Carbon Nanotubes for Space Photovoltaic Applications

Carbon nanotubes (CNTs) can be envisioned as an individual graphene sheet rolled into a seamless cylinder (single-walled, SWNT), or concentric sheets as in the case of a multi-walled carbon nanotube (MWNT) (1). The role-up vector will determine the hexagonal arrangement and "chirality" of the graphene sheet, which will establish the nanotube to be metallic or semiconducting. The optoelectronic properties will depend directly on this chiral angle and the diameter of the SWNT, with semiconductor types exhibiting a band gap energy (2). Characteristic of MWNTs are the concentric graphene layers spaced 0.34 nm apart, with diameters from 10-200 nm and lengths up to hundreds of microns (2). In the case of SWNTs, the diameters range from 0.4 - 2 nm and lengths have been reported up to 1.5 cm (3). SWNTs have the distinguishable property of "bundling" together due to van der Waal's attractions to form "ropes." A comparison of these different structural types is shown in Figure 1. The use of SWNTS in space photovoltaic (PV) applications is attractive for a variety of reasons. Carbon nanotubes as a class of materials exhibit unprecedented optical, electrical, mechanical properties, with the added benefit of being nanoscale in size which fosters ideal interaction in nanomaterial-based devices like polymeric solar cells. The optical bandgap of semiconducting SWNTs can be varied from approx. 0.4 - 1.5 eV, with this property being inversely proportional to the nanotube diameter. Recent work at GE Global Research has shown where a single nanotube device can behave as an "ideal" pn diode (5). The SWNT was bridged over a SiO2 channel between Mo contacts and exhibited an ideality factor of 1, based on a fit of the current-voltage data using the diode equation. The measured PV efficiency under a 0.8 eV monochromatic illumination showed a power conversion efficiency of 0.2 %. However, the projected efficiency of these junctions is estimated to be > 5 %, especially when one considers the enhanced absorption (from nanotubes whose bandgap is tailored to illumination) and electromagnetic coupling in a network of nanotubes

On the limits to Ti incorporation into Si using pulsed laser melting

Fabrication of p-Si(111) layers with Ti levels well above the solid solubility limit was achieved via ion implantation of 15 keV 48Ti+ at doses of 1012 to 1016 cm−2 followed by pulsed laser melting using a Nd:YAG laser (FWHM = 6 ns) operating at 355 nm. All implanted layers were examined using cross-sectional transmission electron microscopy, and only the 1016 cm−2 Ti implant dose showed evidence of Ti clustering in a microstructure with a pattern of Ti-rich zones. The liquid phase diffusivity and diffusive velocity of Ti in Si were estimated to be 9 × 10−4 cm2/s and (2 ± 0.5) × 104 m/s, respectively. Using these results the morphological stability limit for planar resolidification of Si:Ti was evaluated, and the results indicate that attaining sufficient concentrations of Ti in Si to reach the nominal Mott transition in morphologically stable plane-front solidification should occur only for velocities so high as to exceed the speed limits for crystalline regrowth in Si(111).Engineering and Applied Science

Review of Graphene Technology and Its Applications for Electronic Devices

Graphene has amazing abilities due to its unique band structure characteristics defining its enhanced electrical capabilities for a material with the highest characteristic mobility known to exist at room temperature. The high mobility of graphene occurs due to electron delocalization and weak electron–phonon interaction, making graphene an ideal material for electrical applications requiring high mobility and fast response times. In this review, we cover graphene’s integration into infrared (IR) devices, electro-optic (EO) devices, and field effect transistors (FETs) for radio frequency (RF) applications. The benefits of utilizing graphene for each case are discussed, along with examples showing the current state-of-the-art solutions for these applications

Doping and Transfer of High Mobility Graphene Bilayers for Room Temperature Mid-Wave Infrared Photodetectors

High-performance graphene-HgCdTe detector technology has been developed combining the best properties of both materials for mid-wave infrared (MWIR) detection and imaging. The graphene functions as a high mobility channel that whisks away carriers before they can recombine, further contributing to detection performance. Comprehensive modeling on the HgCdTe, graphene, and the HgCdTe-graphene interface has aided the design and development of this MWIR detector technology. Chemical doping of the bilayer graphene lattice has enabled p-type doping levels in graphene for high mobility implementation in high-performance MWIR HgCdTe detectors. Characterization techniques, including SIMS and XPS, confirm high boron doping concentrations. A spin-on doping (SOD) procedure is outlined that has provided a means of doping layers of graphene on native substrates, while subsequently allowing integration of the doped graphene layers with HgCdTe for final implementation in the MWIR photodetection devices. Successful integration of graphene into HgCdTe photodetectors can thus provide higher MWIR detector efficiency and performance compared to HgCdTe-only detectors. New earth observation measurement capabilities are further enabled by the room temperature operational capability of the graphene-enhanced HgCdTe detectors and arrays to benefit and advance space and terrestrial applications

Novel Commercial Protective Face Mask Technology to Mitigate Disparities in Personal Safety

