Production Mechanisms of NH and NH2 Radicals in N2−H2 Plasmas

The potential of multicylindrical dielectric barrier discharge plasma for diesel-contaminated soil remediation and biocompatibility assessment

This study explored the use of multicylindrical dielectric barrier discharge (MC-DBD) plasma technology to eliminate diesel fuel contamination from the soil. This study also assessed the environmental impact of plasma-generated reactive species on soil properties, plant growth, and the safety of microbial and human skin cells using various analytical methods. MC-DBD plasma was characterized using the current-voltage analysis and optical emission spectroscopy (OES). Gas Fourier transform infrared spectroscopy was employed to detect reactive species, such as O3, NO, NO2, N2O, and HNO3, in the plasma-treated air. The diesel fuel concentration in the soil was measured before and after plasma treatment using a gas chromatography-flame ionization detector. The efficacy of the MC-DBD plasma treatment was evaluated based on soil characteristics (pH and moisture), discharge parameters (power), and reactive species (O3 and NOx). Using only power of 30 W, the MC-DBD achieved a 94.19% removal of diesel fuel from the soil and yielded an energy efficiency of 1.78 × 10-2 m3/kWh within a 60-min treatment period. Neutral soil with a moisture content of 2% proved more effective in diesel fuel removal compared with acidic or alkaline soil with higher moisture content. O3 was the most efficient plasma-generated reactive species for diesel fuel removal and is involved in oxidation-induced fragmentation and volatilization. Overall, the potential of the MC-DBD plasma technology for remediating diesel fuel-contaminated soils is highlighted, and valuable insights for future applications are provided.

Large Area Ultrathin InN and Tin Doped InN Nanosheets Featuring 2D Electron Gases

Indium nitride (InN) has been of significant interest for creating and studying two-dimensional electron gases (2DEG). Herein we demonstrate the formation of 2DEGs in ultrathin doped and undoped 2D InN nanosheets featuring high carrier mobilities at room temperature. The synthesis is carried out via a two-step liquid metal-based printing method followed by a microwave plasma-enhanced nitridation reaction. Ultrathin InN nanosheets with a thickness of ∼2 ± 0.2 nm were isolated over large areas with lateral dimensions exceeding centimeter scale. Room temperature Hall effect measurements reveal carrier mobilities of ∼216 and ∼148 cm² V^-1 s^-1 for undoped and doped InN, respectively. Further analysis suggests the presence of defined quantized states in these ultrathin nitride nanosheets that can be attributed to a 2D electron gas forming due to strong out-of-plane confinement. Overall, the combination of electronic and plasmonic features in undoped and doped ultrathin 2D InN holds promise for creating advanced optoelectronic devices and functional 2D heterostructures.

Wafer-scalable chemical modification of amino groups on graphene biosensors

Graphene's remarkable attributes make it suitable for application to biosensors for biomolecular recognition. Specific and precise target detection is realized by designing robust methods for immobilization of probe molecules, such as oligonucleotides, antibodies, receptors, and sugar chains, to a device surface. In this research, we developed a chemical modification method with a plasma treatment of amino groups on natural defects of graphene, which is compatible with a wafer-scalable semiconductor process, to prevent deterioration of the carrier mobility. The plasma treatment was optimized in terms of the efficiency of the amino radical generation, length of the mean free path, and reaction energy on graphene. The density of the modified amino groups on graphene was approximately 0.065 groups/nm², and the change in the ΔI_d/ΔV_g characteristic of the graphene field-effect transistor (FET) was negligible. DNA probes were then attached to the amino groups on the graphene FET. The target complementary DNA was detected at 1 nM after hybridization using the graphene FET devices. The plasma-assisted modification of the amino groups on the graphene surface was developed for immobilization of the DNA probes, and hybridization with the target DNA was demonstrated without deterioration of the carrier mobility.

A Review about the Recent Advances in Selected NonThermal Plasma Assisted Solid-Gas Phase Chemical Processes

Plasma science has attracted the interest of researchers in various disciplines since the 1990s. This continuously evolving field has spawned investigations into several applications, including industrial sterilization, pollution control, polymer science, food safety and biomedicine. nonthermal plasma (NTP) can promote the occurrence of chemical reactions in a lower operating temperature range, condition in which, in a conventional process, a catalyst is generally not active. The aim, when using NTP, is to selectively transfer electrical energy to the electrons, generating free radicals through collisions and promoting the desired chemical changes without spending energy in heating the system. Therefore, NTP can be used in various fields, such as NOx removal from exhaust gases, soot removal from diesel engine exhaust, volatile organic compound (VOC) decomposition, industrial applications, such as ammonia production or methanation reaction (Sabatier reaction). The combination of NTP technology with catalysts is a promising option to improve selectivity and efficiency in some chemical processes. In this review, recent advances in selected nonthermal plasma assisted solid-gas processes are introduced, and the attention was mainly focused on the use of the dielectric barrier discharge (DBD) reactors.

