排序方式: 共有46条查询结果,搜索用时 0 毫秒
31.
LEED, AES, UPS and EELS have been used to observe the growth of thallium in the Stranski-Krastanov mode on copper(100). In the sub-monolayer range, thallium forms three commensurate ordered overlayer structures. The transition from the first overlayer structure to the second involves a transition from a one-dimensional to a two-dimensional structure. The resulting change in co-ordination number reduces the binding energy of the thallium 5d core levels and increases their width. 相似文献
32.
We report on the magnetic behaviour of films of Fe nanoparticles deposited from the gas phase with sizes in the range 2–3 nm embedded in Ag and Co matrices and Co nanoparticles of the same size embedded in Ag matrices. Magnetometry measurements, using a VSM, of very low volume fraction (1–2%) assemblies of Fe and Co in Ag show perfect superparamagnetism and enable us to confirm that the size distribution of the particles in the matrix is the same as that of the free particles prior to deposition. The hysteresis loops at 2 K, which is below the blocking temperature, show that the particles have a uniaxial anisotropy that is randomly oriented in three dimensions with the Co nanoparticles having a much higher anisotropy than the Fe particles. The soft magnetic behaviour of pure Fe and Co nanoparticle films with no matrix is well described by a random anisotropy model and is consistent with the formation of a correlated super-spin glass (CSSG) characteristic of amorphous materials. The Co nanoparticle films appear to have a lower random anisotropy than the Fe ones in contrast to the behaviour observed for the isolated particles. Films of Fe nanoparticles embedded in Co matrices, whose saturation magnetization exceeds the Slater–Pauling curve, also show magnetic behaviour consistent with a CSSG. At high volume fractions, the films of Fe nanoparticles embedded in Co matrices behave almost identically to films of pure Co nanoparticles. 相似文献
33.
C. Binns S.H. Baker M.J. Maher S.C. Thornton S. Louch S.S. Dhesi N.B. Brookes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):189-192
A portable UHV-compatible gas aggregation cluster source, capable of depositing clean mass-selected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in
the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters
show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe.
The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably
decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than
the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages
the deposited clusters are super-paramagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges
as the cluster density increases and for cluster films with a thickness greater than 50 ?(i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional
deposition source. Thick cluster-assembled film show a strong in-plane anisotropy.
Received 14 December 2000 相似文献
34.
A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified. 相似文献
35.
Powerful recombination centers resulting from reactions of hydrogen with carbon–oxygen defects in n‐type Czochralski‐grown silicon 下载免费PDF全文
36.
Stephen Binns 《Mathematical Logic Quarterly》2003,49(4):327-335
This is a contribution to the study of the Muchnik and Medvedev lattices of non‐empty Π01 subsets of 2ω. In both these lattices, any non‐minimum element can be split, i. e. it is the non‐trivial join of two other elements. In fact, in the Medvedev case, ifP > M Q, then P can be split above Q. Both of these facts are then generalised to the embedding of arbitrary finite distributive lattices. A consequence of this is that both lattices have decidible ?‐theories. 相似文献
37.
We have studied the magnetic behaviour of polycrystalline dysprosium films grown in their pure state and containing Fe impurity. The films were grown by MBE in ultra-high vacuum and Fe impurity was introduced either as Fe atoms from a conventional MBE source or as 1.8 nm diameter Fe nanoparticles from a gas aggregation source. We show that with a suitable magnetothermal history it is possible to produce a large thermal hysteresis up to room temperature in all samples. In the Dy ferromagnetic state both types of Fe impurity cause a reduction in the observed magnetisation but the reduction of average moment observed in the case of the Fe nanoparticles is much greater than that for atoms for a similar quantity of Fe. Despite the low solubility of Fe in Dy EXAFS data clearly indicates alloying in the case of embedded Fe nanoparticles. We attribute the low moment in the Dy films containing nanoparticles to alloying within the particles producing a significant proportion of high-Fe-concentration Dy-Fe alloy. 相似文献
38.
Stephen Binns 《Mathematical Logic Quarterly》2013,59(3):206-218
We investigate a directed metric on the space of infinite binary sequences defined by where C(X?n‖Y?n) is the Kolmogorov complexity of X?n given Y?n. In particular we focus on the topological aspects of the associated metric space—proving that it is complete though very far from being compact. This is a continuation of earlier work investigating other geometrical and toplogical aspects of this metric. 相似文献
39.
Chris Binns Pilar Prieto Stephen Baker Paul Howes Ruggero Dondi Glenn Burley Leonardo Lari Roland Kr?ger Andrew Pratt Sitki Aktas John K. Mellon 《Journal of nanoparticle research》2012,14(9):1-16
In this study, efforts were placed in giving some in vitro key clues to the question on which is more efficient for the cancer hyperthermia between intracellular and extracellular modalities. Near infrared (NIR) photothermal responsive gold nanorods (GNRs) were adopted to cause cellular thermolysis either from inside or outside of cells. GNRs were synthesized with the size of 30.4?nm (in length)?×?8.4?nm (in width). Demonstrated by ICP-MS (inductively coupled plasmon mass spectroscopy), UV?CVis spectroscopy and transmission electron microscopy analyses, various cell uptake doses of nanoparticles were differentiated due to different molecular designs on GNRs surfaces and different types of cells chosen (three cancer cell lines and three normal ones). Under our continuous wavelengths (CW) NIR irradiation, it resulted that the cells which internalized GNRs died faster than the cells surrounded by GNRs. Furthermore, fluorescent images and flow cytometry data also showed that the NIR photothermal therapeutic effect was greater when the amount of internalized GNRs per cell was larger. Generally speaking, the GNRs assisted intracellular hyperthermia exhibited more precise and efficient control on the selective cancer ablation. To a larger degree, such a relationship between GNRs distribution and hyperthermia efficiency might be applied to wider spectra of cell types and heat-producing nanoparticles, which provided a promise for future cancer thermal therapeutic designs. 相似文献
40.
S. Laureti D. Peddis L. Del Bianco A.M. Testa G. Varvaro E. Agostinelli C. Binns S. Baker M. Qureshi D. Fiorani 《Journal of magnetism and magnetic materials》2012
We have studied the Exchange Bias (EB) effect in nanocomposite films consisting of Fe nanoparticles (mean size ∼1.9 nm) embedded in an antiferromagnetic Mn matrix. They were produced by co-deposition through a gas aggregation cluster source and molecular beam epitaxy and have different Fe volume filling fractions (2.2% and 24.8%). The exchange field, higher in the sample with higher Fe concentration (at T=5 K, Hex∼460 Oe for 24.8% and ∼310 Oe for 2.2% ), in both the samples decreases with increasing T, finally disappearing at T∼40 K. The EB properties have been studied in conjunction with results on the thermal dependence of the magnetic coercivity, zero-field-cooled and field-cooled magnetization and thermoremanence. The different Fe content strongly affects the magnetothermal properties, featuring superparamagnetic relaxation in the diluted sample and a reentrant ferromagnet-type transition in the concentrated one. Hence, the EB properties of the two samples have been discussed in consideration of such peculiarities of the magnetic behavior and highlighting the role of the Mn matrix. 相似文献