Study on OH Radical Production Depending on the Pulse Characteristics in an Atmospheric-Pressure Nanosecond-Pulsed Plasma Jet.

Hydroxyl radicals (OH) play a crucial role in plasma-bio applications. As pulsed plasma operation is preferred, and even expanded to the nanosecond range, it is essential to study the relationship between OH radical production and pulse characteristics. In this study, we use optical emission spectroscopy to investigate OH radical production with nanosecond pulse characteristics. The experimental results reveal that longer pulses generate more OH radicals. To confirm the effect of pulse properties on OH radical generation, we conduct computational chemical simulations, focusing on two types of pulse properties: pulse instant power and pulse width. The simulation results show that, similar to the experimental results, longer pulses generate more OH radicals. In the nanosecond range, reaction time is critical for OH radical generation. In terms of chemical aspects, N2 metastable species mainly contribute to OH radical generation. It is a unique behavior observed in nanosecond range pulsed operation. Furthermore, humidity can turn over the tendency of OH radical production in nanosecond pulses. In a humid condition, shorter pulses are advantageous for generating OH radicals. Electrons play key roles in this condition and high instant power contributes to them.

New noncentrosymmetric tellurite phosphate material: synthesis, characterization, and calculations of Te2O(PO4)2.

A new noncentrosymmetric polar ternary tellurium(IV) oxide phosphate, Te(2)O(PO(4))(2), has been synthesized by a standard solid-state reaction, and the structure was determined by single crystal X-ray diffraction. The material shows a three-dimensional framework structure that is composed of slightly distorted TeO(5) square pyramids and PO(4) tetrahedra. Within the framework three-, four-, and seven-membered ring channels are observed along the [100] direction. In addition to structural characterization, second-harmonic generation (SHG) and piezoelectric measurements were performed. Powder SHG measurement on the Te(2)O(PO(4))(2), using 1064 nm radiation, indicated the material has a SHG efficiency of approximately 50 x alpha-SiO(2). Converse piezoelectric measurements revealed a d(33) value of 20 pm V(-1). Thermogravimetric analysis, UV-vis diffuse reflectance, and infrared spectroscopy were also performed, as were electronic structure calculations. Crystal data: Te(2)O(PO(4))(2), monoclinic, space group Cc (No. 9), with a = 5.3819(7) A, b = 13.6990(19) A, c = 9.5866(12) A, V = 686.73(16) A(3), and Z = 4.

Alignment of lone pairs in a new polar material: synthesis, characterization, and functional properties of Li2Ti(IO3)6.

A new polar noncentrosymmetric material, Li(2)Ti(IO(3))(6), has been synthesized and characterized. The material is built up from a TiO(6) octahedron that is linked to six IO(3) polyhedra. These polyhedral groups are separated by Li(+) cations. The Ti(4+) and I(5+) cations are in asymmetric polar coordination environments attributable to second-order Jahn-Teller effects. The distortion associated with the Ti(4+) cation is negligible, since the TiO(6) octahedra are completely surrounded by IO(3) polyhedra. The I(5+) cation is in a highly polar asymmetric coordination environment attributable to its stereoactive lone pair, which was qualitatively described by pseudopotential calculations of the electron localization function. The macroscopic polarity of Li(2)Ti(IO(3))(6) may be attributed to parallel alignment of the stereoactive lone pairs on the I(5+) cations. This parallel alignment profoundly influences the material's functional properties: second-harmonic generation, piezoelectricity, and pyroelectricity. The material is, however, not ferroelectric, as the polarization associated with I(5+) is not switchable.

Polar or nonpolar? A+ cation polarity control in A2Ti(IO3)6 (A = Li, Na, K, Rb, Cs, Tl).

