High aspect ratio diamond nanosecond laser machining.

Laser processing of diamond has become an important technique for fabricating next generation microelectronic and quantum devices. However, the realization of low taper, high aspect ratio structures in diamond remains a challenge. We demonstrate the effects of pulse energy, pulse number and irradiation profile on the achievable aspect ratio with 532 nm nanosecond laser machining. Strong and gentle ablation regimes were observed using percussion hole drilling of type Ib HPHT diamond. Under percussion hole drilling a maximum aspect ratio of 22:1 was achieved with 10,000 pulses. To reach aspect ratios on average 40:1 and up to 66:1, rotary assisted drilling was employed using > 2 M pulse accumulations. We additionally demonstrate methods of obtaining 0.1° taper angles via ramped pulse energy machining in 10:1 aspect ratio tubes. Finally, effects of laser induced damage are studied using confocal Raman spectroscopy with observation of up to 36% increase in tensile strain following strong laser irradiation. However, we report that upon application of 600 °C heat treatment, induced strain is reduced by up to ~ 50% with considerable homogenization of observed strain. Supplementary Information: The online version contains supplementary material available at 10.1007/s00339-023-06755-2.

Diamond rotors.

The resolution of magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra remains bounded by the spinning frequency, which is limited by the material strength of MAS rotors. Since diamond is capable of withstanding 1.5-2.5x greater MAS frequencies, compared to state-of-the art zirconia, we fabricated rotors from single crystal diamond. When combined with bearings optimized for spinning with helium gas, diamond rotors could achieve the highest MAS frequencies to date. Furthermore, the excellent microwave transmission properties and thermal conductivity of diamond could improve sensitivity enhancements in dynamic nuclear polarization (DNP) experiments. The fabrication protocol we report involves novel laser micromachining and produced rotors that presently spin at ωr/2π = 111.000 ±â€¯0.004 kHz, with stable spinning up to 124 kHz, using N2 gas as the driving fluid. We present the first proton-detected 13C/15N MAS spectra recorded using diamond rotors, a critical step towards studying currently inaccessible ex-vivo protein samples with MAS NMR. Previously, the high aspect ratio of MAS rotors (∼10:1) precluded fabrication of MAS rotors from diamond.

Photochemical electron transfer reactions of tirapazamine.

The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy.