- Electrical and Computer Engineering
- Doctor of Philosophy, Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 1991
- Master of Science, Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 1987
- Bachelor of Science, Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 1985
Prof. Dallesasse has over 20 years of experience in the Optoelectronics Industry, and has held a wide range of positions in technology development and management, including Vice President of MicroLink Devices and Senior Director of Engineering and Technology for Emcore’s Fiber Optics Division. Most recently, he was the Chief Technology Officer, Vice President, and co-founder of Skorpios Technologies, Inc., a venture-capital funded startup that is developing and commercializing silicon photonic ICs based upon a wafer-scale process for selective integration of III-V materials on SOI substrates. His technical contributions include, with Nick Holonyak, Jr., the discovery of III V Oxidation, which has become an important process technology in the fabrication of high-speed VCSELs. Prof. Dallesasse has also been an active participant in the IEEE 802.3 standards effort, and was an important contributor in the definition of the 10GBASE-LX4 port type for use with installed “legacy” multimode fiber.
- Associate Professor, University of Illinois at Urbana-Champaign, Department of Electrical and Computer Engineering, January 2012 - Present
For more information
- ECE News: Dallesasse Named Fellow of the Optical Society
- ECE News: Dallesasse Selected as IEEE Fellow
- ECE News: Transistor-Injected Quantum Cascade Laser
- CS Magazine: Accessing the Mid-Infrared and Beyond
Other Professional Employment
- Chief Technology Officer, Vice President, and Co-Founder, Skorpios Technologies, Inc., Albuquerque, NM, August 2010 - December 2011
- Vice President, MicroLink Devices, Inc., Niles, IL, March 2009 - August 2010
- Senior Director of Development and Engineering, Emcore Corporation, Naperville, IL, October 2003 - March 2009
- Manager of Group Engineering, Molex, Inc., Downers Grove, IL, 1999 - October 2003
Major Consulting Activities
- Expert Witness, VCSEL and LED Non-infringement and Invalidity Analysis
- Technical Advisory Board, Vega Wave Systems, West Chicago, IL, August 2012 - Present
- Member, Technical Advisory Board, Skorpios Technologies, Inc., Albuquerque, NM, July 2012 - October 2016
- Chief Technology Advisor, Skorpios Technologies, Inc., Albuquerque, NM, January 2012 - October 2016
- Chair, Technical Advisory Board, Skorpios Technologies, Inc., Albuquerque, NM, April 2011 - July 2012
- Co-founder of Skorpios Technologies, a silicon photonics company developing optical ICs based upon template-assisted bonding
- First to Commercialize 10GBASE-LX4 Optical Transceivers, an important Ethernet port type for 10 Gbps upgrades to networks with legacy multimode fiber
- Co-Inventor of III-V Oxidation, an important process technology for compound semiconductor devices, especially VCSELs
A key attraction of making the transition from a successful career in industry to an academic position is the ability to pass on years of accumulated experience to a new generation. Through the course of my career I have had the ability to mentor many young engineers, helping them grow both personally and professionally. This has been one of my greatest sources of satisfaction, and a key motivation for my career growth into engineering management. There is tremendous satisfaction in seeing a spark of insight turn into a flame of knowledge. Making a positive impact on the lives of others through helping them learn and then seeing the contributions that they, in turn, are able to make provides a fulfillment that cannot be measured.
