Mechanical forces exist in many cellular processes, including deformation, division and differentiation. In Addition, the transformation of normal cells to cancer cells also involves biomechanical processes. It is consequently important to investigate the mechanical properties of cells including determination of traction forces, in order to understand the physical mechanisms of cancer cell formation and develop novel strategies for cancer diagnostics and treatment. Here we measure the deflection of fluorescent nanowires to assess cellular forces. Compared to other cellular force measurement methods such as optical tweezers, micropipette and micropillar arrays, nanowires have an ultra-small (

Perovskite solar cells (PSCs) have attracted much attention in recent years. Their metal halide composition holds the promise of achieving highly efficient and cost effective devices due to high quality crystalline perovskite thin films with tunable absorption edge and high extinction coefficient. Fully solution processed devices are advantageous for future large-scale industrial applications. Methylammonium lead iodide (MAPbI3) with a bandgap of 1.55 eV and an absorption onset in the near infra-red (800 nm) is mostly investigated for PSCs since it can absorb photons in both visible and near-infrared solar spectrum. Furthermore, its capability of acting simultaneously as a hole conductor and electron transporter makes it suitable for planar heterojuntion PSCs. Recently, it was observed that replacing the methylammonium cation (CH3NH3+) by a formamidinium cation (CH(NH2)2+) in the lead iodide perovskite lead to a decreased band gap value (1.47 eV) and a shift in the absorption edge to 850 nm of the perovskite thin film. In this research, we report the fabrication of a high efficiency planar heterojuction formamidinium PSCs. The device architecture is defined by a fluorine-doped tin oxide glass substrate coated with a titanium dioxide (TiO2) thin film, a FAPbI3 absorber layer, a 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD) hole transporting layer and silver electrodes. The purity and quality of the perovskite thin film were determined by UV-vis spectroscopy, X-rays diffraction (XRD) and energy diffraction spectroscopy (EDS). Field emission scanning electron microscopy (FE-SEM) was used to characterize the morphology of the absorber layer. Furthermore, the device performances were studied as a function of the relative humidity (RH) (%).The impact of RH content on the device characteristics and charge carrier dynamics will be discussed. The stability of FAPbI3 based films and devices will be compared to those based on MAPbI3.

The recent emergence of two dimensional (2D) materials has enabled the realization of atomically thin heterostructure devices with vertically stacks of disparate 2D materials. The monolayer thick structure of these materials allows electrostatic doping modulation of the overlying layers in a vertically stacked heterostructure.1 While a majority of work is focused on stacking varying combinations of 2D materials only, an all 2D structure is not necessary to achieve gate-tunable devices. Here, we demonstrate a gate-tunable p-n heterojunction diode using one dimensional semiconducting single-walled carbon nanotubes (s-SWCNTs) and 2D single-layer molybdenum disulfide (SL-MoS2) as p-type and n-type semiconductors, respectively.2 The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias over a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104. The transfer characteristics of this p-n heterojunction has a unique 'anti-ambipolar' characteristic with two off-states at either extremes of gate voltage range with a current maxima in between them.2 The continuous transition from a positive to negative transconductance in an anti-ambipolar characteristic enables operation of analog communication circuits with a reduced number of circuit components compared to unipolar transistors. This anti-ambipolar characteristic can be widely generalized to heterojunctions of other materials such as s-SWCNTs and n-type amorphous indium gallium zinc oxide (a-IGZO), ultimately leading to all solution processed heterojunctions on a wafer scale.3 References: 1. Jariwala, D.; Sangwan, V. K.; Lauhon, L. J.; Marks, T. J.; Hersam, M. C. ACS Nano 2014, 8, 1102�1120. 2. Jariwala, D.; Sangwan, V. K.; Wu, C.-C.; Prabhumirashi, P. L.; Geier, M. L.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 18076�18080. 3. Jariwala, D.; Sangwan, V. K.; Seo, J. T.; Xu, W.; Smith, J.; Kim, C. H.; Lauhon, L. J.; Marks, T.; Hersam, M. C. 2014, (submitted).

