Energy Hν Research Articles

Growth and Characterization of TCNQ-Doped Ni(II)TAAB Thin Film As a New π-Conjugated Organic Semiconductor

The aim of this work was to obtain a π-conjugated organic semiconductor with the macrocycle Ni(II)(TAAB) ([tetrabenzo (b, f, j, n) [1,5,9,13]tetraazacyclohexadecine]Ni(II) and the electronic acceptor TCNQ (tetracyano-π-quinodimethane), in which hydrogen bonds are formed between TCNQ and Ni(II)(TAAB). Theoretical calculations based on DFT with dispersion force analysis were carried out in order to simulate molecular interaction and to establish the nature of the bonds between both fragments. Thin films of TCNQ-doped Ni(II)TAAB organic semiconductor were obtained through high vacuum evaporation and were structurally and morphological characterized by IR spectroscopy, X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The absorption coefficient (α) and photon energy (hν) were calculated from UV–Vis spectroscopy and used to determine the Tauc band gap of the film. This quasi-experimental band gap was compared with that obtained by DFT; both results are in the range established for organic semiconductors. The electrical properties of the organic semiconductor have been obtained from a simple anode|TCNQ-doped Ni(II)TAAB|cathode device. The conductivity of this device was determined from electrical measurements of I(V). TCNQ-doped Ni(II)TAAB has semiconducting characteristics and its conductivity values are of order 10–5 S cm–1. Band gap determination and the I(V) study were both carried out in order to analyze the effect of doped TCNQ in the macrocycle. This work suggests that TCNQ-doped Ni(II)TAAB represents an alternative approach to obtaining a semiconductor-like behaviour that may be suitable for organic electronic applications.

Triplet Excitation and Electroluminescence from a Supramolecular Monolayer Embedded in a Boron Nitride Tunnel Barrier.

We show that ordered monolayers of organic molecules stabilized by hydrogen bonding on the surface of exfoliated few-layer hexagonal boron nitride (hBN) flakes may be incorporated into van der Waals heterostructures with integral few-layer graphene contacts forming a molecular/two-dimensional hybrid tunneling diode. Electrons can tunnel through the hBN/molecular barrier under an applied voltage VSD, and we observe molecular electroluminescence from an excited singlet state with an emitted photon energy hν > eVSD, indicating upconversion by energies up to ∼1 eV. We show that tunneling electrons excite embedded molecules into singlet states in a two-step process via an intermediate triplet state through inelastic scattering and also observe direct emission from the triplet state. These heterostructures provide a solid-state device in which spin-triplet states, which cannot be generated by optical transitions, can be controllably excited and provide a new route to investigate the physics, chemistry, and quantum spin-based applications of triplet generation, emission, and molecular photon upconversion.

Photoemission studies of organic semiconducting materials using open Geiger-Müller counter

We investigated an open ionization cell based on the Geiger-Müller counter principle in a gas mixture at atmospheric pressure and demonstrated that the photoemission signals as weak as 1 electron per second are detectable. This finding allowed us to investigate more accurately the photoemission spectrums, especially in the vicinity of the photoemission threshold. Using such a cell, we investigated a number of organic semiconductor materials, tested various ways to analyze the results of the measurements of photoemission spectrums, and demonstrated an efficient way to determine ionization potential by using the square root of the derivative of the yield dependence on the light quanta energy (dY1/d(hν))1/2. This method leads to more evident graphical representation of the measurement results and better Ip estimation in comparison to the results estimated by using the traditional method of plotting Y1/n dependence on the quanta energy hν.

The calculate of optical gap energy and urbach energy of Ni1−xCoxO thin films

The effect of Co doping on optical, structural and electrical properties of Ni1−xCoxO thin films has been successfully deposited on glass substrate by Sol–Gel Sping coating technique. The main objective of this research is to study the Ni1−xCoxO thin films to determine the optical gap energy by various methods and compare of calculated values. The transmission spectra show that the Ni1−xCoxO thin films have a good optical transparency in the visible region. The optical gap energy was varied between 3.8 and 4.05 eV, which was determined by various methods and equations. These are found in the drawn of A, A2, α, α2 (Ahν)2 and (αhν)2 as a function of the photon energy hν, the suitable method to calculate the optical energy was observed for (Ahν)2 versus hν, but this method can not be related to the film thickness. The urbach energy of the Ni1−xCoxO thin films also was determined by the curves of LnA and Lnα as a function of photon energy hν. The deduce by LnA versus hν is also suitable to estimate the urbach energy. However, the Ni0.96Co0.04O thin films have a few defects with minimum value of urbach energy. XRD patterns of the Ni1−xCoxO thin films indicate that some films are polycrystalline with cubic structure. The electrical conductivity of our films is in the order of 8.2*10−3(Ω.cm)1.

