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At least 145 records · Page 8

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NASA NTRS1999

Measurement of Temperature Fluctuations and Microscopic Growth Rates in a Silicon Floating Zone and Microgravity

A silicon crystal growth experiment has been accomplished using the floating-zone technique under microgravity on a sounding rocket (TEXUS 36). Measurements of temperature fluctuations in the silicon melt zone due to time dependent thermocapillary convection (Marangoni convection) and an observation of the microscopic growth rate were simultaneously performed during the experiment. Temperature fluctuations of about 0.5 - 0.7 C with a frequency range < 0.5Hz were detectable. The microscopic growth rate fluctuates considerably around the average growth rate of 1 mm/min: Growth rates up to 3 to 4mm/min, close to zero mm/min, as well as negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. They were characterized by Spreading Resistance measurements and Differential Interference Contrast microscopy. The frequencies of temperature fluctuations, microscopic growth rates, and the dopant inhomogeneities correspond quite well, with main frequencies between 0.1 and 0.3 Hz. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, and the characteristic temperature amplitudes and frequencies. At a position 3.4mm above the interface and 1.4mm inside the melt, equivalent to the sensor tip position in the experiment, temperature fluctuations up to 1.8 C and frequencies ? 0.25Hz were found in the simulations.

Schweizer, Markus↗

NASA NTRS1999

Measurement of Temperature Fluctuations and Microscopic Growth Rates in a Silicon Floating Zone on TEXUS36

Several pg experiments on sounding rockets and the Space Shuttle have shown that time-dependent thermocapillary (Marangoni) convection is the major cause for the formation of dopant striations in floating-zone grown semiconductor crystals, at least in small-scale systems not employing RF heating. To quantify this correlation, a silicon floating-zone experiment was performed during the TEXUS36 flight (February 7, 1 998) in the monoellipsoid mirror furnace TEM02-ELLI. During the experiment, temperature fluctuations in the silicon melt zone and the microscopic growth rate were simultaneously measured. Temperature fluctuations of 0.5 C - 0.7 C with main frequencies between 0.1 Hz and 0.3Hz were detectable. The microscopic growth rate fluctuated considerably around the average growth rate of 1 mm/min: rates from 4mm/min to negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. They were characterized by Spreading Resistance measurements and Differential Interference Contrast microscopy. The frequencies associated with the dopant inhomogeneities correspond quite well with those of the temperature fluctuations and microscopic growth rates. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, to evaluate characteristic temperature amplitudes and frequencies, and to give insight into the instability mechanisms of Marangoni convection in this configuration. The simulations were in good agreement with the experimental values, showing temperature fluctuations with frequencies? 0.25 Hz and amplitudes up to 1.8 C at a position equivalent to that of the sensor tip in the experiment.

Croell, Arne↗

NASA NTRS1999

Measurement of Temperature Fluctuations and Microscopic Growth Rates in a Silicon Floating Zone on TEXUS36

Several earlier (micro)g experiments have shown that time-dependent thermocapillary (Marangoni) convection is the major cause for the formation of dopant striations in floating-zone grown semiconductor crystals, at least in small-scale systems not employing RF heating. To quantify this correlation, a silicon floating-zone experiment was performed on the TEXUS36 flight (February 7, 1 998) in the monoellipsoid mirror furnace TEM02-ELLI. During the experiment, temperature fluctuations in the silicon melt zone and the microscopic growth rate were simultaneously measured. Temperature fluctuations of 0.5 C - 0.7 C with main frequencies between 0.1 Hz and 0.3 Hz were detectable. The microscopic growth rate fluctuated considerably around the average growth rate of 1 mm/min: rates from 4mm/min to negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. The frequencies associated with the dopant inhomogeneities correspond quite well with those of the temperature fluctuations and microscopic growth rates. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, to evaluate characteristic temperature amplitudes and frequencies, and to give insight into the instability mechanisms of Maran-goni convection in this configuration. The simulations were in good agreement with the experimental values, showing temperature fluctuations with frequencies f? 0.25 Hz and amplitudes up to 1.8 C at a position equivalent to that of the sensor tip in the experiment.

