We propose a probe storage using a carbon film deposited by electron cyclotron resonance plasma (ECR) sputtering as a recording material. Such storage has a potential to achieve an electrical data storage with small writing voltage and ultra high recording density due to super hardness and large electric conductivity of the ECR sputtered carbon (ECR-C). The ECR-C film is deposited on a silicon substrate covered by a thermal oxide. Recording experiments are performed by a conductive atomic force microscope with a gold coated tip. The electrical resistance of the film surface is decreased locally by applying voltages smaller than 2V between the film and the tip. The resistance decrease of the film by the voltage application are caused by a thermal reaction due to Joule's heat at contact portion of the film with the tip. Data bits with size of about 70nm can be formed by applying a pulse row as a writing voltage.

High quality growth of InSe on Si(111) was achieved by insertion of GaSe buffer layer. Rhombohedral polytypes were formed in both the InSe and GaSe layers. Twinning and stacking disorder was often detected in these materials due to their layered structure. Moreover, in samples with a thin GaSe layer, strong interdiffusion of indium into the GaSe layer was detected that resulted in the formation of an InxGaySe phase. The dominant threading defects present in these InSe/GaSe heterostructures were screw dislocations, which may act as nonradiative recombination centers.

In this work crystallization of an InSbTe alloy in Blu-ray Disc rewritable (BD-RE) media is studied using Transmission Electron Microscopy (TEM). Two different crystalline states can be formed in a thin InSbTe layer depending on crystallization conditions. These two states give rise to different reflectivity levels of the recording stack as well as a different level of normalized media noise. It is shown that the two states correspond to the same phase (R 3 m), but that they show clear differences in morphology as well as in texture.

We used scanning nonlinear dielectric microscopy to observe the position of electrons and holes in the gate SiO2-Si3N4-SiO2 (ONO) film of metal-oxide-nitride-oxide semiconductor type Flash memory. The electrons were detected in the Si3N4 part of the ONO film. The holes, on the other hand, were found in the Si3N4 film as well as in the bottom SiO2 film.

The recent research works of optical properties and crystallization kinetics of phase change Ge-Sb-Te-(N) alloy by using ellipsometry are reviewed.

The complex refractive index spectra of phase-change Ge2Sb2+xTe5 thin films and those of the nitrogen Ge2Sb2Te5 thin films have been determined.

The crystallization behavior of amorphous Ge2Sb2Te5 thin films investigated by in situ ellipsometry revealed that the crystallization process of Ge2Sb2Te5 near 140°C is a two-step process. The kinetic exponent of the Johnson-Mehl-Avrami equation was about 4.4 for the first stage and 1.1 for the second stage. Ex situ study confirmed the cascaded crystallization behavior of phase-change Ge2Sb2Te5 films.

A passive type single wavelength ellipsometer adopting a DOAP (division-of-amplitude photopolarimeter) configuration with nanosecond time resolution is developed to monitor the phase transformation of Ge2Sb2Te5 caused by a high power nanosecond laser pulse in real time. The two-step process - the fast nucleation-dominant stage followed by the slow anomalous grain growth stage is confirmed.

Based on the recent analysis of the ellipsometric isotherm at moderately elevated temperature, we found for the first time that the fast nucleation dominant crystallization of Ge2Sb2Te 5 can be better explained by a modified JMA equation that illustrates the nucleation dominated process where the creation rate of a new nucleus is proportional to the density of preexisting nuclei and growth rate is negligible.

This paper describes a basic new scientific and technological approach for information and computing use. It is based on Ovonic cognitive devices that utilize an atomically engineered Ovonic chalcogenide material as the active medium. We demonstrate how such a device possesses many unique functions including an intrinsic neurosynaptic functionality that permits the processing of information in a manner analogous to that of biological neurons and synapses. Our Ovonic cognitive devices can not only accomplish conventional binary computing, but are capable of non-binary generation of information, storage, encryption, higher mathematics, modular arithmetic and factoring. Uniquely, almost all of these functions can be accomplished in a single nanosized device. These devices and systems are robust at room temperature (and above). They are non-volatile and also can include other volatile devices such as the Ovonic Threshold Switch and Ovonic multi-terminal threshold and memory devices that can replace transistors.

