N-methylacetamide (NMA) crystal forms one-dimensional hydrogen-bond chains, which are similar to those in an acetanilide (ACN) crystal for which an unconventional vibrational band accompanying the amide-I band has been observed. Infrared spectra of NMA crystals show an additional band on the small-wave-number side of the amide-II band as the temperature is lowered. There is a close resemblance between this band and the band of ACN. It is likely that these bands appear by the same mechanism. The polaron model, which has been employed to explain the band of ACN, was found to be applicable also to the case of NMA, although the main vibrational mode is amide I in ACN and amide II in NMA. Acetanilide (ACN) and N-methylacetamide (NMA) are amides, which have characteristic infrared bands called amide I -VI. ' ACN forms one-dimensional hydrogenbond chains in the crystal and shows an unconventional vibrational band at low temperatures on the smallwave-number side of amide I, which is mainly attributed to the C =0 stretching vibration. ' The above band has been discussed in terms of the soliton model, the polaron model, ' or the Fermi-coupling model. Among these, the polaron model is the most reasonable, although some open questions still remain. NMA crystal has a melting point of 28 C and undergoes a phase transition at approximately 10'C. ' The low-temperature phase consists of one-dimensional hydrogen-bond chains similar to those in ACN crystal. "Dellepiane et al. ' reported that NMA crystal shows an unconventional infrared band around 1525 cm '. They interpreted this band in terms of the Fermi resonance between amide II, a band attributed mainly to the in-plane bending vibration of~N -H, and an overtone of amide V. However, we found that the overtone of amide V exists independently with a wave number almost twice that of amide V. The intensity of the unconventional band increases on cooling without apparent change in the wave number. There is an isosbestic point between this band and amide II, indicating that these bands exchange the intensity as the temperature is changed. It was also found that the unconventional band has its overtone.These observations are very similar to those in the case of ACN. Therefore, we analyzed the intensity of the band of NMA in terms of the polaron model, and compared the results with those for ACN. It has been reported that an unconventional Raman band was observed for NMA near amide I at a low temperature. ' However, we could not ascertain the existence of this band, nor could we observe a corresponding band in infrared spectra. Thus, we conclude that there is no unconventional band accompanying amide I of NMA crystal. N-methylacetamide (from the Tokyo Kasei Kogyo Co.) was purified three times by distillation under reduced pressure and once by sublimation at a low temperature. Since NMA is hygroscopic and oxidized in air, all the operations were made in a nitrogen-gas atmosphere. Samples of NMA for the infrared measurements were prepared by compressing the crystalline powder with KBr ...
The intrinsic and parasitic gate capacitance of In0.7Ga0.3As‐channel high electron mobility transistors (HEMTs) are estimated by the gate delay analysis. We prepared 80‐nm InGaAs HEMTs with different geometry of T‐gate electrodes to discuss how the T‐gate electrode affects parasitic gate delay. The results indicate that the both of the top part and stem of the T‐gate electrode has an influence on the cutoff frequency of 80‐nm‐gate HEMTs and in total the parasitic gate delay caused by the T‐gate electrode is more than half of the total gate delay. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier concentration (N) in the channel layers of pseudomorphic In0.5Ga0.5P/In0.2Ga0.8As/GaAs heterostructure field-effect transistors (HFETs) is evaluated by Raman scattering measurements. The coupled mode between the InGaAs longitudinal optical phonons and electrons in the InGaAs channel shifts continuously to a low wave number with an increasing N in the InGaAs channel. Preliminary calculation indicates that N can be determined with an error of less than 0.35×1018/cm3 in the 1018/cm3 order range, which corresponds to a 100 mV HFET threshold voltage. Raman scattering measurement is nondestructive and has a high spatial resolution as small as 1 μm in diameter. Thus, this measurement is promising in HFET wafer selection.
Metal-organic vapor phase epitaxy (MOVPE) of GaN and InGaN was investigated using a combination of triethylamine (TEA) and ammonia (NH 3 ) as the nitrogen source. The reaction of TEA and NH 3 in the gas phase was verified by quadrupole mass spectrometry. By using this nitrogen source, a GaN epitaxial layer was grown at 600 C with a peak photoluminescence at 375 nm. An In x Ga 1Àx N (x ¼ 0:6) eptaxial layer was also grown at 600 C. The indium to gallium concentration ratio was verified by secondary ion-microprobe mass spectrometry (SIMS) and X-ray diffraction. It is confirmed that this is an effective nitride source for the efficient growth of GaN and InGaN.
Metal-organic vapor-phase epitaxy (MOVPE) growth of InP was investigated by using both triethylphosphine (TEP) and phosphine (PH 3 ) simultaneously as phosphorus sources. Excellent surface morphology was obtained at 630 and 660 ˚C by using both TEP and phosphine simultaneously at an optimized balance even though the phosphine supply amount was drastically reduced. The regular monolayer-step array of the sample surface indicates the enhancement of step-flow growth attributed to the enhancement of phosphorus source supply. By using this method, we obtained the InP recess-etching stopper layers of InP-based high electron mobility transistors (HEMTs) with excellent etching selectivity. Low-temperature InP growth at 475 ˚C and below was also examined for the growth of emitter in InP-based heterojunction bipolar transistors (HBTs). It is confirmed that this growth method is quite effective for the improvement of InP crystal quality of InP-based epiwafers and the cost reduction for epiwafer production.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.