Nitya Nand Gosvami | University of Pennsylvania (original) (raw)
Papers by Nitya Nand Gosvami
Journal of Physics: Conference Series, 2007
We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky... more We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T 3 -(CH 2 ) 4 -HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.
J Electroceram, 2006
Crystalline CeO 2 films grown in aqueous solutions at 45 • C on glass slides formed by the island... more Crystalline CeO 2 films grown in aqueous solutions at 45 • C on glass slides formed by the island growth mode. The film had a refractive index of 1.83 and indicated that the film had a porosity of 41.3%, which significantly lowered the elastic stiffness of the film. The film cracked only after drying in a mud crack pattern when it reached a critical thickness. This indicated that the film cracked under tensile stress due to the accumulation of tensile strains generated from grain coalescence during growth, thermal expansion mismatch during cooling and capillary stress during drying.
Realisation of the first working sensor based on quantum tunneling between arrays of nanowires[1,... more Realisation of the first working sensor based on quantum tunneling between arrays of nanowires[1,2,3] is presented. The sensing element consists of 12,000 nanowires, each 90 nm wide and 5 mm long (~1:55,000 aspect ratio), on an area of 5 x 4.3 mm. The sensing element was fabricated using phase shift mask lithography and dry etch processes followed by CMP. Characterisation was carried with SEM and AFM.
Science, 2015
has a small, yet nonzero, quantum defect. The corresponding lifetime of Cs(36F) is t 36F ≈ 18 ms ... more has a small, yet nonzero, quantum defect. The corresponding lifetime of Cs(36F) is t 36F ≈ 18 ms (25). The fact that the decay of the molecular state is different from the purely radiative decay of the Cs(nS) Rydberg state, and closer to the nearby (n -4)F state, is another indication of the degenerate mixing involved in the formation of the hybrid trilobite molecules.
Journal of Molecular Recognition, 2014
e Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native env... more e Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native environment (embedded in a membrane and in buffer solution) at~1 nm spatial resolution. It has been most successful on membrane proteins reconstituted in 2D crystals and on some specialized and densely packed native membranes. Here, we report on AFM imaging of purified plasma membranes from Xenopus laevis oocytes, a commonly used system for the heterologous expression of membrane proteins. Isoform M23 of human aquaporin 4 (AQP4-M23) was expressed in the X. laevis oocytes following their injection with AQP4-M23 cRNA. AQP4-M23 expression and incorporation in the plasma membrane were confirmed by the changes in oocyte volume in response to applied osmotic gradients. Oocyte plasma membranes were then purified by ultracentrifugation on a discontinuous sucrose gradient, and the presence of AQP4-M23 proteins in the purified membranes was established by Western blotting analysis. Compared with membranes without over-expressed AQP4-M23, the membranes from AQP4-M23 cRNA injected oocytes showed clusters of structures with lateral size of about 10 nm in the AFM topography images, with a tendency to a fourfold symmetry as may be expected for higherorder arrays of AQP4-M23. In addition, but only infrequently, AQP4-M23 tetramers could be resolved in 2D arrays on top of the plasma membrane, in good quantitative agreement with transmission electron microscopy analysis and the current model of AQP4. Our results show the potential and the difficulties of AFM studies on cloned membrane proteins in native eukaryotic membranes.
Scanning Probe Microscopy, 2010
The Journal of Physical Chemistry C, 2008
We report a comparative study of charge transport across a n-decanethiol (C10SH) self-assembled m... more We report a comparative study of charge transport across a n-decanethiol (C10SH) self-assembled monolayer (SAM) on Au(111) using conducting atomic force microscopy (C-AFM). The experiments are performed in nonpolar liquids (hexadecane and OMCTS) and ambient air. AFM force measurements in liquid mediums reveal discrete solvation layering close to the SAM interface. The liquid layering between the AFM probe and the SAM surface does not affect the measured contact resistance value, provided all the confined liquid layers are squeezed out of the contact. The contact resistance, however, can vary by orders of magnitude when measured in different mediums. This is mainly governed by the mechanical behavior of the monolayer. Force vs current measurements and contact stiffness measurements using sample modulation AFM show how the mechanical response of the SAM junction varies in the different surrounding mediums and supports the observed variation in measured contact resistance values.