VO2 is a material with reversible thermo-chromic properties. The reversible phase transition of a strain-free single-crystalline VO2, at a transition temperature (Tt) 68°C, is accompanied with changes in crystal structure, optical and electrical properties. With different processing conditions during thin film deposition, different transmittance loops will be resulted upon thermal cycling. The residual stress of the thin films with poor crystallinity, as determined from X-ray diffractometry, is found to be an important factor responsible for the Tt that increases with increasing residual stress. Residual stress affects the hysteresis span of the transmittance loop. The relationship between residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen under the residual stress are also delineated.

Manganese doped perovskites are promising materials for non-magnetic data storage. Systems with low doping concentration, such as Mn:YAlO3 are high-quality optical crystals, demonstrating significant photorefractive effect. Optically and electrically induced quasi-permanent change in low-field conductivity was observed in the materials with high concentration of manganese such as single crystals and films of LaGa1−xMnxO3 (x= 0.1–1). These memory effects can last for a long time at room temperature and can be easily erased by heating up to 230 C. We explain our experimental results by photoinduced or thermoinduced local phase transition with the oxidation of Mn ions.

A third order nonlinear optical material, As2Se3 was proposed for super resolution near field structure disk. As2Se3 was deposited by thermal evaporation technique. Composition, phase, surface morphology, linear/non-linear optical properties were obtained from EPMA, XRD, AFM, UV-VIS-NIR spectrophotometer and VASE. As2Se3 thin film showed large non-linear optical characteristics (XR(3) =7.42×10-7 m2/w, γ=1.268×10-5m2/w) and self-focusing phenomenon. Super resolution effects of the As2Se3 thin films were measured by using the laser beam profiler. As a result, recording density can be enhanced by 2.3 times, in case of 350nm As2Se3 thin film was deposited as super-RENS.

The amorphous-to-polycrystal transition has been studied in Ge2+xSb2Te5 (x = 0.0 and 0.5) films through X ray diffraction analysis and in situ electrical measurements. Phase separation has been observed in samples with excess of Ge, which cannot be completely converted into thence phase at temperatures lower than 170 °C.By using in situ transmission electron microscopy, the growth velocity and the nucleation rate in Ge2Sb2Te5 films have been measured at different annealing temperatures. Activation energies of 2.8 eV and 2.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated.

This paper addresses the crystallization of amorphous Sb3.6Te films (40 nm thick) and 5 at.% Ge containing Sb3.6Te films (10, 20 and 40 nm thick) as studied using in-situ annealing in a Transmission Electron Microscope (TEM). These materials show growth-dominated crystallization, in contrast to Ge2Sb2Te5 that shows nucleation-dominated crystallization. Particularly the crystal-growth velocity in these systems is measured as a function of temperature from which the activation energy for growth can be derived. The strong effect of the 5 at.% Ge addition on the total crystallization behavior is revealed: Ge increases the crystallization temperature (from 95 to 150 °C), increases the activation energy for growth (from 1.58 to 2.37 eV), increases the nucleation rate and decreases the growth anisotropy.

Attempts at the practical utilization of Sb-Te based alloys beyond optical data storage have been made recently by employing these materials in both scanning probe type memories, and in electrical memory devices - namely Phase-Change Random Access Memory (PC-RAM). We have developed models to simulate the electrical, thermal, and phase-change characteristics of this important class of material. In this paper we describe the physical basis of our models and present simulation results for different memory configurations and operating conditions.

The electrical induced structural transformation of Ge2Sb2Te5 thin film in phase change memory device was investigated using micro-Raman spectroscopy and transmission electronic microscopy (TEM). Selected area electron diffraction (SAD) pattern showed that the electrical-induced Ge2Sb2Te5 film was crystallized into a face-centered cubic structure. Micro-Raman spectra show that the Ge2Sb2Te5 active layer at the high resistance state exhibited two minor peaks superposed on the broad peak after several switch cycles, which is identical to those of the Ge2Sb2Te5 active layer at the low resistance state. This is most likely due to the accumulation of segregated crystallites. TEM results suggest that the existence of nano-sized nuclei clusters resulted in the reduced resistance for the Ge2Sb2Te5 active layer at the high resistance state after first several switches. The dependence of resistance on the cycle number indicates that the deterioration of the Ge2Sb2Te5 active layer is resulted from the incomplete amorphization process, which is consistent with the micro-Raman results.