Croell, Arne↗

NASA NTRS2000

Microscope-Based Fluid Physics Experiments in the Fluids and Combustion Facility on ISS

At the NASA Glenn Research Center, the Microgravity Science Program is planning to conduct a large number of experiments on the International Space Station in both the Fluid Physics and Combustion Science disciplines, and is developing flight experiment hardware for use within the International Space Station's Fluids and Combustion Facility. Four fluids physics experiments that require an optical microscope will be sequentially conducted within a subrack payload to the Fluids Integrated Rack of the Fluids and Combustion Facility called the Light Microscopy Module, which will provide the containment, changeout, and diagnostic capabilities to perform the experiments. The Light Microscopy Module is planned as a fully remotely controllable on-orbit microscope facility, allowing flexible scheduling and control of experiments within International Space Station resources. This paper will focus on the four microscope-based experiments, specifically, their objectives and the sample cell and instrument hardware to accommodate their requirements.

Doherty, Michael P.↗

NASA NTRS2001

A Hydrodynamic Theory for Spatially Inhomogeneous Semiconductor Lasers: Microscopic Approach

Starting from the microscopic semiconductor Bloch equations (SBEs) including the Boltzmann transport terms in the distribution function equations for electrons and holes, we derived a closed set of diffusion equations for carrier densities and temperatures with self-consistent coupling to Maxwell's equation and to an effective optical polarization equation. The coherent many-body effects are included within the screened Hartree-Fock approximation, while scatterings are treated within the second Born approximation including both the in- and out-scatterings. Microscopic expressions for electron-hole (e-h) and carrier-LO (c-LO) phonon scatterings are directly used to derive the momentum and energy relaxation rates. These rates expressed as functions of temperatures and densities lead to microscopic expressions for self- and mutual-diffusion coefficients in the coupled density-temperature diffusion equations. Approximations for reducing the general two-component description of the electron-hole plasma (EHP) to a single-component one are discussed. In particular, we show that a special single-component reduction is possible when e-h scattering dominates over c-LO phonon scattering. The ambipolar diffusion approximation is also discussed and we show that the ambipolar diffusion coefficients are independent of e-h scattering, even though the diffusion coefficients of individual components depend sensitively on the e-h scattering rates. Our discussions lead to new perspectives into the roles played in the single-component reduction by the electron-hole correlation in momentum space induced by scatterings and the electron-hole correlation in real space via internal static electrical field. Finally, the theory is completed by coupling the diffusion equations to the lattice temperature equation and to the effective optical polarization which in turn couples to the laser field.

Li, Jianzhong↗

NASA NTRS2002

Microscopic Foundation and Simulation of Coupled Carrier-Temperature Diffusions in Semiconductor Lasers

A typical semiconductor-based optoelectronic device, such as a diode laser, consists of three subsystems: an optical field, an electron-hole plasma (EHP), and a host crystal lattice. The physics of such a device involves the interplay of optical, electrical and thermal processes. A proper description of such a device requires that all three processes are treated on equal footing and in a self-consistent fashion. Furthermore, since a semiconductor laser has intrinsic spatial inhomogeneity, such a self-consistency naturally leads to a set of partial differential equations in space and time. There is a significant lacking of research interest and results on the transport aspects of optical devices in the literature with only a few exceptions. Even the most important carrier diffusion coefficient has not been properly derived and studied so far for optically excited plasma, while most of the work adopted results from electronics community where heavily doped semiconductors with mainly one type of carriers are dealt with. The corresponding transport equation for plasma energy or temperature has received even less attention. In this talk we describe our recent results on such a self-consistent derivation of temperature and carrier-density diffusion equations coupled with the lasing process. Starting from the microscopic semiconductor Bloch equations (SBEs) including the Boltzmann transport terms in the distribution function equations for electrons and holes, we derived a closed set of diffusion equations for carrier densities and temperatures with self-consistent coupling to Maxwell's equation and to an effective optical polarization equation. The coherent many-body effects are included within the screened Hartree-Fock approximation, while scatterings are treated within the second Born approximation including both the in- and out-scatterings. Microscopic expressions for electron-hole (e-h) and carrier-LO (c-LO) phonon scatterings are directly used to derive the momentum and energy relaxation rates. These rates expressed as functions of temperatures and densities lead to microscopic expressions for self- and mutual-diffusion coefficients in the coupled density-temperature diffusion equations. Approximations for reducing the general two-component description of the electron-hole plasma (EHP) to a single-component one are discussed. In particular, we show that a special single-component reduction is possible when e-h scattering dominates over c-LO phonon scattering. The ambipolar diffusion approximation is also discussed and we show that the ambipolar diffusion coefficients are independent of e-h scattering, even though the diffusion coefficients of individual components depend sensitively on the e-h scattering rates. Our discussions lead to new perspectives into the roles played in the single-component reduction by the electron-hole correlation in momentum space induced by scatterings and the electron-hole correlation in real space via internal static electrical field. Finally, the theory is completed by coupling the diffusion equations to the lattice temperature equation and to the effective optical polarization which in turn couples to the laser field. The equations derived above are implemented in various limiting cases to a typical diode laser to study the consequences of nonlinear diffusion and the cross diffusion terms on laser behavior, especially the dynamic behavior of a diode laser under modulation. Detailed results will be presented by comparing with the standard rate equation results.

