Laser Vaporization Method Research Articles

Formation of Cobalt−C60 Clusters: Tricapped Co(C60)3 Unit

Cobalt (Co)−C60 mixed clusters were produced by the combination of laser vaporization and molecular beam methods. Cationic Con(C60)m+ clusters were produced predominantly with the compositions (n, ...

Multiple dumbbell structures of vanadium–C60 clusters

Vanadium (V)–C60 mixed clusters were produced by two laser vaporization methods. In the mass spectra of cationic Vn(C60)m+, the abundant clusters were produced at the composition of (n,m)=(1,1), (1,2), (2,3), (3–4,4), and (5,5). This pattern is explicable in terms of a multiple dumbbell structure; V atom and C60 are alternatively piled up. The ionization energy and the reactivity of the dumbbell clusters toward O2 and CO show V1(C60)2 takes a structure of V1(η6−C60)2.

Structures and stabilities of 3 d -transition metal-benzene organometallic clusters

In the gas phase, we have successfully synthesized organometallic clusters, Mn(benzene)m (M=3d transition metal atoms), by using a laser vaporization method. The measurements of mass spectra and ionization energies (Ei) have revealed that the organometallic clusters can take two types of structures; layered sandwich structures (m = n + 1) and metal clusters saturatedly covered with benzenes. For early transition metals of Sc, Ti, and V, only the multiple decker sandwich structure clusters were preferentially produced, in which benzene and metal atoms are alternately piled up. For late transition metals of Co and Ni, the metal clusters saturatedly surrounded by benzenes were also produced as well as the sandwich clusters. Furthermore, the Eis of M1(benzene)2 (M = Sc-Ni) were systematically measured and their electronic properties will be discussed.

Kinetics of fullerene formation by electric-arc vaporization of graphite

01 Since the discovery of the new exotic form of molecular carbon—fullerenes ~C60 , C70 , etc.! —obtained by laser vaporization of graphite, they have become an object of intense experimental and theoretical study. The introduction of a new method of synthesis of fullerenes by arc vaporization of graphite in a helium or argon atmosphere has made it possible to obtain these compounds in macroscopic quantities and has substantially motivated experimental studies of the physical-chemical properties of these extraordinary carbon formations. This method has been used by many research groups with C60 and C70 production yields typically at the 5–15% level, while Parkev et al. measured the total fullerene yield—from C60 to C240—and report a value of 44% of the material deposited on the cold reactor walls, where this material consisted of a mixture of soot and fullerenes. The method of laser vaporization of graphite, followed by vacuum expansion of the helium–carbon cluster mixture, proved to be most suitable for studies of mass-spectra and the isomeric composition of the carbon clusters. Quite a few papers in the pre-fullerene period examined the distribution of small carbon clusters Cn for n,25 ~both neutrals and positive and negative ions!. In particular, ‘‘magic’’ numbers were discovered for clusters of carbon and also of other elements ~metals and noble gases!, that is to say, concentrations of some carbon clusters in the observed massspectra significantly exceeded the mean level. Clusters with n526–32 were hardly ever observed; lines in the massspectra corresponding to odd mass numbers were either not observed or were significantly weaker than the even lines for n.32. In this wide spectral range significantly higher intensities are observed for ‘‘magic’’ clusters with n560, 70, and a number of others. The results of Ref. 8 show that for carbon clusters ~positive ions! linear structures ~chains! exist up to C10 1 . Some families of isomers have the structure of planar rings: monocyclic rings start at C 7 1 and extend to C40 1 ; bicyclic rings are first observed at C21 1 and extend to C40 1 , followed by tricyclic rings starting at C30 1 , and an extremely limited quantity of tetracyclic rings starting at C40 1 . Fullerenes, i.e., spherical hollow particles are first observed at C30 1 and become dominant above C50 1 . According to present thinking, the path of carbon cluster growth can be represented in the following way: carbon atoms → linear chains → monocyclic rings → polycyclic rings → fullerenes. A structural analysis of clusters in addi-

Structures and Properties of Semiconductor Microclusters. Study on Electronic Structures of Silicon Clusters by Hetero-Atom Doping.