We report a strategy of using vapor transport chemical vapor deposition (CVD) to prepare well-faceted, high crystal quality organic-based lead halide perovskite platelets on muscovite mica substrates. The well-defined single crystal nanoplatelets of lead halides were first grown on mica substrate utilizing van der Waals epitaxial growth following by thermally intercalating of methyl amino halide (gas phase) into pre-grown lead halide platelets. The resulted CH3NH3PbI3 platelets showed an electron diffusion length of more than 200 nm which is approximately two times higher than that of the solution processed film. This synthesis approach will create a new platform to exploit the physical properties of the organic-based lead halide perovskites. The as-grown platelet crystals exhibit excellent optical properties, as studied by optical absorption and photoluminescence spectroscopy. Notably, we demonstrate an optically pumped room-temperature near infrared laser based on the CH3NH3PbIaX3-a (X= I, Br, Cl) nanoplatelets. Their large exciton binding energies, long diffusion lengths and naturally formed high-quality planar whispering-gallery mode cavities ensure adequate gain and efficient optical feedback for low-threshold in-plane lasing. The whispering-gallery type planar perovskite nanolasers have pronounced optical gain and tunable optical modes, which can be potentially expanded with controllable emission from UV to NIR. Our research opens alternative routes beyond III-V nanostructures in achieving near infrared solid state nanolasing and will inspire more designs of low-threshold near-infrared nanolasers pumped optically and electrically.

2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Lithium-ion batteries and supercapacitors are widely used to power mobile devices, but the energy and power densities of the electrode materials still need improvement. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials. The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials comprised of layers of different cathode materials may be possible by reassembling different nanosheets. These sandwich structures could potentially result in unique synergistic effects and novel redox behavior due to the interactions from different sheets. Finally, we can obtain better understanding of the structure of complex layered cathode materials through exfoliation and high resolution ex-situ microscopy studies. Here we present our synthesis of 2D nanosheets of two common lithium-ion battery materials, LiCoO2 (LCO) and LiNi1/3Mn1/3Co1/3O2 (NMC). Nanosheets were obtained by exfoliation of LCO and NMC particles using traditional osmotic swelling with tetraethylammonium (TEA). TEM, SEM and AFM analysis showed that the particles were successfully exfoliated nanosheets with around 2 nm thickness. XRD and electron diffraction pattern analysis showed that these materials had hexagonal structures with good crystallization. A reassembly process was developed and applied to obtain LCO, NMC, and LCO/NMC hybrid particles. Electrochemical evaluation of the particles as electrodes for lithium-ion batteries and supercapacitors were performed. Our work is a firm step forward on improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.

Nanowires offer exciting opportunities in quantum optics. Using quantum dots in semiconducting nanowires, we demonstrate the generation of single photons as well as pairs of entangled photons. Making electrical contacts to semiconducting nanowires, we make a single quantum dot LED where electroluminescence from a single quantum dot can be studied. Superconducting nanowires also offer application in quantum optics: we demonstrate efficient single photon and single plasmon detection with superconducting nanowire single photon detectors. I will also address quantum circuits where quantum light sources, circuits and detectors are all combined on a chip.

