Interaction between the substrate and probe in liquid metal Ga: experimental and theoretical analysis.

Interaction between two bodies in a liquid metal is an important topic for development of metallic products with high performance. We conducted atomic force microscopy measurements and achieved the interaction between the substrate and the probe in liquid Ga of an opaque and highly viscous liquid. The interaction cannot be accessed with the normal atomic force microscopy, electron microscopy, and beam reflectometry. We performed a theoretical calculation using statistical mechanics of simple liquids by mixing an experimentally derived quantum effect. From both experiment and theory, we found an unusual behaviour in the interaction between the solvophobic substances, which has never been reported in water and ionic liquids. Shapes of the interaction curves between several solvophobic and solvophilic pairs in liquid Ga are also studied.

Fundamental and higher eigenmodes of qPlus sensors with a long probe for vertical-lateral bimodal atomic force microscopy.

The detection of vertical and lateral forces at the nanoscale by atomic force microscopy (AFM) reveals various mechanical properties on surfaces. The qPlus sensor is a widely used force sensor, which is built from a quartz tuning fork (QTF) and a sharpened metal probe, capable of high-resolution imaging in viscous liquids such as lubricant oils. Although a simultaneous detection technique of vertical and lateral forces by using a qPlus sensor is required in the field of nanotribology, it has still been difficult because the torsional oscillations of QTFs cannot be detected. In this paper, we propose a method to simultaneously detect vertical and lateral force components by using a qPlus sensor with a long probe. The first three eigenmodes of the qPlus sensor with a long probe are theoretically studied by solving a set of equations of motion for the QTF prong and probe. The calculation results were in good agreement with the experimental results. It was found that the tip oscillates laterally in the second and third modes. Finally, we performed friction anisotropy measurements on a polymer film by using a bimodal AFM utilizing the qPlus sensor with a long probe to confirm the lateral force detection.

Controlled Growth of Organosilane Micropatterns on Hydrophilic and Hydrophobic Surfaces Templated by Vacuum Ultraviolet Photolithography.

In this report, micropatterns of (3-aminopropyl)trimethoxysilane (APTMS) were developed on hydrophilic and hydrophobic surfaces after patterning using 172 nm vacuum ultraviolet (VUV) photolithography. Self-assembled monolayers (SAMs) formed on Si substrates through UV hydrosilylation of 1-hexadecene (HD) and 10-undecenoic acid (UDA) were used as hydrophilic and hydrophobic surfaces, respectively. For templating the HD- and UDA-SAMs, the VUV light was exposed to HD- and UDA-SAMs from the slits of photomasks in atmospheric and evacuated environments, respectively. Various oxygenated groups were generated at the exposed domains of HD-SAM, while the COOH groups were trimmed from the irradiated domains of UDA-SAM. The APTMS molecules were immobilized on the domains that were terminated by oxygenated groups after chemical vapor deposition (CVD). The thicknesses of the developed APTMS micropatterns increased significantly by raising the CVD temperature and in the presence of ambient air in the CVD Teflon container as well. The increase in thicknesses was ascribed to the formation of APTMS multilayers, which were mediated by H3N+ ions. Also, the developed APTMS micropatterns on the UDA-SAM patterned by VUV light irradiation in a high-vacuum environment (HV-VUV) were thicker than those on the VUV/(O) patterned HD-SAM due to the presence of inactive oxygenated groups at the surface of VUV/(O)-terminated domains of HD-SAM such as COO-C and C-O-C groups. The presence of water or ambient air facilitated the silane coupling between the silyl groups with the oxygenated and amino groups The combination of VUV photolithography and the CVD method with control of the conditions would enable us to control the thicknesses and shapes of the developed APTMS micropatterns. These findings illustrate the applicability of VUV photolithography for templating hydrophobic and hydrophobic surfaces toward the development of organosilane architectures, which can be feasible for several applications.

Chemical Etching of Silicon Assisted by Graphene Oxide in an HF-HNO3 Solution and Its Catalytic Mechanism.

