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Ga2TeSb7 films were deposited on SiOx/Si(100) wafers by radio-frequency magnetron sputtering to assess its potential as a phase-change memory material. Electrical resistance of the film versus temperature (R-T) was measured at various heating rates. Crystallization kinetics was analyzed using the R-T curves. Crystallization temperature 253-260 °C and activation energy of crystallization 5.76 eV were deduced using Kissinger's plot. The kinetic exponent (n) obtained from Ozawa's plot decreases from 2.5 to 1.0 upon crystallization at 253 to 265 °C. The n value is less than 1.5 when crystallizing at ≥257 °C, denoting a growth-dominated mechanism. X-ray diffraction shows that the amorphous phase crystallizes into the R3m Sb-structure and surface roughness of the crystallized Ga2TeSb7 is 0.3 nm at all annealing temperatures. X-ray photoelectron spectra reveal little change in bonding status of the three elements before and after crystallization. [ABSTRACT FROM AUTHOR]

Influence of post-treatment processes on the morphology of Fe-catalyst and the characteristics of the subsequently grown carbon nanotubes were systematically investigated. The reducing agent, which is either H2 gases species or cracked ammonia, NH3, imposed most marked effect on the morphology of Fe-clusters. The Fe-catalysts, which were prepared from 0.1 M Fe(OR)3 in xylene and were reduced by NH3 gas species, are nano-sized (50 nm), isolated and uniformly distributed. They result in carbon nanotubes of the highest purity and most density populated, exhibiting the largest electron field emission capacity. The Fe catalysts prepared by other conditions are interconnected or coarsened particulates, which induces the formation of carbon soots. The electron field emission capacity of the CNTs films is thus markedly decreased. These results imply that spin coating of Fe(OR)3 is a simple and inexpensive method for preparing catalyst of good quality, which can produce high purity carbon nanotubes, provided that the processing parameters are well controlled. A simple and inexpensive method for preparing Fe-catalyst of good quality, spin coating of Fe(OR)3 technique, was developed. This technique has the potential for scaling up and for selectively growing CNTs for electron emitters’ application. [Copyright &y& Elsevier]

Background and Purpose: The purpose of this study was to determine whether diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) can be used to distinguish brain abscesses from cystic or necrotic brain tumors, which are difficult to distinguish by conventional magnetic resonance imaging (MRI) techniques. Methods: Eleven consecutive patients with brain abscesses [10 pyogenic and 1 toxoplasmosis (in an AIDS patient)] and 15 with cystic or necrotic brain gliomas or metastases were enrolled in this study. None of these lesions had apparent hemorrhage based on T1-weighted image (T1WI). The DWI was performed using a 1.5-T system, single-shot spin-echo echo-planar pulse sequence with b=1000 s/mm2. The ADC was calculated using a two-point linear regression method at b=0 and b=1000 s/mm2. The ratio (ADCR) of the lesion ADC to control region ADC was also measured. Results: Increased signal was seen in all of the pyogenic abscess cavities to variable degrees on DWI. In vivo ADC maps showed restricted diffusion in the abscess cavity in all pyogenic abscesses [0.65±0.16×10−3 (mean±S.D.) mm2/s, mean ADCR=0.63]. The case with multiple toxoplasmosis abscesses showed low signal intensity on DWI and high ADC values (mean 1.9×10−3 mm2/s, ADCR=2.24). All cystic or necrotic tumors but one showed low signal intensity on DWI and their cystic or necrotic areas had high ADC values (2.70±0.31×10−3 mm2/s, mean ADCR=3.42). One fibrillary low-grade astrocytoma had a high DWI signal intensity and a low ADC value in its central cystic area (0.44×10−3 mm2/s, ADCR=0.49). Postcontrast T1WIs yielded a sensitivity of 60%, a specificity of 27.27%, a positive predictive value (PPV) of 52.94%, and a negative predictive value (NPV) of 33.33% in the diagnosis of necrotic tumors. DWI yielded a sensitivity of 93.33%, a specificity of 90.91%, a PPV of 93.33%, and a NPV of 90.91%. The area under receiver operating characteristic (ROC) curves for postcontrast T1WI was 0.44 and DWI was 0.92. Analysis of these areas under the ROC curves indicates significant difference between postcontrast T1WI and DWI (P<.001). Conclusion: With some exceptions, DWI is useful in providing a greater degree of confidence in distinguishing brain abscesses from cystic or necrotic brain tumors than conventional MRI and seems to be a valuable diagnostic tool. [Copyright &y& Elsevier]

