Self-organization of magnetic nanogroove arrays by LaserMBE and hydrogen reduction.

2007 ◽  
Vol 1032 ◽  
Author(s):  
Akifumi Matsuda ◽  
Takahiro Watanabe ◽  
Yasuyuki Akita ◽  
Makoto Hosaka ◽  
Kouji Koyama ◽  
...  
Keyword(s):  
Self Assembly ◽  
Quantum Interference ◽  
Hydrogen Reduction ◽  
Magnetic Nanostructures ◽  
High Energy ◽  
The Other ◽  
Ex Situ ◽  
Force Microscopy ◽  
Self Organized ◽  
Other Hand

AbstractThe epitaxially grown magnetic nanostructures including nanodots, nanowires and nanorings have been attracting much scientific and engineering interests because of their expected unique physical characteristics due to quantum effects. These epitaxial nanomagnets and their array are undoubtedly thought to make major contribution to the development of future SPINTRONICS devices, ultra-high density magnetic random access memory (MRAM) and magnetic switching devices for examples, and other quantum devices. In this case, epitaxial growth of the nanomagnets and the resulting anisotropic properties are one of the largest interest as well as fine-nanostructuring. There have been some concerns such as throughput rate with conventional nanoprocessing techniques involving FIB lithography and e-beam lithography, and/or minimization-limit with photolithography due to the wavelength. On the other hand, self-assembly or self-organized methods could also be used for construction of nanopatterns, in which such nanostructures are directly built up from separate atoms. Here we report about formation and characterization of self-organized nanomagnet arrays made of metals and oxides. We have epitaxially grown ferrimagnetic Fe3O4 (111), (Mn0.55Zn0.35Fe0.10)Fe2O4 (111), ferromagnetic Ni (111) and antiferromagnetic NiO (111) nanodots, nanowires and nanogroove arrays on the atomically stepped ultra-smooth sapphire (0001) substrate by LaserMBE. The sapphire (a-Al2O3single crystal) substrates have atomic steps of 0.2 nm in height and atomically flat terraces of 50-100 nm in width so that self-assembly processes of nanomagnet arrays were strongly induced by the energetic instability at the straight and periodic step-edges. In this study, NiO worked as a antiferromagnetic exchange bias layer. On the other hand, NiO was also reduced into ferromagnetic Ni metal by annealing in hydrogen atmosphere in some situations for further applications. Crystallographic and morphology analyses of the nanomagnets were made by in-situ reflection high-energy electron diffraction (RHEED), ex-situ X-ray diffraction (XRD), transmission electron microscope (TEM). and atomic force microscopy (AFM). Magnetic properties were characterized by superconducting quantum interference device (SQUID) magnetometer and magnetic force microscopy (MFM). Further experimentals are conducted for magneto-optical characterizations for above mentioned metal and/or oxide nanomagnet arrays.

Well-Ordered Self-Assembly Growth of Strain-Modulated SrTiO3 Thin Films: Templates for Complex Oxide Quantum Wires

2005 ◽  
Vol 475-479 ◽  
pp. 4255-4260 ◽  
Author(s):  
Yan Rong Li ◽  
Jin Long Li ◽  
Ying Zhang ◽  
Xin Wu Deng ◽  
Fan Yang ◽  
...  
Keyword(s):  
Compressive Stress ◽  
Self Assembly ◽  
Quantum Wires ◽  
Complex Oxide ◽  
High Energy ◽  
The Self ◽  
Ex Situ ◽  
Force Microscopy ◽  
Atomic Force ◽  
Self Assembled

Well-ordered self-assembled SrTiO3 thin film, as a template for complex oxide quantum wires, was fabricated on LaAlO3 (100) single crystal substrates with laser molecular beam epitaxy. The self-assembled growth was in-situ monitored by reflective high energy electron diffraction. The morphology evolutions of the films as a function of thickness were studied by ex-situ atomic force microscopy. As the thickness of the films increased from 3.875nm to 46.5nm gradually, the compressive stress-induced SrTiO3 films exhibited a periodic well-ordered ripple structure, which formed a unique nanoassembled template for the fabrication of quantum wires. Small angle X-ray scattering technique was employed to investigate the structure. Symmetric satellite peaks were discovered, indicating the well-ordered superstructure. In contrast, the similar superstructure was not observed during the growth of the tensile stress-induced LaAlO3 films on SrTiO3 substrates. The Compressive stress was considered as the main reason of the self-assembled growth, and systematical elucidation about strain mechanism was discussed. These results might provide an efficient method for the controllable formation of well-aligned template of quantum wire for complex oxide with desirable structure via proper modulation of strains.

