Our department of 25 faculty, 374 undergraduates, and 167 graduate students welcomes you. Established in 1867, we have a long tradition of excellence in teaching, research, and service.
Leslie H. Allen
I have several areas of research which focus mainly on the basic materials processes such as nucleation and growth processes in metal/semiconductor systems. We work on problems which have a direct connection to microelectronics applications. Some examples include the following:
Silicides for Silicon Source/Drain contacts
Phys. Rev. B 49,13501-13511 (1994), Appl. Phys. Lett. 65, 561-563 (1994), J. Appl. Phys. 77, 4384-4388(1995), "Symposium for Microelectronic Silicides," MRS (1996).
GaN [APL 64, pg.1003, 1994]; GaAs [APL. 51, pg. 326, 1987]
US Patent #5,023,201 (1991), US Patent #5,138,432 (1992), JAP, 79, 2446-2457 (1996), APL, 60 3179 (1996), Patent Filed #96-096, (1996).The second area of research involves the development of a new tool for materials studies:
Our group has invented a new Thin Film Scanning Calorimetry TDSC device. TDSC is the most sensitive scanning calorimetry device yet reported being 100-1000 times more sensitive than conventional systems. Our objective is to use the technique in two new areas: dynamic energy measurements at surfaces and sensor technology. The first steps toward these objectives have been extremely successful.
Differential Scanning Calorimetry (DSC) is a technique to measure heat exchange during chemical reactions or phase transformations. We have taken the old concept of scanning calorimetry and transformed it into a new powerful characterization/sensor device using micro-machining techniques. This has expanded DSC from traditional 3-D bulk systems to 2-D surface systems. Our TDSC is built upon the idea of the micro-heater, a thin strip of metal which we heat at extremely fast rates ~ 1,000,000 C/s by pulsing large currents through it. The TDSC is the most sensitive calorimetry system yet reported (0.2 nJ), capable of measuring the energy equivalent to melting 0.1 monolayer of atoms.
Size-Dependent Melting Point
We demonstrated the power of TDSC in our melting point study of Sn nanostructures. We are the first to show that both the melting point Tm and the heat of fusion Hm decrease when the physical size of the Sn structures decreases (<20nm). When 1è of Sn is deposited onto an inert substrate, the Sn atoms self-assemble into small islands (nanostructures) consisting of ª 1000 atoms. We found that these islands melt at Tm = 110C, far below the bulk value of 232C. At this stage, our TDSC technique is posed to answer key questions about the basic nature of the melting process, especially regarding surface pre-melting. Melting point depression of small particles has two strong implications for microelectronics technology: (i) control of crystallographic texture for metals during the early stages of film growth during island formation, and (ii) the stability/reliability of aluminum interconnect lines which will have dimensions of only 70 nm by the year 2002. Will these lines be solid or liquid at these dimensions?
S. L. Lai, J. Y. Guo, V. Petrova, G. Ramanath, and L. H. Allen, "Size-Dependent Melting Properties of Small Tin Particles: Nanocalorimetric Measurements," Phys. Rev. Lett. 77, (1996): 99.
S. L. Lai, J. Carlsson and L. H. Allen, "Melting Point Depression of Al Clusters Generated During the Early Stages of Film Growth: Nanocalorimetry Measurements," Appl. Phys. Lett. 72, (1998): 1098.
S. S. Sengupta, S. M. Park, D. A. Payne and L. H. Allen, "Origins and evolution of stress development in sol-gel derived thin layers and multi-deposited coatings of lead titanate," J. Appl. Phys. 83, (1998): 2291.
L. H. Allen and S. L. Lai, "MEMS-based Scanning Calorimeter for Thermodynamic Properties of Nanostructures," Microscale Thermophysical Engineering 2, (1998): 11.
G. Ramanath, J. E. Greene, J. R. A. Carlsson, V. C. Hornback, D. J. Allman, L. H. Allen, "W deposition and titanium fluoride formation during WF/sub 6/ reduction by Ti: Reaction path and mechanisms," J. Appl. Phys. 85, (1999): 1961.
D. J. Allman, V.C. Hornback G. Ramanath, and L. H. Allen, Method for Tungsten Nucleation from WF6 Using Titanium as a Reducing Agent. US Patent, 5,963,828, filed Oct. 1999.
G. Ramanath, J. E. Greene, I. Petrov, J. E. Baker, G. Gillen, L. H. Allen, "Channeling-induced asymmetric distortion of depth profiles from polycrystalline-TiN /Ti /TiN(001) trilayers during secondary ion mass spectrometry," Journal Vacuum Science and Technology B, JVST B, 18, (2000): 1369.
M. Y. Efremov, F. Schiettekatte, M. Zhang, E. A. Olson, A. T. Kwan, R. S. Berry and L. H. Allen, "Discrete Periodic Melting Points in Nanostructure," Phys. Rev. Lett. 85, (2000): 3560.
M. Zhang, M. Y. Efremov, F. Schiettekatte, E. A. Olson, A. T. Kwan, L. S. Lai, J. E. Greene and L. H. Allen, "Melting Point Depression of Nanostructures using Heat Capacity Measurements: Nanocalorimetry Technique," Phys. Rev. B., 62, (2000): 10548.
E. A. Olson, M. Yu. Efremov, A. T. Kwan, S. Lai, F. Schiettekatte, J. T. Warren, T. Wisleder, M. Zhang, V. Petrova, and L. H. Allen, "Scanning Nanocalorimeter for Nanoliter Scale Liquid Samples," Appl. Phys. Lett. 77, (2000): 2671.
