Kim Jinhong, Mironov Andrey, Park Sehyun, Kim Changgong, Park Sung-Jin, Eden J Gary
Laboratory for Optical Physics and Engineering, Department of Electrical and Computer Engineering, University of Illinois, 306 N Wright St, Urbana, IL 61801 USA.
Intel Corp., 2501 NE Century Blvd, Hillsboro, OR 97124 USA.
Eur Phys J D At Mol Opt Phys. 2023;77(5):73. doi: 10.1140/epjd/s10053-023-00651-3. Epub 2023 May 11.
In honor of Professor Kurt Becker's pioneering contributions to microplasma physics and applications, we report the capabilities of arrays of microcavity plasmas in two emerging and disparate applications. The first of these is the generation of ultrasound radiation in the 20-240 kHz spectral range with microplasmas in either a static or jet configuration. When a array of microplasma jets is driven by a 20-kHz sinusoidal voltage, for example, harmonics as high as = 12 are detected and are produced by controlling the spatial symmetry of the emitter array. The preferential emission of ultrasound in an inverted cone having an angle of with respect to the surface normal of the jet array's exit face is attributed to interference between spatially periodic, outward-propagating waves generated by the arrays. The spatial distribution of ultrasound generated by the arrays is analogous to the radiation patterns produced by Yagi-Uda phased array antennas at RF frequencies for which radiation is emitted broadside to arrays of parallel electric dipoles. Also, the nonperturbative envelope of the ultrasound harmonic spectrum resembles that for high-order harmonic generation at optical frequencies in rare gas plasmas and attests to the strong nonlinearity provided by the pulsed microplasmas in the sub-250-kHz region. Specifically, the relative intensities of the second and third harmonics exceed that for the fundamental, and a "plateau" region is observed extending from the 5th through the 8th harmonics. A strong plasma nonlinearity appears to be responsible for both the appearance of fractional harmonics and the nonperturbative nature of the acoustic harmonic spectrum. Multilayer metal-oxide optical filters designed to have peak transmission near 222 nm in the deep-UV region of the spectrum have been fabricated by microplasma-assisted atomic layer deposition. Alternating layers of ZrO and AlO, each having a thickness in the 20-50 nm range, were grown on quartz and silicon substrates by successively exposing the substrate to the Zr or Al precursor (tetrakis(dimethylamino) zirconium or trimethylaluminum, respectively) and the products of an oxygen microplasma while maintaining the substrate temperature at 300 K. Bandpass filters comprising 9 cycles of 30-nm-thick ZrO/50-nm-thick AlO film pairs transmit 80% at 235 nm but < 35% in the 250-280 nm interval. Such multilayer reflectors appear to be of significant value in several applications, including bandpass filters suppressing long wavelength (240-270 nm) radiation emitted by KrCl (222) lamps.
为纪念库尔特·贝克尔教授在微等离子体物理与应用方面的开创性贡献，我们报告了微腔等离子体阵列在两种新兴且不同应用中的能力。其中第一个应用是利用静态或射流配置的微等离子体在20 - 240 kHz频谱范围内产生超声辐射。例如，当由20 kHz正弦电压驱动微等离子体射流阵列时，可检测到高达(n = 12)的谐波，并且通过控制发射器阵列的空间对称性来产生这些谐波。相对于射流阵列出射面的表面法线成(\theta)角的倒锥内优先发射超声，这归因于阵列产生的空间周期性向外传播波之间的干涉。阵列产生的超声的空间分布类似于Yagi - Uda相控阵天线在射频频率下产生的辐射方向图，对于射频频率，辐射垂直于平行电偶极子阵列发射。此外，超声谐波谱的非微扰包络类似于稀有气体等离子体中光频率下高次谐波产生的包络，并证明了250 kHz以下区域脉冲微等离子体提供的强非线性。具体而言，二次谐波和三次谐波的相对强度超过基波，并且观察到从第5谐波到第8谐波的“平台”区域。强等离子体非线性似乎是分数谐波出现和声谐波谱非微扰性质的原因。通过微等离子体辅助原子层沉积制备了在光谱深紫外区域具有接近222 nm峰值透射率的多层金属氧化物光学滤波器。通过依次将衬底暴露于Zr或Al前驱体（分别为四（二甲基氨基）锆或三甲基铝）以及氧微等离子体的产物，同时将衬底温度保持在300 K，在石英和硅衬底上生长了厚度在20 - 50 nm范围内的交替的ZrO和AlO层。由9个30 nm厚的ZrO / 50 nm厚的AlO膜对周期组成的带通滤波器在235 nm处透射率为80%，但在250 - 280 nm区间透射率小于35%。这种多层反射器在包括抑制KrCl（222）灯发射的长波长（240 - 270 nm）辐射的带通滤波器等多种应用中似乎具有重要价值。
