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Alkanes composed of C-C and C-H show a low electric polarization, and therefore, there is only very weak interaction between alkanes and adsorbents. Thus, it is difficult to separate a specific alkane from a mixture of alkanes by adsorption. Here, two activated "channel-like" crystals generated from brominated thiacalix[4]arene propyl ethers, which adopt 1,3-alternate and partial cone conformations, recognize specific alkane vapors depending on alkane-shape and -size, sorting in three-type alkane guests such as linear, branched, and cyclic alkanes. Two activated crystals, which are prepared by removal of solvent upon heating under reduced pressure, incorporate branched and/or cyclic alkane vapors by a unique "gate-opening" mechanism via a crystal transformation in the process. Linear alkane vapors do not trigger gate opening and are not taken up by the activated crystals. The shape and size molecular-recognition properties of the activated crystals promises considerable usefulness for the separation of linear, branched, and cyclic alkanes.

A terahertz linear polarizer was developed using a single crystal of methyl 4-nitrobenzoate. Flat molecules are arranged in parallel in the crystal and the intramolecular vibrations efficiently absorb terahertz waves with high anisotropy. Several infrared-active intramolecular vibrations with parallel moments of transition concentrate in a frequency band between 2.2 and 3.2 THz. The highest degree of polarization of 76% was achieved at 2.74 THz (Tmax = 80%, Tmin = 11%). This result establishes a new category of polarizer that can be manufactured in a simple process at low cost.

The adsorption behavior of energy-related gases onto ZIF-8 was investigated using terahertz waves. Comparison of the terahertz transmission spectra of ZIF-8 before and after exposure to the gases revealed that the 2 THz vibrational mode was involved in the gate-opening motion of organic linker molecules. The adsorption properties of each gas were detailed by monitoring the intensities of the 2 THz absorption peak.

Nonadecane, normal alkane C19H40, has an orientationally disordered phase (rotator phase) between the melting point (305 K) and the transition temperature (293 K). The phase transition from the disordered phase to the ordered phase during the cooling process beyond the transition temperature was simulated based on the rate equation focusing on the state of molecules rotating or fixed. An experimental time profile curve of the disordered-ordered phase transition progression obtained by terahertz spectroscopy was reproduced successfully, allowing visualization of the transition and the formation of orientational domain structures in computer simulations.

Terahertz transmission spectra of nonadecane (C 19 H 40 ) in the crystalline and rotator phases were measured over the frequency range of 1–5.5 THz. The absorption peak at 2.2 THz, related to intermolecular interaction, was observed only in the crystalline phase. Using the absorbance at this frequency, the transition between the two phases was investigated. A model of the orientational order–disorder transition of the molecule is presented to qualitatively explain the transition rate.

Ligand exchange reactions of a monomeric zirconium carbonate complex with carboxylic acids were studied by means of extended X-ray absorption fine structure (EXAFS), UV absorption spectrophotometry and Raman spectrometry. Three carboxylic acids, gluconic acid, and L-tartaric acid and citric acid, which are mono-, di- and tri-carboxylic acids, respectively, were employed in this study. These three carboxylic acids gave different spectral signatures and concentration dependences, respectively. In the gluconic acid system, the peaks on Fourier transform of EXAFS spectrum and Raman spectrum caused by carbonate ion coordinating to zirconium atom were obviously decreased with increasing gluconic acid concentration compared to the other two carboxylic acid systems. This indicates the high association ability of gluconic acid to zirconium, which was revealed by UV spectrophotometric analysis.

The anisotropy of terahertz absorption was investigated for a B-form single crystal of stearic acid. A polarized terahertz spectrometer was used to obtain absorption spectra over the range of 1–5 THz. Seven vibrational modes were observed; four exhibited significant angular dependence. Additionally, we demonstrated a simple approach for estimating the angle of the dipole moment for each vibrational mode.