Electronic properties of small silicon clusters (n≤11), produced by a laser vaporization method, were investigated by photoelectron spectroscopy of their anions. The doping of F or Na atoms enables us to substract or add an electron from/into the silicon clusters without any serious geometric rearrangement, revealingelectronic structures of the silicon clusters. Both the doped F and Na atoms areattached onto the surface of the silicon clusters, which is in agreement with abinitio theoretical calculation on electronic and geometric structures of the Si-F and Si-Na binary clusters. The cluster size dependence of HOMO-LUMO gaps in the neutral silicon clusters were measured experimentally with the F atom doping, and the electronic structures above the LUMO of the neutral silicon clusters were revealed with the Na atom doping. The doping of C atoms, furthermore, induces some geometric change of the silicon clusters, and the substitution of Si atoms to C atoms results in a phase transition.

Production and mass spectroscopic characterization of ammonium halide clusters

The ammonium halide clusters from solid crystals of NH 4X (X = F, Cl, I) have been investigated by using a laser vaporization method and time of flight mass spectrometry. Positive ion clusters of NH 4 +(NH 3) n (HF) m ( n≤5, m≤5) and NH 4 +(NH 3) n (HI) m ( n≤10, m≤5) are detected with remarkable size effects. However, essentially no NH 4 +(NH 3) n (HCl) m and negative ammonium halide clusters are observed. These results are interpreted within the framework of intra-cluster interactions and transitions from a hydrogen bonded complex to an ionic crystal of the ammonium halide clusters.

Extractions of Y@C60, Ba@C60, La@C60, Ce@C60, Pr@C60, Nd@C60, and Gd@C60 with Aniline

Recently many endohedral metallofullerenes such as M@C{sub 74}, M@C{sub 80}, and M@C{sub 82} (M: metal atom) have been successfully isolated by the high performance liquid chromatography (HPLC) technique. Some M@C{sub 60} were prepared in primary soots by an arc-heating or a laser-vaporization method, but the isolation of M@C{sub 60} has not yet been achieved because of the difficulties in extraction; only the extraction of Ca@C{sub 60} with pyridine has been reported as for. Recently we found that aniline is a suitable extraction solvent for Ca@C{sub 60} and Sr@C{sub 60}. For the isolation of M@C{sub 60} by an HPLC technique it is important to find a suitable extraction solvent for M@C{sub 60}. In the present study, we report the successful extraction of Y@C{sub 60}, Ba@C{sub 60}, La@C{sub 60}, Ce@C{sub 60}, Pr@C{sub 60}, Nd@C{sub 60}, and Gd@C{sub 60} with aniline under an air atmosphere. 14 refs., 2 figs.

Highly flexible self-expanding meshed metal stents for palliation of malignant esophagogastric obstruction.

Palliative treatment methods for esophageal and cardiac cancer include dilation, laser vaporization and other thermal methods, alcohol injection, and stent insertion. None of these procedures, however, has proved to be a simple, well-tolerated, and lasting method. We present here our results with a new, highly flexible self-expanding metal stent made of nitinol, which is considered to be particularly useful for difficult (long and tortuous) malignant strictures. From November 1991 to December 1994, 114 patients with unresectable esophagogastric malignancies or tumor recurrences (92 men, 22 women, mean age 64 years) were treated using 138 highly flexible meshed self-expanding metal stents. Regular clinical and endoscopic follow-up was performed, and stent obstruction or overgrowth was treated by argon plasma coagulation (APC). Patients were followed up until death (n = 78; average follow-up 17 weeks, range 1-90 weeks). Thirty-six patients were alive in December 1994 and had had an average of 20 weeks of follow-up (range 1-160 weeks). Stent insertion was technically successful in 97% of cases, and led to a reduction of dysphagia (graded 0-4) from a mean score of 3.5 to a mean score of 1.5. Preparatory treatment to open tight strictures was necessary in 80% of cases. Balloon dilation to support stent expansion was carried out in 42 patients (37%). During follow-up, tumor ingrowth occurred in 66% of cases after a mean of seven weeks, and was successfully treated by APC. Including preparatory treatment and re-treatment, patients underwent a mean of 3.5 endoscopic procedures (range 1-12 procedures), which led to good clinical success in 73% of cases. Ninety-six percent of the patients continued to be able to swallow (dysphagia score < or = 2) during follow-up. Highly elastic self-expanding metal stents can be successfully implanted in the majority of patients, particularly in those with difficult malignant strictures not easily amenable to other methods. The devices provide good palliation with effective relief of dysphagia, easy handling and implantation, and offer a satisfactory quality of life to the patient. However, tumor ingrowth is a significant problem, even though it can be successfully managed by APC. Adequate covering of the stent that does not affect its mechanical properties or firm anchoring should solve at least some of these problems.

