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The origin of the 'coffee-bean' contrast seen in transmission electron microscopy images of quantum dot structures is examined.

CdSe/ZnSe quantum dot structures were investigated for growth and vertical correlation.

Research into Co/Pd multilayers deposited on either Ta or indium tin oxide seed layers as a possible perpendicular recording media is presented. It is concluded that the indium tin oxide underlayer is beneficial to the basic perpendicular magnetic media properties. It gives a magnetic multilayer that is less exchanged coupled than the Ta underlayer.

A micromagnetic study employing OOMMF1 simulator of magnetic switching wave propagation along magnetic data channels is presented. The optimization of the wave propagation as a function of geometry and physical parameters is investigated, which resulted in an order of magnitude increase in the depth of magnetic signal propagation. Unlike unoptimized rapidly decaying waves, the resulting wave stays practically the same throughout the channel, improving wave detection characteristics. When the in-plan dimensions of the channel are scaled proportionally, the optimized propagation length remains relatively constant. This indicates a possibility of the scalability in the data channel, which has significant technological applications. [ABSTRACT FROM AUTHOR]

InAs quantum dot (QD) layers grown by molecular-beam epitaxy were investigated by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. To achieve the highest possible In concentration in the QDs, InGaAs (instead of GaAs) cap layers with different In concentrations were deposited after the growth of the InAs QD layer. We combine different TEM techniques to determine the shape, size, and composition of the QDs. By applying a post-processing procedure, we are able to reconstruct the In concentration in the QDs which is measured too low in TEM due to the embedding of the QDs in material with lower In concentration and averaging along the finite TEM sample thickness. The determination of the composition of the layers on an atomic scale shows that the In concentration in the QDs increases in growth direction and reaches values up to 90%. Redistribution of indium during the InGaAs cap layer growth leads to a decrease of the In concentration in the cap layer with respect to the nominal In concentration. The observed redshift of the PL peak with increasing In concentration in the cap layer is attributed to the enlargement of island size and the change of the strain in the QD layers. [ABSTRACT FROM AUTHOR]

The influence of the conditions during growth of InAs/GaAs quantum-dot structures on GaAs(001) by molecular-beam epitaxy was investigated systematically with respect to achieving quantum-dot photoluminescence in the 1 eV range. The growth temperature, As flux, growth rate, InAs deposit, and growth interruption time before cap layer growth were varied. Photoluminescence spectroscopy and transmission electron microscopy were used to study the optical and structural properties. Large InAs quantum dots with photoluminescence in the 1 eV range were obtained at a low growth rate of 0.0056 ML/s. Analyzing in particular the low-growth-rate regime, we found that an InAs deposition of at least 2.4 ML and a growth temperature of 500-510 °C were crucial to obtain large quantum dots with a high size uniformity. Composition analyses by transmission electron microscopy revealed a significantly higher In concentration in the quantum dots grown at low growth rate compared to high-growth-rate samples. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to explore three-dimensional magnetic recording as a next generation recording technology. To defer the superparamagnetic limit in magnetic recording substantially beyond the 1 Tbit/in.2 mark, it is proposed to stack magnetic bits in a third (vertical) dimension. The vertical stacking underlies the concept of three-dimensional (3D) magnetic memory and recording—the primary subject of this paper. A clear distinction between absolute 3D memory and its trivial multilevel implementation is drawn. The paper focuses on the study of the media design and write and read processes. To minimize the intersymbol interference and improve stability, it is proposed to pattern the recording media in all three dimensions. Basic Co/Pd-based 3D recording media necessary for this study are fabricated using cosputter deposition. Focused-ion-beam-based fabrication is used to pattern the recording media into nanoscale bit cells. The physics of 3D magnetic recording is also investigated theoretically with Landau-Lifshits-Gilbert-based micromagnetic modeling. The ultimate goal of this paper is to help understand the physics of 3D and multilevel magnetic recordings and trigger wide interest in the studied concept. [ABSTRACT FROM AUTHOR]