Determination of allowed transitions types and the optical parameters of Se–Ge–Ag chalcogenide films

Amorphous Se0.68Ge0.24Ag0.08 films were prepared by the known thermal evaporation method. X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis were used to identify the structure of the prepared samples. Transmittance T(λ) was measured at room temperature in the wave length range (400–2500 nm) for the investigated films of different thicknesses in range (221.2–815.2 nm). Swanepoel’s method was used to calculate the index of refraction n and absorption k. The allowed transitions in the studied composition are indirect. Values of optical band gap Egopt were determined using two different methods. The obtained values of Egopt are equal 1.90 and 1.91 eV, also the value of Urbach energy Ee equal 0.50 ± 0.01 eV. Dispersion of refractive index n is analyzed using a single-oscillator model. The optical high frequency dielectric constant e∞ and the optical dispersion parameters (Eo and Ed) were calculated by analyzing the obtained values of n. The obtained values of Eo, Ed and the average value of e∞ are found to be 5.36 eV, 18.86 eV and 4.60, respectively. The ratio N∕m* for the investigated composition is 3.87 × 1055 m−3. The dependence of real e1 and imaginary e2 parts of dielectric constant, relaxation time τ and the optical conductivity σopt on photon energy hν was also studied for Se0.68Ge0.24Ag0.08 films. The obtained results showed that e1, e2, τ and σopt increased with photon energy.

Influence of composition on structural properties and optical parameters of thermally evaporated Ge10-xSe60Te30Inx (0 ≤ x ≤ 6) thin films

Thin films of Se based chalcogenide glassy alloys Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) were deposited on to glass substrate by vacuum evaporation technique. Glassy nature of the film has been confirmed by DSC and XRD technique. Optical characterization of the thin films has been investigated by analyzing the absorption spectra measured at normal incidence in the spectral range 300–1000 nm. The optical constants viz absorption coefficient (α), extinction coefficient (k), optical band gap (Eg), and refractive index (n) have been studied. It has been observed that absorption coefficient (α) increases with increase in photon energy (hν). Extinction coefficient (k) is found to decrease with the increase of wavelength. Both absorption coefficient (α) and extinction coefficient (k) are found to decrease with In concentration for all compositions under considerations. Optical band gap (Eg) is evaluated and found to increase with increasing In content in Ge-Se-Te matrix. Refractive index (n) of the sample investigated has been estimated using Moss equation and is recorded to have a decreasing trend with increasing In incorporation in the ternary alloy. A correlative study of the optical bandgap and electronegativity of alloys indicate that optical band gap has increasing trend with decrease of electronegativity.

Electronic Processes in CdIn2Te4 Crystals

The results of investigations of electrical, optical, and photoelectric properties of CdIn2Te4 crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass mn = 0.44m0 and the mobility 120–140 cm2/(V s), which weakly depends on temperature. CdIn2Te4 behaves as a partially compensated semiconductor with the donor-center ionization energy Ed = 0.38 eV and the compensation level K = Na/Nd = 0.36. The absorption-coefficient spectra at the energy hν < Eg = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.

TCNQ molecular semiconductor of the Cu(II)TAAB macrocycle: Optical and electrical properties

The present study reports the doping of a semiconducting molecular material through the formation of hydrogen bonds between the macrocycle Cu(II)(TAAB) and the electronic acceptor TCNQ. According to density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis, the doped compound has the shape of a distorted square pyramid, with four nitrogen atoms in the equatorial position and the apical oxygen atom from the water ligands. These water molecules can generate strong hydrogen bonds with TCNQ and the TAAB metallic complex. Thin films of copper molecular material were obtained through high vacuum evaporation and were structurally characterized by IR spectroscopy, EPR and scanning electron microscopy (SEM). Additionally, the absorption coefficient (α) and photon energy (hν) were calculated from UV–vis spectroscopy and used to determine the optical activation energy in each film, from which its semiconducting behavior was established. An important aspect to consider is that the presence of hydrogen bonds is essential to establish the semiconducting nature of these species; this chemical behavior, as well as the resulting electronic mobility, have been studied by DFT theoretical calculations, which reinforce the experimental conclusion of a relationship between Cu(II)TAAB and TCNQ moieties generated by a weak bond. Finally, I–V characteristics have been obtained from a glass/ITO/doped molecular semiconductor/Ag device using Ag and ITO electrodes. Results for the copper-based device show that, at low voltages, the conduction process is of an ohmic nature while, at higher voltages, space-charge-limited current (SCLC) is found. It is highly probable that the doping effect in TCNQ favors electronic transport due to the formation of conduction channels caused by dopant-favored anisotropy.

