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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Growth, strain relaxation properties and high-κ dielectric integration of mixed-anion GaAs{sub 1-y}Sb{sub y} metamorphic materials

Mixed-anion, GaAs{sub 1-y}Sb{sub y} metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs{sub 1-y}Sb{sub y} materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs{sub 1-y}Sb{sub y}. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sb compositions in the GaAs{sub 1-y}Sb{sub y} structures. Selected high-κ dielectric materials, Al{sub 2}O{sub 3}, HfO{sub 2}, and Ta{sub 2}O{sub 5} were deposited using atomic layer deposition on the GaAs{sub 0.38}Sb{sub 0.62} material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs{sub 0.38}Sb{sub 0.62}, indicating the potential of utilizing these dielectrics on GaAs{sub 0.38}Sb{sub 0.62} for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al{sub 2}O{sub 3} and HfO{sub 2} showed a conduction band offset of >2 eV on GaAs{sub 0.38}Sb{sub 0.62}, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs{sub 1-y}Sb{sub y} material systems and the detailed band alignment analysis of multiple high-κ dielectric materials on a fixed Sb composition, GaAs{sub 0.38}Sb{sub 0.62}, provides a pathway to utilize GaAs{sub 1-y}Sb{sub y} materials in future microelectronic and optoelectronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A high density two-dimensional electron gas in an oxide heterostructure on Si (001)

We present the growth and characterization of layered heterostructures comprised of LaTiO{sub 3} and SrTiO{sub 3} epitaxially grown on Si (001). Magnetotransport measurements show that the sheet carrier densities of the heterostructures scale with the number of LaTiO{sub 3}/SrTiO{sub 3} interfaces, consistent with the presence of an interfacial 2-dimensional electron gas (2DEG) at each interface. Sheet carrier densities of 8.9 × 10{sup 14} cm{sup −2} per interface are observed. Integration of such high density oxide 2DEGs on silicon provides a bridge between the exceptional properties and functionalities of oxide 2DEGs and microelectronic technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electrostatic capacitance and Faraday cage behavior of carbon nanotube forests

Understanding of the electrostatic properties of carbon nanotube (CNT) forests is essential to enable their integration in microelectronic and micromechanical devices. In this study, we sought to understand how the hierarchical geometry and morphology of CNT forests determines their capacitance. First, we find that at small gaps, solid micropillars have greater capacitance, yet at larger gaps the capacitance of the CNT forests is greater. The surface area of the CNT forest accessible to the electrostatic field was extracted by analysis of the measured capacitance, and, by relating the capacitance to the average density of CNTs in the forest, we find that the penetration depth of the electrostatic field is on the order of several microns. Therefore, CNT forests can behave as a miniature Faraday cage. The unique electrostatic properties of CNT forests could therefore enable their use as long-range proximity sensors and as shielding elements for miniature electronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Physical mechanisms of SiN{sub x} layer structuring with ultrafast lasers by direct and confined laser ablation

In the production process of silicon microelectronic devices and high efficiency silicon solar cells, local contact openings in thin dielectric layers are required. Instead of photolithography, these openings can be selectively structured with ultra-short laser pulses by confined laser ablation in a fast and efficient lift off production step. Thereby, the ultrafast laser pulse is transmitted by the dielectric layer and absorbed at the substrate surface leading to a selective layer removal in the nanosecond time domain. Thermal damage in the substrate due to absorption is an unwanted side effect. The aim of this work is to obtain a deeper understanding of the physical laser-material interaction with the goal of finding a damage-free ablation mechanism. For this, thin silicon nitride (SiN{sub x}) layers on planar silicon (Si) wafers are processed with infrared fs-laser pulses. Two ablation types can be distinguished: The known confined ablation at fluences below 300 mJ/cm{sup 2} and a combined partial confined and partial direct ablation at higher fluences. The partial direct ablation process is caused by nonlinear absorption in the SiN{sub x} layer in the center of the applied Gaussian shaped laser pulses. Pump-probe investigations of the central area show ultra-fast reflectivity changes typical for direct laser ablation. Transmission electron microscopy results demonstrate that the Si surface under the remaining SiN{sub x} island is not damaged by the laser ablation process. At optimized process parameters, the method of direct laser ablation could be a good candidate for damage-free selective structuring of dielectric layers on absorbing substrates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Mechanism of β-FeSi{sub 2} precipitates growth-and-dissolution and pyramidal defects' formation during oxidation of Fe-contaminated silicon wafers

