Junction Thickness Research Articles

Mercury−Mercury Tunneling Junctions. 1. Electron Tunneling Across Symmetric and Asymmetric Alkanethiolate Bilayers

Electron tunneling experiments involving Hg−Hg junctions incorporating two alkanethiolate monolayers are described. Formation of a symmetric junction (Hg−SCn−CnS−Hg) is accomplished by bringing in contact two small (3 × 10-3 cm2) mercury drop electrodes in a 5−20% (v/v) hexadecane solution of an alkanethiol. Formation of asymmetric junctions (Hg−SCn−CmS−Hg) and junctions containing n-alkane-3-thiopropanamide bilayers are also described. Tunneling currents in the junctions were measured for voltage biases extending to ±1.5 V. The currents decrease exponentially with the junction thickness yielding the tunneling decay constant, β = 0.89 ± 0.1 per CH2. The decay constant exhibits only a weak dependence on the voltage bias suggesting that electron tunneling follows a through-bond mechanism. Tunneling currents in the n-alkane-3-thiopropanamide bilayer junctions were larger than those in alkanethiolate junctions with the same number of atoms suggesting that introduction of an amide group increases the strength of the electronic coupling through these types of σ-bonded systems.

Ultrasound evaluation of the uterine zonal anatomy during in-vitro fertilization and embryo transfer.

This study was designed to establish if ultrasound could detect differences in uterine zonal anatomy between conception and non-conception in-vitro fertilization (IVF)/embryo transfer cycles. A transvaginal ultrasound scan was performed on the day of down regulation (D0), on day 8 of ovulation induction (D8), on the day of human chorionic gonadotrophin (HCG) injection, at the time of oocyte retrieval, and at embryo transfer. Thicknesses of endometrium, junctional zone, myometrium and full thickness of the uterus were recorded for every patient and comparisons made at all the assessment points. Differences between measurements on D0 and all other measurements (temporal changes) and between every subsequent measurement (dynamic changes) were also compared. There were no statistically significant differences in endometrial thickness between pregnant and non-pregnant groups at any time. The diameter of the uterus increased during therapy and was significantly greater in the pregnant subset at the time of HCG injection, oocyte retrieval and embryo transfer (P < 0.02, 0.03 and 0.02 respectively). The myometrium was significantly thicker in the pregnant group on D0, on D8 and at HCG administration (P < 0.03, 0.004 and 0.02). There was a decrease in junctional zone thickness in both groups during the first week of ovulation induction, and on D8 the junctional zone in pregnant patients was significantly thinner (P < 0.04). The junctional zone became significantly thicker at embryo transfer in the pregnant group (P < 0.01). This was confirmed by significant temporal and dynamic changes at the time of oocyte retrieval and embryo transfer (P < 0.01, 0.0001 and P < 0.05, 0.01 respectively). In the patients who did not conceive, changes in the junctional zone were less pronounced. In conclusion, it was not possible to predict the likelihood of pregnancy from endometrial thickness at any time during the IVF cycle, but changes occurred in other uterine layers that were more pronounced in conception cycles. The responsiveness of the junctional zone seems to be associated with implantation, and its measurements at the time of downregulation and embryo transfer can be used to predict treatment outcome.

ACCURACY AND REPRODUCIBILITY OF TEE MEASUREMENTS OF THE ASCENDING AORTA

S97 INTRODUCTION: Transesophageal echocardiography (TEE) is often used to assess ascending aortic dimensions. We sought to determine the accuracy and reproducibility of these measurements. METHODS: The TEE video recordings of 32 patients requiring repair of Type A aortic dissection (31 undergoing emergency surgery) were retrospectively reviewed under an IRB-approved protocol. The aortic diameter was measured at four locations (aortic annulus, sinuses of Valsalva, sinotubular junction, and right pulmonary artery level) and aortic wall thickness was measured at the level of the right pulmonary artery by two independent observers. In 12 patients who had preoperative CT exams, the maximal aortic diameter was compared with the maximal TEE diameter to assess the accuracy of the TEE measurements. Bias and limits of agreement were assessed using the method of Bland and Altman. Two-factor ANOVA calculations without replication were performed on 5 measured variables (aortic annulus, sinuses of Valsalva, sinotubular junction, mid-ascending aorta, and aortic wall thickness). Intraclass correlation coefficients were calculated for each of the variables. RESULTS: The comparison of TEE and CT yielded a bias of +0.2 cm (limits of agreement: -1.5 to +2.0 cm). The intraclass correlation coefficients for the interobserver measurements are listed in Table 1.Table 1: Intraclass Correlation CoefficientsDISCUSSION: The CT and TEE comparison showed wide limits of agreement. One possible explanation is that CT exams cannot determine the level of the aortic valve, and thus it is difficult to coordinate the exact levels where measurements are made. The interobserver comparison of TEE exams showed excellent agreement of aortic diameter measurements at all levels. The wall thickness measurements were not reproducible, possibly related to the small dimensions involved (mean =2.5 mm).