Optical absorption and electrical properties of MPc (M =Fe, Cu, Zn)-TCNQ interfaces for optoelectronic applications

This research is related to the growth and characterization of doped molecular semiconductor metallophthalocyanine-tetracyanoquinodimethane (MPc-TCNQ) films, with M = Fe, Zn, Cu. FT-IR and Raman spectroscopies were employed to study the chemical interactions taking place in the MPc-TCNQ films. XRD was carried out to determine the crystalline structure present in the samples, due to the facility of the MPcs to be in alpha and/or beta phases. The thin films were analized by SEM and UV–vis spectroscopy in order to study their morphological and optical properties. The absorption spectra recorded in the UV–Vis region for the deposited samples showed two bands, namely the Q and Soret bands. The absorption coefficient (α) and photon energy (hν) were calculated from the UV–vis spectra, to in turn determine the optic activation energy in each film and its semiconductor behavior. The values obtained for direct transitions due to the crystallinity of the films were: 1.2, 1.4 and 2 eV for FePc-TCNQ (MMFe), ZnPc-TCNQ (MMZn) and CuPc-TCNQ (MMCu), respectively. Additionally, I-V characteristics have been obtained from fabricated glass/ITO/MM/Ag devices using ohmic contacts both after annealing. The electrical properties of the devices, e.g. carrier mobility and concentration of thermally generated holes, were extracted from the J-V characteristics. The results show that the conduction process is ohmic for the MMZn and MMCu devices, at low voltages, while at high voltages, a space-charge-limited conduction (SCLC) is present. The effect of temperature on conductivity was also measured in these samples and the lower thermal activation energy calculated was 0.37 eV for MMZn. Moreover, it was found that the temperature-dependent electric current is always higher for the MMZn device and suggests a semiconductor-like behavior with an important conductivity of the order of 103 S cm−1. Anyhow, in terms not only of electric properties, but also of optic behavior, the results suggest that all three devices manufactured, MMFe, MMCu and MMZn, are of potential use in optoelectronics. The doping effect of TCNQ favors the electronic transport, most likely due to the formation of conduction channels caused by the anisotropy induced by the dopant.

Электронные процессы в кристаллах CdIn-=SUB=-2-=/SUB=-Te-=SUB=-4-=/SUB=-

AbstractThe results of investigations of electrical, optical, and photoelectric properties of CdIn_2Te^4 crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass m _ n = 0.44 m _0 and the mobility 120–140 cm^2/(V s), which weakly depends on temperature. CdIn_2Te_4 behaves as a partially compensated semiconductor with the donor-center ionization energy E _ d = 0.38 eV and the compensation level K = N _ a / N _ d = 0.36. The absorption-coefficient spectra at the energy hν &lt; E _ g = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.

Monte Carlo method for computing relativistic photon-Maxwellian electron scattering cross sections

Compton and inverse Compton scattering from relativistic Maxwellian electrons both have an important feature, i.e. calculating the radiation transport in high-temperature and full-ionized plasma. Description and evaluation of relativistic photon-Maxwellian electron scattering are numerically complex and computationally time consuming. A Monte Carlo method is proposed to simulate photon scattering with relativistic Maxwellian electron and compute the scattering cross-sections. To compute the total cross-section of a photon of energy hν interacting with electrons at temperature Te in the laboratory coordinate, the calculation steps of Monte Carlo scheme are described as follows. The first step is to sample the velocity of an electron, the directions are isotropically sampled, and the speed is sampled from the relativistic Maxwellian distribution at temperature Te. The second step is to transform the photon energy hν into the photon energy in the coordinate in which the electron is at rest. The third step is to use the exact Klein-Nishina formula to compute the cross-sections. The fourth step is go back to the first step, and cycle this many times. The last step is to summarize all computed cross-sections and averaged them, and the average value is what we need. The operation and corresponding formula for each step are described in this paper. A better method of sampling the speed of a relativistic electron is expected to be found.A Monte Carlo processor is developed to compute the scattering cross-section of a photon of any energy, interacting with electrons at any temperature. To check this method, scatterings of the photons of various energies with electrons with various temperatures are simulated, and the results are compared with those from the numerical integration method. The comparison indicates that the simulated cross-sections are in pretty good agreement with those from the multiple integration method for the cases of electron temperature less than 25 keV. But unfortunately, the difference is obvious for the case of temperature more than 25 keV, and the error increases with temperature increasing. Why so? When the temperature is more than 25 keV, the sampling of electron speed is inaccurate when using the present method, which maybe results in this difference. So, we need to find a more accurate method of sampling relativistic electron speed to solve this problem in the future.

