We successfully synthesized Cu/Cu2O nanocomposites using the wet chemical synthesis method. All X-ray diffraction (XRD), Reference Intensity Ratio (RIR), and Rietveld refinement methods confirmed that the compounds Cu and Cu2O are free of impurities. Scanning Electron Microscope (SEM) and Transmission electron microscopy (TEM) images show the morphology and interactions of Cu and Cu2O in the structure. The formation mechanism is also explained by five stages: precursor, nucleation, growth, aging, and reduction. The changes in crystallization parameters under variations in reaction temperature (Tv) and stirring speed (Sv) were confirmed by agreement with the XRD database. The lattice constant in the crystal of nanocomposite increases with rising temperature in the reaction, leading to unit cell expansion, while increasing the stirring—rate leads to a random size distribution of the lattice parameter. Due to the imperfect growth of the crystal, the induced crystallite size was calculated using the Williamson-Hall model, and the precise lattice parameter values were calculated using the Nelson-Riley function.

Quantum spectroscopy in solids directly detects nonlinear changes created exclusively by quantum fluctuations of light. So far, it has been realized only by projecting a large set of measurements with a coherent-state laser to a specific quantum-light response. We present two complementary experimental approaches to realize intense and ultrafast thermal-state sources. We investigate the effects of continuous excitation from a superluminescent diode (SLD) as well as an ensemble-averaging technique using phase-modulated pulses. By measuring excitonic nonlinearities in gallium arsenide, we demonstrate that the experimentally realized thermal-state source produces significantly reduced many-body nonlinearities compared to a coherent-state excitation. We also review experimental approaches toward future realization of quantum spectroscopy with thermal states.

We describe a simple experiment observing oscillations of fluid in a drinking straw immersed in a bath of water. The motion of this oscillator system with changing mass is matched remarkably well by a model derived from Newton's laws with the inclusion of only a phenomenological damping coefficient. We compare the frequency of the oscillations to Hooke's law for small displacements and find 0.25% discrepancy. This experiment can be shown as a demonstration of oscillations of fluids, or it can be performed by students as a laboratory activity in upper-division undergraduate physics and engineering courses.

The past, present, and future are not fundamental properties of Minkowski spacetime. It has been suggested that they are properties of a class of information gathering and utilizing systems (IGUSs). A human is a model IGUS robot. We provide a demonstration that what is perceived as past, present, and future is not uniquely determined from the laws of physics by constructing a robot that process information differently and therefore experience different “presents.” We construct a customized virtual reality (VR) system which allows an observer to switch between present and past moments. This “robot” (human with VR system) can experience immersion in the immediate past ad libitum. Being able to actually construct an IGUS that has the same “present” at two different coordinates along the worldline lends support to the IGUS approach for explaining the psychological nature of past/present/future.

I estimated the time for the moon to completely transit the disk of the sun during a solar eclipse using no tools beyond a water bottle with calibrated markings and a ball-point pen and no facts beyond everyday common knowledge. A remarkable agreement with the observation of 0.4% indicates that this strategy is successful at estimating the relative motion of the sun and moon as witnessed from the earth.

We performed nonlinear optical two-dimensional Fourier transform spectroscopy measurements using an optical resistive high-field magnet on GaAs quantum wells. Magnetic fields up to 25 T can be achieved using the split helix resistive magnet. Two-dimensional spectroscopy measurements based on the coherent four-wave mixing signal require phase stability. Therefore, these measurements are difficult to perform in environments prone to mechanical vibrations. Large resistive magnets use extensive quantities of cooling water, which causes mechanical vibrations, making two-dimensional Fourier transform spectroscopy very challenging. Here, we report on the strategies we used to overcome these challenges and maintain the required phase-stability throughout the measurement. A self-contained portable platform was used to set up the experiments within the time frame provided by a user facility. Furthermore, this platform was floated above the optical table in order to isolate it from vibrations originating from the resistive magnet. Finally, we present two-dimensional Fourier transform spectra obtained from GaAs quantum wells at magnetic fields up to 25 T and demonstrate the utility of this technique in providing important details, which are obscured in one dimensional spectroscopy.

