This review is presented as a common foundation for scientists interested in nanoparticles, their origin, activity, and biological toxicity. It is written with the goal of rationalizing and informing public health concerns related to this sometimes-strange new science of 'nano', while raising awareness of nanomaterials' toxicity among scientists and manufacturers handling them. We show that humans have always been exposed to tiny particles via dust storms, volcanic ash, and other natural processes, and that our bodily systems are well adapted to protect us from these potentially harmful intruders. The reticuloendothelial system in particular actively neutralizes and eliminates foreign matter in the body, including viruses and non-biological particles. Particles originating from human activities have existed for millennia, e.g. smoke from combustion and lint from garments, but the recent development of industry and combustion-based engine transportation has profoundly increased anthropogenic particulate pollution. Significantly, technological advancement has also changed the character of particulate pollution, increasing the proportion of nanometer-sized particles -"nanoparticles" and expanding the variety of chemical compositions. Recent epidemiological studies have shown a strong correlation between particulate air pollution levels, respiratory and cardiovascular diseases, various cancers, and mortality. Adverse effects of nanoparticles on human health depend on individual factors such as genetics and existing disease, as well as exposure, and nanoparticle chemistry, size, shape, agglomeration state, and electromagnetic properties. Animal and human studies show that inhaled nanoparticles are less efficiently removed than larger particles by the macrophage clearance mechanisms in the lung, causing lung damage, and that nanoparticles can translocate through the circulatory, lymphatic, and nervous systems to many tissues and organs, including the brain. The key to understanding the toxicity of nanoparticles is that their minute size, smaller than cells and cellular organelles, allows them to penetrate these basic biological structures, disrupting their normal function. Examples of toxic effects include tissue inflammation, and altered cellular redox balance toward oxidation, causing abnormal function or cell death. The manipulation of matter at the scale of atoms, "nanotechnology", is creating many new materials with characteristics not always easily predicted from current knowledge. Within the near-limitless diversity of these materials, some happen to be toxic to biological systems, others are relatively benign, while others confer health benefits. Some of these materials have desirable characteristics for industrial applications, as nanostructured materials often exhibit beneficial properties, from UV absorbance in sunscreen to oil-less lubrication of motors. A rational science-based approach is needed to minimize harm caused by these materials, while supporting continued study and appropriate industrial develop...

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When a thin film is deposited by physical vapor deposition, with the vapor flux arriving at an oblique angle from the substrate normal, and under conditions of sufficiently limited adatom mobility to create a columnar microstructure, the resulting structure is somewhat porous and grows at an angle inclined toward the vapor source. For a given material and set of deposition conditions, there is a fixed relationship between the angle of vapor flux incident on the substrate and the inclination angle at which the columnar thin film grows. As the porosity of the film is also dependent on the incident flux angle, column growth angle and porosity cannot be chosen independently. If a large columnar angle (more parallel to the substrate) is desired, the flux must be deposited at a large oblique angle resulting in a very porous film. Conversely, if a near vertical columnar film is desired, the flux must arrive more perpendicular to the substrate and the resulting film has a tightly packed, dense microstructure. We present a technique, based on glancing angle deposition, employing substrate motion during deposition, which allows the columnar growth inclination angle and film density to be controlled independently. With this method, microstructurally controlled materials can be fabricated with three dimensional control on a 10 nm scale for use in optical, chemical, biological, mechanical, magnetic, and electrical applications.

Sculptured thin films with three dimensional microstructure controlled on the 10 nm scale were fabricated with an evaporation technique. Glancing angle deposition (GLAD) and substrate motion were employed to “sculpt” columnar thin film microstructure into desired forms ranging from zigzag shaped to helical to four-sided “square” helical. Computer control of substrate motion was used to accurately position the substrate and to achieve the desired film structures. The growth mechanics of this novel thin film deposition technique are investigated with density measurements, scanning electron microscopy analysis, and measurements of effective refractive index. Adatom diffusion and atomic shadowing are the dominant growth mechanisms with glancing angle deposition conditions creating extreme shadowing. With controlled rotation of the substrate about two axes during deposition, a dense capping layer can be produced on top of the porous sculptured films. The success of the capping process was found to be strongly dependent on the technique used, with an exponential decrease (θ∝[1−A⋅eB⋅t]) with time of incident flux angle found to be the best to reduce filling of the porous film and fracturing of the capping film. The GLAD technique was found to have potentially promising application in optical, biological, and chemical devices and materials.

