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Overcoming Zn segregation in CdZnTe with the temperature gradient annealing
Kim, K.,Bolotnikov, A.E.,Camarda, G.S.,Hossain, A.,James, R.B. Elsevier 2016 Journal of crystal growth Vol.442 No.-
<P><B>Abstract</B></P> <P>The availability of large volume crystals with the same energy gap in melt-grown CdZnTe (CZT) is restricted due to the Zn segregation in CdTe hosts. We observed the migration of Zn in the solid phase along the positive temperature gradient direction both <I>in situ</I> and post-growth temperature gradient annealing (TGA) of CZT. Diffusivity of Zn obtained from the <I>in situ</I> TGA was approximately 10<SUP>−5</SUP> cm<SUP>2</SUP>/s order and completely different mechanism with that of post-growth. The CZT ingots obtained through <I>in situ</I> TGA have uniform Zn and resistivity of <SUP> 10 10 </SUP> Ω cm orders. The CZT detectors fabricated from <I>in situ</I> TGA applied ingots exhibit 10% of energy resolution for 59.5keV peak of <SUP>241</SUP>Am.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zn migrates in the solid phase along the positive temperature gradient. </LI> <LI> Zn migration mechanism is different in <I>in situ</I> and post-growth CdZnTe annealing. </LI> <LI> Zn segregation in CdZnTe can be solved by temperature gradient annealing. </LI> <LI> <I>In situ</I> CdZnTe annealing is a useful method to obtain highly uniform bandgap detector. </LI> </UL> </P>
New Insight into the 1.1-eV Trap Level in CdTe-based Semiconductor
김기현,최종학,A. E. Bolotnikov,G. S. Camarda,A. Hossain,G. Yang,Y. Cui,R. B. James 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.4
We investigated trap levels in detector-grade CdZnTe (CZT) material grown by using three different methods, viz, the Bridgman, traveling heater method (THM), and high-pressure Bridgman method (HPB), by current deep-level transient spectroscopy (I-DLTS). All CZT detectors contained deep trap levels located at around 1.1 eV (which we designated DE1), which has been attributed to Te vacancies induced one. However, our crystal growth and characterization results indicated that dislocations induced by Te secondary defects (inclusions/precipitates)were a more probable origin than Te vacancies. Also, a theoretical calculation of the electron de-trapping time associated with DE1 can explain well the abnormal residual current behavior at temperatures slightly above room temperature. Our results show better control of the concentrations and the sizes of Te secondary defects is critical to improving the detector’s performance at room temperature by reducing lagging effects.
Roy, U.N.,Bolotnikov, A.E.,Camarda, G.S.,Cui, Y.,Hossain, A.,Lee, K.,Lee, W.,Tappero, R.,Yang, Ge,Cui, Y.,Burger, A.,James, R.B. Elsevier 2015 Journal of crystal growth Vol.411 No.-
<P><B>Abstract</B></P> <P>We grew CdTe<SUB> <I>x</I> </SUB>Se<SUB>1−<I>x</I> </SUB> crystals with nominal Se concentrations of 5%, 7%, and 10% by the vertical Bridgman technique, and evaluated their compositional homogeneity and structural quality at the NSLS’ X-ray fluorescence and white beam X-ray topography beam lines. Both X-ray fluorescence and photoluminescence mapping revealed very high compositional homogeneity of the CdTe<SUB> <I>x</I> </SUB>Se<SUB>1−<I>x</I> </SUB> crystals. We noted that those crystals with higher concentrations of Se were more prone to twinning than those with a lower content. The crystals were fairly free from strains and contained low concentrations of sub-grain boundaries and their networks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CdTeSe crystals were grown by the vertical Bridgman technique. </LI> <LI> Very high compositional homogeneity. </LI> <LI> Low concentration of sub-grain boundaries. </LI> <LI> Almost free from sub-grain boundary network. </LI> </UL> </P>
New Virtual Frisch-Grid CdZnTe Detector Design With Sub-Millimeter Spatial Resolution
Kisung Lee,Bolotnikov, Aleksey,Seungbin Bae,Roy, Utpal,Camarda, Giuseppe,Petryk, Matthew,Yonggang Cui,Hossain, Anwar,Ge Yang,Dedic, Vaclav,Kihyun Kim,James, Ralph B. Professional Technical Group on Nuclear Science 2014 IEEE transactions on nuclear science Vol.61 No.5
