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  1. Self-Organization in Disordered Networks.

A.    Intermediate Phases in Chalcogenide Glasses

B.    Intermediate Phases in Oxide Glasses

C.    Rigidity Transitions in Chalcohalide Glasses

 

Discovery of Intermediate Phases1,2,3,4 in network or molecular glasses has opened a novel paradigm to understand the physical behavior of glasses at a basic level. These phases manifest as global connectivity of molecular networks are systematically changed, and acquire a critical value. These ideas have led to a glass structure based classification5,6,7 in terms of their elastic properties, Floppy-intermediate-stressed rigid. Intermediate Phases are non-mean-field phases, and represent stress-free or self-organized phases of disordered systems. Their physical behavior are examined in controlled laboratory experiments in molecular glasses. For additional details click here. No aging in glasses. GexSbxSe100-2x sample synthesis.

 

This work is supported by National Science Foundation grants DMR-01-01808 and INT-0138707 with France under an  NSF-CNRS collaboration.

 

1. D.Selvanathan, W.J.Bresser, P.Boolchand, B.Goodman. Solid State Commun.111,619(1999) (article in pdf format).

2. D.Selvanathan, W.J.Bresser and P.Boolchand. Phys.Rev B61,15061(2000) (article in pdf format).

3. P.Boolchand, D.G.Georgiev, B.Goodman. J.Optoelectronics and Adv. Materials 3,703(2001) (article in pdf format).

4. Y. Wang, J.Wells, D.G.Georgiev, P.Boolchand, K.Jackson, M.Micoulaut. Phys.Rev.Lett.87,185503(2001)(article in pdf format) .

5. M.Micoulaut ( unpublished)

6. J.C.Phillips, Phys. Rev. Letters 88, 216401 (2002).

7. M.F.Thorpe, D.J.Jacobs, M.V.Chubynsky, J.C.Phillips. J.Non-Cryst. Solids 266-269,859(2000) (article in pdf format).

  1.  Solid Electrolytes

     

    A.     Ag as an additive in Chalcogenide Glasses

    B.     New Glass Phases of Solid Electrolytes

    C.     Ionic-Conduction in Solid Electrolyte Glasses

     

    Ag as an additive in Chalcogenide glasses has attracted widespread interest1,2 in optical recording and information storage technologies. Ag as a chemical additive plays a dual role3; in Se-rich glasses it macroscopically phase separates into a Ag-rich glass phase, and in Se deficient glasses becomes a network former to replace Ge in select local environments. The Ag-rich glass phase is thought to be a solid electrolyte4 with a stoichiometry close to Ag2Se, and is characterized by a glass transition of 230˚C. An equally important consequence of Ag addition to oxide and chalcogenide base glasses is the several orders of magnitude enhancement of electrical conductivity5,6 of the alloyed glasses. Several models5 have been proposed to understand the conductivity enhancement. Central to the problem are aspects of glass structure, in particular the distribution of Ag in these materials, issues that continue to be debated at present.

     

    This work is supported by Arizona State University on a subcontract from Axon Technologies Inc.

     

    1. H.Fritzsche. Philos. Mag. B 68, 561(1993).

    2. M.Mitkova in Insulating and Semiconducting Glasses, Ed. P.Boolchand, World Scientific Press, Inc., p.653.

    3. M.Mitkova, Yu Wang, P.Boolchand, Phys.Rev. Lett. 83, 3848(1999) (article in pdf format).

    4. P.Boolchand  and W.J.Bresser, Nature 410,1070(2001) (article in pdf format).

    5. J.Kincs and S.W.Martin Phys. Rev. Lett. 76, 70(1996) (article in pdf format).

    6. J.Swenson, R.L.McGreevy, R.Borjesson, J.D.Wicks, W.S.Howells, J.Phys. Cond. Matter, 8,3545(1996).

     

  2. Rare-Earth Additives In Chalcogenide Glasses and Crystalline Oxides

A.     Chemical Aspects of Alloying

B.     Light-Induced and Emission Effects

C.     BAM Phosphor

Rare-earth as additives in Chalcogenide glasses have attracted widespread interest as optical amplifiers, lasers, mid-IR photonic materials because of the high refractive index and mid IR transparency1. Most rare-earth ions in  solids stabilize in the trivalent state, although exceptions  can occur for Eu (divalent) and Ce(tetravalent). For these reasons trivalent  Ga as an additive in the chalcogenide glasses has been extensively studied2,3. Although Rare-earth ions can replace Ga sites in such glasses, this does not necessarily have to be the case. In some cases, Rare-earth ions can also occupy distorted rocksalt environment, as is found for the case of  Rare-earth monosulfides such as LaS 4. Some of these Ga-alloyed Chalcogenides display pronounced photobleaching effects5, whose molecular origin remains open for debate. An issue of continuing interest is the role of host Photoluminescence excitation on light emission efficiency from rare-earth emitter guests1. Eu chemical environment in BAM Phosphor is elucidated by Mossbauer spectroscopy.

