Isotropic Optical Properties Research Articles

Thermal radiative energy exchange between a closely-spaced linear chain of spheres and its environment

In this work, we present expressions for radiative heat transfer between pairs of spheres in a linear chain and between individual spheres and their environment. The expressions are valid for coated spheres of arbitrary size, spacing, and isotropic optical properties. The spheres may be small and closely-spaced, which violates the assumptions foundational to classical radiative transfer. We validate our results against existing formulations of radiative heat transfer, namely the thermal discrete dipole and boundary element methods. Our results have important implications for the modeling and interpretation of near-field radiative heat transfer experiments between spherical bodies.

Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties

Few-layer Tellurium, an elementary semiconductor, succeeds most of striking physical properties that black phosphorus (BP) offers and could be feasibly synthesized by simple solution-based methods. It is comprised of non-covalently bound parallel Te chains, among which covalent-like feature appears. This feature is, we believe, another demonstration of the previously found covalent-like quasi-bonding (CLQB) where wavefunction hybridization does occur. The strength of this inter-chain CLQB is comparable with that of intra-chain covalent bonding, leading to closed stability of several Te allotropes. It also introduces a tunable bandgap varying from nearly direct 0.31 eV (bulk) to indirect 1.17 eV (2L) and four (two) complex, highly anisotropic and layer-dependent hole (electron) pockets in the first Brillouin zone. It also exhibits an extraordinarily high hole mobility (∼105 cm2/Vs) and strong optical absorption along the non-covalently bound direction, nearly isotropic and layer-dependent optical properties, large ideal strength over 20%, better environmental stability than BP and unusual crossover of force constants for interlayer shear and breathing modes. All these results manifest that the few-layer Te is an extraordinary-high-mobility, high optical absorption, intrinsic-anisotropy, low-cost-fabrication, tunable bandgap, better environmental stability and nearly direct bandgap semiconductor. This “one-dimension-like” few-layer Te, together with other geometrically similar layered materials, may promote the emergence of a new family of layered materials.

Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties.

A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) 3∞[Eu2(BDC)3]·2DMF·2H2O (BDC2- = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.

Gyroid Optical Metamaterials: Calculating the Effective Permittivity of Multidomain Samples

Gold gyroid optical metamaterials are known to possess a reduced plasma frequency and linear dichroism imparted by their intricate subwavelength single gyroid morphology. The anisotropic optical properties are, however, only evident when a large individual gyroid domain is investigated. Multidomain gyroid metamaterials, fabricated using a polyisoprene-b-polystyrene-b-poly(ethylene oxide) triblock terpolymer and consisting of multiple small gyroid domains with random orientation and handedness, instead exhibit isotropic optical properties. Comparing three effective medium models, we here show that the specular reflectance spectra of such multidomain gyroid optical metamaterials can be accurately modeled over a broad range of incident angles by a Bruggeman effective medium consisting of a random wire array. This model accurately reproduces previously published results tracking the variation in normal incidence reflectance spectra of gold gyroid optical metamaterials as a function of host refractive index and volume fill fraction of gold. The effective permittivity derived from this theory confirms the change in sign of the real part of the permittivity in the visible spectral region (so, that gold gyroid metamaterials exhibit both dielectric and metallic behavior at optical wavelengths). That a Bruggeman effective medium can accurately model the experimental reflectance spectra implies that small multidomain gold gyroid optical metamaterials behave both qualitatively and quantitatively as an amorphous composite of gold and air (i.e., nanoporous gold) and that coherent electromagnetic contributions arising from the subwavelength gyroid symmetry are not dominant.

