Optical doping and damage formation in AIN by Eu implantation

AlN films grown on sapphire were implanted with 300 keV Eu ions to fluences from 3×1014 to 1.4×1017 atoms/cm2 in two different geometries: “channeled” along the c-axis and “random” with a 10° angle between the ion beam and the surface normal. A detailed study of implantation damage accumulation is presented. Strong ion channeling effects are observed leading to significantly decreased damage levels for the channeled implantation within the entire fluence range. For random implantation, a buried amorphous layer is formed at the highest fluences. Red Eu-related photoluminescence at room temperature is observed in all samples with highest intensities for low damage samples (low fluence and channeled implantation) after annealing. Implantation damage, once formed, is shown to be stable up to very high temperatures.FCT - POCI/FIS/57550/2004FCT - PTDC/FIS/66262/2006FCT - PTDC/CTM/100756/200

Smart Meters - Keeping Users Privacy

Electric power distribution systems are evolving toward more intelligent models allowing distribution organizations to have a perspective on how consumption is happening. However, these systems may allow for violation of consumer privacy, as they can identify the equipment in use, allowing for profiling of user activities. This work addresses the need to develop a mechanism to protect privacy, and presents an option for creating this protection for individual electric power consumer units through intermediate encryption of readings from these individual units, allowing suppliers access not to individual readings, but sum of their total

The VISTA Orion mini-survey: star formation in the Lynds 1630 North cloud

The Orion cloud complex presents a variety of star formation mechanisms and properties and it is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star forming region, including the stellar clusters NGC 2068 and NGC 2071, in the Orion molecular cloud B and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-colour criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7 M$_\odot$ and a fraction of sub-stellar objects of $\sim$20%. The fraction of YSOs still surrounded by disk/envelopes is very high ($\sim$85%) compared to other star forming regions of similar age (1-2 Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation ($\sim$129 M$_\odot$ pc$^{-2}$), points towards a still on-going star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR) and density of star formation of L1630N are within the ranges estimated for galactic star forming regions by the Spitzer "core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.Comment: 22 pages, 9 figure

pH-Dependent fluorescence of [La(OH)(2)](+)[ARS](-) hybrid nanoparticles for intracellular pH-sensing

Saline inorganic–organic hybrid nanoparticles (IOH-NPs) [La(OH)2]+[ARS]− (ARS: alizarin red S) are prepared in water as a new compound (particle size: 47 ± 7 nm, ARS load: 65 wt%). The IOH-NPs not only show a pH-dependent absorption colour but also a pH-dependent fluorescence with green emission at pH 5.0–9.0 and red emission at pH < 4.5. According to first in vitro studies, the pH-dependend fluorescence can be used to monitor nanoparticle internalization in cells as well as the respective intracellular pH

Functionalizing self-assembled GaN quantum dot superlattices by Eu-implantation

Self-assembled GaN quantum dots (QDs) stacked in superlattices (SL) with AlN spacer layers were implanted with Europium ions to fluences of 1013, 1014, and 1015 cm−2. The damage level introduced in the QDs by the implantation stays well below that of thick GaN epilayers. For the lowest fluence, the structural properties remain unchanged after implantation and annealing while for higher fluences the implantation damage causes an expansion of the SL in the [0001] direction which increases with implantation fluence and is only partly reversed after thermal annealing at 1000 °C. Nevertheless, in all cases, the SL quality remains very good after implantation and annealing with Eu ions incorporated preferentially into near-substitutional cation sites. Eu3+ optical activation is achieved after annealing in all samples. In the sample implanted with the lowest fluence, the Eu3+ emission arises mainly from Eu incorporated inside the QDs while for the higher fluences only the emission from Eu inside the AlN-buffer, capping, and spacer layers is observed. © 2010 American Institute of PhysicsFCT-PTDC/CTM/100756/2008program PESSOA EGIDE/GRICESFCT-SFRH/BD/45774/2008FCT-SFRH/BD/44635/200

Composition and luminescence studies of InGaN epilayers grown at different hydrogen flow rates

Indium gallium nitride (In(x)Ga(1-x)N) is a technologically important material for many optoelectronic devices, including LEDs and solar cells, but it remains a challenge to incorporate high levels of InN into the alloy while maintaining sample quality. A series of InGaN epilayers was grown with different hydrogen flow rates (0-200 sccm) and growth temperatures (680-750 °C) to obtain various InN fractions and bright emission in the range 390-480 nm. These 160-nm thick epilayers were characterized through several compositional techniques (wavelength dispersive x-ray spectroscopy, x-ray diffraction, Rutherford backscattering spectrometry) and cathodoluminescence hyperspectral imaging. The compositional analysis with the different techniques shows good agreement when taking into account compositional gradients evidenced in these layers. The addition of small amounts of hydrogen to the gas flow at lower growth temperatures is shown to maintain a high surface quality and luminescence homogeneity. This allowed InN fractions of up to ~16% to be incorporated with minimal peak energy variations over a mapped area while keeping a high material quality

The nature of the dense core population in the pipe nebula: core and cloud kinematics from C18O observations

We present molecular-line observations of 94 dark cloud cores identified in the Pipe nebula through near-IR extinction mapping. Using the Arizona Radio Observatory 12m telescope, we obtained spectra of these cores in the J=1-0 transition of C18O. We use the measured core parameters, i.e., antenna temperature, linewidth, radial velocity, radius and mass, to explore the internal kinematics of these cores as well as their radial motions through the larger molecular cloud. We find that the vast majority of the dark extinction cores are true cloud cores rather than the superposition of unrelated filaments. While we identify no significant correlations between the core's internal gas motions and the cores' other physical parameters, we identify spatially correlated radial velocity variations that outline two main kinematic components of the cloud. The largest is a 15pc long filament that is surprisingly narrow both in spatial dimensions and in radial velocity. Beginning in the Stem of the Pipe, this filament displays uniformly small C18O linewidths (dv~0.4kms-1) as well as core to core motions only slightly in excess of the gas sound speed. The second component outlines what appears to be part of a large (2pc; 1000 solar mass) ring-like structure. Cores associated with this component display both larger linewidths and core to core motions than in the main cloud. The Pipe Molecular Ring may represent a primordial structure related to the formation of this cloud.Comment: Accepted to ApJ. 14 pages, 11 figures. Complete table at end of documen

Persistent Chaos in High Dimensions

An extensive statistical survey of universal approximators shows that as the dimension of a typical dissipative dynamical system is increased, the number of positive Lyapunov exponents increases monotonically and the number of parameter windows with periodic behavior decreases. A subset of parameter space remains in which topological change induced by small parameter variation is very common. It turns out, however, that if the system's dimension is sufficiently high, this inevitable, and expected, topological change is never catastrophic, in the sense chaotic behavior is preserved. One concludes that deterministic chaos is persistent in high dimensions.Comment: 4 pages, 3 figures; Changes in response to referee comment