Control over the orientational order of liquid crystals (LCs) is critical to optical switching and display applications. Porous polymer networks have been used to in¯uence the orientation of embedded chiral liquid crystals 1 , yielding for example re¯ective displays. Here we show that inorganic ®lms with a porous structure engineered on the submicrometre scale by glancingangle deposition 2,3 can be used to control the orientation of LCs impregnated into the voids. The inorganic material contains helical columns that orient rod-like nematic LCs into a phase similar to a chiral nematic 1,4 but with direct control of the local molecular arrangement (for example, the helical pitch) imposed by the inorganic microstructure. We also show that reactive LC molecules in this composite material can be crosslinked by photopolymerization while retaining the imposed structure.Thin ®lms deposited at an oblique angle onto rotating substrates were ®rst investigated in 1959 5 , and were found to display optical activity at one optical wavelength. In 1992, Azzam 6 described a number of optical properties and devices that might be expected to result from thin ®lms with a helical variation in optical anisotropy, based on oblique deposition (see, for example, refs 7, 8) onto rotating substrates. Robbie and Brett 9 found in 1994 that porous ®lms could be fabricated with submicrometre control of the constituent columnar structure. With motivation from theoretical investigations by Lakhtakia and Weiglhofer 10 , we then fabricated thin ®lms with porous helical structures and demonstrated optical activity over a range of optical wavelengths 11±13 . The ®lms exhibit optical rotation and circular dichroism as would be predicted from comparisons with other chiral systems, including isotropic chiral mediums such as solutions of chiral molecules 14 , and chiral LCs 15 . This technique, which we named glancing-angle deposition (GLAD), was then used to produce a wide range of porous thin®lm structures with various materials 2,16 , was expanded to allow greater structural control 3 , and was investigated for use with sputtered ®lms 17 .Liquid crystals embedded in porous networks have been studied extensively in recent years because of their important present role, and promising future, in electro-optic switching and display technologies 1 . Con®ning LCs in small-scale porous structures signi®cantly affects the molecular ordering, and response to external ®elds, of the LC molecules, allowing electro-optic properties to be tailored. In most of this work, LCs are con®ned to organic polymeric networks formed either by phase separation or by emulsi®ca-tion. Inorganic porous networks, such as porous aerogels, Anopore membranes (aluminium oxide membranes containing cylindrical honeycomb pores) and porous glasses, have also been investigated. Twisted orientational structures have been observed in LCs con®ned in submicrometre spherical 18 and cylindrical 19 cavities, but elastic energy prevents multiple rotations of the molecular helix without adding chira...

Microstructure and optical properties of submicron porous silicon thin films grown at low current densitiesAn evaporation process has been developed for depositing highly porous insulator or metal films with densities as low as 15% of bulk. The process utilizes either multiple evaporation sources or substrate movement to provide a symmetrical but very oblique ͑Ͼ80%͒ flux incident on the substrate. Extreme self-shadowing produced a vertical columnar microstructure consisting of isolated and evenly spaced columns including a unique zigzag structure in a number of insulator films. Features of the film are often anisotropic, leading to conductivity differences of as much as a factor of two along perpendicular axes in the plane of the film surface. The direction of anisotropic growth was observed to switch orientation as the incident flux angle was increased to very oblique, beyond approximately 80°. A line segment simulator incorporating ballistic deposition and minimization of chemical potential has been used to aid in the understanding of the growth mechanisms of these films and to optimize the evaporation process. The simulator helped to confirm that self-shadowing was the dominant mechanism in this porous structure formation.

Superconductivity in the simple elements is of both technological relevance and fundamental scientific interest in the investigation of superconductivity phenomena. Recent advances in the instrumentation of physics under pressure have enabled the observation of superconductivity in many elements not previously known to superconduct, and at steadily increasing temperatures. This article offers a review of the state of the art in the superconductivity of elements, highlighting underlying correlations and general trends.

An ultrahigh vacuum apparatus for the deposition of thin films with controlled three-dimensional nanometer-scale structure is described. Our system allows an alternate, faster, cheaper way of obtaining nanoscale structured thin films when compared to traditional procedures of patterning and etching. It also allows creation of porous structures that are unattainable with known techniques. The unique feature of this system is the dynamic modification of the substrate tilt and azimuthal orientation with respect to the vapor source during deposition of a thin film. Atomic-scale geometrical shadowing creates a strong directional dependence in the aggregation of the film, conferring control over the resulting morphological structure on a scale of less than 10 nm. Motion can create pillars, helixes, zig-zags, etc. Significant features of the apparatus include variable substrate temperature, insertion and removal of specimens from atmospheric conditions without venting the deposition system, computer controlled process parameters, and in situ analysis capabilities. The deposition system was successfully employed for the fabrication of a variety of nanostructured thin films with a wide range of potential applications.