Measurements of optical properties of epitaxially grown CdMnTe quantum dots are presented. Magnetic ions are incorporated into the structure by passivating the substrate surface with Mn prior the quantum dot deposition. As expected, the intensity of intra-Mn transition increases with the time of manganese passivation. The formation of magnetic quantum dots is evidenced by presence of single emission lines in the micro-photoluminescence spectrum. The width of single dot emission lines is much broader than observed for non-magnetic quantum dots. The broadening is caused by thermal fluctuations of magnetization in quantum dots. Resonant spectroscopy results indicate that the exciton-optical phonon scattering is the main energy relaxation mechanism in these structures. The measurements suggest that post-growth thermal processing offers the possibility of tuning the magnetic properties of these structures.

SiGe quantum devices were demonstrated by AFM oxidation and selective wet etching with features size down to 50 nm. To passivate the devices and eliminate the interface states between Si/SiO2, low temperature regrowth of epitaxial silicon over strained SiGe has been tested. The silicon regrowth on Si0.8Ge0.2 was done by rapid thermal chemical vapor deposition (RTCVD) at 700 °C using a hydrogen pre-cleaning process at 800 °C and 10 torr. SIMS analysis and photoluminescence (PL) of strained SiGe capped with epitaxial regrown silicon show a clean interface. Nano-gaps between doped SiGe filled and overgrown with epitaxial silicon show an electrical insulating property at 4.2 K.

We have fabricated PbS particles in glass of average size from 1.2 nm to 3 nm. This allows us to tune the energy of the lowest electron-hole pair transition from 1.7 eV to 0.8 eV respectively. Optical absorption spectra show a pronounced quantum peak, implying a narrow size distribution. We have performed pump-probe spectroscopy where the probe is cw and the pump is nanosecond; this allows us to investigate a wide time scale. We have observed bleaching of the lowest quantum peak with lifetimes of ∼2 microseconds. We interpret this in terms of trapped carriers. Phenomenological description of observed effect is also presented.

Nanocrystalline diamond thin films of sub-micron thickness have been covalently modified with DNA oligonucleotides. Quantitative studies of hybridization of surface-bound oligonucleotides with fluorescently tagged complementary and non-complementary oligonucleotides were performed. The results show no detectable nonspecific adsorption, with extremely good selectivity between matched and mismatched sequences. Impedance spectroscopy measurements were made of DNA-modified boron-doped nanocrystalline diamond films. The results show that exposure to non-complementary sequences induce only small changes in impedance, while complementary DNA sequences produce a pronounced decrease in impedance. The combination of high stability, selectivity, and the ability to directly detect DNA hybridization via electrical means suggest that diamond may be an ideal substrate for continuously-monitoring biological sensors.

Today, the overall performance of a multi-chip computing system is limited by the interconnection delay between chips. Conventional interconnects based on metal lines are expected to cause unmanageable problems with speed and power dissipation. Optical interconnects provide a solution to these problems. However, the low quantum efficiency associated with radiative recombination in silicon has so far prevented the demonstration of a practical laser. Recently stimulated emission has been demonstrated in Si nanocrystals prepared by ion-implantation. The reported material gain is high enough to realize a practical Si based laser. However, the optical filling factor in these samples was less than 10% due to the poor wave guiding nature of these structures.

In this work, we explore a possible way to achieve optical gain in nanocrystalline silicon superlattices. The samples are produced by growing alternating layers of amorphous silicon and SiO2 and then using a two step crystallization method to transform each amorphous silicon layer into a high density array of silicon nanocrystals having identical size. The waveguide structure is formed by sandwiching the superlattice between cladding layers. To measure optical gain we use the variable stripe length method where the amplified spontaneous emission emitted from the edge is measured as a function of the excitation length. Tuning from loss to gain was observed by just varying the pump power.