In this work, we present cross-coupled plasma-enhanced ALD (PEALD) ZnO thin-film transistor oscillators that operate at frequencies of 10MHz. To be compatible with flexible substrates used in large-area electronic systems, thin-film transistor (TFT) circuits are processed below 250oC. However, such TFTs typically exhibit reduced cutoff frequencies ft compared to their high-temperature counterparts. Resonant TFT circuits can enable oscillation frequencies above ft by negating the impact of parasitic capacitances within the resonant network. We find numerous applications for these circuits at such frequencies, including efficient wireless transmission of power and signals [1,2]. Previously, we demonstrated a-Si cross-coupled oscillators with 5MHz oscillations at an overdrive voltage VOV of 12V [3]. By changing the TFT technology in our oscillators from a-Si to higher-mobility PEALD ZnO, we doubled oscillation frequency, reduced overdrive voltage by 4X, and maintained process temperatures below 200oC. Our cross-coupled LC oscillators consist of two PEALD ZnO TFTs (?>10cm2/Vs, Vth~3V, subthreshold slope~200mV/decade [4]) where the gate of TFT 1 is connected to the drain of TFT 2, and vice versa. Planar coil Cu inductors patterned on freestanding polyimide connect both drain terminals to the supply voltage Vdd, and both source terminals are grounded. Several challenges must be addressed in order to increase the oscillation frequency of these circuits. To begin oscillating, the circuit must meet a positive feedback condition: (gm/Cpar)*(L/(Rind+Rg))>1, where gm is the TFT transconductance, Cpar is dominated by the TFT gate-to-drain capacitance, L is the inductance of the Cu inductor, and Rind and Rg are the resistances of the inductor and the TFT gate [1]. A large inductor allows this condition to be met more easily, but reduces the oscillation frequency, 1/(2??(LC)). A large overdrive voltage increases gm, enabling smaller-valued inductors and thus higher frequencies, but also elevates power consumption and endangers the gate dielectric (and thus the robustness of the circuit). Our ZnO circuits were able to meet the oscillation condition at low enough L to oscillate at 10MHz at a Vdd of just 6V (3V VOV). This was accomplished by (1) substantially reducing gate resistance from 100?/sq to 10MHz. [1] Hu et al., CICC 2012 [2] Huang et al, ISSCC 2013 [3] Rieutort-Louis et al., IEEE JPV Jan. 2014 [4] Mourey et al., IEEE TED, Feb. 2010.

In this communication, we report the successful transfer of CVD (Chemical Vapor Deposition) grown MoS2 to Au antenna fabricated using electron beam (e-beam) lithography, and we investigate the photoluminescence properties of this hybrid plasmonic-excitonic system. The ultimately thin 2D MoS2 layer has the great advantage of introducing a well controlled local absorber (and emitter) in the plasmonic near-field of the Au antenna. The work is focused on the plasmonic mediated pumping of the MoS2 photoluminescence emission. Off- and in-resonance excitation of the surface plasmons showed drastically different behaviors of the photoluminescence emission from the MoS2. For plasmonically mediated pumping, we found a significant enhancement (~65%) of the photoluminescence intensity, a clear evidence that the optical properties of MoS2 monolayer are strongly influenced by the nano-antenna surface plasmons. In addition, a systematic photoluminescence broadening and red-shift in nano-antenna locations is observed which is interpreted in terms of plasmonic enhanced optical absorption and subsequent heating of the MoS2 monolayers. Using a temperature calibration procedure based on photoluminescence spectral characteristics, we were able to estimate the local temperature changes. We found that the plasmonically induced MoS2 temperature is 4 times larger than the MoS2 reference temperature. Based on Green Dyadic theory simulations of the plasmonic properties of the Au antenna, combined with heat dissipation calculations, we discuss the contribution of the Au antenna heating to the measured temperature increase. We found that the results can be interpreted in terms of efficient light absorption by the plasmonic antenna and its conversion into electron-hole pair excitations of the 2D MoS2 layer thus leading to enhanced excitonic photoluminescence and local heating. This study shines light on the plasmonic-excitonic interaction in the hybrid MoS2/Au semiconductor/metal nano-structures and provides a unique approach for engineering new light-to-current conversion opto-devices such as high sensitivty photodetectors, bio-sensors and plasmonic controlled field-effect transistors.

