Monolithic MgO Research Articles

Performance analysis of MgO/ZnO multilayer thin film as heat spreader on Al substrates for high-power LED thermal management applications

Towards improving structural, surface, and thermal properties of MgO heat spreader, ZnO thin film was interstacked into MgO. This would improve heat dissipation and keeping the temperature as well as the junction temperature of LEDs in safe operating conditions and make the MgO/ZnO multilayer thin film as a reliable heat spreader material in thermal management application. XRD measurements, FESEM, and AFM analysis were employed in examining the structure, morphology, particle size, and topography of the spin-coated monolithic MgO and multilayer MgO/ZnO thin films, respectively. Improvement in crystal size, reduction in residual stress, lattice strain, and dislocation density were recorded for MgO/ZnO multilayer films. Similarly, introduction of ZnO into MgO resulted an improvement in surface morphology with large particle size (76 nm) and decrease in surface roughness from 19.1 to 9.6 nm. From thermal transient analysis, a noticeable difference in junction temperature raise (ΔTJ = 27.07 °C) and high difference in total thermal resistance (ΔRth-tot = 5.3 K/W) were recorded for LED fixed on 6:4 L MgO:ZnO thin film-coated aluminum substrate. Introduction of ZnO into MgO improves the structure and surface qualities as well as thermal performance of MgO thin film and LEDs mounted on them. The optimized multilayer MgO/ZnO ceramic-ceramic composite thin film could be employed for efficient, reliable, and longer life LEDs thermal management as heat spreader.

Fabrication of MgO/Graphene Composites by Combustion Synthesis and Spark Plasma Sintering

MgO/Graphene ceramic composites were fabricated by combining combustion synthesis with spark plasma sintering. MgO/Graphene mixture powders were prepared by the combustion reaction between Mg powders and CO2 gas. Dense MgO/Graphene composites were fabricated by spark plasma sintering (SPS) using LiF as the sintering additive. The effect of the sintering temperature on microstructure and mechanical properties of the prepared MgO/Graphene ceramics was discussed. The sintering temperature of the MgO/Graphene mixture powders increased from 900°C to 1300°C. The highest density of 3.43g/cm3 and hardness of 2133MPa were obtained at 1100°C. Compared with monolithic MgO ceramics, the hardness of MgO/Graphene ceramics at the same sintering temperature was increased from 840MPa to 2133MPa.

Mechanical and thermal properties of graphene nanosheets/magnesia composites

Abstract Highly dense graphene nanosheets (GNSs)/magnesia (MgO) composites were prepared by hot-pressing. The effect of GNSs content (0 vol%–7 vol%) on microstructural, mechanical and thermal properties was evaluated, and the mechanisms were identified. Incorporating GNSs inhibited the sintering and grain growth of MgO and produced a significant strengthening and toughening effect. With the increase in GNSs content, both flexural strength and fracture toughness increased and then decreased: the highest strength of 265 MPa and toughness of 3.3 MPa m 1/2 were obtained at 2 vol%, increasing by 37.3% and 32%, respectively, compared with monolithic MgO. Vickers hardness and modulus declined linearly. Thermal conductivity in the hot pressing direction decreased from 55.8 W/(m K) for MgO to 33.9 W/(m K) for 7 vol% GNSs/MgO. With the increase in temperature, both monolithic MgO and 2 vol% GNSs/MgO exhibited a decrease in thermal conductivity, which tended to be consistent and constant beyond 700 °C. The 2 vol% GNSs/MgO composite also showed nearly the same CTE as that of monolithic MgO.

Structural, thermal properties and stability of monolithic and hollow MgO nanocubes: Atomistic simulation

The atomistic simulations of structural, thermal properties and stability of monolithic as well as hypothetical hollow MgO nanocubes as functions of their sizes and morphology are performed. We show the increasing of stability with growth of the number of the atomic walls for both hollow nanocubes and prismatic-like tubes; whereas the most stable are the monolithic nanocubes. We show also that the structure of MgO cube-like nanoparticles should be stable over a wide temperature range. According to our estimations, the multi-walled nanocubes persist with quite insignificant atomic distortions up to T ∼ 2000 K, whereas perfect monolithic nanocubes retain initial shape up to the temperatures close to melting point of crystalline MgO ( T m ∼ 3100 K).

Subharmonic-pumped continuous-wave parametric oscillator

We have operated a doubly resonant optical parametric oscillator (OPO) whose pump wave is generated in the OPO cavity itself by resonant frequency doubling of an injected subharmonic wave. The subharmonic-pumped oscillator employs a miniature monolithic MgO:LiNbO3 resonator and is pumped by a single-frequency Nd:YAG laser at 1064 nm. The threshold power was 120 mW at 1064 nm, and an efficiency of 7% for the conversion from 1064 to 1063/1065 nm via the nonresonant 532 nm wave was reached at 300 mW infrared input power. Single-frequency operation for up to one-and-a-half hours was observed.