We report the characteristic terahertz spectra of a plastic crystal and the alterations caused by phase transitions. The low-frequency vibrational modes of 1-cyanoadamantane in orientationally ordered and disordered (plastic) phases were investigated with a terahertz spectrometer. The frequencies of the intramolecular vibrational modes were in good agreement with theoretical calculations. The librational mode, which was directly observed for the first time, appeared at a lower frequency for the plastic phase.

We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pump-laser pulses using scanning-tunneling-microscope (STM) light emission synchronized with ps-probe-laser pulses delayed by times t after individual pump pulses. We determined the gap energy Δ E at the F point in the band diagram of Sb2Te3 from the STM light-emission spectra as a function of the delay time t. We found that Δ E increased monotonically with t from the original value of 1.62 eV for a delay time of 0 to 15.3 ps and it decreased toward that original value (1.62 eV) for t in the time span between 15.3 and 28 ps; we saw no change in Δ E for t ≥ 28 ps. By comparing this t-dependence of Δ E with the dielectric functions of the crystalline and amorphous phases of Sb2Te3, we have concluded that the phase transition from the crystalline phase toward the amorphous phase is induced by the pump pulses. The phonon energy of the A2u mode is clearly seen in the STM light-emission spectra when Δ E is 1.62 eV, but not when Δ E is increased above 1.62 eV by pump-pulse irradiation. This feature appears to be consistent with the Raman signals, which are much stronger for the crystalline phase than for the amorphous phase.We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pump-laser pulses using scanning-tunneling-microscope (STM) light emission synchronized with ps-probe-laser pulses delayed by times t after individual pump pulses. We determined the gap energy Δ E at the F point in the band diagram of Sb2Te3 from the STM light-emission spectra as a function of the delay time t. We found that Δ E increased monotonically with t from the original value of 1.62 eV for a delay time of 0 to 15.3 ps and it decreased toward that original value (1.62 eV) for t in the time span between 15.3 and 28 ps; we saw no change in Δ E for t ≥ 28 ps. By comparing this t-dependence of Δ E with the dielectric functions of the crystalline and amorphous phases of Sb2Te3, we have concluded that the phase transition from the crystalline phase toward the amorphous phase is induced by the pump pulses. The phonon energy of the A2u mode is clearly seen in the STM light-emission spectra when Δ...

A novel method for synthesizing large scorodite (FeAsO4 .2H2O) particles was recently developed for the fixation of arsenic. This method involves the coprecipitation of scorodite particles from an Fe(II) and As(V) aqueous solution at approximately 95 � C by oxygen injection. In order to understand the process of coprecipitation of scorodite particles by this method, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used for characterizing reaction products extracted from the suspension during the reaction. The SEM observation showed that the formation of large scorodite particles was almost completed after a reaction time of 3 h, and then, fine particles precipitated on the large particles by further reactions. The XRD results indicated that scorodite particles with specific lattice parameters were formed in the reaction. The XPS results indicated that the arsenic composition on the surface of the scorodite particles decreased until 3 h from the start of precipitation reaction and increased thereafter. These results correspond to the results on the morphology of the scorodite particles obtained by SEM. Furthermore, X-ray absorption spectra (XAS) in the range of X-ray absorption near edge structure (XANES) were measured for gel-like reaction products formed in the initial stages of the reaction. The spectra revealed that the gel-like reaction products were composed of Fe(II) and Fe(III). The coprecipitation of scorodite particles synthesized by the novel method is discussed on the basis of these results together with previous results on the analyses of iron and arsenic concentrations in solution. [doi:10.2320/matertrans.M-M2009804]

The solid-state synthesis of a tetrathiafulvalene–chloranil (TTF–CA) complex was demonstrated, and progress in the formation of the complex was monitored using a GaP Raman terahertz (THz) spectrometer. Clear transitions in the THz absorption spectra indicated that the mixture of TTF and CA became the black phase TTF–CA complex. The results of X-ray diffraction, Raman scattering, and FTIR spectra are presented as supporting evidence.