Proximity Effect and Josephson Coupling in the SO(5) Theory of High-TcSuperconductivity

We consider proximity effect coupling in Superconducting/Antiferromagnetic/Superconducting (S-A-S) sandwiches using the recently developed SO(5) effective theory of high temperature superconductivity. We find that, for narrow junctions, the A region acts like a strong superconductor, and that there is a critical junction thickness which depends on the effective SO(5) coupling constants and on the phase difference across the junction, at which the A region undergoes a Freedericksz-like transition to a state which is intermediate between superconductor and antiferromagnet. For thick junctions, the current-phase relation is sinusoidal, as in standard S-N-S and S-I-S junctions, but for thin junctions it shows a sharp break in slope at the Freedericksz point.

Some aspects of the nonlocal electrodynamics of infinite Josephson junctions

We derive the basic equations of nonlocal Josephson electrodynamics, valid for any ratios of the characteristic scale of phase-difference variations and junction thickness. The spectrum of generalized Swihart waves is obtained. We also study the effect of finite surface resistance of the superconducting electrodes on the dynamics of vortex structures characteristic of nonlocal electrodynamics.

Adenomyosis: specificity of 5 mm as the maximum normal uterine junctional zone thickness in MR images.

Our objective was to investigate the specificity of the criterion stating that a diagnosis of adenomyosis can be made confidently from MR images of the uterus when the junctional zone is thicker than 5 mm. Twenty clinically normal women volunteers (chosen by strict criteria) underwent MR imaging of the uterus. Images were independently evaluated by two experienced observers who measured the greatest thickness of the junctional zone in the anterior, posterior, right and left walls of the uterine corpus and at the top of the fundus. The mean value of the greatest junctional zone thickness (averaged for both observers) was 4.4 +/- 2.1 mm (mean +/- SD, range, 1-9 mm) for the anterior and posterior walls of the corpus, 4.3 +/- 2.1 mm (range, 1-10 mm) for the right and left walls, and 2.3 +/- 1.1 mm (range, 1-5 mm) for the fundus. At least one region of the junctional zone was found to be thicker than 5 mm by at least one observer in 13 (65%) of the 20 subjects; at least one region was found to be thicker than 5 mm by both observers in eight (40%) subjects. At least two regions were measured as thicker than 5 mm by both observers in six (30%) subjects. Serial studies of three volunteers showed transient irregular focal or diffuse thickening (up to 12 mm) of the junctional zone and focal myometrial bulging, probably due to myometrial contractions. Our results suggest that if a diagnosis of adenomyosis is based solely on junctional zone thickness in MR images, 5 mm should not be assumed as the upper limit of normal, because this assumption may result in a high false-positive rate.

Intrinsic Josephson effects in high-Tc superconductors.

We have investigated the coupling between ${\mathrm{CuO}}_{2}$ layers in high-${\mathit{T}}_{\mathit{c}}$ superconductors by direct measurements of all dc and ac Josephson effects with current flow in the c-axis direction. The measurements have been performed on small single crystals of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$, (${\mathrm{Pb}}_{\mathit{y}}$${\mathrm{Bi}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$, ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$, and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ and on a-axis-oriented ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{7}$ thin films. The results clearly show that all materials behave like stacks of superconductor-insulator-superconductor Josephson junctions. The current-voltage characteristics exhibit large hystereses and multiple branches, which can be explained by a series connection of highly capacitive junctions. From the modulation of the critical current in a magnetic field parallel to the layers, we infer a junction thickness of approximately 15 \AA{}. In our microwave emission experiments we were able to prove explicitly that every pair of ${\mathrm{CuO}}_{2}$ double or triple layers forms a working Josephson contact. An exception is ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, where only flux-flow behavior has been observed.

Weak-Link Characteristics and Transport Properties of Tl-1223 Tape-Shaped Wire

Tl-1223 has potential as a practical superconductor for use at the temperature of liquid nitrogen because of strong pinning behavior and an attractive T c of 120 K. In this study, we investigated the transport properties of granular Tl-1223 tape-shaped wire in magnetic fields and compared them with properties of Y- and Bi-based tapes. It was found that the transport properties of Tl-1223 tape in a magnetic field are well explained by the granular superconductor model of Peterson and Ekin [Phys. Rev. B 37 (1988) 9848], and are similar to those of the Y-123 tape. The effective junction thickness of Tl-1223 is improved to 1/10 that of Y-123. The weak-link behavior of Tl-1223 tape-shaped wire is discussed.