Our work is concerned with the occurrence and distribution of the sphalerite, wurtzite, and rocksalt phases, which can be present in the ZnMnSe system, and the analysis of structural defects. For this purpose, ZnMnSe layers with thicknesses between 700 and 1000 nm and Mn concentrations of 0%, 4%, 11%, 14%, 17%, 29%, 31%, 43%, 50%, 70%, 85%, and 100% were deposited by molecular-beam epitaxy on GaAs (001) substrates. The structure analyses were performed by transmission electron microscopy. A high density of stacking faults exceeding 109 cm-2 is already present for a Mn concentration of 14% suggesting that lower Mn concentrations should be used for spin-aligning layers. A significant volume fraction of twinned regions is contained in the Zn0.69Mn0.31Se layer. ZnMnSe layers with Mn concentrations of 43%, 50%, and less than 30% consist exclusively of the sphalerite phase. The sphalerite and a small volume fraction of the wurtzite phase are contained in the sample with 31% of manganese. A mixture of the sphalerite, wurtzite, and rocksalt phases is observed for Mn concentrations of 70% and 85%. The presence of the wurtzite phase is correlated with regions, which contain particularly high densities of stacking faults. Only the rocksalt and the sphalerite phases remain for pure MnSe. [ABSTRACT FROM AUTHOR]

Using the well-known experimental data, the inverse problem of neutrino diagnostics of reactor core is considered. The solution of this problem makes it possible to determine distantly the current value of nuclear density of each nuclear fuel components with known accuracy and also opens up the possibility for the development of neutrino on-line technology of temporal evolution of nuclear fuel isotopic structure and reactor power. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, a detailed overview of the methodology to design a write transducer for recording onto perpendicular media at areal densities beyond 1 Tbit/in.2 is presented. The two basic modes of perpendicular recording, single-layer recording media in combination with a ring type head and double-layer recording media with a soft underlayer in combination with a single pole head, are compared with each other theoretically and experimentally. Moreover, perpendicular recording is compared to longitudinal recording from the perspective of the writing process. The system efficiency is redefined for perpendicular recording to take into account the critical role of the soft underlayer. The effects of using “soft” magnetic shields around the trailing pole are analyzed. It is shown that at least a factor of 2 increase in the field can be obtained at areal densities beyond 500 Gbit/in.2 if shields are used. Such an open issue as the skew angle sensitivity in perpendicular recording is analyzed. It is shown that using soft magnetic shields around the trailing pole substantially improves the skew angle sensitivity. Moreover, using shields substantially improves the system efficiency and to some degree fulfills the role of the soft underlayer in perpendicular recording. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic force microscopy measurements of perpendicular media with a CoCr-based hard layer and a CoFe soft underlayer has been made to investigate skew angle effects. The recorded tracks were produced using a focused ion beam made single pole head with a track width of approximately 400 nm and a gap thickness of approximately 1 µm at a 25 nm flying height. Magnetic force microscopy images of tracks recorded at write currents above and below the saturation value of approximately 100 mA turn were studied at different values of the linear density, 20-100 kfci, at zero skew angle as well as -15° and + 15°. Calculated perpendicular recording fields versus the distance down the track, and across the track, near the trailing pole edge was performed using three-dimensional boundary element modeling and compared to the results from the microscopy data. Drawbacks and possible solutions to the skew angle problem for perpendicular recording are discussed. [ABSTRACT FROM AUTHOR]

The influence of the growth conditions during capping of CdSe/ZnSe quantum structures grown on GaAs(001) by molecular-beam epitaxy (MBE) were systematically investigated by high-resolution x-ray diffraction, transmission electron microscopy, and temperature dependent, partly time-resolved photoluminescence spectroscopy. The results clearly indicate formation of quantum wells with potential fluctuations if conventional MBE is used for capping the CdSe by ZnSe. In contrast, quantum dot formation occurs using migration enhanced epitaxy for this growth step. In the latter case, quantum dots can be obtained without formation of stacking faults. [ABSTRACT FROM AUTHOR]

Domain wall dynamics in magnetic nanodots is critical to the understanding of the magnetization reversal mechanisms in bit-patterned arrays, the issues of writeablility, data rate maximization, and bit stability. In this work, micromagnetic simulations were carried out to investigate the dynamics of domain walls in disk-shaped nanostructures with large built-in perpendicular anisotropy. Due to the strong demagnetizing effect, the domain wall motion falls into the supercritical regime. A 90 degrees phase shift of the wall velocity is developed due to the finite thicknesses. The mean value of the wall velocity increases as the domain wall propagates away from the center. This induced asymmetry causes the frequency of the wall oscillations to be halved. At large diameters, the wall acceleration deceases and the periodicity is lost. The in-plane magnetization configuration shows that multiple spin wave modes are present. The absence of the coherency in the magnetization orientations causes phase canceling. The out-of-phase motion of neighboring segments reduces the wall acceleration.