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ABSTRACTIntroductionThere is a growing need for alternative models to advance current non-clinical experimental models because they often fail to accurately predict drug responses in human clinical trials. Human organ-on-a-chip models have emerged as promising approaches for advancing the predictability of drug behaviors and responses.Areas coveredWe summarize up-to-date human gut-on-a-chip models designed to demonstrate intricate interactions involving the host, microbiome, and pharmaceutical compounds since these models have been reported a decade ago. This overview covers recent advances in gut-on-a-chip models as a bridge technology between non-clinical and clinical assessments of drug toxicity and metabolism. We highlight the promising potential of gut-on-a-chip platforms, offering a reliable and valid framework for investigating reciprocal crosstalk between the host, gut microbiome, and drug compounds.Expert opinionGut-on-a-chip platforms can attract multiple end users as predictive, human-relevant, and non-clinical model. Notably, gut-on-a-chip platforms provide a unique opportunity to recreate a human intestinal microenvironment, including dynamic bowel movement, luminal flow, oxygen gradient, host-microbiome interactions, and disease-specific manipulations restricted in animal and invitrocell culture models. Additionally, given the profound impact of the gut microbiome on pharmacological bioprocess, it is critical to leverage breakthroughs of gut-on-a-chip technology to address knowledge gaps and drive innovations in predictive drug toxicology and metabolism.

Micro-/nanotopographical cues have emerged as a practical and promising strategy for controlling cell fate and reprogramming, which play a key role as biophysical regulators in diverse cellular processes and behaviors. Extracellular biophysical factors can trigger intracellular physiological signaling via mechanotransduction and promote cellular responses such as cell adhesion, migration, proliferation, gene/protein expression, and differentiation. Here, we engineered a highly ordered nanowrinkled graphene oxide (GO) surface via the mechanical deformation of an ultrathin GO film on an elastomeric substrate to observe specific cellular responses based on surface-mediated topographical cues. The ultrathin GO film on the uniaxially prestrained elastomeric substrate through self-assembly and subsequent compressive force produced GO nanowrinkles with periodic amplitude. To examine the acute cellular behaviors on the GO-based cell interface with nanostructured arrays of wrinkles, we cultured L929 fibroblasts and HT22 hippocampal neuronal cells. As a result, our developed cell-culture substrate obviously provided a directional guidance effect. In addition, based on the observed results, we adapted a deep learning (DL)-based data processing technique to precisely interpret the cell behaviors on the nanowrinkled GO surfaces. According to the learning/transfer learning protocol of the DL network, we detected cell boundaries, elongation, and orientation and quantitatively evaluated cell velocity, traveling distance, displacement, and orientation. The presented experimental results have intriguing implications such that the nanotopographical microenvironment could engineer the living cells’ morphological polarization to assemble them into useful tissue chips consisting of multiple cell types.

An electrochemical nanopattern formation (ENF) surface treatment was developed to overcome the limitations of conventional surface treatments. This study aimed to evaluate the cytocompatibility and preclinical efficacy of the newly developed ENF surfaces in comparison to conventional surfaces. The cytocompatibility of human mesenchymal stem cells, degree of bone formation, bone-to-implant contact (BIC) ratio, and implant stability quotient (ISQ) were investigated using rabbit and beagle models. Overall, the ENF surfaces showed greater cytocompatibility than other surfaces. The ISQs of implants in rabbit tibias showed that ENF surfaces provided greater stability than other surfaces. In contrast, the ISQs of implants in beagle mandibles were similar for ENF and sandblasted large-grit acid-etched (SLA) surfaces. In the rabbit model, the degree of bone formation and BIC ratio were significantly higher for ENF surfaces than for other surfaces. However, the removal torque (RT) during implant removal was significantly higher for SLA surfaces than ENF surfaces. Thus, it was confirmed that ENF-treated dental implants can replace conventional implants, but further research is required to improve the surface roughness to increase the RT. [ABSTRACT FROM AUTHOR]

