Time-Resolved and Nicrostructural Studies of Solidification in Undercooled Liquid Silicon

1988 ◽  
Vol 100 ◽  
Author(s):  
D. H. Lowndes ◽  
S. J. Pennycook ◽  
R. F. Wood ◽  
G. E. Jellison ◽  
S. P. Withrow
Keyword(s):  
Heat Flow ◽  
Near Infrared ◽  
Laser Energy ◽  
Solidification Process ◽  
Sample Surface ◽  
Undercooled Liquid ◽  
Time Resolved ◽  
Plan View ◽  
Model Calculations ◽  
Fine Grained

ABSTRACTNanosecond resolution visible (633 nm) and near-infrared (1152 nm) reflectivity measurements have been used, together with transmission electronmicroscopy (TEM), to study pulsed KrF (248 nm) laser melting and subsequent solidification of thick (190–410 nm) amorphous (a) silicon layers. The measurements cover the entire laser energy density (El) range between the onset of melting (∼ 0.12 J/cm2) and the completion of epitaxial crystallization (∼1.1 J/cm2). Four distinct El-regimes of melting and solidification are found for the 410-nm thick a-Si layers. For El > 0.25 J/cm2, the time of formation, velocity and final depth of “explosively” propagating undercooled liquid layers were measured in specimens that had been uniformly implanted with Si, Ge, or Cu. TEM shows that the “fine-grained polycrystalline Si” produced by explosive crystallization (XC) actually contains large numbers of disk-shaped Si flakes that have largely amorphous centers and are visible only in plan view. The optical and TEM measurements suggest (1) that flakes are the crystallization events that initiate XC, and (2) that lateral heat flow (parallel to the sample surface) must be taken into account in order to understand flake formation. Results of new two-dimensional (2-D) model calculations of heat flow and solidification are presented. These calculations confirm the importance of 2-D heat flow and crystallite growth early in the solidification process. For 0.3 4 < El > 1.0 J/cm2, pronounced changes in both the shape and the duration of the reflectivity signals provide information about the growth of polycrystalline grains; this information can be correlated with post-irradiation plan and cross-section view TEM microstructural measurements.

Time-Resolved Studies of Rapid Solidification in Highly Undercooled Molten Silicon

1984 ◽  
Vol 35 ◽  
Author(s):  
D.H. Lowndes ◽  
G.E. Jellison ◽  
R.F. Wood ◽  
S.J. Pennycook ◽  
R.W. Carpenter
Keyword(s):  
Liquid Layer ◽  
Laser Energy ◽  
Surface Region ◽  
Experimental Information ◽  
Molten Silicon ◽  
Undercooled Liquid ◽  
Time Resolved ◽  
Model Calculations ◽  
Near Surface ◽  
Si Substrates

ABSTRACTA KrF (248 nm) pulsed laser was used to melt 90-, 190-, and 440-nm thick amorphous silicon layers produced by Si ion implantation into (100) crystalline Si substrates. Time-resolved reflectivity measurements at two different probe wavelengths (633 nm and 1.15 μm) and post-irradiation TEM measurements were used to study the formation of an undercooled liquid Si phase and the subsequent solidification processes. The time-resolved measurements provide new experimental information about the nucleation of fine-grained Si crystallites in undercooled liquid Si, at low laser energy densities (Eℓ), and about the growth of large-grained Si in the near-surface region at higher Eℓ. Measurements with the infrared probe beam reveal the presence of a buried, propagating liquid layer at low ??. Model calculations indicate that this liquid layer is generated in part by the release of latent heat associated with the nucleation and growth process.

Pulsed Laser Melting of Amorphous Silicon: Time-Resolved and Post-Irradiation Studies

1983 ◽  
Vol 23 ◽  
Author(s):  
D. H. Lowndes ◽  
R. F. Wood ◽  
C. W. White ◽  
J. Narayan
Keyword(s):  
Pulsed Laser ◽  
Threshold Value ◽  
Dynamical Response ◽  
Cross Sectional ◽  
Time Resolved ◽  
Model Calculations ◽  
Fine Grained ◽  
Transmission Electron ◽  
Incident Laser Pulse ◽  
Thermal Melting

ABSTRACTMeasurements of the time of the onset of melting of self-implantation amorphized (a) Si, during an incident laser pulse, have been combined with modified melting model calculations and measurements of surface melt duration to demonstrate that the thermal conductivity, Ka, of a-Si is very low (≃0.02 W/cm-K). Ka is also shown to be the dominant parameter determining the dynamical response of ionimplanted Si to pulsed laser radiation; the latent heat and melting temperature of a-Si are relatively unimportant. Cross-sectional transmission electron micrographs on implantation-amorphized Si layers of several different thicknesses show that for energy densities less than the threshold value for complete annealing there are usually two distinct regions in the re-solidified a-Si, consisting of fine-grained and large-grained polycrystalline Si, respectively. The presence of the fine-grained poly-Si suggests that bulk nucleation occurs directly from the highly undercooled liquid phase. Thermal melting model calculations suggest that the nucleation temperature, Tn is ≃1200°C.