Photonic integration is a necessity for next-generation optical networks. As the number of applications that demand significant bandwidth increase, the ability of existing networks to serve those needs is compromised. Solutions that enable the existing fiber infrastructure to carry more data, such as advanced optical modulation formats based upon phase-shift-keying and polarization multiplexing, require complex optical transmitters and coherent optical receivers assembled using discrete components. These solutions are too expensive for broad deployment, and face fundamental challenges in reducing system cost. The most promising approach to overcoming these challenges is photonic integration. Both Silicon Photonics and Monolithic Integration on InP face fundamental challenges. Silicon is an outstanding material for complex electronics and waveguides, but its indirect bandgap and weak nonlinear optical properties create challenges with regard to the generation, efficient detection, and active control of light. Compound semiconductor materials, especially those that are lattice matched to InP or GaAs, are outstanding materials for these functions but are costly and not ideal for the fabrication of complex electronics, especially ICs such as network processors. Past attempts to bring these materials together have not progressed past the R&D stage due to limitations in performance, reliability, or manufacturability. Direct epitaxial growth of GaAs or InP on silicon faces the problem of having a high defect-density metamorphic layer that can impact device reliability. Wafer bonding techniques, which have been successfully employed in the LED area as well as in the fabrication of SOI wafers, show promise but also face challenges. Direct bonding at high temperature creates significant stress, as the thermal expansion coefficients of Si and III-Vs are not well matched. This stress has an unacceptable impact on device reliability. Lower-temperature bonding techniques using plasma activation, chemical treatment, or atomically thin interface layers show promise but require further development. An integration approach that recognizes and addresses material compatibility issues and manufacturability should be able to overcome prior barriers to commercialization and enable broad deployment of photonic integrated circuits. What to integrate is also a key area of interest. Recent progress on the Feng-Holonyak Transistor Laser suggests that it may be able to serve as a fundamental device element in photonic-electronic integrated circuits, but further research on device integration is required.
Undergraduate Research Opportunities
The Advanced Semiconductor Device and Integration Group welcomes the participation of undergraduates in the research process through independent study projects, undergraduate thesis projects, and through information working relationships. A limited number of slots are available, but interested individuals are encouraged to contact Professor Dallesasse or one of his graduate students.
- Transistor Lasers and Light Emitting Transistors
- Compound Semiconductor Materials
- Compound Semiconductor Devices
- Photonic Integration & Silicon Photonics
- Micro and Nanoelectronics
Chapters in Books
- Handbook of GaN Semiconductor Materials and Devices, CRC Press, Taylor & Francis Group, "Theoretical Model of InGaN/GaN Self Assembled Quantum Dots," G.-L. Su, J.M. Dallesasse, P.K. Bhattacharya, Oct. 18, 2017, ISBN 9781498747134 - CAT# K27029.
Selected Articles in Journals
- “Red and Near-Infrared III-Nitride Quantum Dot Lasers,” A. Hazari, T. Frost, G.-L. Su, J.M. Dallesasse, and P. Bhattacharya, IEEE J. of Sel. Top. Quant. 23, 1901409 (2017).
- “Integrated spectroscopic analysis system with low vertical height for measuring liquid or solid assays,” Y. Wan, J. A. Carlson, S. A. Al-Mulla, W. Peng, K. D. Long, B. A. Kesler, P. Su, J. M. Dallesasse, B. T. Cunningham, Sensors and Actuators B: Chemical, vol. 255, pp. 935-943, 2018.
- “1.3 μm Optical Interconnect on Silicon: A Monolithic III-Nitride Nanowire Photonic Integrated Circuit,” Arnab Hazari, Fu-Chen Hsiao, Lifan Yan, Junseok Heo, Joanna M. Millunchick, John M. Dallesasse, and Pallab Bhattacharya, IEEE J. Quantum Electron. 53, 6300109 (2017).
- “Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera,” Y. Wan, J.A. Carlson, B.A. Kesler, W. Peng, P. Su, S.A. Al-Mulla, S.J. Lim, A.M. Smith, J.M. Dallesasse, and B.T. Cunningham, Scientific Reports 6, 29117 (2016).
- "Facilitating Single-Transverse-Mode Lasing in VCSELs via Patterned Dielectric Anti-Phase Filters," B. Kesler, T. O'Brien, G.-L. Su, and J.M. Dallesasse, IEEE Photon. Tech. Lett. 28, 1497-1500 (2016).
- "Physical model for high indium content InGaN/GaN self-assembled quantum dot ridge-waveguide lasers emitting at red wavelengths (λ ∼ 630 nm)," G.L. Su, T. Frost, P. Bhattacharya, and J.M. Dallesasse, Optics Express 23, 12850-12865 (2015).
- "Detailed model for the In0.18Ga0.82N/GaN self-assembled quantum dot active material for λ=420 nm emission," G.L. Su, T. Frost, P. Bhattacharya, J.M. Dallesasse, and S.L. Chuang, Optics Express 22, 22716-22729 (2014).
- "Effect of the energy barrier in the base of the transistor laser on the recombination lifetime," R. Bambery, C. Wang, J.M. Dallesasse, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 104, 081117-081117-4 (2014).
