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发信人: loafer (快乐的化身), 信区: Chemistry
标 题: FAQ:Quantum Dots and Programmable Matter[转]
发信站: 哈工大紫丁香 (Fri Jul 11 09:37:18 2003)
发信人: nichloas (nil), 信区: Chemistry
标 题: FAQ: Quantum Dots and Programmable Matter
发信站: 北大未名站 (2003年01月19日19:30:59 星期天), 转信
寄件者：Wil McCarthy (wmccarth@sprynet.com)
主旨：FAQ: Quantum Dots and Programmable Matter
View: Complete Thread （共有 4 条留言）
Original Format
新闻群组：sci.chem
日期：2002-12-17 08:38:07 PST
FAQ: Quantum Dots and Programmable Matter
Wil McCarthy / Version 1.0 / 16 December 2002
(C) Copyright 2002 by Wil McCarthy. This FAQ may be transmitted or
distributed freely without alterations, appendices, or annotations.
Please do not make changes to this text without the author's
permission. Thank you.
2,082 words. 14,137 bytes.
Keywords: "quantum dot", "artificial atom", "programmable atom",
"designer atom", "programmable matter", "wellstone", "quantum dot
fiber", "SET", "single-electron transistor"
Q1: What is programmable matter?
Q2: What is wellstone?
Q3: Is this science fiction?
Q4: Where is programmable matter research being conducted?
Q5: Is programmable matter the same thing as nanotechnology?
Q6: Is programmable matter the same thing as MEMS?
Q7: I've heard the term "programmable matter" used to describe a
cellular automaton computer simulation. Is this accurate?
Q8: Does an LCD screen qualify as programmable matter? Does a
transistor?
Q9: What is doping?
Q10: What are quantum dots and artificial atoms? Are they the same
thing?
Q11: What is a quantum well?
Q12: What is programmable matter made of?
Q13: How is programmable matter made?
Q14: Can programmable matter mimic the substances on the periodic
table?
Q15: Can programmable matter mimic transuranic elements?
Q16: Aren't these transuranic elements highly unstable?
Q17: Can programmable matter be used to create superstrong materials?
Q18: What does "unnatural properties" mean?
Q19: What does matter made of artificial atoms feel like? Is it
solid?
Q20: What is programmable matter good for?
Q21: Who is Wil McCarthy, and why is he posting this FAQ?
--
Q1: What is programmable matter?
A1: Programmable matter is any bulk substance whose physical
properties can be adjusted in real time through the application of
light, electrical voltages, electric or magnetic fields, etc.
Primitive forms may be capable of only limited adjustment of one or
two traits (e.g., the photodarkening material of light-sensitive
sunglasses), but there are theoretical forms which, using known
principles of electronics, should be capable of emulating a broad
range of naturally occurring materials, or of exhibiting unnatural
properties which cannot be produced by other means.
--
Q2: What is wellstone?
A2: Wellstone is a hypothetical form of programmable matter first
proposed by Wil McCarthy in his novella "Once Upon a Matter Crushed"
(Science Fiction Age, May 1999), consisting of nanoscopic
semiconductor threads covered with quantum dots. These threads can be
woven together to form a bulk solid with real-time programmable
properties. The terms "wellstone" and "programmable matter" are
occasionally used interchangeably, although many other forms of
programmable matter exist.
--
Q3: Is this science fiction?
A3: No. Various forms of programmable matter have appeared in
fiction, but are in many cases based on technologies which exist
today, or on reasonable extrapolations from them.
--
Q4: Where is programmable matter research being conducted?
A4: Various aspects of programmable matter are under investigation in
labs all over the world. Major players include (but are by no means
limited to) IBM, Nippon Telehone and Telegraph, Fujitsu, Delft
University, MIT, Harvard, Stanford, Princeton, Cornell, CalTech, and
The University of California at Santa Barbara.
--
Q5: Is programmable matter the same thing as nanotechnology?
A5: Yes and no. The word "nanotechnology" simply means "technology
on the scale of nanometers," or billionths of a meter, i.e. technology
on the molecular scale. Most forms of programmable matter rely on
nanoelectronic circuitry, designer molecules, or both, so in this
literal sense they are nanotechnology. However, as originally coined
by K. Eric Drexler in the 1980s and as commonly used by lay persons
today, the word nanotechnology implies nanoscale _machinery_, more
properly known as molecular nanotechnology or MNT.