Solidification of highly undercooled liquid silicon produced by pulsed laser melting of ion-implanted amorphous silicon: Time-resolved and microstructural studies

1987 ◽  
Vol 2 (5) ◽  
pp. 648-680 ◽  
Author(s):  
D. H. Lowndes ◽  
S. J. Pennycook ◽  
G. E. Jellison ◽  
S. P. Withrow ◽  
D. N. Mashburn
Keyword(s):  
Pulsed Laser ◽  
Optical Measurements ◽  
Undercooled Liquid ◽  
Laser Melting ◽  
Time Resolved ◽  
Fine Grained ◽  
Explosive Crystallization ◽  
Epitaxial Regrowth ◽  
Surface Melt ◽  
Melt Duration

Nanosecond resolution time-resolved visible (632.8 nm) and infrared (1152 nm) reflectivity measurements, together with structural and Z-contrast transmission electron microscope (TEM) imaging, have been used to study pulsed laser melting and subsequent solidification of thick (190–410 nm) amorphous (a) Si layers produced by ion implantation. Melting was initiated using a KrF (248 nm) excimer laser of relatively long [45 ns full width half maximum (FWHM)] pulse duration; the microstructural and time-resolved measurements cover the entire energy density (E1) range from the onset of melting (at ∼ 0.12J/cm2) up to the onset of epitaxial regrowth (at ∼ 1.1 J/cm2). At low E1 the infrared reflectivity measurements were used to determine the time of formation, the velocity, and the final depth of “explosively” propagating buried liquid layers in 410 nm thick a-Si specimens that had been uniformly implanted with Si, Ge, or Cu over their upper ∼ 300 nm. Measured velocities lie in the 8–14 m/s range, with generally higher velocities obtained for the Ge- and Cu-implanted “a-Si alloys.” The velocity measurements result in an upper limit of 17 (± 3) K on the undercooling versus velocity relationship for an undercooled solidfying liquid-crystalline Si interface. The Z-contrast scanning TEM measurements of the final buried layer depth were in excellent agreement with the optical measurements. The TEM study also shows that the “fine-grained polycrystalline Si” region produced by explosive crystallization of a-Si actually contains large numbers of disk-shaped Si flakes that can be seen only in plan view. These Si flakes have highly amorphous centers and laterally increasing crystallinity; they apparently grow primarily in the lateral direction. Flakes having this structure were found both at the surface, at low laser E1, and also deep beneath the surface, throughout the “fine-grained poly-Si” region formed by explosive crystallization, at higher E1. Our conclusion that this region is partially amorphous (the centers of flakes) differs from earlier results. The combined structural and optical measurements suggest that Si flakes nucleate at the undercooled liquid-amorphous interface and are the crystallization events that initiate explosive crystallization. Time-resolved reflectivity measurements reveal that the surface melt duration of the 410 nm thick a-Si specimens increases rapidly for 0.3E1 <0.6 J/cm2, but then remains nearly constant for E1 up to ∼ 1.0 J/cm2. For 0.3 < E1 < 0.6 J/cm2 the reflectivity exhibits a slowly decaying behavior as the near-surface pool of liquid Si fills up with growing large grains of Si. For higher E1, a flat-topped reflectivity signal is obtained and the microstructural and optical studies together show that the principal process occurring is increasingly deep melting followed by more uniform regrowth of large grains back to the surface. However, cross-section TEM shows that a thin layer of fine-grained poly-Si still is formed deep beneath the surface for E1<0.9 J/cm2, implying that explosive crystallization occurs (probably early in the laser pulse) even at these high E1 values. The onset of epitaxial regrowth at E1 = 1.1 J/cm2 is marked by a slight decrease in surface melt duration.

Time-resolved optical studies of oxide-encapsulated silicon during pulsed laser melting

1988 ◽  
Vol 3 (3) ◽  
pp. 498-505 ◽  
Author(s):  
G. E. Jellison ◽  
D. H. Lowndes ◽  
J. W. Sharp
Keyword(s):  
Laser Annealing ◽  
Laser Energy ◽  
Threshold Energy ◽  
Pulsed Laser ◽  
Silicon Layer ◽  
Oxide Thickness ◽  
Time Resolved ◽  
Model Calculations ◽  
Near Surface ◽  
Surface Profiling

