Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films

In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required

Nanoscale resolution immersion scanning thermal microscopy

Nanoscale thermal properties are becoming of extreme importance for modern electronic circuits that dissipate increasing power on the length scale of few tens of nanometers, and for chemical and physical properties sensors and biosensors using nanoscale sized features. While Scanning Thermal Microscopy (SThM) is known for its ability to probe thermal properties and heat generation with nanoscale resolution, until today it was perceived impossible to use it in the liquid environment due to dominating direct heat exchange between microfabricated thermal probe and surrounding liquid that would deteriorate spatial resolution. Nonetheless, our theoretical analysis of SThM in liquids showed that for certain design of SThM probe with resistive heater located near the probe tip, their thermal signal is only moderately affected, by less than half on immersion in a dodecane environment. More significantly, its spatial resolution, surprisingly, would remain practically unaffected, and the thermal contact between the tip apex and the studied sample would be beneficially improved. Our experimental trials of such immersion SThM, or iSThM, were fully successful and here we report for the first time nanoscale SThM measurements of thermal conductivity of Ultra Large Scale Integration polymerceramic metal interconnects with the spatial thermal resolution down to 50 nm. Further studies of heat transport in nanoscale graphite flakes in iSThM suggested, in particular, that highly anisotropic thermal conductivity in graphene layers may play significant role in the nanoscale thermal transport in liquid environment. New iSThM opens a wide range of applications from noncontact measurements of thermal transport in semiconductor devices to exploring graphene energy storage, catalytic reactions and heat generation in biological systems

Oral composition

Oral care composition comprising a polymer obtainable by copolymerising a mixture of comonomers, from 5 to 95 mol % of the mixture of comonomers is constituted by a como no mer having the formula (I): (I) in which R is hydrogen or a methyl group, L is a divalent organic linking group incorporating a benzylor a carboxyl functionality, n is an integer of from 1 to 4 and Y is an amine, quaternized amine or quaternary ammonium group; and in which the balance of the mixture of co monomers is constituted by neutral and/or anionic comonomers; said composition being in the form of anyone of a toothpaste, gel, foam, chewing gum, deformable strip or mouthwash and being suitable for use in the oral cavity

Frequency-dependent drag from quantum turbulence produced by quartz tuning forks in superfluid He4

We have measured the drag force from quantum turbulence on a series of quartz tuning forks in superfluid helium. The tuning forks were custom made from a 75-μm-thick wafer. They have identical prong widths and prong spacings, but different lengths to give different resonant frequencies. We have used both the fundamental and overtone flexure modes to probe the turbulent drag over a broad range of frequencies f=ω/2π from 6.5 to 300 kHz. Optical measurements show that the velocity profiles of the flexure modes are well described by a cantilever beam model. The critical velocity for the onset of quantum turbulence at low temperatures is measured to be vc≈0.7κω−−−−−√ where κ is the circulation quantum. The drag from quantum turbulence shows a small frequency dependence when plotted against the scaled velocity v/v