Sulfur and selenium derivatives of 2-phosphaindolizines

The 2-phosphaindolizines 1 react with hydrogen sulfide and elemental sulfur to give the new zwitterionic heterocyclic systems 2 of the N-pyridiniomethyl dithiophosphinate type. In contrast, no reaction is observed with sulfur alone. MeI methylates 2e,f at sulfur. The analogous pyridiniodiselenophosphinate 5 results from the reaction of 1a with 1,3,2,4-diselenadiphosphetane-2,4-diselenide, 4a, in the absence of an additional base. As a further product, the perselenophosphinic anhydride 6 is identified. In the presence of triethylamine, 1a reacts with each of the diselenides 4a–c to give the new triethylammonium diselenophosphinates 7a–c, respectively. This reaction can be extended to 1-aza-2-phosphaindolizine, 8, which yields with each of 4a,b and NEt₃ the diselenophosphinates 9a,b, respectively. The anhydride 6 and the diselenophosphinates 7 and 9 result from an electrophilic substitution at the phosphaindolizine ring. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:445–452, 1998     

Determination of polycyclic aromatic hydrocarbons by high-performance liquid chromatography-particle beam-mass spectrometry

In this article, we report a high-performance liquid chromatography-particle beam-mass spectrometric (HPLC-PB-MS) method for the determination of polycyclic aromatic hydrocarbons (PAHs). The PB interface consists of a concentric ultrasonic nebulizer with temperature-controlled desolvation chamber and a three-stage momentum separator. The HPLCPB-MS method showed greater sensitivity for PAHs with molecular weights above 178 than for those PAHs with molecular weights below 178. The percent relative standard deviations for the determination of 0.5 ng chrysene, 1.0 ng dibenzo[a,h]anthracene, 1.0 ng benzo[g,h,i]perylene, and 2.5 ng coronene were 20%, 2.5%, 13.7%, and 6%, respectively. The detection limits at signal/noise = 3 were 0.2 ng for chrysene, 1.0 ng for dibenzo[a,h]anthracene, 0.5 ng for benzo[g,h,i]perylene, and 1.5 ng for coronene.     

Crystal Structure of N,N'‐Bis(3‐(o‐dimethylaminoimino‐ethyl) ‐2‐hydroxy‐5‐methyl)‐benzylpiperazine

The structure of the synthesized title compound, C₃₀H₄₆N₆O₂ , was solved by using X‐ray diffraction techniques. The compound crystallized in monoclinic space group P2₁/n with cell dimensions a = 14.0629(7), b = 6.5696(3), c = 17.7948(8)Å, β = 111.35(2)°, V = 1531.2(1)ų, Z = 2, D_cal = 1.134 Mgm^‐3 and T = 293(2)K. The molecule possesses a center of symmetry, and hence, there is half a molecule in the asymmetric unit. The piperazine ring adopts chair conformation with the substituents at the equatorial position, subtending a dihedral angle of 88.87(1)° with the phenyl ring. The phenyloxy hydrogen is involved in an intramolecular O‐H...N type of hydrogen bond.     

Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review

Ultrathin silicon wafer technology is reviewed in terms of the semiconductor applications, critical challenges, and wafer pre-assembly and assembly process technologies and their underlying mechanisms. Mechanical backgrinding has been the standard process for wafer thinning in the semiconductor industry owing to its low cost and productivity. As the thickness requirement of wafers is reduced to below 100 μm, many challenges are being faced due to wafer/die bow, mechanical strength, wafer handling, total thickness variation (TTV), dicing, and packaging assembly. Various ultrathin wafer processing and assembly technologies have been developed to address these challenges. These include wafer carrier systems to handle ultrathin wafers; backgrinding subsurface damage and surface roughness reduction, and post-grinding treatment to increase wafer/die strength; improved wafer carrier flatness and backgrinding auto-TTV control to improve TTV; wafer dicing technologies to reduce die sidewall damage to increase die strength; and assembly methods for die pick-up, die transfer, die attachment, and wire bonding. Where applicable, current process issues and limitations, and future work needed are highlighted.