Strain-induced long range ferroelectric order and linear electro-optic effect in epitaxial relaxor thin films

Relaxor ferroelectrics have neither long range ferroelectric order nor structural transformation down to the lowest temperatures, and display isotropic optical properties like quadratic electro-optic effect. However, if an anisotropy is forced through an external agent, like electric field or uniaxial strain, a ferroelectric and structural long range order can be induced in these materials. Here, we show that epitaxial strain in relaxor ferroelectric thin films can be employed to induce a linear electro-optic effect, opening the path to new strain-controlled electro-optic materials. Epitaxial thin films with Pb1-3x/2LaxZr0.2Ti0.8O3 (x = 0.22) composition grown by pulsed laser deposition on (001) SrRuO3/SrTiO3 single crystal heterostructures become tetragonal below the susceptibility peak, which occurs at a temperature 140 K higher as compared to bulk. These films show piezoelectric properties and almost linear electro-optic behaviour.

Synthesis and Multiscale Evaluation of LiNbO3‐Containing Silicate Glass‐Ceramics with Efficient Isotropic SHG Response

AbstractA study of bulk second harmonic generation (SHG) response of lithium niobium silicate glass‐ceramics is presented. The observed macroscopic SHG signals have an isotropic 3D nature. To interpret this particular nonlinear optical response, a multiscale approach is used in which clear correlations between structure and optical response are characterized from the sub‐micrometer to the millimeter scale. In particular, it is inferred that the radial distribution of the LiNbO3 crystallites in spherulite domains is at the origin of the isotropic bulk second order optical property. It is suggested that spherulitic crystallization in glass‐ceramic is a challenging method to elaborate isotropic nonlinear optical properties in inorganic materials.

Structure and optical function of amorphous photonic nanostructures from avian feather barbs: a comparative small angle X-ray scattering (SAXS) analysis of 230 bird species

Non-iridescent structural colours of feathers are a diverse and an important part of the phenotype of many birds. These colours are generally produced by three-dimensional, amorphous (or quasi-ordered) spongy β-keratin and air nanostructures found in the medullary cells of feather barbs. Two main classes of three-dimensional barb nanostructures are known, characterized by a tortuous network of air channels or a close packing of spheroidal air cavities. Using synchrotron small angle X-ray scattering (SAXS) and optical spectrophotometry, we characterized the nanostructure and optical function of 297 distinctly coloured feathers from 230 species belonging to 163 genera in 51 avian families. The SAXS data provided quantitative diagnoses of the channel- and sphere-type nanostructures, and confirmed the presence of a predominant, isotropic length scale of variation in refractive index that produces strong reinforcement of a narrow band of scattered wavelengths. The SAXS structural data identified a new class of rudimentary or weakly nanostructured feathers responsible for slate-grey, and blue-grey structural colours. SAXS structural data provided good predictions of the single-scattering peak of the optical reflectance of the feathers. The SAXS structural measurements of channel- and sphere-type nanostructures are also similar to experimental scattering data from synthetic soft matter systems that self-assemble by phase separation. These results further support the hypothesis that colour-producing protein and air nanostructures in feather barbs are probably self-assembled by arrested phase separation of polymerizing β-keratin from the cytoplasm of medullary cells. Such avian amorphous photonic nanostructures with isotropic optical properties may provide biomimetic inspiration for photonic technology.

Properties of amorphous and crystalline titanium dioxide from first principles

We used first-principles methods to generate amorphous TiO2 (a-TiO2) models and our simulations lead to chemically ordered amorphous networks. We analyzed the structural, electronic, and optical properties of the resulting structures and compared with crystalline phases. We propose that two peaks found in the Ti–Ti pair correlation correspond to edge-sharing and corner-sharing Ti–Ti pairs. Resulting coordination numbers for Ti (∼6) and O (∼3) and the corresponding angle distributions suggest that local structural features of bulk crystalline TiO2 are retained in a-TiO2. The electronic density of states and the inverse participation ratio reveal that highly localized tail states at the valence band edge are due to the displacement of O atoms from the plane containing three neighboring Ti atoms; whereas, the tail states at the conduction band edge are localized on over-coordinated Ti atoms. The $$\Upgamma$$ -point electronic gap of ∼2.2 eV is comparable to calculated results for bulk crystalline TiO2 despite the presence of topological disorder in the amorphous network. The calculated dielectric functions suggest that the amorphous phase of TiO2 has isotropic optical properties in contrast to those of tetragonal rutile and anatase phases. The average static dielectric constant and the fundamental absorption edge for a-TiO2 are comparable to those of the crystalline phases.

