Laser Ablation In Superfluid Helium Research Articles

Oxidation of Formaldehyde on PdNi Nanowires Synthesized in Superfluid Helium

The possibility of using a boron-doped diamond electrode with a net structure of PdNi alloy nanowires deposited on its surface by laser ablation in superfluid helium as a formaldehyde sensor is considered. High sensitivity of such an electrode to trace amounts of formaldehyde was shown.

Electron-Stimulated Phase Transitions in Tin and Indium–Tin Nanowires Produced by Laser Ablation in Superfluid Helium

Electron-Stimulated Phase Transitions in Tin and Indium–Tin Nanowires Produced by Laser Ablation in Superfluid Helium

Experimental research of condensation processes occurring under laser ablation in superfluid helium and vacuum

The dynamics of thermal radiation accompanying the condensation of tungsten nanoparticles in superfluid helium and vacuum was studied experimentally in the visible range. It was shown that during the first 100 μs the accompanying thermal energy of process in the case of superfluid helium is considerably higher than in vacuum at comparable temperatures after that it levels up. From a standpoint of the process’ kinetics it is demonstrated that the reasons for this are, on one hand, an increased condensation rate in superfluid helium (due to the concentration of nanoparticles in quantized vortices), and on the other hand, higher efficiency of heating of the condensation products in superfluid helium (due to the prevalence of processes involving particles of similar sizes).

Oxidation of polycrystalline indium nanowires induced by electron bombardment: An in situ TEM study

Thin (d < 10 nm) polycrystalline indium nanowires were prepared by pulsed laser ablation in superfluid helium and studied by means of transmission electron microscope (TEM). Nanowires showed disordered fcc structure unlike bulk indium that has tetragonal structure. Oxidation of indium nanowires induced by probing electron beam and yielding single-crystalline In2O3 nanowires was observed by TEM in situ. The oxidation reaction was found to proceed in a mode frontal propagation along the wire axis.

Inner structure of ZnO microspheres fabricated via laser ablation in superfluid helium

ZnO microspheres fabricated via laser ablation in superfluid helium were found to have bubble-like voids. Even a microsphere demonstrating clear whispering gallery mode resonances in the luminescence had voids. Our analysis confirmed that some voids are located away from the surface and have negligible or little effect on the whispering gallery mode resonances since the electromagnetic energy localizes near the surface of these microspheres. The existence of the voids indicates that helium gas or any evaporated target material was present within the molten microparticles during the microsphere formation.

Magnetic trapping of superconducting submicron particles produced by laser ablation in superfluid helium

We produced spherical superconducting submicron particles by laser ablation of their base metal tips in superfluid helium, and trapped them using a quadrupole magnetic field owing to the diamagnetism caused by the Meissner effect. We also measured their critical temperatures of superconductivity, by observing the threshold temperatures for the confinement of superconducting submicron particles in the trap.

Application of Au–Cu nanowires fabricated by laser ablation in superfluid helium as catalysts for CO oxidation

The copper-doped gold nanowires (4 nm in diameter) were produced by the novel technique based of laser ablation of Au–Cu alloy inside superfluid helium. The principle of the method is using the quantized vortices as the 1D template for the condensation of the ablation products into thin threads. The nanowires were applied as the catalyst in СО oxidation with oxygen. The activity of Au–Cu nanowires deposited on glass filters was compared with that for monometallic and bimetallic Au and Cu particles (3–8 nm in diameter) deposited on alumina by traditional deposition–precipitation and impregnation techniques. The apparent activation energies of the reaction (Еа) were 95 and 98, 150, and 147 kJ/mol for Au–Cu nanowires and Au–Cu, Au, and Cu particles, respectively. During running-in of the Au–Cu nanowire–based catalyst, Еа decreased to 20 kJ/mol and retained at this level in the subsequent cycles of lowering and raising the reactor temperature.

Production of ultrathin nanowires from refractory metals (Nb, Re, W, Mo) by laser ablation in superfluid helium

The ablation of targets in superfluid helium with a short-pulse laser allows introducing into liquid the atoms and small clusters of any metal. The metal is then concentrated in the core of 1D quantized vortices nucleating in the laser focus and expanding into the liquid. Subsequent metal coagulation within the vortex results in the formation of thin nanowires with perfect shape and structure. For refractory metals these wires are expected to be especially thin. The diameters of nanowires grown from niobium, molybdenum and tungsten are indeed 4.0, 2.0 and 2.5 nm, respectively. Unfortunately, under ablation of unannealed rhenium the main product is flat ‘flakes’ having irregular shape and 20–50 nm size. Short nanowires (with a 1.5 nm diameter) were present in small amounts.The wires produced by this method contain no additional impurities and have a free lateral surface. By using a diode-pumped Nd:LSB microlaser (1.06 μm wavelength, 0.4 ns pulse duration, 100 μJ pulse energy and 4 kHz repetition rate) the amounts of nanoweb sufficient for many physical and chemical applications could be produced in a single low-temperature experiment. Ultrathin wires of molybdenum and tungsten show promise for creating ‘cold’ cathodes whereas a niobium nanoweb should be an excellent catalyst.