Very thin YBa2Cu3O7 step-edge Josephson junctions

Step-edge Josephson junctions were fabricated from 20 and 10 nm thick epitaxial YBa2Cu3O7 films on SrTiO3 substrates. The junction cross sections were in the 10-8 cm2 range, similar to those in standard 200-300 nm thick junctions. The current-voltage characteristics, with and without microwave irradiation, were of resistively-shunted-junction (RSJ) type. The junction resistivities were in the range 10-8-10-7 Omega cm2 range, up to two orders of magnitude higher than in standard junctions, while the IcRns were comparable. This behaviour was explained by a strong decrease in the number of parallel point-contact-type connections with the junction thickness. The junctions deteriorated quickly upon thermal cycling.

The energy profile of polymorphous PbTe films. II. Recombination in heterophase PbTe films at high levels of optical excitation

For pt.I see ibid., vol.4, p.8997 (1992). Picosecond photoconductivity measurements of polymorphous PbTe films have been performed. Excess carriers were excited in the films by means of a picosecond YAG:Nd laser with pulse duration t=12 ps. The instantaneous relaxation times of photoconductivity were obtained as a function of the excess carrier concentration Delta N from the kinetic analysis. The heterophase junction nature of the comparatively thin (d approximately=1 mu m) films was confirmed by their high photosensitivity. The junction thickness was evaluated from the interpretation of the instantaneous lifetime dependence on the excess carrier concentrations.

Evaluation of the stimulated menstrual cycle by magnetic resonance imaging

Changes in uterine zonal anatomy in six women during a cycle of treatment with clomiphene citrate is studied by magnetic resonance imaging. There was a rapid rate of increase in endometrial thickness during the periovulatory period that was similar to the pattern seen in a prior study of women with normal (nonstimulated) cycles. Junctional zone thickness did not parallel the endometrial pattern and differed from the response seen in nonstimulated cycles. Results of large scale studies may help to further understand the effects of these medications.

Silicided Shallow Junction Formation Using Ion Implantation and Thermal Annealing

ABSTRACTThe combination of arsenic and boron implantation with rapid thermal annealing (RTA) has been investigated to form shallow p-n junctions under a titanium silicide (TiSi2) metallization. The use of TiSi2 as a connection material can lead to the destruction of the junction if the kinetics of silicidation and doping are not well controlled. The purpose of this study is to better understand and control these kinetics, using far-from equilibrium processing such as ion implantation and RTA. The structures were characterized by Rutherford Backscattering Spectometry (RBS) for arsenic and silicide profiling, Secondary Ion Mass Spectometry (SIMS) for boron profiling, Scanning Electron Microscopy (SEM), and electrical sheet resistance measurements. Two procedures were investigated. Both involved the thermal reaction of Ti thin films, sputter-deposited with thicknesses ranging between 40 and 80 nm. In the first experiment, the as-deposited films were implanted with either 115 keV arsenic or 28 keV boron to form the junction, disperse the native oxide, and ion beam mix the Ti and Si. The films were then subjected to an RTA at 750°C for 15 to 60 seconds, which leads to TiSi2 formation in unimplanted films. Implantation was found to actually prevent TiSi2 formation. Ion transport calculations indicated that dopant pile-up at the interface might inhibit silicidation while higher energies and larger implant doses can more effectively ion beam mix Ti and Si. A more attractive solution consists of first forming TiSi2 from the as-deposited Ti by RTA, and then implanting to form the junction. This resulted in better control of the junction thickness. A sharp increase in the TiSi2 resistivity was found after implantation but the original value could be restored by a second RTA. This RTA also electrically activated the dopants and recrystallized the junction. The material properties of Ti/Si and TiSi2/Si under ion bombardment, RTA, doping, and conventional furnace annealing will be discussed.

Anin SituStudy of a Sclerosing Solution in Rabbit Medial Collateral Ligaments and Its Junction Strength

A double-blind study was conducted to assess the influence of a sclerosing solution on rabbit medial collateral ligaments (MCL) in situ. It was shown that repeated injections of 5% sodium morrhuate into the MCL and its bony attachments significantly increased its bone-ligament-bone junction strength, ligament mass and thickness when compared to saline-injected controls. Morphometric analysis of electron micrographs showed a highly significant corresponding increase of the collagen fibril diameters in the experimental ligament compared against the control MCL. These composite findings suggested that the sclerosing solution had a significant influence on dense connective tissue at the insertion sites. The mechanisms for these changes are uncertain and are the basis for future investigations.