Tunable In-Plane Optical Anisotropy of Ag Nanoparticles Deposited by DC Sputtering onto SiO2 Nanocolumnar Films

This work reports an easy-to-handle method for growing two-dimensional assemblies of Ag nanostructures presenting a tunable in-plane optical anisotropy. Ag is deposited by DC sputtering in an Ar plasma at room temperature onto bundled nanocolumnar SiO2 thin films grown by glancing angle physical vapor deposition. In contrast with previously reported processes involving the grazing angle deposition of the metal, DC sputtering is performed at normal incidence. By varying the deposition angle of SiO2 and the Ar pressure, it was possible to tune the deposited amount of Ag and thus the topology of the Ag deposit from isolated spherical Ag nanoparticles with isotropic optical properties to strongly dichroic Ag nanostripes oriented along the bundling direction of the SiO2 nanocolumns. Based on simple calculations taking into account the shadowing effects during metal deposition, it is proposed that the width and shape of the tip of the bundled SiO2 nanocolumns influence significantly the metal local atom flux arriving to them and thus the final structure of the deposit.

Controlled chemical phase separation in binary and ternary composites: A pathway to isotropic optical and electrical behavior for device applications

AbstractThere are many applications for nanocrystalline thin films in optical devices that require isotropic optical properties. A novel way to obtain these isotropic properties for the index of refraction and/or optical absorption constant, etc., and at the same time to minimize microscopic strain is presented in this article. This approach is based on strain reduction mechanisms that occur in the intermediate phases, IPs, of non‐crystalline glasses and thin films. In these compositional regimes, either site percolation, or volume percolation, each above an applicable critical value, provides a quantitative understanding of the microscopic bonding arrangements associated with strain‐reducing chemical bonding self‐organizations. A similar framework, presented for the first time in this article, develops a microscopic understanding of macroscopic strain reduction in several different phase‐separated composites. This understanding has emerged from focussed research on qualitatively different hetero‐structure device structure constituents, e.g.; (i) high‐k replacement dielectrics for SiO2 in field effect transistors gate stacks for advanced semiconductor devices, and (ii) active and passive thin films for optically switched memory cells. In each instance strain reduction and its intrinsic relationship to low densities of defects and defect precursors has provided a driving force in the identification of a narrow range of compositions that satisfy technological needs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Anisotropic optical emission of single CdSe/CdS tetrapod heterostructures: Evidence for a wavefunction symmetry breaking

Semiconductor tetrapods are expected to exhibit isotropic optical properties due to their tetrahedral symmetry. We have investigated the optical polarization properties of individual $\mathrm{Cd}\mathrm{Se}∕\mathrm{Cd}\mathrm{S}$ tetrapods of high structural quality. In contrast to the light absorption behavior, a pronounced anisotropy is observed in the optical emission. This unexpected result can only be explained by assuming a symmetry breaking in the electronic wavefunction. Calculations reveal that slight differences between the arm diameters induce the polarized emission and a decrease in the photoluminescence intensity.

Optical properties of epitaxial plzt thin films

In the epitaxial (Pb1−x , La x )(Zr1−y , Ti y )1−x/4O3 [PLZT] films, the composition dependence of the refractive index and electric-optic (EO) coefficient near the morphotropic phase boundary (MPB) composition was investigated. A (100/001)-oriented PLZT 10/65/35 epitaxial film is found to have isotropic optical properties. Highly (100/001)-oriented epitaxial PLZT films with compositions near the MPB on Nb–SrTiO3 substrates were fabricated using a sol–gel process. The value of birefringence from 4 × 10−3 to 5 × 10−4 in PLZT epitaxial film was smaller than that of lithium niobate single crystal. The refractive index decreases with increasing lanthanum content. The difference in the refractive index obtained depended upon the lanthanum content up to 2%. This value is adequate for fabrication of waveguide structures. The EO coefficient of PLZT 9/65/35 thin films was 45 pm/V, which is larger than that of lithium niobate single crystal. A very small polarization dependence of the EO coefficient was also observed.

