Control of material transport through pulse shape manipulation-a development toward designer pulses

The variety of laser systems available to industrial laser users is growing and the choice of the correct laser for a material target application is often based on an empirical assessment. Industrial master oscillator power amplifier systems with tuneable temporal pulse shapes have now entered the market, providing enormous pulse parameter flexibility in an already crowded parameter space. In this paper, an approach is developed to design interaction parameters based on observations of material responses. Energy and material transport mechanisms are studied using pulsed digital holography, post process analysis techniques and finite-difference modelling to understand the key response mechanisms for a variety of temporal pulse envelopes incident on a silicon (1/1/1) substrate. The temporal envelope is shown to be the primary control parameter of the source term that determines the subsequent material response and the resulting surface morphology. A double peak energy-bridged temporal pulse shape designed through direct application of holographic imaging data is shown to substantially improve surface quality. © 2014 IEEE.

On-chip focusing of light by Metallic Nanotip

We investigate numerically and experimentally the on-chip nanoscale focusing of surface plasmon polaritons (SPPs) in metallic nanotip coupled to the silicon waveguide. Strong field enhancement is observed at the apex of the tip. © 2010 Optical Society of America.

Atom probe tomography for advanced metallization

In microelectronics, the increase in complexity and the reduction of devices dimensions make essential the development of new characterization tools and methodologies. Indeed advanced characterization methods with very high spatial resolution are needed to analyze the redistribution at the nanoscale in devices and interconnections. The atom probe tomography has become an essential analysis to study materials at the nanometer scale. This instrument is the only analytical microscope capable to produce 3D maps of the distribution of the chemical species with an atomic resolution inside a material. This technique has benefit from several instrumental improvements during last years. In particular, the use of laser for the analysis of semiconductors and insulating materials offers new perspectives for characterization. The capability of APT to map out elements at the atomic scale with high sensitivity in devices meets the characterization requirements of semiconductor devices such as the determination of elemental distributions for each device region. In this paper, several examples will show how APT can be used to characterize and understand materials and process for advanced metallization. The possibilities and performances of APT (chemical analysis of all the elements, atomic resolution, planes determination, crystallographic information...) will be described as well as some of its limitations (sample preparation, complex evaporation, detection limit, ...). The examples illustrate different aspect of metallization: dopant profiling and clustering, metallic impurities segregation on dislocation, silicide formation and alloying, high K/metal gate optimization, SiGe quantum dots, as well as analysis of transistors and nanowires. © 2013 Elsevier B.V. All rights reserved.

Effect of natural dissolved humic material on bioavailability and acute toxicity of fenpropathrin to the grass carp, Ctenopharyngodon idellus

The effects of aquatic humic acids on the bioconcentration and acute toxicity of fenpropathrin were evaluated using grass carp, Ctenopharyngodan idellus, in laboratory freshwater systems. The results demonstrated that both bioavailability and acute toxicity decreased in the presence of aquatic humic acid 5 and 10 mg/liter. In addition, the extent of influence increased with increasing concentration of aquatic humic acid, (C) 1999 Academic Press.

First-principles prediction of the magnetism of 3d transition-metal-doped Rocksalt MgO

Using first-principles band structure methods, we have systematically studied the electronic structures, magnetic stabilities, and half-metal properties of 3d transition-metal (TM) doped Rocksalt MgO compounds TMMg3O4 (TM = V, Cr, Mn, Fe, Co, and Ni). The calculations reveal that only CrMg3O4 has a ferromagnetic stability among the six compounds, which is explained by double-exchange mechanism. The magnetic stability is affected by the doping concentration of TM if the top valance band is composed of partially occupied t(2g) states. In addition, CrMg3O4 is a half-metallic ferromagnet. The origins of half-metallic and ferromagnetic properties are explored. The Curie temperature (T-c) of CrMg3O4 is 182 K. And it is hard for CrMg3O4 to deform due to the large bulk modulus and shear modulus, so it is a promising spintronic material. Our calculations provide the first available information on the magnetic properties of 3d TM-doped MgO.

Electronic structure and optical properties of GaN with Mn-doping

Calculations of the electronic structure and the density of states of GaN with Mn are carried out by means of first-principles plane-wave pesudopotential method based on density functional theory. The results reveal a 100% spin polarized impurity band in band structure of Ga1-xMnxN due to hybridization of Mn 3d and N 2p orbitals. The material is half metallic and suited for spin injectors. In addition, a peak of refractive index can be observed near the energy gap. The absorption coefficient increases in the UV region with the increase of the Mn content.

Fabrication of nanoscale metallic air-bridges by introducing a SiO2 sacrificial layer

A new method to fabricate nanoscale metallic air-bridges has been investigated. The pillar patterns of the air-bridge were defined on a SiO2, sacrificial layer by electron-beam lithography combined with inductively coupled plasma etching. Thereafter, the span (suspended part between the pillars) patterns were defined with a second electron-beam exposure on a PMMA/PMMA-MAA resist system. The fabrication process was completed by subsequent metal electron-beam evaporation, lift-off in acetone, and removal of the sacrificial layer in a buffered hydrofluoric (HF) solution. Air-bridges with two different geometries (line-shaped and cross-shaped) were studied in detail. The narrowest width of the air-bridges was around 200 nm, and the typical length of the air-bridges was 2-5 mu m. The advantages of our method are the simplicity of carrying out electron-beam exposure with good reproducibility and the capability of more accurate control of the pillar sizes and shapes of the air-bridge. (C) 2007 Elsevier Ltd. All rights reserved.

