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1. Generation of Reactive Species in Water Film Dielectric Barrier Discharges Sustained in Argon, Helium, Air, Oxygen and Nitrogen

   https://doi.org/10.1088/1361-6463/aba21a  

   Mohades, Soheila ; Lietz, Amanda M ; Kushner, Mark J ( July 2020 , Journal of Physics D: Applied Physics)

   Activation of liquids with atmospheric pressure plasmas is being investigated for envi-ronmental and biomedical applications. When activating the liquid using gas plasma produced species (as opposed to plasmas sustained in the liquid), a rate limiting step is transport of these species into the liquid. To first order, the efficiency of activating the liquid is improved by in-creasing the ratio of the surface area of the water in contact with the plasma compared to its vol-ume – often called the surface-to-volume ratio (SVR). Maximizing the SVR then motivates the plasma treatment of thin films of liquids. In this paper, results are discussed from a computa-tional investigation using a global model of atmospheric pressure plasma treatment of thin water films by a dielectric barrier discharge (DBD) sustained in different gases (Ar, He, air, N2, O2). The densities of reactive species in the plasma activated water (PAW) are evaluated. The resi-dence time of the water in contact with the plasma is increased by recirculating the PAW in plasma reactor. Longer lived species such as H2O2aq and NO3−aq accumulate over time (aq de-notes an aqueous species). DBDs sustained in Ar and He are the most efficient at producing H2O2aq, DBDs sustained in argon produces the largest density of NO3−aq with the lowest pH, and discharges sustained in O2 and air produce the highest densities of O3aq. Comparisons to experi-ments by others show agreement in the trends in densities in PAW including O3aq, OHaq, H2O2aq and NO3−aq, and highlight the importance of controlling desolvation of species from the activated water. 

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2. Effects of Downstream Plasma Exposure on β-Ga 2 O 3 Rectifiers

   https://doi.org/10.1149/2162-8777/ac0500  

   Xia, Xinyi ; Xian, Minghan ; Fares, Chaker ; Ren, Fan ; Kim, Junghun ; Kim, Jihyun ; Tadjer, Marko ; Pearton, Stephen J. ( June 2021 , ECS Journal of Solid State Science and Technology)

   The effects of downstream plasma exposure with O 2 , N 2 or CF 4 discharges on Si-doped Ga 2 O 3 Schottky diode forward and reverse current-voltage characteristics were investigated. The samples were exposed to discharges with rf power of 50 W plasma at a pressure of 400 mTorr and a fixed treatment time of 1 min to simulate dielectric layer removal, photoresist ashing or surface cleaning steps. Schottky contacts were deposited through a shadow mask after exposure to avoid any changes to the surface. A Schottky barrier height of 1.1 eV was obtained for the reference sample without plasma treatment, with an ideality factor of 1.0. The diodes exposed to CF 4 showed a 0.25 V shift from the I–V of the reference sample due to a Schottky barrier height lowering around 14%. The diodes showed a decrease of Schottky barrier height of 2.5 and 6.5% with O 2 or N 2 treatments, respectively. The effect of plasma exposure on the ideality factor of diodes treated with these plasmas was minimal; 0.2% for O 2 and N 2 , 0.3% for CF 4 , respectively. The reverse leakage currents were 1.2, 2.2 and 4.8 μ A cm −2 for the diodes treated with O 2 , and CF 4 , and N 2 respectively. The effect of downstream plasma treatment on diode on-resistance and on-off ratio were also minimal. The changes observed are much less than caused by exposure to hydrogen-containing plasmas and indicate that downstream plasma stripping of films from Ga 2 O 3 during device processing is a relatively benign approach. 

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3. In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection

   https://doi.org/10.1088/1741-4326/acee98  

   Effenberg, F. ; Abe, S. ; Sinclair, G. ; Abrams, T. ; Bortolon, A. ; Wampler, W. R. ; Laggner, F. M. ; Rudakov, D. L. ; Bykov, I. ; Lasnier, C. J. ; et al ( August 2023 , Nuclear Fusion)

   Experiments have been conducted in the DIII-D tokamak to explore thein-situgrowth of silicon-rich layers as a potential technique for real-time replenishment of surface coatings on plasma-facing components (PFCs) during steady-state long-pulse reactor operation. Silicon (Si) pellets of 1 mm diameter were injected into low- and high-confinement (L-mode and H-mode) plasma discharges with densities ranging from 3.9–$7.5\times {10}^{19}$m⁻³and input powers ranging from 5.5 to 9 MW. The small Si pellets were delivered with the impurity granule injector at frequencies ranging from 4 to 16 Hz corresponding to mass flow rates of 5–19 mg s⁻¹(1–$4.2\times {10}^{20}$Si s⁻¹) at cumulative amounts of up to 34 mg of Si per five-second discharge. Graphite samples were exposed to the scrape-off layer and private flux region plasmas through the divertor material evaluation system to evaluate the Si deposition on the divertor targets. The Si II emission at the sample correlates with silicon injection and suggests net surface Si-deposition in measurable amounts. Post-mortem analysis showed Si-rich coatings containing silicon oxides, of which SiO₂is the dominant component. No evidence of SiC was found, which is attributed to low divertor surface temperatures. Thein-situand ex-situ analysis found that Si-rich coatings of at least 0.4–1.2 nm thickness have been deposited at 0.4–0.7 nm s⁻¹. The technique is estimated to coat a surface area of at least 0.94 m²on the outer divertor. These results demonstrate the potential of using real-time material injection to form Si-enriched layers on divertor PFCs during reactor operation.

