Adsorption of atomic and molecular oxygen on Si(100)2x1: coverage dependence of the Auger O KVV lineshape.

By means of Auger electron spectroscopy (AES) we have monitored the room temperature adsorption of O2 and N2O on the clean Si(0 0 1)2 × 1 surface. We have found, for the first time, a significant variation in the intensity ratio of the K L1 L1 and K L23 L23 O Auger lines in the submonolayer range. This variation can be related to a change in bonding configuration of the oxygen atom/molecule in the initial adsorption stage in which the influence of inter-atomic matrix elements of the Auger process cannot be neglected

Reconstructions and phase transitions of the Ge(001) surface

The authors have calculated the energy differences between the four members of the 2*1 family (b(2*1), c(4*2), p(2*2) and p(4*1)) of the Ge (001) surface by taking only electrostatic interactions between the dimers into account. They have found that p(2*2) is the lowest-energy reconstruction at zero temperature. The phase transitions from ordered p(2*2) to disordered (2*1) and ordered c(4*2) to disordered (2*1) are discussed using the authors' energy calculations, the mean-field approximation, the Ising model and Onsagers' exact solution. A second-order phase transition is found at about 200-250 K from an ordered p(2*2) (c(4*2)) dimer reconstruction to a disordered (2*1) dimer reconstruction assuming a charge transfer of 0.08e between the up atom and the down atom of the asymmetric dimer

Fabrication of 45 degrees template grain boundary junctions using a CaO lift-off technique

45 degrees grain boundary junctions have been made using (100) MgO substrates, a CeO2 template layer and an YBa2Cu3O7 top layer. To minimize the damage to the MgO surface, which will occur if the CeO2 is structured using ion milling, the CeO2 layer has been structured using the CaO lift-off technique. Electrical measurements of these junctions as a function of temperature, microwave irradiation and magnetic field will be discussed in this paper

Response of YBCO/PCBO/YBCO ramp type Josephson junctions to near MM wave irradiation

A high Tc Josephson device for high frequency detection applications is being developed, consisting of an YBCO/PBCO/YBCO ramp type junction and a broad band log-periodic antenna. In this contribution we present the response of such a device to (near) mm wave irradiation. Shapiro steps have been observed up to very high voltage values - nearly 4 mV at 10 K, at the maximum of the radiation power. The modulation of the step amplitudes shows very good resemblence with the predictions from the Resistively Shunted Junction model

Multilayer studies and applications in template bi-epitaxial DC SQUIDS

Multilayer deposition for the creation of a well-defined grain boundary, based on different in-plane orientations of c-axis oriented thin YBa2O2Cu3O7-δ layers on a single substrate, has been performed on three different kinds of substrates: (1102)-oriented Al2O3 , (100) SrTiO3, and (100) MgO. The multilayers consist of combinations of SrTiO3, MgO, CeO2, and YBa2O2Cu3O7-δ. The YBa 2O2Cu3O7-δ top layers on (1102) Al2O3 and (100) SrTiO3 were polycrystalline. Josephson junctions and DC superconducting quantum interference devices (SQUIDs) have been structured in the layers on MgO. Shapiro steps were observed. The Jcρn-product of the junctions at 4.2 K is on the order of 1 mV. The critical current decreases in good approximation linearly with increasing temperature, whereas the normal state resistance is nearly temperature independent. Voltage modulation was observed at temperatures up to 77 K

Observation of the AC Josephson effect up to THZ frequencies in YBCO/PBCO/YBCO ramp-type Josephson junctions

We present the response to 100 GHz irradiation of high-Tc Josephson junction devices for mixer/detector applications in the (sub-) mm wave range. These devices consist of a YBCO/PBCO/YBCO ramp-type junction combined with a planar logarithmic periodic antenna. The critical current and the first two Shapiro steps modulate with 100 GHz power according to the resistively shunted junction (RSJ) model. At 10 K clear Shapiro steps have been observed up to a voltage of about 7.5 mV. This corresponds to phase locking of 3.6 THz AC Josephson oscillations by the 36th harmonic of the 100 GHz signal. The number of observed steps is currently limited by the available power, but they are present up to voltages strongly exceeding the IcRn product of the junction at all temperatures

Fabrications aspects of microwave devices, including ramp-type high-Tc Josephson junctions and log-periodic antenna's

We describe the development of high-Tc Josephson junction devices for applications at millimeter wave frequencies. These devices consist of ramp type YBCO/PBCO/YBCO Josephson junctions that are equipped with a noble metal log-periodic antenna. Growth conditions of all layers, as well as etching, cleaning and annealing procedures are being optimized, to guarantee well-defined device properties. Lowering the deposition temperature of the thick PBCO layer strongly improved its isolating properties, which is of extreme importance for good reproducability of junction fabrication. Special attention is being focused on the optimization of the contact of noble metal to YBCO as well its adhesion to the substrate. Best results are obtained using sputtered gold contacts, after a soft Ar ion sputter clean treatment of the damaged YBCO surface, followed by an anneal procedure

Subharmonic Shapiro steps in high‐Tc Josephson junctions

We studied the response of high‐Tc biepitaxial grain boundaryjunctions to 100 GHz radiation in the presence of a magnetic field. Integer as well as subharmonic constant voltage steps are observed, even at one‐fifth of the voltage separation between integer (Shapiro) steps. Our results indicate that this behavior is due to the synchronized motion of Josephsonvortices along the junction. We show that this effect is directly related to the width of the junction, and not to an array of weaker regions in the barrier

Early and Late Results Following Choledochoduodenostomy and Choledochojejunostomy

Objective —To evaluate the results and complications of choledochoduodenostomy and choledochojejunostomy for benign and malignant disease and to review them in the light of the survival of the underlying disorders

Detecting time-fragmented cache attacks against AES using Performance Monitoring Counters

Cache timing attacks use shared caches in multi-core processors as side channels to extract information from victim processes. These attacks are particularly dangerous in cloud infrastructures, in which the deployed countermeasures cause collateral effects in terms of performance loss and increase in energy consumption. We propose to monitor the victim process using an independent monitoring (detector) process, that continuously measures selected Performance Monitoring Counters (PMC) to detect the presence of an attack. Ad-hoc countermeasures can be applied only when such a risky situation arises. In our case, the victim process is the AES encryption algorithm and the attack is performed by means of random encryption requests. We demonstrate that PMCs are a feasible tool to detect the attack and that sampling PMCs at high frequencies is worse than sampling at lower frequencies in terms of detection capabilities, particularly when the attack is fragmented in time to try to be hidden from detection