A laser vaporization, laser ionization time-of-flight mass spectrometer for the probing of fragile biomolecules

We report the design and evaluation of a new spectrometer for probing fragile biomolecules in the gas phase. The spectrometer is based on a laser vaporization method to transfer biomolecules up to several hundred thousand dalton into the gas phase as intact, neutral species. This method requires the formation of a thin film containing a dye molecule and the analyte of interest which is molecularly vaporized using a high energy, pulsed laser. The gas phase, neutral analyte molecules are laser vaporized directly into a laser ionization region without the need of a pulsed nozzle. The molecules are subsequently ionized using multiphoton ionization; two-color, two-photon laser ionization is reported here. The resulting ions are detected using time-of-flight mass spectrometry. The spectrometer employs a four grid extraction system which both filters unwanted ions produced in the initial vaporization step and extracts the laser ionized species into the field free drift region. A hybrid copper–beryllium dynode with a dual microchannel plate detector is employed as the high mass ion detector and amplifier before external amplification. Anthracene-tagged nucleotides and some small test molecules are vaporized and ionized to evaluate the spectrometer.

Sodium doped binary clusters II: Electron shell of InnNam and AunNam clusters

Sodium doped binary clusters of indium and gold were produced by a laser vaporization method using two independent lasers. Photoionization efficiency spectra of these binary clusters were measured. The ionization potentials thus determined indicate the occurrence of the electron shell structure in these binary clusters.

Sodium doped binary clusters I: Ionization potentials of SinNam clusters

Sodium doped silicon clusters (SinNam, 3≤n≤11, 1≤m≤4) were produced by two independent laser vaporization methods and their ionization potentials were measured by scanning the wavelength of the UV dye laser. The IPs of most SinNam clusters decrease monotonously with the number of Na atoms, but IPs of Si7Nam and Si10Nam clusters show an apparent even-odd alternation; odd numbers of Na atoms efficiently decrease the IP but even numbers of Na atoms never significantly decrease the IPs. In addition, the reactivity of SinNam clusters for NO molecules was investigated with a fast flow reactor, and an anti-correlation between IP and the reactivity was clearly observed; clusters having high IP show low reactivity andvice versa.

Electronic shell structure of indium-sodium (InnNam) bimetallic clusters examined by their ionization potentials and mass distributions

Indium-sodium (In n Na m ) bimetallic clusters were produced by two independent laser vaporization methods. Ionization potentials (IPs) of the In n Na m clusters were measured up to m=2 using a tunable ultraviolet layer combined with a time-of-flight (TOF) mass spectrometer. At small sizes (n=3-15), the ionization potentials decrease by 0.1-0.8 eV with the addition of Na atom(s), whereas the IPs of larger In n (15≤n≤27) clusters do not decrease with Na addition

Ionization potentials of cobalt–sodium bimetallic clusters (ConNam)