Junction profiles of nonplanar polycrystalline CuxS/CdS solar cells

AES depth profiles were obtained from nonplanar CuxS/CdS solar cells fabricated by the ’’wet’’ ion exchange technique. The horizontal junction (cap) thickness was determined by utilizing a focused electron beam with a spot size less than the diameter of a single grain. This technique minimized the introduction of profile artifacts caused by the nonplanar junction morphology. The cap thickness was compared to the thickness determined by a conventional electrochemical analysis developed for CuxS. No correlation was found to exist between the two results. The AES depths ranged from 0.08 to 1.16 of the electrochemical result. The S peak shape was also investigated and the identification of the chemical state of the S was used to determine the location of the CuxS/CdS interface. This method agreed well with the crossover in the Cu and Cd profiles.

Calcium effects on gap junction structure and cell coupling.

PROTOPLASMIC molecules of low molecular weight are known to travel freely across the boundaries between most neighbouring cells through small intercellular channels generally thought to be at the intramembranous particles of gap junctions1–3. The permeability of the channels can be decreased to a complete interruption of cell communication by a variety of treatments2–10. Most of these treatments raise the concentration of ionised calcium, [Ca2+], in the cytoplasm8, suggesting that calcium may be the uncoupling agent in both vertebrate9 and invertebrate cells2,8. In some systems glutaraldehyde fixation has also been shown to produce uncoupling3; however, this type of uncoupling does not seem to be triggered by calcium10. In parallel with functional uncoupling reversible structural changes have been described in gap junctions of crayfish characterised by an increase in tightness and regularity of particle aggregation and a decrease in junctional thickness and particle size10. These changes, interpreted as reflecting conformational rearrangements in the protein framework of the channels resulting in channel obliteration, were recently confirmed in the rat11 although in the latter, functional uncoupling was not measured electrophysiologically, but only presumed on the basis of reasonable comparative arguments. It remains uncertain whether or not the changes in both the gap junction structure and the cell coupling are due to a direct action of calcium on the junctional membranes. We show here that the junctional change is indeed a calcium effect, triggered by [Ca2+] as low as 5×10−7 M.

LED fundamentals: Comparison of front- and edge-emitting diodes

We establish a criterion for the maximum amount of power that can be launched into an optical fiber relative to a front-emitting diode of given active layer (junction) thickness. According to this criterion it should be possible to obtain 7.5 times the amount of power from a light-emitting diode (LED) of optimum design relative to a front-emitting LED whose active layer of equal intrinsic brightness is 2.5 μm thick. We also discuss the performance of edge-emitting diodes and find that the LED's of our examples are capable of providing approximately 50 percent of the power expected from the ultimate diode configuration.

Cold pressure welded copper-constantan thermocouples

Cold pressure welding has been used to produce a lap junction between 0.15 mm thick strips of copper and constantan which had been plated with 2 mu m of nickel. The junction thickness after welding was 0.10 mm, and after further cold rolling to 0.06 mm a thermocouple performance within the requirements of BS 1041 (1966) was obtained.

Impurity diffusion into semiconductors

A method is described by which it is possible to obtain thin diffusion layers with various impurity distributions within the layer. Calculations and graphs are given which may be used to determine the junction thickness and impurity concentration at any point of the diffusion layer when the diffusion conditions are known.

Gold-germanium junctions as particle spectrometers

Gold-germanium p-n junctions for the detection of α-particles and fission fragments are reported in the References. The present investigation, using protons, deuterons, α-particles and He3 ions, shows that the output pulse is proportional to the incident energy, providing the particle range does not exceed the effective junction thickness. Measurements on the maximum pulse heights obtainable from protons and deuterons agree on the effective junction thickness; however, the exact value varies with method and conditions of manufacture and increases with the voltage across the junction. The output pulse height is not dependent on the type of particle provided the junction bias is maintained above the minimum value (about 1 volt) required to prevent recombination. The pulse height is independent of crystal temperature if the voltage on the crystal is fixed, but as the temperature decreases the signal/noise ratio increases. At liquid-nitrogen temperature the resolution of 5 MeV α-particles (2–3%) is not determined by the signal/noise ratio. A value of 2.84 ± 0.12 eV, in accord with that previously reported, has been found for the energy required to produce an electron-hole pair in germanium. Pulse rise times have been shown to be less than 3 millimicrosec and are believed to be much shorter than this.Applications of these detectors in charged-particle spectroscopy are discussed.