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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Laser nanoablation of diamond surface at high pulse repetition rates

The chemical etching of the surface of a natural diamond single crystal irradiated by subpicosecond laser pulses with a high repetition rate (f⩽500 kHz) in air is experimentally investigated. The irradiation has been performed by the second-harmonic (515 nm) radiation of a disk Yb : YAG laser. Dependences of the diamond surface etch rate on the laser energy density and pulse repetition rate are obtained. (interaction of laser radiation with matter)

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Using Minority Carrier Lifetime Measurement to Determine Saw Damage Characteristics on Si Wafer Surfaces

The damage on the Si wafer surfaces, caused by ingot cutting, is determined from measurement of minority carrier lifetime (..tau..eff). Samples are sequentially etched to remove thin layers from each surface and lifetime is measured after each etch step. The thickness-removed at which the lifetime reaches a peak value corresponds to the damage depth. This technique also allows the depth distribution of the damage to be quantified in terms of surface recombination velocity (SRV). An accurate measurement of ..tau..eff requires corrections to optical reflection, and transmission to account for changes in the surface morphology and in the wafer thickness.

14 SOLAR ENERGY↗
DOE OSTI2021

Pinhole Formation in Poly-Si/SiOx Passivating Contacts on Si(111)-Oriented Textures

Poly-Si/SiOx passivating contacts were grown on inverted pyramid and random pyramid textured wafers to investigate the hypothesis that pinhole formation is most susceptible at the valleys and edges of a textured surface. Tetramethylammonium hydroxide (TMAH) etching and electron beam induced current (EBIC) were used to assess pinhole formation and charge-carrier transport. Scanning electron microscopy revealed that TMAH etching can expose pinhole locations on textured surfaces. We show that pinholes may preferentially form at the vertices of inverted pyramids. Our TMAH and EBIC analyses on random pyramids show no preferential oxide breakup at the pyramid valleys.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2024

High-resolution chemical patterns from negative tone resists for the integration of extreme ultraviolet patterns of metal-oxide resists with directed self-assembly of block copolymers

Extreme ultraviolet (EUV) lithography faces significant challenges in designing suitable resist materials that can provide adequate precision, while maintaining economically viable throughput. These challenges in resist materials have led to printing failures and high roughness in EUV patterns, compromising the performance of semiconductor devices. Integrating directed self-assembly (DSA) of block copolymers (BCPs) with EUV lithography offers a promising solution because, while the BCPs register to the EUV-defined chemical guiding pattern, the thermodynamically determined structures of the BCPs automatically rectify defects and roughness in the EUV pattern. Despite the superior resolution of metal-oxide EUV resists (MORs), their application to DSA is limited by the difficulty in converting them into chemical patterns that allow effective transfer of the rectified patterns of DSA films into inorganic materials. To address this challenge, this study introduces a novel strategy for fabricating chemical patterns using hydrogen silsesquioxane (HSQ), a high-resolution negative tone inorganic resist, as a model system for MORs. Initially, a sacrificial Cr pattern is generated from HSQ patterns via reactive ion etching. The sacrificial Cr pattern is converted into a chemical pattern by first grafting a water-soluble polyethylene oxide brush onto the substrate, then wet etching the Cr, and finally grafting nonpolar polystyrene brushes. Assembling polystyrene-block-poly(methyl methacrylate) on these patterns results in structures oriented and registered with the underlying pattern, achieving 24 nm full-pitch resolutions. In conclusion, this approach has the potential to integrate MOR patterns into the DSA process, thereby enabling the generation of high-quality sub-10 nm patterns with high-χ BCPs.

Atomic force microscopy↗
DOE OSTI2018

Influence of Processing Techniques on the Surface Microstructure of V{sub 85}Ni{sub 15} Membrane Alloy

Vanadium-based alloys with a BCC structure are considered to be an alternative to palladium alloys for hydrogen purification. Since the performance of membranes is influenced by not only their bulk characteristics but also their surface condition, we have investigated the effect of different surface preparation techniques (abrasive grinding and polishing, electrolytic polishing, and ion etching) on the surface microstructure of V{sub 85}Ni{sub 15} membrane alloy using X-ray photoelectron spectroscopy. After electrolytic polishing and ion etching, we observed an increase in the percentages of vanadium and nickel metals in the surface layer of the alloy in comparison with its state after abrasive polishing. Such changes are expected to be favorable for an increase in the rate of hydrogen dissociation and recombination on the surface of the membrane material, eventually improving hydrogen transport efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Defect-related luminescence in silicon p{sup +}–n junctions

Ultra-shallow p{sup +}–n junctions fabricated by the silicon planar technology based on the short-time nonequilibrium diffusion of boron from the gas phase into n-Si (100) substrates upon their preliminary oxidation and the opening of windows in SiO{sub 2} by electron lithography and reactive ion etching are examined. The electroand photoluminescence spectra measured in the study demonstrate emission in the range 1–1.6 µm, which is indicative of the presence of a high concentration of defects that probably appear as a result of the amorphizing effect of ions in the etching stage.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Investigation of the fabrication processes of AlGaN/AlN/GaN HEMTs with in situ Si{sub 3}N{sub 4} passivation