Chemical etching of silicon assisted by various types of carbon materials is drawing much attention for the fabrication of silicon micro/nanostructures. We developed a method of chemical etching of silicon that utilizes graphene oxide (GO) sheets to promote the etching reaction in a hydrofluoric acid-nitric acid (HF-HNO3) etchant. By using an optimized composition of the HF-HNO3 etchant, the etching rate under the GO sheets was 100 times faster than that of our HF-H2O2 system used in a previous report. Kinetic analyses showed that the activation energy of the etching reaction was almost the same at both the bare silicon and GO-covered areas. We propose that adsorption sites for the reactant in the GO sheets enhance the reaction frequency, leading to a deeper etching in the GO areas than the bare areas. Furthermore, GO sheets with more defects were found to have higher catalytic activities. This suggests that defects in the GO sheets function as adsorption sites for the reactant, thereby enhancing the etching rate under the sheets.

Microstructured SiOx/COP Stamps for Patterning TiO2 on Polymer Substrates via Microcontact Printing.

Microcontact printing (µCP) techniques have sparked a surge of interests in microfabrication since they help produce arrays on a wide range of target substrates in a facile and efficient manner. Polydimethylsiloxane (PDMS), as a well-established material for stamps, has constraints resulting from its hydrophobicity and softness, and the replication of PDMS stamps usually requires rigid masters or processes using a photoresist. Herein, a novel µCP stamp based on cyclo-olefin polymer (COP) is produced through vacuum ultraviolet (VUV) lithography. 2,4,6,8-Tetramethylcyclotetrasiloxane is selectively deposited at the affinity-patterns on the COP surface, and these patterned siloxane films are converted into SiOx meanwhile protecting the COP beneath them from the VUV photoetching. By this means, a patterned relief is fabricated on the COP plates, resulting in a hydrophilic SiOx/COP µCP stamp with punch heights of ∼180 nm. The novelty arises from the simplicity of the master- and photoresist-free microstructuring, and the higher stiffness of SiOx/COP stamps prevents the deformation during pressing. Finally, an example µCP is given to transfer titania precursor gel and produce TiO2 micropatterns on flexible polymer substrates. The SiOx/COP stamps and the µCP of TiO2 provide simple and cost-effective patterning techniques, which should contribute to the future design and creation of flexible devices.

Formation of submicron-sized silica patterns on flexible polymer substrates based on vacuum ultraviolet photo-oxidation.

Formation of precise and high-resolution silica micropatterns on polymer substrates is of importance in surface structuring for flexible device fabrication of optics, microelectronic, and biotechnology. To achieve that, substrates modified with affinity-patterns serve as a strategy for site-selective deposition. In the present paper, vacuum ultraviolet (VUV) treatment is utilized to achieve spatially-controlled surface functionalization on a cyclo-olefin polymer (COP) substrate. An organosilane, 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS), preferentially deposits on the functionalized regions. Well-defined patterns of TMCTS are formed with a minimum feature of ∼500 nm. The secondary VUV/(O)-treatment converts TMCTS into SiO x , meanwhile etches the bare COP surface, forming patterned SiO x /COP microstructures with an average height of ∼150 nm. The resulting SiO x patterns retain a good copy of TMCTS patterns, which are also consistent with the patterns of photomask used in polymer affinity-patterning. The high quality SiO x patterns are of interests in microdevice fabrication, and the hydrophilicity contrast and adjustable heights reveal their potential application as a "stamp" for microcontact printing (µCP) techniques.

1,2-Epoxyalkane: Another Precursor for Fabricating Alkoxy Self-Assembled Monolayers on Hydrogen-Terminated Si(111).

This work describes the UV alkoxylation of a series of 1,2-epoxyalkanes on the hydrogen-terminated silicon (H-Si) substrate. The formation of alkoxy self-assembled monolayers (SAMs) and the nature of bonding at the surface of H-Si were examined using water contact angle goniometer, spectroscopic ellipsometer, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy. UV exposure to 1,2-epoxyalkane mesitylene solution for 60 min formed alkoxy-SAMs onto H-Si with hydrophobic properties. The local molecular environment of the alkyl chains transitioned from a disordered, liquid-like state to an ordered, crystalline-like structure with increasing the chain length. XPS and FTIR indicated that the reaction of H-Si with 1,2-epoxyalkane produced Si-O-C linkages. The Si-H bond homolysis and electron/hole were the plausible mechanistic routes for the grafting of 1,2-epoxyalkanes.

