Vincent Marrello

Reversibility and stability of tellurium alloys for optical data storage applications

We demonstrate for the first time that Te87Ge8Sn5 films, which are amorphous as deposited, can be optically switched between the crystalline and amorphous states more than 106 times. The measured reflectivity changed from 40% to 60% and the transmission changed from 3% to 1.5%, respectively, between the amorphous and crystalline states. The crystallization temperature of the cycled spots is ≊75 °C and these spots are observable after >20 weeks. It is found that the crystallization temperature of cycled spots is typically about 20 °C lower than that of the unwritten film. Increasing the Ge concentration leads to increased crystallization temperature and increased minimum crystallization time without affecting reversibility.

The memory effect of ZnS : Mn ac thin‐film electroluminescence

The electroluminescence of ZnS : Mn thin‐film memory devices is observed to occur in two components, one which is spatially homogeneous and one from localized bright regions less than ∼1 μm in diameter. The brightness‐voltage hysteresis, or memory effect, is observed to reside exclusively in the luminescence of the localized bright regions in our devices. It is concluded that the memory effect arises from a negative resistance of a filamentary ac conduction mechanism in these regions.

Electroluminescence efficiency profiles of Mn in ZnS ac thin‐film electroluminescence devices

We report a direct measurement of relative Mn electroluminescence (EL) efficiency in an ac EL device as a function of position normal to the ZnS film plane. The Mn EL efficiency decreases strongly with distance from the cathodic to anodic region of the ZnS layer. The cathodic‐to‐anodic efficiency ratio is about two orders of magnitude. In addition, the first ∼0.2 μm of ZnS deposited exhibits a significantly lower Mn EL efficiency relative to the remaining ZnS.

AC thin film electroluminescence, filamentary emission and its memory effect

Abstract A ZnS:Mn ac thin film electroluminescence device can exhibit a brightness vs. voltage hysteresis loop or “memory effect”. We show that this “memory effect” is associated with the filamentary nature of the dissipative current. The filaments show a bistability in their conductive state, i.e., the nature of the “ac negative resistance” involved is current controlled. Experimental results on single filament switching under voltage, pulse width and light address are presented.

Ablative hole formation process in thin tellurium and tellurium‐alloy films

Static measurement data of contrast ratio versus laser power of single layer Te and Te alloys on polymethylmethacrylate substrates are reported. It is shown that these films can exhibit two regimes of hole formation depending upon laser power. In the lower power regime hole opening must be initiated by voids in the film while for higher powers voids are not necessary for hole opening. This interpretation leads to a better understanding of the hole ablation process as well as some practical consequences.

Filamentary AC electroluminescence in ZnS:Mn

Steady state and switching behavior of single luminescence filaments in a-BaTiO3/ZnS:Mn/a-BaTiO3 ac thin film electroluminescence devices have been studied. The brightness-voltage amplitude hysteresis, or memory effect, of these devices results from the ensemble behavior of luminescing filaments that are bistable in their luminescence level. A trap depth of 1-1.2eV is estimated on the assumption that the voltage threshold for luminescence involves electric field emission from traps. The temperature dependence of electroluminescence near the threshold voltage is investigated.