Novel Commercial Protective Face Mask Technology to Mitigate Disparities in Personal Safety Kevin Shah, I. Gherasoiu, M. Fasullo, and H. Efstathiadis The current health emergency is caused by a coronavirus, SARS-COV-2, that is believed to be transmitted with preponderance through aerosolized virions. For the medical personnel and for the public at large, the use of effective and safe face masks is part of the arsenal of measures that can limit the spread of the respiratory disease known as COVID-19. Thus, there is a critical need for a filtration device able to retain or deactivate all biological agents irrespective of size, that should be reliable, mechanically robust and reusable for hundreds or thousands of times after simple cleaning, while the fabrication process should be capable of producing large numbers of such filtering elements, fast, at low cost and using pre-installed technology in U.S. based facilities. Towards addressing this need, this project proposes the use of high intensity electric fields to inactivate the virus. This new approach uses the interaction between an external electric field and the field produced by the uneven electron density of the molecules that makeup the viral envelope. The design of the filter cartridge allows the generation of extremely intense electric fields of up to 4.5 MV/m. The operation of such a device while able to destroy viral particles will not endanger the safety of the user. The interaction primarily enables the disruption of the molecular integrity leading to the impairment of the viral ability to connect to the cellular membrane and infect. The main objective of this proposal is to fabricate and test an electrostatic air filter that can be integrated with commercially available respirators and face masks that are suitable for personnel exposed to biological agents. A reusable face mask with a battery-operated electrostatic filter element can be both medical equipment provided to care facilities as well as a consumer project. A consumer technology such as this will ensure that anyone can have access to an effective, affordable, protective face covering. This will be instrumental in eliminating the disparities in the quality of equipment available for personal health and safety. The successful completion of the project will have a great impact on preventing the spread of viruses including COVID-19. The main impact will be the fabrication of multi-purpose filtering elements using existing semiconductor manufacturing base in U.S.A., to be integrated with commercial respirators, leading to the elimination of the need for non-reusable face masks. The shortage of such masks reported in the early days of the COVID-19 epidemic in the USA and also in other countries is still affecting the safety of regular citizens and that of the essential personnel including the medical personnel. This shortage led to the “War of Mask” as it is still called, i.e., governments biding on the mask price and competing with each other. The global face mask market size was valued at $206 million in 2018, and in a 2020 projection the market value will surpass$21 Billion by 2026

Highly Transparent Conductive Electrode with Ultra-Low HAZE by Grain Boundary Modification of Aqueous Solution Fabricated Alumina-Doped Zinc Oxide Nanocrystals

Commercial production of transparent conducting oxide (TCO) polycrystalline films requires high electrical conductivity with minimal degradation in optical transparency. Aqueous solution deposited TCO films would reduce production costs of TCO films but suffer from low electrical mobility, which severely degrades both electrical conductivity and optical transparency in the visible spectrum. Here, we demonstrated that grain boundary modification by ultra-violet laser crystallization (UVLC) of solution deposited aluminium-doped zinc oxide (AZO) nanocrystals results in high Hall mobility, with a corresponding dramatic improvement in AZO electrical conductance. The AZO films after laser irradiation exhibit electrical mobility up to 18.1 cm2 V−1 s−1 with corresponding electrical resistivity and sheet resistances as low as 1 × 10−3 Ω cm and 75 Ω/sq, respectively. The high mobility also enabled a high transmittance (T) of 88%-96% at 550 nm for the UVLC films. In addition, HAZE measurement shows AZO film scattering transmittance as low as 1.8%, which is superior over most other solution deposited transparent electrode alternatives such as silver nanowires. Thus, AZO films produced by the UVLC technique have a combined figure of merit for electrical conductivity, optical transparency, and optical HAZE higher than other solution based deposition techniques and comparable to vacuumed based deposition methods

Development and characterization of transparent and conductive InZnO films by magnetron sputtering at room temperature

a b s t r a c t The electrical and optical properties of InZnO for use as a transparent conducting oxide (TCO) is reported through the investigation of the concentration of indium and oxygen in the film. InZnO films (10-30 wt.% In) were deposited by magnetron sputtering without substrate heating or annealing from a ceramic ZnO and a metallic indium target. The film's properties were investigated by X-ray photoelectric spectroscopy (XPS), 4-point probe, UV-vis spectroscopy (UV-vis), spectroscopic ellipsometry, and Hall measurements. InZnO films obtained properties with low resistivity, on the order of $5.5 Â 10 À4 ohm-cm, with a mobility$35 cm 2 /V S, and carrier concentrations $3 ⁄ 10 20 cm À3 . The band-gap ranged from 2.7 to 3.2 eV with transmission of several samples >80%. InZnO has demonstrated properties adequate for photovoltaic applications

Highly Transparent Conductive Electrode with Ultra-Low HAZE by Grain Boundary Modification of Aqueous Solution Fabricated Alumina-Doped Zinc Oxide Nanocrystals

Commercial production of transparent conducting oxide (TCO) polycrystalline films requires high electrical conductivity with minimal degradation in optical transparency. Aqueous solution deposited TCO films would reduce production costs of TCO films but suffer from low electrical mobility, which severely degrades both electrical conductivity and optical transparency in the visible spectrum. Here, we demonstrated that grain boundary modification by ultra-violet laser crystallization (UVLC) of solution deposited aluminium-doped zinc oxide (AZO) nanocrystals results in high Hall mobility, with a corresponding dramatic improvement in AZO electrical conductance. The AZO films after laser irradiation exhibit electrical mobility up to 18.1 cm2 V−1 s−1 with corresponding electrical resistivity and sheet resistances as low as 1 × 10−3 Ω cm and 75 Ω/sq, respectively. The high mobility also enabled a high transmittance (T) of 88%-96% at 550 nm for the UVLC films. In addition, HAZE measurement shows AZO film scattering transmittance as low as 1.8%, which is superior over most other solution deposited transparent electrode alternatives such as silver nanowires. Thus, AZO films produced by the UVLC technique have a combined figure of merit for electrical conductivity, optical transparency, and optical HAZE higher than other solution based deposition techniques and comparable to vacuumed based deposition methods