Vacuum Ultraviolet Treatment of Acid- and Ester-Terminated Self-Assembled Monolayers: Chemical Conversions and Friction Reduction.

We have prepared COOH- and COOCH3-terminated self-assembled monolayers (SAMs) from undec-10-enoic acid (UDA) and methyl undec-10-enoate (MUDO) molecules on hydrogen-terminated silicon (H-Si) substrates through ultraviolet (UV) irradiation. The as-prepared UDA- and MUDO-SAMs were exposed to 172 nm vacuum-UV (VUV) light in a high vacuum environment (HV, <10-3 Pa) for different periods. The presence of COO components at the surfaces of these SAMs without prior oxidation would simplify the understanding of the origin of the chemical conversions and the changes of surface properties, as the prior oxidation would change the surface properties and generate different oxygenated groups. After the HV-VUV treatment, the abundance of COOH and COOCH3 components of these SAMs decreased without significant dissociation of their C-C backbones. Degradation of these components occurred through dissociating their C-O bonds, resulting in different C═O components. Also, the occurrence of Norrish type pathways resulted in a slight decrease of carbon content and produced CH3 components. We have applied the HV-VUV lithography to control the abundance of COOH and COOCH3 components in well-defined areas and to investigate the friction differences between the irradiated and masked areas. The irradiated areas exhibited lower friction than the masked areas without observing significant height contrasts between these areas. The reduction in friction was attributed to the conversion of the COOH and COOCH3 components to less adhesive components such as C═O and CH3. These experiments suggest the HV-VUV treatments as an approach for low damage dry surface modifications and reductive lithographic techniques at surfaces terminated by acid and ester groups.

Decoration of reduced graphene oxide by gold nanoparticles: an enhanced negative photoconductivity.

Photodetection in a visible light region is important in various applications, including computation, environmental monitoring, biological detection and industrial control. Due to this, research studies to develop photoconductive devices have great significance. We report a study on the photoconductivity of reduced graphene oxide (rGO)/gold nanoparticle (AuNP) nanocomposites, emphasizing the enhancement effect induced by AuNPs. rGO/AuNP photoelectric devices were prepared by spincoating rGO onto an AuNP-array-covered silicon substrate. Photoelectric responses under visible light illumination were measured and the results showed that the negative photoelectric responsivity of rGO was improved by 3 orders of magnitude due to AuNPs. The effects of AuNPs on negative photoconductivity (NPC) properties of rGO were investigated, and it was found that AuNPs affected NPC in three aspects: (1) AuNPs form discrete electrodes separated by nanoscale gaps which generated new conduction paths, and hence the conductivity of rGO was enhanced by 3 orders of magnitude; (2) localized surface plasmon resonance (LSPR) of AuNPs effectively enhances total light absorption of rGO; (3) photocurrent between AuNPs and rGO can weaken the NPC property of rGO. The low-cost and mass-producible rGO/AuNP nanocomposites demonstrate high photoelectric responsivity, which hold much promise for NPC devices.

Low Damage Reductive Patterning of Oxidized Alkyl Self-Assembled Monolayers through Vacuum Ultraviolet Light Irradiation in an Evacuated Environment.

Through 172 nm vacuum ultraviolet light irradiation in a high vacuum condition (HV-VUV), well-defined micropatterns with a varied periodic friction were fabricated at the surface of self-assembled monolayers (SAMs) terminated with oxygenated groups. No apparent height contrast between the HV-VUV-irradiated and -masked areas was observed, which indicated the stability of the C-C skeleton of the assembled molecules. The trimming of oxygenated groups occurred through dissociating the C-O bonds and promoting the occurrence of α- and ß-cleavages in the C═O-containing components. Hence, the HV-VUV treatment trimmed the oxygenated groups without degrading the C-C skeleton. The HV-VUV treatment influenced the order of the assembled molecules, and the step-terrace structure was distorted. The decrease in friction at the HV-VUV-irradiated domains was attributed to the dissociation of oxygenated groups. (3-Aminopropyl)trimethoxysilane (APTMS) aggregated at the masked areas of the HV-VUV-patterned SAM, where the oxygenated groups worked as anchors. APTMS aggregations did not exist at the irradiated areas, indicating the trimming of the oxygenated groups at these areas. The direct assembling of APTMS on the Si substrate at the irradiated areas was prevented by the remaining C-C skeleton.