All-in-one treatments represent a paradigm shift in future medicine. For example, inflammatory bowel disease (IBD) is mainly diagnosed by endoscopy, which could be applied for not only on-site monitoring but also the intestinal lesion-targeted spray of injectable hydrogels. Furthermore, molecular conjugation to the hydrogels would program both lesion-specific adhesion and drug-free therapy. This study validated this concept of all-in-one treatment by first utilizing a well-known injectable hydrogel that underwent efficient solution-to-gel transition and nanomicelle formation as a translatable component. These properties enabled spraying of the hydrogel onto the intestinal walls during endoscopy. Next, peptide conjugation to the hydrogel guided endoscopic monitoring of IBD progress upon adhesive gelation with subsequent moisturization of inflammatory lesions, specifically by nanomicelles. The peptide was designed to mimic the major component that mediates intestinal interaction with Bacillus subtilisflagellin during IBD initiation. Hence, the peptide-guided efficient adhesion of the hydrogel nanomicelles onto Toll-like receptor 5 (TLR5) as the main target of flagellin binding and Notch-1. The peptide binding potently suppressed inflammatory signaling without drug loading, where TLR5 and Notch-1 operated collaboratively through downstream actions of tumor necrosis factor-alpha. The results were produced using a human colorectal cell line, clinical IBD patient cells, gut-on-a-chip, a mouse IBD model, and pig experiments to validate the translational utility.

Layering two-dimensional van der Waals materials provides a high degree of control over atomic placement, which could enable tailoring of vibrational spectra and heat flow at the sub-nanometer scale. Here, using spatially resolved ultrafast thermoreflectance and spectroscopy, we uncover the design rules governing cross-plane heat transport in superlattices assembled from monolayers of graphene (G) and MoS2(M). Using a combinatorial experimental approach, we probe nine different stacking sequences, G, GG, MG, GGG, GMG, GGMG, GMGG, GMMG, and GMGMG, and identify the effects of vibrational mismatch, interlayer adhesion, and junction asymmetry on thermal transport. Pure G sequences display evidence of quasi-ballistic transport, whereas adding even a single M layer strongly disrupts heat conduction. The experimental data are described well by molecular dynamics simulations, which include thermal expansion, accounting for the effect of finite temperature on the interlayer spacing. The simulations show that an increase of ∼2.4% in the layer separation of GMGMG, relative to its value at 300 K, can lead to a doubling of the thermal resistance. Using these design rules, we experimentally demonstrate a five-layer GMGMG superlattice “thermal metamaterial” with an ultralow effective cross-plane thermal conductivity comparable to that of air.

Semiconducting MoTe2is one of the few two-dimensional (2D) materials with a moderate band gap, similar to silicon. However, this material remains underexplored for 2D electronics due to ambient instability and predominantly p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type MoTe2transistors with the highest performance to date, including high saturation current (>400 μA/μm at 80 K and >200 μA/μm at 300 K) and relatively low contact resistance (1.2 to 2 kΩ·μm from 80 to 300 K), achieved with Ag contacts and AlOxencapsulation. We also investigate other contact metals (Sc, Ti, Cr, Au, Ni, Pt), extracting their Schottky barrier heights using an analytic subthreshold model. High-resolution X-ray photoelectron spectroscopy reveals that interfacial metal-Te compounds dominate the contact resistance. Among the metals studied, Sc has the lowest work function but is the most reactive, which we counter by inserting monolayer hexagonal boron nitride between MoTe2and Sc. These metal-insulator-semiconductor (MIS) contacts partly depin the metal Fermi level and lead to the smallest Schottky barrier for electron injection. Overall, this work improves our understanding of n-type contacts to 2D materials, an important advance for low-power electronics.

Miniature batteries can accelerate the development of mobile electronics by providing sufficient energy to power small devices. Typical microbatteries commonly use thin-film inorganic electrodes based on Li-ion insertion reaction. However, they rely on the complicated thin-film synthesis method of inorganics containing many elements. Graphene, one atomic layer thick carbon sheet, has diverse physical and chemical properties and is compatible with conventional micron-scale device fabrication. Here, we study the use of chemical vapor deposition (CVD) grown monolayer graphene in a two-dimensional configuration, as a future Li–oxygen microbattery cathode. By maximizing the dissolution of discharge intermediates, we obtain 2610 Ah/ggrapheneof capacity corresponding to 20% higher areal cathode energy density and 2.7 times higher cathode specific energy than that can be derived from the same volume or mass of conventional Li-ion battery cathode material. Furthermore, a clear observation on the discharge reaction on composite electrodes and their role in the charging reaction was made, thanks to the two-dimensional monolayer graphene Li–oxygen battery cathode. We demonstrate an easy integration of two-dimensional CVD graphene cathode into microscale devices by simply transferring or coating the target device substrate with flexible graphene layers. The ability to integrate and use monolayer graphene on arbitrary device substrates as well as precise control over a chemical derivation of the carbon interface can have a radical impact on future energy-storage devices.