While bulk materials incorporating MNT may have programmable
properties, they also have moving parts. The term "programmable
matter" does not rule out such materials, but more typically refers to
substances whose properties can be adjusted in the solid state, with
no moving parts other than photons and electrons.
--
Q6: Is programmable matter the same thing as MEMS?
A6: No. Micro Electromechanical Systems, or MEMS, are microscopic
machines crafted using standard methods for the manufacture of
microchips. MEMS have many useful applications in the real world, but
are far too large to exhibit the quantum effects necessary to affect
the bulk properties of matter. However, the "Utility Fog" substance
proposed by J. Storrs Hall in the early 1990s, consisting of millions
or billions of micromachines -- each with with 12 retractable,
linkable arms -- has numerous adjustable bulk properties and can thus
be considered a crude, mechanical form of programmable matter.
--
Q7: I've heard the term "programmable matter" used to describe a
cellular automaton computer simulation. Is this accurate?
A7: Yes, although technically speaking, a cellular automaton can only
contain _virtual_ programmable matter, whereas physical examples which
meet the definition are available in the real world.
--
Q8: Does an LCD screen qualify as programmable matter? Does a
transistor?
A8: An LCD screen's optical properties can be dramatically altered by
the application of electrical signals. Thus, it is clearly a form of
programmable matter, albeit a simple one. A transistor can switch
between an electrically conductive state and an electrically
insulative one, but is properly a "device" rather than a substance.
However, a bulk material fashioned from transistors (transistronium?)
would be electrically switchable between these two states, and
possibly numerous intermediate states. This meets (trivially) the
definition for programmable matter stated above.
In general, the more capable forms of programmable matter rely on the
doping effects of "artificial atoms" or "quantum dots" inside a bulk
material.
--
Q9: What is doping?
A9: Doping is the addition of impurities (dopants) to a bulk material
(the substrate) in order to adjust its electrical, thermal, optical,
or magnetic properties. The addition of one dopant atom per million
atoms of substrate is often sufficient to cause major changes in the
material's behavior.
--
Q10: What are quantum dots and artificial atoms? Are they the same
thing?
A10: A quantum dot is any device capable of confining electrons in
three dimensions, in a space small enough that their quantum
(wavelike) behavior dominates over their classical (particle-like)
behavior. Under cryogenic conditions, this typically occurs with
dimensions of 1000 nm or less. At room temperature, confinement
spaces of 20-30 nm or smaller are required.
Once the electrons are confined, they repel one another and also obey
the Pauli Exclusion Principle, which forbids any two electrons from
having the same quantum numbers. Thus, the electrons in a quantum dot
will form shells and orbitals highly reminiscent of (though larger
than) the ones in an atom, and will in fact exhibit many of the
optical, electrical, thermal, and (to some extent) chemical properties
of an atom. This electron cloud is therefore referred to as an
artificial atom.
In their various forms, quantum dots may be referred to as
single-electron transistors, controlled potential barriers, Coulomb
islands, zero dimensional electron gases, colloidal nanoparticles or
semiconductor nanocrystals.
--
Q11: What is a quantum well?
A11: A quantum well is a device for confining electrons in one
dimension, such that their quantum (wavelike) behavior dominates over
their classical (particle-like) behavior along the confined axis,
while classical behavior dominates along the other two axes,
permitting the electrons to flow two-dimensionally through the
material like billiard balls on a table. A typical quantum well
consists of an N-type semiconductor, doped with electron donor atoms,
trapped between two layers of P-type semicondictor, doped with
electron borrower atoms.
A quantum well is the primary component of miniature laser pointers.
--
Q12: What is programmable matter made of?
A12: Programmable matter is composed of manmade objects too small to
perceive directly with the human senses. This may include microscopic
or nanoscopic machines, but more typically refers to fixed
arrangements of conductors, semiconductors, and insulators designed to
trap electrons in artificial atoms.
--
Q13: How is programmable matter made?