MBE Growth of IV-VI Nanowires on a Self-organized Template

2010 ◽  
Vol 1258 ◽  
Author(s):  
Lee Andrew Elizondo ◽  
Patrick McCann ◽  
Joel Keay ◽  
Matthew Johnson
Keyword(s):  
Quantum Wires ◽  
High Energy ◽  
Ex Situ ◽  
Mbe Growth ◽  
One Dimensional ◽  
Force Microscopy ◽  
Self Organized ◽  
Atomic Force ◽  
Low Dimensional

AbstractWe present the experimental results for the first known molecular beam epitaxy (MBE) growth of quasi-one-dimensional PbSe wires on technologically relevant silicon.In this work, we describe the growth and characterization of low-dimensional IV-VI semiconductors as they evolve from one-dimensional dot/dot-chains to one-dimensional structures on a self-organized template epitaxially grown on Si(110). In situ and ex situ characterization were performed at various stages throughout growth by reflection high energy electron diffraction, scanning electron microscopy, and non-contact atomic force microscopy. Initial growths resulted in some preferential alignment of the PbSe dot-chains parallel to the self-organized template in the [-110] direction. By reducing the substrate temperature and increasing the supplemental Se flux, the morphology of dot-chains extend into lengthened one-dimensional structures. This is an important milestone in the fabrication of PbSe quantum wires on technologically relevant silicon.

Dynamics of InAs Quantum Dots Formation on AlAs and GaAs

2000 ◽  
Vol 648 ◽  
Author(s):  
M. Yakimov ◽  
V. Tokranov ◽  
S. Oktyabrsky
Keyword(s):  
Quantum Dots ◽  
Self Assembly ◽  
Single Layer ◽  
High Energy ◽  
Ex Situ ◽  
Inas Quantum Dots ◽  
Force Microscopy ◽  
Atomic Force ◽  
Kinetics Of

AbstractWe have studied the formation of InAs quantum dots (QDs) grown by molecular beam epitaxy on top of GaAs and 2 ML-thick AlAs layers in the temperature range from 350 to 500°C. In-situ reflection high energy electron diffraction (RHEED) patterns were recorded in real time during the growth and analyzed to characterize the 2D-to-3D transition on the surface, including QD formation, and ripening process. The kinetics of QD formation was studied using the InAs growth rates ranging from 0.01 to 1 ML/s and different ratios of As2/In fluxes. RHEED patterns and ex-situ atomic force microscopy images were analyzed to reveal the development of sizes and shapes of the single-layer and stacked QD ensembles. The critical InAs coverage for QD formation was shown to be consistently higher for dots grown on the AlAs overlayer than for those grown on GaAs surface. Self-assembly of multilayer QD stacks revealed the reduction of the critical thickness for dots formed in the upper layers.

On the Nature of Weak Spots in High-k Layers Submitted to Anneals

2004 ◽  
Vol 811 ◽  
Author(s):  
J. Pétry ◽  
W. Vandervorst ◽  
O. Richard ◽  
T. Conard ◽  
P. DeWolf ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Strong Correlation ◽  
Positive Charge ◽  
The Other ◽  
Physical Analysis ◽  
Force Microscopy ◽  
Atomic Force ◽  
Other Hand ◽  
High K ◽  
High K Dielectric

ABSTRACTIn the path to the introduction of high-k dielectric into IC components, a large number of challenges have still to be solved. Some of the major issues concern the low mobility of carriers and the reliability of the devices. Trapped charges in the stack have been identified as being the cause of these issues. With this in mind, we used Conducting Atomic Force Microscopy, combined with physical analysis to understand the nature of these charges. In this contribution, we have studied the uniformity of thin HfO2 layers, with and without anneal. The Conducting Atomic Force microscopy measurements show spots of higher conductivity. Recording local IV's in those ‘weak’ spots suggests that they consist of positive charge. On the other hand, XPS and ToFSIMS analysis show a diffusion of the interfacial SiO2 upwards into the high-k layer. Finally, the comparison of samples with differing high-k material and crystallinity indicates a strong correlation between the weak spots and the presence of silicon in the film.

Instability Study of Repetitive Nanosecond Pulsed Discharge Plasma in a Plasma Assisted Burner

2020 ◽  
Author(s):  
Saeid Zare ◽  
Omid Askari
Keyword(s):  
High Velocity ◽  
Discharge Plasma ◽  
Diffusion Flames ◽  
High Energy ◽  
Discharge Voltage ◽  
Low Energy ◽  
Peak Discharge ◽  
The Other ◽  
Other Hand ◽  
Point To Point