Coherent terahertz waves are generated by exciting phonon-polariton mode in GaP crystal. We have developed high power, wide frequency tunable terahertz generators and spectrometers, and revealed molecular resonance spectra of biomolecules, such as saccharides, DNA- or RNA-related molecules, amino acids and liquid crystals. It is demonstrated that THz spectral imaging has a possibility to distinguish the cancerous region from the normal tissue. TUNNETT diode, of which fundamental oscillation frequency exceeds 700 GHz, can be utilized for sub-terahertz imaging system for medical and other applications.

The terahertz transmission spectra of crystalline metallocenes and decamethyl metallocene were clearly measured in the range of 0.7–6.2 THz by a recently developed GaP Raman terahertz spectrometer. The low-frequency mode of ring–metal–ring bending and CH 3 out-of-plane oscillation were observed, and the force constants of bending were estimated from the absorption frequencies based on a three-body model.

Terahertz (THz) dichroism of a nematic liquid N -( p -methoxybenzylidene)- p -butylaniline (MBBA) was measured using a GaP Raman THz spectrometer. MBBA on a rubbed plastic substrate generates a band at around 4.0 THz: its liquid crystal phase shows strong dichroism, which well corresponds to that of the IR absorption caused by π(C H) of MBBA molecule reported in the literature. Based on inferences drawn from the present THz and the published IR dichroic results, the 4.0 THz band probably stems from lateral intermolecular or intramolecular interactions of MBBA molecules aligned to the rubbing direction. The results clearly demonstrate that THz spectroscopy is powerful for discussing of phase transition and dichroism of liquid crystals.

One of the most important uses of THz spectrometry is to detect defects in molecular structure or in crystals efficiently. We applied GaP Raman THz (GRT) spectrometer to detect and evaluate defects in inorganic and organic materials. High THz-wave absorption due to high defect density of GaSe crystal lowered the efficiency of THz wave generation, when the crystal is used as nonlinear material for DFG (Difference Frequency Generation). Defects in organic molecules could be observed as changes in frequency, intensities of the absorption, and broadenings of the spectra.

We have constructed two types of THz spectrometers using the frequency-tunable THz wave generators based on difference-frequency generation (DFG) in GaP crystal. The OPO-source system is for high accuracy measurement to detect fine structures in THz absorption spectra. The Cr:F-source system has merit in simple structure, easy maintenance and low-cost, but still has sufficient resolution for room temperature observation of solids or liquids. Comparing the absorption spectra of saccharides measured with these spectrometers and those measured with FT-IR or TDS, our spectrometers have superiority in frequency range and resolution, enough to record sub peaks, which can be analyzed as structural defects in organic compounds. (Contributed by Jun-ichi NISHIZAWA, M.J.A.)

We constructed a terahertz (THz) spectroscopic imaging system using a GaP THz-wave generator with automatic scanning control, and demonstrated power-transmission imaging measurements. To characterize the system, images of polyethylene pellets containing cytosine powder at various concentrations were taken. At a resonance frequency of 2.86 THz, the imaging system detected 5000 ppm cytosine. In addition, we demonstrated that THz imaging has a possibility to distinguish regions of metastatic cancer from normal tissue in liver, by comparing a THz-wave image at 0.835 THz with that at 1.465 THz.

We have investigated the relation between deep levels in Mg-doped p-type GaP liquid phase epitaxy (LPE) layers and stoichiometry of the surface of the substrates by PHCAP measurement. Concentration of a deep donor level at E C −1.9–2.1 eV is higher in an n-type undoped GaP substrate annealed with applying phosphorus vapor pressure of 20 kPa than in sample annealed beneath a carbon cover. Next, Mg-doped LPE layers are grown on substrates that have been pre-annealed under phosphorus vapor pressure just before the growth. The densities of deep levels at E V +0.85 and E V +1.5 eV in long-time (2 h) pre-annealing sample are greatly decreased, but a deep level at E C −1.9–2.1 eV shows opposite tendency. The latter is thought to be identical to a deep level detected in the substrate, probably phosphorus interstitial atoms.