Graphene, a two-dimensional (2D) carbon nanomaterial, has received great attention owing to its advantageous characteristics, including superior electrical, chemical and physical properties. In particular, exfoliation of graphite with strong oxidants has been explored to prepare a suspension of individual 2D graphene oxide (GO) nanosheets dispersed in various types of solvents. This colloidal suspension can readily be employed in a wide range of promising potential applications. However, one major challenge is to assemble such individual nanosheets on defined areas of surfaces forming specific structures. Here, we developed a simple and robust one-step strategy to create highly regular ordered nanostructures composed of chemically reduced graphene oxide (rGO) nanosheet building blocks on SiO2/Si or glass substrates over large areas. An aqueous suspension of rGO nanosheets dispersed in a volatile solvent was subjected to a confined geometry to induce a spontaneous formation of rGO patterned arrays with unprecedented regularity by utilizing both a controlled coffee ring effect and consecutive stick-slip motions of rGO solutions during the drying process. As a result, the generation of ultrathin nanotextured films in the form of micropatterns (i.e., concentric gradient rGO coffee rings) was effectively tailored. As a biological approach, to fully utilize patterned rGO associated with the nanoscale surface topography, we used these patterned rGO arrays as a biomimetic in vitroarchitecture to study interfacial interactions of living cells such as fibroblasts, myoblasts, and neuronal cells. The observed results show that the patterned rGO arrays can be used as manipulated cellular responsive templates to form living cell assemblies and related patterns that are useful for regenerative tissue engineering.

In recent years, much research has been suggested and examined for the development of tissue engineering scaffolds to promote cellular behaviors. In our study, RGD peptide and graphene oxide (GO) co-functionalized poly(lactide-co-glycolide, PLGA) (RGD-GO-PLGA) nanofiber mats were fabricated via electrospinning, and their physicochemical and thermal properties were characterized to explore their potential as biofunctional scaffolds for vascular tissue engineering. Scanning electron microscopy images revealed that the RGD-GO-PLGA nanofiber mats were readily fabricated and composed of random-oriented electrospun nanofibers with average diameter of 558 nm. The successful co-functionalization of RGD peptide and GO into the PLGA nanofibers was confirmed by Fourier-transform infrared spectroscopic analysis. Moreover, the surface hydrophilicity of the nanofiber mats was markedly increased by co-functionalizing with RGD peptide and GO. It was found that the mats were thermally stable under the cell culture condition. Furthermore, the initial attachment and proliferation of primarily cultured vascular smooth muscle cells (VSMCs) on the RGD-GO-PLGA nanofiber mats were evaluated. It was revealed that the RGD-GO-PLGA nanofiber mats can effectively promote the growth of VSMCs. In conclusion, our findings suggest that the RGD-GO-PLGA nanofiber mats can be promising candidates for tissue engineering scaffolds effective for the regeneration of vascular smooth muscle.

ABSTRACTAn integral effect test was successfully performed to provide data to assess the capability of the system analysis code to simulate a complete loss of reactor coolant system (RCS) flow rate (CLOF) scenario for the SMART (System-integrated Modular Advanced ReacTor) design. The steady-state conditions were achieved to satisfy initial test conditions presented in the test requirement, its boundary conditions were accurately simulated, and the CLOF scenario in the SMART design was reproduced properly using the VISTA-ITL facility. The natural circulation flow rate in the RCS was about 12.0% of the rated RCS flow rate and the flow rate in the passive residual heat removal system (PRHRS) loop was about 10.6% of its rated value in the early stage of the PRHRS operation. In this paper, the major experimental results of the CLOF test are discussed. The test results were analyzed using the best-estimate system analysis code, MARS-KS, to assess its capability to simulate a CLOF scenario for the SMART design.

In the present study, we analyzed the effect of Angelica gigasNakai (AGN) on LPS-induced inflammatory responses in RAW264.7 mouse macrophage cells. For this purpose, we treated RAW264.7 cells with various concentrations of AGN and LPS for indicated times. Then, we performed WST assay, trypan blue assay, counting of activated cells, FACS analysis and western blot. We found that AGN inhibited cell proliferation in a dose-dependent manner. AGN caused G1 cell cycle arrest, and prevented the phosphorylation of AKT, ERK, p38 and NF-κB induced by LPS. AGN also reduced iNOS and Cox-2 mRNA expression level induced by LPS. It also diminished intracellular ROS level induced by LPS. Moreover, AGN decreased mitochondrial membrane potential and induced PARP and caspase-3 cleavage suggesting that AGN causes apoptosis. Our study clearly showed that AGN may be beneficial to prevent/treat inflammatory diseases and cancer.

