Punit Boolchand - Profile on Academia.edu (original) (raw)
Papers by Punit Boolchand
![Research paper thumbnail of Intermediate Phase Spectroscopy of (Na$_{\mathrm{2}}$O)$_{\mathrm{x}}$[(B$_{\mathrm{2}}$O$_{\mathrm{3}})_{\mathrm{y}}$(GeO$_{\mathrm{2}})_{\mathrm{1-y}}$]$_{\mathrm{1-x}}$ glasses](https://attachments.academia-assets.com/121970243/thumbnails/1.jpg)
](Bulletin of the American Physical Society, 2017
Phase Spectroscopy of (Na 2 O) x [(B 2 O 3 ) y (GeO 2 ) 1-y ] 1-x glasses AARON WELTON, RALPH CHB... more Phase Spectroscopy of (Na 2 O) x [(B 2 O 3 ) y (GeO 2 ) 1-y ] 1-x glasses AARON WELTON, RALPH CHBEIR, ANDREW CZAJA, PUNIT BOOLCHAND, The University of Cincinnati -The titled ternary is of interest because the two end members, viz., y= 0, i.e., Sodium Germanate 1 , and y = 1, Sodium Borate 2 have been studied earlier and show the isostatically rigid Intermediate Phase (IP) to occur in the x = 0.14 to x = 0.19 range and in the x = 0.20 to x = 0.40 range of soda respectively. In the present work we now report on bulk glasses at y = 0.75 synthesized over a wide range x = 0 to x = 0.30 of soda. Our motivation is to understanding the evolution of the IP in the pseudo-ternary glasses as the base glass connectivity is altered. Preliminary MDSC experiments show T g (x) to increase with x and to reveal a broad maximum at 510 C centered near x = 0.25. Furthermore, an IP is found in the x = 0.20 to x = 0.33 range of soda where a reversibility window is observed. The window is centered near the T max g content at x= 0.25. IR reflectance show modes of BO 4 and BO 3 units but also those of bonded water. Raman scattering largely shows modes observed earlier in Sodium borate glasses 2 . 1 V.
Bulletin of the American Physical Society, 2015
Structural manifestations of aging in Se-rich glasses 1 S. DASH, S. RAVINDREN, P. CHEN, P. BOOLCH... more Structural manifestations of aging in Se-rich glasses 1 S. DASH, S. RAVINDREN, P. CHEN, P. BOOLCHAND, Univ of Cincinnati -We examine weakly cross-linked GexSe100-x (0%<x<7%) binary glasses in modulated DSC and Raman scattering experiments. Homogeneity of melts was carefully verified using FT-Raman line profiling. Upon aging at RT for 4 months, we find the width of the glass transition W(x) steadily decreasing from 10C at 7% Ge to 2C for pure Se. The 5-fold reduction of W(x) with a decrease of Ge content is accompanied by a 2-fold increase in the non-reversing enthalpy. Rejuvenation of the aged glasses changes W(x) from 15C at 7% Ge to 7C for pure Se. Tg is found to decrease upon rejuvenation with the difference (Tg(aged)-Tg(rejuv)) showing a maximum near 3% Ge and vanishing for pure Se and 6% of Ge, which are topological thresholds. These results in Se-rich glasses are consistent with aging induced decoupling of Se8 crowns and growth of extended range structural correlations between polymeric Sen chains due to lone pair interactions. At higher x, near 8-10% of Ge, eutectic effects are manifested.
Bulletin of the American Physical Society, 2014
The American Physical Society Fragility, network adaptation, rigidity-and stress-transitions in h... more The American Physical Society Fragility, network adaptation, rigidity-and stress-transitions in homogenized binary Ge x S 100-x glasses 1 SHIBALIK CHAKRABORTY, PUNIT BOOLCHAND, University of Cincinnati -Binary Ge x S 100-x glasses reveal elastic and chemical phase transitions driven by network topology. With increasing Ge content x, well defined rigidity (x c (1)=19.3%) and stress(x c (2)=24.85%) transitions and associated optical elasticity power-laws are observed in Raman scattering. Calorimetric measurements reveal a square-well like minimum with window walls that coincide with the two elastic phase transitions. Molar volumes show a trapezoidallike minimum with edges that nearly coincide with the reversibility window. These results are signatures of the isostatically rigid nature of the elastic phase formed between the rigidity and stress transitions. Complex C p measurements show melt fragility index, m(x) to also show a global minimum in the reversibility window, underscoring that melt dynamics encode the elastic behavior of the glass formed at T g . The strong nature of melts formed in the IP has an important practical consequence; they lead to slow homogenization of non-stoichiometric batch compositions reacted at high temperatures. Homogenization of chalcogenides melts/glasses over a scale of a few microns is a pre-requisite to observe the intrinsic physical properties of these materials.
