Klabunde Free Atoms, Clusters, and Nanoscale Particles

1. Auflage 2012
ISBN: 978-0-08-092406-9
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 311 Seiten

This book presents coherent and systematic coverage of the broad and dynamic field of free atom and cluster atom chemistry. The text provides a comprehensive overview of the current literature and describes the mostimportant experimental techniques developed since 1980 including bimetallic clusters/catalysts, carbon clusters (fullerenes) and trapped single atoms. Metal atoms, clusters, and particles are covered in sequence with the Periodic Table.

Autoren/Hrsg.

Klabunde, Kenneth J.

Inhaltsverzeichnis

1;Front Cover;1
2;Free Atoms, Clusters, and Nanoscale Particles;4
3;Copyright Page;5
4;Table of Contents;8
5;Dedication
;6
6;Preface;12
7;CHAPTER 1. Introduction
;14
7.1;I. Free Atoms, Clusters, and Nanoscale Particles;14
7.2;II. Extremes in Temperatures and Energies;15
7.3;III. Organization of the Book;15
7.4;IV. Chemistry Headings;16
7.5;References;16
8;CHAPTER 2. New Laboratory Techniques and Methods;18
8.1;I. Introduction;18
8.2;II. "Optical Molasses" Apparatus (Atomic Beam Cooling);18
8.3;III. Pulsed Cluster Beam (PCB);20
8.4;IV. Continuous Flow Cluster Beam (CFCB);22
8.5;V. Ionized Cluster Beam (ICB);23
8.6;VI. Gas Evaporation Method (GEM);24
8.7;VII. Laser Plume Method (LPM);25
8.8;VIII. Preparative-Scale Matrix Isolation Apparatus for Use with Small Molecules (N2, O2, H2, CO, CH4 , NO, C2H4)12;25
8.9;IX. Solvated Metal Atom Dispersion (SMAD) Apparatus for Producing SMAD Catalysts;26
8.10;References;28
9;CHAPTER 3. Alkali and Alkaline Earth Elements (Groups 1 and 2);29
9.1;I. Free Atoms (Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba);29
9.2;II. Free Clusters;39
9.3;III. Bimetallic and Other Binuclear Clusters/Particles;50
9.4;References;56
10;CHAPTER 4. Early Transition-Metal Elements (Groups 3-7) ;63
10.1;I. Early Transition-Metal Atoms (Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, Ta, W, Re);63
10.2;II. Early Transition-Metal Clusters;85
10.3;III. Bimetallic and Other Binuclear Systems;95
10.4;References;105
11;CHAPTER 5. Late Transition Metals (Groups 8-10);111
11.1;I. Late Transition-Metal Atoms (Fe, Co, Ni, Ru, Rh, Pd, as, Ir, Pt);111
11.2;II. Late Transition-Metal Clusters;137
11.3;III. Bimetallic and Binuclear Systems;159
11.4;References;165
12;CHAPTER 6. Copper and Zinc Group Elements (Groups II and 12);173
12.1;I. Copper and Zinc Group Metal Atoms (Cu, Ag, Au, Zn, Cd, Hg);173
12.2;II. Copper and Zinc Group Metal Clusters;183
12.3;III. Bimetallic and Binuclear Systems;190
12.4;IV. Particles and Films;192
12.5;References;201
13;CHAPTER 7. Boron Group (Group 13);207
13.1;I. Boron Group Atoms (B, AI, Ga, In, TI);207
13.2;II. Boron Group Clusters;220
13.3;III. Bimetallic and Binuclear/Trinuclear Systems;226
13.4;IV. Thin Films;233
13.5;References;235
14;CHAPTER 8. Carbon Group (Group 14) ;241
14.1;I. Carbon Group Atoms and Vapors (C, Si, Ge, Sn,Pb);241
14.2;I. Carbon Group Clusters Including Fullerenes C60 and Related Cluster Cage Molecules;246
14.3;III. Binuclear Systems;275
14.4;IV. Films of Si, Ge, Sn, and Their Oxides Prepared by Vaporization and Ionized Cluster Beam Methods;280
14.5;References;280
15;CHAPTER 9. Phosphorus and Sulfur Groups (Heavier Elements of Groups 15 and 16);290
15.1;I. Phophorus and Sulfur Group Vapors: Atoms and Clusters (P, As, Sb, Bi, Se, Te);290
15.2;II. Binuclear and Polynuclear Species;296
15.3;III. Thin Films;299
15.4;References;300
16;CHAPTER 10. Lanthanides and Actinides;302
16.1;I. Lanthanide and Actinide Atoms;302
16.2;II. Lanthanide and Actinide Clusters;306
16.3;References;308
17;Index;310