The purpose of this study is to investigate the effect of new materials from the traditional herbal medicines which induce anti-aging and anti-melanogenesis process of skin in vitro. Among 22 traditional herbal medicines which were tested in this study, Rhus verncifluastokes (RVS) showed prominent effects for anti-aging and whitening of skin compared to other herbal extracts. In our study, RVS showed the highest elastase inhibitory effect and a higher anti-tyrosinase activity. Pretreatment with RVS significantly inhibited the expressions of UVB-induced MMP-1 protein and mRNA in a dose-dependent manner, and also inhibited the UV-induced activation of extracellular signal regulated kinase (ERK). In whitening, it was found that RVS significantly inhibits melanin biosynthesis in a dose-dependent manner. Moreover, α-MSH-induced increases of microphthalmia-associated transcription factor (MITF) and tyrosinase were significantly inhibited in B16F1 melanoma cells treated with RVS. Therefore, these data suggest that RVS extracts could be a potential agent for the prevention and treatment of skin photoaging and hyperpigmentation.

Previous studies demonstrated that Prunella vulgaris, Scutellaria baicalensis and Lonicera japonica have Chungyul activity, anti-inflammatory activity, anti-oxidant activity, and anti-cancer activity. They are also known to have the effect on degenerative cerebropathia of cranial nerve system, cerebrovascular diseases and brain tumors. We selected those herbs (Chungyul medicines herbs) and performed experiments to investigate whether they have anti-oxidant and anti-inflammatory effects in human neuroblastoma cells, SH-SY5Y. We found that Prunella vulgaris has the highest total phenolic contents and DPPH radical scavenging activity suggesting that DPPH scavenging activity is associated with total phenolic level of the extracts. The highest superoxide radical scavenging activity was also shown in Prunella vulgaris. We also observed that Prunella vulgaris, Scutellaria baicalensis, and Lonicera japonica suppressed 6-hydroxydopamine (6-OHDA)-induced TBARS increase suggesting that Chungyul medicines herbs have antioxidant activity. Additionally, catalase (CAT) level which was reduced by 6-OHDA was restored by Chungyul medicines. The herbs reduced NO production induced by 6-OHDA and Prunella vulgaris decreased cell viability in a dose-dependent manner. Prunella vulgaris suppressed 6-OHDA-induced expression of iNOS and COX-2. Our study demonstrates that Chungyul medicines herbs have anti-oxidant and anti-inflammatory activity in SH-SY5Y cells and Prunella vulgaris seems to be the most effective herb for the treatment of inflammatory diseases.

The root cortex of Paeonia suffruticosaAndrews (PSA), also known as Moutan Cortex, is known to have anti-allergic and anti-inflammatory properties. This study investigates the effect and mechanism of PSA by in vivoand in vitromethods. Treatings the root cortex from PSA with up to 0.4 mg/ml of an ethanol extract showed no cytotoxicity in human mast cells. The ethanol extract of PSA (200 mg/kg) significantly inhibited the passive cutaneous anaphylaxis reaction in vivo, and suppressed the release of histamine from rat peritoneal mast cells induced by compound 48/80. It was also found that PSA decreased the expressions of TNF-alpha and IL-6 in PMA- and A23187-stimulated HMC-1 cells. The results show the inactivation of IkappaB-alpha and NF-kappaB, as well as suppression of the phosphorylation of extracellular signal-regulated kinase (ERK). Our findings therefore suggest that PSA could be promising for anti-allergic inflammation by inhibiting the NF-kappaB/IkappaB-alpha signaling pathway and the phosphorylation of ERK.

We investigated the effects of herb extracts, Rhus verniciflua, Agrimonia pilosa, Sophora japonica, and Paeonia suffruticosa, on the lowering of blood glucose levels and thiobarbituric acid reactive substances (TBARS) in streptozotocin (STZ)-induced diabetic rats. After 4 weeks, oral administration of Rhus vernicifluaextract (50 mg/kg) exhibited a significant decrease in blood glucose levels in diabetic rats (P<0.05). Blood TBARS concentrations, the products of glucose oxidation in blood, were also lowered by Rhus vernicifluaextract supplementation. In addition, Sophora japonicaand Paeonia suffruticosaextracts significantly reduced TBARS levels versusdiabetic controls. Serum concentrations of liver-function marker enzymes, GOT and GPT, were also restored by Rhus verniciflua(50 mg/kg) supplementation in diabetic rats.

