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Atomic Layer Deposition (ALD) of ZrO<sub>2</sub> in Ultrahigh Vacuum (UHV)
Roy, Probir Chandra,Jeong, Hyun Suck,Doh, Won Hui,Kim, Chang Min Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
The atomic layer deposition (ALD) of $ZrO_2$ was conducted in ultrahigh vacuum (UHV) conditions. The surface was exposed to $ZrCl_4$ and $H_2O$ in sequence and the surface species produced after each step were identified in situ with X-ray photoelectron spectroscopy (XPS). $ZrCl_4$ is molecularly adsorbed at 140 K on the $SiO_2$/Si(111) surface covered with OH groups. When the surface is heated to 300 K, $ZrCl_4$ loses two Cl atoms to produce $ZrCl_2$ species. Remaining Cl atoms of $ZrCl_2$ species can be completely removed by exposing the surface to $H_2O$ at 300 K followed by heating to 600 K. The layer-by-layer deposition of $ZrO_2$ was successfully accomplished by repeated cycles of $ZrCl_4$ dosing and $H_2O$ treatment.
Interaction of Methanol and Hydrogen on a ZnO (0001) Single Crystal Surface
Roy, Probir C.,Doh, Won Hui,Jo, Sam K.,Kim, Chang Min American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.29
<P>Thermal reactions of CH<SUB>3</SUB>OH on a ZnO (0001) surface with and without coadsorbed atomic hydrogen have been investigated using a temperature-programmed desorption (TPD) technique. Both H<SUB>2</SUB> and CH<SUB>2</SUB>O desorb at 510 and 580 K during CH<SUB>3</SUB>OH decomposition on ZnO(0001). When H atoms are adsorbed on ZnO(0001), the recombinative desorption of H<SUB>2</SUB> takes place at around 450 K. In the process of CH<SUB>3</SUB>OH decomposition on ZnO(0001), H<SUB>2</SUB> desorption is not observed until the surface temperature reaches 510 K. These observations indicate that surface-bound H atoms are not produced up to 510 K. When CD<SUB>3</SUB>OD and H are coadsorbed, the desorption of both H<SUB>2</SUB> and HD is observed at 445 K. HD should be formed by the exchange reaction between CD<SUB>3</SUB>O–D and H on the surface, which indicates that the CD<SUB>3</SUB>O–D bond is partially broken to form an associative CD<SUB>3</SUB>···D complex. We suggest two different pathways for the formation of CH<SUB>2</SUB>O from CH<SUB>3</SUB>OH on ZnO(0001). At 510 K, CH<SUB>2</SUB>O and H<SUB>2</SUB> are formed from the surface reaction of CH<SUB>3</SUB>O and H. Desorption of CH<SUB>2</SUB>O at 580 K is related to the complete decomposition of CH<SUB>3</SUB>O.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-29/jp403913h/production/images/medium/jp-2013-03913h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp403913h'>ACS Electronic Supporting Info</A></P>
Paramita Bhattacharjee,Probir Kumar Ghosh 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.5
Methyl eugenol-rich extracts from dried tuberose flowers (Polianthes tuberosa L.) of Calcutta single variety were obtained using supercritical carbon dioxide (SC-CO2) extraction. The optimized conditions for highest yield of methyl eugenol were 50 oC, 300 bar, 135 min with 1 L min−1 flow rate of gaseous CO2. Solubilities of methyl eugenol under different SC-CO2 extraction conditions were evaluated by Hildebrand solubility parameter and Chrastil equation. The extraction curve of methyl eugenol followed plug flow model. Steady state extraction occurred up to 100min, followed by unsteady state. Release of methyl eugenol from tuberose flowers followed first-order kinetics (Peppas model) and non-Fickian diffusion. Packed bed characterization was carried out using dimensionless numbers of mass transfer, considering steady and unsteady states of extraction. These findings could be used in the development of the pilot plant and commercial scale extraction of methyl eugenol from floral matrices.
Mun, Bongjin S.,Liu, Zhi,Motin, Md Abdul,Roy, Probir C.,Kim, Chang Min Elsevier 2018 International journal of hydrogen energy Vol.43 No.18
<P><B>Abstract</B></P> <P>The interaction of H<SUB>2</SUB> molecules with a ZnO (0001) single crystal surface has been studied over a wide pressure (10<SUP>−6</SUP>–0.25 Torr) and temperature (300–600 K) range using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). ZnO is well-known for interstitial hydrogen and hydrogen atoms in ZnO are believed to be incorporated by the dissociative adsorption of H<SUB>2</SUB> molecules in the atmosphere and their subsequent diffusion into the bulk. The dissociative adsorption of H<SUB>2</SUB> has been investigated at elevated pressures because H<SUB>2</SUB> molecules are not dissociated on the ZnO single crystal surface under ultrahigh vacuum (UHV) conditions. When the pressure is increased to several mTorr, the dissociative adsorption of H<SUB>2</SUB> takes place to form OH bonds on the surface. At 0.25 Torr, the ZnO surface is saturated with H atoms and the coverage is estimated to be 1.1 × 10<SUP>15</SUP> atoms/cm<SUP>2</SUP> at 300 K. At higher surface temperatures, the equilibrium between the dissociative adsorption of gas-phase H<SUB>2</SUB> molecules and the associative desorption of surface H atoms is established. While maintaining the equilibrium, the surface has been monitored successfully <I>in situ</I> by utilizing AP-XPS.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Surface OH bond on ZnO under hydrogen environment has been characterized. </LI> <LI> The surface was monitored <I>in situ</I> over a wide pressure range using AP-XPS. </LI> <LI> Pressure plays an import role for the dissociation of H<SUB>2</SUB> on ZnO. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>