The influence of growth temperature and input V/III ratio on the initial nucleation and material properties of InN on GaN by MOCVD

The effects of growth temperature and V/III ratio on the InN initial nucleation of islands on the GaN (0 0 0 1) surface were investigated. It is found that InN nuclei density increases with decreasing growth temperature between 375 and 525 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters of less than 100 nm, whereas at elevated temperatures the InN islands can grow larger and well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. At a given growth temperature of 500 degrees C, a controllable density and size of separated InN islands can be achieved by adjusting the V/III ratio. The larger islands lead to fewer defects when they are coalesced. Comparatively, the electrical properties of the films grown under higher V/III ratio are improved.

Simulation of light coupling enhancement and localization of transmission field via subwavelength metallic gratings

Surface plasmons(SPs) generated in nano metallic gratings on medium layer can greatly enhance the transmission field through the metallic gratings. The enhancement effect is achieved from lambda = 500 nm to near-infrared domain. The enhancement rate is about 110 % at the wavelength of about 6 10 nm and about 180 % at lambda = 700 nm and 740 nm where most kinds of thin film solar cells have a high spectral response. These structures should provide a promising way to increase the coupling efficiency of thin film solar cells and optical detectors of different wavelength response.

Electromagnetic-field-induced cohesive force enhancement in a metallic nanowire

We theoretically study the conducting electronic contribution to the cohesive force in a metallic nanowire irradiated under a transversely polarized external electromagnetic field at low temperatures and in the ballistic regime. In the framework of the free-electron model, we have obtained a time-dependent two-level electronic wavefunction by means of a unitary transformation. Using a thermodynamic statistical approach with this wavefunction, we have calculated the cohesive force in the nanowire. We show that the cohesive force can be divided into two components, one of which is independent of the electromagnetic field (static component), which is consistent with the existing results in the literature. The magnitude of the other component is proportional to the electromagnetic field strength. This extra component of the cohesive force is originally from the coherent coupling between the two lateral energy levels of the wire and the electromagnetic field.

Radiation hardness improvement of separation-by-implantation-of-oxygen/silicon-on-insulator material by nitrogen ion implantation

In our work, nitrogen ions were implanted into separation-by-implantation-of-oxygen (SIMOX) wafers to improve the radiation hardness of the SIMOX material. The experiments of secondary ion mass spectroscopy (SIMS) analysis showed that some nitrogen ions were distributed in the buried oxide layers and some others were collected at the Si/SiO2 interface after annealing. The results of electron paramagnetic resonance (EPR) suggested the density of the defects in the nitrided samples changed with different nitrogen ion implantation energies. Semiconductor-insulator-semiconductor (SIS) capacitors were made on the materials, and capacitance-voltage (C-V) measurements were carried out to confirm the results. The super total dose radiation tolerance of the materials was verified by the small increase of the drain leakage current of the metal-oxide-semiconductor field effect transistor with n-channel (NMOSFETs) fabricated on the materials before and after total dose irradiation. The optimum implantation energy was also determined.

Fabrication of arrayed waveguide grating based on SOI material

An arrayed waveguide grating based on SOI material was fabricated by inductive coupled plasma (ICP) etching technology. The central wavelength of the device was designed at 1.5509 mu m and the channel spacing was 200 GHz. Comparing with the values of the design, the differences of the central wavelength and the channel spacing in the test were 0.28 nm and 0.02 nm, respectively. The adjacent channel crosstalk was about 10 dB, and the uniformity of the five channels' insertion loss was only 0.7 dB. The results show that the device can be used as a demultiplexer.

A convenient way of determining the ferromagnetic transition temperature of metallic (Ga,Mn)As

We have studied magnetic and transport properties of insulating and metallic (Ga,Mn)As layers before and after annealing. A dramatic increase of the ferromagnetic transition temperature T-C by postgrowth annealing has been realized in both insulating and metallic (Ga,Mn)As. The as-grown insulating (Ga,Mn)As can be turned into metallic by the low-temperature annealing. For all the metallic (Ga,Mn)As, a characteristic feature in the temperature dependence of sheet resistance appears around T-C. This phenomenon may provide a simple and more convenient method to determine the T-C of metallic (Ga,Mn)As compared with superconducting quantum interference device (SQUID) measurement. Moreover, the T-C of the metallic (Ga,Mn)As obtained by this way is in good agreement with that measured by a SQUID magnetometer. (C) 2005 American Institute of Physics.

Photonic crystal vertical-cavity surface-emitting laser based on GaAs material

A photonic crystal vertical-cavity-surface-emitting laser ( PC-VCSEL) with a wavelength of about 850 nm was realized. The direct-current electrically-driven PC-VCSELs with a minimum threshold current of 2 mA and a maximum threshold current of 13.5 mA were obtained. We fabricated a series of PC-VCSEL chips whose lattice constants are in the range from 0.5 to 3 mu m with different filling factors, and found that the laser characterization depends on the lattice constant, the filling factor, the size of cavity, etc.

Thermally induced Fe atom transition from substitutional to interstitial sites in InP and its influence on material property

As-grown Fe-doped semi-insulating InP single crystal has been converted into n-type low-resistance material after high temperature annealing. Defects in the InP materials have been studied by conventional Hall effect measurement, thermally stimulated current spectroscopy, deep level transient spectroscopy and X-ray diffraction respectively. The results indicate that Fe atoms in the InP material change from the substitutional to the interstitial sites under thermal activation. Consequently, the InP material loses its deep compensation centers which results in the change in types of conduction. The mechanism and cause of the phenomena have been analyzed through comparison of the sites of Fe atom occupation and activation in doping, diffusion and ion implantation processes of InP.