A13: Current forms of programmable matter fall into three types:
colloidal films, bulk crystals, and electrostatic confinement quantum
dot chips. Quantum dots can be grown chemically as nanoparticles of
semiconductor surrounded by an insulating layer, usually of organic
molecules. These particles can then be deposited onto a substrate,
such as a semiconductor wafer patterned with metal electrodes, or they
can be crystalized into bulk solids by a variety of methods. Either
substance can be stimulated electrically or optically (e.g., with
lasers) in order to change its properties.
Electrostatic quantum dots are patterns of conductor (usually a metal
such as gold) laid down on top of a quantum well, such that varying
the electrical voltage on the conductors can drive electrons into and
out of a confinement region in the well -- the quantum dot. This
method offers numerous advantages over colloidal films, including a
greater control over the artificial atom's size, composition, and
shape. Numerous quantum dots can be placed on the same chip, forming
a semiconductor material with a programmable dopant layer near its
surface.
Rolling such chips into cylindrical fibers produces "wellstone," a
hypothetical woven solid whose bulk properties are broadly
programmable.
--
Q14: Can programmable matter mimic the substances on the periodic
table?
A14: Yes. Artificial atoms can easily be constructed which mimic the
properties of any natural atom, except that they are larger and their
electrons are bound less strongly. However, these artificial atoms
have negligible mass, and can exist only inside the quantum-dot
substrate which generates them, usually a semiconductor. Thus, the
final properties of the material are a blend of the simulated element
and the underlying substrate.
--
Q15: Can programmable matter mimic transuranic elements?
A15: Yes. An artificial atom can contain any number of electrons,
from 1 to over 1000. The form and properties of highly transuranic
atoms (atomic number >> 92) are dramatically different from those of
natural atoms.
--
Q16: Aren't these transuranic elements highly unstable?
A16: The nuclei of highly transuranic elements are unstable.
However, an artificial atom does not have a nucleus of its own,
relying instead on geometry, insulative barriers, and/or electrostatic
repulsion to confine its electrons inside a semiconductor substrate.
--
Q17: Can programmable matter be used to create superstrong materials?
A17: Probably not. The binding energy of artificial atoms cannot
exceed the binding energy of the semiconductor substrate. However,
using diamond fibers as a substrate should allow for some very tough
programmable materials. Also, changes in the magnetic behavior of a
material can affect its stiffness and tensile/compressive strength in
useful ways.
--
Q18: What does "unnatural properties" mean?
A18: Unlike natural atoms, artificial atoms can be square, pyramidal,
two-dimensional, highly transuranic, composed of charged particles
other than electrons (e.g., "holes"), and can even be asymmetrical.
Their size, energy, and shape are variable quantities. Thus,
artificial atoms exhibit optical, electrical, thermal, magnetic,
mechanical, and (to some extent) chemical behaviors which do not occur
in natural materials. This variety is bounded but infinite, in sharp
contrast to the 92 stable atoms of the periodic table.
--
Q19: What does matter made of artificial atoms feel like? Is it
solid?
A19: Artificial atoms can exist only inside a semiconductor
substrate. They are charge discontinuities rather than physical
objects, so they don't feel like anything. However, their doping
effects can dramatically alter the properties of the substrate,
causing it to feel different. For example, a dramatic increase in
thermal and electrical conductivity would make the semiconductor feel
(and look, and behave) like a metal.
--
Q20: What is programmable matter good for?
A20: Almost anything. It can improve the efficient collection,
storage, distribution, and use of energy from environmental sources.
It can be used to create novel sensors and computing devices, probably
including quantum computers. It can create materials which are not
available by other means, and which change their apparent composition
on demand. Currently, the design of new materials is a time- and
labor-intensive process; with programmable matter, it becomes more of
a software issue.
--
Q21: Who is Wil McCarthy, and why is he posting this FAQ?
A21: Wil McCarthy, an aerospace engineer, is a contributing editor
for WIRED magazine, the science columnist for the SciFi channel web
site www.scifi.com, and an author of numerous book-length works of
science fact and science fiction. He has written extensively about
quantum dots and programmable matter, and faces a consistent set of
questions, objections, and misconceptions when presenting this
material. The FAQ is intended to promote intelligent discussion of
programmable matter and quantum dots by increasing awareness of their
underlying issues and principles.