Zeitschrift für Naturforschung A, 1996
Bulk glasses of Te3 _zSez-(CI or Br)2+y , the composition spanning the glass forming range, were ... more Bulk glasses of Te3 _zSez-(CI or Br)2+y , the composition spanning the glass forming range, were characterized by differential scanning calorimetry, 125Te absorption, and 129I emission Mössbauer spectroscopy. The results reveal that the stoichiometric glasses Te3(Cl or Br)2 consists of c-Te3 Cl2 -like chain fragments about 1.5 nm long and terminated by one-fold coordinated halogen atoms. The 125Te electric hyperfine structure results reveal that Te replacement by Se (z ≠ 0) leads to preferential occupancy at those Te sites in the chains that are two-fold coordinated, and in a rather striking fashion demonstrate that the average length of the chain fragments remains independent of Se concentration. Halogen atoms in the glasses act as chain terminators, and also bond to Te-sites in the chains to produce four-fold coordinated sites. The low glass transition temperatures (Tg~ 70 -90°C), the low average coordination number of the proposed chain-fragments, along with the hyperfine structu...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2005
Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si substrates by pu... more Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si substrates by pulsed laser deposition. The values of deposition parameters (chamber pressure, substrate temperature, substrate-to-target separation, laser energy, repetition rate, and spot size on the target) leading to a successful growth of films in their cubic rocksalt structure are identified. The films are golden yellow in appearance with a mirror-like surface morphology and possess a sheet resistance around 0.1Ω∕square. X-ray diffraction analysis of thick films (several microns) leads to a lattice constant of 5.863(7)Å, which is close to the bulk LaS value. High-resolution transmission electron microscopy reveals the films to be comprised of nanocrystalline regions separated by amorphous ones. The root-mean-square variation of film surface roughness measured over a 1μm×1μm area is found to be 1.74nm by atomic force microscopy. These films have potential for semiconductor, vacuum microelectronics, ...
Physical Review B, 1996
One-fold-coordinated atoms in a covalent network mechanically soften a network if it is overcoord... more One-fold-coordinated atoms in a covalent network mechanically soften a network if it is overcoordinated, and conversely, mechanically stiffen the network if it is undercoordinated. They play no part in network rigidity if the network is optimally coordinated. These features follow directly from constraint theory and provide a quantitative basis to understand the observed nanoindentation hardness of diamond and silicon carbide networks upon progressive hydrogenation when the contribution of one-fold-coordinated atoms is taken into account explicitly.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2001
We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS)... more We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS). Powder x-ray diffraction scans of the samples show the rocksalt phase with a lattice constant a0=5.857(2) Å and 5.694(2) Å for LaS and NdS, respectively. In Raman scattering, one observes the vibrational density of states (cubic symmetry) and identifies the longitudinal optical and transverse acoustic phonons at 261(284) and 100(92) cm−1 with LaS(NdS), respectively. These rare-earth monosulfides offer attractive alternatives to the commonly used cesiated surfaces to reach negative electron affinity at various III–V semiconductor surfaces.
Chemical alloying induced collapse of reversibility windows in ternary As-S-I glasses* FEI WANG, ... more Chemical alloying induced collapse of reversibility windows in ternary As-S-I glasses* FEI WANG, Department of EE, California Polytechnic State University, P. BOOLCHAND, Department of ECECS, University of Cincinnati -Thermally reversing windows represent glass compositions across which glass transitions are thermally reversing in character. These windows have been observed in several chalcogenide glasses, and are identified 1 with self-organized phases of glassy networks. Upon alloying halogen (iodine) in base chalcogenide glasses (Ge-Se, Ge-S), the reversibility windows collapse 2 about the mean-field rigidity transition. We attempt to understand this behavior better. We have now synthesized ternary glass compositions of the type, (AsI 3 ) x (As 0.30 S 0.70 ) 1-x and (AsI 3 ) y (As 2 S 3 ) 1-y over wide composition ranges of x and y, and have examined them systematically in Raman scattering and MDSC experiments. Along with earlier results 3 on binary As z S 1-z glasses, the present results permit mapping the reversibility window over the glass forming range of the present As-S-I ternary. The results show the window region to be of nearly triangular shape, with a base extending in the 0.20 < z < 0.27 range and a vertex located near y = 0.28. A possible interpretation of the results will be presented. * Supported by NSF grant DMR-04 -56472 1. P.Boolchand et al.
Giant photocontraction effects in obliquely-deposited chalcogenide glass thin-films* M. JIN, P. B... more Giant photocontraction effects in obliquely-deposited chalcogenide glass thin-films* M. JIN, P. BOOLCHAND, University of Cincinnati, T. RAJAGOPALAN, K.L. CHOPRA, Indian Institute of Technology, New Delhi -Ge x Se 1-x thin-films at several obliqueness angles α (= 0, 20, 45, 60, 80) and compositions x ( = 0.15, 0.20, 0.23, 0.25 and 0.33) were vapor-deposited, and examined in Raman scattering and SEM measurements both in the pristine and illuminated state. The films, placed in an inert ambient, were exposed to Hg lamp radiation, and photo-contraction of the films established using a profilometer. Raman scattering of the pristine and exposed films were studied as a function of depth using a confocal microscope attachment. Our results show (i) Raman scattering of the normally deposited (α = 0) films in the pristine state are similar to those of corresponding bulk glasses, (ii) obliquely deposited films at x = 1/3 reveal Raman lineshapes that change qualitatively with α, suggestive of nanoscale phase separation of the films, while those at x = 0.23 show Raman lineshapes that are largely independent of α, (iii) the photocontraction effect maximizes in the 0.20< x < 0.25 range, confirming the earlier finding (ref1) (iv) light illumination partially undoes effects associated with nanoscale phase separation. Possible interpretation of these results in relation to origin of photocontraction effects will be presented. *Supported by NSF grant DMR 04-56472.
