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1.
x Si1-x/Si heterostructures have been obtained. Here the chemical effects seem to be of less importance. The Fermi-level effect determines
the ionized boron solubilities in GexSi1-x and in Si, as well as the thermal equilibrium concentration of the singly-positively-charged crystal self-interstitials I+ which governs the boron diffusion process. The junction carrier concentration affects the concentration of I+ and solubility of B in the region and hence controls B diffusion across the heterojunction.
Received: 20 August 1998/Accepted: 23 September 1998 相似文献
2.
Inverse problems in statistical physics are motivated by the challenges of ‘big data’ in different fields, in particular high-throughput experiments in biology. In inverse problems, the usual procedure of statistical physics needs to be reversed: Instead of calculating observables on the basis of model parameters, we seek to infer parameters of a model based on observations. In this review, we focus on the inverse Ising problem and closely related problems, namely how to infer the coupling strengths between spins given observed spin correlations, magnetizations, or other data. We review applications of the inverse Ising problem, including the reconstruction of neural connections, protein structure determination, and the inference of gene regulatory networks. For the inverse Ising problem in equilibrium, a number of controlled and uncontrolled approximate solutions have been developed in the statistical mechanics community. A particularly strong method, pseudolikelihood, stems from statistics. We also review the inverse Ising problem in the non-equilibrium case, where the model parameters must be reconstructed based on non-equilibrium statistics. 相似文献
3.
V. Grossi M. Passacantando G. Impellizzeri L. Ottaviano 《Applied Surface Science》2008,254(24):8093-8097
Single crystal germanium nanowires have been grown by vapour-liquid-solid deposition onto silicon oxide substrates with Au catalyst nanoparticles. They have been doped by two different techniques: Ge and Mn co-evaporation during growth and post-growth Mn implantation. Scanning electron microscopy images show that Mn-implanted nanowires have a lower surface density and a smaller average diameter (18.8 nm) than the un-doped ones and those Mn doped by co-deposition. The effectiveness of Mn doping has been verified by X-ray photoemission spectroscopy and by energy-dispersive X-ray measurements, indicating in the two cases significant Mn atomic concentration in the nanowire. X-ray diffraction indicates that the nanowires are single crystals and that they do not contain precipitates of Mn extrinsic phases. Both SEM and XPS experimental evidences are in line to indicate that the Mn doping by ion implantation is preferable with respect to that one performed by co-evaporation as it reduces the thickness of the outer oxide sheath of the nanowires and their diameter. 相似文献
4.
Bernd Tillack Bernd Heinemann Dieter Knoll Holger Rücker Yuji Yamamoto 《Applied Surface Science》2008,254(19):6013-6016
Incorporation of high doping concentrations and the creation and maintaining of steep doping profiles during processing are key enabler for high level RF performance of heterojunction bipolar transistors (HBTs). In this paper, we discuss results of base doping and dopant profile control for npn and pnp SiGe HBTs fabricated within 0.25 μm BiCMOS technologies. High level of electrically active B and P doping concentrations (up to 1020 cm−3) have been incorporated into SiGe. By adding C to SiGe steep doping profiles have been maintained due to the prevention of dopant diffusion during device processing. It is shown that broadening of P doping profiles caused by segregation could be reduced by lowering the deposition temperature for the SiGe cap. B and P atomic layer doping is shown to be suitable for the creation of steep and narrow doping profiles. This result is demonstrating the capability of the atomic layer processing approach for future devices with critical requirements of dopant dose and location control. 相似文献
5.
Chemically disordered face-centered cubic (fcc) FePt nanoparticles (NPs) with a mean diameter of 9 nm were synthesized via pyrolysis of iron(III) ethoxide and platinum(II) acetylacetonate. The surface ligands of these NPs were then exchanged from oleic acid to tetramethylammonium hydroxide (TMAOH) to measure the longitudinal (T1) and transverse (T2) proton relaxation times of aqueous dispersion of FePt NPs. Magnetic resonance relaxometry reveals that TMAOH-capped FePt NPs have a higher T2-shortening effect than conventional superparamagnetic iron oxide NPs, indicating that fcc-phase FePt NPs might be superior negative contrast agents for magnetic resonance imaging. 相似文献
6.
