Crystal Bar Research Articles

Defect Engineering in 2D Photonic Crystals Fabricated by Electrochemical Etching of Silicon

We propose electro-tunable composite structure of microcavity based on silicon 2D photonic crystal bar with a trench defect infiltrated with a liquid crystal. The device is fabricated by joint photo-electrochemical etching of deep macropores and trenches with subsequent trench opening from the substrate side. The optimized geometry and etching regime enables to minimize the lattice distortion introduced by trenches and to reduce roughness of the trench side walls. It was demonstrated that the structures with reach- through trenches and dead-end macropores are suitable for selective filling with a liquid crystal.

Multiaxial Low Cycle Fatigue Test Method for Cruciform Specimen of Nickel-Base Single Crystal Superalloy

This paper presented the multiaxial low cycle fatigue test method for cruciform specimens of YH61 nickel base single crystal superalloy . The elastic compliances were obtained in tensile and torsion tests using single crystal bar specimens whose specimen axis was aligned to the crystal growth directions of [100] and [110]. Elastic finite element analysis was performed to determine specimen shape and relationship between the specimen axis and crystal growth direction. Multiaxial low cycle fatigue tests were performed using the cruciform specimens whose x axis was aligned to the [001] direction and the y axis to [010], [110] and [210] directions both x and y axis were aligned to the<110> direction. Mises equivalent strain was not a suitable parameter and Mises equivalent stress was proved to be available for the correlating the multiaxial fatigue lives of the single crystal superalloy.

Formation of 2D photonic crystal bars by simultaneous photoelectrochemical etching of trenches and macropores in silicon

Joint electrochemical etching of deep macropores and trenches in n-Si (100) has been studied. After the substrate was removed, regions of a sample, bounded on all sides by a closed contour of through trenches, were extracted from the sample, with narrow bars of a 2D photonic crystal remaining. The influence exerted by the distance between pores and a trench and by the modes of etching and subsequent oxidation on the roughness of the side walls of the structures and also on the size and shape of pores near the trench is analyzed for the example of a photonic crystal with a square lattice of macropores. Conditions are found in which the lattice distortion of the photonic crystal is at a minimum and the side walls of the structure are the smoothest (root-mean-square roughness height ∼60 nm).

Fatigue Behavior of Single Crystal Superalloy Bars Joined by Capacitor Discharge Welding

This work concerns single crystal Ni-based superalloy welded through the capacitor discharge welding (CDW) process. The static and fatigue behavior of CMSX-4 type single crystal alloy has been analyzed, performing mechanical tests on square specimens in order to establish in detail the superalloy behavior at the expected service stresses. Tests have been conducted both at room and working temperatures (800°C), comparing base material and capacitor discharge welded joints. The material microstructure has been observed with optical and scanning electron microscopy in order to characterize welding parameters effects on the weld characteristics, analyzing base material and as-welded specimens; this way, the CDW process has been studied to perform butt joint with the better characteristics ad achieving sound welds. Microstructural modifications and the heat affected zones have been observed in the welded section as well as the interaction between weld material and parent metal. The research activities have been conducted in the frame of AWFORS project, financed by the European community.

Design, Fabrication, and Characteristics of a MEMS Micromirror With Sidewall Electrodes

This paper presents a 2-DOF silicon-on-insulator (SOI) microelectromechanical systems (MEMS) mirror with sidewall (SW) electrodes. The biaxial MEMS mirror with SW is actuated by electrostatic actuators. The dimension of mirror plate is 1000?m × 1000?m, with a thickness of 35 ?m. The analytical modeling, fabrication process, and performance characteristics are described. This paper analyzes the effects of the three-end single crystal serpentine torsion bar width and the bottom and SW electrodes on the performance of the mirror. A new fabrication process based on SOI wafer, hybrid bulk/surface micromachined technology, and a high-aspect-ratio shadow mask is presented. In comparison to previous fabrication processes and the Optical iMEMS process, the process is novel, easily understood, and simple to realize. The measured maximum angular deflection achieved is ±11°(mechanical angle) at a static operating voltage and is ± 21°(mechanical angle) at resonance frequency driving. This mirror is well suited for applications where these characteristics are critical, such as in confocal or endoscopic scanning elements