Pressure Raman experiments on Ge x As x Se 1-2x glasses * PING CHEN, P. BOOLCHAND, Univ. of Cinci... more Pressure Raman experiments on Ge x As x Se 1-2x glasses * PING CHEN, P. BOOLCHAND, Univ. of Cincinnati -It is known 1 that variations in the non-reversing enthalpy associated with glass transitions, ∆H nr (x), display a global minimum (∼0) in the 0.09 < x < 0.16 range and the term increases at x > 0.16 and at x < 0.09 in the titled glasses. In this reversibility window, glasses are thought to in the Intermediate phase and form stress-free networks. Since the size of As, Ge and Se are nearly the same, Raman pressure experiments using a DAC provide a useful way to check the stress-free nature of glasses in the window 2 . Preliminary results at x = 0.11, and 0.14, compositions in the reversibility window, reveal Raman frequency of the symmetric stretch of Ge(Se 1/2 ) 4 tetrahedra to blueshift linearly with external pressure (P) once P>0. At x = 0.18, a composition in the stressed-rigid phase, a blue-shift of the mode is also observed but only once P exceeds a threshold (P c ) value of 14 kbar. The present finding of a finite value of P c at x = 0.18, but its vanishing at x = 0.11 and 0.14, is quite similar to a previous one in binary Ge x Se 1-x glasses 2 . We are now examining other glass compositions in the present ternary. * Supported by NSF grant DMR 04-56472 1 T. Qu et al.
Boson mode, Intermediate Phase, and glass molecular structure of heavy metal Oxides 1 S. CHAKRABO... more Boson mode, Intermediate Phase, and glass molecular structure of heavy metal Oxides 1 S. CHAKRABORTY, P. BOOLCHAND, U. of Cincinnati -We have synthesized bulk glasses of (B 2 O 3 ) 5 (TeO2) 95-x (V 2 O 5 ) x ternary and examined their thermal and optical properties as a function of composition "x." The enthalpy of relaxation at T g shows a global minimum in the Vanadia concentration of 24% < x < 26.5%, which we identify 2 as the intermediate phase (IP) with compositions at x < 24% to be in stressed-rigid and those at x > 26.5% in the flexible phase. Raman scattering reveals a rich lineshape including a Boson mode, whose scattering strength steadily decreases with increasing x, possibly due to bifurcation of weak (Te-O axial ) and strong (Te-O equatorial ) springs characteristic of TeO 2 building blocks. 3 Vanadia alloying brings in isostatic building blocks, pyramidal V(O 1/2 ) 3 and quasi-tetrahedral O= V(O 1/2 ) 3 as suggested by present Raman scattering and recent 51 V NMR data. 4 We describe the structure evolution of these glasses in terms of the Te-centered and V-centered local structures.
Fragility, slow homogenization and Intermediate Phase in the Si x Ge x Te 100-2x ternary 1 K. GUN... more Fragility, slow homogenization and Intermediate Phase in the Si x Ge x Te 100-2x ternary 1 K. GUNASEKERA, P. BOOLCHAND, University of Cincinnati, S. MAMEDOV, Horiba Jobin Yvon Inc. -Small sized (0.5g) melts were synthesized by reacting pure elements in 5mm ID quartz tubes at 950C, and examined after 1 week and then 2 weeks of reaction. Bulk glass formation is realized in 6%<x<16% range with Tg(x) increasing linearly in 6%<x<12% range, and decreasing thereafter (x>12%). The enthalpy of relaxation at Tg shows a flat bottomed minimum in 7.5%<x<9.0% range with the term increasing sharply at x>9% and at x<7.5%. We identify the 7.5%<x<9.0% range with the Intermediate Phase. Fragility(m) of melts were established in complex Cp measurements, and show a global minimum (m<30) in the IP range, and a value of m=26 at x=8.5%. The slow homogenization of Telluride melts results from the strong character of IP melts. Raman scattering, excited using low power density of 785nm radiation, shows evidence of a broad mode near 160cm -1 (characteristic of a-Te chains) and a narrower one near 127cm -1 (group IV crosslinking units). The scattering strength of the 127cm -1 mode increases at the expense of the 160cm -1 mode as x increases. The nature of structure evolution with glass composition will be commented upon.