DNA-based electrochemical sensors can be defined as nucleic acid layers with electrochemical transducers. DNA is especially appropriate for biosensing applications because interactions between complementary sequences are specific and robust to provide a simple and accurate biosensor for patient diagnosis. Electrochemical methods are appropriate for DNA diagnostics, giving a direct electronic signal [1]. But, there is still an extensive discussion about how charge transport occurs over DNA distance. MicroRNAs are small sequences that regulate a wide range of cellular processes. There has been a huge interest in studying their expression in human cancers [2]. We proposed to transform MicroRNA into DNA and develop a �MicroDNA� electrochemical biosensor to detect miR-200a sequence (22-mer) related with breast cancer. Au electrodes were cleaned using standard procedures [3] and experiments were performed at room temperature. 1 �M thiol � modified single-stranded probe sequence was dissolved in a pH 7 DNA solution (1 M phosphate buffer, 1 M NaCl, 5 mM MgCl2 and 1 mM EDTA), and immobilized for 18 h. Sequence 1 mM 6 � mercapto - 1 � hexanthiol in MilliQ water was immobilized for 1 h and the hybridization with complementary strand dissolved in pH 7.4 hybridized solution (10 mM phosphate buffer, 1 mM EDTA, 1 M NaCl) for 1h. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were applied to control biosensor development. CV was carried out in a 10 mL electrochemical cell composed by modified working electrode, Ag|AgCl|1 M KCl reference electrode and platinum wire as auxiliary electrode. The measurements were performed in 5 mM potassium ferrocyanide and 10 mM phosphate buffer, cycled from -0.1 to 0.5 mV at 100 mV.s-1. EIS was performed in the same electrochemical cell used for CV. Frequencies varied from 100 kHz down to 0.05 Hz with 10 mV amplitude and single sine. The solutions employed in each step were studied and proved to be crucial to overall device performance. Specially MgCl2 in DNA immobilization solution neutralizes the negative charges of single-stranded probes and promotes a huge surface coverage. The increase of immobilized single-stranded improves the electrochemical impedance spectroscopy hybridization signal. The analytical curve indicates the percent of hybridization as a function of complementary strand concentration. The results of electrochemical techniques will be also compared to quartz crystal microbalance experiments. This work was funded by CNPq, CAPES and FAPESP Brazilian agencies. Reference [1] T. G. Drummond, M. G. Hill and J. K. Barton, Electrochemical DNA sensors. Nature Biotechnology 21(2003) 1192 � 1199. [2] A. Esquela-Kerscher and F. J. Slack, Oncomirs - microRNAs with a role in cancer. Nat. Rev. Cancer 6 (2006) 259�269. [3]L. M. Fiscger, M. Tenje, A. R. Heiskasen, et al. Gold cleanning methods for electrochemical detection applications. Microelectronic Engineering 86 (2009) 1282 � 1285.

Semiconductor nanowires (NWs) have the ability to collect and trap the light into a sub-wavelength volume [1]. Even stronger light absorption ability is manifested by metallic nano-antennas that convert freely propagating optical radiation into localized energy [2]. The combination of these two systems opens a way to novel technological applications that use optical fields to manipulate and control the semiconducting properties of NWs. Recently we have shown how optical absorption in nanowires can be enhanced or reduced by the interaction with metal nanoparticles positioned on the NW facets [3]. For a broad enhancement of light absorption, an accurate design of the nano-antennas is required [4,5]. In this work, the nano-antennas geometry around GaAs nanowires has been studied theoretically and experimentally. The nano-antennas have been fabricated around the NW with electron beam lithography (E-BEAM). We demonstrate enhancement in light absorption, as well as for second order phenomena such as the generation of second harmonics and Raman scattering [4]. We perform photoconductivity measurements demonstrating that a hybrid structure formed by GaAs NWs and an array of bow-tie antennas is able to modify the polarization response of a NW[6]. The large increase in light absorption for transverse polarized light changes the NW polarization response, including the inversion. This study makes a step forward to the understanding of light coupling in engineered nanodevices and opens the way to a broad band of applications that aim to combine the plasmonic properties of metal nanostructures with the semiconducting properties of NWs. NWs and nanoantennas can constitute the basic elements of future high efficiency solar cells, optical switches and lasers. References [1]P. Krogstrup, et al., Nature Photonics, vol 7, 306-310 (2013) [2]C. Forestiere, et al., Nano Letters, vol 12, 2037-2044 (2012) [3]C. Colombo, et al., New Journal of Physics, vol 13, 123026 (2011) [4]A. Casadei, et al., Nano Letters, vol 14, 2271-2278 (2014) [5]S. Heeg, et al., Nano Letters, vol 14, 1762-1768 (2014) [6]A. Casadei, et al, Scientific Report, (under review)