Fabrication and Lasing Properties of Single-Crystalline Semiconductor Microspheres with Anisotropic Crystal Structures

ABSTRACTWe fabricated single-crystalline microspheres of wide-gap semiconductors with anisotropic crystal structures, such as ZnO and ZnSe, by laser ablation in superfluid helium and investigated their lasing properties. Whispering gallery mode lasing at their band edges in ultraviolet region was clearly observed under the optical excitation, reflecting their high sphericity and crystal quality.

Experimental setup for investigation of nanoclusters at cryogenic temperatures by electron spin resonance and optical spectroscopies.

We present the design and performance of an experimental setup for simultaneous electron spin resonance (ESR) and optical studies of nanoclusters with stabilized free radicals at cryogenic temperatures. A gas mixture of impurities and helium after passing through a RF discharge for dissociation of molecules is directed onto the surface of superfluid helium to form the nanoclusters of impurities. A specially designed ESR cavity operated in the TE011 mode allows optical access to the sample. The cavity is incorporated into a homemade insert which is placed inside a variable temperature insert of a Janis (4)He cryostat. The temperature range for sample investigation is 1.25-300 K. A Bruker EPR 300E and Andor 500i optical spectrograph incorporated with a Newton EMCCD camera are used for ESR and optical registration, respectively. The current experimental system makes it possible to study the ESR and optical spectra of impurity-helium condensates simultaneously. The setup allows a broad range of research at low temperatures including optically detected magnetic resonance, studies of chemical processes of the active species produced by photolysis in solid matrices, and investigations of nanoclusters produced by laser ablation in superfluid helium.

Fabrication of single-crystalline microspheres with high sphericity from anisotropic materials.

Microspheres with high sphericity exhibit unique functionalities. In particular, their high symmetry makes them excellent omnidirectional optical resonators. As such perfect micrometre-sized spheres are known to be formed by surface tension, melt cooling is a popular method for fabricating microspheres. However, it is extremely difficult to produce crystalline microspheres using this method because their surfaces are normally faceted. Only microspheres of polymers, glass, or ceramics have been available, while single-crystalline microspheres, which should be useful in optical applications, have been awaiting successful production. Here we report the fabrication of single-crystalline semiconductor microspheres that have surfaces with atomic-level smoothness. These microspheres were formed by performing laser ablation in superfluid helium to create and moderately cool a melt of the anisotropic semiconductor material. This novel method provides cooling conditions that are exceptionally suited for the fabrication of single-crystalline microspheres. This finding opens a pathway for studying the hidden mechanism of anisotropy-free crystal growth and its applications.

Optical Fabrication of Semiconductor Single-Crystalline Microspheres in Superfluid Helium

ABSTRACTWe successfully fabricated semiconductor microspheres of ZnO, ZnSe, etc., by laser ablation in superfluid helium and investigated their morphology and optical properties. Time-resolved photoluminescence spectroscopy in ultraviolet region of single ZnO microspheres shows luminescence spectra with mode structures and remarkable reduction of the luminescence decay time compared to that of polycrystals or non-spherical microparticles. This indicates strong light-matter interaction due to efficient light-confinement in the ZnO microspheres. In addition, the fabricated ZnSe microspheres also show the photoluminescence spectra with typical mode structures indicating their high sphericity.

Optical fabrication of wide‐gap semiconductor nanoparticles in superfluid helium

AbstractThe nanoparticles have been fabricated from CuCl powder by laser ablation in superfluid helium. We found that most of nanoparticles are CuCl nanocrystals with single‐crystal quality by means of electron diffraction and high‐resolution transmission electron microscope. Moreover, we performed cathodoluminescence spectroscopy of single nanoparticle prepared by laser ablation with use of a scanning electron microscope. I1 bound exciton luminescence which is characteristic in the bulk CuCl was clearly observed in the nanoparticle at 15 K. In addition, we found that the cathodoluminescence spectrum changes by the electron beam irradiation. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optical manipulation of CuCl nanoparticles under an excitonic resonance condition in superfluid helium

AbstractIn order to prepare the optimal condition for the resonant optical manipulation, a lot of CuCl particles with a broad size‐distribution ranging from 10 nm to 10 μm have been directly fabricated from a bulk sample by laser ablation in superfluid helium. We irradiated these particles with the laser light covering the excitonic resonance levels of particles smaller than 100 nm in order to transport them onto a target silicon substrate by using resonant radiation force. As a result, we have observed that many particles of from 10 to 50 nm diameters adhere to the substrate. This means that these nanoparticles are transported by the resonant radiation force much stronger than the gravitational force. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Formation of fullerene(C 60) by laser ablation in superfluid helium at 1.5 K

C 60 fullerene was detected in the deposit produced by the laser ablation of graphite rod in the superfluid helium at 1.5 K. From the mass spectrometry, it was found that the ratio, 12C 60/ 12C 59 13C, differs from statistical one calculated by Poisson distribution for natural graphite. Assuming the recombination of atomic carbons to C 2 molecules as an initial stage for C 60 formation, the different isotopic ratio within C 60 from Poisson statistics was ascribed to the tunneling recombination between 12C and 13C atoms in the bubble state.