Magnetic and structural properties of a Finemet type alloy (Fe73.5Ge15.5Nb3B7Cu1) without Si and high Ge content were studied. Amorphous material was obtained by the melt spinning technique and was heat treated at different temperatures for 1 h under high vacuum to induce the nanocrystallization of the sample. The softest magnetic properties were obtained between 673 and 873 K. The role of Ge on the ferromagnetic paramagnetic transition of the as-quenched alloys and its influence on the crystallization process were studied using a calorimetric technique. Mössbauer spectroscopy was employed in the nanocrystallized alloy annealed at 823 K to obtain the composition of the nanocrystals and the amorphous phase fraction. Using this data and magnetic measurements of the as-quenched alloy, the magnetic contribution of nanocrystals to the alloy annealed at 823 K was estimated via a linear model. 相似文献
7.
A.D. Arelaro E. Lima Jr L.M. Rossi P.K. Kiyohara H.R. Rechenberg 《Journal of magnetism and magnetic materials》2008
The influence of different M2+ cations on the effective magnetic anisotropy of systems composed of MFe2O4 (M=Fe, Co and Mn) nanoparticles was investigated. Samples were prepared by the high-temperature (538 K) solution phase reaction of Fe (acac)3, Co (acac)2 and Mn (acac)2 with 1,2 octanodiol in the presence of oleic acid and oleylamine. The final particles are coated by an organic layer of oleic acid that prevents agglomeration. Transmission electron microscopy (TEM) images show that particles present near spherical form and a narrow grain size distribution, with mean diameters in the range of 4.5–7.6 nm. Powder samples were analyzed by ac susceptibility and Mössbauer measurements, and Keff for all samples was evaluated using both techniques, showing a strong dependence on the nature of the divalent cation. 相似文献
8.
Investigation of magneto-anisotropy field for system of particles with near superparamagnetic volume
L.P. Ol’khovik A.S. Kamzin E.L. Karyakina Z.I. Sizova E.V. Shurinova 《Journal of magnetism and magnetic materials》2008
We obtained the temperature dependence for low-field boundary of the anisotropy field distribution in a system of barium hexaferrite nanocrystals in the temperature range from 300 to 700 K. We treated the experimental data taking into account the influence of thermal fluctuations on the anisotropy field and the transition of particles into the paramagnetic state, stimulated by external magnetic field. We showed that the dependence under consideration is formed by particles of different volume, which increased from 3.5×10−18 to 40×10−18 cm3 while the particles lost their magnetic stability with the temperature growth. 相似文献
9.
Z.F. Zi Y.P. Sun X.B. Zhu Z.R. Yang J.M. dai W.H. Song 《Journal of magnetism and magnetic materials》2008
M-type strontium hexaferrite (SrFe12O19) particles had been prepared by a modified chemical co-precipitation route. Structural and magnetic properties were systematically investigated. Rietveld refinement of X-ray powder diffraction results showed that the sample was single-phase with the space group of P63/mmc and cell parameter values of a=5.8751 Å and c=23.0395 Å. The results of field-emission scanning electronic microscopy showed that the grains were regular hexagonal platelets with sizes from 2 to 4 μm. The composition determined by energy dispersive spectroscopy is the stoichiometry of SrFe12O19. The ferrimagnetic to paramagnetic transition was sharp with Curie temperature TC=737 K, which further confirmed that the samples were single phase. However, it was found that the coercivity, saturation magnetization and the squareness ratio of the synthesized SrFe12O19 samples were lower than the theoretical values, which could be explained by the multi-domain structure and the increase of the demagnetizing factor. 相似文献
10.
T. Eimüller P. Fischer M. Köhler M. Scholz P. Guttmann G. Denbeaux S. Glück G. Bayreuther G. Schmahl D. Attwood G. Schütz 《Applied Physics A: Materials Science & Processing》2001,73(6):697-701
X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism
in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission
X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution
down to 25 nm were used to image out-of-plane magnetized (4 ?Fe / 4 ?Gd)×75 systems. Magnetic domains could be studied in
arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced
using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nmCr / 50 nmFe / 6 nmCr
film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible
applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the
sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II.
Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献