Philosophical Magazine, 2007
ABSTRACT The tribological properties, such as coefficient of friction, adhesion and wear durabili... more ABSTRACT The tribological properties, such as coefficient of friction, adhesion and wear durability of an ultra-thin (<10 nm) dual-layer film on a silicon surface were investigated. The dual-layer film was prepared by dip-coating perfluoropolyether (PFPE), a liquid polymer lubricant, as the top layer onto a 3-glycidoxypropyltrimethoxy silane self-assembled monolayer (epoxy SAM)-coated Si substrate. PFPE contains hydroxyl groups at both ends of its backbone chain, while the SAM surface contains epoxy groups, which terminate at the surface. A combination of tests involving contact angle measurements, ellipsometry, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) was used to study the physical and chemical properties of the film. The coefficient of friction and wear durability of the film were investigated using a ball-on-disk tribometer (4mm diameter Si(3)N4 ball as the counterface at a nominal contact pressure of similar to 330 MPa). AFM was used to investigate the adhesion forces between a sharp Si3N4 tip and the film. This dual-layer film had a very low coefficient of friction, adhesion and wear when compared to epoxy SAM-coated Si only or bare Si surface. The reasons for the improved tribological performance are explained in terms of the lubrication characteristics of PFPE molecules, low surface energy of PFPE, covalent bonding between PFPE and epoxy SAM coupled with reduced mobile PFPE. The low adhesion forces coupled with high wear durability show that the film has applications as a wear resistant and anti-stiction film for microcomponents made from Si.
Journal of Applied Physics, 2007
The evolution of nanopatterned InP surfaces by low-energy Ar+-ion irradiation and their dependenc... more The evolution of nanopatterned InP surfaces by low-energy Ar+-ion irradiation and their dependence on incidence angle were investigated by field emission scanning electron microscopy, atomic force microscopy, and Raman scattering. Ordered surface nanodots of high aspect ratio were created. At large ion incidence angle the dot density decreases and the size varies in the range of 65–130 nm with height
Applied Surface Science, 2006
Tuning the charge transport through a metal-molecule-metal junction by changing the interface pro... more Tuning the charge transport through a metal-molecule-metal junction by changing the interface properties is widely studied and is of paramount importance for applications in molecular electronic devices. We used current sensing atomic force microscopy (CSAFM) as a tool to study the contact resistance of metal-molecule-metal (MmM) junctions formed by sandwiching self-assembled monolayers (SAMs) of alkanethiols with various end groups (-CH 3 , -OH and -NH 2 ) between Au(1 1 1) substrates and Au coated AFM tips. The effect of interface chemistry on charge transport through such SAMs with varying end groups was studied in an inert, non-polar liquid (hexadecane) environment. We find that the contact resistances of these MmM junctions vary significantly based on the end group chemistry of the molecules. #
Applied Surface Science, 2007
... 12]. Chini et al. ... bombardment. Datta and Chini [11] demonstrated the evolution of ripple ... more ... 12]. Chini et al. ... bombardment. Datta and Chini [11] demonstrated the evolution of ripple pattern, as a function of ion dose, on Si (1 0 0) surface induced by 60 keV Ar + -ion beam incident at oblique incidence with respect to the surface normal. ...
Single asperity measurements on Si wafers with variable SiO 2 layer thickness, yet identical roug... more Single asperity measurements on Si wafers with variable SiO 2 layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO 2 layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO 2 layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model.
Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be ... more Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be studied in detail by means of friction force microscopy. Atomic-scale variations of the lateral force allow investigation of microscopic mechanisms of sliding. Friction force microscopy even reveals surface reconstruction of the gold surface as a modulation of the lateral force signal. Experiments indicate that the mobility of surface atoms at room temperature and plastic deformation mechanisms give rise to neck formation between gold and microscopic asperities in sliding contact. The frictional properties of gold surfaces change dramatically at temperatures below 150 K, where the surface diffusion is greatly reduced. Insight into the lubrication properties of self-assembled monolayers is provided by molecular-scale modulations of frictional forces. Molecular-scale maps of the friction force also allow identification of the relevant surface structure in experiments on electrochemically modified gold surfaces. Variation of the electrochemical potential is a means to reversibly switch between low and high friction states on gold surfaces.
We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microsco... more We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microscope tip and a graphite surface. Solvation layering occurs for both liquids but marked differences in the squeeze out mechanics are observed for ordered or disordered monolayers. The squalane monolayer at 25 C is an ordered solid, as verified by direct imaging, and the squeeze out can be modeled using elastic continuum mechanics. HMN is in a disordered state at 25 C and cannot be modeled as a single elastic asperity even in solid-solid contact because HMN liquid is trapped in the contact zone.
Using frequency-modulation atomic force microscopy ͑FM-AFM͒ at sub-nanometer vibration amplitudes... more Using frequency-modulation atomic force microscopy ͑FM-AFM͒ at sub-nanometer vibration amplitudes, we find in the system n-dodecanol/graphite that solvation layers may extend for several nanometers into the bulk liquid. These layers maintain crystalline order which can be imaged using FM-AFM. The energy dissipation of the vibrating tip can peak sharply upon penetration of molecular layers. The tip shape appears critical for this effect.
Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscop... more Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscopy Rev. Sci. Instrum. 83, 123708 (2012) Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers Rev. Sci. Instrum. 83, 126103 (2012) Switching spectroscopic measurement of surface potentials on ferroelectric surfaces via an open-loop Kelvin probe force microscopy method Appl. Phys. Lett. 101, 242906 (2012) Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues Rev. Sci. Instrum. 83, 121101 Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phaselocked loop Rev. Sci. Instrum. 83, 113705 (2012) Additional information on J. Appl. Phys.
The properties and interactions of hydrophobic surfaces in water are determining factors in a wid... more The properties and interactions of hydrophobic surfaces in water are determining factors in a wide range of industrial applications, and represent a fundamental scientific problem that is far from solved. Langmuir-Blodgett (LB) lipid monolayers have often been used as model hydrophobic surfaces, but are only metastable, which compromises the interpretation of experiments. Using frequency-modulation atomic force microscopy (FM-AFM), we find that LB-deposited monolayers of dioctadecyldimethylammonium bromide (DODAB) on mica undergo two transitions upon immersion in water: (i) a rapid molecular rearrangement from a complete monolayer coverage to a more densely packed monolayer with holes exposing the mica substrate, followed by; (ii) a gradual flipping of lipids in the monolayer to form bilayers, at a timescale of many days, orders of magnitudes slower than previously reported. The (meta)stability of the monolayer shows little dependence on the deposition pressure (5-25 mN m 21 ), but strongly depends on the cleanliness of the preparation and, in AFM experiments, is reduced from days to minutes when the force applied by the AFM tip is not kept to well below 1 nN. When properly prepared and analysed, the DODAB/mica surface thus yields a well-defined structure of sufficient stability to study intersurface forces, albeit with a heterogeneity that gives rise to very distinct forces above the bare mica on one hand, and on the monolayer and bilayer areas on the other.
Journal of Physics: Conference Series, 2007
We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky... more We use Ballistic Electron Emission Microscopy (BEEM) technique to determine directly the Schottky barrier distribution over silver /H-T 3 -(CH 2 ) 4 -HS (abbreviated as T3C4SH) self assembled monolayer interface area with nanometer scale spatial resolution. The selfassembled monolayer is absorbed on template stripped gold. BEEM images show spatially non-uniform carrier injection. A Wentzel Kramel Brillouin (WKB) calculation is performed and compared with BEEM spectra. The results show that the measured currents are four orders of magnitude larger than the direct tunnelling contribution, indicating molecular levels being accessed. To further substantiate the findings, characterization by STM distance versus potential spectroscopy is carried out to determine injection barriers at the interface. The results from these two techniques are compared and the implications of which will be discussed.