The optimum mode of the in situ plasma-chemical etching of a Si{sub 3}N{sub 4} passivating layer in C{sub 3}F{sub 8}/O{sub 2} medium is chosen for the case of fabricating AlGaN/AlN/GaN HEMTs. It is found that a bias of 40–50 V at a high-frequency electrode provides anisotropic etching of the insulator through a resist mask and introduces no appreciable radiation-induced defects upon overetching of the insulator films in the region of gate-metallization formation. To estimate the effect of in situ Si{sub 3}N{sub 4} growth together with the heterostructure in one process on the AlGaN/AlN/GaN HEMT characteristics, transistors with gates without the insulator and with gates through Si{sub 3}N{sub 4} slits are fabricated. The highest drain current of the AlGaN/AlN/GaN HEMT at 0 V at the gate is shown to be 1.5 times higher in the presence of Si{sub 3}N{sub 4} than without it.

36 MATERIALS SCIENCE↗
DOE OSTI2018

InGaN/GaN QDs Nanorods: Processing and Properties

InGaN/GaN nanorod structure is presented for the fabrication of light-emitting diodes by means of plasma-chemical etching. Processes of the etching of nanorods and the defect passivation in a planar InGaN/GaN quantum dot heterostructure are studied. The obtained results allow creating the light-emitting diode nanostructure with a greater efficiency compared to the classical planar technology.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Photoanodization of n-Si in the Presence of Hydrogen Peroxide: Voltage Dependence

The fundamental aspects of the electrochemical etching of lightly doped n-Si under backside illumination conditions are studied in a solution with a low HF concentration and a high concentration of hydrogen peroxide. The data obtained are compared with those for a control electrolyte containing no H{sub 2}O{sub 2}. The morphology of the self-organized macropores, their growth rate, porosity, effective valence, and the amount of dissolved silicon are examined in relation to the applied voltage. The anodization kinetics at low and high bias voltages is analyzed. It is found that, under the same illumination, the initial photocurrent in the peroxide electrolyte is approximately twice lower than in the aqueous electrolyte, which makes it possible to state that the quantum efficiency of the photocurrent is lower. As, however, the etching duration is made longer, the current in the peroxide electrolyte strongly increases to become higher than that in the control electrolyte based on H{sub 2}O. It is found that, in the presence of H{sub 2}O{sub 2}, the depthwise growth rate of the macropores increases by more than a factor of 2, and the porosity decreases. The vertical macropore channels have a diameter smaller than that for macropores formed in the aqueous electrolyte and their walls are poorly passivated, which causes branching and the formation of secondary mesopores, the number of which grows with increasing voltage. The effective valence of silicon dissolution in the presence of H{sub 2}O{sub 2} decreases to less than 2. The results are interpreted in terms of the Gerischer and Kolasinski models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Silicon Nanopillar Microarrays: Formation and Resonance Reflection of Light

Abstract—The results of investigating the spectral characteristics of reflection from silicon nanopillar (Si NP) microarrays in the wavelength region from 400 to 1100 nm are presented. The Si nanopillars are formed by electron lithography on a negative resist with subsequent reactive ion etching. The Si nanopillars are etched through a resist mask and SiO{sub 2} 100 nm thick. In the spectra of reflection from nanopillar microarrays, minima are observed, the position of which depends strongly on the Si nanopillar diameter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Oxide Removal from the InSb Plate Surface to Produce Lateral Spin Valves

Abstracts: The formation conditions of a smooth and oxide-free surface of InSb semiconductor with the purpose of fabricating lateral spin devices based on it are investigated. The dry etching rate by Ar ions of the surface of the crystalline faces (100) of InSb plates as well as a variation in their roughness depending on the power supplied to ion etching devices are investigated. The degree of oxidation of the semiconductor surface exposed to air after ion cleaning and annealing in molecular hydrogen are evaluated. Based on comparison of the efficiency of spin injection in devices formed with semiconductors subjected to various types of treatment, a conclusion is made about the parameters of optimal preparation of the surface of the InSb wafers for the fabrication of lateral spin devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ohmic Contacts to CVD Diamond with Boron-Doped Delta Layers

Various methods for the formation of ohmic contacts to boron-doped δ layers in CVD-diamond epitaxial structures are investigated. In the first variant, an additional thin heavily doped layer was formed on the diamond surface to which an ohmic contact is formed. Then, the surface p{sup +} layer between the contact pads is etched out; therefore, the current in the structure flows only through a buried δ layer. In the second approach, the doped diamond selectively grows in the contact windows under a metallic mask after preliminary etching of the undoped diamond layer (cap) up to the δ layer. In this case, the heavily doped p{sup +} layer forms an end contact to the δ layer. These two variants differ in terms of the conditions of applicability, the complexity of the manufacturing technology, the value of the contact resistance, and can be used to solve problems in which it is necessary to have a different quality of the contacts, such as the formation of transistor structures or test cells for measuring physical characteristics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Simulation of Local Error Correction of the Surface Shape by a Low-Dimensional Ion Beam