Exposure to ammonia (NH3) increases the dark current (DC) in porous silicon (PS), but evaporated selenium (Se) deposited on PS decreases DC. Photoluminescence (PL) measurement shows that there are two types of centers. PL in one region of PS (Peak ∼ 800nm) initially increases with the NH3 exposure and then decreases. But the PL from another region of PS has a peak at ∼ 780nm and it decreases continuously with the NH3 exposure. Dipping PS in water and drying in air shifts the PL peak at 800 nm to 744 nm. Atomic Force Microscopy (AFM) shows that the as prepared sample has wires of diameters 2.4nm, 3.4nm, 4.6nm and bigger. However, in the AFM images of the water treated sample the wires of diameters 3.4nm and 4.6nm are absent. The PL results are explained using the AFM data and the John-Singh model of quantum confinement.

Optical spectroscopy and Scanning Tunneling Microscopy are used to study the size and shape dependence of the electronic states in CdSe quantum rods. The quantum rods were grown using colloidal chemistry synthesis methods, with good control over size and size distribution. Samples having average rod dimensions ranging from 10 to 60 nm in length and 3.5 to 7 nm in diameter, with aspect ratios varying between 3 to 12, were investigated. Both optical (at 10 K) and tunneling (at 4.2 K, on single rods) spectra show that the level structure depends primarily on the rod diameter and not on length. With increasing diameter, the band gap and the excited state level spacings shifted to the red. The level structure is assigned using a multi-band effective-mass model, showing relatively good agreement with experiment. We shall also discuss the effect of single electron charging on the tunneling spectra, possibly reflecting the quantum rod level degeneracy.

We employ the method of phase-modulated KrF excimer pulsed laser interference crystallization to fabricate nanometer-sized crystalline silicon (nc-Si) with the two-dimensional (2D) patterned distribution within the ultra-thin a-Si:H single-layer. The local crystallization occurs after interference laser irradiation under proper energy density. The results of atomic force microscopy, Raman scattering spectroscopy, cross-section transmission electron microscopy and scanning electron microscopy demonstrate that Si nano-crystallites are formed within the initial a-Si:H single-layer, selectively located in the discal regions with the diameter of 350 nm and patterned with the same 2D periodicity of 2.0 μm as the phase-shifting grating. The results show that the present method can be used to fabricate patterned nc-Si films for device applications.

Nakamura and co-workers were first to report the observation of spontaneously formed In-rich clusters in InGaN quantum wells (QW), using transmission electron microscopy (TEM) [1,2]. Some of the present authors have argued that the exceptional optical efficiency of nitride devices is due to the presence of nearly pure InN QD which form accidentally during crystal growth [3]. Pure InN QD with very small radius would emit light in the required spectral region, under the opposing effects of intrinsic electric fields and quantum confinement [4]. We have recently used extended X-ray absorption fine stucture to examine nanostructure [5]of molecular beam epitaxial (MBE) quantum boxes (QB), and photoluminescence excitation spectroscopy to examine their optical properties [6]. As revealed by AFM, QB are densely packed mesoscopic structures, 10–40 nm wide and 2–3 nm high. Our analysis of the QB EXAFS shows that the filling factor is of order 1%: each QB therefore contains a single QD. The optical evidence suggests that InN dots may be cubic. In contrast, TEM shows that QD in thick epilayers are sparsely distributed [7]. We re-examine recent TEM data on QW in the light of these results.