This research work is performed in collaboration with Professor Marc Cahay.

1. S.G.Bishop, D.A.Turnbull, B.G.Aitken, J.Non Cryst. Solids 266-269,876(2000).

2. M.Yamane and Y.Asahara, Glasses for Photonics, Cambridge University Press,,2000.

3. Liuchun Cai and P.Boolchand ( unpublished).

4. P.Boolchand in Insulating and Semiconducting Glasses, Ed. P.Boolchand, World Scientific Press, Inc., Singapore, 2000, p.217.

5. S.H.Messaddeq, M.Siu Li, D.Lezal, Y.Messaddeq, S.J.L.Riberio, L.F.C.Oliveira, J.M.D.A.Rollo, J. Optoelectronics and Adv. Mater. 3,295(2001).

6. M.Stephan, P.C.Schmidt, R,C,Mishra, M.Raukao, A.Ellens, P.Boolchand. Z.Phys.Chem, 215, 1347 (2001).

The work on BAM is supported by Osram Sylvania.

  1. Negative Electron Affinities, New Cold Cathode and Organic Light Emitting Diodes

     

    A.  LaS based trilayered Structure

     

    Rare-earth monosulphides, such as LaS and NdS, are unusual metals as they possess low work-functions1. These materials in conjunction with  III-V or II-VI semiconductors  and separately with light emitting polymers2, can be used as efficient cold cathode emitters3,4 and light emitting devices5. An effort to synthesize bulk materials of the rare-earth sulfides, and grow thin-films of the rare-earth sulfides by sputtering and evaporation is made, to fabricate new solid state cold cathode emitters and efficient and durable organic light emitting diodes ( OLEDS).

    Current research efforts are directed towards growth of thin-films of various rare-earth sulfides on compound semiconductors by RF  magnetron sputtering deposition6,7

     

    This research in collaboration with Professor Marc Cahay, is funded by National Science Foundation grant ECS 9906053, and Wright-Patterson AFB under contract No. F33615-98-C-1204.

     

    1. O.Eriksson, J.Willis, P.D.Mumford, M.Cahay and W.Eriz, Phys.Rev.B 57,4067(1998).

    2. O.E.Eriksson, M.Cahay, J.Willis, Phys.Rev.B65, 033304(2002).

    3. P.D.Munford and M.Cahay, J.Appl.Phys.79,2176(1996).

    4. P.D.Mumford and M.Cahay, J.Appl.Phys. 81,3707(1997).

    5. M.Lueck, P.Draviam and M.Cahay ( unpublished)

    6. Y.Modukuru, J.Thachery, H.Tang, A.Malhotra, M.Cahay and P.Boolchand, J.Vac. Sci. and Tech.B 19,1958(2001).

    7. Y.Modukuru, J.Thachery, M.Cahay, P.Boolchand, Proceedings of the Second Intl. Symposium   on Cold Cathodes, May 12-17(2002)        

     

  2. Synthesis and Nanostructure of Super Hard Thin-Films

     

    A. Diamondlike Carbon Films

    B. B-N-C Thin-films

     

    Films in the B-N-C ternary are of interest because of their super hardness.  The ternary encompasses some of the hardest crystalline materials known including diamond, BN, B2C. A collaborative effort to synthesize and characterize nanostructure of vapor deposited thin-films is ongoing with Professor Raj Singh (Materials Science and Engineering, University of Cincinnati) and  with Professor Hans-Joachim Kleebe (Colorado School of Mines). At the core of the research effort is an ECR microwave plasma enhanced CVD facility1(Professor R.Singh)  for growth of the ternary alloy films. The films are characterized2 by x-ray diffraction, and Raman scattering  (Professor P.Boolchand) and Electron microscopy3 including HRTEM, SEM and EELS (Professor H.-J.Kleebe). The mechanical properties of these films including Hardness, Elastic Moduli, and thermal conductivity (Professor Singh) are measured. Constraint counting algorithms  along with aspects of nanostructure are used to understand their physical behavior

    The project is funded by the National Science Foundation as a Focused Research Group grant DMR-0200839 and a NIRT grant 0210351.

    1. R.N. Singh  Proc. Xth International Conf. On CVD, Ed. G.W.Cullen, The Electrochemical Society V.87-8,543(1987).

    2. P.Boolchand, M.Zhang, B.Goodman Phys. Rev B, 53,11188(1996) (article in pdf format).

    3. H.J Kleebe, Phys. Stat. Sol. (A) 166,297(1998).

 

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