Perceptual completion fills the gap for discrete perception to become continuous. Similarly, dynamic perceptual completion (DPC) provides an experience of dynamic continuity. Our recent discovery of the ‘ happening ’ (H) element of DPC completes the total experience for dynamism in the flow of time (FOT). However, a phenomenological explanation for these experiences is essential. The Snapshot Hypotheses especially the Dynamic Snapshot View provides the most comprehensive explanation. From that understanding the ‘two times’ problem (TTP) can be addressed. The static time of spacetime cosmologies has been irreconcilable with the dynamic FOT. Dismissing the FOT as an illusion is unsatisfactory. Therefore, we provide four hypotheses for the TTP. 1) Since cosmological static time demands that all events (cerebral included) are discrete, DPC elements for dynamism should likewise be expected to be discrete and accounted for by a snapshot phenomenology such as the DSV. 2) If temporality can be demonstrated to be similar to apparent motion by being a snapshot phenomenon and not demanding temporal extension it would confirm the DSV and permit reconciliation with static time. 3) If the ‘present moment’ (of the FOT) is subjective as static time theories suggest, it should be possible experimentally for an observer to choose his own ‘present’ by moving (perceptually) to various points in the past with the aid of virtual reality. 4) If dynamism e.g. motion can be precluded without significant information loss or violating physics principles it is a cognitive add-on, thereby contradicting non-static time theories which suggest that time is ‘real.’ We confirm those hypotheses.

Flowandpassageof time puzzles were analyzed by first clarifying their roles in the current multidisciplinary understanding of time in consciousness. All terms ( flow,passage,happening,becoming) are carefully defined.Flowandpassageare defined differently, the former involving the psychological aspects of time and the latter involving the evolving universe and associated new cerebral events. The concept of the flow of time (FOT) is deconstructed into two levels: (a) a lower level ― a perceptual dynamic flux, orhappening, orflowof events (not time); and (b) an upper level ― a cognitive view of past/present/future in which the observer seems to move from one to the other. With increasing evidence that all perception is a discrete continuity provided by illusory perceptual completion, the lower-level FOT is essentially the result of perceptual completion. The brain conflates the expressionflow(passage, for some) of time with experiences of perceptual completion. However, this is an illusory percept. Converging evidence on the upper-level FOT reveals it as a false cognition that has the illusory percept of object persistence as its prerequisite. To research this argument, an experiment that temporarily removes the experience of the lower-level FOT might be conducted. The claustrum of the brain (arguably the center of consciousness) should be intermittently stimulated to create a scenario of discrete observations (involving all the senses) with long interstimulus intervals of non-consciousness and thereby no perceptual completion. Without perceptual completion, there should be no subjective experience of the lower-level FOT.

One difficulty with spacetime theories is the absence of falsifications tests. Because the observer is part of quantum mechanics (QM) and therefore an obligatory part of cosmological theories that incorporate QM, the neurological sciences have a legitimate role. We examined six different QM based cosmological theories. They make implications about various aspects of the flow of time (FOT)--the past/present/future experience including subjective dynamism). First, a distinction is made between the FOT and the physical passage of time (POT), the occurrence of a new physical event at the periphery of an expanding universe. Four theories suggesting a real POT are the Evolving Block Universe, the Spacetime Dynamics Theory, Causal Set Cosmology; and Muller’s cosmology. However, they retain the past/present components of the Block Universe and imply that the upper level FOT (the experience that the ‘present’ is unique) is illusory. A falsification experiment is proposed utilizing Hartle’s proposed Information and Gathering and Utilizing Systems (IGUSs), which have different experiences of the ‘present’. A virtual reality IGUS which can experientially navigate between past and present is suggested. It could confirm their implication that the experience of past/present events is not unique (i.e., it is a variable cognition). Barbour’s timeless theory involves relative configuration spaces which contain enough information to provide an illusory dynamic scene. That experience of dynamism within that scene is said to be an illusion. A second falsification experiment is proposed to remove dynamism suggesting it is an irrelevant experience. It involves intermittent stimulation of the newly discovered consciousness center (the claustrum) to create brief intervals of unconsciousness. Doing this precludes the recently discovered ‘happening’ percept which can account for the entirely of dynamism (the lower level FOT). The negative implication for Temporal Naturalism in the Cosmological Natural Selection theory is briefly discussed.