--
The latest version of this FAQ can be found at
http://www.wilmccarthy.com/pmfaq.htm .
Feel free to reply to postings of this FAQ with additional questions.
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寄件者：Wil McCarthy (wmccarth@sprynet.com)
主旨：FAQ: Quantum Dots and Programmable Matter
View: Complete Thread （共有 4 条留言）
Original Format
新闻群组：sci.chem
日期：2002-12-17 08:38:07 PST
FAQ: Quantum Dots and Programmable Matter
Wil McCarthy / Version 1.0 / 16 December 2002
(C) Copyright 2002 by Wil McCarthy. This FAQ may be transmitted or
distributed freely without alterations, appendices, or annotations.
Please do not make changes to this text without the author's
permission. Thank you.
2,082 words. 14,137 bytes.
Keywords: "quantum dot", "artificial atom", "programmable atom",
"designer atom", "programmable matter", "wellstone", "quantum dot
fiber", "SET", "single-electron transistor"
Q1: What is programmable matter?
Q2: What is wellstone?
Q3: Is this science fiction?
Q4: Where is programmable matter research being conducted?
Q5: Is programmable matter the same thing as nanotechnology?
Q6: Is programmable matter the same thing as MEMS?
Q7: I've heard the term "programmable matter" used to describe a
cellular automaton computer simulation. Is this accurate?
Q8: Does an LCD screen qualify as programmable matter? Does a
transistor?
Q9: What is doping?
Q10: What are quantum dots and artificial atoms? Are they the same
thing?
Q11: What is a quantum well?
Q12: What is programmable matter made of?
Q13: How is programmable matter made?
Q14: Can programmable matter mimic the substances on the periodic
table?
Q15: Can programmable matter mimic transuranic elements?
Q16: Aren't these transuranic elements highly unstable?
Q17: Can programmable matter be used to create superstrong materials?
Q18: What does "unnatural properties" mean?
Q19: What does matter made of artificial atoms feel like? Is it
solid?
Q20: What is programmable matter good for?
Q21: Who is Wil McCarthy, and why is he posting this FAQ?
--
Q1: What is programmable matter?
A1: Programmable matter is any bulk substance whose physical
properties can be adjusted in real time through the application of
light, electrical voltages, electric or magnetic fields, etc.
Primitive forms may be capable of only limited adjustment of one or
two traits (e.g., the photodarkening material of light-sensitive
sunglasses), but there are theoretical forms which, using known
principles of electronics, should be capable of emulating a broad
range of naturally occurring materials, or of exhibiting unnatural
properties which cannot be produced by other means.
--
Q2: What is wellstone?
A2: Wellstone is a hypothetical form of programmable matter first
proposed by Wil McCarthy in his novella "Once Upon a Matter Crushed"
(Science Fiction Age, May 1999), consisting of nanoscopic
semiconductor threads covered with quantum dots. These threads can be
woven together to form a bulk solid with real-time programmable
properties. The terms "wellstone" and "programmable matter" are
occasionally used interchangeably, although many other forms of
programmable matter exist.
--
Q3: Is this science fiction?
A3: No. Various forms of programmable matter have appeared in
fiction, but are in many cases based on technologies which exist
today, or on reasonable extrapolations from them.
--
Q4: Where is programmable matter research being conducted?
A4: Various aspects of programmable matter are under investigation in
labs all over the world. Major players include (but are by no means
limited to) IBM, Nippon Telehone and Telegraph, Fujitsu, Delft
University, MIT, Harvard, Stanford, Princeton, Cornell, CalTech, and
The University of California at Santa Barbara.
--
Q5: Is programmable matter the same thing as nanotechnology?
A5: Yes and no. The word "nanotechnology" simply means "technology
on the scale of nanometers," or billionths of a meter, i.e. technology
on the molecular scale. Most forms of programmable matter rely on
nanoelectronic circuitry, designer molecules, or both, so in this
literal sense they are nanotechnology. However, as originally coined
by K. Eric Drexler in the 1980s and as commonly used by lay persons
today, the word nanotechnology implies nanoscale _machinery_, more
properly known as molecular nanotechnology or MNT.