Immobilization of Reduced Graphene Oxide on Hydrogen-Terminated Silicon Substrate as a Transparent Conductive Protector.

Silicon is a promising electrode material for photoelectrochemical and photocatalytic reactions. However, the chemically active surface of silicon will be easily oxidized when exposed to the oxidation environment. We immobilized graphene oxide (GO) onto hydrogen-terminated silicon (H-Si) and reduced it through ultraviolet (UV) and vacuum-ultraviolet (VUV) irradiation. This acted as an ultrathin conductive layer to protect H-Si from oxidation. The elemental evolution of GO was studied by X-ray photoelectron spectroscopy, and it was found that GO was partially reduced soon after the deposition onto H-Si and further reduced after UV or VUV light irradiation. The VUV photoreduction demonstrated ca. 100 times higher efficiency compared to the UV reduction based on the irradiation dose. The saturated oxygen-to-carbon ratio (RO/C) of the reduced graphene oxide (rGO) was 0.21 ± 0.01, which is lower than the photoreduction of GO on SiO2 substrate. This indicated the H-Si played an important role in assisting the photoreduction of GO. No obvious exfoliation of rGO was observed after sonicating the rGO-covered H-Si sample in water, which indicated rGO was immobilized on H-Si. The electrical conductivity of H-Si surface was maintained in the rGO-covered region while the exposed H-Si region became insulating, which was observed by conductive atomic force microscopy. The rGO was verified capable to protect the active H-Si against the oxidation under an ambient environment.

Correction: Chemical conversion of self-assembled hexadecyl monolayers with active oxygen species generated by vacuum ultraviolet irradiation in an atmospheric environment.

Correction for 'Chemical conversion of self-assembled hexadecyl monolayers with active oxygen species generated by vacuum ultraviolet irradiation in an atmospheric environment' by Ahmed I. A. Soliman et al., Soft Matter, 2015, 11, 5678-5687.

Vacuum-Ultraviolet Promoted Oxidative Micro Photoetching of Graphene Oxide.

Microprocessing of graphene oxide (GO) films is of fundamental importance in fabricating graphene-based devices. We demonstrate the photoetching of GO sheets using vacuum-ultraviolet (VUV, λ = 172 nm) light under controlled atmospheric pressure. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and differential interference contrast microscopy (DIC) studies revealed that the photoetching of GO films successfully proceeded in the regions exposed to VUV irradiation in the oxygen-containing atmosphere. Precise photoetching of the GO sheets was achieved at a vacuum pressure of 5 × 10(3) Pa with VUV light irradiation for 20 min. This was followed by VUV irradiation in a high vacuum (<10(-3) Pa) and sonication in water. The photoetched GO sheets then transformed into reduced GO (rGO) patterns. The minimum feature fabricated by this method was 2 µm wide lines aligned at an interval of 4 µm. This method provides a cost-effective way to fabricate rGO patterns with fewer boundaries between rGO sheets and offers a better integrity of rGO, which can be promising for further applications in micro mechanics, micro electrochemistry, optoelectronics, etc.

Chemical conversion of self-assembled hexadecyl monolayers with active oxygen species generated by vacuum ultraviolet irradiation in an atmospheric environment.

Vacuum ultraviolet (VUV, λ = 172 nm) irradiation of alkyl self-assembled monolayers (SAMs) in the presence of dry air alters their surface properties. In this work, UV photochemically prepared hexadecyl (HD)-SAMs on hydrogen-terminated silicon substrates were irradiated by VUV light in dry air, which generated active oxygen species upon excitation of the atmospheric oxygen molecules. These active oxygen species converted the terminal methyl groups of the SAMs to polar functional groups, which were examined quantitatively by X-ray photoelectron spectroscopy (XPS) and chemical labeling. At the first stage of VUV irradiation, the surface of SAMs was functionalized, and the ratios of the generated polar functional groups markedly increased. With the elongation of the irradiation period, the SAMs gradually degraded, and the total polar group percentages gradually decreased. The difference between the oxygenated carbon components derived by the deconvolution of the XPS carbon (C1s) spectrum and the chemical labeling of polar groups revealed enormous quantities of ethereal and ester groups that cannot react with the labeling reagents but are included in the C1s spectral envelope. These modifications were reflected on morphological structures of SAMs, which were gradually distorted until a complete amorphous structure was obtained after the complete elimination of HD-SAMs.