Li, J.↗

NASA NTRS2003

The Athena Microscopic Imager Investigation

The Athena science payload on the Mars Exploration Rovers (MER) includes the Microscopic Imager (MI) [1]. The MI is a fixed-focus camera mounted on the end of an extendable instrument arm, the Instrument Deployment Device (IDD; see Figure 1).The MI was designed to acquire images at a spatial resolution of 30 microns/pixel over a broad spectral range (400 - 700 nm; see Table 1). Technically, the microscopic imager is not a microscope: it has a fixed magnification of 0.4 and is intended to produce images that simulate a geologist s view through a common hand lens. In photographers parlance, the system makes use of a macro lens. The MI uses the same electronics design as the other MER cameras [2, 3] but has optics that yield a field of view of 31 31 mm across a 1024 1024 pixel CCD image (Figure 2). The MI acquires images using only solar or skylightillumination of the target surface. A contact sensor is used to place the MI slightly closer to the target surface than its best focus distance (about 66 mm), allowing concave surfaces to be imaged in good focus. Because the MI has a relatively small depth of field (3 mm), a single MI image of a rough surface will contain both focused and unfocused areas. Coarse focusing will be achieved by moving the IDD away from a rock target after the contact sensor is activated. Multiple images taken at various distances will be acquired to ensure good focus on all parts of rough surfaces. By combining a set of images acquired in this way, a completely focused image can be assembled. Stereoscopic observations can be obtained by moving the MI laterally relative to its boresight. Estimates of the position and orientation of the MI for each acquired image will be stored in the rover computer and returned to Earth with the image data. The MI optics will be protected from the Martian environment by a retractable dust cover. The dust cover includes a Kapton window that is tinted orange to restrict the spectral bandpass to 500-700 nm, allowing color information to be obtained by taking images with the dust cover open and closed. The MI will image the same materials measured by other Athena instruments (including surfaces prepared by the Rock Abrasion Tool), as well as rock and soil targets of opportunity. Subsets of the full image array can be selected and/or pixels can be binned to reduce data volume. Image compression will be used to maximize the information contained in the data returned to Earth. The resulting MI data will place other MER instrument data in context and aid in petrologic and geologic interpretations of rocks and soils on Mars.

K E Herkenhoff↗

NASA NTRS2005

CHAMP - Camera, Handlens, and Microscope Probe

CHAMP (Camera, Handlens And Microscope Probe) is a novel field microscope capable of color imaging with continuously variable spatial resolution from infinity imaging down to diffraction-limited microscopy (3 micron/pixel). As an arm-mounted imager, CHAMP supports stereo-imaging with variable baselines, can continuously image targets at an increasing magnification during an arm approach, can provide precision range-finding estimates to targets, and can accommodate microscopic imaging of rough surfaces through a image filtering process called z-stacking. Currently designed with a filter wheel with 4 different filters, so that color and black and white images can be obtained over the entire Field-of-View, future designs will increase the number of filter positions to include 8 different filters. Finally, CHAMP incorporates controlled white and UV illumination so that images can be obtained regardless of sun position, and any potential fluorescent species can be identified so the most astrobiologically interesting samples can be identified.

Mungas, G. S.↗

NASA NTRS2001

Compact Microscope Imaging System Developed

The Compact Microscope Imaging System (CMIS) is a diagnostic tool with intelligent controls for use in space, industrial, medical, and security applications. The CMIS can be used in situ with a minimum amount of user intervention. This system, which was developed at the NASA Glenn Research Center, can scan, find areas of interest, focus, and acquire images automatically. Large numbers of multiple cell experiments require microscopy for in situ observations; this is only feasible with compact microscope systems. CMIS is a miniature machine vision system that combines intelligent image processing with remote control capabilities. The software also has a user-friendly interface that can be used independently of the hardware for post-experiment analysis. CMIS has potential commercial uses in the automated online inspection of precision parts, medical imaging, security industry (examination of currency in automated teller machines and fingerprint identification in secure entry locks), environmental industry (automated examination of soil/water samples), biomedical field (automated blood/cell analysis), and microscopy community. CMIS will improve research in several ways: It will expand the capabilities of MSD experiments utilizing microscope technology. It may be used in lunar and Martian experiments (Rover Robot). Because of its reduced size, it will enable experiments that were not feasible previously. It may be incorporated into existing shuttle orbiter and space station experiments, including glove-box-sized experiments as well as ground-based experiments.