Two‐flux method for transient thermal analysis in a layer of polymer fiber

AbstractTransient radiative and conductive heat transfer in a translucent medium with isotropic optical properties is investigated. The radiative two‐flux equation is coupled with the transient energy equation and both equations are solved simultaneously. Transient solutions are obtained for a plane layer with refractive index equal to or larger than one, and with external convection and radiation at each boundary. Illustrative results obtained with the two‐flux method show the effects of changing parameters such as optical thicknesses, refractive index, conduction–radiation parameter, and scattering on the transient temperature distribution within the layer. Results are given at different instances during the transient, and the distribution for the largest time is at or very close to steady state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2277–2283, 2006

Sensitive identification and measurement of a weak anisotropic thin film from the reflectance angular spectrum

A technique for determining the optical constants of an anisotropic thin film is developed here. Instead of complicated phase measurement, an optical arrangement that involves at least two resonant dips in the reflectance angular spectrum supports a method for sensitively determining the anisotropic optical constants and clearly distinguishing the anisotropic from the isotropic optical properties. Multi-resonant dips including waveguide modes and surface plasmon resonance are applied in detecting the ellipsoid distribution of the refractive index.

AFM, SEM and GIXRD studies of thin films of red polycarbazolyldiacetylenes

In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl- N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl- N-carbazolyl)-6-( N-carbazolyl)-2,4-hexadyine] (poly a-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl- N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings.

Polarization of the Electroluminescence of Alkali-Halide Crystals Inactivated and Activated with Europium

Among works devoted to the electroluminescence (EL) of alkali-halide crystals (AHCs), there are no works devoted to an analysis of the polarization characteristics, though the polarization is an important luminescence characteristic. A comprehensive analysis of this problem can give new information not only on the structure of the luminescence centers but also on the mechanism of luminescence excitation. From the simplest classical emission theory based on the concept of elementary emitters – dipoles – it follows that light emitted in an elementary act is linearly polarized. As is well known [1], cubic crystals have isotropic optical properties. This is due to the fact that the distribution of anisotropic centers oriented along the С4, С3, and С2 symmetry axes of the corresponding orders as well as along different symmetry axes of the fixed order is uniform, that is, the anisotropy of luminescence centers in these crystals is latent. The anisotropy of these centers can arise only in external anisotropic fields (linearly polarized light or uniform electric and magnetic fields). In the literature devoted to the photoluminescenсe, there is information on the study of the polarization characteristics of AHC luminescence. Varenko et al. [2] studied the polarization characteristics of Eu centers in AHCs. The polarization luminescence characteristics were investigated at 100 and 300 K. In [2] it was found that the luminescence at λ = 480 nm was polarized by 10–14%, and the polarization ratio changed only slightly when the temperature increased from 100 to 300 K. The polarization of the luminescence of Eu centers (λ = 428 nm) was not observed in [2] even at 100 K. This confirms once again that the luminescence bands centered at 428 and 480 nm are caused by different activator centers (Еu and Eu, respectively). Varenko et al. [2] measured the azimuth dependences of the polarization ratio for the luminescence band centered at 480 nm. The comparison of these azimuth polarization dependences with the results of theoretical calculations performed by Feofilov [3] demonstrated that the elementary emitters of 480-nm band radiation were oriented along the С4 crystal axis, that is, along the cation-anion direction. Unfortunately, Varenko et al. [2] failed to establish unambiguously the luminescence polarization type (linear or circular) because of small values of the measured polarization ratio. An analysis of the EL polarization will allow the influence of electric fields with strengths up to 10 V/m on the intracenter processes to be evaluated. In our previous works devoted to an analysis of the EL polarization characteristics, we measured the azimuth dependences of the polarization ratio for AHCs inactivated and activated with europium. The activated crystalline phosphors were preliminary quenched; therefore, only the emission band at λ = 428 nm was observed in the EL spectra. Measurements were performed at room temperature, because according to [2], the polarization ratio is independent of the temperature. The electroluminescence was excited upon exposure to pulses of a superstrong electric field >10 V/m. A setup for measuring brightness waves of the AHC electroluminescence was used, in which a rotating cylinder with polarization glass (МР1 3 Zs 4 polarizer) was placed in front of a 39А photomultiplier. The cylinder had divisions corresponding to the polaroid rotation angle from 0 to 360°. The intensity of radiation transmitted through the polarizer was registered with the photomultiplier. The brightness wave was observed on the screen of a storage oscilloscope.