Atomic Layer Deposition of Cobalt Using H2-, N2-, and NH3-Based Plasmas: On the Role of the Co-reactant

This work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp₂) as the precursor. Three different processes were compared: an AB process using NH₃ plasma, an AB process using H₂/N₂ plasma, and an ABC process using subsequent N₂ and H₂ plasmas. A connection was made between the plasma composition and film properties, thereby gaining an understanding of the role of the various plasma species. For NH₃ plasma, H₂ and N₂ were identified as the main species apart from the expected NH₃, whereas for the H₂/N₂ plasma, NH₃ was detected. Moreover, HCp was observed as a reaction product in the precursor and co-reactant subcycles. Both AB processes showed self-limiting half-reactions and yielded similar material properties, that is, high purity and low resistivity. For the AB process with H₂/N₂, the resistivity and impurity content depended on the H₂/N₂ mixing ratio, which was linked to the production of NH₃ molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NH _x,x≤3 species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp₂ chemisorbs in the precursor subcycle and NH _x species eliminate the remaining Cp in the consecutive subcycle.

Use of NH (A3Π–X3Σ−) sonoluminescence for diagnostics of nonequilibrium plasma produced by multibubble cavitation

The sonoluminescence spectrum of an aqueous ammonia solution allows the characterization of the nonequilibrium plasma produced by multibubble cavitation.

Microwave Plasma-Activated Chemical Vapor Deposition of Nitrogen-Doped Diamond. I. N2/H2 and NH3/H2 Plasmas

We report a combined experimental/modeling study of microwave activated dilute N2/H2 and NH3/H2 plasmas as a precursor to diagnosis of the CH4/N2/H2 plasmas used for the chemical vapor deposition (CVD) of N-doped diamond. Absolute column densities of H(n = 2) atoms and NH(X(3)Σ(-), v = 0) radicals have been determined by cavity ring down spectroscopy, as a function of height (z) above a molybdenum substrate and of the plasma process conditions, i.e., total gas pressure p, input power P, and the nitrogen/hydrogen atom ratio in the source gas. Optical emission spectroscopy has been used to investigate variations in the relative number densities of H(n = 3) atoms, NH(A(3)Π) radicals, and N2(C(3)Πu) molecules as functions of the same process conditions. These experimental data are complemented by 2-D (r, z) coupled kinetic and transport modeling for the same process conditions, which consider variations in both the overall chemistry and plasma parameters, including the electron (Te) and gas (T) temperatures, the electron density (ne), and the plasma power density (Q). Comparisons between experiment and theory allow refinement of prior understanding of N/H plasma-chemical reactivity, and its variation with process conditions and with location within the CVD reactor, and serve to highlight the essential role of metastable N2(A(3)Σ(+)u) molecules (formed by electron impact excitation) and their hitherto underappreciated reactivity with H atoms, in converting N2 process gas into reactive NHx (x = 0-3) radical species.

A broadband absorption spectrometer using light emitting diodes for ultrasensitive, in situ trace gas detection

A broadband absorption spectrometer has been developed for highly sensitive and target-selective in situ trace gas measurements. The instrument employs two distinct modes of operation: (i) broadband cavity enhanced absorption spectroscopy (BBCEAS) is used to quantify the concentration of gases in sample mixtures from their characteristic absorption features, and (ii) periodic measurements of the cavity mirrors' reflectivity are made using step-scan phase shift cavity ringdown spectroscopy (PSCRDS). The latter PSCRDS method provides a stand-alone alternative to the more usual method of determining mirror reflectivities by measuring BBCEAS absorption spectra for calibration samples of known composition. Moreover, the instrument's two modes of operation use light from the same light emitting diode transmitted through the cavity in the same optical alignment, hence minimizing the potential for systematic errors between mirror reflectivity determinations and concentration measurements. The ability of the instrument to quantify absorber concentrations is tested in instrument intercomparison exercises for NO(2) (versus a laser broadband cavity ringdown spectrometer) and for H(2)O (versus a commercial hygrometer). A method is also proposed for calculating effective absorption cross sections for fitting the differential structure in BBCEAS spectra due to strong, narrow absorption lines that are under-resolved and hence exhibit non-Beer-Lambert law behavior at the resolution of the BBCEAS measurements. This approach is tested on BBCEAS spectra of water vapor's 4v+delta absorption bands around 650 nm. The most immediate analytical application of the present instrument is in quantifying the concentration of reactive trace gases in the ambient atmosphere. The instrument's detection limits for NO(3) as a function of integration time are considered in detail using an Allan variance analysis. Experiments under laboratory conditions produce a 1sigma detection limit of 0.25 pptv for a 10 s acquisition time, which improves with further signal averaging to 0.09 pptv in 400 s. Finally, an example of the instrument's performance under field work conditions is presented, in this case of measurements of the sum of NO(3)+N(2)O(5) concentrations in the marine boundary layer acquired during the Reactive Halogens in the Marine Boundary Layer field campaign.