    

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4. Towards Horizontal Heterojunctions for Tunnel Field Effect Transistors with Template Assisted Selective Epitaxy via MOCVD

   Brunelli, Simone ; Markman, B ; Wu, J ; Tseng, HY ; Goswami, A ; Rodwell, M ; Palmstrøm, P ; Klamkin, K ( June 2018 , International conference on MOVPE)

   Tunneling field effect transistors (TFETs) have gained much interest in the previous decade for use in low power CMOS electronics due to their sub-thermal switching [1]. To date, all TFETs are fabricated as vertical nanowires or fins with long, difficult processes resulting in long learning cycle and incompatibility with modern CMOS processing. Because most TFETs are heterojunction TFETs (HJ-TFETs), the geometry of the device is inherently vertically because dictated by the orientation of the tunneling HJ, achieved by typical epitaxy. Template assisted selective epitaxy was demonstrated for vertical nanowires [2] and horizontally arranged nanorods [3] for III-V on Si integration. In this work, we report results on the area selective and template assisted epitaxial growth of InP, utilizing SiO2 based confined structures on InP substrates, which enables horizontal HJs, that can find application in the next generation of TFET devices. The geometries of the confined structures used are so that only a small area of the InP substrate, dubbed seed, is visible to the growth atmosphere. Growth is initiated selectively only at the seed and then proceeds in the hollow channel towards the source hole. As a result, growth resembles epitaxial lateral overgrowth from a single nucleation point [4], reaping the benefits of defect confinement and, contrary to spontaneous nanowire growth, allows orientation in an arbitrary, template defined direction. Indium phosphide 2-inch (110) wafers are used as the starting substrate. The process flow (Fig.1) consists of two plasma enhanced chemical vapor deposition (PECVD) steps of SiO2, appropriately patterned with electron beam lithography (EBL), around a PECVD amorphous silicon sacrificial layer. The sacrificial layer is ultimately wet etched with XeF2 to form the final, channel like template. Not shown in the schematic in Fig.1 is an additional, ALD deposited, 3 nm thick, alumina layer which prevents plasma damage to the starting substrate and is removed via a final tetramethylammonium hydroxide (TMAH) based wet etch. As-processed wafers were then diced and loaded in a Thomas Swan Horizontal reactor. Successful growth conditions found were 600°C with 4E6 mol/min of group III precursor, a V/III ratio of 400 and 8 lpm of hydrogen as carrier gas. Trimethylindium (TMIn) and tertiarybutylphosphine (TBP) were used as In and P precursors respectively. Top view SEM (Fig.2) confirms growth in the template thanks to sufficient Z-contrast despite the top oxide layer, not removed before imaging. TEM imaging shows a cross section of the confined structure taken at the seed hole (Fig.3). The initial growth interface suggests growth was initiated at the seed hole and atomic order of the InP conforms to the SiO2 template both at the seed and at the growth front. A sharp vertical facet is an encouraging result for the future development of vertical HJ based III-V semiconductor devices. 

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5. Influence of nickel manganese cobalt oxide nanoparticle composition on toxicity toward Shewanella oneidensis MR-1: redesigning for reduced biological impact

   https://doi.org/10.1039/C6EN00453A  

   Gunsolus, Ian L. ; Hang, Mimi N. ; Hudson-Smith, Natalie V. ; Buchman, Joseph T. ; Bennett, Joseph W. ; Conroy, Daniel ; Mason, Sara E. ; Hamers, Robert J. ; Haynes, Christy L. ( January 2017 , Environmental Science: Nano)

   Lithium nickel manganese cobalt oxide (Li x Ni y Mn z Co 1−y−z O 2 , 0 < x , y , z < 1, also known as NMC) is a class of cathode materials used in lithium ion batteries. Despite the increasing use of NMC in nanoparticle form for next-generation energy storage applications, the potential environmental impact of released nanoscale NMC is not well characterized. Previously, we showed that the released nickel and cobalt ions from nanoscale Li 1/3 Ni 1/3 Mn 1/3 Co 1/3 O 2 were largely responsible for impacting the growth and survival of the Gram-negative bacterium Shewanella oneidensis MR-1 (M. N. Hang et al. , Chem. Mater. , 2016, 28 , 1092). Here, we show the first steps toward material redesign of NMC to mitigate its biological impact and to determine how the chemical composition of NMC can significantly alter the biological impact on S. oneidensis . We first synthesized NMC with various stoichiometries, with an aim to reduce the Ni and Co content: Li 0.68 Ni 0.31 Mn 0.39 Co 0.30 O 2 , Li 0.61 Ni 0.23 Mn 0.55 Co 0.22 O 2 , and Li 0.52 Ni 0.14 Mn 0.72 Co 0.14 O 2 . Then, S. oneidensis were exposed to 5 mg L −1 of these NMC formulations, and the impact on bacterial oxygen consumption was analyzed. Measurements of the NMC composition, by X-ray photoelectron spectroscopy, and composition of the nanoparticle suspension aqueous phase, by inductively coupled plasma-optical emission spectroscopy, showed the release of Li, Ni, Mn, and Co ions. Bacterial inhibition due to redesigned NMC exposure can be ascribed largely to the impact of ionic metal species released from the NMC, most notably Ni and Co. Tuning the NMC stoichiometry to have increased Mn at the expense of Ni and Co showed lowered, but not completely mitigated, biological impact. This study reveals that the chemical composition of NMC nanomaterials is an important parameter to consider in sustainable material design and usage. 

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