2 experiments. We have now undertaken mDSC experiments as a function of modulation frequency to e... more 2 experiments. We have now undertaken mDSC experiments as a function of modulation frequency to establish the compositional dependence of complex C p (x), and deduce the variation of fragility m(x). We find the fragility to be rather low, m < 20, across the 22% < x < 38% range, and to rapidly increase at x < 22% to acquire a value of 43 near x = 3%. We show that the slow melt homogenization is a direct consequence of the "strong" character of melts that serves as a bottleneck in melt-mixing at high temperatures. Once homogenized, physical properties of glasses, such as density, glass transition temperature T g (x), the Intermediate phase, and variation of enthalpy of relaxation at T g (x) differ significantly from their inhomogeneous counterparts.
Raman scattering and modulated-DSC experiments on Potassium Germanate glasses* N. WANG, D. NOVITA... more Raman scattering and modulated-DSC experiments on Potassium Germanate glasses* N. WANG, D. NOVITA, P. BOOLCHAND, University of Cincinnati -We have synthesized titled glasses in the 0 < x < 0.16 range by traditional melt-quenching, and have examined them in Raman scattering and modulated-DSC (MDSC) experiments. Raman lineshapes observed in the present work are quite similar to those reported by Henderson and Wang 1 . Preliminary MDSC experiments reveal glass transition temperatures, T g (x), starting from a value of 570˚C at x = 0, to decrease to 508˚C near x = 0.06, and to increase thereafter almost linearly to 552˚C as x increases to 0.15. On the other hand, the non-reversing enthalpy associated with T g provides evidence of a global minimum in the 0.08 < x < 0.10 range, the reversibility window 2 . These results are consistent with glasses at x < 0.08 as Stressed-Rigid, those at x > 0.10 as Floppy, while those in the reversibility window as representing the Intermediate Phase 2 . The space filling nature of the Intermediate Phase is, independently, corroborated by trends in molar volumes which show a broad global minimum in the 9-11% range. Identification of the three elastic phases provides a physical basis to understand the origin of the Germanate anomaly, and the electrical conductivity threshold when glasses become mechanically floppy. *Supported by NSF grant DMR 04-56472. 1
We have synthesized titled glasses in the 0 < x < 0.16 range, and have examined them in mod... more We have synthesized titled glasses in the 0 < x < 0.16 range, and have examined them in modulated DSC experiments. The starting materials, As2S3 and Ag2S lumps, were reacted in evacuated fused quartz tubings, and glasses synthesized by water-quench of homogenized melts. Thermal measurements used a TA instruments model 2920 operated at 3 C/min scan rate and 1 C/100s
Network glasses differ from their crystalline counterparts in a significant way- the presence of ... more Network glasses differ from their crystalline counterparts in a significant way- the presence of an excess of low-frequency vibrations. Here we show that in a covalent ootnotetextP. Chen et al. ArXiv 0810.3637 ( AsxS1-x) and in a super-ionic ootnotetextD. Novita et al. ArXiv 0808.1154 (AgI(x)AgPO3(1-x)) glass system, Raman Bose peak scattering strength (IB) displays commonalities; in the flexible phase of
Bulletin of the American …, 2011
Over the years, bulk glasses have been synthesized by reacting starting materials in evacuated (1... more Over the years, bulk glasses have been synthesized by reacting starting materials in evacuated (10$^{-5} $ Torr to 10$^{-7} $ Torr) quartz tubings for various periods at suitable elevated temperatures. The lack of a non-invasive structural probe to track spatial ...
Bulk glasses were synthesized over the 0 < x < 25% range, and examined in FT-Raman, m-DSC, ... more Bulk glasses were synthesized over the 0 < x < 25% range, and examined in FT-Raman, m-DSC, Electric Force Microscopy (EFM) and complex impedance experiments. Ag2Se as an additive to GeSe4 base glass leads to macroscopic phase separation as revealed by bimodal Tgs ( base glass-Tg =168 C, additive glass Tg = 230 C at low x 16%), a third Tg near 211 C is observed, and its strength increases with increasing x. EFM confirms the heterogeneous character of the glasses displaying a conducting phase that is segregated at low x (16%). Electrical conductivity results show a step-like jump of nearly 2 orders of magnitude in the 16% < x < 20% range. Frequency of the Raman active corner-sharing mode of GeSe4 units (200 cm-1) steadily decreases with increasing x, suggesting that the third phase (Tg=211 C) most likely is a conducting GeSe4-Ag2Se phase. These data are consistent with a volume percolation^2 of solid electrolyte phases near x˜ 16% contributing to the step-like jump in cond...
Physical Review Letters, 1986
The solid electrolyte glass, AgI, possesses a low mean coordination number [1], and when alloyed ... more The solid electrolyte glass, AgI, possesses a low mean coordination number [1], and when alloyed in the base oxide glass, AgPO3, steadily lowers the connectivity of the alloyed glass, (AgI)x(AgPO3)1-x, as reflected in reduction of glass transition temperatures Tg(x). Non-reversing enthalpy associated with Tgs vanish in the 0.10 < x < 0.35 range, the reversibility window, which we identify with the Intermediate elastic phase [2]. Glasses at x 0.35 to the Floppy elastic phase. Electrical conductivity, sigma(x), reveal a mild increase near x = 0.10 as glasses become unstressed, and a pronounced increase near x = 0.35, when glasses become floppy. The correlation between sigma(x) and the elastic phases opens a new paradigm in understanding electrical transport in glasses. Chains of PO4 tetrahedra ( Q^2) present in the pristine oxide are steadily cut and eventually transformed into rings as networks become less connected with increasing x, as revealed by Raman and P^31 NMR measureme...