Production and characterization of large single crystals made of ferromagnetic shape memory alloys Ni–Mn–Ga

Ferromagnetic shape memory alloys (MSMA) are well-known smart materials for actuation applications, due to their large shape change in applied magnetic fields. Off-stoichiometric Ni–Mn–Ga single crystals of MSMA exhibit a magnetic-field induced strain of about 10%. In the past decade a lot of effort has been put into understanding and optimizing the properties of Ni-Mn-Ga alloys in terms of the magnetic shape memory effect, starting with the production of single crystals and going all the way to heat treatment and magneto-mechanical training.Here we focus on and present the production and characterization of single crystal Ni–Mn–Ga alloys with off-stoichiometric composition. The molten material was cast into preheated ceramic shells and directionally solidified in a Bridgman-type process. Cylindrical single crystal bars of diameters up to 48 mm and a length of 110 mm were obtained by using suitable grain selectors. Only small misorientations between the single crystal c-axis and the bar axis were found in these bars. The crystals were characterized in terms of composition, segregation, crystal orientation and microstructural features by means of SEM/EDS, EBSD and light microscopy.

Wavelength shifter strips and G-APD arrays for the read-out of the z-coordinate in axial PET modules

The measurements presented in this paper are related to the development of a PET camera based on a 3-D axial geometry with excellent 3-D spatial, timing and energy resolution. The detector modules consist of matrices of long axially oriented scintillation crystal bars, which are individually coupled to photodetectors. The axial coordinate is derived from wavelength shifting (WLS) plastic strips orthogonally interleaved between the crystal bars and readout by G-APD arrays. We report on results from measurements with two LYSO crystal bars, read with PMTs, and two WLS strips readout with G-APD devices from Hamamatsu (called MPPC). The WLS strips are positioned orthogonally underneath the LYSO bars. Yields of about 80 photoelectrons from the WLS strips for an energy deposition in the LYSO crystals equivalent to the absorption of 511 keV photons are observed. The axial coordinate in the LYSO bars is reconstructed with a precision of about 1.9 mm (FWHM) using a digital reconstruction method. The resolution of an analog coordinate reconstruction method, which uses the pulse height measurement from the WLS strips is 2.8 mm (FWHM). This resolution is still compromised by the availability of only two WLS strips and will improve with a full stack of LYSO crystals interleaved with WLS strip arrays, which is presently under development for a PET demonstrator set-up.

Formation of Stripe Domains in Cobalt Bars Via a Magnetic Soft Mode Instability

We theoretically study the relation between stripe domains at remanence and magnetic normal modes in a single crystal Co bar. We find different stripe patterns depending on field history and in each case the domain structure can be related to a soft mode that triggers a phase transition. The stripe domain structure when the external field is along the long axis of the bar is shown to be generated by a standing wave mode, which has the same spatial structure as the stripes. At all fields this mode has the lowest frequency of all the standing wave modes. This mode goes soft at a second-order phase transition where the stripe domains emerge. For other directions of the field, the symmetry of soft modes is found to be consistent with the change in symmetry of the ground state and that the phase transition can be first order. An analytical model relating phase transitions and soft mode behavior is also briefly discussed

An automatic crystal alignment system for producing high quality oscillators

Crystal oscillator products are widely used in a wide range of industry applications, such as global positioning satellites, wireless applications and cellular networks technologies. The quality of crystal oscillators normally depends on how they are cut from crystal bars. However, the current manual crystal bar alignment procedure is very much dependant on operator skill, and is not repeatable, leading to variations of the oscillators’ quality. The research is to develop an automated alignment system for aligning quartz crystal bars prior to being cut. The paper investigates the magnitude of the effects of rotational misalignments in the y-axis. Axis errors in the y-axis are found to create x-axis misalignments of up to thirty percent of the y-axis error. The feasibility of such a system is also analysed in terms of the required mechanical and electrical requirements, and a test-bed is built to carry out future experiments and automate the alignment process.