Anisotropically Nanostructured Silicon as an Efficient Optical Retarder

Silicon (Si) is the materials basis for the majority of integrated electronic devices. However, a key limitation of its application for active and passive optical devices stems from its indirect band gap and highly isotropic cubic lattice structure. In this paper we demonstrate a new way of realisation of silicon-based optical retarders which can be integrated in optical communication lines. Lorentz has demonstrated that for cubic lattices only a weak dependence of the refractive index value (n) on the light wave vector direction exists [1]. For instance, in bulk Si the maximum value of birefringence for light propagating along the [110] direction was found to be extremely small: An = n [110] - n [100] = 5 x 10 -6 , where subscripts denote the direction of the electric field vector [2]. Obviously this value does not allow to perform silicon-based devices controlling of the polarisation state of light. Porosified (100) Si surfaces have isotropic in-plane optical properties due to the equivalence of their [010] and [001] crystallographic directions [3]. Preferential alignment of nanocrystals in [100] etching direction results in a larger dielectric constant for the light polarised along [100] direction [4,5]. Thus, birefringence can be observed for light propagating along the layer. However, for most of practical applications an in-plane birefringence is required. To achieve in-plane uniaxial symmetry we have employed the electrochemical etching of lower-symmetry (110) Si wafers. In Ref. [6], the selective crystallographic pore propagation and, respectively, alignment of nanocrystals in equivalent [010] and [100] directions tilted to the (110) surface plane has been demonstrated. According to effective medium predictions, the projection of those on the (110) plane ([110] direction) would result in an uniaxial surface symmetry with a dielectric constant e [110] being different from e [001] . Bulk Si is not an anisotropic crystal, but its porous modification becomes intrinsically uniaxial for this plane due to anisotropic dielectric nanostructuring. Since nanocrystals retain the diamond-like crystalline structure and their sizes (1 to 50 nm, depending on wafer and etching parameters used [7]) are much smaller than the wavelength of light, porous layers still can be considered as a continuous optical medium.

Tricontinuous Double Gyroid Cubic Phase in Triblock Copolymers of the ABA Type

We report the synthesis and morphological characterization of two triblock copolymers of the ABA type, where A is polystyrene (PS) and B polyisoprene (PI). The volume fraction of the minority component, PS or PI, is approximately 1/3. Cubic microdomain morphologies, already found in diblock and star block copolymers with the same composition range, are observed for the first time in the case of linear triblock copolymers. The two ABA triblocks are on opposite sides of the phase diagram, which signifies that both the A end blocks and the B midblock are capable of forming the interconnected double network structure. Investigation of the morphology was done via birefringence, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Birefringence measurements showed each triblock structure to have isotropic optical properties. The characteristic ratio of the observed Bragg peaks, q2/q1, was approximately / for each sample, indicating a set of eight possible cubic space groups. TEM data showed an interconnected tricontinuous microdomain structure. Since the two triblocks have essentially complementary structures (PS = 0.32 in one and PI = 0.36 in the other), the TEM images of OsO4-stained thin sections are complementary and the diffraction patterns of the images are approximately equal according to Babinet's principle. Examination of high-symmetry projections demonstrated p6mm, p4mm, and c2mm symmetry present in the TEM images. Comparison with the 〈111〉, 〈100〉, and 〈110〉 projections of the eight cubic space groups satisfying the SAXS data eliminated all but the Fm3̄m and Ia3̄d groups as possible structures. Due to the observed connectivity of the structure, the Fm3̄m structure could be eliminated by inspection of possible network structures and the resultant symmetries. Computer simulations of a model structure (double gyroid) based on level surfaces with Ia3̄d symmetry and their Fourier transforms showed excellent agreement with the high-symmetry projections and their respective optical transforms.

