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Optical and magnetic materials in nanoland
Current Opinion in Solid State and Materials Science 4 (1999) 179
Editorial overview
Optical and magnetic materials in nanoland R. White a , C. Weisbuch b , * a
Department of Electronical and Computer Engineering, Carnegie-Mellon University, Pittsburgh, PA 15213 -3891, USA b ` Condensee ´ , Ecole Polytechnique, 91120 Palaiseau, France Laboratoire de Physique de la Matiere
The past few years have seen exciting growth in optical and magnetic phenomena based on the synthesis of novel materials. This is well exemplified in this issue of Current Opinion in Solid State & Materials Science by the contributions on laser action in organic thin films, optical limiting materials, infrared glasses, and new laser materials for diode-pumped solid state lasers. In addition to new materials, new fabrication and characterization techniques have led to the development of novel structures at an intermediate scale between the atomic scale and micron-sized structures the nanometer scale or nanoscale. Although a number of naturally occurring nanostructured materials have existed for a long time, it is only recently that systematic structuring at such a scale has been undertaken in many materials systems. This is due to a combination of factors that complement each other: in microelectronics (i.e. silicon devices), the everdecreasing feature size has reached the few nanometer range making nanoscale electronics routine. As a result, fabrication techniques for nanoscale structures have become widely available for non-silicon materials. A good example is the contribution given in this issue on nanomagnetic structures at surfaces. The capacity to fabricate such tiny structures, in itself, would not be sufficient to generate the large effort that we witness worldwide if there were not a strong demand for the study of the novel phenomena occurring at such sizes. These new phenomena can be desirable or non-desirable. Mainstream electronics is sometimes complicated by quantum effects occurring at the nanoscale. However, in other areas, there are efforts to exploit such effects as Coulomb blockade or quantum interference to develop nanoelectronic devices with improved performance over their classical counterparts. A similar trend is perceptible in nanomagnetism: whereas it was suspected that ferromag*Corresponding author. Tel.: 133-01-69333959; fax: 133-0169333004. E-mail address: [email protected] (C. Weisbuch)
netic properties would be modified at the nanoscale, particularly at surfaces, there is a widespread effort to search for novel magnetic properties at the nanoscale. The nanoscale can also be a ‘natural’ scale for materials with desired properties: in the optical range, materials periodically structured at the wavelength scale, i.e. a few tens of nanometers, could provide a major new family of optical materials with specifically engineered properties. These photonic crystals control light propagation in the same manner as crystals control electron propagation with conduction and valence bands separated by forbidden gaps. The hope is to forbid spontaneous light emission from emitters placed in such materials, thus leading the way to light emitters with tailored emission beams. For spin dependent tunneling also, the nanometer is the natural length. Through recent advances in controlled fabrication techniques, various spin-dependent-tunneling phenomena can be exploited to yield new physics such as giant magnetoresistance, or new devices such as spin transistors. The nanoscale is also becoming more manageable because nanoscale characterization techniques, such as the scanning tunneling microscope (STM), the atomic force microscope (AFM), the near-field scanning optical microscope (NSOM) and their likes, have exploded in the past 10–15 years. The latest member in the family is the magnetic force microscope (MFM), which is providing a great deal of useful insight in nanoscale magnetic materials. We should emphasize at this point that there still remains a strong need for better materials and novel devices despite the dramatic progress that has been made. In every topic discussed in this issue, one can see that the understanding gained at the nanoscale level will lead to major applications, sometimes of revolutionary importance: novel ultra-small and ultra-low power electronics based on the electron spin, magnetic memories with nanoscale bit cells, unit efficiency or quantum light emitters, etc. Clearly, we have not yet realized the potential of nanoscale devices.
1359-0286 / 99 / $ – see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-0286( 99 )00025-X
Editorial overview
Optical and magnetic materials in nanoland R. White a , C. Weisbuch b , * a
Department of Electronical and Computer Engineering, Carnegie-Mellon University, Pittsburgh, PA 15213 -3891, USA b ` Condensee ´ , Ecole Polytechnique, 91120 Palaiseau, France Laboratoire de Physique de la Matiere
The past few years have seen exciting growth in optical and magnetic phenomena based on the synthesis of novel materials. This is well exemplified in this issue of Current Opinion in Solid State & Materials Science by the contributions on laser action in organic thin films, optical limiting materials, infrared glasses, and new laser materials for diode-pumped solid state lasers. In addition to new materials, new fabrication and characterization techniques have led to the development of novel structures at an intermediate scale between the atomic scale and micron-sized structures the nanometer scale or nanoscale. Although a number of naturally occurring nanostructured materials have existed for a long time, it is only recently that systematic structuring at such a scale has been undertaken in many materials systems. This is due to a combination of factors that complement each other: in microelectronics (i.e. silicon devices), the everdecreasing feature size has reached the few nanometer range making nanoscale electronics routine. As a result, fabrication techniques for nanoscale structures have become widely available for non-silicon materials. A good example is the contribution given in this issue on nanomagnetic structures at surfaces. The capacity to fabricate such tiny structures, in itself, would not be sufficient to generate the large effort that we witness worldwide if there were not a strong demand for the study of the novel phenomena occurring at such sizes. These new phenomena can be desirable or non-desirable. Mainstream electronics is sometimes complicated by quantum effects occurring at the nanoscale. However, in other areas, there are efforts to exploit such effects as Coulomb blockade or quantum interference to develop nanoelectronic devices with improved performance over their classical counterparts. A similar trend is perceptible in nanomagnetism: whereas it was suspected that ferromag*Corresponding author. Tel.: 133-01-69333959; fax: 133-0169333004. E-mail address: [email protected] (C. Weisbuch)
netic properties would be modified at the nanoscale, particularly at surfaces, there is a widespread effort to search for novel magnetic properties at the nanoscale. The nanoscale can also be a ‘natural’ scale for materials with desired properties: in the optical range, materials periodically structured at the wavelength scale, i.e. a few tens of nanometers, could provide a major new family of optical materials with specifically engineered properties. These photonic crystals control light propagation in the same manner as crystals control electron propagation with conduction and valence bands separated by forbidden gaps. The hope is to forbid spontaneous light emission from emitters placed in such materials, thus leading the way to light emitters with tailored emission beams. For spin dependent tunneling also, the nanometer is the natural length. Through recent advances in controlled fabrication techniques, various spin-dependent-tunneling phenomena can be exploited to yield new physics such as giant magnetoresistance, or new devices such as spin transistors. The nanoscale is also becoming more manageable because nanoscale characterization techniques, such as the scanning tunneling microscope (STM), the atomic force microscope (AFM), the near-field scanning optical microscope (NSOM) and their likes, have exploded in the past 10–15 years. The latest member in the family is the magnetic force microscope (MFM), which is providing a great deal of useful insight in nanoscale magnetic materials. We should emphasize at this point that there still remains a strong need for better materials and novel devices despite the dramatic progress that has been made. In every topic discussed in this issue, one can see that the understanding gained at the nanoscale level will lead to major applications, sometimes of revolutionary importance: novel ultra-small and ultra-low power electronics based on the electron spin, magnetic memories with nanoscale bit cells, unit efficiency or quantum light emitters, etc. Clearly, we have not yet realized the potential of nanoscale devices.
1359-0286 / 99 / $ – see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-0286( 99 )00025-X