- "Integrated tunable CMOS laser," T. Creazzo, E. Marchena, S.B. Krasulick, P.K.L. Yu, D. Van Orden, J.Y. Spann, C.C. Blivin, L. He, H. Cai, J.M. Dallesasse, R.J. Stone, and A. Mizrahi, Optics Express 21, 28048-28053 (2013).
- "III-V Oxidation: Discoveries and Applications in Vertical-Cavity Surface-Emitting Lasers," J.M. Dallesasse and D.G. Deppe, Proc. IEEE 101, 2234-2242 (2013).
- "Voltage and Current Modulated 20Gbit/s Operation of a Transistor Laser at Room Temperature," R. Bambery, F. Tan, M. Feng, J. M. Dallesasse, and N. Holonyak, Jr., IEEE Photon. Tech. Lett. 25, 859-862 (2013).
- "Oxidation of Al-bearing III-V materials: A review of key progress," J.M. Dallesasse and N. Holonyak, Jr., Applied Physics Reviews, J. Appl. Phys. 113, 051101-051101-11 (2013).
- “Light Emission from an AlGaAs Single-Quantum-Well Heterostructure by Electron Excitation from a Micromachined Field Emitter Source,” H. Busta, J. Dallesasse, S. Smith, J. Pogemiller, B. Zimmerman, and R. Mathius, J. Micromech. Microeng. 4, 55-59 (1994).
- “Properties and Use of In0.5(AlxGa1-x)0.5P and AlxGa1-xAs Native Oxides in Heterostructure Lasers,” F. A. Kish, S. J. Caracci, N. Holonyak, Jr., K. C. Hsieh, J. E. Baker, S. A. Maranowski, A. R. Sugg, J. M. Dallesasse, R. M. Fletcher, C. P. Kuo, T. D. Osentowski, and M. G. Craford, J. Electron. Mater. 21, 1133-1139 (December 1992).
- “Native-Oxide Masked Impurity-Induced Layer Disordering of AlxGa1-xAs Quantum Well Heterostructures,” J. M. Dallesasse, N. Holonyak, Jr., N. El-Zein, T. A. Richard, F. A. Kish, A. R. Sugg, R. D. Burnham, and S. C. Smith, Appl. Phys. Lett. 58, 974-976 (4 March 1991).
- “Native-Oxide Defined Coupled-Stripe AlxGa1-xAs-GaAs Quantum-Well Heterostructure Lasers,” J. M. Dallesasse, N. Holonyak, Jr., D. C. Hall, N. El-Zein, A. R. Sugg, S. C. Smith, and R. D. Burnham, Appl. Phys. Lett. 58, 834-836 (25 February 1991).
- “Native-Oxide Stripe-Geometry AlxGa1-xAs-GaAs Quantum Well Heterostructure Lasers,” J. M. Dallesasse and N. Holonyak, Jr., Appl. Phys. Lett. 58, 394-396 (1991).
- “Hydrolyzation Oxidation of AlxGa1-xAs-AlAs-GaAs Quantum Well Heterostructures and Superlattices,” J. M. Dallesasse, N. Holonyak, Jr., A. R. Sugg, T. A. Richard, and N. El-Zein, Appl. Phys. Lett. 57, 2844-2846 (1990).
- “Hydrogenation of Si- and Be-Doped InGaP,” J. M. Dallesasse, I. Szafranek, J. N. Baillargeon, N. El-Zein, N. Holonyak, Jr., G. E. Stillman, and K. Y. Cheng, J. Appl. Phys. 68, 5866-5870 (1990).
- “Hydrogenation-Defined Stripe-Geometry In0.5(AlxGa1-x)0.5P Quantum Well Lasers,” J. M. Dallesasse, N. El-Zein, N. Holonyak, Jr., R. M. Fletcher, C. P. Kuo, T. D. Osentowski, and M. G. Craford, J. Appl. Phys. 68, 5871-5873 (1990).
- “Environmental Degradation of AlxGa1-xAs-GaAs Quantum-Well Heterostructures,” J. M. Dallesasse, N. El-Zein, N. Holonyak, Jr., K. C. Hsieh, R. D. Burnham, and R. D. Dupuis, J. Appl. Phys. 68, 2235-2238 (1990).