Leseproben

Chapter 2 New Laboratory Techniques and Methods
I Introduction
In this chapter are collected schematic diagrams of special apparatus developed for studies of the species of interest. Brief explanations for their operation are given. II “Optical Molasses” Apparatus (Atomic Beam Cooling)
Figure 2-1 describes an instrument capable of trapping the vapors of relatively volatile metals in the gas phase and holding them essentially motionless (thereby at micro-Kelvin temperatures) in a vacuum.1 This is done by the use of focused laser beams arranged in such a way that metal atoms that drift into a laser beam are “pushed back” by the photon energies. With several such lasers, the atom/atoms can be trapped for long periods of time, allowing many spectroscopic measurements to be carried out on motionless, gas-phase atoms. Figure 2-1 Optical molasses (atomic beam cooling) apparatus for isolation of gas-phase metal atoms (after Ertmer1). Basically “light pressure” forces atoms to absorb photons and their momentum from a light beam. In a short time (~ 10 nsec) the atoms spontaneously remit a photon (fluorescence). Since the direction of the emitted photon is random, overall the absorbed photon can cause directional change. With the advent of tunable dye lasers, this hitherto theoretical approach to laser cooling and storage of atoms has become a reality. The basic scheme consists of an atomic beam and a counterpropagating laser beam. The atoms absorb momentum and are decelerated. Thus, a Na atom can lose an average of 3 cm/sec speed per absorption, when the laser is tuned to the sodium D2 line. Typically, a Na atom traveling at 600 m/sec needs about 20,000 absorptions to be stopped. The time scale for complete deceleration is about 1 msec over a distance of less than 1 m. In one scheme of operation, a Na atomic beam was cooled below 10 mK with a density of 106 atoms/cm3. Table 2-1 shows the cooling limits of some elements (atoms) studied when such a polarized cooling laser beam is carefully mode-matched to the weakly diverging atomic beam. Table 2-1 Cooling Limits of some Atoms by Laser Coolinga Na 589 16 0.8 Rb 780 27 0.1 Cs 852 32 0.07 Ca 423 4.6 0.9 Ca 657 4 × 105 0.4 Mg 285 2 3.3 Mg 457 2.3 × 106 1.3 a “? is the cooling (laser) wavelength, t denotes the natural lifetime of the upper level of the cooling transition, and Tr refers to temperature motion because of photon recoil. The interest in producing such cold gas-phase atoms is clearly for the ability to obtain exact spectroscopic information. Optical or microwave frequency standards are of obvious interest. Other applications may be in the areas of collision physics, surface physics, photon statistics, quantum effects, and isotope separation schemes. III Pulsed Cluster Beam (PCB)
First developed by Smalley and co-workers,2-4 this technique utilizes a laser pulse to evaporate any desired element. The vapor plume is ejected into a flow tube where a pulse of cold He is simultaneously injected. This supersonic beam of atoms/inert gas finds itself in a relatively high pressure of the inert gas. The atoms begin to aggregate and are cooled to about 1–20 K as they form. The cluster growth can be moderated by the He pressure, flow rate, and laser pulse power. The flowing clusters and inert gas enter a skimmer where a small amount is differentially pumped so that a portion is led into a chamber where the clusters are ionized by a second laser and then mass analyzed. In more elaborate setups, certain ionized clusters can be magnetically separated and held in a vacuum cell for subsequent further study. Figure 2-2 shows a schematic cross section of an improved, miniaturized version of the CB apparatus, especially constructed for generation of cluster ions that can be trapped and studied by FT - ICR (Fourier transform-ion cyclotron resonance).4 The laser target rod is rotated and translated under computer control so that fresh surface is always available for vaporization. The vaporization laser (second harmonic of a Nd-YAG, 10–30 mJ/pulse, 5 nsec pulse length focused on a 0.07-cm-diam spot) is fired on the leading edge of the rising carrier gas pulse. This allows the vapor plume to expand unimpeded for a short while before it