Fe-implanted Si-wafers have been oxidized at 900 °C and 1100 °C in order to investigate the behaviour of Fe atoms at the growing SiO{sub 2}/Si interface and the impact on the integrity of microelectronic devices of an involuntary Fe contamination before or during the oxidation process. As-implanted and oxidized wafers have been characterized using secondary ion mass spectroscopy, atom probe tomography, and high-resolution transmission electron microscopy. Experimental results were compared to calculated implantation profiles and simulated images. Successive steps of iron disilicide precipitation and oxidation were evidenced during the silicon oxidation process. The formation of characteristic pyramidal-shaped defects, at the SiO{sub 2}/Si interface, was notably found to correlate with the presence of β-FeSi{sub 2} precipitates. Taking into account the competitive oxidation of these precipitates and of the surrounding silicon matrix, dynamic mechanisms are proposed to model the observed microstructural evolution of the SiO{sub 2}/Si interface, during the growth of the silicon oxide layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Boron nitride nanowires synthesis via a simple chemical vapor deposition at 1200 °C

A very simple chemical vapor deposition technique is used to synthesize high quality boron nitride nanowires at 1200 °C within a short growth duration of 30 min. FESEM micrograph shows that the as-synthesized boron nitride nanowires have a clear wire like morphology with diameter in the range of ∼20 to 150 nm. HR-TEM confirmed the wire-like structure of boron nitride nanowires, whereas XPS and Raman spectroscopy are used to find out the elemental composition and phase of the synthesized material. The synthesized boron nitride nanowires have potential applications as a sensing element in solid state neutron detector, neutron capture therapy and microelectronic devices with uniform electronic properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

The efficacy of post porosity plasma protection against vacuum-ultraviolet damage in porous low-k materials

As of today, plasma damage remains as one of the main challenges to the reliable integration of porous low-k materials into microelectronic devices at the most aggressive node. One promising strategy to limit damage of porous low-k materials during plasma processing is an approach we refer to as post porosity plasma protection (P4). In this approach, the pores of the low-k material are filled with a sacrificial agent prior to any plasma treatment, greatly minimizing the total damage by limiting the physical interactions between plasma species and the low-k material. Interestingly, the contribution of the individual plasma species to the total plasma damage is not fully understood. In this study, we investigated the specific damaging effect of vacuum-ultraviolet (v-UV) photons on a highly porous, k = 2.0 low-k material and we assessed the P4 protective effect against them. It was found that the impact of the v-UV radiation varied depending upon the v-UV emission lines of the plasma. More importantly, we successfully demonstrated that the P4 process provides excellent protection against v-UV damage.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Tailoring the optical constants in single-crystal silicon with embedded silver nanostructures for advanced silicon photonics applications

Plasmonic effects associated with metal nanostructures are expected to hold the key to tailoring light emission/propagation and harvesting solar energy in materials including single crystal silicon which remains the backbone in the microelectronics and photovoltaics industries but unfortunately, lacks many functionalities needed for construction of advanced photonic and optoelectronics devices. Currently, silicon plasmonic structures are practically possible only in the configuration with metal nanoparticles or thin film arrays on a silicon surface. This does not enable one to exploit the full potential of plasmonics for optical engineering in silicon, because the plasmonic effects are dominant over a length of ∼50 nm, and the active device region typically lies below the surface much beyond this range. Here, we report on a novel method for the formation of silver nanoparticles embedded within a silicon crystal through metal gettering from a silver thin film deposited at the surface to nanocavities within the Si created by hydrogen ion implantation. The refractive index of the Ag-nanostructured layer is found to be 3–10% lower or higher than that of silicon for wavelengths below or beyond ∼815–900 nm, respectively. Around this wavelength range, the optical extinction values increase by a factor of 10–100 as opposed to the pure silicon case. Increasing the amount of gettered silver leads to an increased extinction as well as a redshift in wavelength position for the resonance. This resonance is attributed to the surface plasmon excitation of the resultant silver nanoparticles in silicon. Additionally, we show that the profiles for optical constants in silicon can be tailored by varying the position and number of nanocavity layers. Such silicon crystals with embedded metal nanostructures would offer novel functional base structures for applications in silicon photonics, optoelectronics, photovoltaics, and plasmonics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Synthesis and field emission behaviour of well faceted In{sub 2}Se{sub 3} micro-crystals