Bulletin of the American Physical Society, 2017
Phase Spectroscopy of (Na 2 O) x [(B 2 O 3 ) y (GeO 2 ) 1-y ] 1-x glasses AARON WELTON, RALPH CHB... more Phase Spectroscopy of (Na 2 O) x [(B 2 O 3 ) y (GeO 2 ) 1-y ] 1-x glasses AARON WELTON, RALPH CHBEIR, ANDREW CZAJA, PUNIT BOOLCHAND, The University of Cincinnati -The titled ternary is of interest because the two end members, viz., y= 0, i.e., Sodium Germanate 1 , and y = 1, Sodium Borate 2 have been studied earlier and show the isostatically rigid Intermediate Phase (IP) to occur in the x = 0.14 to x = 0.19 range and in the x = 0.20 to x = 0.40 range of soda respectively. In the present work we now report on bulk glasses at y = 0.75 synthesized over a wide range x = 0 to x = 0.30 of soda. Our motivation is to understanding the evolution of the IP in the pseudo-ternary glasses as the base glass connectivity is altered. Preliminary MDSC experiments show T g (x) to increase with x and to reveal a broad maximum at 510 C centered near x = 0.25. Furthermore, an IP is found in the x = 0.20 to x = 0.33 range of soda where a reversibility window is observed. The window is centered near the T max g content at x= 0.25. IR reflectance show modes of BO 4 and BO 3 units but also those of bonded water. Raman scattering largely shows modes observed earlier in Sodium borate glasses 2 . 1 V.
Bulletin of the American Physical Society, 2015
Structural manifestations of aging in Se-rich glasses 1 S. DASH, S. RAVINDREN, P. CHEN, P. BOOLCH... more Structural manifestations of aging in Se-rich glasses 1 S. DASH, S. RAVINDREN, P. CHEN, P. BOOLCHAND, Univ of Cincinnati -We examine weakly cross-linked GexSe100-x (0%<x<7%) binary glasses in modulated DSC and Raman scattering experiments. Homogeneity of melts was carefully verified using FT-Raman line profiling. Upon aging at RT for 4 months, we find the width of the glass transition W(x) steadily decreasing from 10C at 7% Ge to 2C for pure Se. The 5-fold reduction of W(x) with a decrease of Ge content is accompanied by a 2-fold increase in the non-reversing enthalpy. Rejuvenation of the aged glasses changes W(x) from 15C at 7% Ge to 7C for pure Se. Tg is found to decrease upon rejuvenation with the difference (Tg(aged)-Tg(rejuv)) showing a maximum near 3% Ge and vanishing for pure Se and 6% of Ge, which are topological thresholds. These results in Se-rich glasses are consistent with aging induced decoupling of Se8 crowns and growth of extended range structural correlations between polymeric Sen chains due to lone pair interactions. At higher x, near 8-10% of Ge, eutectic effects are manifested.
Bulletin of the American Physical Society, 2014
The American Physical Society Fragility, network adaptation, rigidity-and stress-transitions in h... more The American Physical Society Fragility, network adaptation, rigidity-and stress-transitions in homogenized binary Ge x S 100-x glasses 1 SHIBALIK CHAKRABORTY, PUNIT BOOLCHAND, University of Cincinnati -Binary Ge x S 100-x glasses reveal elastic and chemical phase transitions driven by network topology. With increasing Ge content x, well defined rigidity (x c (1)=19.3%) and stress(x c (2)=24.85%) transitions and associated optical elasticity power-laws are observed in Raman scattering. Calorimetric measurements reveal a square-well like minimum with window walls that coincide with the two elastic phase transitions. Molar volumes show a trapezoidallike minimum with edges that nearly coincide with the reversibility window. These results are signatures of the isostatically rigid nature of the elastic phase formed between the rigidity and stress transitions. Complex C p measurements show melt fragility index, m(x) to also show a global minimum in the reversibility window, underscoring that melt dynamics encode the elastic behavior of the glass formed at T g . The strong nature of melts formed in the IP has an important practical consequence; they lead to slow homogenization of non-stoichiometric batch compositions reacted at high temperatures. Homogenization of chalcogenides melts/glasses over a scale of a few microns is a pre-requisite to observe the intrinsic physical properties of these materials.
