Soft x-ray absorption spectroscopy is a powerful probe of surface electronic and geometric structure in metals, semiconductors, and thin films. Because these techniques generally require ultrahigh vacuum, corresponding studies of volatile liquid surfaces have hitherto been precluded. We describe the design and implementation of an x-ray experiment based on the use of liquid microjets, permitting the study of volatile liquid surfaces under quasi-equilibrium conditions by synchrotron-based spectroscopy. The liquid microjet temperatures are also characterized by Raman spectroscopy, which connects our structural studies with those conducted on liquid samples under equilibrium conditions. In recent experiments, we have observed and quantified the intermolecular surface relaxation of liquid water and methanol and have identified a large population of ''acceptor-only'' molecules at the liquid water interface.

We have studied the radiative cooling of negatively charged fullerene ions by following the thermionic emission as a function of time after injection into the heavy-ion storage ring ASTRID. It is argued that electron emission can be used as a calibrated thermometer to measure the cooling rate. For C 60 2 at ϳ1500 K the cooling corresponds to a radiation intensity of ϳ190 eV͞s, which is 2 orders of magnitude more than expected from infrared active vibrations. [S0031-9007(96)01602-X] The formation of fullerene molecules is a surprisingly commonplace phenomenon, accompanying, for example, soot formation when you burn a candle [1]. And yet, the physics and chemistry of the process are far from simple and are still incompletely understood. We address here the radiative cooling of hot C 60 molecules. In Ref.[1], Smalley argues that electronic transitions can hardly be important because of the large HOMO-LUMO gap (highest occupied to lowest unoccupied molecular orbital, about 1.7 eV). Instead, he suggests that the radiation is emitted by the infrared active vibrations [2].An estimate of the cooling rate at T ϳ 1800 K was obtained by Kolodney, Budrevich, and Tsipinyuk from observation of the depletion of thermal C 60 beams by fragmentation, and they conclude that the measured cooling is much faster than expected from emission by infrared active vibrations [3]. It is difficult to judge the accuracy of this result because it is derived from observation in a rather short time interval of the competition between cooling and fragmentation, C 60 ! C 58 1 C 2 , and the activation energy for this process is not known. We have studied the cooling of negatively charged fullerenes by observation over two decades in time of the competition between cooling and electron emission. The electron affinity is well known [1,4], and, with the additional information available on attachment cross sections for low-energy electrons [5-7], a reliable statistical formula can be established for thermionic electron emission. The formula can be tested against lifetimes measured for C 60 2 molecules with definite temperature [6], and hence thermionic emission can be used as a calibrated thermometer.The experiments were performed at the heavy-ion storage ring ASTRID [8]. A pulse of negatively charged fullerene ions from an electron-impact ion source was injected into the ring at 50 keV, and the decay of the stored current was followed by the observation of neutral decay products with a channel-plate detector in one of the four 90 ± magnets of the ring. As shown in Fig. 1, there is initially a high rate which is attributed to thermionic emission from the hot molecules. The rate decreases by 3-4 orders of magnitude until at t ϳ 100 ms it becomes so low that the yield of neutrals is dominated by collisions with rest-gas molecules, mainly H 2 . This contribution to the yield decays exponentially with a lifetime of order 10 s, corresponding roughly to a geometrical cross section for destruction.To interpret the data, we use a statistical model. The electro...

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A composite optical microcavity, in which nitrogen vacancy (NV) centers in a diamond nanopillar are coupled to whispering gallery modes in a silica microsphere, is demonstrated. Nanopillars with a diameter as small as 200 nm are fabricated from a bulk diamond crystal by reactive ion etching and are positioned with nanometer precision near the equator of a silica microsphere. The composite nanopillar-microsphere system overcomes the poor controllability of a nanocrystal-based microcavity system and takes full advantage of the exceptional spin properties of NV centers and the ultrahigh quality factor of silica microspheres.

Abstract. Thermionic emission from hot fullerene anions, C − N , has been measured in an electrostatic storage ring for even N values from 36 to 96. The decay is quenched by radiative cooling and hence the observations give information on the intensity of thermal radiation from fullerenes. The experiments are analysed by comparison with a simulation which includes the quantisation of photon energy and the statistics of emission. Experiments with heating of the molecules with a laser beam confirm the interpretation of the observations in terms of radiative cooling and give an independent estimate of the cooling rate for C − 60 . The measured cooling rates agree in general within a factor of two with the prediction from a classical dielectric model of a thermal radiation intensity of ∼ 300 eV/s for C60 at 1 400 K, scaling approximately with the 6th power of the temperature and with the number of atoms in the molecule. PACS