Nanosecond time-resolved reflectivity and ellipsometry experiments have been performed on (100) Si wafers encapsulated by 5.5–76.2 nm thick thermal oxides, using pulsed KrF (248 nm) laser energy densities sufficient to melt the Si beneath the oxide. Post-irradiation nulling ellipsometry, optical microphotography, and surface profiling measurements were carried out. It was found that the threshold energy density required to melt the Si varies with oxide thickness; this is explained primarily by the reflective properties of the oxide overlayer. The time-resolved reflectivity and ellipsometry measurements show that rippling of the SiO2 layer occurs on the 20–40 ns timescale and results in a decrease in specular reflectivity of the rippled silicon surface beneath. Optical model calculations suggest that pulsed laser annealing through a thick oxide layer results in a damaged near-surface silicon layer (∼ 30 nm thick); this layer contains defects that are probably responsible for the degraded performance of devices.

Time Resolved Transmission and Reflectivity of Pulsed Ruby Laser Irradiated Silicon

1981 ◽  
Vol 4 ◽  
Author(s):  
Douglas H. Lowndes ◽  
G. E. Jellison ◽  
R. F. Wood
Keyword(s):  
Ruby Laser ◽  
Crystalline Silicon ◽  
Laser Energy ◽  
Pulsed Laser ◽  
Quantitative Agreement ◽  
Laser Wavelength ◽  
Time Resolved ◽  
Model Calculations ◽  
Thermal Melting ◽  
Apparent Disagreement

ABSTRACTThe time resolved optical transmission, T (atλ = 1152 nm), and reflectivity, R (at 633 nm and 1152 nm), have been measured for n-type single crystalline silicon (c-Si) during and immediately after pulsed ruby laser irradiation (λ = 693 nm, FWHM pulse duration 14 nsec), for a range of pulsed laser energy densities, El. The T is found to go to zero, and to remain at zero, for a period of time that increases with increasing El, in apparent disagreement with earlier measurements elsewhere that used semi-insulating Si and a different pulsed laser wavelength. Measured reflectivities during the high R phase agree within experimental error with reflectivities calculated from the optical constants of molten Si. Quantitative agreement is also found between both our T and R measurements and detailed time– and El-dependent results of thermal melting model calculations.

Mineral and Trace Element Identification in Jezero Crater, Mars, with SuperCam’s Time-Resolved Raman (TRR) and Luminescence (TRL) Techniques

2021 ◽  
Author(s):  
Ann Ollila ◽  
Olivier Beyssac ◽  
Gorka Arana ◽  
Stanley Mike Angel ◽  
Karim Benzerara ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Near Infrared ◽  
Landing Site ◽  
Raman Signal ◽  
Time Resolved ◽  
Fine Grained ◽  
Breakdown Spectroscopy ◽  
Early Results ◽  
Laser Induced Breakdown ◽  
Opaque Minerals

&lt;p&gt;In February 2021, NASA&amp;#8217;s Perseverance rover will begin its exploration of Jezero crater near a putative ancient delta. Orbital mineralogy indicates the presence of carbonates and clay minerals in the landing site, which will be key targets for study. The SuperCam instrument provides an important tool for remotely surveying for these and other minerals using multiple techniques: Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman (TRR) and Luminescence (TRL) spectroscopies, Visible-Near Infrared (VisIR) spectroscopy, micro-imaging, and acoustics. TRR and TRL use a pulsed 532 nm laser with an adjustable gate width, from 100 ns to several ms. The time at which the gate opens is also adjustable, from coincident with the laser pulse to obtain Raman and fast luminescence out to 10 ms or more to capture the lifetimes of luminescence signals. These techniques will operate at distances up to 7 m from the rover mast and will be most effective if LIBS first removes dust from the targets and chemistry is subsequently obtained at the same location. Early lab results show that TRR is effective for detecting certain carbonates (magnesite, hydromagnesite, siderite, ankerite, calcite, and dolomite), sulfates (gypsum, anhydrite, barite, epsomite, and coquimbite), phosphates (apatite), and silicates (e.g., quartz, feldspar, forsteritic olivine, topaz, and diopside). Many of these minerals are high-priority targets for astrobiology studies because they represent habitable environments and have high biosignature preservation potential in terrestrial rocks. Raman signal strength is significantly decreased in fine-grained materials, however, and clay minerals will be a challenge to detect, as will opaque minerals such as Fe-oxides. TRL will be useful for identifying rare earth elements in phosphates and zircon, Fe&lt;sup&gt;3+ &lt;/sup&gt;in silicates such as feldspar, Mn&lt;sup&gt;2+&lt;/sup&gt; in carbonates, and Cr&lt;sup&gt;3+&lt;/sup&gt; in Al-oxides and some silicates. TRL may also be able to identify fast (&lt;100 ns) fluorescence that may indicate the presence of organic materials, which could then be analyzed more closely with the rover&amp;#8217;s other instruments. Early results from the Jezero crater will be presented, if available.&amp;#160; &amp;#160;&lt;/p&gt;

