Preliminary Approach to Implementing a COVID-19 Thoracic Radiation Therapy Program.

The value of low-dose whole thoracic radiation therapy (LD-WTRT) for SARS-CoV-2 (COVID-19) pneumonia is unknown. Should ongoing clinical trials demonstrate that LD-WTRT proves effective for COVID-19 pneumonia recovery, widespread rapid implementation will be helpful globally. Our aim was to outline a pragmatic process for safe and efficient administration of LD-WTRT to patients with COVID-19 pneumonia that could be implemented successfully in a community hospital setting based on participation in the PreVent clinical trial of LD-WTRT.

B-Doped δ-Layers and Nanowires from Area-Selective Deposition of BCl3 on Si(100).

Atomically precise, δ-doped structures forming electronic devices in Si have been routinely fabricated in recent years by using depassivation lithography in a scanning tunneling microscope (STM). While H-based precursor/monatomic resist chemistries for incorporation of donor atoms have dominated these efforts, the use of halogen-based chemistries offers a promising path toward atomic-scale manufacturing of acceptor-based devices. Here, B-doped δ-layers were fabricated in Si(100) by using BCl3 as an acceptor dopant precursor in ultrahigh vacuum. Additionally, we demonstrate compatibility of BCl3 with both H and Cl monatomic resists to achieve area-selective deposition on Si. In comparison to bare Si, BCl3 adsorption selectivity ratios for H- and Cl-passivated Si were determined by secondary ion mass spectrometry depth profiling (SIMS) to be 310(10):1 and 1529(5):1, respectively. STM imaging revealed that BCl3 adsorbed readily on bare Si at room temperature, with SIMS measurements indicating a peak B concentration greater than 1.2(1) × 1021 cm-3 with a total areal dose of 1.85(1) × 1014 cm-2 resulting from a 30 langmuir BCl3 dose at 150 °C. In addition, SIMS showed a δ-layer thickness of ∼0.5 nm. Hall bar measurements of a similar sample were performed at 3.0 K, revealing a sheet resistance of ρ□ = 1.9099(4) kΩ â–¡-1, a hole carrier concentration of p = 1.90(2) × 1014 cm-2, and a hole mobility of µ = 38.0(4) cm2 V-1 s-1 without performing an incorporation anneal. Finally, 15 nm wide B δ-doped nanowires were fabricated from BCl3 and were found to exhibit ohmic conduction. This validates the use of BCl3 as a dopant precursor for atomic-precision fabrication of acceptor-doped devices in Si and enables development of simultaneous n- and p-type doped bipolar devices.

Reaction of Hydrazine with Solution- and Vacuum-Prepared Selectively Terminated Si(100) Surfaces: Pathways to the Formation of Direct Si-N Bonds.

The reactivity of liquid hydrazine (N2H4) with respect to H-, Cl-, and Br-terminated Si(100) surfaces was investigated to uncover the principles of nitrogen incorporation into the interface. This process has important implications in a wide variety of applications, including semiconductor surface passivation and functionalization, nitride growth, and many others. The use of hydrazine as a precursor allows for reactions that exclude carbon and oxygen, the primary sources of contamination in processing. In this work, the reactivity of N2H4 with H- and Cl-terminated surfaces prepared by traditional solvent-based methods and with a Br-terminated Si(100) prepared in ultrahigh vacuum was compared. The reactions were studied with X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy, and the observations were supported by computational investigations. The H-terminated surface led to the highest level of nitrogen incorporation; however, the process proceeds with increasing surface roughness, suggesting possible etching or replacement reactions. In the case of Cl-terminated (predominantly dichloride) and Br-terminated (monobromide) surfaces, the amount of nitrogen incorporation on both surfaces after the reaction with hydrazine was very similar despite the differences in preparation, initial structure, and chemical composition. Density functional theory was used to propose the possible surface structures and to analyze surface reactivity.