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BEGIN:VEVENT
DTSTAMP:20261024T030954Z
LAST-MODIFIED:-11130T050000Z
DTSTART:20111209T200000Z
DTEND:20111209T210000Z
UID:event409@bu.edu
URL:http://physics.bu.edu/internal/events/show/409
SUMMARY:Diamond Nanoelectromechanical Resonators:  Dissipation and Supercon
	ductivity
DESCRIPTION:Featuring Matthias Imboden\n\nPart of the PhD Final Oral Exams.
	\n\nExamining Committee:  Raj Mohanty\, Steve Ahlen\, Robert Carey\, Anders
	 Sandvik\, Shyam Erramilli\, William SkocpolAbstract:Nanoelectromechanical 
	systems (NEMS) have become a viable commercialtechnology and are becoming m
	ore and more prevalent in researchapplications. Through miniaturization\, t
	he mechanical response to externalsources becomes ever more sensitive. This
	 transduction\, coupled to anelectrical readout circuit\, results in unprec
	edented sensitivity.This thesis examines dissipation in diamond NEMS resona
	tors in the MHz toGHz range.  NCD (Nano-crystalline diamond) has extraordin
	ary propertiesthat make it an intriguing material to study. To begin with\,
	 themechanical hardness allows for a boost in resonance frequency\, but bey
	ondthat\, boron-doped diamond also shows extraordinary electrical behavior.
	Although scaling benefits speed and sensitivity\, dissipation increasesdram
	atically with miniaturization\, negating some of the gains insensitivity. T
	he dissipative mechanisms at play in the MHz range areidentified at high te
	mperatures. It is found that extrinsic dissipationmechanisms\, mainly circu
	it and clamping losses\, can limit the qualityfactor (inverse of the dissip
	ation). Furthermore\, due to the highsurface-to-volume ratio of NEMS\, surf
	ace defects become significant at thenano-scale.  For the first time\, quan
	tum dissipation due to assistedphonon tunneling of two level systems is obs
	erved in diamond NEMSresonators at millikelvin temperatures. Through scalin
	g\, it is shown thatthe low temperature behavior is universal for a broad r
	ange of MHzresonators\, including silicon and gallium arsenide\, as well as
	 grapheneand carbon-nanotubes.Beyond the mechanical response\, the supercon
	ducting properties of highlyboron-doped diamond (BDD) are studied.  It is f
	ound that the criticaltemperature of 3.3 K for the thin-film is maintained 
	at the nano-scale.The high critical field\, on the order of 3 T for thin-fi
	lms\, is stronglysuppressed\, already at the micro-scale. The zero resistan
	ce state iscompromised with fields as low as 0.1 T for submicron wide const
	rictions.It is known that the superconducting state will couple to the stra
	infield. Here\, the piezoresistive detection technique is developed for BDD
	structures in the MHz range at room as well as cryogenic temperatures.This 
	serves as a framework for future studies of strain-superconductivitycouplin
	g.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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