Understanding the role of nanostructuring in photoelectrode performance for light-driven water splitting

The analysis of capacitance data for regular nanostructured photoelectrodes is revisited using a hematite nanorod array as an example. The effects of the cylindrical nanorod geometry on the capacitance-voltage behaviour are outlined, and the limiting case of complete depletion is discussed in terms of the residual geometric capacity at the base of the nanorods. Since nanorod arrays generally leave areas of the substrate exposed, it is necessary to consider the parallel capacitance associated with the fraction of uncovered surface. The sensitivity of the capacitance fitting to parameter variation is explored. The enhancement of external quantum efficiency (EQE) by nanostructuring is also discussed using hematite nanorod arrays as experimental examples. It is shown that, although very substantial EQE enhancement should be achieved by simple geometric effects, the performance of nanostructured hematite electrodes in the visible region of the spectrum is considerably lower than predicted if all charge carriers generated in the space charge region (SCR) were collected. Further analysis reveals that the internal quantum efficiency increases with photon energy, suggesting that the probability of generating free, rather than bound, electron-hole pairs in hematite depends on the excess energy hν - Egap.

Polarization-dependent X-ray photoemission spectroscopy for High-[formula omitted] cuprate superconductors

We have performed photon energy (hν) and linear polarization dependent X-ray photoemission for optimal doped Pb-Bi2Sr2CaCu2O8+δ (Bi2212) to investigate the ground Cu 3d orbital symmetry. We identified that the bulk Cu 3d components in valence-band spectra develop with decreasing hν from 7900eV to 460eV. Moreover, the photoelectron intensity ratio of the valence-band spectra measured at hν = 460eV has shown that the Cu 3dx2−y2 orbital contributions are dominant near the Fermi level (EF). Meanwhile, we revealed that the bulk Cu 2p3/2 core-level spectra without the Bi 4s component is detected at hν = 1550eV compared with hν and linear-polarization-dependent spectra.

Consciousness as a Function of Brain Waves and Physical Constant Conscire

This article proposes that a physical constant Conscire C - derived from the Latin con (with) and scire (to know) - working on the brain waves creates consciousness in us. This is similar to the other physical constants - Gravitational constant G creating gravitational force between two masses, Boltzmann constant K converting absolute temperature to kinetic energy, Planck constant h converting light frequency ν to energy hν, etc. Consciousness does not exist if there are no brain waves. The Conscire C multiplied by the brain wave frequencies creates the brain energy and consciousness energy. As the brain wave frequency increases, consciousness energy increases. The unit of Conscire C has been given. But the actual value of Conscire C could not be given since the values of brain wave energies at different brain wave frequencies have been not been measured yet.

Study of the optical and photoelectrical properties of TlGaSeS layered single crystals

Transmission spectra (T) of TlGaSeS crystals in the photon energy (hν) range 1.38–2.38eV are used to determine the energy gap. The indirect band gap of 2.30eV was established employing the photon energy dependence of the first derivative dT/d(hν) and the photon energy dependence of absorption coefficient. In order to obtain information about the defect states in the energy gap of TlGaSeS crystals, photoconductivity (PC) measurements are performed in the 140–300K range. Photoconductivity spectra in the photon energy range of 1.77–3.10eV show two peaks related to intrinsic and extrinsic excitations. It was revealed that the first peak shifts slightly towards the low energy side with increasing temperature, whereas the second one shifts more significantly to the high energy range. It was assumed that for latter peak the deviating PC originates from the distributed energy levels in the band gap where the photoelectrons arise or where they go.