Here in, we report synthesis of crystalline Indium Selenide (In{sub 2}Se{sub 3}) elegant microcrystals on Au coated Si substrates using one-step facile thermal evaporation route and their field emission investigations. The as-synthesized In{sub 2}Se{sub 3} micro-crystals were subjected to structural and morphological analysis prior to the field emission studies. The XRD spectrum of the as-synthesized product reveals formation of crystalline hexagonal phase of In{sub 2}Se{sub 3} under the prevailing experimental conditions. Under optimized process variables, the morphology of the as-synthesized product is characterized by presence of well facetted micron size particles of In2Se3. Furthermore, the EDAX analysis confirms the presence of In and Se in the as-synthesized sample. The field emission characteristic of the In{sub 2}Se{sub 3} micro-crystal emitter is found to be superior to the other metal chalcogenides micro-crystal based emitters. The synthesized In{sub 2}Se{sub 3} micro-crystals emitter delivers current density of ∼ 225 µA/cm{sup 2} at an applied electric field of ∼ 7.44 V/µm. The emission current stability investigated at pre-set value of ∼ 3 µA is observed to be fairly good. These observed results demonstrate potential of the In{sub 2}Se{sub 3} cathode as an electron source for practical applications in vacuum microelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Study of multi-functionality of lanthanum ferrite (LaFeO{sub 3})

In the present work, multifunctional behaviors of LaFeO{sub 3} (LFO) are investigated by studying its dielectric and photocatalytic properties, respectively. LFO is synthesized by microwave-assisted co-precipitation route. Orthorhombic structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof suite. Frequency and Temperature dependence dielectric behavior are systematically studied. The dielectric constant of LFO was found to be 2500 – 3000 with dissipation factor less than 5%. Photodegradation of toxic dye (Methylene Blue) using as-prepared LFO is also investigated. UV-visible absorption spectra are used to study the photodegradation behaviour. Photodegradation of methylene blue (MB) taken from textile industries by LFO are reported. The colossal value of dielectric constant of LFO exhibits high potential to use as room temperature capacitive component for device miniaturization in microelectronics as well as photodegradation ability shows good photocatalyst.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Tunable delay time and Hartman effect in graphene magnetic barriers

Tunable group delay and Hartman effect have been investigated for massless Dirac electrons in graphene magnetic barriers. In the presence of magnetic field, dwell time is found to be equal to net group delay plus the group delay contributing from the lateral shifts. The group delay times are discussed in both cases of normal and oblique incidence, to clarify the nature of Hartman effect. In addition, the group delay in transmission can be modulated from subluminality to superluminality by adjusting the magnetic field, which may also lead to potential applications in graphene-based microelectronics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Density functional theory study of the influence of segregation of S or Fe impurities on electromigration in nano-grained copper interconnects

The reliability of the circuits in the modern microelectronic devices remains, during last decades, one of the key topics in research and gains an attention for improving the promising candidates for conductors. Improvement of materials for such applications can be obtained by both electronic and compositional optimization. Ab initio calculations using full potential linearized augmented plane wave method in density functional theory are applied to explain the reduction in electromigration effect in the vicinity of grain boundaries (GB) in nano-structured Cu due to the segregation of some additives to the GB. Several possible mechanisms are considered. It is demonstrated that S atoms segregated to GB of nano-structured Cu lead to the growth of effective mass of the electrons. This decreases the mobility of electrons in external electric field, and, correspondingly, the momentum that they may transfer to atoms in collisions. Fe atoms segregated to GB of Cu create new empty states at the top of the valance band. These non-occupied states may stimulate the current of holes when external electric field is applied to the system, creating the “hole wind” in the direction opposite to the current of electrons. Such “hole wind” will compensate the forces generated by the electron current and therefore will reduce the total momentum transfer between charge carriers and atoms. The calculated electron density maps show that S and Fe segregating to Cu GB increases the strength of covalent bonds reducing the diffusion of Cu atoms in the vicinity of GB.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

An electrically tunable plenoptic camera using a liquid crystal microlens array

Plenoptic cameras generally employ a microlens array positioned between the main lens and the image sensor to capture the three-dimensional target radiation in the visible range. Because the focal length of common refractive or diffractive microlenses is fixed, the depth of field (DOF) is limited so as to restrict their imaging capability. In this paper, we propose a new plenoptic camera using a liquid crystal microlens array (LCMLA) with electrically tunable focal length. The developed LCMLA is fabricated by traditional photolithography and standard microelectronic techniques, and then, its focusing performance is experimentally presented. The fabricated LCMLA is directly integrated with an image sensor to construct a prototyped LCMLA-based plenoptic camera for acquiring raw radiation of targets. Our experiments demonstrate that the focused region of the LCMLA-based plenoptic camera can be shifted efficiently through electrically tuning the LCMLA used, which is equivalent to the extension of the DOF.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Effects of vacuum ultraviolet irradiation on trapped charges and leakage currents of low-k organosilicate dielectrics