Photocapacitance (PHCAP) measurements have been carried out on GaP crystals grown by the liquid-encapsulated Czochralski (LEC) method with heat treatment under various phosphorus-vapor pressures at different temperatures. Electron traps of Ec-1.1 eV, Ec-1.6 eV, Ec-1.9 eV, and a hole trap of Ev+2.26 eV are mainly detected. The phosphorus-vapor pressure dependence of the Ec-1.9 eV trap density and their diffusion behavior indicate that they are interstitial phosphorus atoms. The densities of both Ec-1.1 eV and Ec-1.6 eV traps are strongly dependent on the shallow impurity concentrations. Moreover, the density of Ec-1.1 eV traps increases with increasing phosphorus-vapor pressure. From these results, we suggest that Ec-1.1 eV traps are the complexes of shallow donors and antisite phosphorus atoms. Deep-level densities in GaP crystals after annealing at 860°C or 960°C for 60 min are decreased almost one order of magnitude lower than those in untreated substrate crystals, which should have occurred via out-diffusion of interstitial phosphorus atoms. However, such an effect is not prominent for 800°C treatment for 60 min.

This paper presents a new recognition method using terahertz (THz) spectroscopy. By forming a guest–host diastereomer with an optically active compound (host) as a chiral recogniser, the chirality of the enantiomer (guest) can be clearly discriminated according to its absorption spectra. In this proof-of-concept study, we examined a pair of host–guest (h–g) complexes made of ( R )- or ( S )-α-methylbenzylamine (guest) and cholic acid (host).

The green polymorph of tetrathiafulvalene–p-chloranil (TTF–CA) charge transfer complex was synthesized by grinding fine powders of TTF and CA. The polymorph was identified using terahertz spectroscopy.

Improvement of the intensity and purity of emission from GaP green light emitting diodes (LEDs) has been achieved by pre-annealing of the substrate. With annealing the substrate under 20 kPa of phosphorus vapor for an hour just before the epitaxial growth, emission from deep level disappeared and saturation current density was decreased to 1×10 −16 A/cm 2 . The output power of LED depends on the n-layer thickness in the case of 5-min pre-annealing. In contrast, with 1-h pre-annealing the dependence was not observed. This fact means that some kinds of nonstoichiometric defects diffuse from the surface region of the substrate during the growth of epitaxial layers, and affect the emission characteristics.

Diffusion of nonstoichiometry-related point defects from a LEC-grown GaP substrate to a Te-doped GaP n-type epitaxial layer was investigated by means of photocapacitance. It was revealed that deep donor level at E C −2.1 eV was introduced into GaP substrate with annealing under phosphorus vapor pressure. Thus, the 2.1 eV deep level is thought to be involved with excess P atoms such as interstitial phosphorus atoms. In Te-doped crystal, 2.1 eV level was detected and the density increased as the time of substrate annealing increased. By measuring PHCAP spectra of samples with different thickness of epitaxial layer, diffusion profile of the defects from the substrate interface was obtained. From this, the diffusion coefficient at 850°C is estimated to be ∼8×10 –11 cm 2 /s.

We developed a novel differentiation technique for most textile fibers using terahertz (THz) transmittance spectroscopy. As demonstrations, several kinds of plant-derived fibers, animal fibers, and artificial fibers were milled at 77K, and were examined by THz spectroscopy in the range from 0.5 to 6.2 THz. Absorption spectra of a majority of textile fibers are distinguishable by THz spectroscopy, even for fibers in the same category or species. The advantage of this technique is its sensitivity to the structural differences of the textile fibers, even if they consist largely of the same components.

