Complex Fluids, NMR and Surfaces Group

Group Leader: Carlos Cruz

The objectives of the NMRCFS group are focused on the investigation of physical properties of soft matter with particular emphasis on complex systems and self-organized materials at the nano-scale, on the application of a variety of thin film preparation techniques, and on the structural and morphological characterization of surfaces and materials, by microscopy and solid-state spectroscopy, for optical and electronic applications.

The research efforts of the group include a wide range of subjects both in the field of fundamental physics (structure-properties relations of phases, low dimensional nano-structured systems) and with expectable technological impact namely: liquid crystals (LC), ionic liquids, advanced composite systems for biomedical and energy storage applications, and thin films for electronic devices.

In the field of Liquid Crystals, the objectives of the group include the increasing of research efforts on non-conventional LC phases (e.g. Nb, Ntb, Nx…) by means of electro-optical and also magneto-optical techniques, combined with NMR studies of molecular order and dynamics. The study of those systems is important due the expected technological impact in display technology and the fundamental problems related to their phase structure. It is also intended to pursue the analysis of the electro-optical behaviour of new LC/polymer composite materials in order to develop new adjustable transparency window systems with potential use in architecture.

In recent years Ionic liquids (ILs) arose as potential compounds to be used in the development, design and the use of clean technology and materials to reduce or to eliminate the generation and the employ of dangerous substances. The expected main scientific outcomes from the research activities on this topic encompass the description of molecular dynamics, structure and molecular interactions and their influence on macroscopic properties of ionic liquids based systems. To this end, experimental and theoretical works are planned and it is expected to obtain valuable insights on the role of ionic liquids on the design of task-specific systems in order to translate the scientific output into potential commercial developments and investments.

Study of molecular order and dynamics of soft matter systems as base materials for hosting dopants: These advanced composite systems might present a great variety of applications from drug delivery, in pharmaceutical applications, to enhanced transport properties in membranes, energy storage, gas absorption, in applications such as fuel cell electrolytes, CO2 capture, functionalized ionic liquid systems with magnetic and electric controlled properties.

The development of new fast field cycling NMR relaxometers and the spin-off of this technology to the market is an important objective. Spreading the use of FFC NMR in the study of a diversified set of systems will contribute to enlarge the potential market for this technology.

The AFM characterization of membranes for blood treatment, the tailoring of such membranes to improve hemocompatibility, and the preparation and analysis of biological liquid-crystal photosensitive films is another important objective of the group.

Objectives related to thin films and low dimensional quantum structures include: the application of new dopant predeposition methods at low temperature for the production of CMOS integrated circuits and for a-Si/c-Si heterojunctions of HIT type; the study and application of transparent conductive oxide (TCOs) thin films in sensors, in particular in photodetectors; the deposition of: (0-D) nanospheres of tungsten and molybdenum oxide, (1-D) nanorods of ZnO and ferroelectric NKN, and (2-D) superlattices of (amorphous) a-Si:H/a-SiC:H and (crystalline) GaN/AlGaN.

Foreseen applications are based on higher sensitivity and increased spatial resolution of low dimensional structures e.g. for medical imaging.

One of the major research interests of the CFNMRS group involves the study on thin film deposition, employing various techniques, and the characterization of morphological, structural, and optoelectronic properties. Basic underlying mechanisms in thin films and in low-dimensional samples, like down-to-20-nanometer-sized nanorods and nanospheres, are invoked for describing the relation between sample structure and preparation parameters. Materials ranged from wide-bandgap semiconductors and magnetic films, to thin organic films and biological membranes are also investigated.

The group has long-term experience and appropriate technological installations for deposition by chemical vapour deposition (CVD), rf-plasma enhanced reactive thermal evaporation (PERTE), hybrid pulsed laser deposition (PLD), chemical bath deposition (CBD), and thermal evaporation with subsequent electrolytic transport.

The classical structural characterization methods like SEM and XRD were complemented by manipulation of aggregates using a special electro-pulsed AFM technique. On the spectroscopic side, both recombination and transport are studied by spectroscopic analysis like photoluminescence and current-voltage characteristics and supported by non-invasive and contactless methods like photocapacitance and transient microwave reflection measurements. Minority carrier transport is accessed by a four-wave mixing scheme using a long-coherence length UV laser.

On a higher level, using simple optoelectronic devices like metal-semiconductor diodes or field-effect transistors, the group studies new material systems and process technologies. Examples are the use of copper oxide films in field-effect transistors, the inclusion of ferroelectric thin films for hysteresis and memory effects, the realization of pixel detectors based and zinc oxide thin films, and the fabrication of solar cells using a new doping procedure.