We have synthesized a series of new alkali-metal or Tl(+) titanium iodates, A(2)Ti(IO(3))(6) (A = Li, Na, K, Rb, Cs, Tl). Interestingly the Li and Na phases are noncentrosymmetric (NCS) and polar, whereas the K, Rb, Cs, and Tl analogues are centrosymmetric (CS) and nonpolar. We are able to explain the change from NCS polar to CS nonpolar using cation-size arguments, coordination requirements, and bond valence concepts. The six materials are topologically similar, consisting of TiO(6) octahedra, each of which is bonded to six IO(3) polyhedra. These polyhedral groups are separated by the A(+) cations. Our calculations on Na(2)Ti(IO(3))(6) indicate that polarization reversal is energetically very unfavorable, rendering the material polar but not ferroelectric. For all of the materials, synthesis, structural characterization, electronic structure analysis, infrared spectra, UV-vis and thermogravimetric measurements, and ion-exchange reactions are reported. For the polar materials, second-harmonic generation, piezoelectricity, and polarization measurements were performed. Crystal data: Li(2)Ti(IO(3))(6): hexagonal, space group P6(3) (No. 173), a = b = 9.3834(11) A, c = 5.1183(6) A, Z = 1. Na(2)Ti(IO(3))(6): hexagonal, space group P6(3) (No. 173), a = b = 9.649(3) A, c = 5.198(3) A, Z = 1. K(2)Ti(IO(3))(6): trigonal, space group R3 (No. 148), a = b = 11.2703(6) A, c = 11.3514(11) A, Z = 3. Rb(2)Ti(IO(3))(6): trigonal, space group R3 (No. 148), a = b = 11.3757(16) A, c = 11.426(3) A, Z = 3. Cs(2)Ti(IO(3))(6): trigonal, space group R3 (No. 148), a = b = 11.6726(5) A, c = 11.6399(10) A, Z = 3. Tl(2)Ti(IO(3))(6): trigonal, space group R3 (No. 148), a = b = 11.4167(6) A, c = 11.3953(11) A, Z = 3.

New noncentrosymmetric material--[N(CH3)4]ZnCl3: polar chains of aligned ZnCl4 tetrahedra.

A new organically templated noncentrosymmetric polar zinc chloride, [N(CH(3))(4)]ZnCl(3), has been synthesized hydrothermally, and the structure was determined by single crystal X-ray diffraction. The reported material exhibits a unidimensional crystal structure consisting of chains of anionic ZnCl(4) tetrahedra that are separated by [N(CH(3))(4)](+) cations. Second-harmonic generation (SHG) measurement on the noncentrosymmetric [N(CH(3))(4)]ZnCl(3), using 1064 nm radiation, indicate the material has a SHG efficiency of approximately 15 x alpha-SiO(2). Additional SHG measurements indicate the material is nonphase-matchable (type 1). In addition, converse piezoelectric measurements revealed d(33) values of 10 pm/V. Thermogravimetric analysis, UV-vis diffuse reflectance, and infrared spectroscopy were also performed, as were electronic structure calculations. Crystal data: [N(CH(3))(4)]ZnCl(3), orthorhombic, space group Pmc2(1) (No. 26), with a = 7.2350(14) A, b = 8.8210(18) A, c = 15.303(3) A, V = 976.6(3) A(3), and Z = 4.

Development of a high-speed impedance measurement system for dual-frequency capacitive-coupled pulsed-plasma.

A high-speed impedance measurement system was developed, which enables the measurement of various characteristics of CW and pulsed plasmas with time resolution of less than a microsecond. For this system, a voltage and current sensor is implemented in a printed circuit board to sense the radio frequency signals. A digital board, which has a high-speed analog to digital converter and a field-programmable gate-array, is used to calculate the impedance of the signal. The final output of impedance is measured and stored with a maximum speed of 3 Msps. This sensor system was tested in a pulsed-plasma by applying it to the point between the matching box and the plasma chamber. The experimental equipment was constructed connecting the matching box, a 13.56 MHz generator, a 2 MHz generator that produced pulsed power, and a pulse-signal generator. From the temporal behavior of the measured impedance, we were able to determine the time intervals of transient states, especially of the initial active state. This information can be used to set the pulse frequency and duty for plasma processing.

Cutoff probe using Fourier analysis for electron density measurement.

This paper proposes a new method for cutoff probe using a nanosecond impulse generator and an oscilloscope, instead of a network analyzer. The nanosecond impulse generator supplies a radiating signal of broadband frequency spectrum simultaneously without frequency sweeping, while frequency sweeping method is used by a network analyzer in a previous method. The transmission spectrum (S21) was obtained through a Fourier analysis of the transmitted impulse signal detected by the oscilloscope and was used to measure the electron density. The results showed that the transmission frequency spectrum and the electron density obtained with a new method are very close to those obtained with a previous method using a network analyzer. And also, only 15 ns long signal was necessary for spectrum reconstruction. These results were also compared to the Langmuir probe's measurements with satisfactory results. This method is expected to provide not only fast measurement of absolute electron density, but also function in other diagnostic situations where a network analyzer would be used (a hairpin probe and an impedance probe) by replacing the network analyzer with a nanosecond impulse generator and an oscilloscope.