Zeitschrift für Naturforschung A, 1996
Bulk glasses of Te3 _zSez-(CI or Br)2+y , the composition spanning the glass forming range, were ... more Bulk glasses of Te3 _zSez-(CI or Br)2+y , the composition spanning the glass forming range, were characterized by differential scanning calorimetry, 125Te absorption, and 129I emission Mössbauer spectroscopy. The results reveal that the stoichiometric glasses Te3(Cl or Br)2 consists of c-Te3 Cl2 -like chain fragments about 1.5 nm long and terminated by one-fold coordinated halogen atoms. The 125Te electric hyperfine structure results reveal that Te replacement by Se (z ≠ 0) leads to preferential occupancy at those Te sites in the chains that are two-fold coordinated, and in a rather striking fashion demonstrate that the average length of the chain fragments remains independent of Se concentration. Halogen atoms in the glasses act as chain terminators, and also bond to Te-sites in the chains to produce four-fold coordinated sites. The low glass transition temperatures (Tg~ 70 -90°C), the low average coordination number of the proposed chain-fragments, along with the hyperfine structu...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2005
Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si substrates by pu... more Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si substrates by pulsed laser deposition. The values of deposition parameters (chamber pressure, substrate temperature, substrate-to-target separation, laser energy, repetition rate, and spot size on the target) leading to a successful growth of films in their cubic rocksalt structure are identified. The films are golden yellow in appearance with a mirror-like surface morphology and possess a sheet resistance around 0.1Ω∕square. X-ray diffraction analysis of thick films (several microns) leads to a lattice constant of 5.863(7)Å, which is close to the bulk LaS value. High-resolution transmission electron microscopy reveals the films to be comprised of nanocrystalline regions separated by amorphous ones. The root-mean-square variation of film surface roughness measured over a 1μm×1μm area is found to be 1.74nm by atomic force microscopy. These films have potential for semiconductor, vacuum microelectronics, ...
Physical Review B, 1996
One-fold-coordinated atoms in a covalent network mechanically soften a network if it is overcoord... more One-fold-coordinated atoms in a covalent network mechanically soften a network if it is overcoordinated, and conversely, mechanically stiffen the network if it is undercoordinated. They play no part in network rigidity if the network is optimally coordinated. These features follow directly from constraint theory and provide a quantitative basis to understand the observed nanoindentation hardness of diamond and silicon carbide networks upon progressive hydrogenation when the contribution of one-fold-coordinated atoms is taken into account explicitly.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2001
We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS)... more We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS). Powder x-ray diffraction scans of the samples show the rocksalt phase with a lattice constant a0=5.857(2) Å and 5.694(2) Å for LaS and NdS, respectively. In Raman scattering, one observes the vibrational density of states (cubic symmetry) and identifies the longitudinal optical and transverse acoustic phonons at 261(284) and 100(92) cm−1 with LaS(NdS), respectively. These rare-earth monosulfides offer attractive alternatives to the commonly used cesiated surfaces to reach negative electron affinity at various III–V semiconductor surfaces.
Chemical alloying induced collapse of reversibility windows in ternary As-S-I glasses* FEI WANG, ... more Chemical alloying induced collapse of reversibility windows in ternary As-S-I glasses* FEI WANG, Department of EE, California Polytechnic State University, P. BOOLCHAND, Department of ECECS, University of Cincinnati -Thermally reversing windows represent glass compositions across which glass transitions are thermally reversing in character. These windows have been observed in several chalcogenide glasses, and are identified 1 with self-organized phases of glassy networks. Upon alloying halogen (iodine) in base chalcogenide glasses (Ge-Se, Ge-S), the reversibility windows collapse 2 about the mean-field rigidity transition. We attempt to understand this behavior better. We have now synthesized ternary glass compositions of the type, (AsI 3 ) x (As 0.30 S 0.70 ) 1-x and (AsI 3 ) y (As 2 S 3 ) 1-y over wide composition ranges of x and y, and have examined them systematically in Raman scattering and MDSC experiments. Along with earlier results 3 on binary As z S 1-z glasses, the present results permit mapping the reversibility window over the glass forming range of the present As-S-I ternary. The results show the window region to be of nearly triangular shape, with a base extending in the 0.20 < z < 0.27 range and a vertex located near y = 0.28. A possible interpretation of the results will be presented. * Supported by NSF grant DMR-04 -56472 1. P.Boolchand et al.
Giant photocontraction effects in obliquely-deposited chalcogenide glass thin-films* M. JIN, P. B... more Giant photocontraction effects in obliquely-deposited chalcogenide glass thin-films* M. JIN, P. BOOLCHAND, University of Cincinnati, T. RAJAGOPALAN, K.L. CHOPRA, Indian Institute of Technology, New Delhi -Ge x Se 1-x thin-films at several obliqueness angles α (= 0, 20, 45, 60, 80) and compositions x ( = 0.15, 0.20, 0.23, 0.25 and 0.33) were vapor-deposited, and examined in Raman scattering and SEM measurements both in the pristine and illuminated state. The films, placed in an inert ambient, were exposed to Hg lamp radiation, and photo-contraction of the films established using a profilometer. Raman scattering of the pristine and exposed films were studied as a function of depth using a confocal microscope attachment. Our results show (i) Raman scattering of the normally deposited (α = 0) films in the pristine state are similar to those of corresponding bulk glasses, (ii) obliquely deposited films at x = 1/3 reveal Raman lineshapes that change qualitatively with α, suggestive of nanoscale phase separation of the films, while those at x = 0.23 show Raman lineshapes that are largely independent of α, (iii) the photocontraction effect maximizes in the 0.20< x < 0.25 range, confirming the earlier finding (ref1) (iv) light illumination partially undoes effects associated with nanoscale phase separation. Possible interpretation of these results in relation to origin of photocontraction effects will be presented. *Supported by NSF grant DMR 04-56472.
