Towards an Accurate Measurement of Thermal Contact Resistance at Chemical Vapor Deposition-Grown Graphene/SiO2 Interface Through Null Point Scanning Thermal Microscopy.

In the development of graphene-based electronic devices, it is crucial to characterize the thermal contact resistance between the graphene and the substrate precisely. In this study, we demonstrate that the thermal contact resistance between CVD-grown graphene and SiO2 substrate can be obtained by measuring the temperature drop occurring at the graphene/SiO2 interface with null point scanning thermal microscopy (NP SThM), which profiles the temperature distribution quantitatively with nanoscale spatial resolution (-50 nm) without the shortcomings of the conventional SThM. The thermal contact resistance between the CVD-grown graphene and SiO2 substrate is measured as (1.7 ± 0.27) x 10(-6) M2K/W. This abnormally large thermal contact resistance seems to be caused by extrinsic factors such as ripples and metal-based contamination, which inevitably form in CVD-grown graphene during the production and transfer processes.

Enabling low-noise null-point scanning thermal microscopy by the optimization of scanning thermal microscope probe through a rigorous theory of quantitative measurement.

The application of conventional scanning thermal microscopy (SThM) is severely limited by three major problems: (i) distortion of the measured signal due to heat transfer through the air, (ii) the unknown and variable value of the tip-sample thermal contact resistance, and (iii) perturbation of the sample temperature due to the heat flux through the tip-sample thermal contact. Recently, we proposed null-point scanning thermal microscopy (NP SThM) as a way of overcoming these problems in principle by tracking the thermal equilibrium between the end of the SThM tip and the sample surface. However, in order to obtain high spatial resolution, which is the primary motivation for SThM, NP SThM requires an extremely sensitive SThM probe that can trace the vanishingly small heat flux through the tip-sample nano-thermal contact. Herein, we derive a relation between the spatial resolution and the design parameters of a SThM probe, optimize the thermal and electrical design, and develop a batch-fabrication process. We also quantitatively demonstrate significantly improved sensitivity, lower measurement noise, and higher spatial resolution of the fabricated SThM probes. By utilizing the exceptional performance of these fabricated probes, we show that NP SThM can be used to obtain a quantitative temperature profile with nanoscale resolution independent of the changing tip-sample thermal contact resistance and without perturbation of the sample temperature or distortion due to the heat transfer through the air.

Quantitative measurement with scanning thermal microscope by preventing the distortion due to the heat transfer through the air.

Because of its high spatial resolution, scanning thermal microscopy (SThM) has been developed quite actively and applied in such diverse areas as microelectronics, optoelectronics, polymers, and carbon nanotubes for more than a decade since the 1990s. However, despite its long history and diverse areas of application, surprisingly, no quantitative profiling method has been established yet. This is mostly due to the nonlocal nature of measurement by conventional SThM: the signal measured by SThM is induced not only from the local heat flux through the tip-sample thermal contact but also (and mostly) from the heat flux through the air gap between the sample and the SThM probe. In this study, a rigorous but simple and practical theory for quantitative SThM for local measurement is established and verified experimentally using high-performance SThM probes. The development of quantitative SThM will make possible new breakthroughs in diverse fields of nanothermal science and engineering.

In situ curing of sliding SU-8 droplet over a microcontact printed pattern for tunable fabrication of a polydimethylsiloxane nanoslit.

A tunable process for polydimethylsiloxane (PDMS) nanoslit fabrication is developed for nanofluidic applications. A microcontact printing (µCP) of a laterally spreading self-assembled hexadecanethiol (HDT) layer, combined with in situ curing of a sliding SU-8 droplet, enables precise and independent tuning of a nanoslit-mold width and height using a single µCP master mold. The SU-8 nanoslit-mold is replicated using a hard-soft composite PDMS to prevent channel collapse at low (<0.2) aspect ratio (height over width). The fluidic characteristics as well as dimensions of nanoslits fabricated with various conditions are analyzed using a fluorescein sample and AFM images. Finally, concentration polarization-based sample preconcentration is successfully demonstrated at the nanoslit boundary where an electric double-layer is overlapped.

Quantitative temperature measurement of an electrically heated carbon nanotube using the null-point method.