<P>We evaluated the performance of a position-sensitive virtual Frisch-grid (VFG) CdZnTe detector, 6 mm ×6 mm ×15 mm, via sensing strips on its side surfaces. Once the signals were collected from the anode, and from four or eight strips attached to the detector's sides, we assessed the anode's energy spectra and derived histograms from the side electrodes to evaluate the feasibility of achieving sub-millimeter spatial resolution in the X-Y plane. Using a highly collimated 30-keV X-ray beam at the National Synchrotron Light Source, and applying corrections to the raw data, we determined the photon-interaction points by conventional Anger logic and via a more sophisticated statistics-based positioning (SBP) algorithm. With the VFG detector's current configuration, we achieved a resolution below 1 mm, even for low-energy X-rays.</P>
Ge Yang,Genda Gu,Aleksey E. Bolotnikov,Yonggang Cui,Giuseppe S. Camarda,Anwar Hossain,Utpal N. Roy,Nicholas Kivi,Tiansheng Liu,Ralph B. James 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.3
Cadmium manganese telluride (CdMnTe or CMT), a compound semiconductor, is considered a promising material for the fabrication of high-performance room-temperature x-ray and gamma-ray detectors. The presence of material defects, e.g., high density of Te inclusions, has been a long-standing issue in CMT crystals grown by various Bridgman methods, since these defects degrade the device performance via charge-trapping. To address this issue, we employed the modified floating-zone method (MFZ) to grow CMT crystals and obtained as-grown crystals free of Te inclusions. This represents a new and distinct feature, absence of Te inclusions, compared to CMT crystals grown by Bridgman methods. White-beam x-ray diffraction topography (WBXDT) measurements demonstrated the existence of a high stress field within the MFZ-grown CMT crystals, which originates from the steep temperature gradient near the growth interface. Furthermore, we achieved a resistivity of 109 Ωcm for the MFZ-grown CMT crystals. The low-temperature photoluminescence (PL) measurements show that the intensity of the dislocation-related Y band is much higher than that of the principal exciton peaks, (D0,X) and (A0,X), confirming that the crystalline quality is affected by the high stress field. A long-term in-situ or post-growth thermal annealing will help to release such stress to improve the crystalline quality.
Newer Insights into the Antidiarrheal Effects of Acacia catechu Willd. Extract in Guinea Pig
Matteo Micucci,Roberto Gotti,Ivan Corazza,Gabriella Tocci,Alberto Chiarini,Marta De Giorgio,Luca Camarda,Maria Frosini,Carla Marzetti,Monica Cevenini,Roberta Budriesi 한국식품영양과학회 2017 Journal of medicinal food Vol.20 No.6
Acacia catechu Willd. is a plant diffused in India and other Asian countries, where it is used as a traditional medicine for the treatment of several ailments including diarrhea, one of the most common pathologies worldwide. In this study, we determined the chemical composition of Acacia catechu Willd. extract (AC) and evaluated its effect on spontaneous and induced contractility in isolated guinea pig ileum and proximal colon. Preliminary data about its antimicrobial effect against some pathogen agents versus some microbiota intestinal strain have been also reported. Chemical analysis revealed the presence of catechins, such as (−)-Epicatechin and (+)-Catechin. AC extract reduced frequency and amplitude of colon smooth muscle spontaneous contractility, in a concentration-dependent manner. A weaker effect of the extract was exerted toward ileum smooth muscle spontaneous contractility. The observed calcium antagonistic effect was more potent in proximal colon than in ileum. The extract showed a noncompetitive reversible antagonism to carbachol, both in proximal colon and ileum, with a higher potency in proximal colon. The antimicrobial effects of AC extract were observed toward Campylobacter jejuni, Escherichia coli, and Salmonella spp., while Bifido and Lactobacillus were not affected by treatment. These effects, however, occurred at concentrations fivefold higher than those inhibiting ileum and colon contractility. In conclusion, our results suggest that AC affects intestinal contractility without affecting intestinal bacterial flora and this may result in clinical benefits in patients suffering from nonbacterial diarrhea.