We report a successful unification of standard lithographic approaches (top down), anisotropic etching of atomically smooth surfaces, and controlled crystallization of silicon quantum dots (bottom up) to produce silicon nanoclusters at desired locations. These results complement our previous demonstration of silicon nanocrystal uniformity in size, shape, and crystalline orientation in nanocrystalline silicon (nc-Si)/SiO2 superlattices, and could lead to practical applications of silicon nanocrystals in electronic devices. The goal of this study was to induce silicon nanocrystal nucleation at specific lateral sites in a continuous amorphous silicon (a-Si) film. Nearly all previous studies of silicon nanocrystals are based on films containing isolated nanocrystals with random lateral position and spacing. The ability to define precise two-dimensional arrays of quantum dots would allow each quantum dot to be contacted using standard photolithographic techniques, leading to practical device applications like high-density memories. In this work, a template substrate consisting of an array of pyramid-shaped holes in a (100) silicon wafer was formed using standard microfabrication techniques. The geometry of this substrate then influenced the crystallization of an a-Si/SiO2 superlattice that was deposited on it, resulting in preferential nucleation of silicon nanoclusters near the bottom of the pyramid holes. These clusters are clearly visible in transmission electron microscopy (TEM) images, while no clusters have been observed on the planar surface areas of the template. Possible explanations for this selective nucleation and future device structures will be discussed.

The time-dependent diffusion of particles to an absorbing sphere is investigated with three random walk models. The first uses consecutive independent particles and finds the capture time distributions are exponential for a range of values of the surface absorption probability. The next two models are of the ensemble variety and assume that only a finite number of particles may be absorbed by the sphere. These models investigate depletion effects and concentration dependence. The latter is probed by varying the initial number of diffusing particles. It is found

Three different types of carbon nanotubes being considered for bio-recognition experiments were studied using resonance Raman spectroscopy. Raman spectroscopy, taken using several laser excitation energies, has been shown to provide an effective characterization tool for these carbon nanotubes. The technique yields structural information that both complements and corroborates structural information obtained using electron microscopy techniques, such as TEM, SEM, and AFM.

A comparative study of nanocrystalline silicon thin films grown on 25 nm thick catalyzing metals by dc magnetron sputtering from a highly doped Si target has been performed. In our previous study, the growth of Si was catalyzed by the silicide reactant from sputtered Si and Ni. These new experiments compared the effect of two types of catalyzing metals, Ni and Co. The structural and electrical characteristics of nano-Si were examined by scanning electron microscopy (SEM), cross-section SEM (XSEM), transmission electron microscopy (TEM), four-point-probe measurement and Schottky contact I-V measurement. The SEM and XSEM revealed that, for both catalyzing metals, the nano-Si thin films have columnar nano-grains with length of 500 nm in the vertical direction. However, the diameter of grains strongly depends on the catalyzing metals. For Co, the nano-Si grains had a typical diameter of 30 nm, while for Ni, the grains were much larger. TEM analysis showed that this difference in grain size begins at the initial growth stage. In the later-on growth, the Si grains mainly grow in a vertical direction instead of a lateral direction. This implies that the dimensions of Si nanostructures are strongly determined by the initially formed metal silicide nanoparticles. The current-voltage curve of a fabricated Al Schottky diode on P-type Co catalyzed nano-Si exhibited good rectifying characteristics. The dopant has been naturally synthesized in the Si nanocrystals during the growth of nano-Si by using a doped sputtering target. The above measured electrical properties show that metal induced grown nanocrystalline Si is applicable to various electronic and photonic devices.

We investigate the strength of the coupling of the electronic states with the electromagnetic field in semiconductor nanospheres, taking into account the retardation effect. We show that the coupling strength is particularly strong: the bulk properties are so enhanced that the radiative decay time can reach some 30 picoseconds for quantum dots sizes of some 30 nm.

Tubular Al-doped ZnO particles were prepared by homogeneous precipitation in the mixed solutions of Al(NO3)2, Zn(NO3)2, sodium dodecyl sulfate (SDS) surfactant and urea. At the molar ratio of Metal ions(Mt) : SDS : urea : H2O is 1 : 2 : 20 : 60, tubular products formed by heating at 80°C for 12 h. Plate like ZnO particles were obtained at Mt : SDS : urea : H2O = 1 : 2 : 10 : 60 or 1 : 1 : 20 : 60. The diameter of typical ZnO tube is ca.100 nm, and the length of tube is about 600nm (aspect ratio = 6). The relative surface area of tubular Al-doped ZnO is ca. 40.2 m2/g. The photo-decomposition rate of NO3- ions using tubular Al-doped ZnO particles was higher than standard TiO2 photo-catalysts (P-25) by irradiation >290nm light in 10mM KNO3-10vol%EtOH solutions at 30°C. The obtained materials showed DC conductive properties as compacted substrate by sintered at 400°C.