We describe an upper-division undergraduate physics laboratory experiment that integrates the fabrication and characterization of a p-n junction in silicon. Under standard illumination, this p-n junction exhibits the photovoltaic effect as well as the typical diode rectification behavior when measured in the dark. This experiment introduces students to the physics of solar photovoltaics from the perspective of participating in the fabrication process. Procedures, experimental strategies, and typical student measurement results are presented. This low-cost, engaging, and effective lab can be adapted to undergraduate physics courses at various institutes.

This study examined the effects of heat treatment, the electron transport layer, and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) incorporation on the performance of hybrid bulk heterojunction (BHJ) solar cells composed of tin disulfide (SnS2) nanoparticles (NPs) and low band gap energy polymers poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b; 3,4-b'] dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) or poly({4,8-bis[(2-ethylhexyl) oxy] benzo[1,2-b: 4,5-b'] dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl}) (PBT7). Inserting an electron transport layer (ETL) (i.e., ZnO) on the top of the photoactive layer improved the surface morphology of the photoactive layer, which led to an improvement in charge transport. Moreover, adding a suitable amount of PCBM to the SnS2/polymer active layer enhanced the device performance, such as short circuit current density (J(sc)) and power conversion efficiency (PCE). In particular, adding 0.5 mg of PCBM to the composite solution led to a 25% and 1.5% improvement in the J(sc) value and PCE, respectively. The enhanced performance was due mainly to the improvements in the surface morphology of the photoactive layer, charge carrier mobility within the donor-acceptor interface, and carrier collection efficiency at the cathode. (C) 2018 The Japan Society of Applied Physics

We report a modification of the electromagnetic field distribution associated with a surface plasmon polariton excited on a metal slit array in the vicinity of liquid. By successful operation of a Near-field Scanning Optical Microscope (NSOM) in both dry and wet environments, we found that near-field distribution showed a considerable change from a clear double-periodic distribution (spatial oscillation of electromagnetic field having the period half of that of slit array), which is a signature of surface plasmon excitation, to a single periodic distribution, which denotes that the surface plasmon polariton no longer exists. A simulation performed based on a partial wave expansion combined with a surface impedance boundary conditions show that such change of electromagnetic field distribution are explained by a change of surface plasmon resonance, associated with the change of dielectric constant of the surrounding media.

We have performed two- dimensional Fourier transform spectroscopy on intrinsic and modulation doped quantum wells in external magnetic fields up to 10 T. In the undoped sample, the strong Coulomb interactions and the increasing separations of the electron and hole charge distributions with increasing magnetic fields lead to a nontrivial in-plane dispersion of the magneto-excitons. Thus, the discrete and degenerate Landau levels are coupled to a continuum. The signature of this continuum is the emergence of elongated spectral line shapes at the Landau level energies, which are exposed by the multidimensional nature of our technique. Surprisingly, the elongation of the peaks is completely absent in the lowest Landau level spectra obtained from the modulation doped quantum well at high fields.

SnS nanospheres (NSPs) were synthesized, and the effects of thermal annealing on the structural, morphological, chemical compositional and optical properties were examined. As-synthesized SnS NPSs with a mean size of 3-4 nm underwent a solid state morphological transformation by high temperature annealing in a nitrogen environment. Upon annealing, the size of SnS NSP increased to 5-6 nm with enhanced crystallinity. Also, the photoluminescence (PL) of the nitrogen-annealed samples slightly decreased in intensity with accompanying red-shift in spectrum. The power conversion efficiency of the solar cells using a polymer and the SnS NSPs was ~0.71%. These results confirm that the SnS NSPs demonstrate a potential as an inorganic material to be used in organic-inorganic hybrid bulk heterojunction (BHJ) photovoltaic devices.

