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For polydimethylsiloxane (PDMS), a formation of interconnected pores and an addition of Silwet L-77 are, respectively, made as physical treatment and chemical one to change the material properties involved in the water permeable flow through PDMS. Here, we investigate a change in the water permeable flow through PDMS induced by physicochemical treatment. 28 kinds of physicochemically treated PDMS (pc-PDMS) blocks having different pore sizes of 50–500 µm and different Silwet L-77 concentrations of 0.0–8.0 wt% are prepared using a pressure-assisted compaction and NaCl particle-leaching technique. The values of mass flow rate and flow delay are obtained from pressure-driven water flow through pc-PDMS blocks as indexes for characterizing their water permeable flow. Our physicochemical treatment successfully controls the water permeable flow through PDMS, which means that pc-PDMS can be used for the development of powerless microfluidic regulators for aqueous chemicals in micro-total analysis systems (µ-TAS).

A functional polymer-matrix composite (PMC) with controllable material properties is emerging as a promising material for the smart sensors in structural health monitoring (SHM). A GnF/PDMS composite is developed as a new functional PMC by blending graphite nanoflakes (GnFs) with polydimethylsiloxane (PDMS) where GnF and PDMS are used as a reinforcing/conductive filler and an elastic host matrix, respectively. We characterize the mechanoelectrical property-controllable GnF/PDMS composite, mainly focusing on the following issues: (i) determination of the best solvent for the preparation of a GnF/PDMS composite solution, (ii) exploration of changes in the mechanoelectrical properties of the functional PMC induced by variations in the aspect ratio (AR) and concentration of GnF. Among 9 kinds of common solvents, benzene shows both high GnF dispersibility and excellent PDMS compatibility, therefore being chosen as the optimal solvent. Variations in GnF AR (223–1017) and GnF concentration (1.0–25.0 wt.%) lead to significant changes in the elastic modulus, fracture strain, electrical conductivity, and gauge factor of the functional PMC in the ranges of 0.39–13.8 MPa, 0.09 to 2.54, 6.97 × 10−6 to 221.0 S/m, and 6 to about 37,000, respectively. The empirical models for predicting the mechanoelectrical properties of the functional PMC are also intensively studied. Our GnF/PDMS composite is expected to be used as a functional PMC for the development of smart sensors that detect deformation and fracture in structures.

The graphite nanoflake (GnF)-reinforced polydimethylsiloxane (PDMS) composites (GnF/PDMS composites) are developed as new polymer matrix composites (PMCs) with controllable mechanoelectrical properties. Here, we investigate the effect of GnF concentration on the mechanoelectrical properties (i.e., elastic modulus, fracture strain, and conductivity) of GnF/PDMS composites; the change in the surface morphology of GnF/PDMS composites caused by a variation in GnF concentration is also explored. The mechanoelectrical properties are measured by performing tensile tests on the GnF/PDMS composite specimens with different GnF concentrations of 5.0, 10.0, 12.5, 15.0, 20.0, and 25.0 wt.%. The surface morphology is analyzed in terms of internal void formation and surface roughness. The elastic modulus is measured to be in the range of 1.62 to 13.8 MPa which is proportional to GnF concentration, while the fracture strain and electrical conductivity are respectively characterized to be in ranges of 0.09 to 2.09 and 0.3 to 221.0 S/m which are in inverse proportion to GnF concentration. An increase in GnF concentration leads to increases in internal voids’ amount and surface roughness. The GnF/PDMS composites can be used as sensing materials for detecting both small and large deformations in a variety of engineering applications.

Porosity is suppressible but unavoidable in manufacturing nanocomposites, therefore affecting their mechanical properties like intrinsic properties and other filler-related factors. Despite all the efforts, it is still regarded as challenging to develop theoretical models for mechanical properties of filler-reinforced nanocomposites which consider void defects created during manufacturing process. Here, graphite nanoflake/polydimethylsiloxane (GnF/PDMS) nanocomposites for paint-on applications are manufactured with different processing methods (i.e., solvent casting, hand lay-up, and spray lay-up) to address imperfections involved in each process and their implication to mechanical properties. The manufacturing processes were found to have almost no alternation on filler-related features (i.e., size, orientation, and distribution) except porosity. The evolution of a porosity is best modeled with the logistic function. We establish a set of prediction models for elastic modulus, fracture strength, and elongation at break by combining the previous models (i.e., Tsai-Hahn, Piggott-Leidner, and Landel-Nielsen models) with the logistic function on porosity. The proposed models are in good agreement with the experimental data on GnF/PDMS nanocomposites. The effect of process method on surface morphology is also discussed.

