The spatial resolution from Compton cameras suffers from measurement uncertainties in interaction positions and energies. The degree of degradation in spatial resolution is shift-variant (SV) over the field-of-view (FOV) because the imaging principle is based on the conical surface integration. In our study, the shift-variant point spread function (SV-PSF) is derived from point source measurements at various positions in the FOV and is incorporated into the system matrix of a fully three-dimensional, accelerated reconstruction, i.e. the listmode ordered subset expectation maximization (LMOSEM) algorithm, for resolution recovery. Simulation data from point sources were used to estimate SV and asymmetric parameters for Gaussian, Cauchy, and general parametric PSFs. Although little difference in the fitness accuracy between Gaussian and general parametric PSFs was observed, the general parametric model showed greater flexibility over the FOV in shaping the curve between that for Gaussian and Cauchy functions. The estimated asymmetric SV-PSFs were incorporated into the LMOSEM for resolution recovery. For simulation data from a single point source at the origin, all LMOSEM-SV-PSFs improved the spatial resolution by 2.6 times over the standard LMOSEM. For two point-source simulations, reconstructions also gave a two-fold improvement in spatial resolution and resulted in a greater recovered activity ratio at different positions in the FOV.

In a recent Letter, 1 our group introduced the new idea of "gamma electron vertex imaging (GEVI)" for beam range verification in proton therapy. In the Letter, we mentioned that the proton beam range can be determined within 2-3 mm error by using GEVI. Recently, however, we found that multiple Coulomb scattering (MCS) process for electron was mistakenly omitted in our Geant4 simulation. It was a serious mistake. Therefore, we have repeated the simulation study again including the MCS process, and this letter provides the revised result.FIG. 1. GEVI image and projections. The upper plots show the results for d = 5 cm. The lower plots provide the GEVI image projections (gray square markers) and prompt gamma distributions (red step lines), along with the distributions of absorbed dose (blue dash lines).

The effect of organic inhibitors on pitting in Ruthenium (Ru) was investigated after chemical mechanical planarization (CMP) in near-neutral pH using colloidal silica-abrasive based slurry with an oxidizer, sodium periodate. Organic inhibitors with amine or amide functional groups only demonstrated a strong effect on suppressing pitting, which was proven by the static etch rate, corrosion current density, and oxidation states (RuO3/RuO2 ratio). Ethylenediamine tetraacetic acid had an extremely low surface roughness (∼2 Å) and a reasonable polishing rate (∼1050 Å/min) after CMP, which probably resulted from the relatively low corrosion efficiency (57.7%), low RiO3 content (5.9%), and chelating effect.

For phase-change memory beyond the 30 nm design rule, chemical mechanical planarization ͑CMP͒ performing at a high polishing rate, reasonable selectivity, and no corrosion-induced pits is essential for planarizing nitrogen-doped polycrystalline Ge 2 Sb 2 Te 5 ͑GST͒ deposited on the confined memory cell structure. We develop a new alkaline slurry added with KMnO 4 used as an oxidizer. The alkaline slurry added with 0.3 wt % KMnO 4 has a polycrystalline GST film polishing rate of 5200 Å/min, a polishing rate selectivity between polycrystalline GST and SiO 2 film of 100:1, and no corrosion-induced pit. In addition, polycrystalline GST film CMP using the alkaline slurry added with KMnO 4 is observed to follow a cyclic reaction polishing mechanism.Materials based on Ge-Sb-Te ternary alloy have been extensively researched as data storage media for phase-change memory ͑PCM͒ because of their large difference in electrical resistance between amorphous and polycrystalline states. 1-4 PCM is a unique nonvolatile memory that has write and erase times of several tens of nanoseconds. 5 Among the Ge-Sb-Te-based materials, Ge 2 Sb 2 Te 5 ͑GST͒ has been widely adopted and investigated because of its fast crystallization speed and low energy requirements for the phase change. 5,6 Particularly, nitrogen-doped GST film has been demonstrated to reduce reset current and enhance endurance characteristics. 6-8 Due to a strong thermal crosstalk effect between adjacent cells as the device design rule scales down to less than 30 nm, PCM cell structure has evolved from a conventional T-shaped structure to a confined one. 9 As a unique global planarization method used in the semiconductor manufacturing process, chemical mechanical planarization ͑CMP͒ has been introduced to planarize the GST film surface after gap filling by GST in the confined structure. 9-11 Here, the deposited GST is preferred in a polycrystalline state rather than an amorphous one to achieve a higher speed and a wider sensing margin. Moreover, polycrystalline GST is inevitably used to avoid incomplete contact between electrodes and amorphous GST because an amorphous GST material shrinks by 5-7% volume as it switches from an amorphous to crystalline state by thermal process. 12 Therefore, a CMP slurry with a high polishing rate, a high polishing rate selectivity between GST and surrounding insulator films, and good surface quality of the GST film needs to be developed to achieve the successful CMP process in a PCM fabricated with the confined cell structure, as shown in Fig. 1.However, the polishing rate of a polycrystalline GST film is considerably lower than that of an amorphous GST film, 13,14 and thus, an oxidizer needs to be added to the CMP slurry to enhance the chemical reaction rate of polycrystalline GST film. In our previous study, we reported on the CMP performance in areas such as polishing rate and selectivity for a polycrystalline GST film polished in the alkaline slurry with hydrogen peroxide ͑H 2 O 2 ͒ up to 3.0 wt %. We found that polycrystalline GST film ...