Single-Pulse and multiple-pulse femtosecond spectroscopy of ferroelectric materials

ABSTRACTWe have experimentally Investigated the effects that are associated with Multiple-pulse irradiation in the excimer laser processing of thin Si films on SiO2. Double-pulse irradiation experiments revealed results, which are consistent with that which is known from single-pulse crystallization experiments, and these experiments confirm the applicability of the transformation scenarios, which were derived from single pulse-induced crystallization experiments [1,2]. The results from the Multiple-pulse irradiation experiments clearly show that gradual and substantial grain enlargement can occur — and only occurs — when the irradiation energy density is close to but less than the level that is required to melt the film completely. Based on these findings, we argue that the grain enlargement effect is a near-complete melting phenomenon that is associated with polycrystalline Si films, and we present a grain boundary melting model to account for this phenomenon. A brief discussion on the apparent similarities and physical differences between the observed phenomenon and the solid state grain growth processes is provided herein.

Download Full-text

Laser Damage Thresholds of Several Metal-Containing Acrylic Polymers at Four Different Wavelengths.

MRS Proceedings ◽

10.1557/proc-236-501 ◽

1991 ◽

Vol 236 ◽

Cited By ~ 1

Author(s):

Pearl W. Yip

Keyword(s):

Electron Spectroscopy ◽

Light Transmission ◽

Single Pulse ◽

Laser Damage ◽

Laser Materials ◽

Acrylic Polymers ◽

Multiple Pulse ◽

Chemical Damage ◽

Before And After ◽

Physical And Chemical

AbstractSingle- and multiple-pulse laser damage thresholds of six different metal-containing acrylic polymers were determined at 10.6, 1.06, 0.53 and 0.355 μm. Light transmission of these samples before and after irradiation was measured. A variety of observed laser-materials interactions are discussed in this paper. Physical and chemical damage properties of these metal-containing acrylic polymers were examined and compared with poly (methyl methacrylate) and polycarbonate using scanning electron microscopy (SEM), infrared spectroscopy (IR), and electron spectroscopy for chemical analysis (ESCA). In general, it was found that the multiple-pulse damage thresholds were lower than the single-pulse, and damage thresholds decreased as wavelength of the testing laser beam became shorter.

Download Full-text

Microhardness of the Surface Layer of Tungsten and Molybdenum After Recrystallization With Laser Radiation

Journal of Engineering Materials and Technology ◽

10.1115/1.2903368 ◽

1991 ◽

Vol 113 (1) ◽

pp. 130-134 ◽

Cited By ~ 1

Author(s):

F. Kostrubiec ◽

M. Walczak

Keyword(s):

Surface Layer ◽

Laser Radiation ◽

Laser Beam ◽

Single Pulse ◽

Glass Laser ◽

Multiple Pulse ◽

And Tungsten

We present results of microhardness measurements in melted local regions in molybdenum and tungsten. Microhardness has been measured by the Vickers method. Melted regions have been produced by pulsed Nd-glass laser. The emphasis is on correlation between conditions of recrystallization (energy of laser beam and method of irradiation-single pulse or multiple pulse) and the microhardness value.

Download Full-text

Target Localization Methods Based on Iterative Super-Resolution for Bistatic MIMO Radar

Electronics ◽

10.3390/electronics9020341 ◽

2020 ◽

Vol 9 (2) ◽

pp. 341

Author(s):

Jianhe Du ◽

Meng Han ◽

Libiao Jin ◽

Yan Hua ◽

Shufeng Li

Keyword(s):

Multiple Input Multiple Output ◽

Super Resolution ◽

Single Pulse ◽

Doa Estimation ◽

Mimo Radar ◽

Target Localization ◽

Localization Accuracy ◽

Bistatic Mimo Radar ◽

Multiple Pulse ◽

Direction Of Departure

The direction-of-departure (DOD) and the direction-of-arrival (DOA) are important localization parameters in bistatic MIMO radar. In this paper, we are interested in DOD/DOA estimation of both single-pulse and multiple-pulse multiple-input multiple-output (MIMO) radars. An iterative super-resolution target localization method is firstly proposed for single-pulse bistatic MIMO radar. During the iterative process, the estimated DOD and DOA can be moved from initial angles to their true values with high probability, and thus can achieve super-resolution estimation. It works well even if the number of targets is unknown. We then extend the proposed method to multiple-pulse configuration to estimate target numbers and localize targets. Compared with existing methods, both of our proposed algorithms have a higher localization accuracy and a more stable performance. Moreover, the proposed algorithms work well even with low sampling numbers and unknown target numbers. Simulation results demonstrate the effectiveness of the proposed methods.