Effect of recrystallisation on microstructural evolution and mechanical properties of single crystal nickel base superalloy CMSX-2 Part 1 - Microstructural evolution during recrystallisation of single crystal

Nickel base superalloy CMSX - 2 single crystal bars were shot peened to induce surface residual stresses. Partial solutionising at 1300 ° C revealed a relationship between dissolution of the γ ′ phase into the matrix and recrystallisation. Recrystallisation occurred with dissolution of γ ′ phase in the dendritic core at 1300 ° C. Recrystallisation had preferentially begun at the dendritic core exposed at the shot peened surface and then gradually proceeded to the interdendritic regions. Phases more resistant to dissolution such as the coarse γ ′ particles and the γ - γ ′ eutectic phase in the interdendritic region dissolved into the matrix with recrystallisation, even at 1300 ° C, which is lower than the solutionising temperature of the alloy. Residual stresses assisted dissolution of the existing phases. The recrystallised grains grew preferentially in the dendritic core where rapid dissolution of γ ′ phase occurred. The growth of the recrystallised grains was impeded by the coarse γ ′ particles and the γ - γ ′ eutectic phase in the interdendritic region. Full solutionising of the shot peened specimens resulted in well developed recrystallised grains at the surface.

Effect of recrystallisation on microstructural evolution and mechanical properties of single crystal nickel based superalloy CMSX-2 Part 2 - Creep behaviour of surface recrystallised single crystal

Nickel based superalloy CMSX - 2 single crystal bars were shot peened to induce residual stresses at the surface. Full solutionising of shot peened specimens resulted in well developed recrystallised grains at the surface. Early initiation of surface cracks in recrystallised specimens at 982 ° C and 240 MPa in air did not reduce creep life, however, the life under vacuum was reduced. Early initiation of surface cracks on grain boundaries normal to the applied stress caused a relatively high creep rate in surface recrystallised specimens. Creep behaviour at 871 ° C, 500 MPa in air was similar to that at 982 ° C, 240 MPa under vacuum. Surface oxidation during creep at 982 ° C effectively hindered crack propagation, especially in recrystallised specimens.

Oxidation characteristics of basal ( [formula omitted]) plane and prism ( [formula omitted]) plane in HCP Zr

The oxidation characteristics of (0 0 0 2) basal plane and (1 1 2 ̄ 0) prismatic plane of an unalloyed Zr were investigated. From the Zr crystal bar, the specimen representing a single crystal was prepared to be coarse enough to have its grain be 4×4×1 mm 3 in size. After identifying the crystallographic orientations and planes by X-ray diffraction (XRD), the samples were cut out in such a way as the cutting planes could correspond to the desired crystallographic planes. Oxidation tests were carried out in water at 360 °C. The oxidation rate of the (1 1 2 ̄ 0) prismatic plane was faster than that of the (0 0 0 2) basal plane. The analysis of oxide using the synchrotron XRD revealed that the oxide grown at the basal plane had the preferred (2 0 0) plane in mono-ZrO 2, while the oxide at the prismatic plane grew at both the (2 0 0) and (0 0 2) planes of mono-ZrO 2. In addition, the oxide layer that had formed at the basal plane having only one preferred growth plane exhibited a high fraction of columnar oxide and a relatively wide range of protective barrier layer. These results mean that the characteristics of the preferred planes of mono-ZrO 2 play an important role on the oxidation rate of Zr single crystal.

Electrical spin injection and accumulation at room temperature in an all-metal mesoscopic spin valve.

