Leonard J. Soltzberg

Prediction of Early- and Late-Growth Morphologies of Ionic Crystals

Comparison of early- and late-growth crystal morphologies of several water-soluble ionic materials suggests that early rapid growth is accompanied by a specific type of morphological distortion. This distortion, involving a change in the relative growth rate of just one growth direction, is consistent with our previously proposed mechanism for the transition from normal, polyhedral crystal growth to dendritic growth. Interpretation of this morphological distortion was aided by morphology prediction methods based on computed attachment energies.

Mechanism of crystal dendrite formation in KNO3

KNO 3 dendrites grown from thin layers of supersaturated aqueous solution display dendrite branches growing along the , and crystallographic directions. These directions do not correspond to faces in normal polyhedral crystals of KNO 3 and, thus, are directions of fast growth in normal crystals. As the growth rate of a normal KNO 3 crystal is increased by cooling the solution, a sharp transition occurs from growth in the [010] direction to growth in one or more of these directions. Interference photomicrographs show that this transition is accompanied by a distortion of the concentration field around the crystal, which further accelerates growth along

Metal contamination in matrix-assisted laser desorption/ionization samples prepared with the 'vortex' solvent-free method.

The quality of MALDI (matrix-assisted laser desorption/ionization) mass spectra can be dramatically affected by sample preparation. Solvent-free sample preparation methods, as developed by Trimpin et al. and extended by Hanton and Parees, tend to increase spot-to-spot and shot-to-shot reproducibility, increase signal strength, eliminate the need to find a solvent compatible with both analyte and matrix, and allow the study of insoluble analytes. In the ‘vortex’ method of sample preparation, the sample and matrix are finely ground and intimately mixed by placing the matrix, analyte, and two metal-plated steel shot (BBs) in a 4mL glass vial and agitating vigorously for a few minutes using a vortex mixer. Hanton and coworkers recommend zinc-plated premium BB shot for this method (standard BB shot are plated with copper). We have discovered that, with certain matrices and analytes, metal plating from the shot can produce distinct signals in mass spectra from vortexprepared samples. These signals can be strong enough to potentially cause confusion in interpreting a spectrum. Figure 1 shows the spectrum of an analyte sample (an iridium complex with peaks at m/z 767/769) prepared using zinc-plated BBs and 6-aza-2thiothymine (ATT, MW1⁄4 143.17Da), a matrix sometimes employed to obtain MALDI mass spectra of transition metal complexes. The strong peaks at m/z 144 ([ATTþH]þ) and 285 ([2 ATT –H]þ) are characteristic of the ATT matrix. The peak clusters at m/z 349 and 490, comparable in strength with the analyte itself, show the isotope pattern of Zn (Fig. 1, insets) and correspond respectively to the species [2 ATTþZn(II) – H]þ and [3 ATTþZn(II) – 3H]þ. A blank spectrum of ATT vortexed with zinc-plated BBs shows these same peak clusters. To confirm that the shot were the source of zinc, we substituted copperplated BB shot. The resulting pattern, shown in Fig. 2, is a superposition of terscience.wiley.com) DOI: 10.1002/rcm.3895 [2 ATTþCu(I)]þ at m/z 349/351 and [2 ATTþCu(II) – H]þ at m/z 348/350. The tendency of both Cu(I) and Cu(II) valence states to appear in MALDI spectra of copper-containing species has been reported elsewhere. Perhaps the presence of these metal adducts is not surprising, since cations such as sodium, copper, silver, and ammonium are commonly added to MALDI samples to enhance ionization.

Crystal morphology prediction and morphology variation in NaIO4 and NaIO4.3H2O

Attachment energies computed with only Coulomb potentials have been utilized to predict crystal morphologies for NaIO(4), sodium iodate, and the hydrate NaIO(4).3H(2)O, sodium iodate trihydrate [actually Na(H(3)O)(IO(3))(OH)(3)]. As with other previously studied water-soluble ionic compounds, these two systems exhibit a systematic relationship between the early growth morphology and that of mature crystals; this relationship can in each case be reproduced by adjusting one attachment energy value. Morphology prediction for these two substances is of particular interest because NaIO(4).3H(2)O is a polar crystal and involves extensive hydrogen bonding, and because obtaining the observed morphology for NaIO(4) involved consideration of solvent desorption at the growing faces.