While bulk materials incorporating MNT may have programmable
properties, they also have moving parts. The term "programmable
matter" does not rule out such materials, but more typically refers to
substances whose properties can be adjusted in the solid state, with
no moving parts other than photons and electrons.
--
Q6: Is programmable matter the same thing as MEMS?
A6: No. Micro Electromechanical Systems, or MEMS, are microscopic
machines crafted using standard methods for the manufacture of
microchips. MEMS have many useful applications in the real world, but
are far too large to exhibit the quantum effects necessary to affect
the bulk properties of matter. However, the "Utility Fog" substance
proposed by J. Storrs Hall in the early 1990s, consisting of millions
or billions of micromachines -- each with with 12 retractable,
linkable arms -- has numerous adjustable bulk properties and can thus
be considered a crude, mechanical form of programmable matter.
--
Q7: I've heard the term "programmable matter" used to describe a
cellular automaton computer simulation. Is this accurate?
A7: Yes, although technically speaking, a cellular automaton can only
contain _virtual_ programmable matter, whereas physical examples which
meet the definition are available in the real world.
--
Q8: Does an LCD screen qualify as programmable matter? Does a
transistor?
A8: An LCD screen's optical properties can be dramatically altered by
the application of electrical signals. Thus, it is clearly a form of
programmable matter, albeit a simple one. A transistor can switch
between an electrically conductive state and an electrically
insulative one, but is properly a "device" rather than a substance.
However, a bulk material fashioned from transistors (transistronium?)
would be electrically switchable between these two states, and
possibly numerous intermediate states. This meets (trivially) the
definition for programmable matter stated above.
In general, the more capable forms of programmable matter rely on the
doping effects of "artificial atoms" or "quantum dots" inside a bulk
material.
--
Q9: What is doping?
A9: Doping is the addition of impurities (dopants) to a bulk material
(the substrate) in order to adjust its electrical, thermal, optical,
or magnetic properties. The addition of one dopant atom per million
atoms of substrate is often sufficient to cause major changes in the
material's behavior.
--
Q10: What are quantum dots and artificial atoms? Are they the same
thing?
A10: A quantum dot is any device capable of confining electrons in
three dimensions, in a space small enough that their quantum
(wavelike) behavior dominates over their classical (particle-like)
behavior. Under cryogenic conditions, this typically occurs with
dimensions of 1000 nm or less. At room temperature, confinement
spaces of 20-30 nm or smaller are required.
Once the electrons are confined, they repel one another and also obey
the Pauli Exclusion Principle, which forbids any two electrons from
having the same quantum numbers. Thus, the electrons in a quantum dot
will form shells and orbitals highly reminiscent of (though larger
than) the ones in an atom, and will in fact exhibit many of the
optical, electrical, thermal, and (to some extent) chemical properties
of an atom. This electron cloud is therefore referred to as an
artificial atom.
In their various forms, quantum dots may be referred to as
single-electron transistors, controlled potential barriers, Coulomb
islands, zero dimensional electron gases, colloidal nanoparticles or
semiconductor nanocrystals.
--
Q11: What is a quantum well?
A11: A quantum well is a device for confining electrons in one
dimension, such that their quantum (wavelike) behavior dominates over
their classical (particle-like) behavior along the confined axis,
while classical behavior dominates along the other two axes,
permitting the electrons to flow two-dimensionally through the
material like billiard balls on a table. A typical quantum well
consists of an N-type semiconductor, doped with electron donor atoms,
trapped between two layers of P-type semicondictor, doped with
electron borrower atoms.
A quantum well is the primary component of miniature laser pointers.
--
Q12: What is programmable matter made of?
A12: Programmable matter is composed of manmade objects too small to
perceive directly with the human senses. This may include microscopic
or nanoscopic machines, but more typically refers to fixed
arrangements of conductors, semiconductors, and insulators designed to
trap electrons in artificial atoms.
--
Q13: How is programmable matter made?
A13: Current forms of programmable matter fall into three types:
colloidal films, bulk crystals, and electrostatic confinement quantum
dot chips. Quantum dots can be grown chemically as nanoparticles of
semiconductor surrounded by an insulating layer, usually of organic
molecules. These particles can then be deposited onto a substrate,
such as a semiconductor wafer patterned with metal electrodes, or they
can be crystalized into bulk solids by a variety of methods. Either
substance can be stimulated electrically or optically (e.g., with
lasers) in order to change its properties.
