Spatially inhomogeneous operation of phase-change memory

Kim, Dasol, Soobin Hwang, Taek Sun Jung, Min Ahn, Jaehun Jeong, Hanbum Park, Juhwan Park, Jae Hoon Kim, Byung Joon Choi, and Mann-Ho Cho. "Spatially inhomogeneous operation of phase-change memory." Applied Surface Science (2022): 153026.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0169433222005931

Abstract

Rapid changes in the electrical resistance depending on the phases (amorphous and crystal) are one of the most promising bases for universal memory. Phase-change region is spatially inhomogeneous during memory operation in a unit cell because Joule heat for the phase-change is generated at the interface between the metal and compounds. However, delicate optimization of the electrical and thermal properties at the interface is underexplored compared to the bulk. In this study, we modulate the electrical and thermal conductivities by incorporating oxygen in Ag-In-Sb-Te, superior memory compounds where oxygen is chosen for high accessibility and efficiency for the modulation of conductivity. We further analyze the oxidation and crystallization process at the atomic level. Based on the results, we successfully improve the memory performances such as speed, energy, signal ratio, and reliability simultaneously by inserting the oxygenated layer as an interfacial layer. Our study proves that there is considerable room to optimize memory performance at the interface.

Experimental 

… The optical conductivities of AIST with various thicknesses were obtained from THz-TDS using a Teraview TPS3000 under a N 2 purged state. The time-domain signal after sample transmission has the information of the sample conductivity.....

Terahertz Dielectric Characterization of Low-Loss Thermoplastics for 6G Applications

Zhai, Min, Alexandre Locquet, and D. S. Citrin. "Terahertz Dielectric Characterization of Low-Loss Thermoplastics for 6G Applications." International Journal of Wireless Information Networks (2022): 1-6.

for full paper see https://link.springer.com/article/10.1007/s10776-022-00554-x

Abstract

Common thermoplastics, namely, polycarbonate (PC), poly (methyl methacrylate) (PMMA), and acrylonitrile butadiene styrene (ABS) are low-cost materials with potential applications in emerging 6G communications systems, ranging from microelectronics packaging to metasurfaces for reflectors and filters. In addition, low-loss materials are also needed for more pedestrian applications, such as packaging for entire handheld devices, subassemblies, and high-frequency windows where low-cost is key and long lifetime might not be a requirement. In this work, we utilize terahertz time-domain spectroscopy from 500 GHz to 2 THz to characterize the dielectric properties and loss tangent for each thermoplastic above. The plastics investigated have refractive index (∼ 1.6–1.7) in the 6G band with low dispersion. The absorption, however, increases at high frequencies as is common in disordered materials, highlighting a key challenge for 6G. Nonetheless, in absolute terms, all the thermoplastics studied present low-loss performance compared with (higher–index) common glasses and ceramics within the entire frequency range, suggesting that they are promising candidates for selected applications for future 6G systems.

… The transmission measurements in this work were performed using a commercial pulsed broadband THz time-domain spectroscopy (TDS) system (TPS Spectra 3000 from TeraView Ltd, UK). Compared to vector network analyzers (VNA), another …

Terahertz-infrared spectroscopy of wafer-scale films of single-walled carbon nanotubes treated by plasma

 Zhukov, S. S., E. S. Zhukova, A. V. Melentev, B. P. Gorshunov, A. P. Tsapenko, D. S. Kopylova, and Albert G. Nasibulin. "Terahertz-infrared spectroscopy of wafer-scale films of single-walled carbon nanotubes treated by plasma." Carbon 189 (2022): 413-421.

for full paper see 

https://www.sciencedirect.com/science/article/abs/pii/S0008622321012355

Abstract

We investigated terahertz-infrared electrodynamic properties of wafer-scale films composed of plasma-treated single-walled carbon nanotubes (SWCNTs) and films comprising SWCNTs grown with different lengths. The spectra of complex conductance of the films were measured at frequencies 5–20 000 cm−1 and in the temperature interval 5–300 K. Terahertz spectral response of films of pristine SWCNTs is well described with the Drude conductivity model and a plasmon resonance located at ≈100 cm−1. Stepwise treatment of the films with oxygen plasma led to a gradual suppression of the Drude spectral weight from the low-frequency side. For films with the nanotubes shorter than 1 μm, i.e., close to electrons mean free path and localization length, scattering of charge carriers at the nanotubes edges is shown to additionally contribute to the carriers scattering rate and to the damping of plasmon resonance. The temperature coefficient of ac resistance (ac TCR) in both kinds of films is found to strongly increase in amplitude during cooling and frequency decrease. The values of ac TCR increase in films with longer time of plasma treatment and nanotubes with shorter length but reach saturation in films with exposure time longer than ≈100 s or composed from SWCNTs shorter than 1 μm.