Finding a means to generate, control and use spin-polarized currents represents an important challenge for spin-based electronics, or 'spintronics'. Spin currents and the associated phenomenon of spin accumulation can be realized by driving a current from a ferromagnetic electrode into a non-magnetic metal or semiconductor. This was first demonstrated over 15 years ago in a spin injection experiment on a single crystal aluminium bar at temperatures below 77 K. Recent experiments have demonstrated successful optical detection of spin injection in semiconductors, using either optical injection by circularly polarized light or electrical injection from a magnetic semiconductor. However, it has not been possible to achieve fully electrical spin injection and detection at room temperature. Here we report room-temperature electrical injection and detection of spin currents and observe spin accumulation in an all-metal lateral mesoscopic spin valve, where ferromagnetic electrodes are used to drive a spin-polarized current into crossed copper strips. We anticipate that larger signals should be obtainable by optimizing the choice of materials and device geometry.

Microinstruments for submicron material studies

We present two microinstruments for submicron scale material characterization. One of the instruments applies torsion on two single crystal silicon bars with square cross sections,1 and 2.25 μm2, until fracture. The maximum shear stress prior to fracture is found tobe 5.6 and 2.6 GPa, respectively. The second instrument applies tension on a composite (aluminum-silicon dioxide) beam, 1 × 1.5 μm2 in cross section. The beam fails at 220 μN.In both the experiments, the samples are designed, patterned, and cofabricated with the instruments. The microinstruments' small size, low thermal mass, vacuum compatibility, and built-in vibration isolation allow material characterization to be performed over a wide range of environmental conditions: high vacuum (electron microscopy and surface analysis), high humidity, high pressure, and high and low temperatures.

Measurement of forces and spring constants of microinstruments

Micromachines, including micro scanning tunneling microscope and high force (≈0.1 mN and higher) actuators, are examples of a new class of silicon-based microinstruments for atomic scale surface imaging and modification, as well as submicrometer scale material investigations. A large class of such microinstruments and sensors consist of actuators, such as interdigitated comb drives, that generate force, F, in the form F=βV2, where β is a constant and V is the applied voltage. Such actuators often move a large distance during actuation so that the restoring force, R, of the springs varies nonlinearly with x, i.e., the springs behave as hard springs, and R=K1x+K3x3+… (restoring force is similar for +ve and −ve x due to symmetry). β and Ki, i=1,3,…, of the micro-actuators usually differ from their design values due to processing nonuniformities. Hence, evaluation of these constants becomes necessary for each actuator, and is essential for the instruments that are employed to study materials’ behavior on a small scale. In this article, a methodology is developed to calibrate microinstruments, i.e., to evaluate the values of β and Ki, i=1,3,… . The method is based on buckling of a long slender beam of known dimensions, and made of a material with known property (elastic modulus). Buckling is achieved by an axial compressive force on the beam applied by the actuator of the microinstrument. β and Ki are derived from the relation between the applied voltage on the actuator, and the post buckling deformation of the beam. The beam is designed and cofabricated with the actuator, and hence the calibration mechanism is integrable with each microinstrument. An analysis is provided to estimate the possible errors in calibration due to errors in the measured dimensions of the calibrating beam. It is shown that the calibration error increases linearly with the error in the measured linear dimensions. The applicability of the method is demonstrated by fabricating microinstruments, which, prior to their calibration, are employed to apply torque on single crystal silicon bars (in the form of pillars), until the bars fracture. The instruments are then calibrated, and the calibrated values of β and Ki are used to evaluate the torques applied on the bars at different voltages. Stresses to fracture of the bars are also estimated. The torsion experiment is an example of the application of integrated microinstruments for small scale material studies.

Sulphated glycosaminoglycans in guinea pig eosinophils studied by means of cationic colloidal gold.