Diverse surface/bulk treatments have been introduced to overcome the interfacial limitations of pristine (or untreated) PDMS, thus extending the possible applications of PDMS in micro/nano device development. Despite of extensive efforts, the temporal wetting change of PDMS induced by surface/bulk treatments still remains incompletely understood. We prepared 3 kinds of physicochemically treated PDMS blocks using widely used surface/bulk treatments-3D interconnected pore network formation, biocompatible surfactant (i.e., Silwet L-77) addition, and combination of both. Their wetting nature was characterized by measuring the time profile of water contact angle. A 3D interconnected pore network formation produced a time-invariant decrease in PDMS wettability; a surfactant addition increased the PDMS wettability in a time-variant way; a combination of pore network formation and surfactant addition had a combined effect. The measurement led to the successful development of a model for predicting the temporal wetting change in PDMS caused by variances in pore size and surfactant concentration. The accuracy of our model was verified by comparing experimental results with model predictions. This model will result in better understanding of polymer interface.

A skin-perforable dissolving microneedle is a promising mediator for painlessly delivering active pharmaceutical compounds across the skin. All the microneedle manufacturing processes so far, however, are much sensitive to input variation and unfavorable for make-to-order approach. Here, a robust method for fabricating mass-customizable master molds is developed to prepare sharp-tipped biodegradable polymer microneedles. Our approach combines the predrying and chip casting (PCC) of an ultrathick photoresist layer with a substrateless, inclined, and rotational exposure (SIR exposure). The PCC achieves the uniform reduction of solvent across the photoresist thickness which is critically required for the formation of a sharp tip; the SIR exposure creates master molds whose geometry is easily customizable and virtually insensitive to a variation in ultraviolet (UV) exposure dose. A theoretical model for the spatiotemporal distribution of UV dose under SIR exposure is established to show the technological superiority of our method. Next, our method's applicability is proven by fabricating a set of poly(lactic-co-glycolic) acid (PLGA) microneedles and performing both porcine skin penetration test and their in vitro degradation test. Our approach is verified to be robust in manufacturing mass-customizable molds for skin-perforable dissolving microneedles and to have high compatibility with almost all existing biodegradable polymers. The findings of this study lead to both a significant growth of dissolving microneedle-mediated drug delivery and better understanding of drug release kinetics.

The reversible migration of adatoms along a basal plane of graphene under electrical bias is experimentally demonstrated. Single-layer graphene oxide with partial oxygen adatom coverage is utilized for this demonstration. The intensity ratio of G and G' Raman modes is used to determine the oxygen adatoms migration. Finally, reversible wettability property of graphene due to oxygen adatom migration is demonstrated.

CMOS utilizing high mobility III–V channels on Si substrates is expected to be one of the promising devices for high performance and low power integrated systems in the future technology nodes, because of the enhanced carrier transport properties. In addition, Tunnel FETs (TFETs) using III–V channel materials are regarded as one of the most promising steep slope devices for the ultra-low power applications. In this presentation, we address the critical issues for realizing III–V MOSFETs and TFETs on the Si CMOS platform. Viable technologies of MOS channel, gate stack, source/drain and tunnel junction formation are introduced for satisfying the device requirements. The electrical properties of ultrathin body InAs MOSFETs, InGaAs/Ge CMOS, InAs/GaSb CMOS, InGaAs TFETs and InGaAs/GaAsSb TFETs are presented.

The dynamic nature of cell adhesion and detachment is critically important to a variety of physiological and pathophysiological phenomena. Much, however, still remains uncertain and controversial about the mechanochemical players and processes involved in cellular adhesion and detachment. This leads to the need for quantitative characterization of the adhesion and detachment of anchorage-dependent cells. Here, cell adhesion and detachment up to subcellular level are examined using gold surfaces modified with a thiol-functionalized arginine-glycine-aspartic acid (RGD) peptide. A thiol self-assembled monolayer (SAM) on top of the gold surfaces is reductively desorbed with activation potential to spatiotemporally manipulate both cell adhesion and detachment. This method maintains cells of interest living and intact during experiments, making it possible to quantify cell adhesion and detachment as close as possible to in vivo conditions. Experimental characterizations for NIH 3T3 fibroblasts are carried out with a focus on the following issues: the effect of the size and geometric shape of gold surfaces on cell adhesion; the effect of cell confluency, cell shape, and activation potential magnitude on cell detachment; changes in the material properties of cells during cell detachment. The findings of this study should lead to better understanding of cellular dynamics in anchorage-dependent cells.