Potential-dependent structures investigated at the perchloric acid solution/iodine modified Au(111) interface by electrochemical frequency-modulation atomic force microscopy.

Electrochemical frequency-modulation atomic force microscopy (EC-FM-AFM) was adopted to analyze the electrified interface between an iodine modified Au(111) and a perchloric acid solution. Atomic resolution imaging of the electrode was strongly dependent on the electrode potential within the electrochemical window: each iodine atom was imaged in the cathodic range of the electrode potential, but not in the more anodic range where the tip is retracted by approximately 0.1 nm compared to the cathodic case for the same imaging parameters. The frequency shift versus tip-to-sample distance curves obtained in the electric double layer region on the iodine adlayer indicated that the water structuring became weaker at the anodic potential, where the atomic resolution images could not be obtained, and immediately recovered at the original cathodic potential. The reversible hydration structures were consistent with the reversible topographic images and the cyclic voltammetry results. These results indicate that perchlorate anions concentrated at the anodic potential affect the interface hydration without any irreversible changes to the interface under these conditions.

Clinical role of Foxp3+ regulatory T cell in Living donor related liver transplantation for prediction of life-threatening complications.

PURPOSES: It is no doubt that regulatory T cells (Foxp3(+)CD4(+)CD25(+)T cells: Treg) play important roles in transplant immunity. We investigated the significance of Treg expression in acute stage of living donorrelated liver transplantation (LDLT) for the possibility of the sensitive marker for immunological state and homeostatic stress after liver transplantation. METHODS: Peripheral blood was drawn from 5 recipients of LDLT preoperatively and on post operative 1, 4, 7, and 14 days. The peripheral blood mononuclear cells (PBMCs) were stained with CD4, CD25, Foxp3, and were analyzed with FACScan. This data was compared with clinical output of LDLT. RESULT: The populations of Treg were significantly decreased in all patients on day 1 after LDLT and significantly increased in patients who had early postoperative complications compared with patients who had no complications. CONCLUSIONS: The population of Treg in peripheral blood may reflect the surgical stress such as life-threatening complications after LDLT.

Potential-dependent hydration structures at aqueous solution/graphite interfaces by electrochemical frequency modulation atomic force microscopy.

Potential-dependent solvation structures of aqueous electrolyte-graphite interfaces were studied using electrochemical frequency modulation atomic force microscopy. Oscillatory modulations on the force curves reversibly changed with the applied potential on the graphite electrode, and also strongly depended on the anion species in electrolyte solutions.

Valproic acid enhances the anti-tumor effect of pegylated interferon-α towards pancreatic cancer cell lines.

BACKGROUND: Valproic acid (VPA) acts as a specific inhibitor of class I HDACs and it use has been proven to be safe since a long time. MATERIALS AND METHODS: In the present study, we investigated the effect of VPA in the combination with pegylated interferon-α (PEG-IFNα) in inhibition of cell proliferation of human pancreatic cancer cell lines. RESULTS: VPA enhanced the effect of PEG-IFNα, and the effect was decreased by the caspase inhibitor. VPA alone and VPA in combination with PEG-IFNα increased the expression of interferon-α receptor and interferon regulatory factor 8. CONCLUSION: The combination of VPA and PEG-IFNα can be useful for the treatment of pancreatic cancer.

Beneficial effects of enteral nutrition containing with hydrolyzed whey peptide on warm ischemia/reperfusion injury in the rat liver.