Pressure Raman experiments on Ge x As x Se 1-2x glasses * PING CHEN, P. BOOLCHAND, Univ. of Cinci... more Pressure Raman experiments on Ge x As x Se 1-2x glasses * PING CHEN, P. BOOLCHAND, Univ. of Cincinnati -It is known 1 that variations in the non-reversing enthalpy associated with glass transitions, ∆H nr (x), display a global minimum (∼0) in the 0.09 < x < 0.16 range and the term increases at x > 0.16 and at x < 0.09 in the titled glasses. In this reversibility window, glasses are thought to in the Intermediate phase and form stress-free networks. Since the size of As, Ge and Se are nearly the same, Raman pressure experiments using a DAC provide a useful way to check the stress-free nature of glasses in the window 2 . Preliminary results at x = 0.11, and 0.14, compositions in the reversibility window, reveal Raman frequency of the symmetric stretch of Ge(Se 1/2 ) 4 tetrahedra to blueshift linearly with external pressure (P) once P>0. At x = 0.18, a composition in the stressed-rigid phase, a blue-shift of the mode is also observed but only once P exceeds a threshold (P c ) value of 14 kbar. The present finding of a finite value of P c at x = 0.18, but its vanishing at x = 0.11 and 0.14, is quite similar to a previous one in binary Ge x Se 1-x glasses 2 . We are now examining other glass compositions in the present ternary. * Supported by NSF grant DMR 04-56472 1 T. Qu et al.
Boson mode, Intermediate Phase, and glass molecular structure of heavy metal Oxides 1 S. CHAKRABO... more Boson mode, Intermediate Phase, and glass molecular structure of heavy metal Oxides 1 S. CHAKRABORTY, P. BOOLCHAND, U. of Cincinnati -We have synthesized bulk glasses of (B 2 O 3 ) 5 (TeO2) 95-x (V 2 O 5 ) x ternary and examined their thermal and optical properties as a function of composition "x." The enthalpy of relaxation at T g shows a global minimum in the Vanadia concentration of 24% < x < 26.5%, which we identify 2 as the intermediate phase (IP) with compositions at x < 24% to be in stressed-rigid and those at x > 26.5% in the flexible phase. Raman scattering reveals a rich lineshape including a Boson mode, whose scattering strength steadily decreases with increasing x, possibly due to bifurcation of weak (Te-O axial ) and strong (Te-O equatorial ) springs characteristic of TeO 2 building blocks. 3 Vanadia alloying brings in isostatic building blocks, pyramidal V(O 1/2 ) 3 and quasi-tetrahedral O= V(O 1/2 ) 3 as suggested by present Raman scattering and recent 51 V NMR data. 4 We describe the structure evolution of these glasses in terms of the Te-centered and V-centered local structures.
Fragility, slow homogenization and Intermediate Phase in the Si x Ge x Te 100-2x ternary 1 K. GUN... more Fragility, slow homogenization and Intermediate Phase in the Si x Ge x Te 100-2x ternary 1 K. GUNASEKERA, P. BOOLCHAND, University of Cincinnati, S. MAMEDOV, Horiba Jobin Yvon Inc. -Small sized (0.5g) melts were synthesized by reacting pure elements in 5mm ID quartz tubes at 950C, and examined after 1 week and then 2 weeks of reaction. Bulk glass formation is realized in 6%<x<16% range with Tg(x) increasing linearly in 6%<x<12% range, and decreasing thereafter (x>12%). The enthalpy of relaxation at Tg shows a flat bottomed minimum in 7.5%<x<9.0% range with the term increasing sharply at x>9% and at x<7.5%. We identify the 7.5%<x<9.0% range with the Intermediate Phase. Fragility(m) of melts were established in complex Cp measurements, and show a global minimum (m<30) in the IP range, and a value of m=26 at x=8.5%. The slow homogenization of Telluride melts results from the strong character of IP melts. Raman scattering, excited using low power density of 785nm radiation, shows evidence of a broad mode near 160cm -1 (characteristic of a-Te chains) and a narrower one near 127cm -1 (group IV crosslinking units). The scattering strength of the 127cm -1 mode increases at the expense of the 160cm -1 mode as x increases. The nature of structure evolution with glass composition will be commented upon.
2 experiments. We have now undertaken mDSC experiments as a function of modulation frequency to e... more 2 experiments. We have now undertaken mDSC experiments as a function of modulation frequency to establish the compositional dependence of complex C p (x), and deduce the variation of fragility m(x). We find the fragility to be rather low, m < 20, across the 22% < x < 38% range, and to rapidly increase at x < 22% to acquire a value of 43 near x = 3%. We show that the slow melt homogenization is a direct consequence of the "strong" character of melts that serves as a bottleneck in melt-mixing at high temperatures. Once homogenized, physical properties of glasses, such as density, glass transition temperature T g (x), the Intermediate phase, and variation of enthalpy of relaxation at T g (x) differ significantly from their inhomogeneous counterparts.