McDowell, Mark↗

NASA NTRS2006

Operation of a Cartesian Robotic System in a Compact Microscope with Intelligent Controls

A Microscope Imaging System (CMIS) with intelligent controls is disclosed that provides techniques for scanning, identifying, detecting and tracking microscopic changes in selected characteristics or features of various surfaces including, but not limited to, cells, spheres, and manufactured products subject to difficult-to-see imperfections. The practice of the present invention provides applications that include colloidal hard spheres experiments, biological cell detection for patch clamping, cell movement and tracking, as well as defect identification in products, such as semiconductor devices, where surface damage can be significant, but difficult to detect. The CMIS system is a machine vision system, which combines intelligent image processing with remote control capabilities and provides the ability to autofocus on a microscope sample, automatically scan an image, and perform machine vision analysis on multiple samples simultaneously.

McDowell, Mark↗

NASA NTRS2007

Tracking of cells with a compact microscope imaging system with intelligent controls

A Microscope Imaging System (CMIS) with intelligent controls is disclosed that provides techniques for scanning, identifying, detecting and tracking microscopic changes in selected characteristics or features of various surfaces including, but not limited to, cells, spheres, and manufactured products subject to difficult-to-see imperfections. The practice of the present invention provides applications that include colloidal hard spheres experiments, biological cell detection for patch clamping, cell movement and tracking, as well as defect identification in products, such as semiconductor devices, where surface damage can be significant, but difficult to detect. The CMIS system is a machine vision system, which combines intelligent image processing with remote control capabilities and provides the ability to auto-focus on a microscope sample, automatically scan an image, and perform machine vision analysis on multiple samples simultaneously.

McDowell, Mark↗

NASA NTRS2007

Tracking of Cells with a Compact Microscope Imaging System with Intelligent Controls

McDowell, Mark↗

NASA NTRS2008

Development and Optical Testing of the Camera, Hand Lens, and Microscope Probe with Scannable Laser Spectroscopy (CHAMP-SLS)

Conducting high resolution field microscopy with coupled laser spectroscopy that can be used to selectively analyze the surface chemistry of individual pixels in a scene is an enabling capability for next generation robotic and manned spaceflight missions, civil, and military applications. In the laboratory, we use a range of imaging and surface preparation tools that provide us with in-focus images, context imaging for identifying features that we want to investigate at high magnification, and surface-optical coupling that allows us to apply optical spectroscopic analysis techniques for analyzing surface chemistry particularly at high magnifications. The camera, hand lens, and microscope probe with scannable laser spectroscopy (CHAMP-SLS) is an imaging/spectroscopy instrument capable of imaging continuously from infinity down to high resolution microscopy (resolution of approx. 1 micron/pixel in a final camera format), the closer CHAMP-SLS is placed to a feature, the higher the resultant magnification. At hand lens to microscopic magnifications, the imaged scene can be selectively interrogated with point spectroscopic techniques such as Raman spectroscopy, microscopic Laser Induced Breakdown Spectroscopy (micro-LIBS), laser ablation mass-spectrometry, Fluorescence spectroscopy, and/or Reflectance spectroscopy. This paper summarizes the optical design, development, and testing of the CHAMP-SLS optics.