A series of interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) were prepared by the simultaneous polymerization method. The PU network was synthesized via the isocyanate-terminated PU prepolymer based on polyethylene glycol (PEG), a highly hydrophilic oligomer, and hexamethylene diisocyanate (HDI). The bulk and surface characteristics of these materials were analyzed by differential scanning calorimetry (DSC), tensile testing, scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and contact angle measurement. The PU/PS IPNs prepared in this study exhibited phase separated structures, which had dispersed PS domains in the continuous PU matrix, in both the bulk and surface showing two transition temperatures. The IPN containing 50 wt% of PS showed good mechanical properties. The enrichment of PU phase in the surface was revealed by SEM, ATR-FTIR, ESCA, and contact angle measurement.

To investigate the effect of hydrophilic and hydrophobic surfaces with phase separated structure on their blood responses, interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) were prepared by simultaneous polymerization. In vitro protein adsorption, in vitro platelet adhesion, and ex vivo A-A shunt test were carried out to evaluate the blood compatibility of the PU/PS IPNs. The results of protein adsorption on the PU/PS IPN surfaces indicated that albumin preferentially adsorbed on the hydrophilic surface (PU), while fibrinogen preferentially adsorbed on the hydrophobic surface (PS). The PU/PS IPNs exhibited suppressive properties for both platelet adhesion and activation. The occlusion time of U50S50 IPN containing 50 wt% of PS was twice as long as that of the PU control (50 min), indicating enhanced blood compatibility, presumably due to the selective adsorption of plasma proteins and the suppression of the adhesion and activation of platelets.

The objective of this study was to investigate the effects of Cervus nippon var. mantchuricuswater extract treated with digestive enzymes (CE) on the promotion of M1 macrophage polarization in murine macrophages. Macrophages polarize either to one phenotype after stimulation with LPS or IFN-γ or to an alternatively activated phenotype that is induced by IL-4 or IL-13. Cell viability of RAW264.7 cells was determined by WST-1 assay. NO production was measured by Griess assay. IL-6, IL-12, TNF-α, and iNOS mRNA levels were measured by RT-PCR. IL-6, IL-12, and IL-10 cytokine levels were determined by ELISA. TLR4/MAPK/NF-κB signaling in RAW264.7 cells was evaluated by western blotting. The level of NF-κB was determined by immunoblotting. CE induced the differentiation of M1 macrophages. CE promoted M1 macrophages to elevate NO production and cytokine levels. CE-stimulated M1 macrophages had enhanced IL-6, IL-12, and TNF-α. CE promoted M1 macrophages to activate TLR4/MAPK/NF-κB phosphorylation. M2 markers were downregulated, while M1 markers were upregulated in murine macrophages by CE. Consequently, CE has immunomodulatory activity and can be used to promote M1 macrophage polarization through the TLR4/MAPK/NF-κB signaling pathways.

Cucurbitacins are triterpenoids commonly found in Cucurbitaceae and Cruciferae and have long been used in traditional medicine. Cucurbitacins demonstrate anti-inflammatory and anti-cancer activities. We investigated whether cucurbitacin D affects viability in breast cancer cells and its mechanism of action. An MTT assay was used to measure the viability of breast cancer cells. Western blot analysis was used to measure the expression of various modulators, such as p-p53, p-Stat3, p-Akt, and p-NF-κB. Doxorubicin and cucurbitacin D affected the viability of MCF7, MDA-MB-231, and SKBR3 cells. Cucurbitacin D and doxorubicin increased p-p53 expression in MCF7, SKBR3, and MDA-MB-231 cells. Cucurbitacin D suppressed p-Akt, p-NF-κB, and p-Stat3 expression in MCF7, MDA-MB-231, and SKBR3 cells. Doxorubicin alone did not decrease p-Akt and p-Stat3 levels. Cucurbitacin D decreased p-NF-κB and p-Stat3 levels. Doxorubicin in combination with cucurbitacin D increased p-p53 levels and suppressed Akt, NF-κB, Stat3, and Bcl-2 expression more than cucurbitacin D alone. Our results clearly demonstrate that cucurbitacin D could be a useful compound for treating human breast cancer.

