n-Type GaAs/AlGaAs heterostructure detector with a 3.2 THz threshold frequency

Terahertz detection using the free-carrier absorption requires a small internal work function of the order of a few millielectron volts. A threshold frequency of 3.2 THz (93 microm or approximately 13 meV work function) is demonstrated by using a 1 x 10(18) cm(-3) Si-doped GaAs emitter and an undoped Al(0.04)Ga(0.96)As barrier structure. The peak responsivity of 6.5 A/W, detectivity of 5.5 x 10(8) Jones, and quantum efficiency of 19% were obtained at 7.1 THz under a bias field of 0.7 kV/cm at 6 K, while the detector spectral response range spans from 3.2 to 30 THz.     

Preparation of (CdO)1−x(PbO)x and (CdS)1−x(PbS)x thin films by spray pyrolysis technique and their characterization

Mixed thin films of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x (x=0.25) were prepared on glass substrates by spray pyrolysis technique for various substrate temperatures 300, 320 and 340 °C. Structural and optical properties were studied. XRD studies reveal the formation of mixed films. The substrate temperature of 340 °C seems to be critical for the formation of CdO-PbO mixed films. It is observed that (CdS)_1−x(PbS)_x mixed films were formed at all the three substrate temperatures. The direct band gap value of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x mixed films is about 2.6 and 2.37 eV, respectively.     

Range‐independent background subtraction algorithm for recovery of Raman spectra of biological tissue

An important requirement for the use of Raman spectroscopy for tissue diagnostic applications is an appropriate algorithm that can faithfully retrieve weak tissue Raman signals from the measured raw Raman spectra. Although iterative modified polynomial‐fitting‐based automated algorithms are widely used, these are sensitive to the choice of the fitting range, thereby leading to significantly different Raman spectra for different start and stop wavenumber selection. We report here an algorithm for automated recovery of the weak Raman signal, which is range independent. Given a raw Raman spectrum and the choice of the start and the stop wavenumbers, the algorithm first truncates the spectrum to include the raw data within this wavenumber range, linearly extrapolates the truncated raw spectrum beyond the points of truncation on the two sides by using coefficients of linear least‐square fit, adds two Gaussian peaks of appropriate height and width on the extrapolated linear wings on either side and then iteratively smoothens the data with all these add‐ons such that the smaller of the ordinate values of the smoothed and the starting raw data serve as the input to each successive round of iterative smoothing until the added Gaussian peaks are fully recovered. The algorithm was compared with the modified polynomial‐based algorithms using mathematically simulated Raman spectrum as well as experimentally measured Raman spectra from various biological samples and was found to yield consistently range‐independent and artifact‐free Raman signal with zero baseline. Copyright © 2012 John Wiley & Sons, Ltd.     

Optical absorption and thermoluminescence studies on LiF-Sb2O3-B2O3 glasses doped with Ni ions

20LiF-(30−x)Sb₂O₃-50B₂O₃:xNiO glasses with the value of x (ranging from 0 to 1.0 mol% in steps of 0.2) were prepared. A number of studies, viz. differential scanning calorimetry, optical absorption, magnetic susceptibility and thermoluminescence, on these glasses were carried out as a function of nickel ion concentration. An anomaly has been observed in all the properties of these glasses when NiO concentration is about 0.6 mol%. The results of these studies were analysed in the light of different environments of nickel ions in the glass network.     

Laser surface modification of Al–4Cu–1Mg alloy for enhanced thermal conductivity

The feasibility of enhancing thermal conductivity of Al–4Cu–1Mg alloy by depositing 80Cu–20Mo coating using high-power lasers has been examined. Coatings of 667±2.5 μm thickness were formed with metallurgically sound interface. Results showed an 86% increase in the thermal conductivity of Al–4Cu–1Mg alloy due to laser-deposited 80Cu–20Mo alloy coating. This coating approach can potentially be used on low coefficient of thermal expansion metal matrix composites to enhance their thermal conductivity in electronic devices.     

Molecular conformation and liquid structure of 2-propanol through neutron diffraction

The neutron diffraction data analysis of deuterated liquid 2-propanol at room temperature to define its molecular conformation is presented. 2-Propanol being a large molecule with twelve atomic sites, the conformation analysis is tricky and an improved method of data analysis is given. The intermolecular structural correlations, i.e., hydrogen-bonded liquid structure, can be modelled accurately to extract the nature of the average hydrogen-bonded molecular association in liquid state at room temperature. Like other alcohols these are mostly hexamer ring chain (HRC) clusters. The cluster analysis of recent X-ray data available in the literature also support the same liquid structure.     

Si doped GaAs/AlGaAs terahertz detector and phonon effect on the responsivity

Terahertz detection capability of an n-type heterojunction interfacial work function internal photoemission (HEIWIP) detector is demonstrated. Threshold frequency, f₀, of 3.2 THz (93 μm) was obtained by using n-type GaAs emitter doped to 1 × 10¹⁸ cm⁻³ and Al_0.04Ga_0.96As single barrier structure. The detector shows a broad spectral response from 30 to 3.2 THz (10–93 μm) with peak responsivity of 6.5 A/W at 7.1 THz under a forward bias field of 0.7 kV/cm at 6 K. The peak quantum efficiency and peak detectivity are 19% and 5.5 × 10⁸ Jones, respectively under a bias field of 0.7 kV/cm at 6 K. In addition, the detector can be operated up to 25 K.     

Long-time-storage mechanism for Tm:YAG in a magnetic field

We obtained a long-time-storage mechanism for spectral features in thulium ions doped into YAG by applying a magnetic field that splits the electronic ground state. We show experimentally that the storage time can be more than 30 s, which is 3 orders of magnitude longer than that of the metastable state that normally is used for information storage in this material. Level splitting and storage lifetimes for various magnetic field strengths of as much as 5 T were investigated. This storage mechanism will be relevant in the many coherent transient-based signal-processing schemes in which Tm:YAG is being used, and we demonstrate long-time storage in a basic data storage application.