Fluorescence↗

NASA NTRSDate not supplied

ELM: Europa Luminescence Microscope

The Europa Luminescence Microscope (ELM) is an automated fluorescence and bright-field microscope designed to meet key objectives defined in the 2016 NASA Europa Lander Study Report, including the identification and characterization of morphological biosignatures. ELM’s heritage stems from a 2U cubesat fluorescence microscope, the Fluorescence Analysis for In situ Research imager, designed and built at NASA Ames Research Center, for the autonomous study of microbial biology in low Earth orbit. For ELM implementation, a sample is autonomously manipulated with a microfluidic system using in-line 10, 1.0, and 0.2 μm pore-size filters to capture successively smaller particles for imaging. For bright-field imaging, ELM uses deep-ultraviolet, ultraviolet and visible light to image organic and inorganic structures with submicron resolution. The ability to detect biosignatures as small as 0.2 μm in size is achieved by imaging native fluorescence and using fluorescence microscopy stains to identify key structural and functional indicators of microbial life (proteins, lipids, nucleic acids). For fluorescence imaging, ELM uses 265, 370, 470, and 530 nm LEDs with five emission bands. The use of multiple excitation and emission wavelengths for native fluorescence imaging enables the detection of a wide range of molecular species and their rough classification. Excitation at 265 nm allows for the detection of smaller polycyclic aromatic hydrocarbons (PAH), aromatic amino acids, and proteins with little to no interference from mineral fluorescence, given proper emission band selection. 370 and 470 nm light excites increasingly larger PAH structures and larger aromatic biomolecules that may be present (e.g., protective pigments). Similarly, inorganic fluorescence can be characterized and separated from organic fluorescence, allowing the recognition and in some cases classification, of minerals and other abiotic particles. ELM is based upon work supported by the NASA COLDTech and ICEE-2 programs.

Richard C Quinn↗

DOE OSTI2022

Spiking retina microscope

A spiking retina microscope comprising microscope optics and a neuromorphic imaging sensor. The microscope optics are configured to direct a magnified image of a specimen onto the neuromorphic imaging sensor. The neuromorphic imaging sensor comprises a plurality of sensor elements that are configured to generate spike signals in response to integrated light from the magnified image reaching a threshold. The spike signals may be processed by a processor unit to generate a result, such as tracking biological particles in a specimen comprising biological material.

Severa, William Mark↗

DOE OSTI2023

Quantum dot microscope apparatus comprising a nanoscale semiconductor on the tip of a fiber, a tunneling electrical lead and a capacitive electrical lead on the fiber

A quantum dot microscope apparatus is provided. A further aspect employs a tilted or tapered end or tip on a microscopic probe. Another aspect of the present apparatus employs a probe including a quantum dot with only one tunneling lead connected to a power source. A manufacturing aspect includes creating a tapered or asymmetrically shaped specimen-facing end of a probe where a quantum dot is located on the end. A further manufacturing aspect includes using focused ion-beam milling to create a tip or end of a quantum dot microscope probe.

Tessmer, Stuart Holden↗

DOE OSTI2023

Avoided Level Crossing and Entangled States of Interacting Hydrogen Molecules Detected by the Quantum Superposition Microscope

Pump–probe measurements by ultrashort THz pulses can be used to excite and follow the coherence dynamics in the time domain of single hydrogen molecules (H 2 ) in the junction of a scanning tunneling microscope (STM). By tailoring the resonance frequency through the sample bias, we identified two spectral signatures of the interactions among multiple H 2 molecules. First, the avoided level crossing featured by energy gaps ranging from 20 to 80 GHz was observed because of the level repulsion between two H 2 molecules. Second, the tip can sense the signal of H 2 outside the junction through the projective measurement on the H 2 inside the junction, owing to the entangled states created through the interactions. A dipolar-type interaction was integrated into the tunneling two-level system model of H 2 , enabling accurate reproduction of the observed behaviors. Furthermore, our results obtained by the quantum superposition microscope reveal the intricate quantum mechanical interplay among H 2 molecules and additionally provide a 2D platform to investigate unresolved questions of amorphous materials.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Microscopic diffusion in hydrated encysted eggs of brine shrimp

We have studied microscopic diffusion of water in fully hydrated encysted eggs of brine shrimp (Artemia). We utilized quasielastic neutron scattering. Dry eggs of brine shrimp were rehydrated using (1) water without additives, (2) eutectic mixture of water and dimethyl sulfoxide, and (3) a concentrated aqueous solution of lithium chloride. Despite the complexity of the hydrated multicellular organism, measurable microscopic diffusivity of water is rather well defined. Pure hydration water in eggs exhibits freezing temperature depression, whereas hydration water in eggs mixed with dimethyl sulfoxide or lithium chloride does not crystallize at all. The characteristic size of the voids occupied by water or aqueous solvents in hydrated brine shrimp eggs is between 2 and 10 nm. Those voids are accessible to co-solvents such as dimethyl sulfoxide and lithium chloride. There is no evidence of intracellular water in the hydrated eggs. The lack of intracellular water in the fully hydrated (but still under arrested development) state must be linked to the unique resilience against adverse environmental factors documented not only for the anhydrous, but also hydrated encysted eggs of brine shrimp.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