Electrostatic quantum dots are patterns of conductor (usually a metal
such as gold) laid down on top of a quantum well, such that varying
the electrical voltage on the conductors can drive electrons into and
out of a confinement region in the well -- the quantum dot. This
method offers numerous advantages over colloidal films, including a
greater control over the artificial atom's size, composition, and
shape. Numerous quantum dots can be placed on the same chip, forming
a semiconductor material with a programmable dopant layer near its
surface.
Rolling such chips into cylindrical fibers produces "wellstone," a
hypothetical woven solid whose bulk properties are broadly
programmable.
--
Q14: Can programmable matter mimic the substances on the periodic
table?
A14: Yes. Artificial atoms can easily be constructed which mimic the
properties of any natural atom, except that they are larger and their
electrons are bound less strongly. However, these artificial atoms
have negligible mass, and can exist only inside the quantum-dot
substrate which generates them, usually a semiconductor. Thus, the
final properties of the material are a blend of the simulated element
and the underlying substrate.
--
Q15: Can programmable matter mimic transuranic elements?
A15: Yes. An artificial atom can contain any number of electrons,
from 1 to over 1000. The form and properties of highly transuranic
atoms (atomic number >> 92) are dramatically different from those of
natural atoms.
--
Q16: Aren't these transuranic elements highly unstable?
A16: The nuclei of highly transuranic elements are unstable.
However, an artificial atom does not have a nucleus of its own,
relying instead on geometry, insulative barriers, and/or electrostatic
repulsion to confine its electrons inside a semiconductor substrate.
--
Q17: Can programmable matter be used to create superstrong materials?
A17: Probably not. The binding energy of artificial atoms cannot
exceed the binding energy of the semiconductor substrate. However,
using diamond fibers as a substrate should allow for some very tough
programmable materials. Also, changes in the magnetic behavior of a
material can affect its stiffness and tensile/compressive strength in
useful ways.
--
Q18: What does "unnatural properties" mean?
A18: Unlike natural atoms, artificial atoms can be square, pyramidal,
two-dimensional, highly transuranic, composed of charged particles
other than electrons (e.g., "holes"), and can even be asymmetrical.
Their size, energy, and shape are variable quantities. Thus,
artificial atoms exhibit optical, electrical, thermal, magnetic,
mechanical, and (to some extent) chemical behaviors which do not occur
in natural materials. This variety is bounded but infinite, in sharp
contrast to the 92 stable atoms of the periodic table.
--
Q19: What does matter made of artificial atoms feel like? Is it
solid?
A19: Artificial atoms can exist only inside a semiconductor
substrate. They are charge discontinuities rather than physical
objects, so they don't feel like anything. However, their doping
effects can dramatically alter the properties of the substrate,
causing it to feel different. For example, a dramatic increase in
thermal and electrical conductivity would make the semiconductor feel
(and look, and behave) like a metal.
--
Q20: What is programmable matter good for?
A20: Almost anything. It can improve the efficient collection,
storage, distribution, and use of energy from environmental sources.
It can be used to create novel sensors and computing devices, probably
including quantum computers. It can create materials which are not
available by other means, and which change their apparent composition
on demand. Currently, the design of new materials is a time- and
labor-intensive process; with programmable matter, it becomes more of
a software issue.
--
Q21: Who is Wil McCarthy, and why is he posting this FAQ?
A21: Wil McCarthy, an aerospace engineer, is a contributing editor
for WIRED magazine, the science columnist for the SciFi channel web
site www.scifi.com, and an author of numerous book-length works of
science fact and science fiction. He has written extensively about
quantum dots and programmable matter, and faces a consistent set of
questions, objections, and misconceptions when presenting this
material. The FAQ is intended to promote intelligent discussion of
programmable matter and quantum dots by increasing awareness of their
underlying issues and principles.
--
The latest version of this FAQ can be found at
http://www.wilmccarthy.com/pmfaq.htm .
Feel free to reply to postings of this FAQ with additional questions.
?2003 Google
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