Abstract High velocity flows, as in aerospace applications require special techniques to stabilize and ignite diffusion flames. Some techniques focus on changing parameters like geometry, conditions of the flow, or fuel composition, but these techniques are usually too expensive or impossible due to major changes in the system. On the other hand, some techniques focus on generating a region of charged/excited species and active radicals upstream of the flame. That can substantially enhance the flame stability even under high strain rate or at lean-limit-flammability conditions. Repetitive nanosecond pulsed (RNP) discharge plasma is a nonthermal plasma technique with some remarkable potential to improve stability and ignitability of high velocity diffusion flames. This technique was used in previous papers in a plasma assisted coaxial inverse diffusion burner and showed some promising results by reducing the lift-off height and delaying detachment and blowout conditions. This burner is prepared to employ the discharges at the burner nozzle and simulate a single element of a multi-element methane burner. However, effectiveness of high-voltage high-frequency RNP plasma was limited by the mode of the discharge. During the tests, three different modes were observed at different combinations of plasma and flow conditions. These three modes are low energy corona, uniformly distributed plasma, and high-energy point-to-point discharge. Among these three, only well-distributed plasma significantly improved the flame. In other cases, plasma deployment was either ineffective or in some cases adversely affected the flame by producing undesirable turbulence advancing blow out. As a result, a comprehensive study of these modes is required. In this work, the transition between these three modes in a jet flame was discussed. It has been expressed as a function of plasma conditions, i.e. peak discharge voltage and discharge frequency. It was shown that increasing flow speed delays increases the voltage and frequency at which transition occurs from low-energy corona discharge to well distributed plasma discharge. Subsequently, the effective plasma conditions are thinned. On the other hand, by increasing the frequency of nanosecond discharges, the chance of unstable point-to-point discharges is decreased. In contrast, the discharge peak voltage causes two different consequences. If it is too low, the pulse intensity is too week that the system will experience no visible plasma discharges or the discharges will not pass the low-energy corona, no matter how high the frequency is. If too high, it will enhance the chance of point-to-point discharges and limits the stabilization outcome of the system. Therefore, an optimal region is found for peak discharge voltage.

scholarly journals Biochemical Composition of Some Selected Aquatic Macrophytes Under Ex-Situ Conditions

2018 ◽  
Vol 44 (1) ◽  
pp. 53-60
Author(s):  
Harich And Hazra ◽  
Md Al Mujaddade Alfasane ◽  
Sharmin Kauser ◽  
Umme Fatema Shahjadee ◽  
Moniruzzaman Khondker
Keyword(s):  
Aquatic Plants ◽  
Biochemical Composition ◽  
Aquatic Macrophytes ◽  
The Other ◽  
Ex Situ ◽  
Human Diet ◽  
Culture Studies ◽  
Ipomoea Aquatica ◽  
Other Hand ◽  
Calcium And Phosphorus

Ex-situ culture studies of five selected aquatic macrophytes, namely Nymphaea nouchali Burm. f., Enhydra fluctuans Lour., Ipomoea aquatica Forsk., Hygroryza aristata (Retz.) Nees ex Wight & Arn. and Limnocharis flava (L.) Buch. were carried out. Comparing the biochemical composition of the above mentioned five aquatic macrophytes, on an average, Enhydra fluctuans was found to contain highest amounts of proteins (18.20%) and Ipomoea aquatica contains highest amounts of carbohydrate (58.60%). Lowest amounts of proteins (14.35%) were recorded in Hygroryza aristata and Limnocharis flava. On the other hand lowest amounts of carbohydrates were obtained in Nymphaea nouchali. Ipomoea aquatica contained highest amounts of energy (321.23 kcal) and lowest amount was observed in Limnocharis flava. The five aquatic plants were low in fiber, fat and also in ash. Among all the five aquatic macrophytes, highest values of calcium and phosphorus were found to be present in Limnocharis flava and iron was highest in Nymphaea nouchali. Lowest values of calcium and phosphorus were present in Ipomoea aquatica and lowest amount of iron was present in Limnochris flava. The present study demonstrated that, these five aquatic macrophytes are the important sources of carbohydrate, protein and minerals, which are suitable for incorporation in human diet and feed also. Asiat. Soc. Bangladesh, Sci. 44(1): 53-60, June 2018

Nanoindentation Assisted Self-Assembly of Quantum Dots

2006 ◽  
Author(s):  
Curtis Taylor ◽  
Eric Stach ◽  
Gregory Salamo ◽  
Ajay Malshe
Keyword(s):  
Quantum Dots ◽  
Self Assembly ◽  
Surface Strain ◽  
Ex Situ ◽  
Atomic Step ◽  
Uniform Size ◽  
Force Microscopy ◽  
Atomic Force ◽  
And Performance ◽  
Spatial Positioning

The ability to pattern quantum dots with high spatial positioning and uniform size is critical for the realization of future electronic devices with novel properties and performance that surpass present technology. This work discusses the exploration of an innovative nanopatterning technique to direct the self-assembly of nanostructures. The technique focuses on perturbing surface strain energy by nanoindentation in order to mechanically bias quantum dot nucleation. Growth of InAs quantum dots on nanoindent templates is performed using molecular beam epitaxy (MBE). The effect of indent spacing and size on the patterned growth is investigated. The structural analysis of the quantum dots including spatial ordering, size, and shape are characterized by ex-situ atomic force microscopy (AFM). Results reveal that the indent patterns clearly bias nucleation with dot structures selectively growing on top of each indent. It is speculated that the biased nucleation is due to a combination of favorable surface strain attributed to subsurface dislocation strain fields and/or multi-atomic step formation at the indent sites, which leads to increased adatom diffusion on the patterned area.

