Motivated by recent experimental observations of Tongay et al. [Nano Lett. 12, 5576 (2012)] we show how the electronic properties and Raman characteristics of single layer MoSe 2 are affected by elastic biaxial strain. We found that with increasing strain: (1) the E and E Raman peaks (E 2g and E 1g in bulk) exhibit significant redshifts (up to ∼30 cm −1 ), (2) the position of the A 1 peak remains at ∼180 cm −1 (A 1g in bulk) and does not change considerably with further strain, (3) the dispersion of low energy flexural phonons crosses over from quadratic to linear, and (4) the electronic band structure undergoes a direct to indirect band gap crossover under ∼3% biaxial tensile strain. Thus the application of strain appears to be a promising approach for a rapid and reversible tuning of the electronic, vibrational, and optical properties of single layer MoSe 2 and similar MX 2 dichalcogenides.

We have investigated the annealing effect on the structural, optical and electrical properties of copper oxide films prepared on glass substrates by chemical deposition. The films were annealed in air for different temperatures ranging from 200 to 350 • C. X-ray diffraction patterns showed that the films as-deposited and annealed at 200 and 250 • C are of cuprite structure with composition Cu 2 O. Annealing at 300 • C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.20 eV to 1.35 eV. Also this conversion was obtained by the dc electrical conductivity and FTIR spectroscopy measurements.

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We presented the results of optical and electrical studies of the properties of hydrogenated amorphous silicon (a-Si:H) film which was prepared by hot wire method. Using transmittance measurements, the dielectric constant of the a-Si:H was determined. The temperature-dependent conductivity was measured using the two-point probe method in the temperature range 115–326 K. It was shown that the temperature-dependent conductivity can be well explained by the nearest-neighbor hopping conduction and the Efros–Shklovskii variable-range hopping conduction models. A clear transition from the nearest-neighbor hopping conduction mechanism to the Efros–Shklovskii variable-range hopping conduction mechanism was also observed. The transition between two conduction regimes and characteristic hopping temperatures, as well as the complete set of parameters describing the properties of the localized electrons (the localization length, the hopping energy, the hopping distance, the width of the Coulomb gap, and the value of the density of states at the Fermi level) were determined.

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In this study, we have investigated the intersection behavior of the forward bias current-voltage (I-V) characteristics of the Al/TiO 2 /p-Si (MIS) structures in the temperature range of 100-300 K. The intersection behavior of the I-V curves appears as an abnormality when compared to the conventional behavior of ideal Schottky diodes and MIS structures. This behavior is attributed to the lack of free charge at a low temperature and in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures, in particular. The values calculated from the temperature-dependent forward bias I-V data exhibit unusual behavior, where the zero-bias barrier height (φ b0 ) and the series resistance (R s ) increase with increasing temperature. Such temperature dependence of φ b0 and R s is in obvious disagreement with the reported negative temperature coefficient. An apparent increase in the ideality factor (n) and a decrease in the φ b0 at low temperatures can be attributed to the inhomogeneities of the barrier height, the thickness of the insulator layer and non-uniformity of the interfacial charges. The temperature dependence of the experimental I-V data of the Al/TiO 2 /p-Si (MIS) structures has revealed the existence of a double Gaussian distribution with mean barrier height values ( φb0 ) of 1.108 eV and 0.649 eV, and standard deviations (σ s ) of 0.137 V and 0.077 V, respectively. Furthermore, the temperature dependence of the energy distribution of interface state density (N ss ) profiles has been determined from forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (φ e ) and n. The fact that the values of N ss increase with increasing temperature has been attributed to the molecular restructuring and reordering at the metal/semiconductor interface under the effect of temperature.

The current-voltage (I-V) characteristics of Al/TiO2/p-Si metal-insulator-semiconductor (MIS) structures have been investigated in the temperature range of 80–300 K. An abnormal decrease in the zero bias barrier height (BH) (ϕb0) and an increase in the ideality factor (n) with decreasing temperature have been explained on the basis of the thermionic emission (TE) theory with Gaussian distribution (GD) of the BHs due to the BH inhomogeneities. The temperature dependence of the experimental I-V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double GD with mean BH values (ϕ¯b0) of 1.089 and 0.622 eV and standard deviations σs of 0.137 and 0.075 V, respectively. Thus, the modified ln(I0/T2)−q2σ02/2(kT)2 versus q/kT plot gives ϕ¯b0 values and Richardson constants (A∗) as 1.108 and 0.634 eV and 31.42 and 23.83 A/cm2 K2, respectively, without using the temperature coefficient of the BH. The value of the effective Richardson constant of 31.42 A/cm2 K2 is very close to the theoretical value of 32 A/cm2 K2 for p-Si. As a result, the temperature dependence of the forward bias I-V characteristics of the Al/TiO2/p-Si (MIS) structure can be successfully explained on the basis of the TE mechanism with a double GD of the BHs.

In this study, the frequency and voltage dependence of the dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ), electric modulus (M′ and M″) and ac electrical conductivity (σac) of Al/TiO2/p-Si (MOS) structures has been investigated using the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics. A TiO2 thin film was deposited on the p-type Si substrate by using the sol–gel dip coating method. These C–V and G/ω–V characteristics were measured by applying a small ac signal of 50 mV amplitude in the frequency range 5 kHz–1 MHz, while the dc bias voltage was swept from (−4 V) to (4 V) at room temperature. Experimental results show that ε′, ε″, tan δ and σac are strongly frequency and voltage dependent. Accordingly, it has been found that as the frequency increases, ε′ and ε″ values decrease while an increase is observed in σac and the electric modulus. The results can be concluded to imply that the interfacial polarization can more easily occur at low frequencies consequently contributing to the deviation of dielectric properties and ac electrical conductivity of Al/TiO2/p-Si/p+ (MOS) structures.