The metamict state: 1993 — the centennial

In 1893, a Norwegian mineralogist, W.C. Brøgger, defined “metamikte” as a third class of naturally occurring, amorphous materials. Metamict minerals were determined to be amorphous based on conchoidal fracture and isotropic optical properties; however, well developed crystal forms evidenced the prior crystalline state.In 1914, A. Hamberg, based on the observation of pleochroic haloes, first suggested that metamictization is a radiation-induced, periodic-to-aperiodic transition caused by α-particles which originate from decay of constituent U and Th. Within a few years, F. Rinne and L. Vegard confirmed by X-ray diffraction that metamict minerals were either amorphous or finely crystalline. By 1940, M. v. Stackelberg and E. Rottenback had established that the decrease in density, refractive indices and birefringence correlated with the breakdown of the structure with increasing α-decay event dose. They tested this hypothesis by bombarding a thin slab of zircon, tetragonal ZrSiO2, with α-particles. The result was inconclusive, but this must have been one of the first experiments in which an “ion-beam” was used to “modify” a ceramic material. Metamict minerals remained a curiosity and a daunting challenge, as compositions were exceedingly complex (lanthanides were abundant) and no structure remained, except that which was restored on heating. In 1952, Adolf Pabst, in his presidential address to the Mineralogical Society of America, carefully tabulated the changes in properties (e.g., release of stored energy and decreased resistance to leaching) which resulted from the radiation damage. Pabst specifically noted that some structures are “resistant” to damage accumulation (e.g., monoclinic ThSiO2) while other polymorphs are often found in the metamict state (e.g., tetragonal ThSiO2).The use of zircon (isostructural with thorite) in U/Pb dating, however, focused substantive studies on the process of radiation damage. Holland and Gottfried (1955) investigated damage accumulation as an age-dating technique in a classic study of natural zircons (570 million years old; doses up to 1016α-decay events/mg = 0.7 dpa); and developed a modern model of damage accumulation. Recent studies are reviewed which include Pu-doped and ion-beam irradiated zircons. With the exception of radiation effects on alumina and silica, zircon is now probably the most studied complex ceramic.

The Metamict State

Recently, the words “metamict” or “metamictization” have been increasingly used instead of “amorphous” or “amorphization” in acknowledgment of the fact that the first recognized example of the transition from the crystalline to the aperiodic state was in natural materials—minerals. The term (originally “metamikte” from Greek for “mix otherwise” because of their complex compositions) was first defined by Broegger in a Danish encyclopedia as one of three classes of amorphous substances: porodine (= colloidal), hyaline, and metamikte. Minerals considered to be metamict were judged amorphous because of their conchoidal fracture and isotropic optical properties; however, well-developed crystal faces evidenced the prior crystalline state.Hamberg was the first to suggest that metamictization is a radiation-induced, periodic-to-aperiodic phase transition caused by alpha particles which originate from constituent radionuclides in the uranium and thorium decay series. Rinne and Vegard confirmed by x-ray diffraction studies that metamict minerals were either amorphous or finely crystalline. Later work supported the idea of a radiation-induced transformation. The work of Stackelberg and Rottenbach established that the decrease in density, refractive indices, and birefringence correlated with the breakdown of the structure with increasing alpha-decay dose. Stackelberg and Rottenback tried to test this hypothesis directly by bombarding a thin slab of zircon with alpha particles. The results were inconclusive because the slab fractured, but this must have been one of the first experiments in which an “ion beam” was used to “modify” a material.