.....complex (amplitude and phase) transmission coefficient measured with the TeraView time-domain...... 

Revealing inscriptions obscured by time on an early-modern lead funerary cross using terahertz multispectral imaging

Dong, Junliang, Ana Ribeiro, Aurélien Vacheret, Alexandre Locquet, and D. S. Citrin. "Revealing inscriptions obscured by time on an early-modern lead funerary cross using terahertz multispectral imaging." Scientific Reports 12, no. 1 (2022): 1-10.

for full paper see https://www.nature.com/articles/s41598-022-06982-2

Abstract 

The presence of a corrosion layer on lead art and archæological objects can severely impede the interpretation of inscriptions, thus hampering our overall understanding of the object and its context. While the oxidation of lead that dominates corrosion may be chemically reversible via reduction, potentially providing some access to inscriptions otherwise obscured by time, corrosion damage is overall neither entirely reversible nor is the reduction process in all cases easy or feasible to carry out. In this study, by taking advantage of the unique penetration ability of terahertz radiation and the abundant frequency bands covered by a single-cycle terahertz pulse, we perform non-destructive terahertz multispectral imaging to look under the corrosion on a sixteenth century lead funerary cross (croix d’absolution) from Remiremont in Lorraine, France. The multispectral images obtained from various terahertz frequency bands are fed into a judiciously designed post-processing chain for image restoration and enhancement, thus allowing us for the first time to read obscured inscriptions that might have otherwise been lost. Our approach, which brings together in a new way the THz properties of the constituent materials and advanced signal- and image-processing techniques, opens up new perspectives for multi-resolution analysis at terahertz frequencies as a technique in archæometry and will ultimately provide unprecedented information for digital acquisition and documentation, character extraction, classification, and recognition in archæological studies.

"Methods 

THz imaging system 

A typical THz time-domain system (TeraView TPS Spectra 3000) operating in a refection geometry was employed in this study. The incident angle of the THz beam was ∼10 degrees. The GaAs photoconductive antenna was excited by an ultrafast laser to produce roughly single-cycle THz pulses with bandwidth extending from 60 GHz to 3 THz. The maximum peak of its power spectrum was located at about 0.3 THz. Each recorded temporal reflected THz waveform contains 4096 data points, and the data sampling period was set to 0.011634 ps. The signal was averaged over 10 shots per pixel to enhance signal to noise. The scanning of the sample was conducted in a temperature-controlled laboratory at 22 ◦C. The humidity in the laboratory was held about 38%."

Magnetic terahertz resonances above the Néel temperature in the frustrated kagome antiferromagnet averievite

Biesner, Tobias, Seulki Roh, Andrej Pustogow, Hong Zheng, J. F. Mitchell, and Martin Dressel. "Magnetic terahertz resonances above the Néel temperature in the frustrated kagome antiferromagnet averievite." Physical Review B 105, no. 6 (2022): L060410.

for full paper see https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.L060410

Abstract

Time-domain magneto-THz spectroscopy is utilized to study the frustrated magnet averievite Cu5−xZnxV2O10(CsCl). Pronounced THz resonances are observed in unsubstituted samples (x=0) when cooling below the onset of short-range magnetic correlations. The influence of external magnetic effects confirms the magnetic origin of these resonances. Increasing Zn substitution suppresses the resonances, as frustration effects dominate, reflecting the nonmagnetic phases for x>0.25 compounds. The temperature evolution of the THz spectra is complemented with electron spin resonance spectroscopy. This comparison allows a direct probe of the different contributions from magnetic order, frustration, and structural properties in the phase diagram of averievite. Our results illustrate the effect of magnetic interactions in THz spectra of frustrated magnets.

… All specimens were measured with a time-domain THz spectrometer (TeraView TeraPulse 4000) attaching a homemade He-bath cryostat and a superconducting magnet (Oxford Instruments). The magneto-THz experiments were performed in …

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