We report a strategy for realizing tunable electrical conductivity in metal-organic frameworks (MOFs) in which the nanopores are infiltrated with redox-active, conjugated guest molecules. This approach is demonstrated using thin-film devices of the MOF Cu3(BTC)2 (also known as HKUST-1; BTC, benzene-1,3,5-tricarboxylic acid) infiltrated with the molecule 7,7,8,8-tetracyanoquinododimethane (TCNQ). Tunable, air-stable electrical conductivity over six orders of magnitude is achieved, with values as high as 7 siemens per meter. Spectroscopic data and first-principles modeling suggest that the conductivity arises from TCNQ guest molecules bridging the binuclear copper paddlewheels in the framework, leading to strong electronic coupling between the dimeric Cu subunits. These ohmically conducting porous MOFs could have applications in conformal electronic devices, reconfigurable electronics, and sensors.

higher voltage is needed in many applications, such as household devices (110 V), battery chargers (12 V), etc. However, the origin of the switching mechanism of the photovoltaic effect in OTP devices is unknown.A switchable photovoltaic effect in lateral devices made by ferroelectric materials has been observed to be caused by "shift current" due to the asymmetric momentum distribution of photogenerated charge carriers, [ 7 ] or in materials with domain boundaries. [ 8 ] Nevertheless, the switchable photovoltaic effect observed in OTP devices cannot be explained as a "bulk photovoltaic effect" because of the independence V OC with respect to the electrode spacing distance and because of the switching capability is reduced at low temperature. [ 6 ] We previously hypothesized that the electromigration of cations or anions could induce p and n doping in proximity of the two electrodes, thus forming a fl ipped p-i-n structure after poling the device with reversed bias, but direct evidence of ion electromigration has not been found yet. The verifi cation of this hypothesis (i.e., ionic electromigration) in OTP devices is important because it can also provide clues for explaining the origin of the photocurrent hysteresis that plagues many OTP solar cell devices. In this paper, we report the direct observation of electromigration of methylammonium ions (MA + ) in MAPbI 3 perovskite fi lms and the consequent formation of a p-i-n structure. The poling process and the dynamic of ions migration in MAPbI 3 fi lm are also studied here at the macroscale.The lateral structure OTP solar cells used in this work consist of a MAPbI 3 fi lm between two gold (Au) electrodes that were deposited on top, as shown in Figure 1 a. Au electrodes with spacing of 8, 50, or 100 µm were deposited on glass by thermal evaporation. The MAPbI 3 perovskite fi lms were formed by the interdiffusion method where the methylammonium iodide (MAI) and lead iodide (PbI 2 ) stacked layers were thermally annealed at 100 °C for 1 h. [ 9 ] Figure 1 b shows the photocurrent for a device with 8 µm electrode spacing before and after poling in different directions. As expected, the lateral device showed zero J sc and V oc before electrical poling (Figure 1 b) because the electrodes, made with the same material (Au), do not induce preferential directionality (asymmetry) for charge transport. However, a photovoltaic effect was clearly observed after poling the device with a positive bias of 10 V (corresponding to an electric fi eld of 1.25 V µm −1 ) for approximately 90 s at room temperature. The lateral structure devices with 175 cells connected in series having the same poling direction can output V OC as high as 70 V (Figure 1 c).To identify the mobile ions and verify the hypothesis that ions electromigration could induce doping in the perovskite fi lm in proximity of the two electrodes, we fi rst applied Organometal trihalide perovskite (OTP) materials have attracted broad attention due to their optical and electrical properties that are promising for solar c...

In this paper, we describe the fabrication and characterization of solution-processed CH 3 NH 3 PbI 3 photodetectors that combine a high photoconductive gain with a broad spectral response, ranging from the UV to the NIR. Benefi tting from the trapped-hole-induced electron injection, the CH 3 NH 3 PbI 3 photodetector works as a photodiode in the dark and shows large photoconductive gain under illumination. The maximum device gain reached 489 ± 6 at a very low driving voltage of −1 V.The devices studied here have a layered inverted structure ( Figure 1 a) where indium tin oxide (ITO) is the cathode, CH 3 NH 3 PbI 3 is the active layer, 4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]-biphenyl (TPD-Si 2 ) serves as the hole transporting/electron blocking layer, molybdenum trioxide (MoO 3 ) is used for anode work function modifi cation, and silver (Ag) as the anode. The CH 3 NH 3 PbI 3 layers were prepared by thermal-annealing induced interdiffusion of the two perovskite precursors (PbI 2 , CH 3 NH 3 I) by way of a method that has recently been developed in our group to fabricate very effi cient solar cells with high yield. [ 8 ] In short, lead iodide (PbI 2 ) fi lms were deposited fi rst on ITO/glass substrates by spin-coating. A second layer consisting of methylammonium iodide (CH 3 NH 3 I) (hereafter MAI) was then spin-coated on top of the dried PbI 2 fi lm, followed by thermal annealing at 105 °C for 60 min. Scanning electron microscopy (SEM) measurements ( Figure S1, Supporting Information) showed that the interdiffusion method allows the preparation of CH 3 NH 3 PbI 3 fi lms on ITO that are continuous and uniform, which is particularly important for obtaining leakage-free photodetectors. The absorption curve in Figure 1 b shows that the CH 3 NH 3 PbI 3 fi lms have a broad absorption spectrum that ranges from 300 nm (UV) to 800 nm (NIR).The photo-and dark-current densities-voltage ( J -V ) curves of CH 3 NH 3 PbI 3 photodetectors (Figure 1 c) show a transition from a diode-rectifying behavior in the dark, to photoconduction under illumination. Under illumination, both the forward and the reverse bias currents increased dramatically, with the reverse bias current increasing more sharply than the forward bias current. The rectifying effect completely disappeared, and an ohmic conduction behavior (symmetrical photocurrent with respect to the y -axis) was observed when exposing the device to white light irradiation (10 mW cm −2 ). For comparison, the J -V curve of a high performance solar cell (where exactly the same CH 3 NH 3 PbI 3 fabrication procedure was applied) with almost 100% external quantum effi ciency under the same light intensity is also shown in Figure 1 c. The reference photovoltaic (PV) device has a structure of ITO/PEDOT:PSS/ MAPbI 3 /[6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) (20 nm)/C 60 (20 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (8 nm)/aluminium (Al) (100 nm). [ 8 ] Although Weak light sensing in the ultraviolet (UV), visible, and nearinfrared (NIR) range has a wide ...