- “Stability of AlAs in AlxGa1-xAs-AlAs-GaAs Quantum Well Heterostructures,” J. M. Dallesasse, P. Gavrilovic, N. Holonyak, Jr., R. W. Kaliski, D. W. Nam, E. J. Vesely, and R. D. Burnham, Appl. Phys. Lett. 56, 2436-2438 (1990).
- “Impurity-Induced Layer Disordering in In0.5(AlxGa1-x)0.5P-InGaP Quantum Well Heterostructures: Visible Spectrum Buried Heterostructure Lasers,” J. M. Dallesasse, W. E. Plano, D. W. Nam, K. C. Hsieh, J. E. Baker, N. Holonyak, Jr., C. P. Kuo, R. M. Fletcher, T. D. Osentowski, and M. G. Craford, J. Appl. Phys. 66, 482-487 (1989).
- “Short-Wavelength (~6400 Å) Room-Temperature Continuous Operation of p-n In0.5(AlxGa1 x)0.5P Quantum Well Lasers,” J. M. Dallesasse, D. W. Nam, D. G. Deppe, N. Holonyak, Jr., R. M. Fletcher, C. P. Kuo, T. D. Osentowski, and M. G. Craford, Appl. Phys Lett. 53, 1826-1828 (1988).
Articles in Conference Proceedings
- "Progress on the transistor-injected quantum-cascade laser", John M. Dallesasse, Kanuo Chen, Fu-Chen Hsiao, invited, Proc. SPIE 10540, Quantum Sensing and Nano Electronics and Photonics XV, 105401P (26 January 2018); doi: 10.1117/12.2282476; https://doi.org/10.1117/12.2282476.
- “Physical model for indium-rich InGaN/GaN self-assembled quantum dot ridge-waveguide lasers emitting at red (λ ∼ 630 nm),” G.-L. Su, T. Frost, P. Bhattacharya, and J.M. Dallesasse, in Photonic Conference, IEEE, Reston, VA, Paper TuE2.3, Oct. 4-8, 2015, 579 – 580.
- "The Transistor-Injected Quantum Cascade Laser: A Novel Three-Terminal Device for Mid-IR Wavelengths Through THz Frequencies," J.M. Dallesasse, Invited Keynote, Optics 2015, Valencia, Spain, September 1-3, 2015.
- "Electronic-Photonic Integration Using the Light-Emitting Transistor," J. Dallesasse, P.L. Lam, and G. Walter, Paper LTu3A, Latin American Optics and Photonics Conference, Cancun Mexico, November 16-21, 2014.
- “Spur-Free Dynamic Range Measurements of the Hybrid Light-Emitting Transistor,” PL Lam, J.M. Dallesasse, and G. Walter, Paper 5.5, CSMANTECH 2014, Denver, May 20-22, 2014.
- “Design and Modeling of Mid-Infrared Transistor-Injected Quantum Cascade Lasers,” K. Chen and J.M. Dallesasse, Paper 5.1, CSMANTECH 2014, Denver, May 20-22, 2014.
- "Composite-CMOS Integrated Photonics for High Bandwidth WDM Optical Interconnects," T. Creazzo, E. Marchena, S.B. Krasulick, P.K.L. Yu, D. Van Orden, J.Y. Spann, C.C. Blivin, L. He, H. Cai, J.M. Dallesasse, R.J. Stone, and A. Mizrahi, Proc. SPIE 8991, Optical Interconnects XIV, 89910N (March 8, 2014).
- "The Discovery of III-V Oxidation, Device Progress, and Applications to Vertical-Cavity Surface-Emitting Lasers," J.M. Dallesasse, invited talk, 2013 International Conference on Compound Semiconductor Manufacturing Technology (CS-MANTECH), May 13-16 2013, New Orleans, p. 33, 2013.
- "Integrated Tunable CMOS Laser for Si Photonics," E. Marchena, T. Creazzo, S.B. Krasulick, P.K.L. Yu, D. Van Orden, J.Y. Spann, C.C. Bliven, J.M. Dallesasse, P. Varangis, R.J. Stone, and A. Mizrahi, OFC/NFOEC Postdeadline Papers, PDP5C.7, 2013.