This paper discusses a crystallization model that takes difference of covalent bond and ionic bond into consideration. Ionic bond makes crystallization easier than covalent bond because ionic bond is more flexible than covalent bond. The diameter and spaces around large minus-ions should also be taken into consideration. Elements••having electronic negativity far from that of Te or Sb has a tendency to form ionic bonds. For example, Tb and In are considered to make chemical bonds having more ionic characteristics than Ge. In the case of already reported Sn or Bi addition, large ion diameter seems to increase crystallization speed.

Laser initialization of the chalcogenide optical-recording medium Ag-In-Sb-Te is investigated using transmission electron microscopy of the resulting microstructure. Initialization beam power and velocity are varied. The average inhomogeneous strain of the chalcogenide is estimated from X-ray peak broadening. At high power and low velocity a clearly defined columnar grain structure with low strain is produced, typical of directional solidification. At low power and high velocity the initialized structure has a high density of defects and high strain; this is attributed to crystallization from the amorphous rather than the liquid state. The beam power and linear velocity of laser initialization may therefore be used to control the microstructure.

Atomic-scale spin-polarized scanning tunneling microscopy results on the manganese nitride Mn3N2 (010) surface are presented. The images show the row-wise antiferromagnetic structure of the surface. It is shown that the bias voltage between tip and sample affects both the magnetic and non-magnetic components of the height profile. In particular, a reversal of the magnetic contrast is shown to occur at a certain bias voltage.

We report the development of novel nanometer-scale manipulative and analytical devices for imaging, chemically analyzing and manipulating nanometer-scaled materials. Two different versions of the nanoworkbench are operating currently at the Surface Science Center of the University of Pittsburgh and at the Seagate Research Center in Pittsburgh. The instrument at Seagate consists of a modified commercially available high resolution scanning electron microscope (lateral resolution ∼1 nm at 10 kV) in combination with a set of four unique nano-manipulators, operating in the pressure range from 102 to 10−7 mbar. At the University of Pittsburgh a home-built UHV version of the nanoworkbench is in operation. In this UHV-instrument, several inter-connected UHV chambers allow in-situ deposition of thin-films and conventional surface analysis. The resolution of the SEM of the UHV system is limited to about 50 nm. We report the first results obtained by using both versions of the nanoworkbench, where we succeeded in writing patterns of ultra-small carbon-containing dots (8nm in diameter) with high position accuracy (<5nm) by electron-beam-induced deposition of carbon-containing background gases. Additionally, four-point probe measurements were performed on a SiGe system.

Room temperature ellipsometric measurements of low dimensional TlMeX2 (Me=Ga, In; X=S,Se,Te) were performed in the photon energy range 1.5–6.5e V.Obtained ellipsometric data were then treated with allowance for optical anisotropy of the above materials. The components of dielectric function tensor were determined. The structures of the obtained dielectric function are interpreted in terms of the angle resolved photoemission and band structure results. The contribution of the atomic states of each atom (Tl, In, Se) in the band states in the point M of the Brillouin zone is traced back using LCAO analysis. An ultraviolet window in the joint density of electronic states of some of TlMeX2 is disclosed and substantiated to be a sign of ferroelectricity at room temperature. For the first time the nanorods of TlMeX2 are demonstrated.

The excess Sb effect for the dynamics of rapid crystallization in eutectic amorphous films are discussed. This crystallization mechanism describe the propagation with high velocity in the interface separating the crystalline and amorphous phase for InSb and AgInSbTe materials. From these analysis, it is clear that the crystallization is grown up in the boundary of crystalline-amorphous region of eutectic materials, which is different from the stoichiometric GeSbTe media. Also, the quantum effect on the melting, crystallization and solidification of phase change media has been discussed.

Scanning Nonlinear Dielectric Microscopy (SNDM) can obtain the linear and nonlinear dielectric constant distribution of dielectric and ferroelectric materials with sub-nanometer resolution. In this paper, we present the new type of SNDM which can control the sample temperature (80K-730K) in vacuum (less than 5×10−7 Torr), and its application to measure the surface polarization state on LiTaO3 single crystal.