This paper presents the simplified analytical and numerical analyses of the ultralarge deflection of circular polydimethylsiloxane (PDMS) microballoons (MBs) under pressure for microelectromechanical systems design. The analytical model assuming spherical symmetry on the deformed shape of MB yields a simplified solution on the pressure-normalized maximum deflection and two in-plane principal strains of the ultralargely deflected MB. The accuracy of the theoretical model is evaluated by comparing against the experimental results. Furthermore, by using a computational analysis that incorporates a Mooney-Rivlin model for a PDMS micromembrane, the properties of the PDMS fabricated at a mixing ratio of 10:1 base to catalyst, a curing temperature of 20°C, and a curing time of 48 h are determined for noncircular PDMS micromembrane analysis. In the experimental study, eight types of PDMS MBs, each of which has a membrane radius of 143, 202, 452, or 904 μm and a membrane thickness of 10 or 20 μm, are characterized in air and in cell culture media. A new strain-measuring method using fluorescent polymer microspheres for the PDMS MB is also introduced. The characterization of the PDMS MBs in air validates our theoretical model and shows an increase in elastic modulus as the membrane thickness decreases. The effect of cell culture media on the membrane rigidity of PDMS is also examined for biological applications of PDMS.

One of the most critical issues for realizing high performance Ge/III-V CMOS, which can be regarded as one of the promising device structures in the future technology nodes, is to establish the gate stack technologies simultaneously satisfying many requirements such as thin EOT, low interface state density (Dit), low slow trap density (Dtrap), high channel mobility and high gate insulator reliability. For this purpose, basic understanding of Ge/III-V MOS interfaces including physical origins of interface defects and the influence on channel mobility is indispensable. In order to realize low Dit, high channel mobility and thin EOT for Ge MOSFETs, we proposed an interfacial layer (IL) formation process employing ECR plasma post oxidation to form ultrathin GeOx through thin ALD Al2O3 [1, 2] or HfO2/Al2O3 [3]. By using the HfO2/Al2O3/GeOx/Ge gate stacks, Ge n- and p-MOSFETs (EOT of 0. 76 nm) with high electron (690 cm2/Vs) and hole (550 cm2/Vs) peak mobility were obtained. However, one of the most difficult challenges for the present GeOx-based ILs is the existence of high Dtrap [4, 5]. The slow traps can exist near GeOx/Ge interfaces, because the trapping characteristics are almost insensitive to the thickness of GeOx and Al2O3 [6]. Recently, inclusion of Y atoms into GeOx has been reported to effectively suppress Dtrap [7, 8]. We are currently working for the reduction in Dtrap by suing the ALD AlYO3/GeOx or Y2O3/GeOx interfaces [9, 10]. While the impact is still limited at present, further improvement in Dtrap is expected. For III-V MOS interface control, understanding of III-V MOS interface defects and establishment of the MOS interface defect control technologies have not been fully obtained yet. There still remain many issues, such as (1) higher Dit and Dtrap at InGaAs MOS gate stacks with Al2O3-based ILs than in Si and Ge MOS gate stacks (2) inferior MOS interface properties on Sb-based materials such as GaSb, GaAsSb and InGaSb (3) poor MOS gate stack reliability [5, 11, 12]. We studied the impact of ALD La2O3/InGaAs MOS interfaces on the performance of InGaAs MOSFETs. It was found that La2O3/InGaAs MOSFETs exhibit lower S. S. and lower carrier trapping properties, while have lower mobility than Al2O3/InGaAs MOSFETs because of higher fixed oxide charge density. Also, it was experimentally found that ALD La2O3 films with thermal budget lower than 300 oC have ferroelectricity in W/La2O3/InGaAs MOS and W/La2O3/W MIM structures. The steep slope characteristics due to the negative capacitance effect have been demonstrated in W/La2O3(15nm)/InGaAs MOSFETs [13]. We also found that BHF/HF pre-treatment is more effective for reduction of the fast interface state density at ALD Al2O3/InxGa1-xAs with higher In content (x=0.7 and 1) in comparison with conventional (NH4)Sy pre-treatment [14, 15]. It was suggested through the XPS analyses that the reduction in Dit is attributable to the dominance of As dangling bonds on Dit with higher In content and the effective passivation of oxygen atoms with these dangling bonds. For GaSb and GaAsSb MOS interface control, ultrathin InAs and InGaAs surface passivation layers have been found to be effective in reducing the fast interface state density [16, 17]. However, the detailed studies on further reduction in Dit and Dtrap and understanding of the relationship between the channel mobility and the interface properties are still strongly needed for Sb-based MOS devices. This work was partly supported by JST-CREST and the Grant in-Aid for Scientific Research through the MEXT (26249038). The authors would like to thank Drs. M. Yokoyama, H. Yamada and T. Yamamoto in Sumitomo Chemical Corporation, and Drs. M. Mitsuhara, H. Sugiyama, T. Hoshi and H. Yokoyama in NTT for their collaborations. References [1] R. Zhang et al., APL. 98, 112902 (2011) [2] R. Zhang et al., TED 59, 335 (2012) [3] R. Zhang et al., TED 60, 927 (2013) [4] R. Zhang et al., IEDM, 642 (2011) [5] G. Groeseneken et al., IEDM, 828 (2014) [6] M. Ke et al., APL. 109, 032101 (2016) [7] C. H. Lee et al., IEDM, 40 (2013) [8] C. Lu et al., IEDM 370 (2015) [9] M. Ke et al., Microelectron. Eng. 147, 244 (2015) [10] M. Ke et al., to be presented in Microelectron. Eng. (2017) [11] S. Deora et al., IEEE TDMR, 507 (2013) [12] J. Franco et al., IRPS, 6A2 (2014) [13] C.-Y. Chang et al., IEDM, 322(2016) [14] K. Nishi et al, APEX. 8, 061203 (2015) [15] C. Yokoyama et al., EDTM, 23 (2017) [16] M, Yokoyama et al., APL. 106, 122902 (2015) [17] T. Gotow et al, SISC, 6. 3. (2016)