Raman scattering and modulated-DSC experiments on Potassium Germanate glasses* N. WANG, D. NOVITA... more Raman scattering and modulated-DSC experiments on Potassium Germanate glasses* N. WANG, D. NOVITA, P. BOOLCHAND, University of Cincinnati -We have synthesized titled glasses in the 0 < x < 0.16 range by traditional melt-quenching, and have examined them in Raman scattering and modulated-DSC (MDSC) experiments. Raman lineshapes observed in the present work are quite similar to those reported by Henderson and Wang 1 . Preliminary MDSC experiments reveal glass transition temperatures, T g (x), starting from a value of 570˚C at x = 0, to decrease to 508˚C near x = 0.06, and to increase thereafter almost linearly to 552˚C as x increases to 0.15. On the other hand, the non-reversing enthalpy associated with T g provides evidence of a global minimum in the 0.08 < x < 0.10 range, the reversibility window 2 . These results are consistent with glasses at x < 0.08 as Stressed-Rigid, those at x > 0.10 as Floppy, while those in the reversibility window as representing the Intermediate Phase 2 . The space filling nature of the Intermediate Phase is, independently, corroborated by trends in molar volumes which show a broad global minimum in the 9-11% range. Identification of the three elastic phases provides a physical basis to understand the origin of the Germanate anomaly, and the electrical conductivity threshold when glasses become mechanically floppy. *Supported by NSF grant DMR 04-56472. 1
We have synthesized titled glasses in the 0 < x < 0.16 range, and have examined them in mod... more We have synthesized titled glasses in the 0 < x < 0.16 range, and have examined them in modulated DSC experiments. The starting materials, As2S3 and Ag2S lumps, were reacted in evacuated fused quartz tubings, and glasses synthesized by water-quench of homogenized melts. Thermal measurements used a TA instruments model 2920 operated at 3 C/min scan rate and 1 C/100s
Network glasses differ from their crystalline counterparts in a significant way- the presence of ... more Network glasses differ from their crystalline counterparts in a significant way- the presence of an excess of low-frequency vibrations. Here we show that in a covalent ootnotetextP. Chen et al. ArXiv 0810.3637 ( AsxS1-x) and in a super-ionic ootnotetextD. Novita et al. ArXiv 0808.1154 (AgI(x)AgPO3(1-x)) glass system, Raman Bose peak scattering strength (IB) displays commonalities; in the flexible phase of
Bulletin of the American …, 2011
Over the years, bulk glasses have been synthesized by reacting starting materials in evacuated (1... more Over the years, bulk glasses have been synthesized by reacting starting materials in evacuated (10$^{-5} $ Torr to 10$^{-7} $ Torr) quartz tubings for various periods at suitable elevated temperatures. The lack of a non-invasive structural probe to track spatial ...
Bulk glasses were synthesized over the 0 < x < 25% range, and examined in FT-Raman, m-DSC, ... more Bulk glasses were synthesized over the 0 < x < 25% range, and examined in FT-Raman, m-DSC, Electric Force Microscopy (EFM) and complex impedance experiments. Ag2Se as an additive to GeSe4 base glass leads to macroscopic phase separation as revealed by bimodal Tgs ( base glass-Tg =168 C, additive glass Tg = 230 C at low x 16%), a third Tg near 211 C is observed, and its strength increases with increasing x. EFM confirms the heterogeneous character of the glasses displaying a conducting phase that is segregated at low x (16%). Electrical conductivity results show a step-like jump of nearly 2 orders of magnitude in the 16% < x < 20% range. Frequency of the Raman active corner-sharing mode of GeSe4 units (200 cm-1) steadily decreases with increasing x, suggesting that the third phase (Tg=211 C) most likely is a conducting GeSe4-Ag2Se phase. These data are consistent with a volume percolation^2 of solid electrolyte phases near x˜ 16% contributing to the step-like jump in cond...
Physical Review Letters, 1986
The solid electrolyte glass, AgI, possesses a low mean coordination number [1], and when alloyed ... more The solid electrolyte glass, AgI, possesses a low mean coordination number [1], and when alloyed in the base oxide glass, AgPO3, steadily lowers the connectivity of the alloyed glass, (AgI)x(AgPO3)1-x, as reflected in reduction of glass transition temperatures Tg(x). Non-reversing enthalpy associated with Tgs vanish in the 0.10 < x < 0.35 range, the reversibility window, which we identify with the Intermediate elastic phase [2]. Glasses at x 0.35 to the Floppy elastic phase. Electrical conductivity, sigma(x), reveal a mild increase near x = 0.10 as glasses become unstressed, and a pronounced increase near x = 0.35, when glasses become floppy. The correlation between sigma(x) and the elastic phases opens a new paradigm in understanding electrical transport in glasses. Chains of PO4 tetrahedra ( Q^2) present in the pristine oxide are steadily cut and eventually transformed into rings as networks become less connected with increasing x, as revealed by Raman and P^31 NMR measureme...