We propose an algorithm for solving the problem of local error correction of the surface shape by a low-dimensional ion beam. The algorithm presumes successive sampling running over protrusions relative to the average height aimed at searching for the optimal etching point satisfying the criterion for the reduction of the sum of derivative moduli on the etching spot. It is shown that the new approach makes it possible to considerably extend the range of spatial frequencies accessible to the action for a given dimension of an ion beam.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Shear Alignment of Diblock Copolymers for Patterning Nanowire Meshes

Metallic nanowire meshes are useful as cheap, flexible alternatives to indium tin oxide – an expensive, brittle material used in transparent conductive electrodes. We have fabricated nanowire meshes over areas up to 2.5 cm 2 by: 1) mechanically aligning parallel rows of diblock copolymer (diBCP) microdomains; 2) selectively infiltrating those domains with metallic ions; 3) etching away the diBCP template; 4) sintering to reduce ions to metal nanowires; and, 5) repeating steps 1 – 4 on the same sample at a 90° offset. We aligned parallel rows of polystyrene-b-poly(2-vinylpyridine) [PS(48.5 kDa)-b-P2VP(14.5 kDa)] microdomains by heating above its glass transition temperature (T g ≈ 100°C), applying mechanical shear pressure (33 kPa) and normal force (13.7 N), and cooling below T g . DiBCP samples were submerged in aqueous solutions of metallic ions (15 – 40 mM ions; 0.1 – 0.5 M HCl) for 30 – 90 minutes, which coordinate to nitrogen in P2VP. Subsequent ozone-etching and sintering steps yielded parallel nanowires. We aimed to optimize alignment parameters (e.g. shear and normal pressures, alignment duration, and PDMS thickness) to improve the quality, reproducibility, and scalability of meshes. We also investigated metals other than Pt and Au that may be patterned using this technique (Cu, Ag).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1993

(abstract) Mechanism of Selective Porosification at Heterojunctions in Group IV Multilayer Structures

Highly selective porosification of SiGe or Ge layers is observed in multilayer Si/SiGe or Si/Ge structures grown on (100)Si. These alternating porous/nonporous structures could potentially be used to fabricate light-emitting devices. The etch-selectivity appears to be dominated by band-structure effects and other factors such as lattice strain and electrochemical potential differences play a minor role. Additional structures and electrolytic etching are being examined to confirm these results.

porosification silicon Si Ge germanium light emitt↗
NASA NTRS2012

320 x 256 Complementary Barrier Infrared Detector Focal Plane Array for Long-Wave Infrared Imaging

A 320 x 256 Complementary Barrier Infrared (CBIRD) focal plane array for long-wavelength infrared (LWIR) imaging is reported. The arrays were grown by molecular beam expitaxy (MBE) with a 300 period 1.9 um thick absorber. The mean dark current density of 2.2 x 10-4 A/cm2 was measured at an operating bias of 128 mV with a long wavelength cutoff of 8.8 ?m observed at 50% of the peak. The maximum quantum efficiency was 54% measured at 5.6 ?m. Operating at T = 80K, the array yielded an 81% fill factor with 97% operability. Good imagery with a mean noise equivalent different temperature (NE?T) of 18.6 mK and a mean detectivity of D* = 1.3 x 1011 cm-Hz1/2/W was achieved. The substrate was thinned using mechanical lapping and neither an AR coating nor a passivation layer was applied. This article provides the details of the fabrication process for achieving low-dark current LWIR CBIRD arrays. Discussion for an effective hard mask for excellent pattern transfer is given and appropriate mounting techniques for good thermal contact during the dry etching process is described. The challenges and differences between etching large 200 ?m test diodes and small 28 ?m FPA pixels are given.

Focal Plane Arrays (FPA)↗
DOE OSTI2017

Nanoporous Atomically Thin Graphene Membranes for Desalting and Dialysis Applications

Dialysis is a ubiquitous separation process in biochemical processing and biological research. State-of-the-art dialysis membranes comprise a relatively thick polymer layer with tortuous pores, and suffer from low rates of diffusion leading to extremely long process times (often several days) and poor selectivity, especially in the 0–1000 Da molecular weight cut-off range. Here, the fabrication of large-area (cm 2 ) nanoporous atomically thin membranes (NATMs) is reported, by transferring graphene synthesized using scalable chemical vapor deposition (CVD) to polycarbonate track-etched supports. In this study, after sealing defects introduced during transfer/handling by interfacial polymerization, a facile oxygen-plasma etch is used to create size-selective pores (≤1 nm) in the CVD graphene. Size-selective separation and desalting of small model molecules (≈200–1355 Da) and proteins (≈14 000 Da) are demonstrated, with ≈1–2 orders of magnitude increase in permeance compared to state-of-the-art commercial membranes. Rapid diffusion and size-selectivity in NATMs offers transformative opportunities in purification of drugs, removal of residual reactants, biochemical analytics, medical diagnostics, therapeutics, and nano-bio separations.

36 MATERIALS SCIENCE↗