Vacuum ultraviolet (VUV) photoemission spectroscopy is utilized to investigate the distribution of trapped charges within the bandgap of low dielectric constant (low-k) organosilicate (SiCOH) materials. It was found that trapped charges are continuously distributed within the bandgap of porous SiCOH and the center of the trapped states is 1.3 eV above the valence band of the tested sample. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies between 7.6 and 8.9 eV was found to deplete trapped charge while UV exposure with photon energies less than 6.0 eV induces more trapped charges in tested samples. Current-Voltage (IV) characteristics results show that the reliability of dielectrics is improved after VUV irradiation with photon energies between 7.6 and 8.9 eV, while UV exposure results in an increased level of leakage current and a decreased breakdown voltage, both of which are harmful to the reliability of the dielectric. This work shows that VUV irradiation holds the potential to substitute for UV curing in microelectronic processing to improve the reliability of low-k dielectrics by mitigating the leakage currents and trapped charges induced by UV irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

On the interplay between relaxation, defect formation, and atomic Sn distribution in Ge{sub (1−x)}Sn{sub (x)} unraveled with atom probe tomography

Ge{sub (1−x)}Sn{sub (x)} has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distribution of Sn-atoms. We concluded that the main relaxation mechanism for these layers is defect generation (misfit dislocations, threading dislocations, etc.), irrespective of the cause (thickness of layer or thermal anneal) of relaxation and is independent of the cluster formation. The low thermodynamic solubility limit of Sn in Ge seems to be the driving force for Sn-cluster formation. Finally, we also discuss the spatial distribution of Sn in clusters and relate them to the theoretically predicted stable Sn clusters [Ventura et al., Phys. Rev. B 79, 155202 (2009)].

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Investigation of electrochemical migration on Sn-0.7Cu-0.3Ag-0.03P-0.005Ni solder alloy in HNO{sub 3} solution

Current issue in lead-free solder in term of its reliability is still under investigation. This high impact research attempts to investigate the electrochemical migration (ECM) on Sn-0.7Cu-0.3Ag-0.03P-0.005Ni solder alloy by Water Drop Test (WDT) in different concentration of HNO{sub 3} solution. The concentration of HNO{sub 3} solution used in this research was 0.05, 0.10, 0.50 and 1M. Optical Microscope (OM), Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-Ray Analysis (EDX) were carried out in order to analysis the ECM behavior based on the growth of dendrite formation after WDT. In general, the results demonstrated that dendrite growth is faster in higher concentration compared with low concentration of HNO{sub 3}. The concentration of HNO{sub 3} solution used has a strong correlation with Mean-Time-To-Failure (MTTF). As the concentration of HNO{sub 3} increases, the MTTF value decreases. Based on the MTTF results the solder alloy in 1M HNO{sub 3} solution is most susceptible to ECM. SnO{sub 2} forms as a corrosion by-product in the samples proved by EDX analysis. The solder alloy poses a high reliability risk in microelectronic devices during operation in 1M HNO{sub 3} solution.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of gamma radiation on micromechanical hardness of lead-free solder joint

Lead-free solders are important material in nano and microelectronic surface mounting technology for various applications in bio medicine, environmental monitoring, spacecraft and satellite instrumentation. Nevertheless solder joint in radiation environment needs higher reliability and resistance to any damage caused by ionizing radiations. In this study a lead-free 99.0Sn0.3Ag0.7Cu wt.% (SAC) solder joint was developed and subjected to various doses of gamma radiation to investigate the effects of the ionizing radiation to micromechanical hardness of the solder. Averaged hardness of the SAC joint was obtained from nanoindentation test. The results show a relationship between hardness values of indentations and the increment of radiation dose. Highest mean hardness, 0.2290 ± 0.0270 GPa was calculated on solder joint which was exposed to 5 Gray dose of gamma radiation. This value indicates possible radiation hardening effect on irradiated solder. The hardness gradually decreased to 0.1933 ± 0.0210 GPa and 0.1631 ± 0.0173 GPa when exposed to doses 50 and 500 gray respectively. These values are also lower than the hardness of non irradiated sample which was calculated as 0.2084 ± 0.0.3633 GPa indicating possible radiation damage and needs further related atomic dislocation study.

36 MATERIALS SCIENCE↗