Christopher R. Perrey

Superhard silicon nanospheres

Abstract Successful deposition and mechanical probing of nearly spherical, defect-free silicon nanospheres has been accomplished. The results show silicon at this length scale to be up to four times harder than bulk silicon. Detailed measurements of plasticity evolution and the corresponding hardening response in normally brittle silicon is possible in these small volumes. Based upon a proposed length scale related to the size of nanospheres in the 20– 50 nm radii range, a prediction of observed hardnesses in the range of 20– 50 GPa is made. The ramifications of this to computational materials science studies on identical volumes are discussed.

Plasma synthesis of single-crystal silicon nanoparticles for novel electronic device applications

Single-crystal nanoparticles of silicon, several tens of nanometres in diameter, may be suitable as building blocks for single-nanoparticle electronic devices. Previous studies of nanoparticles produced in low-pressure plasmas have demonstrated the synthesis of nanocrystals 2–10 nm diameter but larger particles were amorphous or polycrystalline. This work reports the use of a constricted, filamentary capacitively coupled low-pressure plasma to produce single-crystal silicon nanoparticles with diameters between 20 and 80 nm. Particles are highly oriented with predominantly cubic shape. The particle size distribution is rather monodisperse. Electron microscopy studies confirm that the nanoparticles are highly oriented diamond-cubic silicon.

Synthesis of highly oriented, single-crystal silicon nanoparticles in a low-pressure, inductively coupled plasma

Single-crystal nanoparticles of silicon, several tens of nm in diameter, may be suitable as building blocks for single-nanoparticle electronic devices. Previous studies of nanoparticles produced in low-pressure plasmas have demonstrated the synthesis nanocrystals of 2–10 nm diameter but larger particles were amorphous or polycrystalline. This work reports the use of an inductively coupled low-pressure plasma to produce single-crystal silicon nanoparticles with diameters between 20 and 80 nm. Electron microscopy studies confirm that the nanoparticles are highly oriented diamond-cubic silicon.

An Energy Balance Criterion for Nanoindentation-Induced Single and Multiple Dislocation Events

Small volume deformation can produce two types of plastic instability events. The first involves dislocation nucleation as a dislocation by dislocation event and occurs in nanoparticles or bulk single crystals deformed by atomic force microscopy or small nanoindenter forces. For the second instability event, this involves larger scale nanocontacts into single crystals or their films wherein multiple dislocations cooperate to form a large displacement excursion or load drop. With dislocation work, surface work, and stored elastic energy, one can account for the energy expended in both single and multiple dislocation events. This leads to an energy balance criterion which can model both the displacement excursion and load drop in either constant load or fixed displacement experiments. Nanoindentation of Fe-3% Si (100) crystals with various oxide film thicknesses supports the proposed approach.

Experimental investigations into the formation of nanoparticles in a∕nc-Si:H thin films

Hydrogenated amorphous silicon thin films with nanocrystalline silicon inclusions (a∕nc-Si:H) have received considerable attention due to reports of electronic properties comparable to hydrogenated amorphous silicon (a-Si:H) coupled with an improved resistance to the light-induced formation of defects. In this study, a∕nc-Si:H thin films are synthesized via radio-frequency plasma-enhanced chemical-vapor deposition with helium and hydrogen diluted silane. The plasma conditions were chosen to simultaneously deposit both Si nanocrystallites and an amorphous silicon matrix. This structure has been confirmed by transmission electron microscopy (TEM) studies. Both plasma electronic diagnostics and TEM image analysis of a∕nc-Si:H films deposited with and without a temperature gradient between the capacitively coupled reactor electrodes suggest nanoparticle formation in the plasma, as opposed to solid-state nucleation of the nanoparticles in the film. Optical-absorption studies of the a∕nc-Si:H films indicate ele...

Using the FIB to characterize nanoparticle materials

In the 1–100‐nm size regime, the properties of materials can differ significantly from those of their bulk counterparts. The present study applies the focused ion beam (FIB) tool to the characterization of nanoscale structures for scanning and transmission electron microscopy. The strength of this method is its ability to manufacture samples that cannot be produced using traditional means. The films of nanoparticles examined here are examples of such systems; the films are found to be not fully dense, composed of chemically heterogeneous areas and mechanically different from the substrate. Distinct advantages of the application of the FIB for characterization of nanoscale structures are highlighted for several nanoparticle structures. This successful application of FIB techniques provides a pathway to integrate the study of nanoscale production techniques and their resulting structure–property relationships.

Characterization of Mechanical Deformation of Nanoscale Volumes

Abstract : The mechanical properties of nanoscale volumes and their associated defect structure are key to many future applications in nanoengineered products. In this study techniques of mechanical testing and microscopy have been applied to better understand the mechanical behavior of nanoscale volumes. Nanoindentation has been used to investigate important mechanical material parameters such as the elastic modulus and hardness for single nanoparticles. New sample preparation methods must be developed to allow the necessary TEM characterization of the inherent and induced defect structure of these nanoparticles. Issues of chemical homogeneity crystallinity and defect characteristics at the nanoscale are being addressed in this study. This integration of investigative methods will lead to a greater understanding of the mechanical behavior of nanostructured materials and insights into the nature of defects in materials at the nanoscale.

Microscopy of nanoparticles for semiconductor devices

The miniaturization of semiconductor devices brings the impending need for nanoscale components for which nanoparticles of semiconductor materials are uniquely suited. However, their small length scales are known to produce properties unique from those of their bulk form. Full characterization of the nanoparticles suggested for use in devices becomes imperative. This study investigates silicon nanocubes prepared by a constricted-mode capacitive silane-argon plasma. These cubes have been proposed as key components in nanoscale transistors. Various techniques are used to examine these particles and their implementation in a potential device is explored.

Defects and interfaces in nanoparticles

As the dimensions of semiconductors are reduced into the nanoscale, the defects and interfaces that may be present have taken on new importance. In many cases, these nanoscale materials may have properties that are unique to their size and morphology. Using the transmission electron microscope, observations of these interfaces can shed light on the possible formation processes undergone by the nanoparticles and lead to further advances in nanoscale semiconductor manufacturing.

The Effects of Processing on the Morphology of Nanoparticles

One of the major challenges confronting the utilization of nanoparticles in industrial and social applications is that of producing the nanoscale materials. Of the methods of manufacturing nanoscale materials, processes involving plasmas have been shown to be cost-effective and versatile in the production of chemically diverse material. Using transmission electron microscopy, individual nanoparticles produced by a thermal plasma-based production method have been examined. The observations of these studies imply that the thermal history of the nanoparticles during formation is of great importance in the determination of the resulting nanoparticle morphology. Such results have the potential to enable the manufacturing of nanoparticles of a specific size and shape from plasmas.