- "The Discovery and Device Applications of III-V Oxidation," J. M. Dallesasse, LED 50th Anniversary Symposium, October 24th and 25th, 2012.
- "10GBASE-LX4: Technical Feasibility," J. Dallesasse, E. Grann, B. Twu, IEEE 802.3ae Standards Committee Meeting, Nov. 2001.
- “Short-Wavelength (~6350 Å) Continuous 20°C Operation of (AlxGa1-x)0.5In0.5P Quantum Well Lasers,” Device Research Conference, Boulder, June 20-22, 1988.
- “Enhancing Silicon: Progress on Silicon Photonics and Heterogeneous Integration,” J.M. Dallesasse, Invited Plenary Talk, EDSSC 2017, October 18-20, 2017, Hsinchu, Taiwan.
- “Optoelectronic Integration Using the Transistor Laser: Progress and Potential,” J.M. Dallesasse, P. Su, and J. Carlson, Invited Talk, Advances in Optoelectronics and Micro/nano-optics (AOM) 2017, April 2017, Nanjing, China.
- “The History, Operating Principles, and Current Status of the Vertical-Cavity Surface-Emitting Laser,” J.M. Dallesasse, T. O’Brien, and B. Kesler, Invited Tutorial, Advances in Optoelectronics and Micro/nano-optics (AOM) 2017, April 2017, Nanjing, China.
- "The Oxide-Confined Vertical-Cavity Surface-Emitting Laser: From Dust to Light," J.M. Dallesasse, Invited Talk, Session P29.00004, APS March Meeting 2017, Volume 62, Number 4, March 13-17, 2017, New Orleans, LA.
- “Devices and Processes for Electronic-Photonic Integration,” J. Dallesasse, B. Kesler, G. Su, J. Carlson, P. Lam, and G. Walter, Invited Talk, in Photonic Conference, IEEE, Reston, VA, Paper MF2.2, Oct. 4-8, 2015, 482 – 483.
- "The Transistor-Injected Quantum Cascade Laser: A Novel Three-Terminal Device for Mid-IR Wavelengths Through THz Frequencies," J.M. Dallesasse, Invited Keynote, Optics 2015, Valencia, Spain, September 1-3, 2015.
- "Electronic-Photonic Integration Using the Light-Emitting Transistor," J.M. Dallesasse, P.L. Lam, and G. Walter, Invited Talk, Latin American Optics & Photonics Conference, Nov. 16-21, 2014.
- "The Transistor-Injected Quantum Transition Laser: A Novel Device for the Generation and Modulation of THz Signals," invited talk, Workshop W12: Terahertz Technologies - From Materials to Devices and Their Applications, European Microwave Conference 2013, October 6-11, 2013, Nurnberg, Germany.
- "The Discovery and Device Applications of III-V Oxidation," J. M. Dallesasse, LED 50th Anniversary Symposium, October 24-25, 2012.
- “III-V Oxidation and Optical Networking: The Discovery of III-V Oxidation, It’s Application, and Future Process Technologies for Photonic Integration,” J. Dallesasse, University of Notre Dame Graduate Seminar, March 25, 2011.
- “Oxidation Then and Now: The Discovery of III-V Oxidation and Its Commercial Use Today,” J. Dallesasse, The Holonyak Symposium, October 2008.
- “100 Gigabit Ethernet: Limitations for Practical Deployments,” J. Dallesasse, OIDA Panel Discussion, OFC 2007.
- “Technologies for 100 Gigabit Ethernet: Components and Modules for the Physical Layer,” OIDA 16th Annual Forum, August 2006.
- “10GBASE-LX4 Transceivers: Enabling 10 Gigabit Ethernet Deployment Over Existing Multimode Fiber Networks,” J. Dallesasse, R. Ball, B. Lane, P. Wachtel, T. Whitehead, S. Skiest, B. Noble, D. Richardson, J. Scheibenreif, and T. Moretti, Invited Talk, Communications Design Conference, October 2003.
- “Oxidation of Al-Bearing III-V Materials for Optoelectronic Device Fabrication,” J. M. Dallesasse, Invited Talk, Eighth International Conference on Superlattices, Microstructures and Microdevices, Cincinnati, August, 1995.