Interfacial structures of dissimilar materials joined by capacitor-discharge welding

1994 ◽  
Vol 52 ◽  
pp. 534-535
Author(s):  
C. P. Doğan ◽  
R. D. Wilson ◽  
J. A. Hawk
Keyword(s):  
Rapid Solidification ◽  
Fusion Zone ◽  
Dissimilar Materials ◽  
Solidification Process ◽  
Weld Interface ◽  
Capacitor Discharge ◽  
Fine Grained ◽  
Iron Aluminum ◽  
Conductive Ceramics ◽  
Capacitor Discharge Welding

Capacitor Discharge Welding is a rapid solidification technique for joining conductive materials that results in a narrow fusion zone and almost no heat affected zone. As a result, the microstructures and properties of the bulk materials are essentially continuous across the weld interface. During the joining process, one of the materials to be joined acts as the anode and the other acts as the cathode. The anode and cathode are brought together with a concomitant discharge of a capacitor bank, creating an arc which melts the materials at the joining surfaces and welds them together (Fig. 1). As the electrodes impact, the arc is extinguished, and the molten interface cools at rates that can exceed 106 K/s. This process results in reduced porosity in the fusion zone, a fine-grained weldment, and a reduced tendency for hot cracking.At the U.S. Bureau of Mines, we are currently examining the possibilities of using capacitor discharge welding to join dissimilar metals, metals to intermetallics, and metals to conductive ceramics. In this particular study, we will examine the microstructural characteristics of iron-aluminum welds in detail, focussing our attention primarily on interfaces produced during the rapid solidification process.

WLCSP Laminate Removal Using NIR Laser

2018 ◽  
Author(s):  
Chun Haur Khoo
Keyword(s):  
Near Infrared ◽  
Laser Energy ◽  
Photon Emission ◽  
Mechanical Damage ◽  
Consumer Products ◽  
Fault Isolation ◽  
Wafer Level ◽  
Isolation Technique ◽  
Laminate Layer ◽  
Nir Laser

Abstract Driven by the cost reduction and miniaturization, Wafer Level Chip Scale Packaging (WLCSP) has experienced significant growth mainly driven by mobile consumer products. Depending on the customers or manufacturing needs, the bare silicon backside of the WLCSP may be covered with a backside laminate layer. In the failure analysis lab, in order to perform the die level backside fault isolation technique using Photon Emission Microscope (PEM) or Laser Signal Injection Microscope (LSIM), the backside laminate layer needs to be removed. Most of the time, this is done using the mechanical polishing method. This paper outlines the backside laminate removal method of WLCSP using a near infrared (NIR) laser that produces laser energy in the 1,064 nm range. This method significantly reduces the sample preparation time and also reduces the risk of mechanical damage as there is no application of mechanical force. This is an effective method for WLCSP mounted on a PCB board.

scholarly journals Real-time observation of tetrapyrrole binding to an engineered bacterial phytochrome

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yusaku Hontani ◽  
Mikhail Baloban ◽  
Francisco Velazquez Escobar ◽  
Swetta A. Jansen ◽  
Daria M. Shcherbakova ◽  
...  
Keyword(s):  
Real Time ◽  
Rational Design ◽  
Near Infrared ◽  
Fluorescent Proteins ◽  
Covalent Bond ◽  
Binding Pocket ◽  
Tissue Imaging ◽  
Covalent Attachment ◽  
Time Resolved

AbstractNear-infrared fluorescent proteins (NIR FPs) engineered from bacterial phytochromes are widely used for structural and functional deep-tissue imaging in vivo. To fluoresce, NIR FPs covalently bind a chromophore, such as biliverdin IXa tetrapyrrole. The efficiency of biliverdin binding directly affects the fluorescence properties, rendering understanding of its molecular mechanism of major importance. miRFP proteins constitute a family of bright monomeric NIR FPs that comprise a Per-ARNT-Sim (PAS) and cGMP-specific phosphodiesterases - Adenylyl cyclases - FhlA (GAF) domain. Here, we structurally analyze biliverdin binding to miRFPs in real time using time-resolved stimulated Raman spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations. Biliverdin undergoes isomerization, localization to its binding pocket, and pyrrolenine nitrogen protonation in <1 min, followed by hydrogen bond rearrangement in ~2 min. The covalent attachment to a cysteine in the GAF domain was detected in 4.3 min and 19 min in miRFP670 and its C20A mutant, respectively. In miRFP670, a second C–S covalent bond formation to a cysteine in the PAS domain occurred in 14 min, providing a rigid tetrapyrrole structure with high brightness. Our findings provide insights for the rational design of NIR FPs and a novel method to assess cofactor binding to light-sensitive proteins.

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