We present a novel differentiation technique for several kinds of textile fabric using terahertz (THz) transmittance spectroscopy. Our goal is to establish a new method for identification of each of wools from their animal species, as a simple, rapid and reliable method to confront fake textile problem in the market. As demonstrations, several kinds of fabrics were milled at 77K, and were examined by using GaP THz spectrometer in the measurement range from 0.5 to 6.0 THz. The absorption spectra of wool showed quite different spectra from plant-derived fibers and synthetic fibers. Furthermore, the spectra of pure wools showed different transmittance spectra between goat-wool and sheep-wool, in addition among the species of sheep.

We present here the results of applying a membrane method to terahertz (THz) transmittance spectroscopy of amino acids. Two kinds of amino acids dissolved in water or bovine serum were dropped and dried on polymer membranes. Absorbance spectra of the membranes were obtained with a GaP THz spectrometer. The frequency range was 0.6 - 6.0 THz and the line width was 3 GHz. Characteristic absorption peaks attributable to the amino acids were observed with membranes made of suitable materials.

Photocapacitance and excitation photocapacitance methods were applied to reveal the dislocation-induced deep levels in coalescent epitaxial lateral overgrowth layers of InP. Point-contact Schottky barrier junctions with small junction areas were formed on dislocated and dislocation-free regions by using wedge wire-bonding of Au, and photocapacitance measurements were then carried out at $30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In the dislocation-free layers, the dominant deep level was located at $1.30\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below the conduction band, whereas in the dislocated area, dominant deep levels were detected at $0.86\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(\ensuremath{\lambda}=1.44\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$ and $1.05\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(\ensuremath{\lambda}=1.18\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$ below the conduction band. A neutralized state was also detected at $0.66\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the valence band. From the detailed excitation photocapacitance results, it is shown that the defect configuration coordinate diagram of the dislocation-induced deep levels was considered with large Frank-Condon shifts $({d}_{\mathrm{FC}})$ of $0.28\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. This means that the atomic configurations around the deep levels are highly relaxed, as expected from the structures of the dislocation cores.

We report the room temperature terahaertz (THz) transmission spectroscopy measurements of mono- and di-substituted hydroxynaphthalenes in the 0.5- to 6-THz region using a GaP THz wave generator. Several absorption peaks were observed and ascribed to be the fundamental vibrational modes of each of the isomers which were also validated by ab initio calculations. The absorption peak at 4 THz is attributed to the twisting of the 1,4-naphthol about its longer axis while the absorption peak at 5 THz is due to the butterfly motion of the naphthol about its shorter axis.

We measured the terahertz vibrational spectra of a solid solution of L-asparagine and L-aspartic acid monohydrate at 0.5 to 6.0 THz using a GaP Raman THz spectrometer. The absorption peaks at below...

Semi-empirical calculations successfully predicted the terahertz (THz) absorption spectrum associated with intra- and intermolecular interactions in 1,4-dihydroxynaphthalene. Results are in excellent agreement with spectroscopy data in the 0.5-6 THz region using GaP wave THz source.

The effects of substrate pre-annealing on deep level density in Mg-doped GaP liquid-phase epitaxy (LPE) layers were investigated by photocapacitance measurement. With annealing under optimum phosphorus-vapor pressure, concentration of deep donor at EC — 1.9–2.1 eV increased in undoped GaP substrate. Deep level densities in Mg-doped layers were also affected by pre-annealing of the substrates. Densities of dominant deep levels at EV + 0.85 eV and EV + 1.5 eV were an order of magnitude reduced and, in contrast, the level at EC − 2.1 eV in Mg-doped layer increased with long pre-annealing. This level at EC − 2.1 eV is supposed to be involved with P-rich-type nonstoichiometric defects, such as phosphorus interstitial atoms diffused from the surface of the substrate.

Semi-empirical calculations successfully predicted the terahertz (THz) absorption spectrum associated with intra- and intermolecular interactions in 1,4-dihydroxynaphthalene. Results are in excellent agreement with actual spectroscopy data in the 0.5-6 THz region using GaP THz source.