The lower potency of low dose of carboplatin often requires combination with other drugs to improve its efficacy. Newer and more potent carboplatin-based combination therapies are investigated for treatment. We investigated whether paclitaxel, carboplatin, and Angelica gigasNakai (AGN) affect viability of H460 cells by MTT assay. Western blot analysis was used to measure the expression of various modulators, such as p-Stat3, p-Akt, and p-Erk. Paclitaxel, carboplatin, and AGN affected the viability of H460 cells. Paclitaxel, carboplatin, and AGN suppressed p-Akt, p-Erk, and p-Stat3 expression. AGN combined with carboplatin significantly decreased c-Jun, HIF-1α, and VEGF levels. AGN combined with carboplatin significantly increased p21 and p27 levels and suppressed cyclin D1 and cyclin E levels. AGN combined with carboplatin-induced apoptosis by increasing Bax and cleavage of caspase and Parp level and by suppressing Bcl-2 level. Our results clearly demonstrate that AGN combined with carboplatin could be a useful compound for treating lung cancer.

A W interlayer process is demonstrated for fabrication of a through-pore nanoporous anodic aluminum oxide (AAO) scaffold on gold substrates. The W interlayer process comprises anodization of an Al∕W∕Autrilayer for the formation of an AAO scaffold with a WO3extrusion at the pore bottom and selective removal of the WO3to expose the surface of the substrate, without modifying the nanostructure of the scaffold. Structural and kinetic studies of the WO3extrusion formation revealed that the anodization of W consumes a fixed thickness of the W layer in acidic electrolytes and that the thickness depends strongly on the anodic voltage. Based on this study, the optimum thickness of a W interlayer in the Al∕W∕Autrilayer was determined for various anodization conditions. Through-pore AAOs were fabricated on Au substrates using optimum W thicknesses (10 and 20nm) in 0.3Msulfuric acid at 25V, 0.3Moxalic acid at 40V, and 5wt%phosphoric acid at 86V, without a violent O2evolution reaction and without changing the pore diameter. With the resulting AAO scaffolds, vertically aligned freestanding Au and Pt nanowires with diameters ranging from about 12nmto about 120nmwere grown by electrodeposition on a Au substrate. The methodology demonstrated here should be generally applicable to other inert metallic substrates/underlayers.

This study examined the influence of postdeposition annealing on the composition and local structures of amorphous In–Ga–Zn–O (IGZO) thin films using X-ray photoemission/absorption spectroscopy and X-ray diffraction. Upon annealing at high temperatures (800°C)in an N2environment, the Zn content in the a-IGZO films decreased significantly, suggesting ZnO volatilization. The resultant crystallization of the IGZO films was also observed. However, the bipyramidal local structures of Ga and Zn ions were still preserved, even after postdeposition annealing at 1000°C, indicating the replacement of ZnO with GaO1.5without altering the hexagonal In2Ga2ZnO7crystal structure.

Phase change memory cells were fabricated using plasma-enhanced cyclic chemical-vapor-deposited Ge2Sb2Te5(GST) thin films deposited on 300nmdiameter TiN∕Wcontact plugs formed in a SiO2layer. A 2, 4, and 8nmthick atomic deposited TiO2layer was interposed between the GST and underlayer containing the contact plug. The necessary reset current and power decreased with increasing the TiO2interlayer thickness. Adoption of the optimum thickness (4nm)TiO2layer decreased the necessary reset power to ∼45%of the cell without the TiO2layer. This was attributed mainly to the effective heat insulation by the 4nmthick TiO2layer. The structural investigation and electrothermal simulation results for the fabricated cells showed a good match between the electrical performance and phase changed volume, which can explain the improvement in switching parameters of the proper TiO2layer interposed cell.

Ge2Sb2Te5(GST) thin films were deposited on SiO2∕Siand TiN∕Sisubstrates by cyclic metallorganic chemical vapor deposition using Ge(i-C4H9)4, Sb(i-C3H7)3, Te(i-C3H7)2as Ge, Sb, and Te precursors, respectively, with the help of Ar+H2plasma at temperatures ranging from 180 to 290°C. The application of plasma power was essential in obtaining a high growth rate and stoichiometric GST thin films. The chemical composition of the films was properly controlled by the cycling ratio and sequence of each precursor pulse. The stoichiometric films grown at 200°Cshowed a smooth surface morphology, highest density, and lowest impurity concentration. GST film was selectively grown inside the contact hole having a TiN∕Wplug.