Solid-state processing and phase development of bulk (MgO)w/BPSCCO high-temperature superconducting composite

The inherently weak mechanical properties associated with monolithic high-temperature superconductors (HTS) can be improved by introducing properly selected strong ceramic whiskers into the HTS materials. In this research, processing and superconducting properties of monolithic Pb-doped Bi-2223 (BPSCCO) and MgO whisker-reinforced BPSCCO HTS composite materials have been systematically studied. A solid-state processing method is successfully developed to fabricate the (MgO)w/BPSCCO composite. The HTS composite contains a dense and highly pure BPSCCO matrix phase with a preferred grain orientation, which is reinforced by MgO whiskers randomly oriented in the plane perpendicular to the hot-pressing direction. The HTS composite material is shown to exhibit excellent superconducting properties. For example, a transport Jc measured at 77 K in a zero field has been obtained to exceed 5000 A/cm2 in a (MgO)w/BPSCCO composite with 10% MgO whiskers by volume. Relationships among solid-state processing variables, HTS phase development, and superconducting properties of the monolithic BPSCCO and the HTS composite are established in the paper.

81% Conversion efficiency in frequency-stable continuous-wave parametric oscillation

We have studied doubly resonant parametric oscillation in the regime of maximum conversion efficiency. A monolithic MgO:LiNbO3 resonator with a threshold of 28 mW, pumped by a frequency-doubled Nd:YAG laser, was employed. With an active frequency-stabilization scheme, single-mode operation without mode hops at 105 mW combined signal and idler output power was achieved at a pump power four times above threshold, with a conversion efficiency of 81%. Excellent agreement between theory and experiment was found for the dependence of efficiency and depletion on pump power. The efficiency and the nearly complete pump depletion of 94% were limited only by imperfect mode matching of the pump wave and by the small cavity losses.

82% Efficient continuous-wave frequency doubling of 106 μm with a monolithic MgO:LiNbO_3 resonator: errata

We describe a frequency-doubling monolithic standing-wave resonator made of MgO:LiNbO(3) with dielectric mirror coatings for impedance matching near 100 mW input power and near-optimum nonlinear coupling. An external conversion efficiency of 82% has been achieved.

82% Efficient continuous-wave frequency doubling of 106 μm with a monolithic MgO:LiNbO_3 resonator

We describe a frequency-doubling monolithic standing-wave resonator made of MgO:LiNbO(3) with dielectric mirror coatings for impedance matching near 100 mW input power and near-optimum nonlinear coupling. An external conversion efficiency of 82% has been achieved.

Monolithic MgO:LiNbO_3 doubly resonant optical parametric oscillator pumped by a frequency-doubled diode-laser-pumped Nd:YAG laser

We have demonstrated a monolithic MgO:LiNbO(3) doubly resonant optical parametric oscillator (OPO) using an allsolid- state pump. The pump laser was a single-axial-mode monolithic Nd:YAG nonplanar ring oscillator whose diode-laser pump was modulated at 325 kHz to produce relaxation oscillation spikes to higher peak powers at 1.06 microm that were frequency doubled in a resonant cavity to 532 nm. Pump depletions for the OPO of greater than 60% were observed when pumping six times above the calculated 40-mW threshold. The OPO output was temperature tuned from 1.01 to 1.13 microm, producing single-axial-mode output over much of the range. By changing the voltage applied across the OPO, the output wavelength was scanned as much as 11 nm in 310 V.

Efficient monolithic MgO:LiNbO_3 singly resonant optical parametric oscillator

We have operated a monolithic MgO:LiNbO(3) singly resonant optical parametric oscillator (OPO) as both a standing-wave and a ring-geometry resonator. The OPO was pumped by the second harmonic of an amplified single-mode diode-laser-pumped Nd:YAG laser. Pump depletions of greater than 60% were observed when pumping four times greater than the 35-W threshold. The OPO output at the resonant signal tuned with temperature from 834 to 958 nm, while the corresponding idler tuned from 1.47 to 1.2 microm. The spectral characteristics of the OPO signal output and the relative merits of a standing wave versus a ring geometry are discussed.

Second-harmonic generation of a continuous-wave diode-pumped Nd:YAG laser using an externally resonant cavity

We report 13% second-harmonic conversion efficiency of a 15-mW, cw, diode-laser-pumped Nd:YAG oscillator. 2 mW of single-axial-mode 532-mm radiation was generated by externally resonant second-harmonic generation in a monolithic MgO:LiNbO(3) nonlinear crystal cavity. The measured finesse of 450 for the monolithic external cavity indicated that absorption and scatter losses in the doubler were less than 0.8%.