- “Recent Progress on the Oxidation of Al-Bearing III-V Materials: A Novel Technique for Optoelectronic Device Fabrication”, J. M. Dallesasse, R. D. Burnham, and N. Holonyak, Jr., French and American Midwestern Workshop, Chicago, October, 1992.
- 9,709,735 Method and system for heterogeneous substrate bonding for photonic integration
- 9,659,993 Vertical integration of CMOS electronics with photonic devices
- 9,496,431 Coplanar integration of a direct-bandgap chip into a silicon photonic device
- 9,461,026 Method and system for template assisted wafer bonding
- 9,453,965 Systems and methods for photonic polarization rotators
- 9,356,162 High efficiency group III-V compound semiconductor solar cell with oxidized window layer
- 9,316,785 Integration of an unprocessed, direct-bandgap chip into a silicon photonic device
- 9,190,400 Method and system for heterogeneous substrate bonding for photonic integration
- 9,170,373 Systems and methods for photonic polarization-separating apparatuses for optical network applications
- 9,091,813 Systems and methods for photonic polarization beam splitters
- 8,948,226 Semiconductor device and method for producing light and laser emission
- 8,867,578 Method and system for hybrid integration of a tunable laser for a cable TV transmitter
- 8,859,394 Vertical integration of CMOS electronics with photonic devices
- 8,722,464 Method and system for template assisted wafer bonding
- 8,718,484 Laser optical transmission system with dual modulation
- 8,630,326 Method and system of heterogeneous substrate bonding for photonic integration
- 8,615,025 Method and system for hybrid integration of a tunable laser
- 8,611,388 Method and system for heterogeneous substrate bonding of waveguide receivers
- 8,605,766 Method and system for hybrid integration of a tunable laser and mach zehnder modulator
- 8,559,470 Method and system for hybrid integration of a tunable laser and a phase modulator
- 8,445,326 Method and system for template assisted wafer bonding
- 8,368,995 Method and system for hybrid integration of an opto-electronic integrated circuit
- 8,222,084 METHOD AND SYSTEM FOR TEMPLATE ASSISTED WAFER BONDING
- 7,959,363 Optical transceiver with optical multiplexer on a flexible substrate
- 7,941,053 Optical transceiver for 40 gigabit/second transmission
- 5,262,360 AlGaAs native oxide
- 5,373,522 Semiconductor devices with native aluminum oxide regions
- 5,567,980 Native oxide of an aluminum-bearing group III-V semiconductor
- 5,696,023 Method for making aluminum gallium arsenide semiconductor device with native oxide layer
- 6,974,260 Flexible substrate for routing fibers in an optical transceiver
- 7,242,824 Flexible substrate for routing fibers in an optical transceiver
- 7,325,983 10GBASE-LX4 optical transceiver in XFP package
- 7,359,641 Modular optical transceiver
- 7,359,642 Modular optical receiver
- 7,380,993 Optical transceiver for 100 gigabit/second transmission
- 7,463,830 Modular optical transmitter for WWDM transceivers
- 7,465,105 Flexible substrate for routing fibers in an optical transceiver
- 7,578,624 Flexible substrate for routing fibers in an optical transceiver
- 7,583,900 Modular optical transceiver
- Associate Editor, IEEE Journal of Quantum Electronics, 2014-Present
- APS Member
- OSA Fellow
- IEEE Fellow
Other Outside Service
- Associate Editor, IEEE Journal of Quantum Electronics
- IEEE Journal of Lightwave Technology Steering Committee
- IEEE Transactions on Semiconductor Manufacturing, Steering Committee
- List of Teachers Ranked as Excellent by Their Students, Spring 2015, ECE 536 (2015)
- Dean's Award for Excellence in Research, UIUC College of Engineering (April 25, 2016)
- IEEE Fellow (Jan. 1, 2015)
- OSA Fellow (2013)
- ECE 340 - Semiconductor Electronics
- ECE 396 - Honors Project
- ECE 397 - Individual Study in ECE
- ECE 488 - Compound Semicond & Devices
- ECE 496 - Senior Research Project
- ECE 498 - Special Topics in ECE
- ECE 499 - Senior Thesis
- ECE 536 - Integ Optics & Optoelectronics
- ECE 597 - Individual Study in ECE
- ECE 599 - Thesis Research