J Electroceram, 2006
Crystalline CeO 2 films grown in aqueous solutions at 45 • C on glass slides formed by the island... more Crystalline CeO 2 films grown in aqueous solutions at 45 • C on glass slides formed by the island growth mode. The film had a refractive index of 1.83 and indicated that the film had a porosity of 41.3%, which significantly lowered the elastic stiffness of the film. The film cracked only after drying in a mud crack pattern when it reached a critical thickness. This indicated that the film cracked under tensile stress due to the accumulation of tensile strains generated from grain coalescence during growth, thermal expansion mismatch during cooling and capillary stress during drying.
Realisation of the first working sensor based on quantum tunneling between arrays of nanowires[1,... more Realisation of the first working sensor based on quantum tunneling between arrays of nanowires[1,2,3] is presented. The sensing element consists of 12,000 nanowires, each 90 nm wide and 5 mm long (~1:55,000 aspect ratio), on an area of 5 x 4.3 mm. The sensing element was fabricated using phase shift mask lithography and dry etch processes followed by CMP. Characterisation was carried with SEM and AFM.
Science, 2015
has a small, yet nonzero, quantum defect. The corresponding lifetime of Cs(36F) is t 36F ≈ 18 ms ... more has a small, yet nonzero, quantum defect. The corresponding lifetime of Cs(36F) is t 36F ≈ 18 ms (25). The fact that the decay of the molecular state is different from the purely radiative decay of the Cs(nS) Rydberg state, and closer to the nearby (n -4)F state, is another indication of the degenerate mixing involved in the formation of the hybrid trilobite molecules.
Journal of Molecular Recognition, 2014
e Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native env... more e Atomic force microscopy (AFM) is a unique tool for imaging membrane proteins in near-native environment (embedded in a membrane and in buffer solution) at~1 nm spatial resolution. It has been most successful on membrane proteins reconstituted in 2D crystals and on some specialized and densely packed native membranes. Here, we report on AFM imaging of purified plasma membranes from Xenopus laevis oocytes, a commonly used system for the heterologous expression of membrane proteins. Isoform M23 of human aquaporin 4 (AQP4-M23) was expressed in the X. laevis oocytes following their injection with AQP4-M23 cRNA. AQP4-M23 expression and incorporation in the plasma membrane were confirmed by the changes in oocyte volume in response to applied osmotic gradients. Oocyte plasma membranes were then purified by ultracentrifugation on a discontinuous sucrose gradient, and the presence of AQP4-M23 proteins in the purified membranes was established by Western blotting analysis. Compared with membranes without over-expressed AQP4-M23, the membranes from AQP4-M23 cRNA injected oocytes showed clusters of structures with lateral size of about 10 nm in the AFM topography images, with a tendency to a fourfold symmetry as may be expected for higherorder arrays of AQP4-M23. In addition, but only infrequently, AQP4-M23 tetramers could be resolved in 2D arrays on top of the plasma membrane, in good quantitative agreement with transmission electron microscopy analysis and the current model of AQP4. Our results show the potential and the difficulties of AFM studies on cloned membrane proteins in native eukaryotic membranes.
Scanning Probe Microscopy, 2010
The Journal of Physical Chemistry C, 2008
We report a comparative study of charge transport across a n-decanethiol (C10SH) self-assembled m... more We report a comparative study of charge transport across a n-decanethiol (C10SH) self-assembled monolayer (SAM) on Au(111) using conducting atomic force microscopy (C-AFM). The experiments are performed in nonpolar liquids (hexadecane and OMCTS) and ambient air. AFM force measurements in liquid mediums reveal discrete solvation layering close to the SAM interface. The liquid layering between the AFM probe and the SAM surface does not affect the measured contact resistance value, provided all the confined liquid layers are squeezed out of the contact. The contact resistance, however, can vary by orders of magnitude when measured in different mediums. This is mainly governed by the mechanical behavior of the monolayer. Force vs current measurements and contact stiffness measurements using sample modulation AFM show how the mechanical response of the SAM junction varies in the different surrounding mediums and supports the observed variation in measured contact resistance values.