A. T. Kwan, M. Yu. Efremov, E. A. Olson, F. Schiettekatte, M. Zhang, P. H. Geil, L. H. Allen, "Nanoscale calorimetry of isolated polyethylene single crystals," Journal of Polymer Science Part B: Polymer Physics 39, no. 11 (2001): 1237-45.
M. Yu. Efremov, J. T. Warren, E. A. Olson, M. Zhang, A. T. Kwan, and L. H. Allen, "Thin-film Differential Scanning Calorimetry: a New Probe for Assignment of the Glass Transition of Ultra Thin Polymer Films," Macromolecules 35, no. 26 (2001): 1481.
M. Zhang, M. Yu. Efremov, E. A. Olson, Z. S. Zhang, and L. H. Allen, “Real-time heat capacity measurement during thin-film deposition by scanning nanocalorimetry,” Appl. Phys. Lett. 81 (2002): 3801.
E. A. Olson, M. Yu. Efremov, M. Zhang, Z. S. Zhang, and L. H. Allen, “The Design and Operation of a MEMS Differential Scanning Nanocalorimeter for High-speed Heat Capacity Measurements of Ultrathin Films,” IEEE J. Microelectromech. Sys. 13 (2003): 355.
M. Yu. Efremov, E. A. Olson, M. Zhang, and L. H. Allen, “Glass Transition of Thin Films of Poly(2-vinyl pyridine) and Poly(methyl methacrylate): Nanocalorimetry Measurements,” Thermochimica Acta, 403 (2003): 37.
M. Y. Efremov, E. A. Olson, M. Zhang, Z. Zhang & L. H. Allen. “Glass transition in ultra-thin polymer films: calorimetric study,” Phys. Rev. Lett. 91, (2003): 85703.
M. Y. Efremov, Eric A. Olson, Ming Zhang, Zishu Zhang, F. Schiettekatte, and Leslie H. Allen, RSI “Ultra-Sensitive Thin-Film Differential Scanning Calorimeter,” Rev. of Sci. Inst. 75 (2004): 179.
M. Yu. Efremov, E. A. Olson, M. Zhang, S. L. Lai, F. Schiettekatte, Z. S. Zhang, and L. H. Allen, “Thin-Film Differential Scanning Nanocalorimetry: Heat Capacity Analysis” Thermochimica Acta, 412, (2004) :13.
M. Y. Efremov, E. A. Olson, M. Zhang, Z. Zhang & L. H. Allen. “Glass transition in ultra-thin polymer films: calorimetric study: Annealing Study,” Macromolecule, 37, (2004): 4607.
Z. S. Zhang, O.M. Wilson, M. Y. Efremov, E. A. Olson, M. Zhang, P. V. Braun, C. Ober, W. Senaratne & L. H. Allen, "Heat Capacity Measurements of Two-Dimensional Self-Assembled Monolayers On Polycrystalline Gold," Appl. Phys. Lett. 84 (2004): 5198.
E. A. Olson, M. Yu. Efremov, M. Zhang, Z. Zhang, L. H. Allen, “Size-dependent melting of Bi nanoparticles,” J. Appl. Phys. 97 (2005): 034304.
M. Zhang, E. A. Olson, R. D. Twesten, J. G. Wen, M. Marshall, L. H. Allen, I.M. Robertson, and I. Petrov, “Operating MEMS devices in the TEM: A new approach for real-time, in situ studies of nanoscale materials,” JMR J. Materials Research: Special Microscopy Issue (July 2005).
R. K. Kummamuru, L. Hu, L. Cook, M. Y. Efremov, E. A. Olson. and L. H. Allen, “A close proximity self-aligned shadow mask for sputter deposition onto a membrane or cavity”, Journal of Micromechanics and Microengineering, 18 (2008) 095027.
L. Hu, Z. S. Zhang, M. Zhang, M. Y. Efremov, E. A. Olson, L. P. de la Rama, R. K. Kummamuru, L. H. Allen, “Self-Assembly and Ripening of Polymeric Silver-Alkanethiolate Crystals on Inert Surfaces”, Langmuir, 2009, 25(16), 9585–9595.
R. K. Kummamuru, L. de la Rama, L. Hu, M. D. Vaudin, M. Y. Efremov, M. L. Green, D. A. LaVan, L. H. Allen, “Measurement of heat capacity and enthalpy of formation of nickel silicide using nanocalorimetry”, Applied Physics Letter, 2009, 95, 181911.
Y. Anahory, M. Guihard, D. Smeets, R. Karmouch, F. Schiettekatte, P. Vasseur, P. Desjardins, Liang Hu, L.H. Allen, E. Leon-Gutierrez, and J. Rodriguez-Viejo, "Fabrication, characterization and modeling of single-crystal thin film calorimeter sensors," Thermochimica Acta, v510, p126 (2010).
L. Hu, L. P. de la Rama, M. Y. Efremov,Y. Anahory, F. Schiettekatte, and L. H. Allen, "Synthesis and Characterization of Single-Layer Silver-Decanethiolate Lamellar Crystals," Journal of the American Chemical Society (in press 2011).
- Racheff Professor of Materials Science (1991-1993)
- Co-chair MRS Silicide symposium, Boston, MA (1995)
- Co-chair AVS-ICMCTF96: Silicide Session, San Diego (1994-1998)
- Program committee 1st Annual AVS Spring Meeting, San Jose, CA (1999)
- UIUC College of Engineering, Advisor's List for Excellence in Advising (1999)
- Alpha Delta Pi Outstanding Scholar Faculty Recognition, UIUC (1999)
- NSF Sponsored Cornell Nanofabrication Facility Review Board (1999, 2000)
- Program committee 2nd Annual AVS Microelectronics and Interfaces, Santa Clara, CA (2000)
- UIUC College of Engineering, Advisor's List for Excellence in Advising (2002)