Using bone marrow embedded in hydrophilic resin Lowicryl K4M and cationic colloidal gold pH 1.0 labelling, we studied sites of sulphation and sulphated glycosaminoglycans ultrastructurally in various maturational stages of both eosinophil granulocytes and eosinophil granules of guinea pig. Eosinophil granules reacted positively to cationic gold, the pattern of labelling varying according to the degree of cell maturation. The formation of eosinophil granules takes place throughout the myelocyte stage. Early eosinophil myelocytes contain a large Golgi apparatus with active granulogenesis, while late ones contain a small and less active Golgi apparatus. All the immature granules were labelled positively. However, mature granules with a central crystal bar lost their affinity towards colloidal gold. Interestingly, strong colloidal gold labelling was also observed in the trans to transmost Golgi apparatus, especially in immature eosinophil granulocytes. This indicates that sulphation of glycosaminoglycans occurs in the trans to transmost Golgi apparatus of eosinophil granulocytes. Prior absorption with poly-L-lysine prevented colloidal gold labelling of tissue sections. Methylation of sections at 37 degrees C did not alter the gold labelling, whereas the labelling disappeared after methylation at 60 degrees C. Prior treatment with chondroitinase ABC or heparinase I abolished the majority of colloidal gold labelling in immature eosinophil granules. Taking these results together, we conclude that immature eosinophil granules contain sulphated glycosaminoglycans including chondroitin sulphate or heparan sulphate or both.

Calibrations and corrections of a modular cylindrical SPECT system (McSPECT-II)

The authors have developed a modular cylindrical SPECT system (McSPECT-II) for clinical brain imaging. This system features a stationary cylindrical detector and a rotating collimator. The cylindrical detector is comprised of 120 NaI(Tl) crystal bars coupled to a circular array of PMTs. The output signal from each PMT is digitized by an ADC. The position calculation and corrections are performed using software and precalculated lookup tables on a Pentium-based PC. The collimator has four quadrants, and each quadrant consists of a parallel array of 25 collimator units. The four corner wedges between adjacent quadrants are utilized to accommodate line sources for system calibrations. The authors report the calibration and correction procedures developed for the McSPECT-II system. These procedures include: (1) PMT gain normalization, (2) azimuth bar identification, (3) energy correction, (4) axial linearity correction, and (5) uniformity correction. Results of these calibrations and corrections on data acquired by imaging various phantoms are presented.

Modeling of stress relaxation associated with an electrically-induced phase transformation

Stress relaxation due to an electrically-induced phase transformation in a ferroelectric crystal bar stretched by a hard-loading device is studied in the one-dimensional setting of electromechanics. According to the proposed model, the stress relaxation rate is governed by a nonlinear ordinary differential equation which resulted from the kinetic relation that controls the evolution of the phase transformation. A numerical analysis basing on simplifying approximation indicates that the stress starts to decrease when the intensity of the applied electric field reaches a critical value and that a stronger electric field results in a quicker stress reduction.

Lattice theory of crystal edges and bars

In this paper, a lattice theoretical approach to the structure and dynamics of crystal edges is presented. The relaxation of infinite quadratic bars is investigated in detail using various lattice-dynamical models. The phonon spectra of the bars have been calculated and phonon modes have been found which are strongly localized at the tips of the four edges of the bar. Our results obtained in the framework of lattice dynamics are compared with investigations based on continuum theory in the long-wavelength limit.

Dy 2BaCuO 5 distribution size in melt textured DyBa 2Cu 3O y superconductors prepared by the horizontal Bridgman method

Horizontal Bridgman growth on MgO single crystal bars as supports was performed in air with DyBa 2Cu 3O y (1-2-3) stoichiometric sample, prepared by hot forging. The Dy 2BaCuO 5 (2-1-1) size distribution along the growth direction was measured from back scattered electron micrographs using automated image analysis. It was found to be non-uniform and it is concluded that particles coarsen during time spent in the liquid and are pushed by the solid-liquid growth front during the process.