Download Full-text

Effect of Multiple Pulses on the Deformation Behavior of Ultrathin Metal Foils in 3D Micro-Scale Laser Dynamic Forming

ASME 2010 International Manufacturing Science and Engineering Conference, Volume 2 ◽

10.1115/msec2010-34299 ◽

2010 ◽

Author(s):

Ji Li ◽

Gary J. Cheng

Keyword(s):

Deformation Behavior ◽

Laser Energy ◽

3D Structure ◽

Single Pulse ◽

Laser Pulses ◽

High Energy ◽

Shock Pressure ◽

Thickness Variation ◽

Multiple Pulse ◽

Multiple Pulses

Laser dynamic forming (LDF) is a novel high energy rate microfabrication technique, which makes use of the shock pressure induced by laser to generate dynamic high strain rate 3D forming of thin films. In LDF process, a high shock pressure accelerates the workpiece to a high velocity and deforms it into complex 3D shapes. The forming velocity of the workpiece imparted by a single laser pulse with high energy may exceed the critical forming velocity of the material, and thus causing it to fracture. This problem is more severe when 3D structure of large aspect ratio needs to be formed. To overcome this problem, multi-pulse laser dynamic forming is investigated in this study. The total laser energy is evenly distributed in different laser pulses to keep the forming velocity below the critical forming velocity of the material. The effects of the multiple-pulse LDF on the deformation behavior of ultra thin foils are investigated. The deformation depth and thickness variation distribution of the formed 3D features are characterized to reveal these effects. In addition, the effects of vacuum conditions on multiple-pulse LDF process are carried out. It is found that the bounce off of the foil can be effectively reduced by multiple-pulse LDF and the final shape could be controlled much more accurately. By extending single pulse LDF to multi-pulse LDF, the forming capability of LDF is further enhanced, and thus enlarges the applicable range of this technique.

Download Full-text

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173996 ◽

1990 ◽

Vol 48 (4) ◽

pp. 172-173

Author(s):

Naoki Yamamoto ◽

Makoto Kikuchi ◽

Tooru Atake ◽

Akihiro Hamano ◽

Yasutoshi Saito

Keyword(s):

Phase Transition ◽

Electron Microscope Study ◽

Room Temperature ◽

Hexagonal Lattice ◽

Ferroelectric Materials ◽

Temperature Phase ◽

X Ray Diffraction ◽

X Ray ◽

Periodic Arrays ◽

Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

Download Full-text

Investigation of ferroelectrics using conventional and in situ electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170669 ◽

1994 ◽

Vol 52 ◽

pp. 586-587

Author(s):

V. Saikumar ◽

H. M. Chan ◽

M. P. Harmer

Keyword(s):

Nonvolatile Memory ◽

Ferroelectric Materials ◽

Gate Insulator ◽

Sensors And Actuators ◽

In Situ Electron Microscopy ◽

Ferroelectric Domains ◽

Domain Boundaries ◽

Domain Interactions ◽

Memory Applications

In recent years, there has been a growing interest in the application of ferroelectric thin films for nonvolatile memory applications and as a gate insulator in DRAM structures. In addition, bulk ferroelectric materials are also widely used as components in electronic circuits and find numerous applications in sensors and actuators. To a large extent, the performance of ferroelectric materials are governed by the ferroelectric domains (with dimensions in the micron to sub-micron range) and the switching of domains in the presence of an applied field. Conventional TEM studies of ferroelectric domains structures, in conjunction with in-situ studies of the domain interactions can aid in explaining the behavior of ferroelectric materials, while providing some answers to the mechanisms and processes that influence the performance of ferroelectric materials. A few examples from bulk and thin film ferroelectric materials studied using the TEM are discussed below.Figure 1 shows micrographs of ferroelectric domains obtained from undoped and Fe-doped BaTiO3 single crystals. The domain boundaries have been identified as 90° domains with the boundaries parallel to <011>.

Download Full-text

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100170487 ◽

1994 ◽

Vol 52 ◽

pp. 550-551

Author(s):

Wenwu Cao

Keyword(s):

Domain Wall ◽

Domain Walls ◽

High Mobility ◽

Continuum Theory ◽

Polarization Vector ◽

Ferroelectric Materials ◽

Dielectric Constants ◽

Nonlocal Coupling ◽

Cubic Symmetry ◽

Gradient Energy

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

Download Full-text