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Abstract Jet impingement can be particularly effective for removing high heat fluxes from local hotspots. Two-phase jet impingement cooling combines the advantage of both the nucleate boiling heat transfer with the single-phase sensible cooling. This study investigates two-phase submerged jet impingement cooling of local hotspots generated by a diode laser in a 100 nm thick Hafnium (Hf) thin-film on glass. The jet/nozzle diameter is ∼1.2 mm and the normal distance between the nozzle outlet and the heated surface is ∼3.2 mm. Novec 7100 is used as the coolant and the Reynolds numbers at the jet nozzle outlet range from 250 to 5000. The hotspot area is ∼ 0.06 mm2 and the applied hotspot-to-jet heat flux ranges from 20 W/cm2 to 220 W/cm2. This heat flux range facilitates studies of both the single-phase and two-phase heat transport mechanisms for heat fluxes up to critical heat flux (CHF). The temporal evolution of the temperature distribution of the laser heated surface is measured using infrared (IR) thermometry. This study also investigates the nucleate boiling regime as a function of the distance between the hotspot center and the jet stagnation point. For example, when the hotspot center and the jet are co-aligned (x/D = 0), the CHF is found to be ∼ 177 W/cm2 at Re ∼ 5000 with a corresponding heat transfer coefficient of ∼58 kW/m2.K. While the CHF is ∼ 130 W/cm2 at Re ∼ 5000 with a jet-to-hotspot offset of x/D ≈ 4.2. 

Liquid jet impingement is one of the most effective methods for dissipating local hotpot heat fluxes in microelectronics. Due to its normal incident flow-field, jet impingement cooling can achieve heat transfer coefficients (HTCs) approaching ≈1 MW/m 2 ·K due to its ability to thin the local thermal boundary layer in the stagnation region. This experimental study presents HTC data for water jet impingement cooling of a laser heated Hafnium (Hf) thin-film on glass. A laser diode induces local hotspots for either a steady- or pulsed-laser operation mode. The hotspots have areas ranging within 0.04 mm 2 to 0.2 mm 2 and heat fluxes up to ≈3.5 MW/m 2 . A submerged jet impingement configuration is pursued with an inlet jet diameter of ~1.2 mm, jet nozzle to hotspot/surface distance of ~3.2 mm, and the jet Reynolds Number of ~2004. The HTCs are measured using infrared (IR) thermometry using a 1.5-5 μm spectral resolution FLIR camera. Also investigated is the spatial dependence of the HTC relative to the offset between jet/wall stagnation point and the center of the local hotspot. For example, for impinging jets that are co-aligned with the hotspot center, HTCs of ~650 kW/m 2 ·K and ~470 kW/m 2 ·K are measured for steady and pulsed-modulated laser heating (respectively), whereas, for offsets beyond ~6 mm (x/D >5), the measured HTCs are <; 100 kW/m 2 ·K. 

2D PtTe 2 layers, a relatively new class of 2D crystals, have unique band structure and remarkably high electrical conductivity promising for emergent opto-electronics. This intrinsic superiority can be further leveraged toward practical device applications by merging them with mature 3D semiconductors, which has remained largely unexplored. Herein, we explored 2D/3D heterojunction devices by directly growing large-area (>cm 2 ) 2D PtTe 2 layers on Si wafers using a low-temperature CVD method and unveiled their superior opto-electrical characteristics. The devices exhibited excellent Schottky transport characteristics essential for high-performance photovoltaics and photodetection, i.e. , well-balanced combination of high photodetectivity (>10 13 Jones), small photo-responsiveness time (∼1 μs), high current rectification ratio (>10 5 ), and water super-hydrophobicity driven photovoltaic improvement (>300%). These performances were identified to be superior to those of previously explored 2D/3D or 2D layer-based devices with much smaller junction areas, and their underlying principles were confirmed by DFT calculations.