This article provides a comprehensive review of current research activities that concentrate on one-dimensional (1D) nanostructures—wires, rods, belts, and tubes—whose lateral dimensions fall anywhere in the range of 1 to 100 nm. We devote the most attention to 1D nanostructures that have been synthesized in relatively copious quantities using chemical methods. We begin this article with an overview of synthetic strategies that have been exploited to achieve 1D growth. We then elaborate on these approaches in the following four sections: i) anisotropic growth dictated by the crystallographic structure of a solid material; ii) anisotropic growth confined and directed by various templates; iii) anisotropic growth kinetically controlled by supersaturation or through the use of an appropriate capping reagent; and iv) new concepts not yet fully demonstrated, but with long-term potential in generating 1D nanostructures. Following is a discussion of techniques for generating various types of important heterostructured nanowires. By the end of this article, we highlight a range of unique properties (e.g., thermal, mechanical, electronic, optoelectronic, optical, nonlinear optical, and field emission) associated with different types of 1D nanostructures. We also briefly discuss a number of methods potentially useful for assembling 1D nanostructures into functional devices based on crossbar junctions, and complex architectures such as 2D and 3D periodic lattices. We conclude this review with personal perspectives on the directions towards which future research on this new class of nanostructured materials might be directed.

One‐Dimensional Nanostructures: Synthesis, Characterization, and Applications

Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

https://science.sciencemag.org/content/sci/266/5193/1961.full.pdf

Nanomaterials: a membrane-based synthetic approach.

Closure temperature (Tc) of a geochronological system may be defined as its temperature at the time corresponding to its apparent age. For thermally activated diffusion (D=Doe−E/RT it is given by 

$$T_c = R/[E ln (A \tau D_0 /a^2 )]$$

(i) in which R is the gas constant, E the activation energy, τ the time constant with which the diffusion coefficient D diminishes, a is a characteristic diffusion size, and A a numerical constant depending on geometry and decay constant of parent. The time constant τ is related to cooling rate by 

$$\tau = R/(Ed T^{ - 1} /dt) = - RT^2 /(Ed T/dt).$$

(ii) Eq. (i) is exact only if T−1 increases linearly with time, but in practice a good approximation is obtained by relating τ to the slope of the cooling curve at Tc.

Closure temperature in cooling geochronological and petrological systems

https://uhra.herts.ac.uk/bitstream/handle/2299/1986/901994.pdf?sequence=1

Atmospheric polycyclic aromatic hydrocarbons: Source attribution, emission factors and regulation

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

https://science.sciencemag.org/content/sci/273/5277/924.full.pdf

Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001.

Nuclear Tracks in Solids

An extensive discussion of particle tracks in solids, quantitative methods for particle identification from them, and applications of the techniques in a number of fields are presented Applications in geochronology, cosmic ray physics, meteoritic and lunar science, nuclear physics, chemical analysis, micro-chemical mapping, and radiation dosimetry are included Each chapter contains numerous photographs and a substantial bibliography

Nuclear Tracks in Solids. Principles and Applications

Massive charged particles create regions of intense damage (tracks) by passing through bulk samples of insulating materials. These tracks are shown to result from the positively charged region created by ionization. An approximate model of an ``ion explosion spike'' is proposed in which the mutual repulsion of the positive ions ejects them into the surrounding lattice. This model is shown to be generally consistent with a wide range of experimental fact. An additional damage mechanism appears to apply to polymers, in some of which tracks are produced by light projectiles such as α particles. The data here are shown to be consistent with tracks consisting primarily of broken bonds caused by decay of directly excited electrons.

Ion Explosion Spike Mechanism for Formation of Charged-Particle Tracks in Solids

We have identified six circumstellar silicate grains within interplanetary dust particles (IDPs). Their extrasolar origins are demonstrated by their extremely anomalous oxygen isotopic compositions. Three 17O-rich grains appear to originate from red giant or asymptotic giant branch stars. One 16O-rich grain may be from a metal-poor star. Two 16O-poor grains have unknown stellar sources. One of the grains is forsterite, and two are amorphous silicate "GEMS" (glass with embedded metal and sulfides), which is consistent with astronomical identifications of crystalline and amorphous silicates in the outflows of evolved stars. These observations suggest cometary origins of these IDPs and underscore the perplexing absence of silicates among circumstellar dust grains from meteorites.

/pdf/samples-of-stars-beyond-the-solar-system-silicate-grains-in-451z9k89yr.pdf

Samples of stars beyond the solar system: silicate grains in interplanetary dust.

Thirty-seven isotopically highly anomalous presolar Al2O3 grains and one presolar MgAl2O4 grain from a separate of the Tieschitz H3.6 ordinary chondrite were identified out of 17,000 isotopically normal refractory oxide grains by an automatic 16O/18O low mass resolution ion-imaging mapping technique in the ion microprobe. Eight additional presolar Al2O3 grains were found by high mass resolution ion probe measurements of all three stable O isotopes in individual grains, including several that would have been missed by the ion-imaging search. Forty-five of the grains were analyzed for their 16O/17O and 16O/18O ratios. Twenty-four grains were also analyzed for Al-Mg and 17 of them have large excesses of 26Mg, attributable to the radioactive decay of 26Al. The highly anomalous isotopic composition of the grains is evidence for their presolar, stellar origin. The 46 oxide grains of this study together with 42 previously identified presolar grains were divided into four groups. These groups most likely comprise grains from distinct types of stellar sources. Group 1 grains have 17O excesses and moderate 18O depletions, relative to solar, and many of them exhibit 26Mg excesses as well. Group 2 grains have 17O excesses, large 18O depletions, and high inferred 26Al/27Al ratios. Group 3 grains have solar or higher 16O/17O and 16O/18O ratios. Group 4 grains have 17O and 18O enrichments. One Al2O3 grain of this study, T54, has an 16O/17O ratio of 71, lower than any previously observed, and 16O/18O much greater than the solar value. The O-isotopic compositions of Group 1 and Group 3 grains are consistent with an origin in O-rich red giant stars, which have undergone the first dredge-up. The range of O-isotopic ratios of these groups requires multiple stellar sources of different masses and initial isotopic compositions and is well explained by a combination of Galactic chemical evolution and first dredge-up models. The inferred 26Al/27Al ratios of many of these grains indicate that they formed in thermally pulsing asymptotic branch (TP-AGB) stars that had undergone the third dredge-up. Group 2 grains probably formed in low-mass AGB stars as well, and their substantial 18O depletions are the likely result of "extra" mixing (cool bottom processing). The origin of the 18O enrichments in Group 4 grains is unknown, but it might be due to initial compositional differences of the stellar sources or to unusual third dredge-up in low-mass AGB stars. The highly 17O-enriched grain T54 could have formed in an AGB star undergoing hot bottom burning or in a massive star in the Of-WN phase. O-rich circumstellar dust seems to be underrepresented in meteorites, relative to C-rich. Explanations include the possibility that most O-rich stardust grains are silicates and have been destroyed either in the laboratory or in nature and the possibility that presolar Al2O3 has a finer grain size distribution than SiC and graphite.

Robert M. Walker

Papers

Nuclear Tracks in Solids

Nuclear Tracks in Solids. Principles and Applications

Ion Explosion Spike Mechanism for Formation of Charged-Particle Tracks in Solids

Samples of stars beyond the solar system: silicate grains in interplanetary dust.

STELLAR SAPPHIRES: THE PROPERTIES AND ORIGINS OF PRESOLAR Al 2 O 3 IN METEORITES