The effects of quantum dot (QD) size on the optical and electrical properties of InAs/GaAs QD solar cells (QDSCs) were investigated. QDSCs with varying InAs QD size were fabricated by controlling the total InAs deposition thickness (θ) from 0 to 3.0 mono-layers (ML). The optical and electrical properties of the QDSCs were investigated using photoluminescence (PL), time-resolved PL (TRPL), photoreflectance (PR) spectroscopy, capacitance-voltage (C-V), and current-voltage (J-V) measurements. The QD size effects on the p-n junction electric fields (Fpn) and the efficiencies (η) of the QDSCs were revealed. The QDSCs had a maximum η of 21.17% for θ=2.0ML (the efficiency is enhanced by 17.4% over the reference GaAs-SC) and minimized Fpn (113kV/cm) by an enhanced photovoltaic effect caused by improved carrier generation. We find that these optimal properties result from a balance between carrier generation and exhaustion processes through trapping and re-capturing by defects and relatively large QDs.

We employ ultrabroadband THz pulses to expose the high-frequency transport of non-equilibrium Dirac fermions in graphene. Tuning the Fermi level reveals a transient response characteristic of high-energy photo-excited carriers with strongly enhanced interactions.

The transient dynamics of transition-metal dichalcogenides is of significant interest for clarifying fundamental many-particle interactions at the nanoscale as well as for novel applications. We report an ultrafast terahertz study up to 7 THz of the lamellar semiconductor MoS2 to access the non-equilibrium conductivity of photo-excited indirect e-h pairs in this multi-layered parent compound. While the equilibrium transport is Drude-like, near-IR optical excitation results in a complex photo-induced conductivity that consists of two components. Mobile charge carriers dominate the low frequency response below 2 THz, while at low temperatures an additional excess conductivity is observed that is enhanced around 4 THz. Two time scales appear in the dynamics: a slow ns relaxation due to non-radiative recombination and a faster sub-100 ps decay connected to the high-frequency THz feature. We discuss the broad THz peak within a model of intra-excitonic transitions in MoS2. It agrees well with the expected binding energy and oscillator strength, yet results in an anomalous temperature dependence of the exciton fraction requiring an electronically inhomogeneous phase.

We investigated the optical and the electrical properties of InAs quantum-dot solar cells (QDSCs) with various InAs deposition thicknesses ( θ ) via photoluminescence (PL), spectral response (SR), and current density-voltage (J-V) measurements. We fabricated three QDSCs with thicknesses of 2.0, 2.5, and 3.0 monolayers (MLs). Our measurements revealed the effects of the QD size on the spectral response, the conversion efficiency ( η ) and the device parameters. The QDSCs had a maximum η of 17% for θ = 2.0 ML under AM1.5G conditions. The change of device parameters in various QDSCs could be explained by the effects of the balance between enhanced carrier production from the QD layers and carrier trapping/re-capturing by strain-induced defect/QD states.

We investigated the optical and the electrical properties of GaAs solar cells (SCs) by using photoreflectance (PR) spectroscopy and current-voltage (J-V) measurements. The electric fields (Fj) in p-n junctions were evaluated through an analysis of the Franz-Keldysh oscillations (FKOs) of the PR spectra. From the excitation light intensity (Iex) dependence of the PR, we found that the photovoltaic effect resulted in a reduction of the Fj. The Fj was gradually reduced by up to 37% from the dark built-in electric field when the Iex was increased (Iex = 2.3 ∼ 181 mW/cm2). We evaluated the ideality factor (n) of the SC via PR spectroscopy, and the results matched the results of the J-V measurements well. From these results, we demonstrate that the Fj and the n of the SCs can be evaluated by using PR spectroscopy.