is entrained in the rising density of the carrier gas pulse. Figure 2-2 Pulsed cluster beam apparatus for production of gas-phase clusters (supersonic cluster beam source) (after Smalley and co-workers2-4). Operating with a He backing pressure of 10 atm, the pulsed value is capable of putting out 0.05 Torr liter in a 125-µsec pulse. In a 3-liter chamber such a fast pulse temporarily raises the pressure to 2 × 10- 2 Torr. In this design the “waiting room” is the zone in the nozzle where clusters are formed and thermalized. The main flow of the carrier gas then passes through a 2.0-cm-long conical expansion zone. The gas can then undergo a free supersonic expansion with the central 0.2-cm-diameter section of the jet being skimmed about 8.4 cm downstream. After passing through the skimmer the clusters can be ionized by a second laser and trapped or directly analyzed by MS. IV. Continuous Flow Cluster Beam (CFCB)
A variation on this theme due to Riley and co-workers5,6 utilizes a continuous flow of He or Ar. This apparatus allows more control of pressure and temperature, and thus more meaningful kinetic analyses. The main disadvantage is the need for large pumping capacity in order to move the large volume of He gas rapidly enough. A cross section of the central part of the apparatus is shown in Fig. 2-3. An aluminum block with three inserting channels allows a pulsed laser beam to hit the sample rod ejecting vapor into the continuous main flow. (The target rod is continually rotated and translated automatically so that a fresh surface is available as vaporization continues). The ejected vapor is rapidly cooled and nucleation and cluster growth occurs quickly. (An additional flow of gas over the laser window is needed to prevent metal film formation on the window). Figure 2-3 Continuous flow cluster beam (CB) apparatus (after Riley and co-workers6). Cross section of the cluster source/flow tube reactor. Reagent gas can be inlet into the metal cluster/carrier gas mixture through four inlets equally spaced down the circumference of the main channel. Any reaction that is taking place downstream of these inlets is quenched where the mixture expands into vacuum through a 0.1-cm-diameter nozzle at the end of the main channels. A portion of the expanded sample is collected by a skimmer and this passes through several stages of differential pumping to arrive at a time-of-flight mass spectrometer (40 cm downstream from nozzle). Ionization of a portion of the sample is achieved by a second pulsed laser. The vaporization laser used is a XeCl excimer typically operating with a pulse energy of 50 mJ and a repetition rate of 20 Hz. Carrier gas flows used were 500 std cm3/min (sccm) He in the main channel, yielding a pressure of about 30 Torr in the reaction zone. The reagents are usually added as 1–10% diluted in He or as pure gases. Flows ranged from 5 to 310 sccm. Thus, partial pressures of reagent gases were varied from 3 µm to 12 Torr. Flow velocities were typically 5 × 103 cm/sec. Total pressure of cluster species were small, about 0.01 to 0.1 µm The ionization laser was a collimated ArF excimer laser and fluence was kept low (< 1 mJ/pulse). V Ionized Cluster Beam (ICB)
Another major innovation, due to Takagi and co-workers7,8 is the development of the ionized cluster beam source. Mainly used as a method for producing high quality films, this technique utilizes the vaporization of elements and expansion of the vapor through a nozzle into a region where clustering takes place. The ICB method is entirely different from conventional vacuum or sputtering techniques since the kinetic energy of the ion clusters can be controlled by the acceleration voltage. In this way, increased implantation energies can be achieved. ICB techniques are characteristic due to enhanced migration of adatoms on the substrate surface. Figure 2-4 shows an example of an ion source with a direct-heating type of crucible.8 The clusters formed after nozzle vapor ejection are multiply or singly charged. The charged clusters are accelerated and deposited. Film deposition rates can vary from 10 Å to several micrometers per minute. Upon impacting the substrate, the kinetic energy of the accelerated ion clusters may be...