The thermal accommodation of helium and argon on a tungsten wire, deduced from the heat lost by the wire

Watt, W. L.; Moreton, R. B.; Carpenter, L. G.

doi:10.1016/0039-6028(74)90166-6

Cited by 9 publications

(5 citation statements)

References 5 publications

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“…Energy accommodation in collisions of argon with surfaces is expected to be reasonably efficient. For example, the accommodation coefficient for Ar colliding with a heated tungsten surface is ∼0.25, and it should be larger for collisions with ZnS because the surface atom masses are lower . From the perspective of the as-trapped NPs, collisions would be with the ligand layer, and based on scattering measurements for Ar from organic surfaces, , c A for 300 K Ar should be close to unity.…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence of Charged CdSe/ZnS Quantum Dots in the Gas Phase: Effects of Charge and Heating on Absorption and Emission Probabilities

et al. 2014

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Gas phase spectral measurements for CdSe/ZnS core/shell nanocrystal quantum dots (QDs) before and after heating with both infrared (CO2) and visible lasers are reported. As-trapped QDs are spectrally similar to the same QDs in solution; however their photoluminescence (PL) intensities are very low, at least partly due to low absorption cross sections. After heating, the PL intensities brighten by factors ranging from ∼4 to 1800 depending on the QD size and pump laser wavelength. The emission spectra no longer resemble solution spectra and are similar, regardless of the QD diameter. Emission extends from the pump laser wavelength into the near-IR, with strong emission features above the band gap energy, between 645 and 775 nm, and in the near-infrared. Emission spectra from brightened QD ensembles, single QD aggregates, and single QD monomers are similar, showing that even single QDs support PL from a wide variety of states. The heating and cooling processes for QDs in this environment are analyzed, providing limits on the magnitudes of the absorption cross sections before and after thermal brightening. A model, based on absorption bleaching by extra electrons in the conduction band, appears to account for the changes in absorption and emission behavior induced by charging and heating.

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Section: Resultsmentioning

confidence: 99%

Photoluminescence of Charged CdSe/ZnS Quantum Dots in the Gas Phase: Effects of Charge and Heating on Absorption and Emission Probabilities

et al. 2014

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“…40 The accommodation coefficient accounts for the inelasticity of the Ar surface collisions, where Accom = 1 corresponds to collisions where the scattered argon is thermal at T QD and Accom = 0 means no cooling. For a noble gas, Ar is a reasonably efficient collider, with, for example, Accom = 0.24 in collisions with a tungsten filament between 1073 and 1785 K. 41 For 1 mTorr of Ar at 300 K, there would be ∼450 000 collisions per second with a single QD and roughly double that for a QD dimer, assuming that the QDs in the dimer remain unfused, which is probably a reasonable assumption for low temperatures. If we assume Accom = 0.24, then the collisional cooling power equals the laser heat deposition rate at T QD = ∼630 K. This is certainly (see below) well below the temperature where thermal electron or photon emission would be expected and thus seems reasonable.…”

Section: Discussionmentioning

confidence: 99%

Single CdSe/ZnS Nanocrystals in an Ion Trap: Charge and Mass Determination and Photophysics Evolution with Changing Mass, Charge, and Temperature

et al. 2014

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We report measurements of fluorescence intermittency (blinking) and spectral behavior for single semiconductor nanocrystal quantum dots (QDs) isolated in the gas phase and discuss the effects on fluorescence of the QD charge state and heating to the point of sublimation. Core-shell CdSe/ZnS QDs were trapped in a quadrupole ion trap and detected by laser-induced fluorescence. The mass (M) and charge (Q) were determined nondestructively, and both were followed continuously over the course of hours or days. Emission spectra of the trapped QDs are significantly red-shifted relative to the solution-phase emission from the same particles. The temperature of the trapped QDs is determined by the balance between laser heating and collisional cooling and thermal emission, and it is possible to heat the particles to remove ligands or to the point of sublimation. QDs are observed to be emissive during sublimation, for up to 85% mass loss, with emission intensity roughly proportional to the surface area. Eventually, the fluorescence quantum yield drops suddenly, and the QDs begin to blink. The method used is versatile and will allow studies of quantum dot optical properties as a function of size, ligand removal, heating, surface oxidation, and other manipulations, where these properties are continuously correlated with the mass and charge.

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“…The accommodation coefficient a is discussed scarcely anywhere in the literature, probably because it is not easy to measure or calculate it. Almost all available publications [37][38][39][40] consider accommodation coefficients of noble gases or H 2 and O 2 on a tungsten surface. In ref.…”

Section: To Simulate Collisions With Other Ar Particlesmentioning

confidence: 99%

“…In our calculations we use a ¼ 0.25, which is in agreement with the accommodation coefficient of Ar on a tungsten surface. 38,39 2.1.5 The final calculations. To calculate the final spatial distribution of Ar number density, both model and target particles must be simulated after collisions.…”

Section: To Simulate Collisions With Other Ar Particlesmentioning

confidence: 99%

Thermal mechanism for formation of electrical prepeak and pressure waves in a microsecond direct current pulsed glow discharge with a Grimm-type source: a modeling investigation

Voronov

Hoffmann

Büscher

et al. 2012

J. Anal. At. Spectrom.

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The thermal accommodation of helium and argon on a tungsten wire, deduced from the heat lost by the wire

Cited by 9 publications

References 5 publications

Photoluminescence of Charged CdSe/ZnS Quantum Dots in the Gas Phase: Effects of Charge and Heating on Absorption and Emission Probabilities

Photoluminescence of Charged CdSe/ZnS Quantum Dots in the Gas Phase: Effects of Charge and Heating on Absorption and Emission Probabilities

Single CdSe/ZnS Nanocrystals in an Ion Trap: Charge and Mass Determination and Photophysics Evolution with Changing Mass, Charge, and Temperature

Thermal mechanism for formation of electrical prepeak and pressure waves in a microsecond direct current pulsed glow discharge with a Grimm-type source: a modeling investigation

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