Ultralow-Permittivity and Temperature-Stable Ba1-xCaxMg2Al6Si9O30 Dielectric Ceramics for C-Band Patch Antenna Applications.

Ca-substituted Ba1-xCaxMg2Al6Si9O30 ceramics were prepared to explore the relationships among their crystal structural parameters, phase compositions, dielectric properties, and coefficients of thermal expansion and applications in C-band antenna. The maximum solubility of Ba1-xCaxMg2Al6Si9O30 was located at x = 0.25, and Ba1-xCaxMg2Al6Si9O30 ceramics (0 ≤ x ≤ 0.25) crystallized in the space group P6/mcc. In Ba1-xCaxMg2Al6Si9O30 single-phase ceramics, εr was dominated by ionic polarizability and "rattling effects" of Ba2+ and Al(2)3+; Q × f was controlled by the roundness of [Si4Al2O18] inner rings and total lattice energy; and τf was affected by the bond valence of Si/Al(1)-O(1). Notably, the low average coefficients of thermal expansion (2.668 ppm/°C) at -150 °C ≤ T ≤ 850 °C and near-zero coefficients of thermal expansion (1.254 ppm/°C) at -150 °C ≤ T ≤ 260 °C were achieved for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic. Optimum microwave and terahertz dielectric properties were obtained for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic with εr = 5.80, Q × f = 31,174 at 13.99 GHz, τf = -7.10 ppm/°C, and εr = 5.71-5.85 at 0.2 THz ≤ f ≤ 1.0 THz. Also, the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic substrate had been designed as a C-band patch antenna with a high simulated radiation efficiency (87.76%) and gain (6.30 dBi) at 7.70 GHz (|S11| = -38.41 dB).

Enhancement of Entanglement via Incoherent Collisions.

In contrast to the general thought that the collisions are intrinsically dephasing in nature and detrimental to quantum entanglement at room or higher temperatures, here, we show that in the conventional ladder-type electromagnetically induced transparency (EIT) configuration, when the probe field intensity is not very weak as compared to the pump field, the entanglement between the bright pump and probe fields can be remarkably enhanced with the increase of the collisional decay rates in a moderate range in an inhomogeneously broadened atomic system. The strengthened entanglement results from the enhancement of constructive interference and suppression of destructive interference between one-photon and multiphoton transition pathways. Our results clearly indicate that the collisions offer a promising alternative to enhance entanglement at room or higher temperatures despite of the dephasing nature, which provides great convenience for experimental implementation, and opens new prospects and applications in realistic quantum computation and quantum information processing.

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon.

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.