Crystal anisotropy and dendritic crystal growth

Observation of selected low-symmetry crystals growing in the dendritic morphology indicates the importance of crystal structure in determining not only the sidebranch spacing but also the very existence of sidebranching. This evidence provides a perspective which supplements the view of sidebranching as being governed by the continuum dynamics of a moving solid-liquid interface. Direct evidence is presented for a parabolic diffusion field surrounding growing dendrite tips. The existence of this field is consistent with the theoretical analysis which leads to the needle-crystal model of dendritic growth.

Degradation of Ir(ppy) 2 (dtb-bpy)PF 6 iTMC OLEDs

Simplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs (organic light emitting diodes) compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy) 3 (PF 6 ) 2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy) 2 (dtb-bpy)PF 6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy) 2 (dtb-bpy)PF 6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.

Current-Induced Degradation in Polythiophene

The three-year collaboration between Simmons College and the Cornell Center for Materials Research (CCMR) is focused on undergraduate student/faculty research in organic light emitting diodes (OLEDs). The physics of OLED devices is characterized by three major processes: charge injection, charge transfer, and light emission as a result of the electron-hole recombination. In the first year of the program our research has been related to the first two stages. OLEDs based on small molecule as well as polymeric layers have been investigated, The devices were prepared using mostly aluminum (also nickel and iron) as electrodes and PC:TPD or polythiophene as the organic layer. Electrodes of about 20 nm were formed by vacuum evaporation, and organic layers of approximately 100-200 nm were spin-coated. The current-voltage characteristics, measured under forward and reverse bias up to 10 volts, demonstrate typical semiconductor S-shape behavior, and show variations dependent on aging, thickness of the polymer layer, and type and combination of electrodes. The results presented here specifically track the degradation of devices using polythiophene sandwiched between aluminum electrodes. The I-V curves and successive current response as a function of time and under constant voltage drive are presented along with complementary mass spectra and UV-visible and infrared absorption spectra. These measurements along with preliminary computer modeling of HOMO and LUMO energies for a series of thiophene oligomers suggest a correlation between internal changes in the polymer and variations in the electrical characteristics of the devices.

Evolution of the Women in Materials Program: a Collaboration between Simmons College and the Cornell Center for Materials Research

The Women in Materials (WIM) program is an on-going collaboration between Simmons College and the Cornell Center for Materials Research (CCMR). Beginning in 2001, during the initial four years of the project, materials-related curricula were developed, a new joint research project was begun, and nearly 1/2 of Simmons College science majors participated in materials-related research during their first two years as undergraduates. We have previously reported the student outcomes as a result of this initial stage of the project, demonstrating a successful partnership between a primarily undergraduate womens college and a federally funded Materials Research Science and Engineering Center. Here, we report the evolution and impact of this project over the last three years, subsequent to the initial seed funding from the National Science Foundation. The Women in Materials project is now a key feature of the undergraduate science program at Simmons College and has developed into an organizing structure for materials-related research at the College. Initially, three faculty members were involved and now eight faculty members from all three laboratory science departments participate (biology, chemistry, and physics). The program now involves research related to optoelectronics, polymer synthesis, biomaterials, and green chemistry, and each semester about 80% of the students who participate in these projects are st and 2 nd year science majors. This structure has led to enhanced funding within the sciences, shared instrumentation facilities, a new minor in materials science, and a spirit of collaboration among science faculty and departments. It has also spawned a new, innovative curricular initiative, the Undergraduate Laboratory Renaissance, now in its second year of implementation, involving all three laboratory science departments in incorporating actual, ongoing research projects into introductory and intermediate science laboratories. Most importantly, the Women in Materials program has embedded materials-related research into our science curriculum and has deepened and broadened the educational experience for our students; The student outcomes speak to the programs success. Approximately 70% of our science majors go on to graduate school within two years of completing their undergraduate degree. Our students also have a high acceptance rate at highly competitive summer research programs, such as Research Experience for Undergraduates (REU) programs funded by the National Science Foundation.

Women in Materials: A collaborative effort between Simmons College and the Cornell Center for Materials Research

The Women in Materials program, supported by the National Science Foundation, is a collaboration between Simmons College, a predominately undergraduate womens college, and the Cornell Center for Materials Research. For the past four years, this program has provided unusual curricular and research opportunities for undergraduate women at Simmons College. This program demonstrates a successful model for enhancing undergraduate science and technology preparation through collaboration between primarily undergraduate institutions and NSF-supported Materials Research Science and Engineering Centers.