Philosophical Magazine, 2007
ABSTRACT The tribological properties, such as coefficient of friction, adhesion and wear durabili... more ABSTRACT The tribological properties, such as coefficient of friction, adhesion and wear durability of an ultra-thin (<10 nm) dual-layer film on a silicon surface were investigated. The dual-layer film was prepared by dip-coating perfluoropolyether (PFPE), a liquid polymer lubricant, as the top layer onto a 3-glycidoxypropyltrimethoxy silane self-assembled monolayer (epoxy SAM)-coated Si substrate. PFPE contains hydroxyl groups at both ends of its backbone chain, while the SAM surface contains epoxy groups, which terminate at the surface. A combination of tests involving contact angle measurements, ellipsometry, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) was used to study the physical and chemical properties of the film. The coefficient of friction and wear durability of the film were investigated using a ball-on-disk tribometer (4mm diameter Si(3)N4 ball as the counterface at a nominal contact pressure of similar to 330 MPa). AFM was used to investigate the adhesion forces between a sharp Si3N4 tip and the film. This dual-layer film had a very low coefficient of friction, adhesion and wear when compared to epoxy SAM-coated Si only or bare Si surface. The reasons for the improved tribological performance are explained in terms of the lubrication characteristics of PFPE molecules, low surface energy of PFPE, covalent bonding between PFPE and epoxy SAM coupled with reduced mobile PFPE. The low adhesion forces coupled with high wear durability show that the film has applications as a wear resistant and anti-stiction film for microcomponents made from Si.
Journal of Applied Physics, 2007
The evolution of nanopatterned InP surfaces by low-energy Ar+-ion irradiation and their dependenc... more The evolution of nanopatterned InP surfaces by low-energy Ar+-ion irradiation and their dependence on incidence angle were investigated by field emission scanning electron microscopy, atomic force microscopy, and Raman scattering. Ordered surface nanodots of high aspect ratio were created. At large ion incidence angle the dot density decreases and the size varies in the range of 65–130 nm with height
Applied Surface Science, 2006
Tuning the charge transport through a metal-molecule-metal junction by changing the interface pro... more Tuning the charge transport through a metal-molecule-metal junction by changing the interface properties is widely studied and is of paramount importance for applications in molecular electronic devices. We used current sensing atomic force microscopy (CSAFM) as a tool to study the contact resistance of metal-molecule-metal (MmM) junctions formed by sandwiching self-assembled monolayers (SAMs) of alkanethiols with various end groups (-CH 3 , -OH and -NH 2 ) between Au(1 1 1) substrates and Au coated AFM tips. The effect of interface chemistry on charge transport through such SAMs with varying end groups was studied in an inert, non-polar liquid (hexadecane) environment. We find that the contact resistances of these MmM junctions vary significantly based on the end group chemistry of the molecules. #
Applied Surface Science, 2007
... 12]. Chini et al. ... bombardment. Datta and Chini [11] demonstrated the evolution of ripple ... more ... 12]. Chini et al. ... bombardment. Datta and Chini [11] demonstrated the evolution of ripple pattern, as a function of ion dose, on Si (1 0 0) surface induced by 60 keV Ar + -ion beam incident at oblique incidence with respect to the surface normal. ...
Single asperity measurements on Si wafers with variable SiO 2 layer thickness, yet identical roug... more Single asperity measurements on Si wafers with variable SiO 2 layer thickness, yet identical roughness, revealed the influence of van der Waals (vdW) interactions on friction: on thin (1 nm) SiO 2 layers, higher friction and jump-off forces were observed as compared to thick (150 nm) SiO 2 layers. The vdW interactions were additionally controlled by a set of silanized Si wafers, exhibiting the same trend. The experimental results demonstrate the influence of the subsurface material and are quantitatively described by combining calculations of interactions of the involved materials and the Derjaguin-Müller-Toporov model.
Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be ... more Gold surfaces exhibit most interesting frictional properties on the nanometer scale. They can be studied in detail by means of friction force microscopy. Atomic-scale variations of the lateral force allow investigation of microscopic mechanisms of sliding. Friction force microscopy even reveals surface reconstruction of the gold surface as a modulation of the lateral force signal. Experiments indicate that the mobility of surface atoms at room temperature and plastic deformation mechanisms give rise to neck formation between gold and microscopic asperities in sliding contact. The frictional properties of gold surfaces change dramatically at temperatures below 150 K, where the surface diffusion is greatly reduced. Insight into the lubrication properties of self-assembled monolayers is provided by molecular-scale modulations of frictional forces. Molecular-scale maps of the friction force also allow identification of the relevant surface structure in experiments on electrochemically modified gold surfaces. Variation of the electrochemical potential is a means to reversibly switch between low and high friction states on gold surfaces.
We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microsco... more We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microscope tip and a graphite surface. Solvation layering occurs for both liquids but marked differences in the squeeze out mechanics are observed for ordered or disordered monolayers. The squalane monolayer at 25 C is an ordered solid, as verified by direct imaging, and the squeeze out can be modeled using elastic continuum mechanics. HMN is in a disordered state at 25 C and cannot be modeled as a single elastic asperity even in solid-solid contact because HMN liquid is trapped in the contact zone.
Using frequency-modulation atomic force microscopy ͑FM-AFM͒ at sub-nanometer vibration amplitudes... more Using frequency-modulation atomic force microscopy ͑FM-AFM͒ at sub-nanometer vibration amplitudes, we find in the system n-dodecanol/graphite that solvation layers may extend for several nanometers into the bulk liquid. These layers maintain crystalline order which can be imaged using FM-AFM. The energy dissipation of the vibrating tip can peak sharply upon penetration of molecular layers. The tip shape appears critical for this effect.
Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscop... more Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscopy Rev. Sci. Instrum. 83, 123708 (2012) Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers Rev. Sci. Instrum. 83, 126103 (2012) Switching spectroscopic measurement of surface potentials on ferroelectric surfaces via an open-loop Kelvin probe force microscopy method Appl. Phys. Lett. 101, 242906 (2012) Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues Rev. Sci. Instrum. 83, 121101 Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phaselocked loop Rev. Sci. Instrum. 83, 113705 (2012) Additional information on J. Appl. Phys.
The properties and interactions of hydrophobic surfaces in water are determining factors in a wid... more The properties and interactions of hydrophobic surfaces in water are determining factors in a wide range of industrial applications, and represent a fundamental scientific problem that is far from solved. Langmuir-Blodgett (LB) lipid monolayers have often been used as model hydrophobic surfaces, but are only metastable, which compromises the interpretation of experiments. Using frequency-modulation atomic force microscopy (FM-AFM), we find that LB-deposited monolayers of dioctadecyldimethylammonium bromide (DODAB) on mica undergo two transitions upon immersion in water: (i) a rapid molecular rearrangement from a complete monolayer coverage to a more densely packed monolayer with holes exposing the mica substrate, followed by; (ii) a gradual flipping of lipids in the monolayer to form bilayers, at a timescale of many days, orders of magnitudes slower than previously reported. The (meta)stability of the monolayer shows little dependence on the deposition pressure (5-25 mN m 21 ), but strongly depends on the cleanliness of the preparation and, in AFM experiments, is reduced from days to minutes when the force applied by the AFM tip is not kept to well below 1 nN. When properly prepared and analysed, the DODAB/mica surface thus yields a well-defined structure of sufficient stability to study intersurface forces, albeit with a heterogeneity that gives rise to very distinct forces above the bare mica on one hand, and on the monolayer and bilayer areas on the other.