Multifunctional nanomaterials have the potential to integrate the clinical paradigms of imaging and therapy to enable real-time visualization of therapeutic biodistributions in patients. For cancer therapy, nanomaterials with capacities to be remotely detected and triggered for therapy could also close the loop between tumor detection and treatment. In this work, we show that the near-infrared plasmon resonance of gold nanorods (NRs) may be exploited to provide an integrated platform for multiplexed Raman detection and remote-controlled photothermal heating. By screening mixed-monolayer NRs, coated with polyethyleneglycol polymers alongside visible-and NIR-absorbing molecules, we achieved surface-enhanced, resonant Raman scattering (SERRS) and identified three NR formulations that may be uniquely distinguished over a spectral bandwidth of only 6 nm in the near-infrared, a spectral multiplexing density over an order of magnitude greater than attainable with semiconductor quantum dots, [1] organic fluorochromes, and Raleigh scattering nanoparticle imaging approaches. [2][3][4][5] Given the characteristic Raman fingerprint of the molecular labels on the NRs, we refer to them hereafter as SERS-coded NRs. SERS-coded NRs are found to be highly stable, to be detectable down to attomolar particle concentrations, and to have low baseline cytoxicity in vitro. In vivo, SERS-coded NRs were efficiently detected following subcutaneous or intratumoral injection and enabled remote photothermal tumor heating to ablative temperatures. In the future, the dense near-infrared spectral multiplexing of gold NRs should catalyze efficient, multivariable screening of NR surface chemistries in a single animal host, as well as provide a route towards characterizing multicomponent nanoparticle systems with cooperative in vivo functions.Raman imaging of nanomaterials has recently emerged as an attractive alternative to fluorescence approaches. [6][7][8][9][10] Raman spectroscopy is a desirable modality for in vivo imaging because, as opposed to semiconductor quantum dot labels,[1] Raman scattering may be both efficiently excited and detected within the near-infrared optical window ($700-900 nm), where endogenous tissue absorption coefficients are over two orders of magnitude lower than for blue and ultra-violet light.[11] Raman detection is also considerably less sensitive to photobleaching than fluorescence [7,12] and the characteristic bandwidths of Raman lines are up to two orders of magnitude narrower than for fluorescence. To date, Raman scattering from nanomaterials has been utilized to improve diagnostic sensitivity in vitro, [10,[13][14][15] to probe subcellular environments, [16,17] and, very recently, to track spherical gold nanoparticles [6,7] and carbon nanotubes [18] in vivo. These in vivo studies highlight the potential for Raman spectroscopy to serve as an ultra-sensitive medical imaging modality.In addition to their applications in diagnosis and imaging, plasmonic materials have recently attracted attention for their potential...

Progress in nanotechnology is enabled by and dependent on the availability of measurement methods with spatial resolution commensurate with nanomaterials' length scales. Chemical imaging techniques, such as scattering scanning near-field optical microscopy (s-SNOM) and photothermal-induced resonance (PTIR), have provided scientists with means of extracting rich chemical and structural information with nanoscale resolution. This review presents some basics of infrared spectroscopy and microscopy, followed by detailed descriptions of s-SNOM and PTIR working principles. Nanoscale spectra are compared with far-field macroscale spectra, which are widely used for chemical identification. Selected examples illustrate either technical aspects of the measurements or applications in materials science. Central to this review is the ability to record nanoscale infrared spectra because, although chemical maps enable immediate visualization, the spectra provide information to interpret the images and characterize the sample. The growing breadth of nanomaterials and biological applications suggest rapid growth for this field.

Evidence and control of ferroelastic (but not ferroelectric) domains in CH3NH3PbI3 perovskite are provided.

Photothermal induced resonance (PTIR) has recently attracted great interest for enabling chemical identification and imaging with nanoscale resolution. In this work, electron beam nanopatterned polymer samples are fabricated directly on 3D zinc selenide prisms and used to experimentally evaluate the PTIR lateral resolution, sensitivity and linearity. It is shown that PTIR lateral resolution for chemical imaging is comparable to the lateral resolution obtained in the atomic force microscopy height images, up to the smallest feature measured (100 nm). Spectra and chemical maps are produced from the thinnest sample analyzed (40 nm). More importantly, experiments show for the first time that the PTIR signal increases linearly with thickness for samples up to ≈ 1 μm (linearity limit); a necessary requirement towards the use of the PTIR technique for quantitative chemical analysis at the nanoscale. Finally, the analysis of thicker samples provides the first evidence that the previously developed PTIR signal generation theory is correct. It is believed that the findings of this work will foster nanotechnology development in disparate applications by proving the basis for quantitative chemical analysis with nanoscale resolution.

The advent of nanotechnology, and the need to understand the chemical composition at the nanoscale, has stimulated the convergence of IR and Raman spectroscopy with scanning probe methods, resulting in new nanospectroscopy paradigms.