Samuel Graham

Bio: Samuel Graham is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Thermal conductivity & Thermal resistance. The author has an hindex of 48, co-authored 347 publications receiving 9774 citations. Previous affiliations of Samuel Graham include Merck & Co. & United States Military Academy.

Kinetics of environmentally assisted cracking in SiNx barrier films

Abstract: Kinetics of environmentally assisted subcritical cracking in SiNx barrier films is studied by in situ optical microscopy experiments and quantum chemical molecular orbital theory simulations. The activation volume of 0.83–1.11 cm3/mol and the activation energy of 138 kJ/mol (1.43 eV) are experimentally measured for subcritical crack growth in moist air. The quantum chemical simulations reveal the molecular mechanism of stress corrosion in mechanically strained SiNx under water attack, and the predicted activation energy and activation volume are in good agreement with the experimental results. The combined experimental and modeling studies provide a fundamental understanding of subcritical crack growth in SiNx barrier films for flexible electronic device applications.Kinetics of environmentally assisted subcritical cracking in SiNx barrier films is studied by in situ optical microscopy experiments and quantum chemical molecular orbital theory simulations. The activation volume of 0.83–1.11 cm3/mol and the activation energy of 138 kJ/mol (1.43 eV) are experimentally measured for subcritical crack growth in moist air. The quantum chemical simulations reveal the molecular mechanism of stress corrosion in mechanically strained SiNx under water attack, and the predicted activation energy and activation volume are in good agreement with the experimental results. The combined experimental and modeling studies provide a fundamental understanding of subcritical crack growth in SiNx barrier films for flexible electronic device applications.

Development of reliable mW level powers in pseudomorphic ultraviolet light emitting diodes on bulk aluminum nitride substrates

Abstract: The use of low defect density bulk AlN substrates has led to reliable pseudomorphic ultraviolet light emitting diodes capable of mW level power outputs from packaged devices emitting from 250–275 nm.

Ultrabarrier Films for Packaging Flexible Electronics: Examining the Role of Thin-Film Technology

Abstract: The development of organic electronics, such as organic LED (OLED) devices and organic field effect transistors (OFE Ts), as well as thin-film solar cells enable the development of devices with a range of functionality in f lexible form factors [1]-[6].

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Interface engineering of highly efficient perovskite solar cells

Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

Abstract: A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.