Russell F. Pinizzotto

Dictation of the shape of mesoscale semiconductor nanoparticle assemblies by plasmid DNA

We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455‐basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self‐assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates.

The formation and growth of intermetallics in composite solder

The formation and growth of intermetallics at the solder/substrate interface are factors affecting the solderability and reliability of electronic solder joints. This study was performed to better understand the diffusion behavior and microstructural evolution of Cu−Sn intermetallics at the composite solder/copper substrate interface for eutectic solder and solder alloys containing particle additions of Cu, Cu3Sn, Cu6Sn5, Ag, Au, and Ni. Annealing temperatures of 110 to 160°C were used with aging times of 0 to 64 days. The copper-containing composite solders generally formed thinner Cu6Sn5 layers, but thicker Cu3Sn layers than were formed by the eutectic solder alone. These copper-containing additions, therefore, resulted in increased activation energies for Cu6Sn5 formation and decreased activation energies for Cu3Sn formation as compared to the eutectic solder. The activation energy for Cu3Sn formation decreased relative to eutectic solder for silver and gold composite solders even though less Cu3Sn was formed at the substrate interface. Nickel and palladium drastically reduced the Cu3Sn thickness and increased the Cu6Sn5 thickness. However, the Cu6Sn5 contained a substantial volume fraction of voids close to the copper substrate. We propose two mechanisms to explain the effects of the copper-containing and silver particles on the kinetics of intermetallic formation. First, the particles act as tin-sinks which remove tin from the solder and decrease the amount of tin available for reaction at the solder/substrate interface. Second, the particles reduce the cross-sectional area available for tin diffusion, which also reduces the amount of tin available at the interface for reaction.

Porosified Silicon Wafer Structures Impregnated With Platinum Anti-Tumor Compounds: Fabrication, Characterization, and Diffusion Studies

In this work, the incorporation and characterization of cis-platin (cis-diammine dichloroplatinum(II)), carbo-platin [cis-diammine(cyclobutane-1,1-dicarboxylato] platinum(II)), and Pt(en)Cl2 (ethylenediamminedichloro platinum(II)) within layers of calcium phosphate on porous Si/Si substrates are described. These materials have been characterized by scanning electron microscopy, secondary ion mass spectrometry, and X-ray energy dispersive spectroscopy. The diffusion of platinum species from the doped calcium phosphate layers has also been investigated by UV-visible absorption spectrometry and inductively-coupled plasma spectroscopy. The influence of initial platinum concentration, the impact of thermal annealing of the calcium phosphate/porous Si/Si matrix, as well as the effect of varying the ligand coordination sphere of the Pt complex on its ability to be delivered to the surroundings have also been analyzed. For the case of cis-platin, it is found that increasing the concentration of platinum complex in the electrolyte during cathodic growth of calcium phosphate results in a relatively greater concentration of Pt incorporated into the calcium phosphate layers and a larger amount of Pt which subsequently can be delivered to the surrounding medium upon exposure to solvent.

Size control of erbium-doped silicon nanocrystals

This work describes the effects of pyrolysis oven length and erbium precursor on the preparation of discrete erbium-doped silicon nanoparticles. These doped nanoparticles were prepared by the co-pyrolysis of disilane and the volatile complex Er(tmhd)3 (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionato). The particle sizes and size distributions were determined using high resolution and conventional transmission electron microscopy. Erbium-doped silicon nanoparticles exhibit a selected area electron diffraction pattern consistent with the diamond cubic phase and a distinctive dark contrast in the transmission electron microscope. The presence of erbium is confirmed by x-ray energy dispersive spectroscopy. In general, the mean diameter of the individual nanoparticles increases as the length of the pyrolysis oven used during their preparation is increased.

Cross-Sectional Tem Studies of Barium Strontium Titanate Deposited on Silicon by Pulsed Laser Ablation

Barium strontium titanate films were deposited onto silicon substrates using pulsed laser ablation deposition. The films were characterized using conventional and high resolution cross-sectional TEM. It was found that the grains were columnar with an average width of approximately 23 nm. An amorphous interfacial layer formed between the Si and BST in all cases. The interfacial layer thickness increased as the sample exposure to O 2 increased. TiSi 2 was also observed in all the films, although its location at the interface was not directly verified. There are no systematic effects of O 2 overpressure on either the film thickness or film microstructure. However, the film which was fabricated with the greatest exposure to O 2 may contain Ti x O y , and contains more equiaxed grains than the other samples. An interfacial layer was also observed at the Au-Pd/BST interface in a metal/ferroelectric/silicon capacitor. The significance of the results is the observation that BST may never come in direct contact with either capacitor electrode, which may explain why the fatigue behavior and electrical characteristics of ferroelectric capacitors depend so strongly on the interfaces.

Effects of local ambient atmosphere on the stability of electroluminescent porous silicon diodes

In this work, the influence of surrounding ambient atmosphere on the stability of electroluminescent (EL) porous Si (PS) diodes is examined. We have fabricated electroluminescent porous Si layers from anodic oxidation of (1) epitaxially grown p‐type layers on n‐type Si substrates; (2) n‐type substrates with Au/Pd contacts; (3) p‐type substrates with Au/Pd contacts. These structures are characterized using photoluminescence (PL), EL, and infrared (IR) spectroscopies, as well as scanning electron microscopy (SEM). In the case of the porous Si structures fabricated from p‐n junctions, such structures yield orange emission with maxima near 620 nm upon the application of moderate applied voltages (3–7 V). For each type of diode, it is found that in strong oxidizing environments, EL intensity degrades completely within 30 min; in contrast, the integrated intensity remains essentially unchanged in the same time frame in the presence of a vigorous flow of inert gases such as nitrogen and argon. Infrared spectrosc...

The observation of silicon nanocrystals in siloxene

This article discusses the observation of silicon nanocrystals in siloxene using high resolution transmission electron microscopy.

Formation of rare‐earth oxide doped silicon by spark processing

In this work, we report a method for the incorporation of rare‐earth oxides onto silicon surfaces. This process uses a high‐energy dc spark to convert salts of rare‐earth ions such as europium and erbium to the corresponding oxide phase(s) with concomitant formation of a porous layer. Scanning electron micrographs of the silicon substrate show an irregular, pitted surface morphology for those areas exposed to spark processing. Photoluminescence, infrared spectroscopy, and electron microscopy of the spark‐processed regions of the Si substrate are clearly consistent with the formation of the desired luminescent oxide phase.

Scanning tunneling microscopy current–voltage characteristics of carbon nanotubes

Scanning tunneling microscopy (STM) has been used to obtain images and current–voltage (I–V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STM I–V curves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer‐size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images.

Microstructural analysis of nickel silicide formed by nickel/silicon‐on‐oxide annealing

Microstructures of crystalline nickel disilicide thin films formed on SIMOX (separation by implantation of oxygen) Si‐on‐oxide substrates were analyzed using electron microscopy. The samples were examined both in the top‐down plane‐view orientation and in cross section along a [110] direction. The nickel silicide films were formed through thermal reaction of metallic nickel deposited on the top Si layer of the SIMOX substrates. The results were compared with epitaxial NiSi2 layers grown on single crystal silicon substrates. Twin boundaries were observed at the silicide/oxide interface. The oxide layer acts as a diffusion barrier which prevents nickel from diffusing into the substrate resulting in uniform NiSi2 on a SiO2/Si substrate.