly, frontal bossing and a facial gestalt of Sotos syndrome. Birth weight was 3822 g, length 55 cm, and occipitofrontal head circumference 41 cm (all > 97th centile). The magnetic resonance imaging (MRI) scans demonstrated enlargement of the lateral ventricles, the trigones, and the occipital horns, hypoplasia of the corpus callosum, a persistent cavum septum pellucidum and cavum vergae, and macrocisterna magna.

Conclusions

Fetuses at risk for Sotos syndrome may present abnormal sonographic findings of the brain and the skull in association with overgrowth, unilateral hydronephrosis and polyhydramnios in the third trimester. Perinatal MRI studies aid in confirmation of the diagnosis. Copyright © 2002 John Wiley & Sons, Ltd.
Necessity of Axillary Dissection in Elderly Women with Early Breast Cancer
Authors: Newlin Matthew E. , Reiling Richard , Nichols Keith
Published: October 2002

The need for axillary dissection for staging and treating early breast cancer has been questioned recently.
Can a patient forego axillary dissection, with its associated costs,
risks, and morbidity, if it does not affect survival? The study attempted to find a subset of patients with early breast cancer in whom disease‐free survival was independent of axillary lymph node status. If survival does not depend on lymph node status, axillary dissection could be omitted in the care of these patients. This study included 378
women over age 70 with T1 breast cancer diagnosed and treated during January 1992 to December 1999 at both of our institutions: a large tertiary teaching hospital in Columbus, Ohio and a breast cancer treatment center in West Columbia, South Carolina. We compared the disease‐free survival, using the Kaplan‐Meier estimate, in 334
node‐negative patients and 44 node‐positive patients with T1 breast cancer. The 3‐ and 5‐year survival rates of patients with T1N0 tumors were 86% and 77%, respectively; and the 3‐ and 5‐year survival rates for T1 node‐positive tumors were 81% and 69%, respectively
(p = 0.0673). There was no statistical difference between the node‐negative and node‐positive groups. Axillary dissection in women over 70 years of age with early breast cancer may be unnecessary, as the presence of lymph node metastases does not appear to affect disease‐free survival rates significantly in this patient group.