Optical investigation of thermally evaporated Cu5GexTe95−x thin films

Cu5GexTe95−x (x = 14, 16, 18 and 20) thin films were successfully deposited using thermal evaporation technique. The optical transmittance (T) and reflectance (R) spectra in the wavelength range 250–2500 nm were used for the determination of the optical energy gap and the associated optical constants of the deposited thin films. It was found that, the absorption coefficient (α), refractive index (n) and the extinction coefficient (k) spectra vary with increasing Ge concentration. The indirect optical band gap Eg is found to decrease while the Urbach tail energy increases for different film compositions. The refractive index dispersion data were analysed using the Wemple–DiDomenico single-effective-oscillator model. As a result, the oscillator energy (Eso), dispersion energy (Ed), oscillator strength (Sso), and zero-frequency refractive index (no) were determined. The dependence of the optical constants of Cu5GexTe95−x on the photon energy (hν) at different Ge concentrations is discussed.

Laser-initiated explosive electron emission from flat germanium crystals

Flat Sb-doped germanium (100) crystals were investigated in the triode configuration under pulsed tunable laser illumination (pulse duration tlaser = 3.5 ns and photon energy hν = 0.54–5.90 eV) and under DC voltages &amp;lt;104 V. Large bunch charges up to ∼1 μC were extracted from the cathodes for laser pulses &amp;gt;1 MW/cm2 corresponding to a high quantum efficiency up to 3.3% and cathode currents up to 417 A. This laser-induced explosive electron emission (EEE) from Ge was characterized by its voltage-, laser power- and hν-sensitivity. The analysis of the macroscopic surface damage caused by the EEE is included as well. Moreover, we have carried out first direct measurements of electron energy distributions produced during the EEE from the Ge samples. The measured electron spectra hint for electron excitations to the vacuum level of the bulk and emission from the plasma plume with an average kinetic energy of ∼0.8 eV.

Evaluation of valence band top and electron affinity of SiO2 and Si-based semiconductors using X-ray photoelectron spectroscopy

An evaluation method for the energy level of the valence band (VB) top from the vacuum level (VL) for metals, dielectrics, and semiconductors from the results of X-ray photoelectron spectroscopy (XPS) is presented for the accurate determination of the energy band diagram for materials of interest. In this method, the VB top can be determined by the energy difference between the onset of VB signals and the cut-off energy for secondary photoelectrons by considering the X-ray excitation energy (hν). The energy level of the VB top for three kinds of Si-based materials (H-terminated Si, wet-cleaned 4H-SiC, and thermally grown SiO2) has been investigated by XPS under monochromatized Al Kα radiation (hν = 1486.6 eV). We have also demonstrated the determination of the electron affinity for the samples by this measurement technique in combination with the measured and reported energy bandgaps (Eg).

High energy X-ray pinhole imaging at the Z facility.

A new high photon energy (hν > 15 keV) time-integrated pinhole camera (TIPC) has been developed as a diagnostic instrument at the Z facility. This camera employs five pinholes in a linear array for recording five images at once onto an image plate detector. Each pinhole may be independently filtered to yield five different spectral responses. The pinhole array is fabricated from a 1-cm thick tungsten block and is available with either straight pinholes or conical pinholes. Each pinhole within the array block is 250 μm in diameter. The five pinholes are splayed with respect to each other such that they point to the same location in space, and hence present the same view of the radiation source at the Z facility. The fielding distance from the radiation source is 66 cm and the nominal image magnification is 0.374. Initial experimental results from TIPC are shown to illustrate the performance of the camera.

Optical properties and mechanisms of current flow in Cu2ZnSnS4 films prepared by spray pyrolysis

Thin films Cu2ZnSnS4 (up to 0.9 μm thick) with p-type conductivity and band gap Eg = 1.54 eV have been prepared by the spray pyrolysis of 0.1 M aqueous solutions of the salts CuCl2 · 2H2O, ZnCl2 · 2H2O, SnCl4 · 5H2O, and (NH2)2CS at a temperature TS = 290°C. The electrophysical properties of the films have been analyzed using the model for polycrystalline materials with electrically active grain boundaries. The energy and geometric parameters of the grain boundaries have been determined as follows: the height of the barriers is Eb ≈ 0.045–0.048 eV, and the thickness of the depletion region is δ ≈ 3.25 nm. The effective concentrations of charge carriers p0 = 3.16 × 1018 cm–3 and their mobilities in crystallites μp = 85 cm2/(V s) have been found using the technique for determining the kinetic parameters from the absorption spectra of thin films at a photon energy hν ≈ Eg. The density of states at grain boundaries Nt = 9.57 × 1011 cm–2 has been estimated.