Previously, we introduced the double scan technique, which enables quantitative temperature profiling with a scanning thermal microscope (SThM) without distortion arising from heat transfer through the air. However, if the tip-sample thermal conductance is disturbed due to the extremely small size of the sample, such as carbon nanotubes, or an abrupt change in the topography, then quantitative measurement becomes difficult even with the double scan technique. Here, we developed the null-point method by which one can quantitatively measure the temperature of a sample without disturbances arising from the tip-sample thermal conductance, based on the principle of the double scan technique. We first checked the effectiveness and accuracy of the null-point method using 5 µm and 400 nm wide aluminum lines. Then, we quantitatively measured the temperature of electrically heated multiwall carbon nanotubes using the null-point method. Since the null-point method has an extremely high spatial resolution of SThM and is free from disturbance due to the tip-sample thermal contact resistance, and distortion due to heat transfer through the air, the method is expected to be widely applicable for the thermal characterization of many nanomaterials and nanodevices.

Nanoscale range finding of subsurface structures by measuring the absolute phase lag of thermal wave.

The need for a subsurface imaging technique to locate and characterize subsurface defects in multidimensional micro- and nanoengineered devices has been growing rapidly. We show that a subsurface heater can be located accurately using the phase lag of a thermal wave. We deduce that the absolute phase lag is composed of four components. Among the four components, we isolate the component directly related to the position and the structure of the periodic heat source. We demonstrate that the position of the heater can be estimated accurately from the isolated phase lag component.

An autopsy case of postpartum acute myocardial infarction associated with postpartum ergot alkaloids administration in old-aged pregnant women.

Cases of acute myocardial infarction (AMI) that occur during pregnancy or postpartum are rarely reported. Ergot derivatives are known to induce the spasmodic contraction of coronary arteries. Administration of ergot derivatives can cause AMI, even in normal healthy people. In several reported cases, ergot derivatives triggered severe AMI during the postpartum period. Here, we report the case of a forty-year-old woman who was successfully impregnated by artificial fertilization and died after treatment with ergot derivatives. The autopsy revealed AMI with severe coronary atherosclerosis. This is the first case that reports aggravation of pre-existent severe coronary atherosclerosis after postpartum infusion of ergot derivatives.

Efficacy assessment of CellSlide in liquid-based gynecologic cytology.

OBJECTIVE: To evaluate the efficacy of CellSlidetrade mark (CS) method in liquid-based gynecologic cytology. METHODS: We compared 1221 specimens prepared by both CS and conventional techniques to evaluate specimen adequacy and cytologic diagnoses. Sensitivity and specificity of these techniques were analyzed in 54 cases using the available histological data. RESULTS: Quality limiting factors, such as obscuring inflammation or blood, were markedly reduced in CS (0.2%) compared to the conventional smear (4.9%). There was a complete agreement in the Bethesda 2001 diagnosis between these methods in 1132 cases (92.7%) out of 1221. 16.7% more ASC cases and 37.5% more low-grade squamous intraepithelial lesions (LSIL) and 21.4% more high-grade SIL (HSIL) were detected on the CS slides than on the conventional smears. Sensitivity rates, relative to histological data, were 91.4% (CS) and 74.3% (conventional) and specificity rates were same (89.5%) for ASC and more severe lesions. Infectious organisms (Trichomonas and Candida, etc.) were readily identifiable in both methods. CONCLUSIONS: CS preparation is more sensitive and equally specific in detecting epithelial abnormalities when compared to the conventional smear. In addition, it has a lower incidence of unsatisfactory results with hypocellularity or >75% obscuration of cells.

Correlation between cyclooxygenase-2 and tumor angiogenesis in non-small cell lung cancer.

The role of COX-2 expression and angiogenesis of lung cancer is yet to be delineated. Eighty four non-small cell lung cancer (NSCLC) specimens were evaluated for COX-2 expression, microvessel density (MVD), and vascular endothelial growth factor (VEGF) expression by immunohistochemical methods. The relationships between COX-2 expression and MVD, VEGF expression, and survival time were analyzed. COX-2 expression was observed in the cytoplasm and membrane of the carcinoma cells, and premalignant cells. COX-2 was positive in 67 cases (79.8%). There was a statistically significant correlation between COX-2 expression and tumor size, TNM stage, tumor type, VEGF expression, and vascular pattern with survival in univariate analysis. No significant correlation was seen between COX-2, VEGF expression and MVD. A lack of expression of either COX-2 or VEGF expression or both, however, was associated with lower MVD than the group with both expressed. The difference was statistically significant (P=0.005). Statistically significant differences were also observed according to TNM stage, vascular pattern, COX-2 expression, and VEGF expression. With multivariate analysis, only TNM stage and COX-2 expression retained their significance as independent predictors of survival. COX-2 expression takes part in tumor angiogenesis and is a significant poor prognostic factor in the surgically resected NSCLC. COX-2 inhibitor, either in combination therapy with other agents, or for chemoprevention, may be effective via suppression of angiogenesis in this fatal disease.