MEMS-based biological platforms with the capability of both spatial placements and time releases of living cells for cell-to-cell culture experiments have been designed and demonstrated utilizing electrochemical surface modification effects. The spatial placement is accomplished by electrochemical surface modification of substrate surfaces to be either adhesive or non-adhesive for living cells. The time control is achieved by the electrical activation of the selective indium tin oxide co-culture electrode to allow the migration of living cells onto the electrode to start the cell-to-cell culture studies. Prototype devices have a three-electrode design with an electrode size of 50 ? 50 ?m2 and the separation gaps of 2 ?m between them. An electrical voltage of ?1.5 V has been used to activate the electrodes independently and sequentially to demonstrate the dynamic cell-to-cell culture experiments of NIH 3T3 fibroblast and Madin Darby canine kidney cells. As such, this MEMS platform could be a basic yet versatile tool to characterize transient cell-to-cell interactions.

Characterization of the cytoskeleton’s viscoelastic properties is essential for understanding cellular dynamics in many biological functions of the cell, especially cell migration. The viscoelastic properties of the retracting NIH 3T3 fibroblasts are investigated here to shed light on the mechanics and dynamics of cell migration. A part of the cell is detached by electrochemically desorbing a gold-thiol self-assembled monolayer. The viscoelastic properties of the detached and retracting cytoskeleton are then estimated using time-sequential imaging combined with atomic force microscopy. The retracting cytoskeleton exhibits a threefold decrease in stiffness and a 30-fold increase in viscous damping capacity as compared to those in the adhered (stationary) cytoskeleton.

The dynamic nature of cell adhesion and detachment, which plays a critical role in a variety of physiological and pathological phenomena, still remains unclear. This motivates the pursuit of controllable manipulation of cell adhesion and detachment for a better understanding of cellular dynamics. Here we present an addressable, multifunctional, and reusable platform, termed the biological breadboard (BBB), for spatiotemporal manipulation of cell adhesion and detachment at cellular and subcellular levels. The BBB, composed of multiple gold electrodes patterned on a Pyrex substrate, is surface-modified with arginine-glycine-aspartic acid terminated thiol (RTT) and polyethylene glycol (PEG) to achieve a cell-adhesive surface on the gold electrodes and a cell-resistive surface on the Pyrex substrate, respectively. Cell adhesion is regulated by the steric repulsion of PEG chains, while cell detachment is controlled by the reductive desorption of a gold-thiol self-assembled monolayer (SAM) at an activation potential of -0.90 to -1.65 V. Experimental characterizations using NIH 3T3 fibroblasts are presented to demonstrate the utility of our device.