AIM: This study examined the efficacy of enteral nutrition containing hydrolyzed whey peptide (HWP) on warm ischemia/reperfusion (I/R) injury in the rat liver. METHODS: Male Wistar rats were subjected to 30 min of warm hepatic ischemia followed by immediate p.o. intake of enteral nutrition with WHP (HWP group) or 20% glucose solution (control group) (0.025 mL/g). The animals were killed at 6 or 12 h after reperfusion. The serum aspartate aminotransferase (AST) and alanine aminotransferase alt (ALT) levels were measured. The necrotic areas were assessed histologically. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and caspase-3 activation were assessed to evaluate apoptosis. The expressions of hepatic tumor necrosis factor (TNF)-α, interleukin (IL)-6 and nuclear factor (NF)-κB in the liver tissue were assessed by real time reverse transcription polymerase chain reaction. RESULTS: Significant reductions in the serum AST and ALT levels were seen in the HWP group compared with the control group at both 6 and 12 h after reperfusion. The necrotic areas and numbers of TUNEL positive cells were significantly decreased in the HWP group at 6 and 12 h after reperfusion. The caspase-3/7 activities were significantly decreased in HWP group at 6 and 12 h after reperfusion. The mRNA expressions of TNF-α and IL-6 were significantly reduced in the HWP group at 12 h after reperfusion. NF-κB mRNA expression was significantly increased in the HWP group at 6 and 12 h after reperfusion. CONCLUSION: Enteral nutrition containing HWP ameliorated the hepatic warm I/R injury possibly through the suppression of pro-inflammatory cytokine expressions and the induction of NF-κB in the rat liver.

Blood vessel-based liver segmentation using the portal phase of an abdominal CT dataset.

PURPOSE: Blood vessel (BV) information can be used to guide body organ segmentation on computed tomography (CT) imaging. The proposed method uses abdominal BVs (ABVs) to segment the liver through the portal phase of an abdominal CT dataset. This method aims to address the wide variability in liver shape and size, separate liver from other organs of similar intensity, and segment hepatic low-intensity tumors (LITs). METHODS: Thin ABVs are enhanced using three-dimensional (3D) opening. ABVs are extracted and classified into hepatic BVs (HBVs) and nonhepatic BVs (non-HBVs) with a small number of interactions, and HBVs and non-HBVs are used for constraining automatic liver segmentation. HBVs are used to individually segment the core region of the liver. To separate the liver from other organs, this core region and non-HBVs are used to construct an initial 3D boundary surface. To segment LITs, the core region is classified into non-LIT- and LIT-parts by fitting the histogram of the core region using a variational Bayesian Gaussian mixture model. Each part of the core region is extended based on its corresponding component of the mixture, and extension is completed when it reaches a variation in intensity or the constructed boundary surface, which is reconfirmed to fit robustly between the liver and neighboring organs of similar intensity. A solid-angle technique is used to refine main BVs at the entrances to the inferior vena cava and the portal vein. RESULTS: The proposed method was applied to 80 datasets: 30 Medical Image Computing and Computer Assisted Intervention (MICCAI) and 50 non-MICCAI; 30 datasets of non-MICCAI data include tumors. Our results for MICCAI-test data were evaluated by sliver07 (http://www.sliver07.org/) organizers with an overall score of 85.7, which ranks best on the site as of July 2013. These results (average ± standard deviation) include the five error measures of the 2007 MICCAI workshop for liver segmentation as follows. Results for volume overlap error, relative volume difference, average symmetric surface distance, root mean square symmetric surface distance, and maximum symmetric surface distance were 4.33 ± 0.73, 0.28 ± 0.87, 0.63 ± 0.16, 1.19 ± 0.28, and 14.01 ± 2.88, respectively; and when applying our method to non-MICCAI data, results were 3.21 ± 0.75, 0.06 ± 1.29, 0.45 ± 0.17, 0.98 ± 0.26, and 12.69 ± 3.89, respectively. These results demonstrate high performance of the method when applied to different CT datasets. CONCLUSIONS: BVs can be used to address the wide variability in liver shape and size, as BVs provide unique details for the structure of each studied liver. Constructing a boundary surface using HBVs and non-HBVs can separate liver from its neighboring organs of similar intensity. By fitting the histogram of the core region using a variational Bayesian Gaussian mixture model, LITs are segmented and measuring the volumetry of non-LIT- and LIT-parts becomes possible. Further examination of the proposed method on a large number of datasets is required for clinical applications, and development of the method for full automation may be possible and useful in the clinic.