Centrality dependence of total disintegration of target nuclei in high energy nucleus–nucleus interactions

2016 ◽  
Vol 94 (9) ◽  
pp. 884-893 ◽  
Author(s):  
Swarnapratim Bhattacharyya ◽  
Maria Haiduc ◽  
Alina Tania Neagu ◽  
Elena Firu
Keyword(s):  
High Energy ◽  
Average Multiplicity ◽  
The Other ◽  
Multiparticle Production ◽  
Centrality Dependence ◽  
Target Fragmentation ◽  
Other Hand ◽  
Fireball Model

A study of centrality dependence of target fragmentation and multiparticle production has been carried out in 16O–AgBr, 22Ne–AgBr, and 28Si–AgBr interactions at 4.1–4.5 AGeV/c for the total disintegrated (TD) events. Average multiplicity of black particles increases linearly with decreasing centrality while average multiplicity of grey and shower particles decreases with decreasing centrality for the TD events. The decrease of average multiplicity of grey particles is linear; on the other hand, in the case of shower particles, the increase is nonlinear. With the increase of the mass of the projectile beam, the average multiplicity of black particles decreases and the average multiplicity of grey particles increases for the TD events. This observation has been explained on the basis of the fireball model; however, in the case of shower particles, average multiplicity increases with increase of projectile mass.

Surface Reconstruction and Morphology of Hydrogen Sulfide Treated GaAs (001) Substrate

1996 ◽  
Vol 448 ◽  
Author(s):  
Jun Suda ◽  
Yoichi Kawakami ◽  
Shizuo Fujita ◽  
Shigeo Fujita
Keyword(s):  
Hydrogen Sulfide ◽  
Surface Reconstruction ◽  
Substrate Surface ◽  
High Vacuum ◽  
High Energy ◽  
Gaas Surface ◽  
Ex Situ ◽  
Force Microscopy ◽  
Atomic Force ◽  
Strained Quantum Well

AbstractWe report several new results in hydrogen sulfide (H2S) treatment of a GaAs (001) substrate. Surface reconstruction and morphology were investigated by in situ reflection high energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) in terms of the annealing temperature and the H2S irradiation sequence. A (4 × 3) GaAs surface was obtained by annealing the substrate under H2S irradiation (4 × 10-7 Torr). The surface was atomically flat, i.e., large terraces with monolayer steps were clearly observed. A (2 × 6) S-terminated GaAs surface was obtained by irradiation H2S at 300°C on a Ga-terminated surface, which was formed by annealing at 580°C in high vacuum. The molecular beam epitaxy (MBE) growth of ZnSSe-based semiconductors on the (4 × 3) surface results in high quality structures such as a novel ZnSSe/ZnMgSSe tensile-strained quantum well (QW).

Assembly and Optical Properties of Metal Nanoparticles

2019 ◽  
Vol 294 ◽  
pp. 3-10
Author(s):  
E.A. Dawi ◽  
A. Abdelkader
Keyword(s):  
Gold Nanoparticles ◽  
Optical Properties ◽  
Self Assembly ◽  
Silicon Oxide ◽  
Ex Situ ◽  
Visible Range ◽  
Plasmonic Nanostructures ◽  
Electromagnetic Spectrum ◽  
Force Microscopy ◽  
Atomic Force

In this paper, the deposition and optical properties of charge-stabilized gold nanoparticles on silicon oxide substrates is studied, which have been derivatised with (aminopropyl) triemethoxysilane. Monodispersed charged-stabilized colloidal gold nanoparticles with diameters between 20-150 nm were prepared and their self-assembly and optical properties on silica substrates is studied. Atomic force microscopy (AFM) is employed to investigate the nanoparticle monolayers ex situ. Analysis of AFM images provide evidence that the formation of the colloidal nanoparticle monolayers is governed by random sequential adsorption. The results indicate that the ionic strength of the suspension influences the spatial distribution of the nanoparticles. For all sizes of the Au nanoparticles tested, optical simulations of extinction coefficients made by finite-difference time domain (FDTD) indicate a resonance peak in the range of 510-600 nm wavelength of the visible range of the electromagnetic spectrum. The results indicate a simple and inexpensive approach of assembly of plasmonic nanostructures that can find applications in metamaterials and light waveguides.

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