Crystallization behavior of Si-added amorphous Ga19Sb81 films was studied by measuring electrical resistance (R) versus temperature (T) at various heating rates. The crystallization temperatures obtained from the R–T curves increase from 228 to 284°C measured at the heating rate 10°C/min with increasing Si content to 14at.%. All films with full-crystallization show phases of Sb and GaSb. At 9at.% Si the activation energy of crystallization and the rate factor reach the maxima of 9.1eV and 6.8×1084 min−1, respectively. The kinetic exponent (n) of the film with 9at.% Si is below 1.5 which indicates growth-dominated crystallization, while that of other films falls in 1.5≤ n ≤2.5 which denotes decreasing nucleation rate during nuclei growth. Time of 90% crystallization slightly decreases owing to Si addition as estimated using JMA theory. The temperature corresponding to 10-year failure-time obtained through isothermal Arrhenius plot effectively increases from 156 to 217°C as Si content is from 0 to 14at.%. The melting temperature slightly reduces from 591 to 581°C with Si addition. The reset voltage of test cells based on Si4(Ga19Sb81)96 is reduced by 0.5V to ~2.75V and can be set–reset switched within pulse-widths of 40–200ns. [ABSTRACT FROM AUTHOR]

We studied Ga19Sb81 film deposited on SiOx/Si(100) by RF co-sputtering using GaSb and Sb targets aiming for applications in multi-level phase-change memory. Crystallization temperature (Tx ) is 228°C–235°C determined by electrical resistance versus temperature measurements at various heating rates. The dramatic resistance drop is attributed to increased carrier concentration based on Hall measurements. The films show p-type conduction behavior at all temperature regimes. The temperature for ten-year failure-time (T 10y) and the activation energy of crystallization (E a) is 156°C and 4.2eV, respectively, as deduced using Arrhenius plots from as-deposited films. The two-step drop in resistance is attributed to the two-step phase formation as depicted by X-ray diffractometry. Density changes before and after crystallization is 5.3% (Ge2Sb2Te5: 9.5%) as analyzed by the X-ray reflectivity method. Memory switching is carried out by using test cells with a via hole size of 600nm. Set and reset processes can be achieved by using pulse widths of 20–100ns. The cycling test showed performance at least 104 set–reset times. Furthermore, two stable set states are routinely achieved by controlling set voltages. The two states can be operated at least 102 cycles steadily with resistance ratios ~5 and ~22 times, respectively. The two set states arise from the formation of two phases (Sb then GaSb) during set operations. [ABSTRACT FROM AUTHOR]

Abstract: Crystallization and thermal stability of Ge2Sb2Te5 (GST), the benchmark working material in phase-change non-volatile memory, were modified via Si-ion implantation. Through 5×1015 Si-ions/cm2 ion-implantation, crystallization temperature increases from 165°C to 177°C. Furthermore, the activation energy of crystallization increases from 2.9eV in the pristine film to 3.3eV and 4.0eV in films implanted with the doses of 5×1015 and 5×1016 Si-ions/cm2, respectively. Temperatures corresponding to a 10-year failure-time increase from 83°C in the pristine film to 96°C and 107°C in films implanted with 5×1015 and 5×1016 Si-ions/cm2, respectively. Thermal stability of Si-ion implanted GST thus improves significantly. It was also found that grain growth is inhibited with higher implantation doses. In the case of the 5×1016 ion/cm2 dose, the second-phase transition from face-centered cubic to hexagonal closed-packed structure of the GST is completely inhibited. However, crystallization time increases slightly due to Si-ion implantation. [Copyright &y& Elsevier]

Abstract: Ti-added amorphous SiO x films were sputter-deposited into stacks of Pt/SiO x /Pt and Cu/SiO x /Pt. Optimally prepared Pt/SiO x /Pt exhibits unipolar resistive switching over 102 cycles, resistance ratio ∼103, yet wide voltage distribution (2∼7V for SET, 0.5∼1.5V for RESET). Cu/SiO x /Pt exhibit similar endurance, resistance ratio up to 107, and SET and RESET voltages reduced to 1.8∼4.2V and 0.5∼1V, respectively. Cu diffusion into SiO x at the virgin state may play a role in resistive switching of Cu/SiO x /Pt stack besides of filament conduction. Ti-added amorphous SiO x films incorporating Cu electrode shows potential for resistive memory. [Copyright &y& Elsevier]