Efforts to produce stable, derivatized porous silicon have yielded a number of chemical methods capable of functionalizing this interesting material with organic monolayers. Hydride-terminated porous silicon substrates react with alkenes and alkynes in the presence of dilute triphenylcarbenium salt solutions to respectively produce alkyl- and alkenyl-functionalized materials. Characterization by transmission FTIR and solid-state NMR suggests the formation of highly stable silicon-carbon bonds to yield covalently bound organic moieties. Porous silicon passivated in this fashion exhibits a greater resistance than that of the native material to chemical degradation, indicating that the organic functionalities may serve to sterically shield the nanocrystallites from nucleophiles. Hydrosilylation is proposed to proceed via hydride abstraction from the substrate followed by electrophilic attack by the subsequent species upon the alkene/alkyne, a mechanism previously hypothesized for the formation of stabilized β-silyl carbocations. The reaction is tolerant of a variety of substrate functional groups and native porous silicon surfaces but depends markedly upon the identity of the salt counteranion, among other solution parameters.

The dependence of characteristics of multiwalled carbon nanotubes (MWCNT) on the microstructure of cobalt catalysts are intensively investigated by high-resolution transmission electron microscopy (HREM). The cobalt catalysts are prepared by either molecule beam epitaxy (MBE) or by DC magnetron sputtering, followed by MWCNT growth by microwave plasma CVD. The MBE-grown Co thin films consist of large epitaxial grains, whereas the Co nanoparticles of FCC or HCP crystal structures can be directly grown on Si(001) substrates by sputtering. Various HREM technologies are applied to completely characterize the microstructures of those Co catalysts and MWCNT. The results reveal that the morphology and microstructures of MWCNT are greatly controlled by the characteristics of Co catalysts. Better quality of carbon nanotube can be grown by FCC cobalt rather than HCP cobalt. The different effects of cobalt catalysts on MWCNT are discussed in this paper.

Nanocrystalline silicon (n-Si) is formed in a silicon dioxide thin-film matrix by ion implantation followed by thermal annealing in forming gas at 1100 °C for 1 hour. The ion implantation is performed using multiple implants with different implantation energies and doses to create a quasi-flat concentration of silicon atoms throughout the silicon dioxide film. These samples are then analyzed using spectroscopic ellipsometry to characterize their linear optical properties. Implantations with small doses (5 × 1020 Si atoms/cm3) increase the refractive index by a small amount (δn∼0.006 at 600nm), while implantations with moderate dose (5 × 1021 Si atoms/cm3) have a larger increase in refractive index and exhibit optical absorption above ∼1.9 eV (650 nm).

A theoretical model for the electronic structure and transport properties of superlattice (SL) nanowires is presented, based on the electronic tunneling between quantum dots. Due to the periodic potential perturbation, SL nanowires exhibit unusual features in the electronic density of states that are absent in homogeneous nanowires. Transport property calculations of PbSe/PbS SL nanowires are presented, showing improved thermoelectric performance compared to homogeneous nanowires because of a lower lattice thermal conductivity and an enhanced Seebeck coefficient, indicating that SL nanowires are promising systems for thermoelectric applications.

We have succeeded in generating highly charged excitons in InAs self-assembled quantum dots by embedding the dots in a field-effect heterostructure. We discover an excitonic Coulomb blockage: over large regions of gate voltage, the exciton charge remains constant. We present here a summary of the emission properties of the charged excitons.