10 research outputs found
Superconductivity in silicon nanostructures
We present the findings of the superconductivity observed in the silicon
nanostructures prepared by short time diffusion of boron on the n-type Si(100)
surface. These Si-based nanostructures represent the p-type ultra-narrow
self-assembled silicon quantum wells, 2nm, confined by the delta - barriers
heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the
delta - barriers appear to consist of the trigonal dipole centres, which are
caused by the negative-U reconstruction of the shallow boron acceptors. Using
the CV and thermo-emf techniques, the transport of two-dimensional holes inside
SQW is demonstrated to be accompanied by single-hole tunneling through these
negative-U centres that results in the superconductivity of the delta -
barriers. The values of the correlation gaps obtained from these measurements
are in a good agreement with the data derived from the temperature and magnetic
field dependencies of the magnetic susceptibility, which reveal a strong
diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on
Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200
Spin interference in silicon one-dimensional rings
We present the first findings of the spin transistor effect caused by the
Rashba gate-controlled ring embedded in the p-type self-assembled silicon
quantum well that is prepared on the Si (100) surface. The coherence and phase
sensitivity of the spin-dependent transport of holes are studied by varying the
value of the external magnetic field and the gate voltage that are
perpendicular to the plane of the double-slit ring. Firstly, the quantum
scatterers connected to two one-dimensional leads and the quantum point contact
inserted in the one of the arms of the double-slit ring are shown to define the
amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher
conductance oscillations. Secondly, the amplitude and phase sensitivity of the
0.7 feature of the hole quantum conductance staircase revealed by the quantum
point contact inserted are found to result from the interplay of the
spontaneous spin polarization and the Rashba spin-orbit interaction.Comment: 2 pages, 2 figures, presented at the 5th International Conference on
Strongly Correlated Electron Systems, SCES'05, Vienna, Austria, 26-30 July,
200
Magnetic resonance spectroscopy of single centers in silicon quantum wells
We present the new optically-detected magnetic resonance (ODMR) technique
which reveals single point defects in silicon quantum wells embedded in
microcavities within frameworks of the excitonic normal-mode coupling (NMC)
without the external cavity and the hf source.Comment: 8 pages, 7 figure
Quantum conductance staircase of holes in silicon nanosandwiches
The results of studying the quantum conductance staircase of holes in one-dimensional channels obtained by the split-gate method inside silicon nanosandwiches that are the ultra-narrow quantum well confined by the delta barriers heavily doped with boron on the n-type Si (100) surface are reported. Since the silicon quantum wells studied are ultra-narrow (~2 nm) and confined by the delta barriers that consist of the negative-U dipole boron centers, the quantized conductance of one-dimensional channels is observed at relatively high temperatures (T>77 K). Further, the current-voltage characteristic of the quantum conductance staircase is studied in relation to the kinetic energy of holes and their sheet density in the quantum wells. The results show that the quantum conductance staircase of holes in p-Si quantum wires is caused by independent contributions of the one-dimensional (1D) subbands of the heavy and light holes. In addition, the field-related inhibition of the quantum conductance staircase is demonstrated in the situation when the energy of the field-induced heating of the carriers become comparable to the energy gap between the 1D subbands. The use of the split-gate method made it possible to detect the effect of a drastic increase in the height of the quantum conductance steps when the kinetic energy of holes is increased; this effect is most profound for quantum wires of finite length, which are not described under conditions of a quantum point contact. In the concluding section of this paper we present the findings for the quantum conductance staircase of holes that is caused by the edge channels in the silicon nanosandwiches prepared within frameworks of the Hall geometry. This longitudinal quantum conductance staircase, Gxx, is revealed by the voltage applied to the Hall contacts, with the plateaus and steps that bring into correlation respectively with the odd and even fractional values
Evaluating Multisite rCBV Consistency from DSC-MRI Imaging Protocols and Postprocessing Software Across the NCI Quantitative Imaging Network Sites Using a Digital Reference Object (DRO)
The use of rCBV as a response metric in clinical trials has been hampered, in part, due to variations in the biomarker consistency and associated interpretation across sites, stemming from differences in image acquisition and post-processing methods. This study leveraged a dynamic susceptibility contrast magnetic resonance imaging digital reference object to characterize rCBV consistency across 12 sites participating in the Quantitative Imaging Network (QIN), specifically focusing on differences in site-specific imaging protocols (IPs; n = 17), and PMs (n = 19) and differences due to site-specific IPs and PMs (n = 25). Thus, high agreement across sites occurs when 1 managing center processes rCBV despite slight variations in the IP. This result is most likely supported by current initiatives to standardize IPs. However, marked intersite disagreement was observed when site-specific software was applied for rCBV measurements. This study\u27s results have important implications for comparing rCBV values across sites and trials, where variability in PMs could confound the comparison of therapeutic effectiveness and/or any attempts to establish thresholds for categorical response to therapy. To overcome these challenges and ensure the successful use of rCBV as a clinical trial biomarker, we recommend the establishment of qualifying and validating site- and trial-specific criteria for scanners and acquisition methods (eg, using a validated phantom) and the software tools used for dynamic susceptibility contrast magnetic resonance imaging analysis (eg, using a digital reference object where the ground truth is known)
Evaluating Multisite Rcbv Consistency From Dsc-Mri Imaging Protocols And Postprocessing Software Across The Nci Quantitative Imaging Network Sites Using A Digital Reference Object (Dro)
Relative cerebral blood volume (rCBV) cannot be used as a response metric in clinical trials, in part, because of variations in biomarker consistency and associated interpretation across sites, stemming from differences in image acquisition and postprocessing methods (PMs). This study leveraged a dynamic susceptibility contrast magnetic resonance imaging digital reference object to characterize rCBV consistency across 12 sites participating in the Quantitative Imaging Network (QIN), specifically focusing on differences in site-specific imaging protocols (IPs; n = 17), and PMs (n = 19) and differences due to site-specific IPs and PMs (n = 25). Thus, high agreement across sites occurs when 1 managing center processes rCBV despite slight variations in the IP. This result is most likely supported by current initiatives to standardize IPs. However, marked intersite disagreement was observed when site-specific software was applied for rCBV measurements. This study\u27s results have important implications for comparing rCBV values across sites and trials, where variability in PMs could confound the comparison of therapeutic effectiveness and/or any attempts to establish thresholds for categorical response to therapy. To overcome these challenges and ensure the successful use of rCBV as a clinical trial biomarker, we recommend the establishment of qualifying and validating site- and trial-specific criteria for scanners and acquisition methods (eg, using a validated phantom) and the software tools used for dynamic susceptibility contrast magnetic resonance imaging analysis (eg, using a digital reference object where the ground truth is known)
Evaluating the Use of rCBV as a Tumor Grade and Treatment Response Classifier Across NCI Quantitative Imaging Network Sites: Part II of the DSC-MRI Digital Reference Object (DRO) Challenge
We have previously characterized the reproducibility of brain tumor relative cerebral blood volume (rCBV) using a dynamic susceptibility contrast magnetic resonance imaging digital reference object across 12 sites using a range of imaging protocols and software platforms. As expected, reproducibility was highest when imaging protocols and software were consistent, but decreased when they were variable. Our goal in this study was to determine the impact of rCBV reproducibility for tumor grade and treatment response classification. We found that varying imaging protocols and software platforms produced a range of optimal thresholds for both tumor grading and treatment response, but the performance of these thresholds was similar. These findings further underscore the importance of standardizing acquisition and analysis protocols across sites and software benchmarking