Cobalt–sodium bimetallic clusters (ConNam, n=3–48) were produced by a two independent laser-vaporization method. Ionization potentials of the ConNam clusters were measured up to m=3 using a tunable ultraviolet laser combined with a time-of-flight (TOF) mass spectrometer. In general, the ionization potentials decrease monotonically with the number of sodium atoms, and the ionization potentials of ConNam+1 decrease by 0.2–0.8 eV compared to those of the corresponding ConNam cluster. However, the amount of IP decrement by the Na doping is relatively large at n≤17 whereas it is small and constant at n≥18. This feature can be explained by a geometric rearrangement; at small n, the Na doping induces a large geometric rearrangement of the cluster, but at large n, the geometric change is small. Reactivity of ConNam cluster toward H2 was also measured and the effect of the Na doping was studied. The reactivity also suggests the geometric change induced by the Na doping. Moreover, we examined the anticorrelation between IP and reactivity of the ConNam clusters, and no anticorrelation between them could be revealed.

Ionization potentials of aluminum–sodium bimetallic clusters (AlnNam)

Aluminum–sodium bimetallic clusters (AlnNam, n=2–26) were produced by two independent laser vaporization methods. To investigate the electronic structures, ionization potentials of the AlnNam clusters were measured up to m=3 using a tunable ultraviolet laser combined with time-of-flight (TOF) mass spectrometer. In general, the ionization potentials monotonically decrease with the number of sodium atoms, and the ionization potentials of Aln Na1 generally decrease by 0.2–0.6 eV compared to those of the corresponding Aln cluster. In contrast, the ionization potentials of Al13Na1 and Al23Na1 are higher than (or equal to) those of Al13 and Al23. The anomalous change in the ionization potentials of Al13Na1 and Al23Na1 can be explained by the electronic shell model: By the addition of one sodium atom to the bare aluminum clusters, the total number of their valence electrons strictly satisfies the shell closing of 2p and 3s shells, respectively, and therefore, the clusters can be stabilized electronically.

Production of bimetallic clusters containing manganese atoms by laser-vaporization method

Production of bimetallic clusters containing manganese atoms by laser-vaporization method

Reactivity and stability of bimetallic clusters

Using two independent vaporization lasers, bimetallic clusters composed of transition elements and A1 were generated by the laser vaporization method. Reactivity toward hydrogen adsorption of bimetallic clusters was compared with genuine clusters. It was found that A1 which has no reactivity toward hydrogen plays a role of either inhibitor or accelerator of the reaction when A1 is mixed with Nb or Co. Unusual stability of Co12 V1 in contrast to the high reactivity of Co12–13 is attributed to the rigid geometric structure where V occupies the central position.

ChemInform Abstract: Structure and Reactivity of Bimetallic ConVm Clusters.

AbstractBimetallic clusters of Co and V, ConVm with n &gt; m, are synthesized by a laser vaporization method and the reactivity of the clusters toward H2 is studied in comparison with that of pure Con clusters.

Enumeration of the isomers of the gallium arsenide clusters (Ga mAs n)

Possible isomers of the gallium arsenide clusters of the formula Ga m As n containing up to ten atoms and icosahedral clusters are enumerated. The possible parent polyhedrons up to ten vertices are constructed and then Pólya's theorem is applied to each polyhedron to calculate the generating functions for the enumeration of the isomers of gallium arsenide clusters of the formula Ga m As n . The distributions of clusters of Ga m As n clusters observed by Smalley and co-workers using the laser vaporization method is explained. Specifically, generating functions obtained here together with the criteria of bond strengths explain the observed deviations from binomial distributions for smaller clusters.

Management and follow-up of cervical intraepithelial neoplasia treated by CO2 laser vaporization method.

Forty-four patients with cervical intraepithelial neoplasia (CIN) II and 31 patients with CIN III were followed up for up to 6 months after cervical cone vaporization with carbon dioxide laser. In addition to colposcopy and pap smear, all patients underwent cervical biopsies as part of their follow-up. This protocol permitted a diagnosis of persistent disease in the presence of normal colposcopy and pap smear.